Vucheriasis (filariasis): causes, symptoms, diagnosis, treatment

Filariasis is a group of transmissible helminthiases, common mainly in countries with tropical and subtropical climates. Endemic foci of filariasis of the lymphatic system are found in 73 countries. According to WHO, 120 million people are infected with these helminthiases, and 1,100 million live in the risk zone.

Wuchereriasis is a transmissible filariasis, biohelminthiasis, anthroponosis. Adults live in the lymphatic vessels, and larvae (microfilariae) in the blood.

Wuchereria development cycle

Wuchereriasis is transmitted when a person is bitten by mosquitoes of the genera Culex, Anopheles, Aedes or Mansonia. Wuchereria is a biohelminth, and its development cycle involves a definitive and intermediate host. The definitive host is a person, and the intermediate hosts are mosquitoes of the genera Culex, Anopheles, Aedes or Mansonia.

When a mosquito bites a person, the invasive larvae (microfilariae) located in its mouthparts break the shell of the proboscis, get on the skin and actively penetrate it. With the blood flow, they migrate to the lymphatic system, where they grow, molt, and after 3-18 months become sexually mature males and females. The male and female are located together, forming a common ball.

Wuchereria are viviparous. Mature helminths are localized in the peripheral lymphatic vessels and nodes, where females give birth to live second-stage larvae (microfilariae) covered with a sheath. The larvae migrate from the lymphatic system to the blood vessels. During the day, they are found in large blood vessels (carotid artery, aorta) and vessels of internal organs. At night, the larvae migrate to the peripheral blood vessels, and therefore they are called Microfilaria nocturna (night microfilariae). The daily migration of the larvae is associated with the night activity of mosquitoes (carriers of the causative agent of wuchereriasis).

When a female mosquito bites a sick person, the microfilariae enter the insect's digestive tract, shed their case, and penetrate the stomach wall into the body cavity and chest muscles. In the muscles, the larvae molt twice, become fourth-stage invasive larvae, and penetrate the mosquito's mouth apparatus. The duration of the larval development cycle in a mosquito depends on the temperature and humidity of the environment and ranges from 8 to 35 days. Optimal conditions for the development of invasive larvae are a temperature of 29-30 °C and humidity of 70-100%. In the mosquito's body, the larvae remain viable throughout their entire life.

The lifespan of adult helminths in the human body is about 17 years. Microfilariae remain viable in the bloodstream for about 70 days.

Epidemiology of wuchereriosis

Endemic foci of wuchereriasis are found in countries with tropical and subtropical climates. Wuchereriasis is widespread in West and Central Africa, Southeast Asia (India, Malaysia, China, Japan, etc.), South and Central America (Guatemala, Panama, Venezuela, Brazil, etc.), and on the islands of the Pacific and Indian Oceans. In the Western Hemisphere, the range of wuchereriasis is limited to 30° N and 30° S, and in the Eastern Hemisphere - 41° N and 28° S.

Wuchereriasis is primarily a disease of the urban population. The growth of large cities, overcrowding, lack of sanitary control, contaminated water reservoirs, abandoned water supply and sewerage systems favor the reproduction of mosquitoes.

In developing countries in Asia and Africa, where cities and towns are being built, the incidence of Wuchereriasis is increasing.

The source of the spread of the disease are infected people. The carrier of the pathogen in urban conditions is most often mosquitoes of the genus Culex. In rural areas in Africa, South America and some Asian countries, wuchereriasis is carried mainly by mosquitoes of the genus Anopheles, and on the islands of the Pacific Ocean - by mosquitoes of the genus Aedes. Human infection occurs due to the penetration of invasive larvae during a mosquito bite.

What causes wuchereriasis (filariasis)?

Wuchereriasis is caused by Wuchereria bancrofti, has a white thread-like body covered with a smooth cuticle, thinner at the head and tail ends. The length of the female is 80-100 mm, width - 0.2-0.3 mm, and males - 40 mm and 0.1 mm, respectively. Usually, males and females intertwine with each other, forming balls. Larvae (microfilariae) are covered with a transparent case and have a length of 0.13-0.32 mm, and a width of 0.01 mm.

Pathogenesis of Wuchereriasis

In the early stages of the disease, symptoms of wuchereriasis in toxic-allergic reactions appear: fever, swelling, skin rashes, blood eosinophilia, etc. Later (after 2-7 years), inflammation of the skin and deep lymphatic vessels develops. The lymphatic vessels in which adult parasites are located expand, thicken, the walls are infiltrated with lymphocytes and eosinophils. Granulomas form around the helminths. Dead helminths lyse or calcify and are surrounded by fibrous tissue. Necrosis with swelling and pus may develop at the site of death. Granulomatous lymphangitis and lymphadenitis develop. The lymph nodes enlarge, become painful, and swelling of the surrounding tissues develops. The lymph nodes and lymphatic vessels of the lower extremities and genitourinary organs are most often affected. With intensive invasion, the lymphatic vessels become blocked, leading to disruption of lymph outflow, resulting in organ edema (elephantiasis). Sometimes wuchereriasis is complicated by the addition of a secondary infection.

Symptoms of Wuchereria

Symptoms of wuchereriasis depend on the individual immune response caused by various factors - age, degree of infection, etc. The course of this disease is polymorphic. The incubation period of wuchereriasis, lasting from 3 to 18 months, is asymptomatic. In people living in endemic areas and infected with microfilariae, symptoms of the disease may be absent. This is due to the fact that the indigenous people of these areas have developed partial immunity due to reinvasion. The incubation period in local residents lasts 12-18 months. In non-immune visiting citizens with a weak invasion, a sign of the disease may be skin itching; their incubation period is shorter and lasts 3-4 months, which corresponds to the time from the penetration of invasive larvae into the human body to the beginning of the birth of microfilariae by mature females.

In the clinical course of wuchereriosis, acute and chronic forms are distinguished.

The acute form of the disease is characterized by symptoms of wuchereriasis in the form of allergic manifestations, which are caused by increased sensitivity of the body to the helminth. At this stage, lymphadenitis, lymphangitis develop in combination with fever and malaise. The lymphatic system is affected more often in men and manifests itself as furunculitis, epididymitis, orchitis. The frequency of exacerbations of adenolymphangitis varies from 1-2 per year to several per month. During exacerbations, lymphatic edema is noted, which gradually disappears. Over time, the disappearance of edema is incomplete and the disease becomes chronic.

The chronic form of wuchereriasis develops 10-15 years after infection. It is accompanied by the development of persistent edema and elephantiasis, which arise as a result of the progression of lymphostasis, proliferative processes and fibrosis in the skin and subcutaneous tissue. The size of the affected organs (scrotum, lower limbs, mammary glands) is greatly increased. With elephantiasis of the scrotum, its weight can reach 3-4 kg, sometimes 20 kg or more. Elephantiasis develops less frequently and more slowly among local residents than among visitors.

In chronic wuchereriasis, hydrocele often develops. Microfilariae may be found in the fluid puncture.

Sometimes chyluria (the presence of lymph in the urine) is observed, manifested by a milky-white color of urine, chylous diarrhea (diarrhea with an admixture of lymph). This leads to hypoproteinemia due to loss of proteins and to weight loss in patients.

Among residents of endemic foci of wuchereriasis in South and Southeast Asia, the syndrome of "tropical pulmonary eosinophilia" is widespread, characterized by the presence of polylymphadenitis, hepatosplenomegaly, subfebrile fever, night coughing fits, difficulty breathing due to bronchospasm, dry wheezing. An increase in ESR and pronounced eosinophilia (up to 20-50%) are also noted. In the absence of treatment and progression of the disease, pulmonary fibrosis develops.

With a long-term course of the disease, patients may develop symptoms of wuchereriasis, which are a consequence of glomerulonephritis, endomyocardial fibrosis, eye damage (conjunctivitis, iridocyclitis), and a secondary infection may also occur (abscesses of internal organs, peritonitis).

Complications of Wuchereriasis

Complications of wuchereriasis are associated with damage to the lymphatic system (elephantiasis). Sometimes there is blockage of the ureters by coagulants, dysfunction of the limbs with the formation of scars in the joint area, the addition of a secondary infection with the development of acute bacterial lymphangitis and thrombophlebitis.

Wuchereriasis is characterized by a long course. Elephantiasis leads to loss of ability to work. Fatal outcomes occur as a result of secondary infection.

Diagnosis of wuchereriosis

Wuchereriasis is differentiated from tuberculosis of the lymph nodes, lymphocytic leukemia, infectious mononucleosis, bubonic plague and other filariases.

The diagnosis is made on the basis of epidemiological history, clinical data, and results of instrumental and laboratory research methods.

Laboratory diagnostics of wuchereriasis

The diagnosis is confirmed by the presence of microfilariae in the blood. Blood is examined in a fresh drop applied to a glass slide under low magnification of a microscope (blood is collected in the evening or at night). Wuchereriosis is diagnosed using the enrichment method. Immunological methods are sometimes used, but they are not strictly specific.

Treatment of wuchereriosis

Treatment of wuchereriasis is complex. It is carried out in a hospital. Treatment of wuchereriasis includes deworming, suppression of bacterial infections, weakening of the allergic reaction. Often it is necessary to resort to surgical intervention. Lymphadenitis is treated with antihistamines and analgesics. Diethylcarbamazine (DEC, ditrazine) is effective against microfilariae and sexually mature individuals (microfilariae die quickly, and sexually mature individuals within 2-3 weeks). On the 1st day, 50 mg of the drug is prescribed orally after a meal once, on the 2nd - 50 mg 3 times, and in the period from the 4th to the 21st day of treatment - 2 mg / kg 3 times a day. The maximum daily dose is 400 mg. The duration of treatment for wuchereriasis is 21 days. Children are prescribed the drug at 2 mg/kg 3 times a day for 10-14 days. Repeated courses of treatment are prescribed according to clinical indications. Depending on the effectiveness, 3 to 5 courses of treatment are administered with intervals of 10-12 days. Mass death of microfilariae at the beginning of treatment may be accompanied by an allergic reaction (fever, urticaria, lymphangitis). Corticosteroids are used for effective treatment. Hydrocele is effectively treated with surgical methods.

How to prevent Wuchereria?

Early diagnosis and treatment of wuchereriasis prevents the development of elephantiasis. Wuchereriasis can be prevented by observing individual protection from mosquito bites. Repellents, special types of clothing, and bed canopies are used for this purpose. To combat mosquitoes, sewerage and water supply systems in cities and towns are improved. Mosquito breeding sites are destroyed using insecticides.

The complex of measures for the prevention of wuchereriasis includes the identification and treatment of patients, as well as measures to destroy mosquitoes. Mass examinations of the population are carried out to identify people with microfilariae in the blood and their subsequent treatment. For mass chemoprophylaxis of lymphatic filariasis in endemic areas, diethylcarbamazine (DEC) is used. All residents are prescribed a dose of 2 mg/kg orally three times a year in three doses during one day.