Wuchereria bancrofti, Brugia malayi and Brugia timori are the causative agents of Lymphatic filariasis (Elephantiasis). Microfilariae of these nematodes show nocturnal periodicity. They appear in peripheral blood at night time between 9 pm and 2 am. This periodicity is due to biological and evolutionary co-adaptation of the microfilariae to the feeding habit of the mosquito Culex quinquefaciatus i.e. is the principle vector for transmission of this parasite. So, for the diagnosis of the lymphatic filariasis, blood specimen should be collected at late night.  It may be impractical to obtain blood from an ambulatory patient at night time. So, to make the microfilariae appear in the patient’s peripheral blood during day time, DEC provocation test is done. For this, the patient is given with a tablet of DEC orally (2mg/kg). After consuming DEC, microfilariae are stimulated and they appear in peripheral blood within 30 – 45 minutes.

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