Filariasis: Bancroftian filariasis, Malayan filariasis, Loiasis (loa loa), Onchocerciasis (river blindness)
Primary Distribution: Numerous areas of the world, with variants and locations noted below under vectors and agents.
Agents and Vectors: The filarial parasites are tissue-dwelling nematodes (roundworms) whose microfilaria (mf) larvae are transmitted by several species of mosquitos or flies as follows:
Incubation: Variable according to species. Symptoms may begin six months or longer after infection.
Clinical Findings and Treatment: Bancroftian filariasis or Wuchereria bancrofti and Brugia malayi infection (Note: Wuchereria bancrofti and Brugia malayi infections are similar, except that B. malayi is less widely distributed (see above) and the clinical features of B. malayi tend to be less severe.)
Signs and Symptoms: Adult worms live in lymph vessels and nodes, while the mf are found primarily in the blood. Symptoms begin four to twelve months (usually > six) after infection, and not all infected persons are symptomatic. Symptoms usually begin with localized inflammation in genitalia or extremities. Lymphadenitis and lymphangitis begin at a single site and spread regionally within hours. Acute onset recurrent bouts of fever, chills, headache, and malaise also occur. Lymphedema may begin accumulating in the first 24 hours. Acute symptoms of mild attacks resolve within a few days; with lymphedema taking several weeks to resolve. Hydrocele, orchitis, epididymitis, and/or funiculitis are common in males. Filarial abscesses are usually found in the groin or axillae; but among patients from the Pacific Islands, may also occur in deep fascial spaces of muscles. Chronic disease may lead to chronic obstruction of lymph and serous fluid resulting in chronic and permanent (and disabling) elephantiasis of the lower extremities or testes; and to a lesser extent, arms, breasts, labia, and penis. Chyluria (galacturia) results from chyle (lymph and triglyceride in an emulsion) in the urine caused by obstruction between intestinal lymphatics and thoracic duct leading to rupture of renal lymphatics into renal tubules.
Complications: Chronic lymphedema leads to elephantiasis, which includes hyperplasia of skin and subcutaneous tissue - all of which predispose to ulceration and secondary infection. The size and weight of the affected parts lead to disability.
Laboratory Findings: Moderate eosinophilia, elevation of serum concentrations of IgE and antifilarial antibody.
Diagnosis: Note that the life cycle of the mf varies according to species and area in which the disease is contracted and mf concentrations vary according to the time of day (diurnal periodicity) and that depending on these factors, peripheral blood of infected persons may or may not have mfs. Microfilariae are detectable primarily in blood and hydrocele fluid. Giemsa-stained thick blood film is a commonly used test. Polymerase chain reaction-based assays are available for the presence of W. bancrofti and B. malayi in blood and sputum. Ultrasound of the scrotum detects adult worms, nodules, or lymphatic dilatation in 80% of affected men. ELISA, CFT, and IFAT tests for serum are also available and are highly accurate.
Differential Diagnosis: Acute bacterial lymphangitis, thrombophlebitis (although lymphatic filariasis may feature thrombophlebitis), lymphogranuloma inguinale and other infections; other causes of recurrent fever such as tuberculosis or urinary tract infection; other causes of orchitis and related disorders such as gonorrhea, tubercular epididymitis, hernia, trauma, etc. Persons from Ethiopian highlands may present with African "bigfoot" disease, which does not include hydrocele.
Treatment: Ivermectin in a single oral dose of 100-400 mcg/kg; sometimes combined with albendazole. Alternative treatment (first-line in some references) is diethylcarbamazine (DEC) given in graduated doses as follows: Day 1: 50 mg po; day 2: 50 mg po tid; day 3: 100 mg po tid; days 4-21: 6 mg/kg/d in 3 divided doses. Annual single dose treatments with DEC at 6 mg/kg may be used in areas of high endemicity.
Clinical Findings and Treatment: Loiasis
Signs and Symptoms: Loiasis is often asymptomatic among indigenous people of endemic areas, but more problematic among non-indigenous persons who are infected. The worms live in subcutaneous tissues and cause intermittent development of localized areas (> 10 cm) of erythema and angioedema (Calabar swellings), usually on the extremities. Moving worms are sometimes visible in the eye between the bulbar conjunctiva and sclera.
Complications: Rarely seen complications are nephropathy, encephalopathy, and cardiomyopathy.
Laboratory Findings: Eosinophilia, increased antifilarial antibodies, hypergammaglobulinemia, increased IgE, and increased leukocyte and eosinophil counts.
Diagnosis: See Wuchereria bancrofti and Brugia malayi infections above; the presence of a worm in the eye is diagnostic.
Treatment: Diethylcarbamazine (DEC) given in graduated doses as follows: Day 1: 50 mg po; day 2: 50 mg po tid; day 3: 100 mg po tid; days 4-21: 9 mg/kg/d po in 3 divided doses. Alternative treatment is ivermectin in a single oral dose of 100-400 mcg/kg; sometimes combined with lower doses DEC (0.5-1.0 mg/kg/d in combination with corticosteroids. Multiple courses of treatment with DEC are required in about 50% of patients.
Clinical Findings and Treatment: Onchocerciasis
Signs and Symptoms: Unlike other filarial infections, the problems of onchocerciasis are caused by mf rather than adult worms. Very severe pruritus, with or without papular rash is caused by mf in subcutaneous tissue. Subcutaneous nodules (onchocercomata) contain adult worms. The skin may eventually lose its elasticity and become atrophied and fibrous, and in some cases, hypo or hyper-pigmentation. Eczema and secondary infections may result from scratching. Skin involvement among patients in Africa tends to be greatest on the lower extremities, while in Central America, the head is more commonly involved. Involvement of the eyes usually is manifested first by conjunctivitis and photophobia. Neovascularization, keratitis, and corneal scarring occur in a small percentage of patients and lead to blindness. Uveitis, chorioretinitis, and optic atrophy also occur; as may secondary glaucoma. Lymphadenopathy in the femoral and inguinal areas may lead to "hanging groin."
Complications: Cachexia may occur with heavy infestation.
Laboratory Findings: Eosinophilia.
Diagnosis: Skin biopsy (snips) are incubated in tissue culture medium or saline and within 2-24 hours, mf can be visualized in a low power microscope.
Differential Diagnoses: Other causes of pruritis, eczema, nodules, conjunctivitis, and eye infection.
Treatment: Ivermectin in a single oral dose of 150 mcg/kg, repeated every 3-12 months kills mf, but not adult worms. Because of proximity to eyes, nodules on the head are sometimes removed.
Abbasi, I. Githure, J., Ochola, J.J., Agure, R., Koech, D.K., Ramzy, R.M., Williams, S.A., & Hamburger, J. (1999). Diagnosis of Wuchereria bancrofti infection by the polymerase chain reaction employing patient's sputum. Parasitology Research. 85(10), 844-849.
Bell, D. (1995). Tropical Medicine (4th ed.). Oxford: Blackwell Scientific.
Chin, J. (Ed.) (2000). Control of communicable diseases manual (17th ed.). Washington, DC: American Public Health Association.
Mataika, J.U., Kimura, E., Koroivueta, J. & Shimada, M. (1998). Efficacy of five annual single doses of diethylcarbamazine for treatment of lymphatic filariasis in Fiji. Bulletin of the World Health Organization. 76(6), 575-579.
Nutman, T.B. & Weller, P.F. (1998). Filariasis and related infections (loiasis, onchocerciasis, and dracunculiasis). In A.S. Fauci, E. Braunwald, K.J. Isselbacher, J.D. Wilson, J.B. Martin, D.L. Kasper, S.L. Hauser, & D.L. Longo (Eds.). Harrison's Principles of Internal Medicine (14th ed.) (pp. 1212-1216). New York: McGraw-Hill.
Ottesen, E.A., Ismail, M.M., & Horton, J. (1999). The role of albendazole in programmes to eleminate lymphatic filariasis. Parasitology Today. 15(9), 382-386.
Rosenblatt, J.E. (1999). Antiparasitic agents. Mayo Clinic Proceedings. 74(11), 1161-1175.