Microfilariae in the human body are signs of their presence. Dirofilariasis in humans: symptoms and treatment

A person becomes infected with dirofilariasis when bitten by an infected mosquito of the genus Culex, Aedes, or Anopheles. The final hosts of heartworms are animals of the canine, feline, and viverrid families. An infected animal has microfilariae circulating in its blood, which are not infectious to humans or other animals. When a mosquito bites a sick animal, the insect becomes infected. And already in the mosquito’s body, the microfilariae turn into an invasive larva. The infected insect then bites the person and thereby infects him with heartworms. The larva grows in the tissues of the human body, but does not turn into a sexually mature individual. Therefore, it remains unable to reproduce in the human body.

Often, during infection, one larva enters the human body, less often two, and even less often two or four.

Symptoms of the disease

Dirofilaria repens and Dirofilaria immitis cause different forms of the disease. The first is the cause of subcutaneous dirofilariasis, the second is visceral. Subcutaneous dirofilariasis occurs on the territory of post-Soviet countries. And the visceral form is typical for countries such as Japan, USA, Canada, Australia, and Southern Europe.

Symptoms of subcutaneous dirofilariasis

The incubation period lasts from a month to a year. The first symptom of the disease can be considered the appearance of a tumor-like formation under the skin or mucous membrane, which is accompanied by redness and itching in this area of the body. The formation itself may be painful or not bring any unpleasant sensations. A characteristic sign of the disease is the migration of the helminth, which is noted externally as the movement of the formation throughout the body. In two days the larva is able to cover a distance of thirty centimeters.

Often, having discovered a tumor-like formation on the body, people are sent to a surgeon, who suggests a diagnosis of fibroids, atheromas, etc. But during the operation, the doctor discovers an unexpected find in the form of a helminth.

Heartworms have their own “favorite” places in the human body. These are the following areas of the body (as the frequency of damage decreases):

Also, with dirofilariasis, nonspecific symptoms are observed in the form of weakness, fever, pain in the area where the larva is located, which can radiate along the nerve fibers.

In approximately half of the cases, heartworms are localized in the eyes and the membranes surrounding them. The eyelids, conjunctiva, anterior chamber of the eye, sclera, and tissues of the eye fossa are affected.

Such patients may experience a sensation of a foreign body in the eye, redness of the skin of the eyelids, ptosis, and blepharospasm. A tumor forms under the skin.

When the conjunctiva is affected, severe pain, lacrimation and itching caused by the movement of the helminth are noted. The conjunctiva is hyperemic, and sometimes it is possible to view the helminth itself through it.

In many patients, dirofilariasis manifests itself in a relapsing course with periods of exacerbation and extinction of the disease. If the helminth is not removed in a timely manner, inflammation in the soft tissues may develop, as well as the formation of an abscess.

This form of dirofilariasis is often asymptomatic. Sometimes patients may experience chest pain, cough, and hemoptysis.

The disease is detected in most cases suddenly during a chest x-ray or even during lung surgery if a malignant process is suspected. X-rays show nodules in the lungs with a diameter of 1-2 cm.

Diagnostics

An auxiliary diagnostic method may include. With dirofilariasis, antibodies to migratory larvae (Toxocara) may be detected in a person’s blood. A positive ELISA result cannot be the only correct one to determine the final diagnosis.

In addition, methods and can be used at the preoperative stage. In the resulting images, it is possible to detect a small oval or spindle-shaped formation.

It is noteworthy that eosinophilia in a clinical blood test is not typical for dirofilariasis and is observed only in 10% of all cases.

Treatment

In cases where dirofilaria constantly migrates, it is difficult to catch it, but there is a threat of damage to the organ of vision, drugs containing albendazole (vormil, medizol) can be prescribed.

Desensitizing therapy is carried out according to indications.

Prevention

When conducting screening activities, it was found that in different regions of Russia approximately 4-30% of dogs are infected with microfilaria. While in Greece and Iran this figure reaches 25-60%. It is noteworthy that the intensity of human invasion depends on the season. Dirofilariasis in humans is recorded throughout the year, but in most cases it develops in the spring-summer period and less in the autumn-winter period, which is probably due to the exacerbation of dirofilariasis in dogs.

Prevention of the disease consists of three areas:

Mosquito control;
Detection of heartworms in dogs with subsequent treatment;
Preventing human and animal contact with mosquitoes.

Mosquito control

It is known that foci of dirofilariasis form near bodies of water near populated areas. Here, government and medical structures are taking measures to combat insects.

In addition, Culex mosquitoes can live in the basements of multi-story buildings almost all year round. Insects penetrate the ventilation system into apartments, where they bite people and animals. Therefore, appropriate measures should be carried out in the basements of houses.

Detection of dirofilariasis in dogs

Your pet needs to regularly take antihelminthic preventive measures using drugs such as albendazole, ivermectin, levamisole, etc.

You can suspect dirofilariasis in dogs based on certain signs. Changes in the skin come to the fore: baldness, pigmentation, rashes, non-healing wounds, itching.

Gradually, the dog's cardiovascular system is affected by microfilariae. The pet becomes lethargic, passive, loses appetite, the temperature rises, and even with minimal physical activity a cough appears. Often the dog limps, and convulsions may appear.

First of all, it should be noted that in Russia this disease is rare. It is not surprising, therefore, that most doctors have difficulty diagnosing dirofilariasis in humans. What does it consist of? The official name for dirofilariasis is “helminthic infestation caused by roundworms.” Experts call street dogs and cats, as well as mosquitoes, as the main source of the disease - insects are capable of carrying larvae and “implanting” them under the skin. Of course, dirofilariasis, like other diseases of this kind, is most common in hot countries: Africa, India, Vietnam. However, recently more and more cases of infection have been recorded in Russia.

Infection

As mentioned above, heartworm disease in humans can cause heartworm larvae to develop. It may take several months before they appear - this is how long the average incubation period lasts. Naturally, not all people will guess to connect the mysterious manifestations with a month ago.

Symptoms

Affected areas

Treatment

The only way to get rid of the larva is to remove it surgically. It must be emphasized that the use of anthelmintic drugs will not give any result.

Dirofilariasis: prevention

There is no specific prevention as such. It is impossible to be completely sure that the mosquito that bit you is not a carrier of larvae. All you can do is use special insect repellent sprays and try to expose as little skin as possible while outdoors. In order to relieve itching, you can also use products that relieve allergic reactions. If they are not there, then a regular soda solution will do (they wipe the affected area with it). Don't want to allow mosquitoes into closed spaces? Install and purchase several fumigators.

The relevance of the problem of dirofilariasis lies in the constant presence of obligate sources of the disease - animals - near humans and their homes, the widespread distribution of dirofilarias both in animals and in general in natural conditions, low awareness of medical workers and the inclusion of such patients in the wrong direction, namely, doctors of various specialties. For example, most patients with dirofilariasis are seen by doctors with diagnoses such as boils, phlegmon, atheroma, tumor, fibroma, cyst and others.

The first description of dirofilariasis dates back to 1855, when the removal of a worm from the eye of a sick girl by the Portuguese doctor Lusitano Amato was described. Then, with a certain frequency, similar cases are described in France and Italy. In Russia, the first case of dirofilariasis of the eye was described in 1915 in Ekaterinodar by the doctor and scientist A.P. Vladychensky. Already in 1930, the founder of the helminthological school K.I. Scriabin and his students were closely involved in this problem.

Dirofilariasis, upper eyelid

Geographically, dirofilariasis occurs with a certain frequency in Central Asia, Georgia, Armenia, Kyrgyzstan, Kazakhstan, Azerbaijan, Ukraine; in the Russian Federation it is quite rare, mainly in its southern regions (Volgograd region, Krasnodar region, Rostov region, Astrakhan region, and others). However, an analysis of the incidence of recent years has shown that a certain frequency of the disease is also present in regions with a temperate climate (Moscow region, Tula, Ryazan regions, Lipetsk region, Ural, Siberia, Bashkortostan and others). On average, up to 35-40 cases of dirofilariasis are registered in one year in Russia, and in some regions (for example, Rostov) - up to 12 cases per year.

Also, the disease is recorded with varying frequency in North America, Brazil, India, Australia, on the African continent, in Europe (Italy, Spain, France), Sri Lanka, as well as in Canada and Japan. Iran and Greece are considered the most unfavorable countries for dirofilariasis.

Causes of dirofilariasis

The name of the disease comes from the Latin “diro, filium”, which means “evil thread”.
Pathogen in humans– the larval stage (microfilaria) of a filamentous nematode (class Roundworms) of the genus Dirofilaria, which in the human body usually does not reach the mature stage, with rare exceptions (more details in the development cycle).

The vast majority of cases are caused by D. repens and D. Immitis, while the remaining pathogens occur occasionally.

Heartworms

A sexually mature individual up to 30 cm long and up to 1.5 mm wide, thread-like in shape with narrowed
ends. The female has a mouth, esophagus, intestines, nerve ring, vulva, oviducts, uterus and ovaries, while the male has papillae and spicules.

The larvae (or microfilariae) are microscopically small - up to 320 µm long and up to 7 µm wide, have a filamentous appearance with a blunt anterior end and a pointed posterior end. However, due to their size, current flow and lymph can reach “the most remote corners of the human body.”

Source of infection for dirofilariasis– the obligate or obligatory source is domestic animals (dogs in the majority, less often cats – D.repens and D.immitis), isolated cases of the disease are also found among wild animals. The prevalence of urban dogs varies from 3.5 to 30% depending on the region.

Dirofilariasis, source of infection - dogs

The intermediate hosts are mosquitoes of the genus Culex, Aedes, and Anopheles - they transmit invasive larvae (microfilariae) from animals to each other, as well as to humans. The prevalence of mosquito larvae varies from 2.5% (Anopheles) to 30% (Aedes). A role in the transmission of larvae and other blood-sucking insects - fleas, lice, horseflies, ticks - cannot be ruled out. Humans are an occasional and atypical host for heartworm larvae.

Dirofilariasis, the vector of infection is mosquitoes

Mechanism of human infection– transmissible (through the bites of blood-sucking insects - mosquitoes and others), as a result of which larvae from animals enter the human body.

Human sensitivity is universal. There is no dependence on age and gender, however, the majority of patients are in the age group of 30 to 40 years. There is a greater risk of infection in certain groups of people who have direct contact with mosquitoes that transmit heartworm disease. The risk group includes:
- fishermen, hunters, gardeners,
- pet owners (dogs and cats),
- living near rivers, lakes, swamps,
- tourism lovers,
- workers of forestry enterprises and fisheries.

There is a seasonality of the greatest infection with heartworm larvae - spring and summer. The rise in incidence is recorded in two waves: in April-May and October-November.

Heartworm development cycle

A sexually mature individual lives in the cavity of the right ventricle of the heart, as well as the right atrium, pulmonary artery, vena cava, and bronchi of animals. Dirofilariae release large numbers of larvae into the blood (microfilariae-1). Larvae are up to 320 microns long and up to 7 microns wide, that is, microscopically small. The larvae can penetrate through the blood and lymph into small vessels, various organs and tissues, and can also be transmitted from mother to fetus. It is from the blood that blood-sucking carriers mosquitoes and other insects swallow the larvae when sucking blood. During the day, microfilariae-1 are in the mosquito intestine, and then penetrate into the cavities where they molt (microfilariae-2), then reach the lower lip of the mosquito and mature to the invasive stage (microfilariae-3). The duration of maturation in the mosquito’s body is on average 17 days. The mosquito then attaches itself to either the skin of an animal or a person and injects microfilaria-3. For 90 days, the larvae continue their development at the site of the bite (primary affect) - this is in the subcutaneous fat, where they molt twice more, which ultimately leads to the formation of microfilaria-5. Subsequently, it enters the blood and spreads throughout the body, can settle in organs and tissues (usually the heart, pulmonary artery), where it matures to the sexually mature stage within another 3 months. Thus, the entire development cycle lasts up to 8 months. Microfilariae can circulate in the host's blood for up to 3 years.

Dirofilariasis, development cycle

The incubation period (from the moment of invasion until the appearance of the first symptoms) lasts from 30 days to several years and depends on the state of the person’s immune system.

Forms of dirofilariasis:

Dirofilariasis, ocular form

With any form of dirofilariasis, most patients also present general complaints - weakness, irritability, anxiety, sleep disturbances, headaches.

The literature describes rare cases of dirofilariasis - omentum, pleura, male genital organs (scrotum, testicles), fallopian tubes. Cases of dirofilariae damage to the lungs and heart in humans are extremely rare.

Diagnosis of dirofilariasis

1) Primary diagnosis of dirofilariasis clinical and epidemiological. However, as a rule,
collecting an epidemiological history (the presence of dogs near the home, mosquito bites, visits to the forest, fishing, garden plots) is not very informative in terms of making a diagnosis. It is worth paying attention to the patient’s stay in an endemic area during periods of high mosquito activity. Seasonality is also important information: with a short incubation (up to 3 months from the moment of infection), the disease appears in June-July or October-November, and with a long incubation (up to 8 months), the disease appears the next year after infection.
The main role is played by the complaints of patients: the appearance of subcutaneous nodes, which during the day can migrate at a distance of 10-30 cm, inside of which there is a sensation of “crawling”, as well as other characteristic complaints described above. Differential diagnosis is carried out with erythema nodosum, furuncle, carbuncle, abscess, allergic manifestations, conjunctivitis, cholazions (consequences of “styre” of the eye) and other diseases.

Dirofilariasis, microscopically

But doctors do not know everything about the life forms of dirofilaria in the human body; there are cases when all tests are within normal limits, but dirofilaria still lives under the skin - either crawls or lies in a capsule with microfilaria.

Dirofilaria after removal from under the skin

Drug therapy is rarely carried out and ivermectin and diethylcarbamazine are used, however, allergic reactions are possible during therapy.

Concomitant therapy: non-steroidal anti-inflammatory drugs, glucocorticosteroids, antihistamines, sedatives and others.

For the ocular form of dirofilariasis, the main method of treatment is surgical removal of the helminth from under the skin of the eyelid, conjunctiva, followed by the administration of disinfectants and anti-inflammatory drugs: drops of chloramphenicol, sodium sulfacyl, colbiocin, followed by ointments (erythromycin, tetracycline). A number of patients require dexamethasone drops to reduce inflammation. The entire period of therapy is supported by the prescription of antihistamines (Zyrtec, Claritin, Erius, Diazolin and others).

Most often, dirofilariasis in people affects the eyes, due to the fact that there is no official registration of helminthiasis, and medical workers are poorly informed, patients with signs of dirofilariasis are diagnosed by ophthalmologists as a boil, cyst, phlegmon, and so on. In this regard, treatment becomes more complicated and often the true diagnosis poses a danger to the patient.

Causes of the disease

The causative agent of dirofilariasis is a thread nematode, which is in the larval stage. Its size is 320 * 7 microns, the rear end of the larva is slightly pointed, and the front end is blunt. When an individual reaches sexual maturity, its length can be 30 cm and its width 1.5 mm. Females have an oral cavity, esophagus, intestines and reproductive organs. Males have spicules and papillae.

Cats rarely carry heartworm disease; dogs are the most common carriers. If we talk about the intermediate host, then it is a mosquito; it is this insect that carries the larvae. Fleas, lice, ticks and horseflies and other insects that suck blood can also be carriers. Humans are not a typical host for dirofilaria, not even an intermediate host; as a rule, it is an accidental host.

Description of the disease

Fishermen, summer residents, hunters, agricultural workers are people who are at risk. In addition, this group can include tourists, pet lovers and those who live near stagnant bodies of water.

Types of dirofilariasis

The types of dirofilariasis are determined based on where exactly the pathogen is localized in the human body.

Pulmonary. This type is also called the heart type. This name is given because this type of worm lives in the heart of dogs.
Extrapulmonary. It, in turn, is divided into subspecies: subcutaneous, ocular, cardiovascular, visceral - the worm lives in the liver, uterus or abdominal cavity.

To date, 4 cases of detection of the worm in the human heart muscle have been recorded. 2 of them occurred in the USA, one in Brazil and one in Japan. There is a described case of detection of microfilariae in human blood, which means that the worm has reached sexual maturity and began to reproduce.

Many scientists believe that the statistics of people who suffer from pulmonary dirofilariasis are not accurate enough, the disease in most cases is asymptomatic, and besides, a mosquito that can feed on both dog and human blood can infect a large number of people with dirofilariasis.

Worm development cycle

Sexually mature individuals are most often localized in the heart or lung of their host; they lay larvae, which are carried throughout the body through the bloodstream and can enter any organ and vessel of the host. The mother can transmit the larvae to the fetus.

Mosquitoes, which are intermediate hosts, ingest larvae when they suck blood from an animal. The first day the larva remains in the mosquito’s stomach, and then molting occurs, and the larva gradually approaches the mosquito’s lip, where the larva becomes a nematode.

After a bite, larvae are injected into the human bloodstream and in the place where the bite was made, the larva remains for another 3 months. Thus, the larvae are already in the human subcutaneous fat. From there, the blood current carries them throughout the body, and they can settle in organs and tissues. After 3 months, the larva can become a sexually mature individual, but in the human body this happens extremely rarely.

In addition, not a single case has been recorded in which individuals of different sexes were found in the human body, so fertilization in the human body is very doubtful. The entire development cycle of dirofilaria takes 8 months.

Signs of the disease in humans

Diagnosis and symptoms of the disease are complicated by the fact that the incubation period of dirofilariasis can range from a month to several years. Therefore, the symptoms and treatment of the patient are delayed.

With cutaneous dirofilariasis, the symptoms are characteristic of tissue helminthiasis. In the place where the worm is localized, a compaction occurs, which upon palpation responds with pain. Suppuration may occur in this area. Some people report feeling the worm moving through their body.

In this case, no problems with visual acuity arise. Regardless of which organ the worm is located in, a person may experience anxiety and excessive irritability, chronic weakness and fatigue, sleep disturbances, and signs of intoxication of the body.

If at least one of the above symptoms occurs, the person is strongly recommended to consult a doctor and undergo testing for dirofilariasis; treatment can only be effective if correctly diagnosed.

Diagnosis of the disease

The main factor in diagnosis is the patient’s complaints and symptoms. For a more accurate diagnosis, the doctor must know whether the patient has been in endemic areas and whether he is at risk. Then the doctor examines the patient’s eyes for the presence of nodes and also examines the skin.

After all the studies, the doctor can prescribe treatment.

Treatment of dirofilariasis

When a doctor begins to treat dirofilariasis, he sets the following goals:

Subcutaneous dirofilariasis is treated in most cases on an outpatient basis, the patient undergoes all the necessary surgical procedures per day. For pulmonary forms, treatment in a hospital setting is necessary.

Therapy is based on surgery; if the nodules are removed without problems, then no treatment is required after surgery. But before surgical procedures, the doctor may prescribe drug therapy, if required. The most commonly prescribed drugs are Diethylcarbamzin and Ivermectin.

Tetracycline antibiotics are a new approach for the treatment of dirofilariasis; they destroy the bacteria that secrete the filariae, while at the same time the worms themselves die, because the bacteria are their symbionts.

If the diagnosis is made incorrectly, the treatment will be irrational. In medical practice, there was a case when a patient had her breast removed, suspecting she had cancer, but after the operation it turned out that it was a helminth infection. Therefore, it is very important to carry out correct and thorough diagnostics to avoid such errors.

How is the operation performed?

When the helminth is localized in the eye, the doctor uses special instruments to remove the worm, after which the patient takes anti-inflammatory and disinfectants. Treatment of the eye is indicated, for example, with Dexamethasone drops. A course of antihistamines is required.

The prognosis is favorable in the vast majority of cases. Any complications are extremely rare. This may be a pulmonary infarction or nonspecific respiratory symptoms, and there is also evidence of intraocular infections.

Why is it dangerous?

No lethal outcomes have been described; the worst thing that pulmonary dirofilariasis can lead to is a wedge-shaped resection of the area affected by the worm in order to prevent a more serious pathology. Internal hemorrhages can be caused by the visceral form.

Animal diagnostics

To reduce the risk of contracting dirofilariasis, you need to carefully examine your pet; in an animal with signs of the disease, you can observe skin rashes, lumps, wounds and small tumor formations. If helminths live in the heart muscle of an animal, then the animal becomes passive, it loses its appetite, coughs, and the temperature may rise. In particularly severe cases, the dog may experience seizures and lameness.

To prevent helminthiasis in dogs and cats, it is necessary to give the animal antihelminthic drugs promptly and regularly. How often to give the drug and in what dosage is determined by the veterinarian. It is also important to take precautions against fleas and ticks. Treat the fur with special products, comb it out or wear an anti-flea collar.

Video

It is noteworthy that the probability of infection by larvae is much higher in the spring-autumn period of the year. With proper diagnosis and timely surgery, you can completely recover from this disease, which will not leave behind consequences in the form of complications or any restrictions in a person’s life.

Etiology

The cause of the development of dirofilariasis is an insect bite that previously had contact with infected feces of a dog, or less often a cat.

Middle-aged people, from thirty to forty years old, are susceptible to this disease. But there are some groups of people who are most likely to come into contact with the carrier. These groups include:

people with cats or dogs living in their house or apartment;
fishermen and hunters;
those who live in close proximity to bodies of water of any size;
lovers of this type of recreation such as tourism;
agricultural and fishery workers, as well as gardeners.

In the human body, the disease can progress in two forms - ocular and subcutaneous. Less commonly, damage to the mammary glands and scrotum is observed. In a few days, the worm can travel a distance of up to thirty centimeters.

Symptoms

But in almost all known clinical cases, the manifestation of dirofilariasis entails the appearance of the following symptoms:

general weakness of the body;
severe headache;
nausea and vomiting;
slight increase in body temperature;
pain in the place where the worm is located;
pain and swelling of the eyes;
double vision;
sleep disturbance;
irritability;
sensation of movement under the skin or in the eyes.

Diagnostics

Diagnosis of dirofilariasis can be carried out in several ways:

The main way to confirm the diagnosis is a complete examination of the worm that was removed. Therefore, only after the operation the patient is diagnosed with dirofilariasis.

Treatment

It is impossible to get rid of the worm except through surgery. The exception is those cases when a purulent bulge is formed from the presence of a worm under the skin, which may burst on its own. Then the worm can begin to crawl out on its own. If the purulent formation bursts and the contents leak out, but there is no worm there, you need to urgently go to the hospital for medical help.

Since it is possible to diagnose dirofilariasis only after surgery, doctors can treat the patient for completely different diseases. Very often it is possible to detect a large worm during a routine x-ray. But in medical practice, more than half of the cases of dirofilariasis detection occur during other operations.

Only after an ophthalmological examination is it possible to accurately determine where the worm is located in the eyeball - near the pupil or under the upper eyelid. After removing the worm from the eye, the patient is prescribed special eye drops and ointments as treatment, which will need to be placed behind the eyelid.

Prevention

Prevention of dirofilariasis is mainly aimed at:

limiting contact with pets;
timely treatment of this disease in dogs and cats;
personal protection against mosquito bites, in the form of aerosols, ointments and protective clothing.