A repeated cross-sectional study of intestinal parasites in Texas shelter dogs using fecal flotation and saline sedimentation.

Estimates of intestinal parasite prevalence in canine populations have largely been based on use of fecal flotation methods only. Dogs in animal shelters are likely at higher risk of intestinal parasite infection because of their previous exposure history. Our objectives were to estimate the prevalence of intestinal parasites among Texas shelter dogs using centrifugal fecal flotation and saline sedimentation techniques, to identify risk factors for infection, and to compare proportions of positive samples detected via fecal flotation vs. saline sedimentation for the most common parasites. Using a repeated cross-sectional study design, we collected fecal samples from dogs on three visits to each of seven Texas animal shelters between May 2013 and December 2014. Fecal flotation and/or saline sedimentation were used to identify parasites in samples. Fecal samples were collected from 529 dogs. The most frequently detected parasites were Ancylostoma caninum (26.4% via fecal flotation, 20.7% via saline sedimentation) and Trichuris vulpis (12.0% via fecal flotation, 14.1% via saline sedimentation). Risk factors for certain parasites were identified; for example, dogs with abnormal fecal consistency were more likely to be shedding T. vulpis eggs than dogs with normal fecal consistency (OR = 1.8, p = 0.005). The addition of fecal sedimentation not only added to the number of parasite species detected in this study, but it also increased the number of dogs diagnosed with the common intestinal parasites that are primarily detected using fecal flotation methods. Texas shelter dogs carry a high burden of intestinal parasites, including those of zoonotic importance.

Optimizing heartworm diagnosis in dogs using multiple test combinations.

BACKGROUND: Various heartworm (HW) diagnostic testing modalities detect products of, or reactions to, different life cycle stages of Dirofilaria immitis. Microfilariae (Mf) can be directly visualized in blood, antigen (Ag) from immature and adult heartworms may be detected on commercial assays, and antibody (Ab) tests detect the host immune response to larval stages. Ag and Mf tests are commonly used in dogs, which frequently carry adult HW infections, but Ab tests have only been validated for use in cats. In some HW-infected dogs, Ag is blocked by immune complexing leading to false-negative results. Heat-treatment (HT) to disrupt these complexes can increase the sensitivity of HW Ag tests. The aim of this study was to compare different methods for diagnosing HW infection in dogs at high risk using individual and paired diagnostic tests, including an exploration of using Ab tests designed for cats to test canine samples. METHODS: One hundred stray adult (≥ 2-year-old) dogs in Florida shelters were tested using Mf, HW Ag, and HW Ab tests (feline HW Ab tests currently not commercially validated/approved for use in dogs); two versions of each test platform were used. RESULTS: Fourteen dogs tested positive using point-of-care (POC) Ag tests; an additional 2 dogs tested positive with microtiter well assay, and an additional 12 dogs tested positive using HT Ag testing. For individual tests, Ag test sensitivity/specificity compared to HT Ag was 50-57%/100%, and Ab tests were 46-64%/82-94%. Sensitivity estimates for individual tests were higher when comparing to non-HT Ag. Pairing POC Ag tests with Mf tests improved sensitivity without loss of specificity, while pairing POC Ag and Ab tests modestly increased sensitivity at the expense of specificity. CONCLUSIONS: Screening dogs for HW infection using both POC Ag and Mf detection, which is recommended by the American Heartworm Society, improved diagnostic performance in this study compared to single Ag test use, but may have missed more than one in four infected dogs. The need to improve access to highly accurate, rapid, and inexpensive large-scale HW testing for dogs in animal shelters remains largely unmet by current testing availability. The development of practical and validated protocols that incorporate heat or chemical treatment to disrupt Ag-Ab complexes in POC testing or decreasing the cost and time required for such testing in reference laboratories might provide solutions to this unmet need. Similar studies performed in countries where the prevalence of parasites such as D. repens or A. vasorum is different to the USA could potentially yield very different positive predictive values for both HT and non-HT Ag tests.

Heartworm prevalence in dogs versus cats: Multiple diagnostic modalities provide new insights.

The cornerstones of diagnosis of heartworm (HW) in dogs are the detection of circulating antigen from adult female Dirofilaria immitis or the visualization of microfilariae in whole blood. These tests are less sensitive in cats because of the feline immune response leading to low numbers of adult worms, but heartworm antibody tests are also licensed for use in cats. HW antibodies in cats are detectable when there has at least been larval development in the tissues, but positive antibody tests cannot distinguish between current and previous larval infections; thus, cats with positive antibody test results are considered currently or previously infected with D. immitis. The aim of the present study was to use multiple HW diagnostic modalities to maximize detection of infection in dogs and cats at high risk of infection and to compare infection prevalence between these two hosts. Blood samples collected from 100 stray dogs and 100 stray cats at Florida animal shelters were tested for HW antigen (before and after heat treatment) and microfilariae; cats were also tested for HW antibody. Dogs were significantly (P = 0.0001) more likely to be diagnosed with adult HW infection (28 %; 95 % CI: 20.1-37.6%) when compared with cats (4 %; 95 % CI: 1.6-10.2%) on the basis of positive antigen and microfilariae test results. Cats with current or previous adult, immature adult, or larval HW infections comprised 19 % (95 % CI: 12.4%-27.9%) of the feline population, which was not significantly different (P = 0.1) from the prevalence of adult D. immitis infection in dogs. Testing unprotected cats for heartworm antibodies demonstrated a similar, high risk of infection to the matched unprotected dog population in Florida, which supports the use of HW preventives in cats in areas where HW transmission occurs.

Heartworm prevalence in dogs versus cats: Multiple diagnostic modalities provide new insights.

The cornerstones of diagnosis of heartworm (HW) in dogs are the detection of circulating antigen from adult female Dirofilaria immitis or the visualization of microfilariae in whole blood. These tests are less sensitive in cats because of the feline immune response leading to low numbers of adult worms, but heartworm antibody tests are also licensed for use in cats. HW antibodies in cats are detectable when there has at least been larval development in the tissues, but positive antibody tests cannot distinguish between current and previous larval infections; thus, cats with positive antibody test results are considered currently or previously infected with D. immitis. The aim of the present study was to use multiple HW diagnostic modalities to maximize detection of infection in dogs and cats at high risk of infection and to compare infection prevalence between these two hosts. Blood samples collected from 100 stray dogs and 100 stray cats at Florida animal shelters were tested for HW antigen (before and after heat treatment) and microfilariae; cats were also tested for HW antibody. Dogs were significantly (P = 0.0001) more likely to be diagnosed with adult HW infection (28 %; 95 % CI: 20.1-37.6%) when compared with cats (4 %; 95 % CI: 1.6-10.2%) on the basis of positive antigen and microfilariae test results. Cats with current or previous adult, immature adult, or larval HW infections comprised 19 % (95 % CI: 12.4%-27.9%) of the feline population, which was not significantly different (P = 0.1) from the prevalence of adult D. immitis infection in dogs. Testing unprotected cats for heartworm antibodies demonstrated a similar, high risk of infection to the matched unprotected dog population in Florida, which supports the use of HW preventives in cats in areas where HW transmission occurs.

Repeated cross-sectional study of Trypanosoma cruzi in shelter dogs in Texas, in the context of Dirofilaria immitis and tick-borne pathogen prevalence.

BACKGROUND: Vector-borne diseases have an adverse impact on health of dogs, and infected dogs can be sentinels for human infection. Infection with Trypanosoma cruzi, an agent of Chagas disease, causes fatal heart disease in dogs across the southern United States but has been neglected from wide-scale prevalence studies. OBJECTIVES: To determine the prevalence of exposure to T. cruzi, Ehrlichia spp., Anaplasma spp., Borrelia burgdorferi, and infection with Dirofilaria immitis among dogs in shelters across Texas and to identify risk factors for T. cruzi seropositivity. ANIMALS: Six hundred and eight dogs. METHODS: This repeated cross-sectional study was performed by collecting blood from ~30 dogs during each of the 3 visits to 7 shelters. We tested serum for antibodies to T. cruzi using 2 tests in series and for antibodies to Ehrlichia spp., Anaplasma spp., and B. burgdorferi and D. immitis antigen using the IDEXX SNAP 4DX Plus point-of-care test. DNA was extracted from blood clots and tested for T. cruzi DNA and strain type via quantitative polymerase chain reactions (qPCR). We used logistic regression to assess risk factors. RESULTS: One hundred ten (18.1%) of 608 dogs were seropositive for T. cruzi. Prevalence of exposure to the other vector-borne agents was: Ehrlichia spp. 3.6%; Anaplasma spp. 6.9%; B. burgdorferi 0.2%; and D. immitis infection 16.0%. Six of 559 (1.1%) dogs were qPCR-positive for T. cruzi. CONCLUSIONS AND CLINICAL IMPORTANCE: T. cruzi seroprevalence was comparable to D. immitis prevalence and higher than seroprevalence of the tick-borne pathogens. T. cruzi is an underrecognized health threat to dogs across Texas and possibly other southern states where triatomine vectors are endemic.

Identification of Heterobilharzia americana infection in a dog residing in Indiana with no history of travel.

CASE DESCRIPTION: A 1-year-old castrated male dog residing in Indiana was examined because of intermittent vomiting of 4 months' duration. CLINICAL FINDINGS: The dog's condition did not resolve with medication. Diagnostic imaging revealed a possible partial obstruction at the ileocecal junction. An exploratory laparotomy was performed. The jejunum contained diffusely distributed, nodular, intramural lesions; 2 biopsy specimens were collected from representative lesions. The pancreas was grossly swollen, and pancreatitis was presumed present. No other abnormalities were observed in the abdomen. Histologic examination of the submitted biopsy specimens revealed infection with Heterobilharzia americana. TREATMENT AND OUTCOME: After diagnosis, the dog was treated with fenbendazole suspension (48 mg/kg [21.8 mg/lb], PO, q 24 h) for 10 days. This treatment was subsequently repeated 11 and 80 days later. One week after the end of the last fenbendazole treatment, several H americana eggs were detected in a fecal sample via saline sedimentation, and the dog was given praziquantel (25 mg/kg [11.4 mg/lb], PO, q 8 h) for 2 days. No gastrointestinal signs were evident 4 months after that treatment. CLINICAL RELEVANCE: The dog described in this report was the first autochthonous canine case of H americana infection in Indiana, to the authors' knowledge; this case has confirmed that the distribution of this parasite in the Midwestern United States is broader than previously known. Increased awareness of the distribution of H americana should aid veterinarians in early, noninvasive diagnosis and appropriate treatment of affected animals. Repeated treatments and recheck fecal examinations may be necessary when managing these cases.