BackgroundThe diagnosis and management of canine heartworm disease is a growing concern for shelter veterinarians. Although the accuracy of commercial antigen test kits has been widely studied, recent reports have renewed interest in antigen blocking as a causative factor for false “no antigen detected” results. The objectives of this study were to determine the prevalence of false “no antigen detected” results in adult dogs entering shelters in northern, southern, and western regions of the country and to identify historical and clinical risk factors for such results.MethodsSerum samples were evaluated for Dirofilaria immitis antigen using a commercially available point-of-care ELISA; samples in which no antigen was detected underwent a heat treatment protocol and repeat antigen testing. Whole blood samples underwent Knott testing to identify the presence of microfilariae. Historical and clinical findings were analyzed using exact logistic regression.ResultsA total of 616 samples were analyzed. Overall prevalence of positive antigen test results (prior to heat treatment) was 7.3% and frequency of false “no antigen detected” results due to antigen blocking (ie, samples with no antigen detected prior to heat treatment and positive after heat treatment) was 5.2%. Among dogs that had no detectable antigen on the initial tests, dogs that had microfilariae detected via modified Knott testing (OR = 32.30, p-value = 0.013) and dogs that previously received a heartworm preventive (OR = 3.81, p-value = 0.016) had greater odds of antigen blocking than dogs without these factors. Among dogs that were heartworm positive, those without microfilariae detected had greater odds of antigen blocking than dogs with this factor (OR = 11.84, p-value = 0.0005). Geographic region of origin was significantly associated with occurrence of antigen blocking (p = 0.0036); however, blocking occurred in all regions sizably contributing to heartworm diagnoses. Of the 74 dogs found to be infected with heartworms in this study, 39.2% (29) had no detectable antigen prior to heat treatment.ConclusionsHeat treatment of serum samples should be considered to improve diagnostic test accuracy, particularly in dogs that reportedly received a heartworm preventive prior to antigen testing regardless of region of origin.Electronic supplementary materialThe online version of this article (10.1186/s13071-017-2443-7) contains supplementary material, which is available to authorized users.

Case series summary This case series describes three shelter-housed cats concurrently diagnosed with feline infectious peritonitis (FIP). The cats were from a cohort of seven surrendered from the site of a house fire. The three cats presented with mild upper respiratory signs. Within 10 days they clinically declined: progressive signs included pyrexia, icterus, lethargy, anorexia and cavitary effusions. Necropsy followed by histopathology and immunohistochemistry confirmed a diagnosis of FIP in all three. Molecular analysis of the causative feline coronavirus (FCoV) revealed varied amino acid alterations in the spike gene both between cats and between sample types in individual cats. A fourth cat from the cohort remained healthy in the shelter but succumbed to FIP 6 weeks post-adoption. Relevance and novel information This case series places FCoV genetic sequences in the context of clinical signs in a small shelter outbreak. Each of the three cats concurrently developed a slightly different clinical presentation. PCR amplification and genetic sequencing revealed that two cats shared an S1/S2 cleavage site mutation (R790S) previously described to be associated with the development of FIP; one of the cats had an additional S1/S2 cleavage site mutation (R793S). The third cat had a single, identical S1/S2 point mutation (R790G) unique from the other two cats; the R790G mutation has not been previously reported. This case series provides interesting data on point mutations associated with the development of FIP and provides support for a ‘circulating virulent–avirulent theory’ of FIP pathogenesis in a small shelter outbreak.

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A retrospective study using a geographic information system (GIS) was conducted to capture, map, and analyze intake data of caregiver (owner)-surrendered kittens (aged 0-6 months) to the Society for the Prevention of Cruelty to Animals (SPCA) of Tompkins County, NY, from 2009 to 2011. Addresses of caregiver-surrendered kittens during the study period were mapped (n = 1,017). Mapping and analysis of the resultant data set revealed that the distribution of kittens was nonrandom. Seventeen statistically significant (p = .001) clusters were identified, 1 of which was the SPCA of Tompkins County (due to anonymously surrendered nonhuman animals). The remaining 16 clusters were composed of 52 homes; 27.5% (280/1,017) of the kittens in the data set originated from these 52 homes. The majority of kittens within clusters were surrendered from high-density residential and manufactured residential home parks. Analyzing such clusters using GIS is a novel approach for targeting spay/neuter and educational programs to areas contributing disproportionately to shelter populations. This method may prove useful to help shelters more effectively allocate their limited resources, but further evaluation of this and other targeted approaches is needed to assess the long-term efficacy of such programs.