Transmissible porcine gastroenteritis (TPG). Porcine viral gastroenteritis (transmissible porcine gastroenteritis, Doyle and Hitchings disease)
Transmissible porcine gastroenteritis (TPG) is an acute, highly contagious disease, mainly in 2-week-old piglets, manifested by vomiting, diarrhea and dehydration. The morbidity and mortality rate of newborn piglets during the acute course of the disease can reach 100%. In older piglets, clinical signs of the disease are usually absent and no death is observed. Sick sows often present with fever, diarrhea, and decreased or lost milk production. The disease is registered in many countries with intensively developed pig production, and due to the lack of effective means of prevention, it causes serious economic damage. The main feature of TGS is that it is relatively
is one of the most pronounced highly lethal local infections. Piglets are most vulnerable to THS in the first 10 days of life. They are often born infected or become infected in the first hours and days after birth. In the acute course of the disease in a non-immune herd, no more than 24-48 hours pass between infection and clinical manifestation of the disease.
Under these conditions, piglets can only be protected by maternal antibodies obtained from colostrum and milk. J1 actogenic immunity is effective if antibodies in a sufficiently high titer are constantly present in the intestinal lumen of piglets, at least during the first week of life.
All other things being equal, the effectiveness of lactogenic immunity is directly dependent on the specific activity of the amount of colostrum and milk consumed. The incidence and death of piglets from THS will, as a rule, be less under high-milk dams or in small litters. In addition to enterocytes, the defeat of which is accompanied by atrophy of the villi of the small intestine, alveolar macrophages, as well as cells of the tonsils and, possibly, other organs, can serve as target cells for the virus. In the tonsil cells of sick piglets, the TGS virus antigen was detected even more often than in the cells of the jejunum. The disease is accompanied by immunity and the formation of VNA, related to IgA and IgG. In colostrum and then in the milk of convalescent sows, such antibodies are present for several weeks. Piglets from sows that have recovered from the disease or were previously infected under natural conditions are resistant to the disease due to colostral antibodies. Specific prevention of THS still remains an urgent problem. Numerous studies in this area have not yet resulted in the development of effective means of active prevention, although many inactivated and live vaccines and methods of their use have been proposed. The reason for this is associated with the peculiarities of patho- and immunogenesis in TGS, as well as with the difficulties of creating pronounced long-term immunity of the mucous membranes during local infections in general.
Inactivated vaccines are prepared from a virus grown in single-layer primary or continuous cell cultures of porcine origin, usually using an oil adjuvant. Formalin is most often used to inactivate the virus. The antigenic properties of the virus were equally well preserved in the vaccine if formaldehyde or ethyleneimine dimer was used to inactivate the virus. The antigenicity of the emulsified vaccine was higher than that of the sorbed one. Vaccination of pregnant sows was accompanied by pronounced seroconversion (VNA G.230), and the protection of three-day-old piglets during experimental infection was 70.9%.
Numerous inactivated vaccines differ from each other, mainly in the duration of passage of the virus in cell culture and the concentration of the viral antigen included in their composition. Typically, inactivated vaccines are administered intramuscularly to sows twice over 7-10 and 2-4
weeks before farrowing. Such vaccines were used in America, Europe and Asia. The inactivated emulsified vaccine after a double intramuscular injection at a dose of 2 ml caused pronounced seroconversion in pregnant sows. On the day of farrowing, the titer of VL antibodies was 7.5-9.0 log2. In the blood serum of 1 - 15-day-old piglets, the titer of maternal antibodies was in the range of 6.0-6.5 log2. The high immunogenicity of the vaccine has been confirmed under production conditions. Since intramuscular immunization of sows stimulates a weak protective effect as a result of the development of mainly systemic immunity with the predominant synthesis of IgG, the use of inactivated vaccines began to be limited, and preference was given to live ones. Attenuated strains of the TGS virus were obtained by serial passage of virulent strains in primary cultures and permanent cell lines of porcine origin. Approximately 40 passages of the virus are required to noticeably reduce virulence. The fourfold difference in the duration of attenuation by serial passaging in a continuous culture of cells of porcine origin did not significantly affect the antigenic and immunogenic properties of the two attenuated strains of the TGS virus.
The live vaccine from Fort Dodge was tested with double intraudder and intramuscular injections to pregnant sows. The safety of piglets during experimental infection was about 80%. With the first method of vaccine administration, the VNA titer in colostrum and milk was 2-3 times higher, but this method of vaccination cannot be used in widespread practice. The live vaccine was administered orally twice: the first time at the 6th week of gestation, the second time 3 weeks before farrowing. Vaccinated animals developed immunity, as evidenced by the protection of newborn piglets from THS during the disease outbreak.
Due to the low effectiveness of intramuscular vaccination, the search for unconventional methods of immunizing pregnant sows began. Many researchers have administered live vaccines orally, intranasally, and into the udder. Although in a number of cases satisfactory results were obtained, the combined method of immunization nevertheless turned out to be promising. A live vaccine from the RIMS strain, when administered twice intramuscularly to pregnant sows, provided less pronounced protection for piglets than when administered orally. The highest level was observed with the combined administration of the vaccine to sows 4-6 weeks before farrowing orally and intramuscularly 2 weeks before farrowing in order to obtain an optimal booster effect.
The Rhone-Mérier company (France) proposed a vaccine (GASTERIFFA) from an attenuated strain in two forms for two methods of application. In a threatened pig farm for 2-3 months. pregnancy is vaccinated orally, and after
- days - intramuscularly. In a dysfunctional farm, pigs are vaccinated intramuscularly for the first and second time. Vaccination is accompanied by a high level of lactogenic immunity.
Both of the above solutions, despite different priming paths, are based on one principle - the commonality of the immune system of the mucous membranes, i.e. the existence of a close immunological relationship between the intestine, bronchoalveolar tissue and mammary gland. After primary local stimulation (in the first case, the intestines, in the second, the respiratory tract), repeated intramuscular immunization before farrowing caused increased synthesis and secretion of IgA in colostrum and milk. The subunit split vaccine, which appears to be a peplomeric glycoprotein mixed with an adjuvant, induced active immunity in mothers and passive immunity in offspring.
NPO NARVAK has developed a fairly effective inactivated emulsified vaccine. Sows are vaccinated intramuscularly at a dose of 3 ml on days 70-75 and 90-100 of gestation. Replacement gilts are also vaccinated before insemination. Vaccination induces a high level of colostral immunity and protects at least 90% of piglets from disease and death during acute THS in large pig farms.
In the 80s of the last century, a naturally attenuated respiratory variant of the THS virus became widespread, which was easily transmitted horizontally, causing persistence in pigs. Thanks to this, the problem of specific prevention of THS has disappeared in Europe. However, in the United States, when a similar virus is circulating in the pig population, specific prevention of THS remains an urgent problem. A similar situation persists in Russia and Asia. A new variant of the TCV virus, called porcine respiratory coronavirus (PRCV), has been used in some countries to immunize pigs against PCV.
Viral infections of pigs transmissible gastroenteritis of pigs (Gastroenteritis infectiosa suum)
Definition. Transmissible gastroenteritis of pigs (TPG) is a highly contagious, acute infectious intestinal disease, which is characterized by vomiting, debilitating diarrhea, rapid dehydration of the animal body and is accompanied by the death of animals, especially piglets up to 10-14 days of age.
The disease occurs suddenly and pigs of all age groups are susceptible to it. However, piglets under two weeks of age are most susceptible. The death rate varies depending on the age of the animals. Among 1-7 day old piglets it is 90-100%, among 28 day old piglets it does not exceed 25-50% (25).
Historical reference. Transmissible gastroenteritis was first described by American researchers Doyle and Hutchings in 1946 in pigs, who proved its viral nature and the pathogenicity of the virus for piglets. Subsequent outbreaks were noted in Japan (1956), Great Britain (1957), Canada (1964) and in many countries of Europe, Asia and Africa. The prevalence in European countries is about 100%.
Epizootological data. Transmissible gastroenteritis of pigs is characterized by those biological patterns that are inherent in many infectious diseases, i.e. the presence of three links in the epizootic process: the source of the infectious agent, the routes (mechanism) of transmission and infection of susceptible animals in pigs.
The source of the infectious agent is sick and recovered animals - virus carriers. Sick animals shed the virus in their feces for two months after illness. The concentration of the virus in feces is especially high at the beginning of the disease, when watery feces contaminate surrounding objects. The THS virus persists in offal and meat cooled to 3-5°C, obtained after the slaughter of sick and recovered pigs for 15 days.
Infection occurs mainly through nutritional means, less often - aerogenously. Transmission of the virus occurs through contact of healthy animals with sick ones, through feed, water, staff, and transport. Infection of animals by airborne droplets is possible. Our observations show that in most cases, the THS pathogen is transmitted (imported) to healthy farms with sick and recovered animals - virus carriers, as well as with non-neutralized by-products and slaughterhouse waste. These are the main routes for the introduction of the THS pathogen into prosperous farms.
According to foreign and domestic scientists, laboratory animals are not sensitive to the TGS virus. However, after artificial infection of dogs and foxes with the THS pathogen, the coronavirus was excreted in feces for up to 2 weeks. Virus-neutralizing antibodies are detected in dogs after injection of the virus. It has been established that starlings secrete the TGS virus after feeding them pieces of intestine from piglets with gastroenteritis for up to two days. Scientists have often associated the occurrence of THS foci with the migration of starlings.
Transmissible gastroenteritis occurs in the form of an epizootic or enzootic. The epizootic form of TGS is observed when the infection is introduced into pig farms in which animals do not have immunity to the TGS virus and are susceptible to this disease. Outbreaks of THS appear a few days after the import of pigs from a dysfunctional farm, in particular after the import of breeding gilts and boars, as well as feed and animal products. Usually within a few days the disease affects pigs of all age groups. The disease is characterized by diarrhea that appears suddenly and spreads rapidly among animals of all ages, affecting almost 100% of the pig population. Newborn piglets and suckling sows suffer from severe THS. Mortality among newborn piglets up to 10 days of age is 80-90%, 2-3 weeks old - 20-30%, weaned piglets - 3-4%, adult animals - less than 1%.
K.N. Gruzdev, I.I. Skvortsova (1995) experimentally showed high sensitivity of piglets to the TGS virus depending on their age. The incidence of newborn piglets aged 1, 7, 14, 28 and 45 days during experimental infection with the epizootic strain of the TGS virus "Miller" was 100%. The mortality rate of piglets experimentally infected with the THS virus was: at the age of 1 to 7 days - 100%, at the age of 14, 28 and 45 days - 70, 50 and 30%, respectively. The age-related resistance of piglets to THS is shown in Figure 1. According to A.I. Sobko and E.A. Krasnobaev (1987) mortality among newborn piglets under 10 days of age is 80-90% or more, 2-3 weeks old - 20-30%, weaned pigs - 3-4%, adult pigs - less than 1%.
Our observations of the morbidity and mortality of newborn piglets during their experimental infection with a virulent strain of the TGS virus and during natural infection during outbreaks of the disease in pig farms showed the high contagiousness of the causative agent of transmissible gastroenteritis for this age of animals. In one of the pig farms in the Grodno region in 1990, during a primary acute outbreak of THS, 90-100% of newborn piglets from 200 farrowing sows died within 5-7 days.
One of the features of TGS is the seasonality of its occurrence. The disease is most often registered in the autumn-winter-spring months. This is most likely due to the fact that in the cold season the virus is more resistant to external factors than in the summer at high temperatures.
The duration of the TGS epizootic varies depending on the type and size of the pig farm. With a continuous reproduction system in large farms, the epizootic of the disease extends over many months (and even years) due to the continuous year-round farrowing of sows and the production of young animals susceptible to THS. In small pig farms, the duration of the THS epizootic is limited to 3-4 weeks. Sows infected at the onset of the disease acquire immunity after 3 weeks, which they pass on to newborn piglets through colostrum and milk. Piglets obtained from sows that have recovered from THS are usually resistant to the disease for up to 1-1.5 months. In the post-weaning period, they may develop gastroenteritis due to the loss of colostral immunity.
According to the observation of P.I. Pritulina (1975), THS can occur at any time of the year. Outbreaks in pig farms recurred, as a rule, during periods of mass farrowing and weaning of piglets from sows. The emergence and spread of transmissible gastroenteritis is facilitated by unsatisfactory living conditions, inadequate feeding of animals, sudden changes in diets, hypothermia and overheating, and long-term transportation. All of the stress factors mentioned above reduce the body’s resistance, contribute to the occurrence and aggravate the course of viral gastroenteritis in pigs.
THS enzootics are observed in large pig breeding complexes, where sows have acquired immunity as a result of a previous THS infection. After a few months, its intensity decreases and gastroenteritis is registered in piglets older than 6-7 days of age, and in some piglets of the litter the disease occurs in a mild form. Patients do not always vomit. The mortality rate for this form of TGS does not exceed 10-20%. Sows usually do not get sick. Enzootic viral gastroenteritis is associated, as a rule, with the persistence of the virus on the farm, the presence of highly susceptible piglets (continuous farrowing system) or the frequent importation of non-immune pigs sensitive to the TGS virus.
A feature of the enzootic form of THS is the periodic occurrence of outbreaks of gastroenteritis among newborn piglets. It has been noted that the most frequently affected young animals are those obtained from first-parity sows, which have a low level of specific antibodies to the TCV virus (especially when weaned early). If farrowings from first-parity sows occur simultaneously with farrowings from older sows, then gastroenteritis from sick piglets obtained from the first category of animals can be transmitted to piglets obtained from another category of sows. In this regard, V.I. Varganov et al. (1979), when improving the health of farms that are disadvantaged by TGS, considers it advisable to extend the period of use of the main sows to 6-7 farrows and to carry out farrowing of first-parity sows separately from the general herd.
Transmissible gastroenteritis causes significant economic damage to pig farms, which consists of up to 80-90% mortality in suckling piglets. Animals that have recovered from the disease are retarded in growth and development, and weight gain decreases.
Biological properties of the pathogen. The causative agent of transmissible gastroenteritis virus of swine belongs to the Coronaviridae family, genus Coronavirus. Its virions morphologically have the appearance of pleomorphic particles of round or oval shape, consist of a nucleocapsid of spiral symmetry, which contains the viral genome, a lipoprotein shell, on the surface of which there are club-shaped (pear-shaped) processes (spikes), widely spaced from each other and reminiscent of the solar corona. Hence the name coronavirus. The genome of the virus is a single-stranded, linear, unfragmented RNA molecule. In ultrathin sections of infected epithelial cells, TGS virus virions have a diameter of 65-95 nm. The reference strain of the TGS virus is the Purdue strain, isolated in the USA by Doyle and Hutchings.
The TGS virus is sensitive to lipid solvents (ether, chloroform), sodium deoxycholate, is thermolabile and is inactivated at a temperature of 56°C for 30 minutes, at 50°C for 60 minutes. The virus does not change its virulent properties at pH from 4 to 9.0. When stored frozen, it remains viable for many weeks.
The TGS virus is sensitive to light, as well as to the action of disinfectants: 0.5% formaldehyde, 2% sodium hydroxide, a 20% suspension of freshly slaked lime and a suspension of bleach containing 2.5% active chlorine are destructive for the TGS pathogen . At room temperature in the dark, the infectious activity of the virus does not change for 3 days, while in the light it decreases by 99% in one day. The virus is stable for 1-2 years at a temperature of minus 20-70°C, and is not sensitive to antibiotics (penicillin, streptomycin, nystatin, etc.).
The TGS virus is pathogenic for pigs. The most sensitive are newborn piglets 1-7 days old and gnotobiotic piglets. Newborn piglets are 1000 times more sensitive to the THS virus than adults.
Individual epizootic strains and isolates of the TGS virus may differ in virulence to animals. Serial passaging of the virus in cell cultures of porcine origin reduces virulence and makes it attenuated. Often, during passages of attenuated strains of the TGS virus on newborn piglets, the pathogenicity returns to its original state (reversion).
To cultivate the THS virus, piglets are infected and then the small intestine is taken from them or sensitive cell cultures are used. In sick animals, the virus is localized in the epithelial cells lining the villi of the small intestine (jejunum, duodenum). 1 g of tissue of the duodenum or jejunum of a piglet infected with the TGS virus contains 10 6 infectious doses of the pathogen.
Cultivation of the pathogen. The absence of a cytopathogenic effect (CPE) of the virus in cell culture initially hampered the study of its properties. After the report of the isolation of the Shizuoka strain in Japan, which caused CPE in a culture of pig kidney cells, a large number of studies were conducted on the propagation of the virus in the cells of pig testicles, kidneys of fetal pigs, and the thyroid gland. Primary trypsinized cells from the testicles and kidneys of piglets turned out to be the most sensitive to the TGS virus and acceptable for its isolation. The continuous culture of SPEV cells and IBRS turned out to be unsuitable for isolating coronavirus.
The stimulating effect of trypsin on the TGS virus during the formation of plaques has been established. The number of plaques formed by coronavirus strains TO-163, Ukiha and Niigata increased 2.6-3.5 times when trypsin was added to the virus after its adsorption at 4°C for 2 hours during incubation at 37°C in within 1 hour.
The cytopathogenic effect of epizootic strains of the TGS virus on cell culture may be absent or insignificant in the first passages. This depends on the sensitivity of the cell culture to the TGS virus isolate. The pronounced cytopathogenic effect of the virus on a sensitive cell culture most often appears after several successive passages. CPD is characterized by the rounding of cells and their separation from the monolayer.
TGS viruses isolated in different laboratories are usually identical or antigenically similar to the reference strains. However, there is a report in the literature that the CV-777 virus, similar to coronavirus, isolated from sick pigs, causes intestinal damage in piglets, but reproduces more slowly. In light of current data, the named strain of coronavirus causes epizootic diarrhea in pigs. Its antigenic properties differ from the antigenic properties of the TGS virus.
Pathogenesis of transmissible gastroenteritis. The TGS virus enters the digestive tract orally or noso-orally. An aerogenic route of infection of animals cannot be ruled out. The virus's resistance to acids allows it to remain viable in the acidic environment of the stomach, where it does not multiply. Virus replication occurs in epithelial cells covering the villi of the small intestine 5-6 hours after infection. These epithelial cells of the intestinal villi ensure the absorption of nutrients. As a result of virus replication in the epithelial cells of the villi, their destruction occurs. The villi atrophy and shrink, their epithelium is replaced by cuboidal epithelium. The virus does not multiply in cuboidal epithelial cells. The destruction by the TGS virus of epithelial cells responsible for the adsorption of nutrients, villous atrophy leads to disruption of digestion and absorption of proteins, fats, carbohydrates, water, etc. by the body. As a result, diarrhea occurs 12-24 hours after infection.
Sick piglets lose large amounts of fluid, leading to severe dehydration. As a result, metabolism is disrupted and acidosis develops. Piglets affected by TGS develop dysbiosis, which is accompanied by a decrease in the number of lactic acid bacteria and an increase in putrefactive microflora. Complications of THS are caused by enteropathogenic Escherichia coli, clostridia and other microflora.
The death of animals occurs 1-5 days after the disease as a result of dehydration and intoxication. In recovered piglets, regeneration of epithelial cells of the villi of the small intestine occurs 3-4 days after infection; in the next 2-3 days, diarrhea stops.
A feature of the pathogenesis of transmissible gastroenteritis in pigs, which explains the possibility of transmission of the virus by aerogenic means, is the ability of the coronavirus to multiply in the respiratory tract of pigs - in the epithelial cells of the mucous membrane of the nasal cavity and in the lungs. Due to the replication of coronavirus in the respiratory tract, pneumonia develops.
Clinical signs of transmissible gastroenteritis in pigs. The incubation period for natural infection of piglets with the transmissible gastroenteritis virus ranges from 12 hours to 5 days. On average it is 1-3 days. In adult animals it is 1-7 days. Clinical signs of THS and its course directly depend on the age of the animals. The typical clinical sign of the disease in piglets is sudden vomiting, which is accompanied by rapid onset of diarrhea, teat rejection, lethargy and boredom.
The first clinical signs of the disease can be detected in them within a few hours after birth, but more often - on 2-3 days. Feces are usually watery, yellow-green, or less often gray. There may be clots of curdled milk in the stool. Piglets' stubble is stained with feces, causing the skin to become dirty and sticky. There is a rapid loss of animal weight, dehydration and emaciation, a high percentage of morbidity and mortality in piglets up to 2 weeks of age. The severity of clinical signs of the disease, its duration and outcome are directly proportional to the age of the animals. Thus, the death rate of piglets when infected up to 5 days of age is 100%, and in 6-10 days - 67%, in 11-15 days - 30, 15-105 days - 3.5% (66) . Thus, the majority of piglets die from THS from the 2nd to the 7th day after the appearance of clinical signs of the disease.
Clinical signs of THS in older piglets and adult pigs are characterized by depression, partial or complete loss of appetite and short-term diarrhea and vomiting in some animals. The disease lasts 1-5 days, less often 1-2 weeks and, as a rule, ends with recovery. In sick sows, suppression, decrease or complete cessation of milk secretion is noted. Hypo- or agalactia begins in them from the 3rd to 7th day after the disease. In animals that have recovered from the disease, their appetite is restored and their general condition is normalized.
Diagnosis of transmissible gastroenteritis diagnosed in a complex manner on the basis of clinical and epidemiological data, pathological and anatomical changes and laboratory tests.
A preliminary diagnosis of TGS can be made on the basis of clinical, epidemiological and pathological data of the disease. Clinical signs of transmissible gastroenteritis in piglets, as we described earlier, are characterized in some animals by vomiting, gastroenteritis (watery, yellow-green feces), crowding, contamination and darkening of the bristles and skin of piglets, and rapid dehydration of the animals.
When analyzing epidemiological data, the factor of sudden onset of vomiting and diarrhea among pigs of various age groups at any time, often regardless of the feeding and housing conditions of the animals, is taken into account. However, it should be noted that various violations of the conditions of feeding and keeping animals are often a “trigger” mechanism for the occurrence of the disease. The high contagiousness of the disease and its rapid spread, the high percentage of morbidity and mortality of newborn piglets in the first days of life (up to 10-14 days of age) are taken into account. It is also necessary to take into account that the acute course of transmissible gastroenteritis, as a rule, after 3-4 weeks is replaced by a subacute, enzootic form. The percentage of morbidity and mortality is reduced to 50%.
During the postmortem examination of the corpses of piglets who died from this disease, the stomach contains uncoagulated milk, the mucous membrane of the bottom of the stomach is dark red in color with the presence of isolated hemorrhages in certain areas. The mucous membrane of the duodenum, jejunum and partially ileum is swollen and reddened. Mesenteric lymph nodes are juicy, enlarged, hyperemic. No visible pathological changes are found in parenchymal organs (heart, lungs, liver). Often, small pinpoint hemorrhages are found under the kidney capsule, which is difficult to separate.
Histological examination of material from the small intestine (jejunum, ileum) of piglets that died from THS reveals dystrophy and superficial necrosis of the epithelium of the villi of the small intestine. In adult pigs, at autopsy, a picture of catarrhal gastroenteritis is found.
Transmissible gastroenteritis is similar in clinical, epizootological and pathological anatomical characteristics to other infectious diseases of viral etiology (epizootic viral diarrhea, rotavirus disease, enteroviral gastroenteritis of pigs) occurring with diarrhea syndrome. All of them are clinically manifested by gastroenteritis. Therefore, it is practically difficult to distinguish between viral gastroenteritis based on clinical, epizootological and pathological data. In this regard, there is a need to conduct laboratory tests and use laboratory diagnostic methods.
A reliable diagnosis of THS can be made by performing a biological test on newborn piglets under the age of 10 days, kept under the sow or artificially fed with cow's milk or warm milk formula such as "Detolact". For this purpose, piglets are imported from a farm known to be free from transmissible gastroenteritis from seronegative sows. Piglets are inoculated with a 20% sterile germ-free suspension or filtrate of pathological material from killed sick animals. The bioassay is considered positive if the experimental piglets become ill on the 2nd or 3rd day after infection, showing clinical signs characteristic of THS (vomiting, diarrhea, dehydration). Animals usually die on days 3-5. Control piglets are injected with sterile Hanks solution. They should not get sick and remain healthy.
A bioassay is an expensive method for diagnosing TGS, and its production is carried out, if necessary, with the permission of the Main Directorate of Veterinary Medicine of the Ministry of Agriculture of the Republic of Belarus or the Department of Veterinary Medicine of the Ministry of Agriculture of the Russian Federation.
Laboratory methods for diagnosing transmissible gastroenteritis are based on the detection of the TGS virus antigen in the RIF, RDP, the isolation of the TGS virus from animals with gastroenteritis in cell culture and the detection of specific antibodies to the TGS virus in the RN or RNGA.
The immunofluorescence reaction (RIF) is based on the interaction of the TGS virus antigen with specific antibodies to it, which are conjugated with a fluorochrome (fluorescent isothiocyanate - FITC). The resulting antigen-antibody complex glows green under the influence of ultraviolet rays in a fluorescent microscope.
To diagnose transmissible gastroenteritis, we at BelNIIEV have developed a test system for detecting the TGS virus antigen in RIF, which includes a set of diagnostic kits for this reaction. The kit includes: rabbit specific immunoglobulin G to the TGS virus, labeled with FITC; normal rabbit G globulin labeled with FITC; specific rabbit serum for the TGS virus; normal rabbit serum.
The preparations used to detect the antigen of the TGS virus in the RIF are fingerprint smears from the walls of the small intestine, mesenteric lymph nodes of piglets killed for diagnostic purposes, which were prepared by applying fat-free glass slides to the cut surface of the intestinal tissue or lymph node. In addition, for this purpose we used preparations from a culture of cells grown on coverslips and infected with a 20% suspension from the intestines and parenchymal organs (lungs, spleen, kidneys, mesenteric lymph nodes) of sick piglets. 24-48 hours after infection of the cell culture, cover slips with cells were removed from the tubes and mounted on glass slides.
It was also established that the time of selection of material for the study from the onset of THS disease in piglets significantly influenced the effectiveness of the study. In the event that pathological material (segments of the small intestine, mesenteric lymph nodes) was taken from piglets killed no later than the first day after the onset of clinical signs of VTGS, luminescence on 3-4 crosses was detected in 70.8% of cases. If the material was taken from piglets killed 6-7 days after the disease, positive results were found only in 23% of cases. This is apparently due to the fact that in sick piglets the columnar epithelium of the villi of the small intestine is destroyed and replaced by cubic epithelium, in which the virus does not penetrate and, therefore, is not detected in it.
Other express methods for diagnosing TGS include a test system for diagnosing transmissible gastroenteritis using the agar gel diffusion precipitation reaction (DPR). The essence of the reaction is that specific antigens and antibodies diffuse in the agar gel from localization sites towards each other and, interacting with each other, form precipitation bands (lines) in the agar. The rate of diffusion of reaction components depends on their molecular weight. The larger their molecules, the slower the diffusion, and vice versa. The reaction manifests itself at a certain quantitative ratio of the antigen and antibodies to it. To perform the reaction, you need: 1% agar gel, specific rabbit precipitating serum for the TGS virus, positive specific antigen, normal rabbit serum, negative (control) antigen and test antigens.
The reaction is carried out in 2 variants: macro- and micromethod. The macro version of the reaction is carried out on agar in Petri dishes, the micro version - on glass slides. The macro version of the RDP is more acceptable. To do this, add 25.0 ml of molten agar to Petri dishes. In a layer of frozen agar, using a special stamp, wells with a diameter of 5-6 mm were made: 1 well - central, 6 wells - peripheral. The distance between the holes is 4--5 mm. 1 drop of molten agar was added to the bottom of each well to prevent components from leaking under the agar layer.
The reaction is considered positive if there is a pronounced precipitation line between the well with the specific precipitating serum and the test antigen, which smoothly turns into the precipitation line between the well with the specific serum and the positive antigen, forming a closed hexagon in the gel. In the control (specific precipitating serum and negative antigen; normal rabbit serum and positive precipitating antigen) there are no precipitation lines.
RDP for detecting the antigen of the TGS virus is a specific and quite sensitive reaction and, in combination with clinical, epizootological, pathological and anatomical data, allows making a diagnosis of transmissible gastroenteritis.
In order to isolate the TGS virus, virological studies of the pathological material are carried out on a cell culture line sensitive to the TGS virus. Most often, a primary trypsinized culture of piglet kidney cells, testicles, and thyroid glands of piglets is used for this purpose. The method of sampling pathological material for virus isolation is important. Sections of the affected small intestine, pieces of the lung, spleen, kidneys and liver of killed piglets with diarrhea are sent to the laboratory in a Dewar flask with liquid nitrogen or a thermos with ice. A 20% suspension is prepared from the pathological material in Hanks' solution, centrifuged at 3-4 thousand rpm. within 30 min. Antibiotics are added to the supernatant. Maintain at a temperature of 4 0 C for 6 hours, centrifuge at 6000 rpm for 30 minutes. After checking for sterility, the supernatant is used to infect the cell culture. Add 0.2 cm 3 of the material from each sample into 4 test tubes with cell culture, from which the growth medium is first removed and the cell monolayer is washed with Hanks’ solution. After incubating the material in a thermostat at 37 0 C for 30-60 minutes, 0.8-1.0 cm 3 of a supporting medium (medium 199) is added to each test tube. To identify the cytopathogenic effect (CPE) of the TGS pathogen, the cell culture is microscoped daily for 5-7 days.
In the absence of CPP in the 1st passage of the material, a series of successive passages are carried out in cell culture. CPD usually manifests itself in the 3rd to 7th passages and is characterized by swelling, rounding of cells and their rejection from the glass. If a virus isolate is isolated, it is identified in a neutralization reaction on cell culture using antisera.
However, isolation of a virus does not provide proof that it is the cause of gastroenteritis in piglets. It is necessary to reproduce the disease in piglets by experimentally infecting piglets with an isolate of the TGS virus. In this way, it is proven that the virus isolated from sick animals is pathogenic for piglets and is an etiological agent in the occurrence of gastroenteritis.
To diagnose THS, it is enough to detect the virus antigen. For this purpose, RIF, RDP and ELISA are used.
Detection of antibodies to the TGS virus is a retrospective method for diagnosing the disease. For this purpose, a neutralization reaction (RN) is used on tissue culture with blood sera from sick and recovered pigs and the TGS virus. In the RN, blood sera from at least 10 sows are examined, taken 2-3 weeks from the onset of the disease and again at an interval of 14-21 days. The maximum titer of virus-neutralizing antibodies to the TGS virus appears 3 weeks after the onset of the disease. In the body of recovered animals, virus-neutralizing antibodies persist from 3 to 12 months.
For the retrospective diagnosis of THS, the indirect hemagglutination test (IHA) is also used. Specific antibodies are determined in paired blood sera of sick and recovered pigs.
Transimissible gastroenteritis suum. A contagious, acute disease caused by an RNA virus from the Coronaviridae family. The disease affects pigs of all age groups and is characterized by vomiting, debilitating diarrhea, dehydration and high mortality of piglets in the first 10 days of life, up to 70-100% (D.F. Osidze, 1987).
Historical reference. The disease was first described by Hurt in the USA (1934). The viral etiology of the disease was established by Hutchings and Doyle in the USA (1946). Subsequently, the disease was established in Japan (1956) and in England (1957). Currently, the disease is registered in many European countries, America, Japan, Australia and Africa. The disease causes enormous damage due to a large mortality rate of young animals (up to 100%), as well as due to a decrease in the reproductive abilities of sows who have recovered from the disease.
Etiology. The causative agent of the disease is an RNA containing a spherical virus, 70 - 100 nm in size, pathogenic only for pigs. The virus is cultivated in primary trypsinized cells of the thyroid gland, kidneys and testicles of piglets, embryonic pig kidney and lung epithelial cells.
The virus is quite stable in the external environment, remains viable at 4°C for up to 3 months, at room temperature for up to 45 days, the Virus is viable for 10 days in the contents of the stomach. Direct sunlight kills the virus within 2 days. At 80 - 100° it is destroyed in 3 - 5 minutes. Inactivated by a 4% formaldehyde solution in 10 minutes, 2% sodium hydroxide in 20-30 minutes, and bleach in 6 minutes.
Epizootological
data. Pigs of all ages are susceptible to the disease, but piglets in the first days of life are most sensitive. The source of infection is sick and recovered animals, slaughter products, as well as feed, water, care items, and overalls for service personnel.
Infection occurs through the nutritional route or through the respiratory system. Carriers of the virus can be dogs, cats, rats, mice. The disease can occur in epizootic and epidemic forms. Pigs that have recovered from the disease carry the virus for 2 months to a year or more.
Pathogenesis. The virus, having entered the body through the alimentary or respiratory route, multiplies in the mucous membrane of the small intestine and enters other organs. Thus, after 19 hours the virus was detected throughout the gastrointestinal tract, in the mesenteric nodes, kidneys, and after 5 days in the lung tissue. Hence the conclusion that the virus primarily multiplies in the mucosa of the small intestine, and then in the lungs and kidneys (Hoper, Haeltermann, 1966). The cause of death in animals is a violation of parietal digestion as a result of atrophy of the villi of the intestinal mucosa.
Clinical picture of the disease. The incubation period is from 16-20 hours to 3 days. The disease in piglets is manifested by vomiting, watery green-yellow feces with an unpleasant odor and pieces of curdled milk, and dehydration. The piglets become lethargic, crowded together, the skin is dirty and damp. In weaned and fattening pigs, as well as sows, symptoms of the disease are limited to decreased or absent appetite, diarrhea lasting one to several days, and vomiting. Some lactating sows experience increased body temperature, vomiting, diarrhea, and subsequently agalactia.
Pathological changes. The main changes are noted in the stomach (the contents contain curdled milk, in later stages of the disease there are hemorrhages on the stomach wall, fibrinous inflammation and even ulcers) and in the small intestine (catarrhal or catarrhal-hemorrhagic inflammation). Lymph nodes of the mesentery and mesenteric lymph nodes are swollen and hyperemic.
Spleen often hypertrophied with hemorrhages or hemorrhagic infarctions.
The kidneys have hemorrhages under the capsule, and in pregnant sows there are hemorrhages in the bladder. Microscopy reveals atrophy of the villous mucosa of the small intestine.
Diagnosis and differential diagnosis. Install based on epizootic, clinical, pathological data, taking into account the results of laboratory studies: pH, virus isolation, bioassays on piglets, electron microscopy, immunofluorescence - in tissue cultures in sections of affected organs. For retrospective diagnosis, RNGA is offered. Making a diagnosis causes great difficulties due to the fact that the etiology of gastroenteritis in newborn piglets can be based on factors of viral, bacterial, and also nutritional origin. Therefore, the main attention should be paid to differential diagnosis, excluding hemagglutinating encephalomyelitis, rotavirus, enterovirus, TSE-like and other infections.
Immunity. Naturally recovered sows develop both natural and general humoral immunity. The main role in its formation is played by secretory antibodies of the JgA class. Once in the intestines of a newborn piglet, they, along with milk and colostrum, prevent the antigen from penetrating into the cell. The higher the activity of antibodies in milk, the longer the immunity of piglets.
Prevention and control measures
are based on preventing the introduction of the virus into the farm. All pig stock to be sold is tested for the presence of antibodies to the TSE and RNGA viruses before export. Animals are not removed from the farm if the antibody titers in the serum are above 1:16. The same measures are carried out on farms with livestock imported from other countries. Contact is allowed only between farms with the same epizootic situation. Farrowing of replacement sows is carried out only in specially designated rooms, separate from the main sows, given the high sensitivity of piglets to the virus.
To destroy the virus, hot disinfectant solutions and sealing of metal objects with a blowtorch or gas torch are used. All healthy sows are vaccinated in accordance with current guidelines. Restrictive measures will be lifted no earlier than 8 weeks. after signs of the disease have subsided. The pig is then considered TSE seropositive. After the restrictions are lifted, the transfer of gilts to fattening farms is allowed. To improve the health of the farm, a systematic culling of all seropositive animals is carried out. Every 6 months TSE-negative sows and boars are serologically examined. If antibodies are detected in less than 20% of breeding pigs, all positive animals are removed from the farm.
viral gastroenteritis of pigs (Gastroenteritis viralis suum), infectious gastroenteritis, transmissible gastroenteritis, a viral disease characterized by catarrhal-hemorrhagic inflammation of the mucous membrane of the stomach and small intestines, manifested by diarrhea, vomiting, dehydration. V.g.s. registered in countries with developed pig farming, it causes great economic damage to the farm due to the death of animals, a decrease in their weight gain, and the costs of carrying out treatment and preventive measures.
Etiology. The causative agent of the disease is a coronavirus of the Coronaviridae family, containing single-stranded RNA, the size of the virion is 80-150 nm. The virus reproduces in piglet kidney cell culture without exhibiting a cytopathic effect in the first passages. In animals during the period of viremia, the virus is found in the mucous membrane of the gastrointestinal tract, as well as in parenchymal organs. Under environmental conditions, the pathogen quickly loses its virulence. At t 50-60((º))C loses pathogenicity within 1 hour, t 80-100((º))C inactivates the virus within 5 minutes. Does not die in dried pathological material for up to 3 days, when t – 28((º))C remains virulent for up to 3 years. The virus is resistant to phenol and antibiotics; inactivated by a 4% formaldehyde solution in 10 minutes, a 2% sodium hydroxide solution in 20-30 minutes, and bleach in 6 minutes. The virus is not pathogenic for laboratory animals.
Epizootology. The source of the infectious agent is sick pigs. TO IN.G.With. pigs of all ages are susceptible; The younger the animal, the more sensitive it is to the virus; suckling piglets under 10 days of age are especially sensitive. Animals excrete the pathogen from the body with feces and vomit for 2-3 months after illness. Factors of transmission of the infectious agent - contaminated feed, water and other environmental objects; carriers of the virus are rodents, dogs, cats, starlings and other birds. Infection occurs mainly through alimentary routes, possibly aerogenously. Outbreaks of the disease are associated with the introduction of virus-carrying pigs into safe farms. If the disease occurs on a farm for the first time, it causes almost 100% death of piglets in the first days of life. The mortality rate of older young animals is 30-40%, of adult animals 3%. Emergence and rapid spread IN.G.With. contribute to unfavorable factors that reduce the body's resistance.
Immunity. Animals that have recovered from the disease acquire immunity, but its duration and intensity vary. Recovered sows transmit virus-neutralizing antibodies to suckling piglets with colostrum. This colostral immunity does not last long.
Course and symptoms. The incubation period is 2-5 days. The main clinical sign in pigs of all age groups is diarrhea. Fever is absent or short-lived only at the beginning of the disease. The disease is most severe in piglets up to 10 days of age and is accompanied by lethargy, vomiting, and refusal to suck. The piglets are crowded together. Watery gray-green feces are released involuntarily. Almost the entire offspring dies on the 3rd-5th day of the disease. In weaned piglets and adult pigs, the disease is more benign and is characterized by decreased appetite, diarrhea and emaciation. Complications in the form of catarrhal bronchopneumonia and chronic gastroenteritis are possible in weanlings and gilts.
Pathological changes. When opening piglets, catarrhal or catarrhal-hemorrhagic inflammation of the mucous membrane of the stomach and small intestine is found. The stomach is abundantly or partially filled with uncurdled milk. The mucous membrane of the small intestines is gray to burgundy in color, covered with cloudy mucus, and ulcerated in places. The intestinal contents are watery, yellow-gray-red in color; gas bubbles occur. Catarrhal and very rarely hemorrhagic gastroenteritis is found in adult pigs. Histological examination reveals a characteristic sign - atrophy of the villi of the small intestines.
The diagnosis is established on the basis of epizootic, clinical and pathological data and laboratory test results (RNGA, MFA, RN and, in difficult cases, a bioassay on sows 6-7 days before farrowing). IN.G.With. differentiated from colibacillosis, salmonellosis, plague, anaerobic dysentery, rotavirus infections and diarrhea of a nutritional nature.
Treatment. Antibiotics are used to prevent bacterial complications.
Prevention and control measures. For warning IN.G.With. carry out measures to protect healthy farms (strict implementation of veterinary and sanitary rules, quarantining newly arrived livestock, examining them for IN.G.With. and etc.). If a disease occurs, a quarantine is imposed on the pig farm, a set of veterinary and sanitary measures are carried out (isolation and treatment of patients, disinfection with a 2-3% sodium hydroxide solution, vaccination of pregnant sows 35-40 days and 15-21 days before farrowing, etc.) . With the in-line farrowing system, round farrows are introduced by stopping the insemination of the queens for 2-3 months.
Ministry of Agrarian Policy of Ukraine
Kharkov State Veterinary Academy
Department of Epizootology and Veterinary Management
Abstract on the topic:
"Viral gastroenteritis of pigs"
The work was prepared by:
3rd year student, 9th group of FVM
Bocherenko V.A.
Kharkov 2007
Plan
1. Definition of disease
2. Historical background, distribution, degree of danger and damage
3. The causative agent of the disease
4. Epizootology
5. Pathogenesis
6. Course and clinical manifestation
7. Pathological signs
8. Diagnosis and differential diagnosis
9. Immunity, specific prevention
10. Prevention
11. Treatment
12. Control measures
1. Definition of disease
Porcine viral gastroenteritis (Latin - Gastroenteritis infectiosa suum; English - Transmissible gastroenteritis; infectious gastroenteritis, transmissible gastroenteritis, Doyle and Hutchings disease, HCV) is a highly contagious disease of pigs, characterized by catarrhal-hemorrhagic gastroenteritis and manifested by vomiting, diarrhea, dehydration of the body and high mortality piglets in the first 2 weeks of life.
2. Is T orical information, inquiry T injury, degree of danger T and and damage
The disease was first described in the USA by Doyle and Hutchings (1946). Then it was noted in Japan (1956), Great Britain (1957) and in many European countries, as well as in our country.
The disease is registered in all countries of the world with intensive pig farming, and at present there are practically no large pig farms in which viral gastroenteritis has not occurred. The disease causes great economic damage
376 due to the high incidence of newborn piglets and their 100% death, loss of live weight gain (up to 3...4 kg) in fattening pigs and the costs of veterinary and sanitary measures.
3. The causative agent of the disease
The pathogen was first isolated by Japanese researcher Tayima (1970). This is an enveloped, pleomorphic DNA-containing hemadsorbing virus of the Coronaviridae family, genus Coronavirus, a virion with a diameter of 60...160 nm, covered with a glycoprotein layer of club-shaped processes reminiscent of the solar corona.
The “corona” glycoprotein induces the synthesis of virus-neutralizing antibodies in the body. The virus is epitheliotropic, reproduces and accumulates in epithelial cells of the small intestine, alveolar macrophages of the lungs and tonsils. Easily adapts and reproduces in the cytoplasm of primary and transplanted cells of pig organs, without causing CPD in the first passages. The virus strains isolated in different countries are serologically identical, but there is an immunological difference between intestinal field and culture strains. The virus is antigenically related to hemagglutinating coronavirus, which causes encephalomyelitis in piglets, as well as to canine coronavirus and coronavirus, the causative agent of feline infectious peritonitis.
The virus is resistant to trypsin, bile acids and changes in pH from 3.0 to 11.0. When frozen, the virus-containing material can be stored for up to 18 months; when heated to 56 °C, it is inactivated in 30 minutes, at 37 °C in 4 days, and at room temperature in 45 days. In liquid feces of sick pigs in the sun it is inactivated in 6 hours, in the shade - in 3 days. Solutions of phenol (0.5%), formaldehyde (0.5%), sodium hydroxide (2%) kill the virus within 30 minutes.
4. Epizootology
Only pigs of all ages and breeds are susceptible, regardless of the season of the year, and newborn piglets, especially the first weeks of life (2...3 weeks), are more sensitive. Under natural conditions, dogs are also susceptible. Laboratory animals do not become infected.
The sources of the pathogen are sick and recovered pigs, but the epizootic chain can include dogs, cats, foxes, migratory birds and synanthropic rodents. In sick animals, starting from the incubation period and for 3-4 months after illness, the virus is excreted in feces, urine and nasal discharge. In dogs and foxes, the virus multiplies in the intestines, and they can contaminate the external environment with it.
Transmission factors can be all environmental objects contaminated with the virus, as well as meat and pig meat products. Newborn piglets become infected through the gastrointestinal tract and respiratory system from virus-carrying sows. In previously prosperous farms, the virus is more often introduced by vehicles, with newly imported virus-carrying pigs, and slaughterhouse waste. The possibility of the virus being introduced by dogs, birds and rodents should be taken into account. In a fresh epizootic outbreak, the disease manifests itself in the form of an outbreak that covers the entire pig population within 3...4 days. The incidence reaches 80...100%. Suckling piglets up to 2 weeks of age and all young animals born within 2...3 weeks die, and in pigs of other age groups the disease occurs with varying severity. 4...6 weeks after the initial appearance, the intensity of the enzootic decreases. Sows develop immunity, and they pass antibodies to piglets with colostrum, protecting them from infection.
In fattening farms, viral gastroenteritis most often occurs among pigs from newly received batches with subsequent spread to the entire population. Mortality is up to 3%. A 2...3-year periodicity of enzootic disease was noted, which can be associated with the timing of the transfer of colostral immunity by sows to newborn piglets.
5. Pathogenesis
The virus enters the body of pigs of all ages mainly through the mouth and, passing through the stomach, enters the intestines. In the epithelium of the small intestine, it is intensively reproduced, causing the destruction of villi. After a few hours, a large amount of virus accumulates in the intestinal lumen, from where it penetrates into the blood and all internal organs. A secondary reproduction cycle occurs in the lung epithelium, leading to significant damage to alveolar macrophages and lung epithelium. As a result of intense destruction, the columnar epithelium of the intestine is replaced by cubic and flat epithelium, and the villi atrophy.
In 90...95% of newborn piglets, villous atrophy occurs within the first 12...24 hours after infection. Degeneration, atrophy and desquamation of the intestinal epithelium and villi lead to disruption of the electrolyte-water balance in the body, acidosis, digestive and metabolic disorders, which causes profuse diarrhea and the development of severe dysbiosis. Putrefactive microflora begins to predominate in the intestines. Often the disease is complicated by the development of escherichiosis.
6. Course and clinical manifestation
The incubation period lasts 1... 3 days, and in newborn piglets it can be shortened to 12... 18 hours, and in adult pigs it can be extended to 7 days.
A primary outbreak of the disease on a farm is usually characterized by a severe course with typical clinical signs. In lactating non-immune sows, an increase in body temperature to 40.5...41 ° C, refusal to feed, vomiting, thirst, depression and complete agalactia (cessation of milk secretion), mucous discharge from the nasal openings, sometimes wheezing and profuse diarrhea. Within 10...12 days, almost all sows become ill, and they develop immunity and virus carriage.
In piglets older than 30 days of age and fattening pigs, the disease manifests itself with the same clinical signs - hyperthermia, vomiting, thirst, refusal to feed, diarrhea, catarrhal rhinitis. Almost the entire livestock gets sick, the sick recover, remain virus carriers and do not get sick again. Mortality reaches 4...5%. Often in pigs of this age, the disease is complicated by escherichiosis, salmonellosis and respiratory diseases, and mortality increases significantly.
In piglets 6...15 days of age, the disease is more severe than in 30-day-old piglets, with a predominance of profuse diarrhea and complications of escherichiosis. Mortality among piglets of this age group increases to 30...70%.
The disease is especially severe in newborn piglets (1...5 days after birth). Within 1...2 days, all piglets in the litter become ill. They experience vomiting and profuse diarrhea, and they refuse to suckle colostrum. At first, the fecal masses are semi-liquid, yellowish in color, but later their excretion becomes involuntary, they acquire a gray-greenish color and an unpleasant putrefactive odor. Patients experience rapid loss of body weight, cyanotic and sticky skin, impaired coordination of movement, convulsions, then a comatose state occurs. Almost all sick piglets die. Some survive, but are sharply stunted and often die at an older age.
In permanently disadvantaged farms, the virus circulates among sows, and depending on the balance of the virus and the strength of the immune system in their body, outbreaks of the disease are possible among newborn piglets at certain intervals, as well as among new livestock introduced into the herd. Colostral immunity in piglets lasts for 50...60 days, and after birth they receive the virus from sows along with antibodies. In this way, natural simultaneous immunization of newborn piglets is carried out, which ensures their protection against the disease at an older age.
7. Pathological signs
The piglets' skin is bluish, stained with fecal matter, and somewhat dry. The stomach of some animals is filled with curdled milk, while in others it contains only a grayish mucous liquid. The gastric mucosa is hyperemic, and there are pinpoint or banded hemorrhages under the mucous membrane. The small intestine is swollen and usually contains a small amount of cloudy, foamy mucus. The intestinal walls are thin, translucent, flabby, and easily ruptured. The mucous membrane is hyperemic, and pinpoint hemorrhages are visible underneath. The large intestine is filled with liquid feed masses, the mucous membrane is hyperemic.
