Oklahoma State University study reveals better method to test cats for heartworm infections

STILLWATER, Okla. and SHAWNEE, Kan., Jan. 13, 2014 /PRNewswire/ -- New data were published today in Parasites & Vectors from a study conducted at Oklahoma State University (OSU) that identified a method of improving the sensitivity of antigen tests for heartworm (Dirofilaria immitis) infection in cats. The study, funded by Bayer HealthCare LLC Animal Health division, makers of parasiticides, found that heat treatment of feline serum samples prior to testing can considerably improve the sensitivity of antigen assays in feline patients and, in turn, result in a more accurate diagnosis of heartworm infection in cats.

"Heartworm is a very serious disease in cats that can result in significant pulmonary damage and can be fatal," said lead study investigator, Susan E. Little, DVM, Ph.D., Regents professor and Krull-Ewing chair in veterinary parasitology, OSU Center for Veterinary Health Sciences. "We believe this study's findings will enhance detection of heartworm infection in cats, improving both patient care and veterinarians' understanding of the true extent of feline heartworm."

Antigen detection a challenge in cats 

According to the study's authors – which included Byron Blagburn, MS, Ph.D., distinguished university professor, Auburn University College of Veterinary Medicine – the diagnosis of heartworm in cats has been complicated in the past by the difficulty associated with reliable detection of the heartworm antigen in feline samples. In fact, heartworm antigen tests have been considered much less reliable in cats than dogs. The lack of antigen detection has been attributed to low circulating antigenemia (presence of antigens in the blood) resulting from the low number of worms often seen in feline infections. Other feline heartworm assays based on antibody detection can be difficult to interpret since they do not distinguish between past or current infections.

Aiming to determine if antigen-antibody complex formation – antigen blocking – interfered with detection of the heartworm antigen in cats using commercial assays, the study evaluated serum samples from six domestic cats confirmed to be infected with a low number of heartworms. Four different commercially available assays were used before and after heat treatment of sera. The study found that the heartworm antigen was detected in zero to only one of six cats (0 to 16.7 percent), without heat treating the sera, using the assays according to manufacturers' directions. However, after heat treatment of the samples prior to testing, as many as five of six cats (83.3 percent) had detectable antigen – a "dramatic increase," the study's authors noted. Thus, new data suggests that adequate antigen is present in samples from cats infected with heartworm to allow diagnosis, but formation of antigen-antibody complexes may prevent its detection on commercial assays.

The authors concluded, "The data in the present study are exciting in that they suggest that once antigen-antibody complexes are disrupted, antigen tests may be of great value in confirming feline infection with D. immitis, particularly the sensitive microtiter well-based assays. Surveys conducted by antigen testing alone may be greatly underestimating the true prevalence of infection in cats."  

"When antigen based assays were first developed for detecting canine heartworm, the serum was pre-treated with heat or acid to destroy immune complexes prior to testing, as they were recognized as inhibiting detection of antigen in some canine samples," said Dr. Little. "This step is no longer included in protocols of antigen tests, including those labeled for use in cats. I think this study's findings could ultimately lead to a revision in the protocol for feline testing."

"Funding well-designed and carefully-executed research is a vital part of Bayer HealthCare's commitment to our mission, 'Science For a Better Life,'" said Joe Hostetler, DVM, veterinary technical services manager, Bayer HealthCare LLC Animal Health division and a study co-author. "Being part of this study was especially gratifying for me because, once the results were in, we realized the data had the potential to improve feline healthcare in an immediate and important way."

About Oklahoma State University

Oklahoma State University is a modern land-grant university. OSU's Center for Veterinary Health Sciences is the only veterinary college in Oklahoma. One of 30 veterinary colleges in the United States, it is fully accredited by the Council on Education of the American Veterinary Medical Association. The center's Boren Veterinary Medical Teaching Hospital is open to the public and provides routine and specialized care for small and large animals. It also offers 24-hour emergency care and is certified by the American Animal Hospital Association. OSU is preparing students for a brighter future and building a brighter world for all. OSU improves the lives of people in Oklahoma, the nation, and the world through integrated, high quality teaching, research and outreach. For more information, visit www.cvhs.okstate.edu or call (405) 744-7000.

About Bayer HealthCare

The Bayer Group is a global enterprise with core competencies in the fields of health care, agriculture and high-tech materials. Bayer HealthCare, a subgroup of Bayer AG with annual sales of EUR 18.6 million (2012), is one of the world's leading, innovative companies in the healthcare and medical products industry and is based in Leverkusen, Germany. The company combines the global activities of the Animal Health, Consumer Care, Medical Care and Pharmaceuticals divisions. Bayer HealthCare's aim is to discover, develop, manufacture and market products that will improve human and animal health worldwide. Bayer HealthCare has a global workforce of 55,300 employees (Dec. 31, 2012) and is represented in more than 100 countries. More information at www.healthcare.bayer.com.

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[1] Little SE, Raymond MR, Thomas JE, Gruntmeir J, Hostetler JA, Meinkoth JH, Blagburn BL: Heat treatment prior to testing allows detection of antigen of Dirofilaria immitis in feline serum. Parasites & Vectors (13 January 2014).

SOURCE Bayer HealthCare