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) seven years of cross-sectional disease surveys and (2) a four-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. 慢性感染可能对野生生物种群产生负面影响，但在缺乏长期种群监测的情况下，其影响难以被察觉。流产布鲁氏菌（Brucella abortus）是引发牛布鲁氏菌病（bovine brucellosis）的病原菌，可导致野生和家养有蹄类动物（ungulates）发生慢性感染及流产，但其对种群动态的影响尚未被充分阐明。2. 本研究基于两项研究，报道了非洲水牛（African buffalo）的牛布鲁氏菌病感染模式及其与适合度的关联：(1) 为期7年的横断面疾病调查；(2) 在南非克鲁格国家公园（Kruger National Park, KNP）开展的为期4年的纵向研究。随后，我们通过矩阵种群模型（matrix population model）将观测到的感染模式转化为预测的种群水平效应。3. 牛布鲁氏菌病的年血清阳性率介于8.7%（95%置信区间=1.8~15.6）至47.6%（95%置信区间=35.1~60.1）之间，随年龄增长至成年（>6岁）后升高，并在克鲁格国家公园内存在空间差异。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），且感染与死亡率升高2.0倍（95%置信区间=1.1~3.7）相关（χ²=2.039，p=0.036）。身体状况较差的非洲水牛繁殖成功率更低（F=2.683，p=0.034），但布鲁氏菌病感染与妊娠或携带幼崽无显著关联。4. 基于该种群观测到的身体状况评分范围，模型预测：无布鲁氏菌病感染的兽群种群增长率λ=1.11（95%置信区间=1.02~1.21），而当布鲁氏菌病血清阳性率为30%时，兽群种群增长率λ=1.00（95%置信区间=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与环境条件的变化而存在差异，若不开展高强度的纵向监测，这些影响可能难以被发现。