00679-A: Prevalence of Infective Heartworm Larvae in Mosquitoes from Northeastern Wisconsin

Grant Status: Closed

Grant Amount: $8,255
Uwe Pott, PhD; University of Wisconsin, Green Bay
August 1, 2005 - July 31, 2007


Breed(s): -All Dogs
Research Program Area: Immunology and Infectious Disease
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Heartworm disease in canines is caused by the nematode Dirofilaria immitis. Dogs become infected with the nematode when they are bitten by mosquitoes that carry the infective L3 larvae of the parasite. In the canine host, these larvae develop into adult worms which settle in the heart, lung and associated blood vessels. Dogs carrying a high number of adult worms often experience severe heart and lung damage, and may eventually die from congestive heart failure. Heartworm disease can be prevented with chemoprophylaxis. In the most common form of prevention, dogs are given a monthly dose of a macrocyclic lactone, such as ivermectin (e.g. Heartguard�), milbemycin (Interceptor�, Sentinel�) or selamectin (Revolution�). These substances kill the larval stages of the parasite, before they can develop into adults. The duration of the prophylactic treatment depends on the geographic region; recommendations range from year-round treatment in the southern states to about half a year of treatment in the northernmost parts of the United States. However, some of these recommendations apparently fail to consider the temperature dependence of the larval development in the insect host. Based on climate data, heartworm chemoprophylaxis should be required only from July through October in Northeastern Wisconsin. Although the predictions of the HDU model were nicely confirmed in a couple of studies in southern states, the lack of comprehensive empirical data seems to hamper wide acceptance of recommending shorter time periods for heartworm prophylaxis. The goal of this study is to produce additional experimental data on the critical time window in which heartworm infection can occur.


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