Abstract
BackgroundDetection of Dirofilaria immitis, or heartworm, through antigen in sera is the primary means of diagnosing infections in dogs. In recent years, the practice of heat-treating serum prior to antigen testing has demonstrated improved detection of heartworm infection. While the practice of heat-treating serum has resulted in earlier detection and improved sensitivity for heartworm infections, it has been suggested that heat treatment may cause cross reactivity with A. reconditum and intestinal helminth infections of dogs. No studies have assessed the potential cross-reactivity of these parasites with heartworm tests before and after heat treatment using blood products and an appropriate gold standard reference.MethodsCanine sera (n=163) was used to evaluate a heartworm antigen-ELISA (DiroCHEK®) and potential cross-reactivity with common parasitic infections. The heartworm status and additional parasite infections were confirmed by necropsy and adult helminth species verified morphologically or by PCR, and feces evaluated by centrifugal fecal flotation.ResultsIntestinal parasites were confirmed in 140 of the dogs by necropsy, and 130 by fecal flotation. Acanthocheilonema reconditum microfilariae were confirmed in 22 dogs. Prevalence of heartworm infection confirmed by necropsy was 35.6% (58/163). In the 105 dogs without heartworms, specificity remained unchanged at 100% both before and after heat treatment despite confirmed infections with A. reconditum, Ancylostoma caninum, Ancylostoma brasiliense, Trichuris vulpis, Toxocara canis, Dipylidium caninum, Spirometra mansonoides, Macracanthorynchus ingens, Cystoisospora sp., Giardia sp., and Sarcocystis sp.ConclusionsThese findings suggest that the use of heat treatment improves sensitivity of heartworm tests and is unlikely to cause false positive antigen results due to Acanthocheilonema reconditum, intestinal helminths, and protozoal parasites in dogs. Graphical
Highlights
Detection of Dirofilaria immitis, or heartworm, through antigen in sera is the primary means of diagnosing infections in dogs
The presence of D. immitis adult or immature adult worms was verified by necropsy
Of the 30 Modified Knott’s technique (MKT) positive heartworm infected dogs, 15 blood samples had microfilariae morphologically identified as D. immitis only, 1 sample with D. immitis and two microfilariae of an unknown species, 2 samples had microfilariae of A. reconditum only, and 12 with microfilariae of both D. immitis and A. reconditum
Summary
Detection of Dirofilaria immitis, or heartworm, through antigen in sera is the primary means of diagnosing infections in dogs. The practice of heat-treating serum prior to antigen testing has demonstrated improved detection of heartworm infection. While the practice of heat-treating serum has resulted in earlier detection and improved sensitivity for heartworm infections, it has been suggested that heat treatment may cause cross reactivity with A. reconditum and intestinal helminth infections of dogs. Methods: Canine sera (n=163) was used to evaluate a heartworm antigen-ELISA (DiroCHEK®) and potential crossreactivity with common parasitic infections. Recently heat ICD treatment of serum at an elevated temperature of 104 Co has been shown to allow earlier detection and improved sensitivity for D. immitis antigen [3]. No decrease in specificity has been observed in pathogen free dogs when using this elevated heating step or an acid ICD prior to antigen testing [3, 11]. Heat ICD is unlikely to cause false positive results on heartworm tests in dogs infected by O. lupi [13]
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