title: Context-dependent survival, fecundity and predicted population-level consequences of brucellosis in African buffalo.
abstract: 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. 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. 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 (χ(2)  = 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. 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%. 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.
authors.affiliation: Department of Integrative Biology, Oregon State University, Corvallis, OR, 97331, USA.
authors.forename: Erin E
authors.initials: EE
authors.lastname: Gorsich
authors.affiliation: Odum School of Ecology and Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA, 30602, USA.
authors.forename: Vanessa O
authors.initials: VO
authors.lastname: Ezenwa
authors.affiliation: U.S. Geological Survey, Northern Rocky Mountain Science Center, Bozeman, MT, 59715, USA.
authors.forename: Paul C
authors.initials: PC
authors.lastname: Cross
authors.affiliation: Department of Agriculture, Forestry and Fisheries, Directorate of Animal Health, State Veterinary Office, Skukuza, 1350, South Africa.
authors.forename: Roy G
authors.initials: RG
authors.lastname: Bengis
authors.affiliation: Department of Biomedical Sciences, Oregon State University, Corvallis, OR, 97331, USA.
authors.forename: Anna E
authors.initials: AE
authors.lastname: Jolles
mesh_terms: D000818:Animals; D002003:Brucella abortus / Q000472:pathogenicity*; D002006:Brucellosis / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D002020:Buffaloes / Q000382:microbiology*; D003430:Cross-Sectional Studies; D005260:Female; D005298:Fertility; D008137:Longitudinal Studies; D008297:Male; D011157:Population Dynamics; D011247:Pregnancy; D016036:Seroepidemiologic Studies; D013019:South Africa; D016019:Survival Analysis
keywords: African buffalo; Brucella abortus; bacteria; chronic disease; conservation biology; disease ecology; population growth