New study lays groundwork for heartworm vaccine development

With heartworm infections on the rise, researchers from the University of Liverpool have identified two immunosuppressive proteins in Dirofilaria immitis as potential targets for a novel vaccine.

Researchers from the University of Liverpool in the United Kingdom are working toward the development of a heartworm vaccine to combat the growing threat posed by the resistance of Dirofilaria immitis to macrocyclic lactones.

The American Heartworm Society (AHS) estimates that more than a million dogs in the U.S. have heartworm disease. And according to an analysis published in Parasites & Vectors in 2018, infection incidence is on the rise, with AHS reporting a 21.7% increase in average cases per clinic between 2013 and 2016. The analysis lists poor compliance with heartworm prevention guidelines (about two-thirds of dogs don’t receive any heartworm prevention) and emerging resistance to macrocyclic lactones as potential causes for the concerning upward trend.

Pinpointing immunosuppressive proteins

In pursuit of sustainable heartworm prevention, Ben Makepeace, PhD, the study’s principal investigator, and his team first looked at other filarial parasites similar to D. immitis — specifically, Litomosoides sigmodontis and Onchocerca ochengi — and were able to identify two common proteins in both parasite species that interfere with the host’s immune system, making them potential vaccine targets. One of the proteins blocks a pathway alerting the immune system to the parasites’ presence, and the other stops T cells from attacking the worms.

For the current study, which is backed by both AHS and the Morris Animal Foundation, Dr. Makepeace says they will incubate proteins from D. immitis that are equivalent to the ones identified above with white blood cells from healthy donor dogs to determine their effect on the immune response and to see if any of their immunosuppressive effects can be blocked. “This is an essential step before a clinical trial for a vaccine can be performed,” he adds.

An addition to your heartworm prevention toolbox

But even if Dr. Makepeace and his team reach their goal of a heartworm vaccine (a goal that’s suffered serious delays due to the coronavirus pandemic), they don’t see their work as completely cancelling out the need for preventive drugs and mosquito repellents. “It’s more about extending the life of the tools we have so we don’t reach the nightmare scenario of heartworm being unpreventable,” he explains.