Clinical Features:
Lymphatic filariasis most often consists of asymptomatic microfilaremia.  Some patients develop lymphatic dysfunction causing lymphedema and elephantiasis (frequently in the lower extremities) and, with Wuchereria bancrofti, hydrocele and scrotal elephantiasis.  Episodes of febrile lymphangitis and lymphadenitis may occur.  Persons who have newly arrived in disease-endemic areas can develop afebrile episodes of lymphangitis and lymphadenitis.  An additional manifestation of filarial infection, mostly in Asia, is pulmonary tropical eosinophilia syndrome, with nocturnal cough and wheezing, fever, and eosinophilia.  Onchocerciasis can cause pruritus, dermatitis, onchocercomata (subcutaneous nodules), and lymphadenopathies.  The most serious manifestation consists of ocular lesions that can progress to blindness.  Loiasis (Loa loa) is often asymptomatic.  Episodic angioedema (Calabar swellings) and subconjunctival migration of an adult worm can occur.  Infections by Mansonella perstans, while often asymptomatic, can be associated with angioedema, pruritus, fever, headaches, arthralgias, and neurologic manifestations.  Mansonella streptocerca can cause skin manifestations including pruritus, papular eruptions and pigmentation changes.  Eosinophilia is often prominent in filarial infections.  Mansonella ozzardi can cause symptoms that include arthralgias, headaches, fever, pulmonary symptoms, adenopathy, hepatomegaly, and pruritus.

Laboratory Diagnosis:
Identification of microfilariae by microscopic examination is the most practical diagnostic procedure.
Examination of blood samples will allow identification of microfilariae of Wuchereria bancrofti, Brugia malayi, Brugia timori, Loa loa, Mansonella perstans, and M. ozzardi.  It is important to time the blood collection with the known periodicity of the microfilariae.  The blood sample can be a thick smear, stained with Giemsa or hematoxylin and eosin.  For increased sensitivity, concentration techniques can be used.  These include centrifugation of the blood sample lyzed in 2% formalin (Knott's technique), or filtration through a Nucleopore® membrane.
Examination of skin snips will identify microfilariae of Onchocerca volvulus and Mansonella streptocerca.  Skin snips can be obtained using a corneal-scleral punch, or more simply a scalpel and needle.  The sample must be allowed to incubate for 30 minutes to 2 hours in saline or culture medium, and then examined for microfilariae that would have migrated from the tissue to the liquid phase of the specimen.

Diagnostic findings

• Microscopy
• Antigen detection using an immunoassay for circulating filarial antigens constitutes a useful diagnostic approach, because microfilaremia can be low and variable.  A rapid-format immunochromatographic test, applicable to Wuchereria bancrofti antigens, has been recently evaluated in the field.
• Molecular diagnosis using polymerase chain reaction is available for W. bancrofti and B. malayi.
• Identification of adult worms is possible from tissue samples collected during nodulectomies (onchocerciasis), or during subcutaneous biopsies or worm removal from the eye (loiasis).
• Antibody detection is of limited value.  Substantial antigenic cross reactivity exists between filaria and other helminths, and a positive serologic test does not distinguish between past and current infection.
• Special Procedures for Detecting Microfilariae
• Bench aids for filariasis

Treatment:
Different drugs are recommended for the treatment of filariasis depending on the specific causal agent.  For additional information, see the recommendations in The Medical Letter (Drugs for Parasitic Infections).