The Life Cycle of Dirofilaria uniformis Price and Transmission to Wild and Laboratory Rabbits

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Abstract
Ingested microfilariae of D. uniformis, a parasite of Sylvilagus floridanus mallurus, developed in the hemocoele of Anopheles quadrimaculatus and the infective larvae migrated to the proboscis on the 9th day. No development was observed in Aedes aegypti, A. sollicitans, or Culex pipiens. Subcutaneous injections of infective larvae produced experimental infections that developed a microfilaremia in 12 out of 14 wild rabbits and 8 out of 18 laboratory rabbits. The length of the prepatent period was inversely proportional to the number of infective larvae administered. Microfilariae first appeared in the blood between 97 and 222 days after inoculation. The microfilaremia increased in intensity for several months after the prepatent period. There was evidence that the infection may be retained for more than 2 years in wild rabbits. Periodicity studies showed that the heaviest microfilaremia occurred between 4:00 p.m. and midnight. To obtain infections in laboratory rabbits, it was necessary to inject larger numbers of larvae than in the cottontail. This, and the fact that in some laboratory animals the worms were encapsulated and destroyed, indicates that this host is more refractory to infection.

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