According to the American Heartworm Society's (AHS) 2010 Heartworm Incident Survey, cases of heartworm were reported in every state in the U.S.
The AHS believes weather patterns are influencing mosquito populations.
"AHS recommends that veterinarians be vigilant about recommending annual heartworm testing and year-round use of heartworm protection. Without such vigilance, heartworm incidence numbers could climb higher than ever before," the association says.
Right around this time a year ago, the Companion Animal Parasite Council (CAPC) weighed in regarding reports of increasing resistance to heartworm prevention drugs in dogs:
"There is a growing body of anecdotal reports and experimental evidence that currently available heartworm preventives (macrocyclic lactones) may not be completely efficacious in preventing heartworm infection in dogs. Reports of resistance for dogs in the region have resulted in confusion about how best to prevent infection in veterinary patients," CAPC reports.
"At this time, reports of resistance appear to be confined to dogs from the south-central United States where dogs have become infected while on preventives or remain infected following treatments.
"Veterinarians should also continue to emphasize the need for heartworm diagnostic tests at recommended intervals and appropriate times," the statement says.