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

ABSTRACT: 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.

SUBMITTER: Hays KM

PROVIDER: S-EPMC7458388 | biostudies-literature | 2020 Dec

REPOSITORIES: biostudies-literature

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

Hays Kellie M KM Rodriguez Jessica Y JY Little Susan E SE Litster Annette L AL Mwacalimba Kennedy K KK Sundstrom Kellee D KD Amodie Deborah M DM Serrano Maria A MA Guerios Simone D SD Lane Jennifer N JN Levy Julie K JK

Veterinary parasitology: X 20200612

The cornerstones of diagnosis of heartworm (HW) in dogs are the detection of circulating antigen from adult female <i>Dirofilaria immitis</i> 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 t ...[more]

PMID: 32904770

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Project description:BackgroundHeartworm (Dirofilaria immitis) in dogs is considered endemic in Australia, but the clinical heartworm disease caused by the heartworm is rare and prevalence is low. The mainstream prevention of the heartworm is based on macrocyclic lactone (ML) administration. The aim of this study was to confirm endemism of the heartworm under current Australian conditions using a cohort of recent microfilaria-positive dogs which were on variable heartworm prevention.MethodsA hotspot of canine heartworm antigen-positive and microfilaria-positive dogs has been detected recently in Queensland, Australia. Blood samples from 39 dogs from Queensland and two dogs from New South Wales were investigated for canine filarioids. Rapid antigen diagnostic tests capable of detection of D. immitis and real-time PCR for quantification and differentiation between D. immitis from Acanthocheilonema reconditum with quantification of microfilariae in canine blood samples, together with D. immitis specific real-time PCR assay, were applied to microfilaria-positive dogs. The P-glycoprotein genotype was determined to test whether Australian-sourced heartworm shared the same genetic markers as those suspected of ML-resistance in North America.ResultsOnly D. immitis was detected in the samples from Queensland and New South Wales, Australia. Using high resolution melt real-time PCR and D. immitis specific real-time PCR, the calculated microfilaria concentration ranged from 1 to 44,957 microfilariae/ml and from 7 to 60,526 microfilariae/ml, respectively. DNA sequencing of the PCR products confirmed D. immitis. Fifteen of the examined dogs were on putative, rigorous ML prevention. For the remaining dogs, compliance with heartworm prevention was unknown or reported as inconsistent. Wild-type genotype AA-GG of the P-glycoprotein locus of D. immitis sequence has been obtained for three blood samples. Due to the incomplete history, any suggestion of a loss of efficacy of MLs must be treated as 'remotely possible'. In the immediate future, records of preventative administration and annual antigen testing would be required to determine any problems with the efficacy of preventatives.ConclusionsThe prevalence of canine heartworm in Australia remains poorly understood. It is generally assumed to be low by veterinary practitioners. The localised increase in the study area confirms endemism of canine heartworm and a requirement for ongoing vigilance through annual heartworm testing to better understand the changing distribution of canine heartworm, client compliance, as well as to detect any change in ML-susceptibility.

Project description:BackgroundCanine heartworm (Dirofilaria immitis) is a life-threatening infection of dogs with a global distribution. Information on the prevalence of D. immitis and associated risk factors for canine heartworm antigen positivity-and thus disease-in Australia is scarce or outdated. The current reference method for D. immitis diagnosis in dogs is via the detection of heartworm antigen in blood using commercially available microwell-based enzyme-linked immunosorbent assays (ELISAs). Heat treatment of canine plasma prior to testing has been suggested to increase test sensitivity. The aim of the current study was to estimate the prevalence of D. immitis in dogs confined to shelters in Queensland, Australia. The impact of heat treatment on antigen test results was also assessed.MethodsBlood samples (n = 166) were collected directly from dogs in seven shelters across Queensland (latitudinal span of approx. 1700 km) into EDTA blood collection tubes. A commercially available ELISA (DiroCHEK®) was used to detect canine heartworm antigen in untreated and heat-treated plasma. Whole blood was concurrently tested for the presence of microfilariae and D. immitis DNA using a modified Knott's test and real-time PCR, respectively. Risk factors (age, gender, source, location) associated with the odds of positivity for canine heartworm were assessed using binary logistic regression models.ResultsA total of 16 dogs (9.6%; 95% confidence interval [CI]: 5.9-15.2%) were positive for canine heartworm based on combined test results. Heat treatment did not impact on the positivity of D. immitis antigen within samples (Cohen's kappa = 0.98), but the optical density was significantly increased in paired plasma samples for D. immitis antigen-positive samples (Wilcoxon matched-pairs signed rank test, two-tailed P < 0.01). Location of the dog in a shelter in northern Queensland was the only risk factor significantly associated with the odds of a dog being more likely to be D. immitis antigen positive (odds ratio: 4.39; 95% CI: 1.26-13.51). All samples positive for the modified Knott's test were also positive for D. immitis DNA by PCR.ConclusionsThis study demonstrated the presence of heartworm-positive dogs in shelters in Queensland, with positive animals significantly more likely to occur in northern Queensland than southern Queensland. Sustained testing for the presence of D. immitis microfilariae and antigen remain important diagnostic tools in areas with known and re-emerging canine heartworm activity.

Project description:BackgroundFleas (Siphonaptera) are the most clinically important ectoparasites of dogs and cats worldwide. Rising levels of pet ownership, climate change and globalisation are increasing the importance of a detailed understanding of the endemicity and prevalence of flea-borne pathogens. This requires continued surveillance to detect change. This study reports a large-scale survey of pathogens in fleas collected from client-owned cats and dogs in the UK.MethodsRecruited veterinary practices were asked to follow a standardised flea inspection protocol on a randomised selection of cats and dogs brought into the practice in April and June 2018. A total of 326 practices participated and 812 cats and 662 dogs were examined. Fleas were collected, identified to species and pooled flea samples from each host were analysed for the presence of pathogens using PCR and sequence analysis.ResultsOverall, 28.1% of cats and 14.4% of dogs were flea infested. More than 90% of the fleas on both cats and dogs were cat fleas, Ctenocephalides felis felis. Fleas of the same species from each infested host were pooled. DNA was amplified from 470 of the pooled flea samples using conventional PCR, 66 of which (14% ± 95% CI 3.14%) were positive for at least one pathogen. Fifty-three (11.3% ± 95% CI 2.85%) of the pooled flea DNA samples were positive for Bartonella spp., 35 were from cats and 4 from dogs, the remainder had no host record. Seventeen of the Bartonella spp. samples were found to be Bartonella henselae, 27 were Bartonella clarridgeiae (of two different strains), 4 samples were Bartonella alsatica and one was Bartonella grahamii; 4 samples could not be identified. Fourteen (3% ± 95% CI 1.53%) of the flea DNA samples were found to be positive for Dipylidium caninum, 10 of the D. caninum-infected samples were collected from cats and one from a dog, the other 3 positive flea samples had no host species record. Only 3 flea samples were positive for Mycoplasma haemofelis or Mycoplasma haemocanis; 2 were collected from cats and one had no host species record. Three fleas were positive for both D. caninum and Bartonella spp. One flea was positive for both Bartonella spp. and M. haemofelis or M. haemocanis.ConclusionsThis study highlights the need for ongoing flea control, particularly given the relatively high prevalence of Bartonella spp., which is of concern for both animal welfare and human health. The study demonstrates the ongoing need to educate pet owners about the effects of both flea infestation and also the pathogen risks these fleas present.

Project description:BACKGROUND:Urbanization is occurring rapidly on a global scale and is altering mosquito communities, creating assemblages that are characteristically less diverse. Despite high rates of urbanization and ample examples of vector-borne diseases transmitted by multiple species, the effects of urbanization-driven mosquito diversity losses on disease transmission has not been well explored. We investigated this question using the dog heartworm, a filarial parasite vectored by numerous mosquito species. METHODS:We trapped host-seeking mosquitoes in undeveloped areas and neighborhoods of different ages in Wake County, North Carolina, USA, analyzing captured mosquitoes for heartworm DNA. We compared within-mosquito heartworm infection across land-use types by Kruskal-Wallis and likelihood ratio tests. Using zip code level data acquired from dogs in a local shelter, we performed linear regressions of within-host heartworm prevalence by within-mosquito heartworm prevalence as well as by three mosquito diversity measures. We also determined the best predictor of host-level prevalence among models including within-mosquito infection, mosquito diversity and abundance, and socioeconomic status as variables. RESULTS:Suburban areas had lower within-mosquito heartworm prevalence and lower likelihood of heartworm-positive mosquitoes than did undeveloped field sites, although no differences were seen between suburban and undeveloped wooded sites. No relationships were noted between within-mosquito and within-host heartworm prevalence. However, mosquito diversity metrics were positively correlated with host heartworm prevalence. Model selection revealed within-host prevalence was best predicted by a positive relationship with mosquito Shannon-Wiener diversity and a negative relationship with household income. CONCLUSIONS:Our results demonstrate that decreases in mosquito diversity due to urbanization alter vector-borne disease risk. With regard to dog heartworm disease, this loss of mosquito diversity is associated with decreased heartworm prevalence within both the vector and the host. Although the response is likely different for diseases transmitted by one or few species, mosquito diversity losses leading to decreased transmission could be generalizable to other pathogens with multiple vectors. This study contributes to better understanding of the effects of urbanization and the role of vector diversity in multi-vectored pathosystems.

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

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

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