In order to study the periodicity of microfilaria of Dirofilario immitis in a dog naturally infected with this parasite, blood samples are taken from saphen or cephalic vein in every hours of 3 consecutive days and night (72 times). The blood samples were examined by using modified knott method. Our finding revealed a nucturnal periodicity for D. immitis. The highest number of microfilariae was seen at 23 PM. and the lowest at 10 AM. The mean number of microfilariae in day time between 7 AM. to 18 PM. was 6693 comparing with 11906 at dark time of a day. (18 PM. to 7 AM).
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