SEROPREVALENCE OF Trypanosoma vivax, Anaplasma marginale, and Babesia bovis IN DAIRY CATTLE

Abstract In order to determine the prevalence of IgG against Trypanosoma vivax, Anaplasma marginale, and Babesia bovis in dairy cattle in southern Minas Gerais, four hundred cows from 40 dairy farms were randomly selected and distributed in 14 municipalities. Seroprevalence was determined by indirect immunofluorescence assay (IFA). Interviews were conducted to characterize producers and dairy production. Univariate analysis was carried out using chi-square (x2) or Fisher's exact test. The multiple model was constructed with variables associated with p ≤ 0.25 by x2 test using generalized estimating equations (GEE). True prevalence at herd level was 49.6% (31.7-67.5), 100% (92.1-100), and 100% (86.5-100) for T. vivax, A. marginale, and B. bovis, respectively. At individual level, true seroprevalence was 9.9% (6.7-13.1), 96.2% (92.1-99.6), and 93.7% (89.4-97.2), respectively, for T. vivax, A. marginale, and B. bovis. Among the factors adjusted by logistic regression GEE model, "total farm area" (p= 0.021, OR= 0.308, Ic95%= 0.114-0.836) and "fly season" (p= 0.016, OR= 2.133, Ic95%= 1.153-3.948) remained associated with seropositivity for T. vivax. As the State of Minas Gerais is considered non-endemic for T. vivax, producers and veterinarians should be informed about the risk of occurrence of bovine trypanosomiasis.

摘要：为明确巴西米纳斯吉拉斯州南部奶牛体内伊氏锥虫（Trypanosoma vivax）、边缘无浆体（Anaplasma marginale）及牛巴贝斯虫（Babesia bovis）特异性IgG的流行情况，本研究从40个奶牛场中随机选取400头受试奶牛，覆盖该州14个县市。采用间接免疫荧光试验（indirect immunofluorescence assay, IFA）检测血清阳性率；通过访谈调研养殖户基本情况与奶牛养殖生产特征。单变量分析采用卡方（χ²）检验或费希尔精确检验；多因素模型通过广义估计方程（generalized estimating equations, GEE）构建，纳入经χ²检验筛选的p≤0.25的相关变量。
畜群水平上，伊氏锥虫、边缘无浆体和牛巴贝斯虫的真实流行率分别为49.6%（95%置信区间31.7~67.5）、100%（95%置信区间92.1~100）及100%（95%置信区间86.5~100）；个体水平上，三者的真实血清阳性率分别为9.9%（95%置信区间6.7~13.1）、96.2%（95%置信区间92.1~99.6）及93.7%（95%置信区间89.4~97.2）。
经logistic回归GEE模型校正的分析显示，“牧场总面积”（p=0.021，优势比OR=0.308，95%置信区间0.114~0.836）与“蝇媒活动季”（p=0.016，OR=2.133，95%置信区间1.153~3.948）仍与伊氏锥虫血清阳性显著相关。鉴于米纳斯吉拉斯州被认定为伊氏锥虫非流行区，需向养殖户及兽医通报牛锥虫病的发病风险。