Laboratory of Epidemiology and Biostatistics, Department of Preventive Veterinary Medicine and Animal Health, University of São Paulo, Av. Prof. Dr. Orlando Marques de Paiva, 87, São Paulo 05508-270 Brazil.
Laboratory of Parasitic Diseases. Department of Preventive Veterinary Medicine and Animal Health, University of São Paulo, Av. Prof. Dr. Orlando Marques de Paiva, 87, São Paulo 05508-270, Brazil.
J Theor Biol. 2018 Dec 7;458:119-124. doi: 10.1016/j.jtbi.2018.09.011. Epub 2018 Sep 15.
Brazilian Spotted Fever (BSF) is an emerging and lethal disease in South America which basic reproduction number (R) is unknown. Calculating R for this disease is crucial to design control interventions and prevent human deaths. BSF endemic areas are related to the presence of capybaras Hydrochoerus hydrochaeris, amplifier hosts of Rickettsia rickettsii and primary hosts of the tick Amblyomma sculptum, main vector of the agent in this area. Because of the complexity of its dynamics, we calculated R for the BSF system by constructing a next-generation matrix considering different categories of vectors and hosts. Each matrix element was considered as the expected number of infected individuals of one category produced by a single infected individual of a second category. We used field and experimental data to parameterize the next-generation matrix and obtain the final calculation (R ≈ 1.7). We demonstrated the low impact of the matrix elements corresponding to the transovarial transmission and the transmission from infected larvae in the maintenance of R. rickettsii. Sensitivity and elasticity analyzes were performed to quantify the perturbations of each matrix element in R. We noted that the elements equivalent to the number of infected attached nymphs produced by an infected capybara, and the number of infected capybaras produced by an infected attached nymph or adult are the major contributors to changes in R. Our results provide insights into the strategic design of preventive interventions in BSF endemic areas.
巴西出血热（BSF）是南美洲一种新兴且致命的疾病，其基本繁殖数（R）未知。计算这种疾病的 R 值对于设计控制干预措施和预防人类死亡至关重要。BSF 的流行地区与水豚 Hydrochoerus hydrochaeris 的存在有关，水豚是 Rickettsia rickettsii 的扩增宿主，也是该地区主要传播媒介扁虱 Amblyomma sculptum 的主要宿主。由于其动态的复杂性，我们通过构建一个下一代矩阵来考虑不同类别的载体和宿主来计算 BSF 系统的 R 值。每个矩阵元素都被认为是由第二类的单个感染个体产生的一类感染个体的预期感染个体数量。我们使用现场和实验数据来参数化下一代矩阵并获得最终计算结果（R≈1.7）。我们证明了与经卵传播和感染幼虫传播相关的矩阵元素对 R. rickettsii 的维持作用较低。进行了敏感性和弹性分析，以量化 R 中每个矩阵元素的扰动。我们注意到，相当于由感染的水豚产生的附着若虫的感染数量，以及由感染的附着若虫或成虫产生的感染水豚的数量，是 R 变化的主要因素。我们的结果为 BSF 流行地区的预防性干预策略设计提供了深入了解。
