Serologic Surveillance of Anthrax, Tanzania Table 2. Multivariate generalized linear mixed model analysis of risk factors for anthrax seropositivity in dogs, Tanzania, 1996–2009* Predictor Unit Estimate SE z score p value OR (95% CI) Intercept 6.224 1.275 4.881 <0.001 Age Months 0.043 0.011 3.956 <0.001 1.044 (1.022–1.066) Area West Referent Referent Referent Referent 1 Loliondo 4.178 1.696 2.463 0.014 65.21 (2.347–1,811.000) NCA 4.511 1.364 3.308 <0.001 90.97 (6.283–1,317.000) *OR, odds ratio; CI, confidence interval; NA, not applicable; NCA, Ngorongoro Conservation Area. seroprevalence rates and high mortality rates have been reported for cheetahs (15,16). These rates are consistent with the fact that cheetahs do not scavenge, and solitary hunting exposes them to fewer carcasses than group- hunting lions and hyenas. Although data from this study are limited, detection of probable anthrax cases in cheetah and serval is consistent with a higher susceptibility in these carnivore species. Relatively lower seroprevalence rates and higher mortality rates for ungulates than for carnivores suggest less routine exposure, higher susceptibility, or both. Major differences in herbivore susceptibility are inferred from the wide variation in seroprevalence detected in species sharing the same grazing areas, and thus probable exposure patterns. Zebras appear to be highly susceptible; however, buffalo and wildebeest can clearly survive infection. Seroprevalence in buffalo was high (≈50%) compared with previous reports for herbivores (≈7%) (10,17). Comparing seroprevalence in more species would enable assessment of relative roles of exposure versus susceptibility in explaining variable species mortality patterns characteristic for anthrax. The reported species differences have potential implications for serosurveillance. Among wildlife, carnivores are likely to be the most sensitive indicators of whether infection is present in an area, acting as bioaccumulators of infection through consumption of infected carcasses (18). However, because lions and hyenas seroconvert at a relatively young age, temporal patterns of exposure from age seroprevalence data are difﬁcult to detect. Furthermore, hyenas are highly mobile in the Serengeti ecosystem (19), which reduces their utility for identifying speciﬁc high-risk areas. However, more detailed investigations of titer levels in relation to timing and location of anthrax outbreaks, including longitudinal studies of serial titers from known animals, could shed light on immunologic responses and enable more information to be obtained from serologic data. These data suggest a possible utility of serosurveillance in buffalo, whose potential as indicator species has not been explored. Because ≈50% of Serengeti buffalo are seropositive for anthrax, these populations appear to provide a relatively sensitive indicator of the presence and prevalence of anthrax infection, e.g., major differences between populations in SNP and Ngorongoro Crater. Although serologic analysis of wildebeest detected these differences, seroprevalence in wildebeest was lower overall, and the wide-ranging migratory movements of the Serengeti herds limit the utility of these data for detecting spatial patterns. In comparison, buffalo herds range over relatively restricted areas, and serologic data can pinpoint high-risk areas. In many protected areas of Africa, buffalo are already routinely sampled for surveillance of diseases, such as rinderpest, bovine tuberculosis, and foot-and-mouth disease. We suggest that in areas where buffalo surveillance is ongoing, there is added value in using serum samples for monitoring anthrax exposure patterns. Serologic analysis of buffalo and analysis of environmental risk factors could also assist wildlife management strategies, e.g., risks associated with reintroductions of rhinoceros in different areas of the Serengeti, and identify priority areas for enhanced risk-based surveillance. Domestic dogs have high potential value as indicators of human and livestock diseases (1,18). They are regularly exposed to a wide range of infections in disease-endemic areas; they are abundant and widely distributed, especially in developing countries; they are generally accessible for safe handling and sampling; they can be sampled at young ages, which enables reasonably accurate timing of outbreaks; and they live in close association with humans and livestock, which makes them good indicators of risk. In addition, vaccination campaigns present a cost-effective opportunity for obtaining large numbers of domestic dog samples (18). Consistent with these expectations, we have demonstrated that dogs in the Serengeti can be useful indicators of anthrax. They can be used to detect infection in an area, even when anthrax is not identiﬁed in other species; they reﬂect differences in infection prevalence in different areas; they can provide information about the timing of outbreaks (we observed variation in exposure with age) (Table 2); and they serve as an indicator of livestock and human disease risk and provide a basis for risk-based surveillance and targeted implementation of prevention measures (e.g., livestock vaccination or public health campaigns). In conclusion, we demonstrated that serologic investigations of wildlife and domestic animals can provide valuable information about patterns of anthrax transmission and for identifying areas for risk-based surveillance. Serologic approaches also enable retrospective identiﬁcation of infected areas and timing of outbreaks Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 17, No. 3, March 2011 393