Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.
Issue link: http://todaysveterinarypractice.epubxp.com/i/840151
24 AHS HEARTWORM HOTLINE Turning Up the Heat on Heartworm Diagnosis Brian A. DiGangi, DVM, MS, DABVP American Society for the Prevention of Cruelty to Animals, Gainesville, Florida AHS HEARTWORM HOTLINE Antigen testing for Dirofilaria immitis has been a foundational component of model preventive veterinary care for many years, particularly for dogs. For privately owned pets, the results of such testing guide prevention strategies and, in the event of a positive result, treatment for heartworm disease. In shelter populations, the results are often a key determining factor in the management of a dog throughout its stay in the shelter system, including its likelihood of a live release. Although the accuracy of commercially available D immitis antigen test kits has been widely studied, recent reports have sparked renewed interest in the effect of antigen–antibody immune complexes on test results. 1–6 Such complexes can interfere with antigen detection, resulting in "no antigen detected" (NAD) test results in infected animals, and should be considered when NAD test results conflict with clinical expectations. WHAT ARE IMMUNE COMPLEXES? Immune complexes represent soluble antigen bound to endogenous antibody, forming an insoluble unit that remains in circulation. Such complexes are a normal component of a functioning immune system and are cleared by phagocytosis when the balance of antigen to antibody in circulation is maintained. Excess immune complexes in circulation can result in tissue deposition, leading to local inflammatory responses and a variety of autoimmune diseases. Vasculitis, glomerulonephritis, pneumonitis, and arthritis are common sequelae of immune complex deposition in the respective affected organ system. In the case of diagnostic testing methods that rely on soluble antigen for detection (eg, enzyme- linked immunosorbent assay, lateral flow assays), antigen bound in an immune complex may not be available for detection, leading to an NAD result despite the presence of antigen in the test sample. A variety of techniques can be used to dissociate circulating immune complexes in a diagnostic sample. shutterstock.com/atiger The Heartworm Hotline column is presented in partnership between Today's Veterinary Practice and the American Heartworm Society ( heartwormsociety.org ). The goal of the column is to communicate practical and timely information on prevention, diagnosis, and treatment of heartworm disease, as well as highlight current topics related to heartworm research and findings in veterinary medicine. HEARTWORM HOTLINE