New research cited in support of change to heartworm protocol

New research conducted by John McCall, MS, PhD, professor emeritus at the University of Georgia College of Veterinary Medicine, shows that topical application of dinotefuran-permethrin-pyriproxyfen (DPP), the active ingredients in Ceva Animal Health's Vectra 3D, can help block the transmission of Dirofilaria immitis from mosquitoes to dogs. The research was presented during a press conference organized by Ceva promoting a multimodal approach to canine heartworm prevention Aug. 6 during the American Veterinary Medical Association (AVMA) Convention in San Antonio.

An infographic from Ceva contains research and facts about mosquitoes and heartworm disease. Click the image to download the PDF. “In veterinary medicine and in parasitology research, we're always on the lookout for a paradigm shift,” said Byron Blagburn, PhD, parasitology professor and researcher at Auburn University, during the press conference. “This research by my friend and mentor John McCall represents just such a paradigm shift.”

McCall's research was the second phase of a study that, according to Ceva, supports a “double defense” protocol that protects dogs against the heartworm vector-the mosquito-as well as the heartworm itself. This protocol involves use of a topical repellent-insecticide product (DPP, which is indicated for prevention of flea and tick infestations) plus an oral heartworm preventive such as milbemycin oxime. The first phase of the study, presented in March at the Western Veterinary Conference, demonstrated that DPP helped prevent the transmission of heartworms from infected dogs to mosquitoes.

In the most recent study, according to McCall, 32 uninfected dogs were divided into four groups of eight: one group treated with DPP only, one with DPP plus milbemycin oxime, one with milbemycin oxime only, and one with nothing. The dogs were then put into contact with mosquitoes infected with D. immitis strains resistant to milbemycin oxime, which are known to be infecting dogs in the Mississippi Delta region of the United States.

Here are the study results:

Groups (eight dogs each)

Average number of infective larvae transmitted per dog

Number of dogs that developed adult heartworms

Average number of adult heartworms per dog

Control

76

8

41

DPP only

2

3

1.5

Milbemycin oxime only

78

8

17.1

DPP plus milbemycin oxime

1

0

0

“This is a new area to explore in veterinary medicine, and I am very excited about the results,” McCall said in a release from Ceva. “After fighting heartworm the same way for decades, it's time for a new approach, and that includes fighting the mosquito as well as the heartworm.”

Christopher Rehm, DVM, incoming president of the American Heartworm Society and a practice owner in Mobile, Alabama, said during the AVMA press conference that the new research was a “protocol changer.” “Multimodal therapy is nothing new to veterinary medicine,” Rehm said, “and it's about time heartworm caught up with that.”

Rehm says that even though it's “easy” for veterinarians to kill heartworms in infected animals, doing so makes animals sicker in the short term, and necropsies of animals years after treatment can reveal petrified worms in “unbelievable places-around the valve of the heart, in major arteries and so on,” Rehm says. Therefore prevention is vastly preferable to treatment.

According to data from the Companion Animal Parasite Council (CAPC), the incidence of heartworm disease continues to increase nationally. From 2013-2015, there was a 166 percent increase in reported positive heartworm cases, CAPC reports. In addition, the American Heartworm Society has tracked the geographic spread of heartworm disease to all 50 states and its increased prevalence in several regions of the country.

On a more micro level, the eggs laid by a single female mosquito that lives two weeks and takes four blood meals in that period can produce more than 800,000 mosquitoes in the next three months, according to calculations performed by McCall-“and those are conservative figures,” he says.

More information on McCall's research and Ceva's Double Defense campaign can be found at fightheartwormnow.com.