College of Veterinary Medicine, Auburn University, Auburn, AL, USA.
Ross University School of Veterinary Medicine, Basseterre, Saint Kitts and Nevis.
Parasit Vectors. 2022 Oct 13;15(1):367. doi: 10.1186/s13071-022-05459-5.
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.
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.
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).
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.
心丝虫，即犬恶丝虫，已被证实广泛存在于美国的犬猫群体中，但目前尚无全国性的流行率研究。也没有大规模的研究来确定是否有与犬恶丝虫密切相关的物种，即猫恶丝虫，存在于美国。
为了提供这些大规模的数据，我们对 2016 年至 2022 年期间，从美国各地提交给奥本大学分子诊断实验室的 2334 份全血样本进行了检测。使用针对 16S rRNA 的犬恶丝虫定量 PCR（Dirofilaria immitis）和针对细胞色素 c 氧化酶亚基 1 基因的猫恶丝虫定量 PCR（Dirofilaria repens）来确定是否存在心丝虫 DNA。进行 DNA 测序以确认结果。
在来自 17 个州的 1080 只犬中发现了犬恶丝虫 DNA，占比为 6.3%，在来自 4 个州的 1254 只猫中发现了 4 只猫呈阳性，占比为 0.3%。没有犬或猫呈猫恶丝虫阳性。犬中犬恶丝虫 16S rRNA 拷贝数的平均值为 200µl 全血中的 1809604 个，而在 4 只犬恶丝虫阳性猫中仅发现了单个拷贝。不同年龄、性别和品种的犬的犬恶丝虫流行率无显著差异，但南部各州（7.5%，60/803）的流行率明显高于西部（1.7%，1/58）、中西部（3.3%，4/120）和东北部各州（3.1%，3/98）（P<0.05）。在每年的研究中都发现了犬恶丝虫阳性犬（2016 年：4.2%，2/48；2017 年：9.8%，4/41；2018 年：5.1%，8/156；2019 年：4.9%，15/306；2020 年：9.8%，26/265；2021 年：4.9%，13/264）。有趣的是，感染肝血吸病的犬（11.8%，37/313）比没有肝血吸病感染证据的犬（3.9%，30/760）更有可能同时呈犬恶丝虫阳性（P<0.0001）。
据我们所知，这是美国首次对犬猫心丝虫病进行全国性的分子调查，也是全球最大规模的犬猫恶丝虫病分子调查。有必要进一步开展研究，将 PCR 与标准心丝虫诊断相结合，以更好地了解心丝虫病的流行情况，并有助于确定美国犬猫面临的风险。
