Department of Veterinary Medicine, University of Cambridge, Cambridge, United Kingdom.
Department of Veterinary Medicine, University of Cambridge, Cambridge, United Kingdom.
Int J Parasitol. 2020 Feb;50(2):103-110. doi: 10.1016/j.ijpara.2019.11.006. Epub 2020 Jan 29.
Babesia rossi is an important, tick-borne intraerythrocytic protozoan parasite; however, its natural history and epidemiology is poorly understood. Babesia rossi is the most virulent Babesia sp. in domestic dogs and is generally considered to cause severe babesiosis, which is fatal if left untreated. However, subclinical infections and mild disease from B. rossi have been reported, although the clinical progression of these cases was not reported. Therefore, to better understand B. rossi under field conditions, we evaluated its clinical progression and seroprevalence in an owned, free-roaming dog population in Zenzele, South Africa, where the parasite is endemic and prevention is not routine. The entire dog population in Zenzele was monitored intensively at the individual level from March 2008 until April 2014, primarily for a longitudinal study on rabies control. Subsequent evaluation of B. rossi comprised analyses of clinical and laboratory data collected from the Zenzele dog population during the 6 year study period. A substantial proportion (31% (n = 34)) of 109 dogs (randomly selected from every available dog in February/March 2010 older than ~6-8 weeks (n = 246)) tested by Indirect Fluorescent Antibody Test had seroconverted strongly to B. rossi. All 34 dogs were generally consistently healthy adults, determined from regular clinical examinations between March 2008 and April 2014. Blood smear examinations at multiple time points between July 2009 and February 2011 were also undertaken for almost all of these (34) seropositive dogs and all those tested were consistently negative for Babesia spp. Subclinical infections and mild disease were also the main findings for a separate group of 18 dogs positive for Babesia spp. on blood smear examination and confirmed to be infected with B. rossi by Polymerase Chain Reaction - Reverse Line Blot. Almost all of these dogs were positive at only one time point from repeat blood smear examinations between July 2009 and February 2011. We suggest that these observations are consistent with immunity acquired from repeated, low-level exposure to the parasite, generating transient subclinical infections or mild disease. Should this be the case, the use of tick control, particularly in adult dogs in free-roaming populations in B. rossi endemic regions, should be carefully considered.
罗氏巴贝斯虫是一种重要的蜱传红细胞内原生动物寄生虫；然而，其自然史和流行病学仍知之甚少。罗氏巴贝斯虫是犬中最具毒性的巴贝斯虫种，通常被认为会引起严重的巴贝斯虫病，如果不治疗则致命。然而，已经报道了亚临床感染和轻度疾病的存在，尽管这些病例的临床进展情况尚未报道。因此，为了更好地了解野外条件下的罗氏巴贝斯虫，我们评估了其在南非赞泽勒一个拥有自由放养犬群中的临床进展和血清流行率，在该地区寄生虫流行，且预防措施并非常规。从 2008 年 3 月到 2014 年 4 月，对赞泽勒的整个犬群进行了个体层面的密集监测，主要是为了进行一项关于狂犬病控制的纵向研究。在 6 年的研究期间，对从赞泽勒犬群中收集的临床和实验室数据进行了后续的罗氏巴贝斯虫评估。通过间接荧光抗体试验，从 2010 年 2 月/3 月随机选择的每只 6-8 周以上（246 只）的可用狗中，有相当大比例（31%（n=34））的狗强烈地对罗氏巴贝斯虫产生了血清转化。所有 34 只狗都是从 2008 年 3 月至 2014 年 4 月期间定期临床检查中确定的通常健康的成年狗。在 2009 年 7 月至 2011 年 2 月期间，还对几乎所有（34 只）血清阳性的狗进行了多次血涂片检查，所有检测结果均为巴贝斯虫属阴性。对另一个通过血涂片检查阳性的 18 只巴贝斯虫属的狗也发现了亚临床感染和轻度疾病，这些狗通过聚合酶链反应-反向线杂交证实感染了罗氏巴贝斯虫。在 2009 年 7 月至 2011 年 2 月期间的重复血涂片检查中，几乎所有这些狗仅在一个时间点呈阳性。我们认为这些观察结果与从反复、低水平的寄生虫暴露中获得的免疫相一致，从而导致短暂的亚临床感染或轻度疾病。如果情况确实如此，那么应慎重考虑在巴贝斯虫属流行地区的自由放养犬群中使用蜱控制，特别是在成年犬中。
