Enhancing surveillance and quantifying impacts to improve our understanding of endemic anthrax in low resource settings

Anthrax is endemic in many parts of Africa where livelihoods are dependent on animals, yet our understanding of the impact of the disease on people and livestock is limited. Advocating for the prioritization of anthrax requires such evidence. Surveillance – including case detection and diagnosis and subsequent disease reporting – is poor in endemic areas; as such, the incidence of anthrax is largely unknown. Resources are often limited in these affected areas, prompting the need for practical but efficient mechanisms for control. Control interventions leading to a significant reduction in the impacts of the disease will depend on strategies that target the determinants and drivers of anthrax in humans and livestock, many of which are unknown in endemic areas. This multidisciplinary study was carried out in the Ngorongoro Conservation Area of northern Tanzania, an area hyperendemic for anthrax, with the following objectives: 1) Improve our understanding of the impact of anthrax by quantifying the occurrence of the disease in people and livestock and determining the economic losses due to livestock deaths through anthrax incident investigations and a cross-sectional questionnaire-based study in 209 households. Findings show that confirmed anthrax led to losses of over $28,000 in 36 households in six months, and upwards of $88,000 in reported livestock deaths from suspected anthrax over 2 years. Overall 42% and 23% of households living in perceived high-risk and low-risk areas respectively had experienced the disease in animals, with the highest number of those living in Ngoile, Olbalbal and Endulen administrative wards affected. Human anthrax had also been experienced by 19% and 16% of households in these high- and low-risk areas respectively. Communities had a high awareness of anthrax; however, under-reporting was pervasive and animal vaccination rates were poor, with several associated barriers identified. 2) Investigate community experiences and knowledge of anthrax and its management in livestock and people, in addition to the practices driving the risk of anthrax transmission, carried out through the household surveys and additional focus group discussions. Practices that drive the risk of contracting anthrax were related to the handling of suspected carcasses and the movement of livestock and their products. 3) Improve surveillance through animal anthrax confirmation in the field. To this end, the performance of a newly proposed azure B stain for the rapid detection of Bacillus anthracis’ capsule with smear stain microscopy was assessed on samples collected from suspect carcasses. The sensitivity and specificity of azure B was compared with those of polychrome methylene blue (the recommended standard for B. anthracis), Giemsa and Rapi-Diff stains – stains commonly used in veterinary laboratories – as well as polymerase chain reaction (PCR) on blood smear samples using Bayesian latent class analysis. The unavailability of blood smear samples led to a study to investigate the use of other sample materials, namely blood swabs, skin tissues, insects and whole blood for anthrax confirmation with PCR following storage at ambient temperature. The sensitivity and specificity of microscopy using azure B (91% and 100%) was comparable to PMB (92% and 100%). However, Giemsa and Rapi-Diff performed poorly in detecting B. anthracis capsule. Among the various samples tested, skin tissues were available for most carcasses, producing the second highest sensitivity and specificity with PCR after blood smears. In field conditions, the collection of blood smears (when available for microscopy and PCR) and tissue samples (for PCR) for the detection of B. anthracis can greatly improve the surveillance of anthrax in livestock. 4) Understand areas where livestock are at increased risk of contracting anthrax. Participatory mapping was conducted, taking advantage of local disease knowledge, and combined with environmental data in GIS to quantify the environmental conditions favourable to the persistence and transmission of anthrax in these areas. Findings show that perceived high-risk areas are closer to water sources and are characterised by lower organic carbon content compared to low-risk areas. High-risk areas identified occupied central locations within the NCA, increasing the likelihood of animals contracting anthrax during seasonal long-distance movements. Overall, the findings of this study are useful for improving the surveillance and control of anthrax in endemic areas