2005 Guidelines for the diagnosis, prevention and management of heartworm (Dirofilaria immitis) infection in cats.

0304-4017/$ – see front matter doi:10.1016/j.vetpar.2005.07.009 Puerto Rico, U.S. Virgin Islands and Guam. Heartworm transmission has not been documented in Alaska and even with the importation of microfilaremic dogs, it is doubtful the climate this far north will permit maturation of infective larvae. Relocation of infected, microfilaremic dogs appears to be the most important factor contributing to further dissemination of the parasite. The ubiquitous presence of one or more species of vector competent mosquitoes makes transmission possible wherever a reservoir of infection and favorable climatic conditions co-exist. A climate that provides adequate temperature and humidity to support a viable mosquito population, and also sustain sufficient heat to allow maturation of ingested microfilariae to the infective, third-stage larvae (L3) within the intermediate host is a pivotal prerequisite for heartworm transmission to occur. Intermittent diurnal declines in temperature below the developmental threshold of 57 8F (14 8C) for only a few hours retard maturation, even when the average daily temperature supports continued development. At 80 8F (27 8C), 10–14 days are required for development of microfilariae to the infective stage. 1. Preamble