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Infectious Disease And Microbiology – Filariasis
Filariasis is a tropical parasitic disease caused by thread-like nematode worms of the superfamily Filarioidea. These parasites are transmitted to humans by insect vectors and may live in the lymphatic system, skin, connective tissue, serous cavities, or blood vessels. Adult worms can survive in the human host for more than 20 years, causing chronic disease and disability.
Filariasis includes several distinct syndromes. Lymphatic filariasis, caused by Wuchereria bancrofti, Brugia malayi, and Brugia timori, is endemic in many tropical and subtropical regions of Asia, Africa, South and Central America, and the Pacific. More than one billion people are at risk worldwide, with over 120 million infected and tens of millions suffering from disabling disease. Loiasis is confined mainly to the rainforests of western and central Africa. Onchocerciasis, or river blindness, affects millions in Africa and parts of South America and is a major cause of blindness. Dracunculiasis, or Guinea worm disease, occurs mainly in parts of Africa and Yemen. Dirofilariasis is rare in humans but has worldwide distribution, while mansonelliasis occurs in Africa, the Caribbean, and parts of Central and South America.
Major risk factors include living in or traveling to endemic areas and low socioeconomic status. Prevention depends on health education, vector control, and avoidance of insect bites. Recommended measures include sleeping under mosquito nets, wearing long sleeves, and using insect repellents containing at least 30% DEET. For dracunculiasis, prevention also includes drinking clean or filtered water, preventing infected individuals from entering water sources, and treating contaminated water to kill copepods.
The pathophysiology differs by species. In lymphatic filariasis, adult worms damage lymphatic vessels, causing dilation, valvular dysfunction, lymphatic obstruction, and eventually irreversible lymphedema and elephantiasis. In loiasis, larvae introduced by fly bites migrate beneath the skin, causing transient localized swelling known as Calabar swellings. In onchocerciasis, adult worms form nodules in the skin while microfilariae migrate through skin and eyes, causing dermatitis and blindness. In dracunculiasis, ingested larvae mature and female worms migrate to the skin, typically in the lower limbs, where they emerge through painful ulcers. Dirofilariasis often causes localized granulomatous reactions or pulmonary nodules. In mansonelliasis, dying worms provoke inflammatory responses leading to abscesses or granulomas.
The causative organisms include Wuchereria bancrofti, Brugia species, Loa loa, Onchocerca volvulus, Dracunculus medinensis, Dirofilaria species, and Mansonella species. Each is transmitted by a specific vector, such as mosquitoes, blackflies, midges, red tabanid flies, or infected copepods in water.
The clinical manifestations depend on the species involved. Lymphatic filariasis may cause fever, lymphangitis, lymphadenitis, hydroceles, lymphedema, elephantiasis, epididymitis, and occasionally bronchospasm. Loiasis presents with transient swellings, itching, hives, and migration of the worm across the eye. Onchocerciasis causes subcutaneous nodules, severe itching, skin thickening or pigment changes, lymphadenopathy, and visual loss. Dracunculiasis presents with painful skin ulcers from which the worm emerges. Dirofilariasis may cause cough, chest pain, or hemoptysis. Mansonelliasis may cause fever, swelling, rash, itching, headaches, arthralgia, and neurologic symptoms.
Physical examination findings vary accordingly. In lymphatic filariasis, patients may have lymphadenopathy, hydroceles, enlarged spermatic cord, lower extremity lymphedema, or even arthritis. Loiasis often shows visible Calabar swellings or worms migrating beneath the conjunctiva. Onchocerciasis produces characteristic skin changes and nodules, along with ocular disease. Dracunculiasis reveals a visible white worm emerging from an ulcer, usually on the lower extremity. Mansonelliasis may show pruritus, rash, edema, fever, hepatomegaly, and neurologic signs.
Diagnosis depends on the specific infection. Blood smears may reveal microfilariae in lymphatic filariasis or mansonelliasis. Skin snips or biopsies are useful in loiasis and onchocerciasis. Dracunculiasis is usually diagnosed clinically. Histology may be needed for dirofilariasis. Ultrasound can show adult worms in lymphatic vessels, and imaging such as CT or MRI may detect pulmonary nodules or deep skin nodules. Plain radiographs may reveal calcified Guinea worms.
Treatment depends on the species. In lymphatic filariasis, doxycycline is used to target Wolbachia endosymbionts, followed later by albendazole and ivermectin. Loiasis is treated with diethylcarbamazine. Onchocerciasis is treated with ivermectin, repeated after six months, with prednisone used beforehand if the eyes are involved. Dracunculiasis requires slow mechanical extraction of the worm, sometimes aided by metronidazole or mebendazole. Mansonella species are treated with albendazole or ivermectin depending on the species involved. There is no effective medical therapy for dirofilariasis. In general, treatment is more effective against microfilariae than adult worms, so repeated therapy may be necessary.
Supportive care and specialist referral are often needed. Infectious disease consultation may be helpful, and ophthalmologic assessment is essential in onchocerciasis. Surgical treatment may be required for removal of nodules in onchocerciasis or lung lesions in dirofilariasis. Hospitalization is mainly needed for complications such as septicemia from open wounds.
With timely diagnosis and treatment, disability and disfigurement can often be limited. However, complications can be severe, especially in lymphatic filariasis, where elephantiasis and secondary bacterial infection may occur, and in onchocerciasis, where blindness is a major consequence.
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