Dirofilariasis - Causes, symptoms and treatment. MF.

Dirofilariasis refers to geogelmintosis that affects mainly animals( dogs, less often cats), with the heart muscle as the main point of application. Despite zoo-specificity of the disease, cases of human invasion due to the presence of a special carrier of larvae from animals - a mosquito - are more frequent. Data on the incidence among humans vary and are very low due to low detectability, as well as the lack of official registration of parasitosis.

Dirofilariasis is a parasitic disease that affects mainly animals, but also occurs in humans caused by the larval stage of the filamentous nematode of the genus Dirofilaria, characterized by damage to the organs of vision, as well as other organs and systems with predominantly chronic course.

The urgency of the problem of dirofilariasis consists in the constant presence of obligate sources of the disease - animals - near the person and his dwellings, the widespread distribution of dyrophilia in animals and in general in natural conditions, low awareness of medical workers and the entry of such patients not in profile,to doctors of various specialties. For example, most patients with dyrofilariasis go to doctors with such diagnoses as furuncle, phlegmon, atheroma, tumor, fibroma, cyst and others.

For the first time the description of dirofilariasis is dated 1855, when the removal of a worm from the eye of a sick girl by the Portuguese doctor Lusitano Amato is described. Then, with a certain frequency, similar cases are described in France, in Italy. In Russia, the first case of eye diafilariasis was described in 1915 in Ekaterinodar by the doctor and scientist Vladychensky AP.Since 1930, the founder of the helminthological school of KI.Scriabin and his disciples were closely involved in this problem.

Dirofilariasis, the upper eyelid

Geographically, dirofilariasis occurs with a certain frequency in Central Asia, Georgia, Armenia, Kyrgyzstan, Kazakhstan, Azerbaijan, Ukraine, in the Russian Federation is rare, mainly in its southern regions( Volgograd Region, Krasnodar Territory, Rostov Region, Astrakhanarea, and others).However, the analysis of the incidence of recent years has shown that a certain frequency of the disease is present in regions with a moderate climate( Moscow region, Tula, Ryazan regions, Lipetsk region, Ural, Siberia, Bashkortostan and others).On average, up to 35-40 cases of dyrofilariasis are registered in Russia on average, and up to 12 cases per year in some areas( eg, Rostov).

Also the disease with different frequency is registered in North America, Brazil, India, Australia, on the African continent, in Europe( Italy, Spain, France) Sri Lanka, and also in Canada, Japan. Iran and Greece are considered the most unsuccessful for diofilariasis.

Causes of the occurrence of dirofilariasis

The name of the disease came from the Latin "diro, filium", which means "evil thread".
The causative agent of a human is the larval stage( microfilariae) of a filamentous nematode( class of Roundworms) of the genus Dirofilaria, which in the human body does not reach the sexually mature stage( more in the development cycle).

There are several types of dirofilaria:
1) Dirofilaria repens, Dirofilaria immitis( parasitize in dogs and cats),
2) Dirofilaria ursi( brown bear and Amur tiger),
3) Dirofilaria tenuis( raccoons),
4) Dirofilaria subdermataporcupines),
5) Dirofilaria lutrae et spectans( Brazilian and North American otters),
6) Dirofilaria striata( wild American cat).

The vast majority of cases are caused precisely by D. repens and D. Immitis, while the other pathogens occur sporadically.

Dirofilariae

Sexually mature specimen up to 30 cm long and up to 1.5 mm wide, threadlike with narrowed
ends. The female has a mouth, esophagus, intestine, nerve ring, vulva, oviducts, uterus and ovaries, in the male - papillae and spicules.

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

Source of infection in dirofilariasis - obligate or mandatory source - these are domestic animals( dogs in most, less often cats - D. repens and D. immitis), single cases of the disease are found among wild animals. The severity of urban dogs varies from 3.5 to 30%, depending on the region.

Dirofilariasis, the source of infection - dogs

Intermediate hosts are mosquitoes of the genus Culex, Aedes, Anopheles - they carry invasive larvae( microfilariae) from animals to each other, and also to humans. The incidence of mosquitoes by larvae varies from 2.5%( Anopheles) to 30%( Aedes).The role in transferring larvae and other bloodsucking insects - fleas, lice, hills, ticks - is also not excluded. Man is an accidental and atypical host for the larvae of the dirofilaria.

Dirofilariasis, a vector of infection - mosquitoes

The mechanism of human infection is transmissible( through the bites of bloodsucking insects - mosquitoes and others), as a result of which larvae from animals enter the human body.

Man's susceptibility is universal. There is no dependence on age and sex, however the majority of patients 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 the carriers of diofilariasis - mosquitoes. The risk group includes:
- fishermen, hunters, truck farmers,
- owners of animals( dogs and cats),
- living near rivers, lakes, marshes,
- tourism lovers,
- forestry workers, fisheries.

There is a seasonality of the greatest infection with the larvae of the dirofilaria - the spring-summer period. The rise in morbidity is registered by two waves: in April-May and October-November.

The cycle of development of dirofilaria

A mature individual lives in the cavity of the right ventricle of the heart, as well as the right atrium, pulmonary arteries, hollow veins, and bronchi of animals. Dyrofilariae release a large number of larvae into the blood( microfilariae-1).Larvae up to 320 microns in length and up to 7 microns in width, that is, microscopically small. Larvae can penetrate into small vessels, various organs and tissues, and be transmitted from mother to fetus with blood and lymph flow. It is from the blood of sucking mosquitoes and other insects that swallow larvae with bloodsucking. Within a day, microfilariae-1 are found in the mosquito's kitten and then penetrate into the cavities where their molting occurs( microfilaria-2), then reach the lower lip of the mosquito and mature to an invasive stage( microfilaria-3).The duration of maturation in the body of a mosquito is on average 17 days. Then the mosquito sucked either to the skin of the animal, or to the person and the microfilaria-3 is spraying. Within 90 days, the larvae continue their development at the site of the bite( primary affect) - it is in the subcutaneous fat, where they molt twice more, which eventually leads to the formation of microfilaria-5.Later it gets into the blood and spreads through the body, it can settle in the organs and tissues( more often it's the heart, the pulmonary artery), where they mature to the mature stage for another 3 months. Thus, the entire development cycle lasts up to 8 months. In the blood of the host microfilariae can circulate up to 3 years.

Dirofilariasis, the development cycle of

The complete cycle of development of dirofilariae occurs in animals. Man is an accidental and deadlock host of larvae, most of which still die when hit. In humans, both males and females rarely parasitize, so there is no fertilization possibility for the female and, accordingly, separation of the larvae. Also in humans, microfilariaemia( that is, larvae in the blood) is rare enough. These moments allow us to say epidemiologically that a person is not the source of infection.

Pathogenic effect of the dirofilaria on the human body

Most often, only one individual of the dirofilaria is identified. Since fertilization is virtually impossible, the growth of an adult takes about 8-9 months, with the parasite rarely leaving the site of primary localization( i.e., the node in the subcutaneous fat layer).

The main pathogenic effect of dirofilaria is the primary affect( at the site of the mosquito bite) - an inflammatory reaction in the form of changes in subcutaneous fat in the form of seals, inflammations, the appearance of dense formations up to 4 cm or more, accompanied by pain and itching. Pathomorphologically, the node is a cavity formation with serous-purulent contents, inside of which there is a microfilaria, and then a dirofilaria surrounded by a connective tissue capsule. The contents of the node are "rich" with cells of inflammation and connective tissue( neutrophils, leukocytes, eosinophils, macrophages, fibroslastic), as well as abundance of protein. Often the parasite perishes, gradually decomposing.

Clinical Symptoms of Dirofilariasis

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

Forms of dirofilariasis:

a) Skin form is a fairly common form in humans. In the place of introduction
larvae( it coincides with the place of sucking blood sucking insect) appears a small seal, painful to the touch. About half of the patients complain of the migration( migration) of the seal of the parasite itself under the skin. That is, within a day, the compaction changes the location by 10-30 cm, and in the previous place it completely disappears. When cutaneous, patients complain of the feeling of parasite crawling, of stirring in various parts of the body, but always inside the site itself, as well as "phantom" paresthesia( imaginary sensation of the goosebumps), which is more associated with neurosis. The course of the disease with the dermal form is wavy, that is, the periods of exacerbation change during periods of remission( calmness).In the future, in the absence of medical assistance inside the node, an abscess can form, in which there are strong pulling pains in the focus area, redness of the skin above it.
Sometimes with strong combs the knot can open, and the parasite comes out.

b) The eye form is also one of the most common in man( 50% of all cases).It is
in this form that patients quickly seek medical help. The parasite is located under the skin of the eyelids, sometimes under the conjunctiva of the eye, less often in the eyeball itself. Usually the affected area affects the eyelids, the mucous membrane - conjunctiva, anterior chamber of the eye and sclera. The patient has a foreign body feeling in the eye, swelling and redness of the eyelids, soreness when making oculomotor movements, inability to fully lift the eyelids( blepharospasm), profuse lachrymation, itching in the area of ​​the affected eye. Outwardly, the process resembles Quincke's allergic edema. The visual acuity remains unchanged. Just like with the dermal form, with ophthalmic patients complain about a feeling of stirring in the area of ​​the affected eye. Locally - under the skin of the eyelids there is a small tumor-like formation or nodule( granuloma), and when examining the conjunctiva, one can see the dirofilaria itself. With the defeat of the eyeball, the appearance of diplopia( bifurcation), exophthalmos( bulge of the eye).

Dirofilariasis, ophthalmic form

In most of the forms of dirofilariasis, most patients present general complaints - weakness, irritability, anxiety, sleep disorders, headaches.

In the literature, rare cases of dyrofilariasis - omentum, pleura, male genital organs( scrotum, testicles), fallopian tubes are described. Cases of defeat by the dystrophy of the lungs, the heart in humans are extremely rare.

Diagnosis of dirofilariasis

1) Primary diagnosis of diafiliasis Clinical and epidemiological .However, as a rule,
collection of an epidemiological anamnesis( the presence of dogs near the home, mosquito bites, visits to forests, fishing, orchards) is poorly informative in terms of diagnosing. Pay attention is the patient's stay on the endemic territory during the period of high activity of mosquitoes. Also important is the seasonality: with a short incubation( up to 3 months after the infection), the occurrence of the disease in June-July or October-November, and with prolonged incubation( up to 8 months) - the onset of the disease the next year after infection.
The main role is played by complaints of patients: the appearance of subcutaneous nodes, which within a day can migrate at a distance of 10-30 cm, within which there are sensations of "crawling", as well as other characteristic complaints described above. Differential diagnosis is performed with erythema nodosum, furuncle, carbuncle, abscess, allergic manifestations, conjunctivitis, chojazion( the effects of "barley" eyes) and other diseases.

2) Laboratory diagnostics includes:
- a general blood test( eosinophilia up to 10-11%);
- macroscopic examination of the parasite after surgical removal of the helminth from the focus( node): detection of a filiform parasite with a rounded anterior and pointed posterior ends. The internal organs of the parasite, the presence of microfilariae in the uterus of the female are also examined.
- Morphological examination of a distant node or granuloma: a focus of chronic inflammation with a capsule from the outside, inside which is a thin round parasite, coiled into a ball. Distinctive features - the presence of "cuticular spines" - the so-called vertices of longitudinal ridges on the cuticle of the parasite.
- Specific serological responses to the detection of parasite antigen in the blood:
is an ELISA for the detection of somatic antigen, dyrophilia, PCR diagnostics for the purpose of determining repetitive DNA sections of some species of dirofilaria or other antigens, and the immunoblot method for detection of antigens of adults and larvae.

Dirofilariasis, microscopically

3) Instrumental diagnostics ( ultrasound examination of formations and nodes with detection inside the coagulated parasites, radiography and fluoroscopy, MRI, CT).

Treatment of dirofilariasis

Tactics of treatment are determined by the form of the disease. More often than not, it is the parasitization of one individual, and is immature, so toxic antiparasitic treatment is rarely performed.

The main method of treatment is surgical - removal of formations, nodes, granulomas with the subsequent morphological study of education. In order to prevent the migration of the parasite during the operation, the day before is prescribed ditrazine.

Drug therapy is rarely performed and Ivermectin, diethylcarbamazine is used, however, allergic reactions are possible during therapy.

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

With the eye form of dirofilariasis, the main method of therapy is the operative removal of the helminth from
under the skin of the eyelid, conjunctiva with the subsequent administration of disinfectant and anti-inflammatory drugs: drops of levomycetin, sulfacil sodium, and sorbicin followed by ointment( erythromycin, tetracycline).A number of patients require the administration of drops of dexamethasone in order to reduce inflammation. The entire period of therapy is supported by the appointment of antihistamines( zirtek, claritin, erius, diazolinum and others).

Prevention of dirofilariasis

- combating the growth of the population of stray animals( dogs, cats);
- individual protection against bloodsucking insects( repellents, protective clothing);
- deworming of domestic dogs and cats for the prevention in the spring-summer period( vermitane, levamisole, ivermectin, selamectin, dextomax, novomek);
- in the foci of parasitosis - treatment of reservoirs in order to reduce the number of mosquitoes( delirvatsiya).

The doctor infektsionist Bykova N.I.