Laying the groundwork for a canine heartworm vaccine

Prevention has always been key to fighting heartworm disease in dogs, but few preventive drug options are available and resistance to available medications continues to grow. But a new study by Morris Animal Foundation–funded researchers at the University of Liverpool may unlock the solution veterinarians and pet owners need.

The first definitive evidence that dogs could be immunized against heartworm infections was published in 1974, according to Tom Nelson, DVM, past president and current research chair of the American Heartworm Society. But after 25 years and numerous attempts, a successful heartworm vaccine has yet to be produced.

“Fast forward another 20 years, and researchers today are working on a new approach,” Dr. Nelson said.

Previously, the research team identified how other filarial parasites similar to Dirofilaria immitis—the parasitic filarial worm that causes heartworms—avoid destruction by producing a protein that blocks a key pathway alerting the immune system to their presence. They also identified a second protein that prevents T cells from attacking the parasites. These two activities together cripple the host’s immune system, allowing the worms to flourish.

According to the team, the same proteins produced by D. immitis should have a similar effect in dogs. In a new study, the researchers will first confirm this theory and then test how different surface proteins on immature worms interact with white blood cells from donor dogs to discover which stimulate the immune system.

“If we don’t find an alternative, then treating established adult worms will be very difficult in dogs,” Ben Makepeace, BSc (Hons), MSc, PhD, reader at the University of Liverpool and principal investigator on the study, said in a press release.

If the study is successful, the research will then progress to clinical trials in dogs to test the vaccine’s safety and effectiveness. Dr. Makepeace also hopes successful study results can then be applied to cats.

A heartworm vaccine would not only address a major issue with canine health, but it would also address the expanding problem of drug resistance. With at least one million dogs in the United States infected annually, this would be a significant step forward in combatting this vexing disease.