Ans. a (Wuchereria bancrofti) (Ref. H - 16th ed., 1260)Wuchereria bancrofti blocks lymphatic vessels: elephantiasis; takes 9 mo-1 yr after bite to become symptomatic.LYMPHATIC FILARIASIS# Lymphatic filariasis is caused by W. bancrofti, B. malayi, or B. timori.# Humans are the only definitive host for the parasite.# Generally, W. bancrofti is noctumally periodic. (Nocturnally periodic forms of microfilariae are scarce in peripheral blood by day and increase at night, whereas subperiodic forms are present in peripheral blood at all times and reach maximal levels in the afternoon)# Natural vectors for W. bancrofti: Culex fatigans in urban settings and anopheline or aedean mosq in rural areas.# B. malayi has 2 forms distinguished by periodicity of microfilaremia. The more common nocturnal form is transmitted in areas of coastal rice fields, while subperiodic form in forests. B.malayi naturally infects cats and humans.Diagnosis# Microfilariae can be found in blood, hydrocele fluid, or in other body fluids, detection by Knott's concentration technique.# Two tests are commercially available: one is ELISA and the other a rapid-format immunochromatographic card test. Both assays have sensitivities that range from 96 to 100% and specificities that approach 100%.# Doppler examination of the scrotum or the female breast may result in the identification of motile adult worms within dilated lymphatics (termed the filaria dance sign).# Retrogradely evolving lymphangitis is a characteristic feature that helps distinguish filarial lymphangitis from typically ascending bacterial lymphangitis.Treatment# Diethylcarbamazine (DEC, 6 mg/kg daily for 12 days), which has both macro- and microfilaricidal properties, remains the treatment of choice for the individual with active lymphatic filariasis (microfilaremia, antigen positivity, or adult worms on ultrasound), although albendazole has also demonstrated macrofilaricidal efficacy.# Side effects of DEC treatment include fever, chills, arthralgias, headaches, nausea, and vomiting.# Ivermectin has a side effect profile similar to that of DEC when used in lymphatic filariasis.