Sydney School of Veterinary Science, Faculty of Science, The University of Sydney, Sydney, NSW, 2006, Australia.
Parasit Vectors. 2021 Aug 9;14(1):393. doi: 10.1186/s13071-021-04896-y.
Canine 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immitis and associated risk factors for canine heartworm antigen positivity-and thus disease-in Australia is scarce or outdated.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.
Blood 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.
A 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.
This 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.
犬心丝虫（Dirofilaria immitis）是一种危及生命的犬类传染病，分布于全球。关于犬心丝虫的流行情况以及与犬心丝虫抗原阳性相关的风险因素（即疾病）在澳大利亚的信息很少或已经过时。目前，犬心丝虫诊断的参考方法是通过商业上可用的微孔板酶联免疫吸附试验（ELISA）检测血液中的心丝虫抗原。有人建议，在检测前对犬血浆进行热处理可以提高检测的灵敏度。本研究旨在估计澳大利亚昆士兰州收容所中犬的犬心丝虫流行率。还评估了热处理对抗原检测结果的影响。
从昆士兰州七个收容所的犬中直接采集血液样本（n=166），放入 EDTA 采血管中。使用商业上可用的 ELISA（DiroCHEK®）检测未经处理和热处理的血浆中的犬心丝虫抗原。使用改良的 Knott 试验和实时 PCR 分别同时检测全血中微丝蚴和犬心丝虫 DNA 的存在。使用二项逻辑回归模型评估与犬心丝虫阳性相关的年龄、性别、来源、位置等风险因素。
根据联合检测结果，共有 16 只犬（9.6%；95%置信区间[CI]：5.9-15.2%）为犬心丝虫阳性。热处理不会影响样本中犬心丝虫抗原的阳性率（Cohen's kappa=0.98），但对于犬心丝虫抗原阳性样本的配对血浆样本，光学密度显著增加（Wilcoxon 配对符号秩检验，双侧 P<0.01）。犬在北部昆士兰收容所的位置是唯一与犬更有可能为犬心丝虫抗原阳性相关的显著风险因素（优势比：4.39；95%CI：1.26-13.51）。改良 Knott 试验阳性的所有样本通过 PCR 也均为犬心丝虫 DNA 阳性。
本研究表明，昆士兰州的收容所中存在心丝虫阳性犬，在北部昆士兰比南部昆士兰更有可能出现阳性动物。在已知和重新出现犬心丝虫活动的地区，持续检测犬心丝虫微丝蚴和抗原仍然是重要的诊断工具。
