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The mosquito-borne filarial worm, Dirofilaria immitis , causes heartworm disease in dogs. Detection of this parasite in its mosquito intermediate host currently involves dissection and microscopic examination for larval stages. Although this method is used commonly as a screening tool for epidemiological surveys, it lacks both sensitivity and specificity. In this study, a more efficient PCR- and probe-based diagnostic assay was developed. The target selected for this assay is a segment of the 16 S rRNA gene. The assay specifically detects as little as 10 pg of D. immitis genomic DNA, equivalent to DNA derived from one third stage larva (L 3 ), but does not detect 100 ng (10 000-fold excess) of the purified DNA from several other filarial nematodes, including Dirofilaria striata , Dirofilaria tenuis , Dipetalonema reconditum , Wuchereria bancroftii , Brugia pahangi , B. malayi , Onchocerca volvulus or Loa loa . This assay also detects one L 3 of D. immitis , the minimal biological unit of infection, in a pool of 200 mosquito heads. This assay can serve as a highly specific and sensitive tool for efficiently screening the large numbers of mosquitoes to determine, with statistical validity the seasonal transmission pattern of D. immitis in a locality prior to designing a rational preventive medication program for that parasite.

Summary An attempt was made to study periodicity of D. tenuis through mosquito mortality, and determine the effect of the larvae of this filariid on mosquito mortality. Dirofilaria tenuis appears to be nocturnal in periodicity with the microfilariae being at their maximum in the peripheral blood at about midnight. Mosquitoes fed on a lightly infected raccoon reached a peak mortality on the third day. Mosquitoes fed on a heavily infected raccoon suffer greatest mortality on the second day, followed by a high ensuing mortality accented on the eighth and ninth day. As the number of microfilariae ingested by the mosquito increases, it appears that the time it takes the microfilariae to enter the tubules decreases. Generally mosquito mortality increased as the number of microfilariae ingested increased.