Peer-reviewed veterinary case report
Heartworm and related parasites in dogs and cats across the USA
By Smith, Rachel et al.·Published in Parasites & vectors·2022·College of Veterinary Medicine, United States·View original on PubMed →
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Original publication title: Nationwide molecular survey of Dirofilaria immitis and Dirofilaria repens in companion dogs and cats, United States of America.
- Species:
- dog
Plain-English summary
A nationwide study found that 6.3% of dogs tested positive for heartworms (Dirofilaria immitis) across 17 states in the USA, while only 0.3% of cats were positive in 4 states. The study analyzed blood samples from over 2,300 pets between 2016 and 2022. Southern states had a higher prevalence of heartworms in dogs compared to other regions. Interestingly, dogs infected with another parasite, Hepatozoon, were more likely to also have heartworms. This research highlights the importance of regular heartworm testing and prevention for pets, especially in areas where heartworms are more common.
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Abstract
BACKGROUND: Heartworms, Dirofilaria immitis, are known to be widespread in dogs and cats in the USA, but there have been no country-wide prevalence studies performed to date. There have also been no large-scale studies to determine whether the closely related species, Dirofilaria repens, occurs in the USA. METHODS: To provide this large-scale data, we examined whole blood samples (n = 2334) submitted from around the USA to the Molecular Diagnostic Laboratory at Auburn University between 2016 and 2022. Quantitative PCRs for D. immitis (targeting 16S rRNA) and D. repens (targeting cytochrome c oxidase subunit 1 gene) were performed to determine the presence of Dirofilaria DNA. DNA sequencing was performed to confirm the results. RESULTS: Dirofilaria immitis DNA was found in 6.3% (68/1080) of the dogs from 17/39 states, and 0.3% (4/1254) of the cats from 4/42 states. None of the dogs or cats were positive for D. repens. The average 16S rRNA copy number of D. immitis in the dogs was 1,809,604 in 200 µl whole blood, while only a single copy was found in each of the four D. immitis-positive cats. The prevalence of D. immitis in dogs of different ages, sexes, and breeds did not differ significantly, but the prevalence in Southern states (7.5%, 60/803) was significantly higher than in the Western (1.7%, 1/58), Midwest (3.3%, 4/120), and Northeastern states (3.1%, 3/98) (P < 0.05). Dogs positive for D. immitis were identified in each study year (2016: 4.2%, 2/48; 2017: 9.8%, 4/41; 2018: 5.1%, 8/156; 2019: 4.9%, 15/306; 2020: 9.8%, 26/265; 2021: 4.9%, 13/264). Interestingly, dogs infected with Hepatozoon spp. (11.8%, 37/313) were significantly more likely to also be positive for D. immitis than dogs without evidence of Hepatozoon infection (3.9%, 30/760) (P < 0.0001). CONCLUSIONS: To our knowledge, this is the first nationwide molecular survey of Dirofilaria spp. in dogs and cats in the USA, and the largest molecular survey of canine and feline dirofilariosis worldwide. Further studies are warranted to combine PCR with standard heartworm diagnostics to better understand the prevalence of Dirofilaria spp. and aid in determining the risks posed to dogs and cats in the USA.
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Search related cases →Original publication on PubMed: https://pubmed.ncbi.nlm.nih.gov/36229848/