American Heartworm Society releases 2018 canine heartworm guidelines

The American Heartworm Society (AHS) has updated its canine heartworm guidelines to focus on reducing heartworm transmission, clarifying testing recommendations and avoiding shortcuts in treatment, according to an association release. The guidelines, which are updated by the society as needed based on assessment of heartworm research, also address heartworm biology and epidemiology, the association says.

Prevention guidelines have been updated because the latest research has found incidence trending upward, says Chris Rehm, DVM, president of AHS. The data show that the number of dogs diagnosed per clinic has risen by 21 percent in the United States and its territories between 2013 and 2016, he says in the release.

Climate and environmental changes, as well as relocation of heartworm-infected dogs and expansion of the territory of heartworm-infected wild canines, are considered contributing factors to both incidence numbers and the spread of heartworm in areas that were considered non-endemic previously, the release states. Compliance on the part of pet owners also plays a role in effective prevention strategies.

“For these reasons, we continue to stress the importance of year-round administration of macrocyclic lactone preventives, along with practical steps to reduce mosquito exposure, such as eliminating standing water on the property and keeping pets indoors during peak mosquito times,” says Dr. Rehm in the release.  “Year-round prevention is the single most important step owners can take to reduce the risk of heartworms to their pets.”

The 2018 guidelines also recommend that veterinarians consider using EPA-approved mosquito repellents or ectoparasiticides to control the mosquito vector and reduce the risk of heartworm transmission if the risk is high in the area.

“In regions with relatively low heartworm incidence numbers and few mosquitoes, use of heartworm preventives alone can be sufficient to safeguard patients. Where mosquito proliferation and heartworm incidence numbers are high, however, additional measures may be warranted on either a year-round or seasonal basis," says Dr. Rehm. "Individual veterinarians are in the best position to assess the risk for their practices as well as for individual patients.”

According to the release, studies have been done over the last decade to better understand the potential for heat treatment of serum samples to unmask blocked antigen, which raises questions about optimal testing methods. Further testing is needed to better understand the mechanisms at work, but the AHS guidelines note that the high sensitivity of microfilaria tests makes heat treatment unnecessary for routine screening.

The AHS guidelines recommend veterinarians consider heat treating serum when either the presence of circulating microfilariae is detected or the veterinarian suspects active clinical disease in the absence of a positive antigen test, Dr. Rehm notes.

The updated guidelines also reemphasize the AHS protocol for treatment. “Heartworm disease is a complex disease, and there are no shortcuts to appropriate treatment,” says Dr. Rehm, noting that the AHS protocol was designed to kill adult worm infections with minimal complications while stopping the progression of disease. “Skipping any one of these steps can affect both the safety and efficacy of heartworm treatment.”

Dr. Rehm adds that non-arsencial treatment protocols have been studied to understand how to manage heartworm-positive dogs that aren't candidates for melarsomine treatment. “Because some dogs are simply not candidates for adulticide treatment, there is a place for alternatives such as these,” he explains in the release. “However, it's also important for veterinarians to understand that these non-arsenical protocols have serious disadvantages, the most important of which is the length of time required to kill adult worms, during which time heartworm pathology and damage can progress. This also greatly increases the length of time the pet needs strict exercise restriction, which is problematic.”

To see the complete AHS canine and feline heartworm guidelines, visit heartwormsociety.org.