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TDK conference 2018

Diagnostic applicability of the Vetscan VS2-HW antigen test in Dirofilaria immitis and/or Dirofilaria repens infections of dogs
Holló Noémi Petra - year 5
University of Veterinary Medicine Budapest, Department of Internal Medicine
Supervisors: Dr. Károly Vörös, Dr. Zsolt Becker


Serological tests which detect the antigen (Ag) of adult female heartworms play an important role in the diagnosis of canine heartworm disease caused by Dirofilaria immitis, although they do not always provide reliable results. The final, in vivo diagnosis can be achieved by PCR examination of the DNA extracted from the microfilariae. This method is also suitable to diagnose the more common D. repens as well as double infections. There are several international publications on the sensitivity and specificity of Ag tests, but we know only one report which has been published on dogs living in D. repens infected areas. In this paper, some dogs have also been described, in them the Ag test showed a positive result, whilst the PCR-technique confirmed only D. repens infection. The authors of this publication suggested but did not confirm the possibility of cross-reactions between the two Dirofilaria species or simultaneous occurrence of occult heartworm disease and D. repens infections. In occult heartworm disease, no microfilariae can be found in the peripheral blood, despite D. immitis infection. Positive cross reactions have also been reported in other publications caused by Angiostrongylus vasorum and Spirocerca lupi.

We have studied the occurrence of D. immitis and D. repens infections, the sensitivity and specificity of the Vetscan (VS2-HW) Ag test, as well as occult heartworm disease as a possible explanation of cross-reactions. In our study, 71 dogs were included which were examined by the VS2-HW test as well as by the PCR-methods for detection of D. immitits and D. repens.

With the PCR-examinations, there have been 26 dogs being positive for D. immitis and negative for D. repens (Group 1), 21 dogs being both positive for D. immitis and D. repens (Group 2), whilst 24 dogs had only a D. repens infection (Group 3). The sensitivity of the VS2-HW Ag-test was determined from Group 1 and 2 altogether, based on the individuals being PCR positive for D. immitis and it yielded 97.7% (95% Blaker confidence interval 89.0% - 99.8%). The specificity of the VS2-HW test was calculated from Group 3 and it yielded 66.7% (95% Blaker confidence interval 45.6% - 83.1%). Among the 71 dogs, there have been 6 dogs which had a positive VS2-HW Ag test result, whilst the PCR examination demonstrated a negative D. immitis and a positive D. repens result. In these dogs, we have performed the Ag test with the products of other manufacturers as well and received positive result in each occasion. This observation supports the hypothesis that these dogs had both occult heartworm disease and a coinciding D. repens infection.

D. immitis and D. repens infections occurred both separately and simultaneously within the examined population. The VS2-HW Ag test produced excellent sensitivity, whilst moderate specificity in the presence of D. repens infections. Further examinations are necessary to explore the possible roles of A. vasorum and S. lupi.

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