Data from: Context-dependent survival, fecundity, and predicted population-level consequences of brucellosis in African buffalo

1. Chronic infections may have negative impacts on wildlife populations, yet their effects are difficult to detect in the absence of long-term population monitoring. Brucella abortus, the bacteria responsible for bovine brucellosis, causes chronic infections and abortions in wild and domestic ungulates, but its impact on population dynamics is not well understood. 2. We report infection patterns and fitness correlates of bovine brucellosis in African buffalo based on (1) 7 years of cross-sectional disease surveys and (2) a 4-year longitudinal study in Kruger National Park (KNP), South Africa. We then used a matrix population model to translate these observed patterns into predicted population-level effects. 3. Annual brucellosis seroprevalence ranged from 8·7% (95% CI = 1·8–15·6) to 47·6% (95% CI = 35·1–60·1) increased with age until adulthood (>6) and varied by location within KNP. Animals were on average in worse condition after testing positive for brucellosis (F = −5·074, P < 0·0001), and infection was associated with a 2·0 (95% CI = 1·1–3·7) fold increase in mortality (χ2 = 2·039, P = 0·036). Buffalo in low body condition were associated with lower reproductive success (F = 2·683, P = 0·034), but there was no association between brucellosis and pregnancy or being observed with a calf. 4. For the range of body condition scores observed in the population, the model-predicted growth rate was λ = 1·11 (95% CI = 1·02–1·21) in herds without brucellosis and λ = 1·00 (95% CI = 0·85–1·16) when brucellosis seroprevalence was 30%. 5. Our results suggest that brucellosis infection can potentially result in reduced population growth rates, but because these effects varied with demographic and environmental conditions, they may remain unseen without intensive, longitudinal monitoring.1. 慢性感染（chronic infections）可能对野生种群产生负面影响，但在缺乏长期种群监测的情况下，其影响难以被检测到。流产布鲁氏菌（Brucella abortus）是引发牛布鲁氏菌病（bovine brucellosis）的病原菌，可在野生与家养有蹄类动物（ungulates）中引发慢性感染与流产，但其对种群动态的影响尚未被充分阐明。 2. 本研究基于两项调查，揭示了南非克鲁格国家公园（Kruger National Park, KNP）非洲水牛的牛布鲁氏菌病感染模式与适合度关联指标：其一为为期7年的横断面疾病调查（cross-sectional disease surveys），其二为为期4年的纵向研究（longitudinal study）。随后，我们运用矩阵种群模型（matrix population model）将观测到的感染模式转化为种群层面的预测效应。 3. 年度布鲁氏菌病血清阳性率（seroprevalence）介于8.7%（95%置信区间[CI] = 1.8–15.6）至47.6%（95% CI = 35.1–60.1）之间，随年龄增长至成年（>6岁）后升高，且在克鲁格国家公园内不同区域存在差异。布鲁氏菌病检测呈阳性的动物平均身体状况更差（F = −5.074, P < 0.0001），感染与死亡率2.0倍（95% CI = 1.1–3.7）的升高相关（χ² = 2.039, P = 0.036）。身体状况较差的水牛繁殖成功率（reproductive success）更低（F = 2.683, P = 0.034），但布鲁氏菌病感染与妊娠或伴随幼崽出现并无关联。 4. 针对该种群观测到的身体状况评分区间，模型预测：无布鲁氏菌病感染的牛群种群增长率（population growth rate）λ = 1.11（95% CI = 1.02–1.21），当血清阳性率为30%时，牛群种群增长率λ = 1.00（95% CI = 0.85–1.16）。 5. 本研究结果表明，布鲁氏菌病感染可能会降低种群增长率，但由于这些影响随种群统计特征（demographic characteristics）与环境条件而异，若不开展高强度的纵向监测，该影响可能难以被发现。