Filariasis is a group of transmissible helminthic diseases caused by filariasis – nematodes that parasitize the lymphatic system and subcutaneous tissue. Common symptoms of filariasis include fever, lymphadenitis, lymphangitis, skin rashes, lymphostasis with the development of elephantiasis of the hands, feet, scrotum, eye damage, etc. The diagnosis of filariasis is confirmed when microfilariae are detected in smears and a thick drop of blood or skin biopsies; positive results of immunological diagnostics (IFT, PHR, ELISA). In filariasis, antiparasitic therapy with diethylcarbamazine is performed; according to the indications, sanitation of purulent foci, surgical treatment of elephantiasis is carried out.
Filariasis is a common name for intestinal worms similar in epidemiology and manifestations due to extra–intestinal parasitization of nematodes of the order Filariata. Filariatoses are common in Africa, Central and South America, South Asia, in subtropical and typical climatic zones. In total, there are about 140 million people infected with filariae in the world. Depending on the place of parasitization of macrophilaries in the human body, invasions are divided into lymphatic filariasis (vuhereriosis, brugiosis) and filariasis with damage to subcutaneous tissue and serous cavities (onchocerciasis, dipetalonematosis, loiasis, mansonellosis).
Common to all pathogens of filariasis is their belonging to the order Filariata. Filariae are filamentous roundworms (nematodes) that require an intermediate host for development. 8 species of filariasis capable of causing human filariasis have been studied: Wuchereria bancrofti (causative agent of wuchereriosis), Brugia malayi and Brugia timori (causative agents of brugiosis), Loa loa (causative agent of loaosis), Onchocerca volvulus (causative agent of onchocerciasis), Mansonella ozzardi (causative agent of mansonellosis), Dipetalonema perstans and Dipetalonema streptocerca (causative agent of acanthocheilonematosis or dipetalonematosis).
Filariae undergo a complex development cycle; humans and vertebrates serve as their final hosts; blood-sucking insects (mosquitoes, midges, horseflies, woodlice) serve as intermediate hosts and carriers. In the body of a permanent host, adult individuals (macrofilariae) parasitize in lymphoid formations, subcutaneous tissue, serous membranes and body cavities. Larval stages (microfilariae) circulate in the bloodstream or are located in the upper layers of the dermis.
During blood sucking, microfilariae enter the insect’s body, where they reach the invasive stage. Then they migrate into the proboscis of the insect and at the next blood sucking they end up in the body of the final host. With the blood flow, the invasive larvae reach the place of their localization, where they turn into adult filariae. The lifespan of microfilariae is 3-36 months; macrofilariae – years, sometimes more than 20 years.
The pathogenesis of filariasis is associated with local changes in the sites of parasitization of mature helminths, as well as immune reactions developing in response to parasitization of microfilariae. There are signs of productive inflammation in lymph nodes and vessels, proliferation of endothelial cells, proliferation of connective tissue, dilation of vessels with thickening of their walls and damage to valves. Changes in the subcutaneous tissue are caused by lymphatic edema and are characterized by tissue compaction. Immune mechanisms contributing to the development of granulomatous inflammation and fibrosis play a well-known role in the violation of lymph outflow. As a result of inflammatory changes and obstruction of lymphatic vessels by dead worms, lymphedema develops.
Brugiosis and vuhereriosis are filariasis, in which the lymphatic system is affected with the development of elephantiasis (elephantiasis). The incubation period for these filariatoses lasts 12-18 months for local residents and 3-6 months for visitors (non-immune) persons. In children, both of these diseases usually manifest at the age of 3-4 years.
In the early stage, there is a high fever, itchy and painful skin rashes like urticaria, swelling of subcutaneous tissue, conjunctivitis, lymphadenitis and lymphangitis, enlargement of the liver and spleen. The occurrence of eosinophilic infiltrates in the lungs is typical, which is manifested by the clinic of asthmatic bronchitis or pneumonia. The symptoms of filariasis worsen in waves, and the early stage can stretch for 2-7 years.
In the expanded stage, signs of damage to the lymphatic pathways of the genitourinary organs and lower extremities come to the fore. Men often have hydrocele, funiculitis, epididymitis, scrotal soreness. In the case of complete blockage of the lymph outflow, elephantiasis of the legs and arms develops (with vuchereriosis – scrotum, vulva, mammary glands), which is a dense edema of subcutaneous tissue. Possible rupture of the lymphatic vessels of the kidneys and bladder, which is fraught with the development of hiluria. Violation of the integrity of the lymphatic vessels of the intestine is accompanied by chyletic diarrhea, peritoneum — chyletic ascites. In other habitats of filariae (subcutaneous tissue and serous membranes), abscesses form, which can open outward into the abdominal or pleural cavity with the development of peritonitis and pleural empyema.
In the obstructive stage of filariasis, signs of elephantiasis of the limbs and other parts of the body, their deformation and disfigurement are expressed. Secondary skin changes develop over the affected foci – cracks, hyperkeratosis, papillomatous growths. Trophic ulcers occur, muscle atrophy develops. The weight of the scrotum with vuchereriosis can reach 20-30 kg.
Filariasis with lesions of subcutaneous tissue and serous cavities
Local manifestations of acanthocheilonematosis (dipetalonematosis) are characterized by erythematous or spot-papular rashes on the skin, swelling of the face, limbs and scrotum, lymphadenopathy. Of the common symptoms, the most typical are attacks of fever, dizziness, signs of meningoencephalitis. Residents of endemic areas have little or no clinical signs of filariasis.
With loaosis, there is a lesion of soft tissues, eyes, serous membranes. Early signs of invasion associated with the migration of microfilariae include fever, paresthesia and limb pain, rash, eosinophilia. The most typical and permanent sign of loaosis is the Calabar tumor – a limited swelling of the skin and subcutaneous tissue, dense to the touch, slowly (within 5-7 days) developing and regressing just as slowly.
When helminth is parasitized in the eye, a clinic of blepharitis and conjunctivitis develops, severe pain, decreased visual acuity. In the case of penetration of filariae into the submucosal layer of the urethra, dysuric disorders occur. Complications of filariasis can be meningitis, encephalitis, endomyocardial fibrosis, heart failure, intermuscular abscesses.
Unlike other filariatoses, mansonellosis proceeds relatively benign. Pathognomonic manifestations include fever, itchy skin rash, enlarged inguinal lymph nodes, swelling and numbness of the extremities, arthralgia, hydrocele. Onchocerciasis is characterized by lesions of the skin, subcutaneous tissue, eyes, lymphatic system and is discussed in detail in a separate article.
Filariatoses are recognized on the basis of clinical and epidemiological data and laboratory diagnostic results. The determining diagnostic factors are the patient’s stay in filariasis-endemic areas, the development of lymphatic edema, lymphedema, skin and eye lesions. For differential diagnosis, patients need to consult an infectious disease specialist, a lymphologist, according to indications – an oculist, a neurologist, a surgeon, etc.
To confirm the diagnosis of filariasis, a study on microfilariae of a smear or a thick drop of blood with a Romanovsky-Giemse stain, skin biopsies and lymph nodes allows. Immunological studies (PHR, IFT, ELISA) are also carried out. With loaosis and onchocerciasis, adult helminths can be detected in the eye by biomicroscopy.
Treatment of filariasis is carried out inpatient. For the purpose of deworming, the drug diethylcarbamazine (ditrazine) is used, sometimes in repeated courses. The effectiveness of antiparasitic therapy is monitored by laboratory control. With severe allergic reactions, antihistamines and corticosteroids are prescribed. In order to eliminate lymphostasis, the elevated position of the limb, wearing elastic stockings, compression bandaging is shown.
If conservative therapy of lymphedema is ineffective, surgical treatment is performed (lymphovenous anastomosis, tunneling, dermatofasciolipectomy). With a hydrocele, a puncture of the scrotum with fluid aspiration, excision or plastic of the testicular membranes is indicated. Abscesses, purulent pleurisy, peritonitis are also subject to surgical treatment.
Prognosis and prevention
With early diagnosis and timely treatment, recovery occurs. Factors leading to disability and aggravating the prognosis of filariasis are the development of elephantiasis, lesions of the eyes, heart, brain. An unfavorable outcome may be associated with purulent-septic complications. Prevention of filariasis consists in the destruction of microfilariae vectors by treating the foci of their habitat with insecticidal agents, observing personal protection measures against bites of blood-sucking insects. Persons returning from a trip to tropical countries are recommended to be examined for filariasis.