RESEARCH Figure 3. Seroprevalence of anthrax in sampled wildlife populations from Serengeti National Park (white bars) and Ngorongoro Crater (gray bars), Tanzania, 1996–2009. Sample sizes used to calculate seroprevalence are indicated above the bars. Hyenas were not sampled in Ngorongoro Crater. Seropositive zebras were not detected. Error bars indicate 95% conﬁdence intervals based on a binomial distribution of the sample size and the seropositivity range that can be expected. of the appearance of carcasses. Laboratory results may not be conclusive even when diagnostic material is obtained. For example, when multiple blood slides were prepared from 1 buffalo carcass and tested blindly, the results were not consistently positive (only 2 of 6 slides were positive). Some outbreaks are likely to be missed even when probable case detection is used. This suggestion was conﬁrmed by using serosurveillance data; in some agropastoralist areas where anthrax had not been reported, serologic analysis of domestic dogs indicated that the disease had been present. In contrast to sampling of suspected carcasses, serosurveillance of living animals poses no risk for anthrax infection and therefore offers an opportunity for gaining a better understanding of anthrax epidemiology, particularly in relation to patterns of infection and risk factors for exposure, susceptibility, and death. Our serologic data highlight differences between species in exposure and death, which may be explained by behavior and ecology. However, we caution that although our study suggests great potential for the use of this assay for multiple species comparisons, validation of serologic responses across a range of vaccinated species (possibly using zoo collections) would provide more deﬁnitive veriﬁcation of this proposition and should be prioritized. Low mortality rates, combined with high seroprevalence rates (always >50% and approaching 90% in Serengeti populations), suggests that wild carnivores are regularly exposed to anthrax without apparent deaths. Although high mortality rates were reported for Kruger lions after periods of low anthrax incidence (4,10), high seroprevalence rates and low mortality rates are more commonly observed, which suggests a protective immune response presumably associated with more frequent exposure (4,10). Lions and hyenas may be exposed through consumption of infected prey, but domestic dogs may also be exposed when they scavenge infected carcasses (wildlife and livestock). Low Figure 4. Anthrax seroprevalence patterns in carnivores, by age, Tanzania, 1996–2009. Lions (A) in Serengeti and domestic dogs (B) in agropastoralist regions where no outbreaks were detected (black line), in pastoralist regions where repeated outbreaks were detected (red line), and in an agropastoralist village where no outbreaks were reported but serologic surveys indicated previous exposure (blue line). Error bars indicate 95% conﬁdence intervals for age seroprevalence in lions and dogs, but are juxtaposed for dogs to improve readability. Sample sizes used to calculate seroprevalences are indicated. 392 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 17, No. 3, March 2011