In July 2008 the American Heartworm Society (AHS) announced intentions to conduct the most comprehensive heartworm incidence survey to record canine heartworm disease cases in the United States. The survey, made possible through corporate sponsorship, was distributed to more than 40,000 veterinary clinics and hospitals over the summer of 2008. Clinics, hospitals and shelters submitted answers to the survey online to record the number of dogs treated and diagnosed with heartworm disease in 2007. The Society has a three year record of surveys with their last survey in 2004 and their next survey scheduled in 2010.

The Society released the 2008 survey findings in March 2009 showing an increase in heartworm prevalence throughout the United States. The study showed that the Delta, South-central and Southeast regions of the United States have the greatest incidence, with prevalence highest in the Delta region. In many counties and parishes in this region, there were 100 or more cases reported per clinic.  Areas of Oregon and Montana where large areas of the state that previously reported less than one dog diagnosed per clinic rose to between one and five or more dogs per clinic in the 2007.

While the Society promised a ‘comprehensive incidence survey’ the only questions presented to veterinarians and shelters were the number of dogs tested and the number of positive cases. They neglected to ask whether any of the dogs who tested positive were already on heartworm preventatives. They admit “The goal of the 2007 incidence survey was to simply gauge the prevalence of heartworm cases across the U.S.” as stated by Erica Jones.

While it is widely known that the incidence of heartworms is increasing throughout the country, it has been just rumors and word of mouth that many of those cases where already on preventatives. The number of heartworm cases and geographic regions of those cases are not widely known, and were not included in this survey.  Why the AHS did not complete their obligations to the canine community by asking this more important question might be found in the corporate sponsors of the study. Major sponsors of the 2007 survey included Bayer Animal Health, Fort Dodge, IDEXX, Intervet/Schering Plough, Lilly, Merial, Novartis and Pfizer.

An analysis of a more recent AHS online study to identify top research priorities for scientists found many respondents raising questions about this very issue. For example:

Based on your experience in veterinary practice, please describe the importance of research in the following areas: 

3,2/20/2009 6:33:00 PM, “Resistance development of current preventatives” 

Based on your experience as a scientist, please describe the importance of research in the following area as Highly Important”

3,2/21/2009 10:38:00 PM,”development of diagnostic assays that can detect or refute claims of resistance”

5,2/23/2009 2:19:00 PM,”Lack of effectiveness of approved heartworm preventives.”

2/24/2009 1:30:00 AM, Most and currently if resistance is developing to ivermectin.”

2/25/2009 3:30:00 AM,”potential development of resistance to preventatives”

2/27/2009 4:38:00 PM,”Field resistance of heartworm to avermectins

From the perspective of your foundation, please describe the importance of research in the following areas:

3/2/2009 7:05:00 PM,”The possibility that breaks in treatment are due to resisant strains”

Heartworm Incidence Map

Recent evidence shows that resistance to preventatives is spreading through the Mississippi Delta. Until further research is done, dog owners must continue to educate themselves to this growing problem. You may click the link above to view a progressive map showing areas of high infection rates. As high mosquito populations spread throughout areas of the country that were once safe, precautions must be taken to protect dogs from infection. These precautions may include:

• Preventatives: There are a variety of options for preventing heartworm infection in dogs, including daily and monthly tablets and chewables, monthly topicals and a six-month injectable product. Give these preventatives year round.
• Decrease outdoor exposure during times of high mosquito activity.
• Test dogs for heartworm infection regularly regardless of whether the dog is on preventatives or not.

To help determine areas of the country that may have growing resistance, please complete our survey below. Simply click the link and answer three simple questions. Once you submit your reply, you will be able to view the results of the survey.

CLICK HERE TO COMPLETE ONLINE SURVEY