VMBS Researchers Developing Innovative Methods For Diagnosing Heartworms
Story by Megan Bennett, VMBS Marketing & Communications
Approximately 300,000 dogs are diagnosed with heartworms in the United States each year, according to the Companion Animal Parasite Council.
These parasites are more than just pests; a heartworm infection can often prove fatal.
“Heartworms are one of the most important parasites of dogs in North America,” said Dr. Meriam Saleh, a clinical assistant professor at the Texas A&M School of Veterinary Medicine & Biomedical Sciences (VMBS). “They cause multi-systemic disease, and the treatment is expensive and hard on the animal.”
In addition to dogs, heartworms can also infect cats and ferrets, which can develop serious health complications from a heartworm infection.
But even with accessible preventive options, difficulties in heartworm diagnostics play a key role in the disease’s serious impacts on pets. These diagnostic tools are even more important for cats and ferrets because no treatment methods exist for heartworm-established infections in these species; prevention is the only option.
This is why Saleh, clinical assistant professor Dr. Guilherme Verocai, and their VMBS colleagues are dedicated to finding more effective and efficient diagnostic tools for heartworms, whether that be improving current methods or thinking outside of the box and developing new methods altogether.
The Trouble With Diagnostics
One of the most troublesome aspects of diagnosing heartworms is the existing tests’ inability to detect the parasites during certain stages of the heartworm lifecycle.
Heartworms enter a host as infective larvae that migrate to the heart, where they develop into adult heartworms.
When a veterinary clinic checks an animal for heartworms, the animal’s blood is tested for the antigens created by adult female heartworms and a modified Knott’s test is performed, which is used to detect heartworms’ offspring, or immature worms called microfilariae.
“One of the problems is that we can’t detect heartworms immediately after an animal gets infected by a mosquito,” Saleh said. “When we draw a blood sample, it may not contain heartworm antigen; the worms don’t become sexually mature and start to produce antigens and microfilaria until six to seven months post-infection.”
Another challenge with current diagnostics is that with the modified Knott’s test, the microfilariae are detected visually; therefore, the test requires an experienced veterinarian who can recognize the juvenile worms.
As part of the VMBS researchers’ work to improve diagnostics, one recent study found that a qPCR test, a real-time polymerase chain reaction test used to measure DNA, is a more effective alternative for the modified Knott’s test because it looks for microfilariae DNA. This project was led by Dr. Veronica Negron, a 2023 Texas A&M Doctor of Veterinary Medicine (DVM) graduate.
A challenge with the qPCR method is that it’s only available in diagnostic laboratories and still is only effective six to seven months after the initial infection.
“There’s not much we can do to make microfilariae appear sooner, so we have to think about what else we can look for,” Verocai said. “That’s why we’re trying to find different biomarkers that can be useful for early detection of infection.”
Rethinking Traditional Methods
One new method the VMBS researchers are exploring is detecting the Wolbachia bacteria that live symbiotically inside parasitic worms like heartworms.
Over the summer, second-year veterinary student Mary Schech worked in Verocai’s lab as a participant in the 2023 Veterinary Medical Scientist Research Training Program (VMSRTP). Her VMSRTP research project involved looking for Wolbachia DNA to detect microfilariae, rather than looking for microfilariae DNA or using a traditional modified Knott’s test.
She found that not only is Wolbachia a much more accurate marker to test for, but it also has the potential to detect heartworms earlier than any other diagnostic tools.
“This study was aiming to detect Wolbachia that was within circulating microfilaria, but we found out that we can also detect Wolbachia within other life stages of heartworms,” Schech said.
The VMBS researchers are now conducting further testing on this method, such as seeing how soon after infection the test is effective and if it works on cats as well as dogs.
Verocai and Saleh are also studying other potential biomarkers like micro-RNA, as well as options that would indicate the stage of infection. To assist in these heartworm-related projects, Verocai recently enrolled Dr. Tiana Sanders, a recent DVM graduate from Oklahoma State University, as a new Ph.D. student and resident in veterinary parasitology, a position funded by Merck Animal Health.
Expanding The Scope
In addition to looking at new diagnostic methods, Verocai and Saleh have a variety of ongoing or recently completed heartworm-related research projects, including using urine instead of blood for antigen tests and testing for heartworms in other species like cats, coyotes, and wild carnivores kept at zoological facilities.
The team often presents its work at national and international conferences, including the annual American Association of Veterinary Parasitologists Conference and the triennial symposium of the American Heartworm Society.
Although early detection does not currently guarantee that heartworm treatment will be more effective or easier on the animal, Verocai and Saleh are hopeful that as detection methods improve, treatment methods will as well.
“Currently, there might not be a safe and effective drug that will kill that early infection we’re trying to find, but I think advances in diagnostics will push advances in medicine and vice versa,” Verocai said. “Knowing that we can detect earlier might push other researchers to figure out how we can intervene earlier and make that animal healthier faster.”
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Note: This story originally appeared in the Fall 2023 issue of VMBS Today.
For more information about the Texas A&M College of Veterinary Medicine & Biomedical Sciences, please visit our website at vetmed.tamu.edu or join us on Facebook, Instagram, and Twitter.
Contact Information: Jennifer Gauntt, Director of VMBS Communications, Texas A&M College of Veterinary Medicine & Biomedical Sciences; jgauntt@cvm.tamu.edu; 979-862-4216
