(HW) infection is caused by filarial organism, Dirofilaria immitis.  At least 70 different species of mosquitoes can serve as intermediate hosts.  Infections are possible in numerous wild and companion animal species.  Wild animal reservoirs include wolves, coyotes, foxes and raccoons.  Companion animal reservoirs are primarily dogs, cats and ferrets.  Infected mosquitoes are capable of transmitting (HW) infections to humans, however, there are no reports of such infections becoming serious.  The severity of cardiopulmonary pathology in dogs is determined by worm numbers, host immune response, duration of infection, and host activity level.  In dogs, infection should be identified by serological testing prior to the onset of clinical signs.  The antigen detection test is the preferred diagnostic method, however, there are semiquantitative (ELISA) tests for anti-dirofilaria IgG in serum or plasma.