Anthrax threatens human and animal health, and people’s livelihoods in many rural communities in Africa and Asia. In these areas, anthrax surveillance is challenged by a lack of tools for on-site detection. Furthermore, cultural practices and infrastructure may affect sample availability and quality. Practical yet accurate diagnostic solutions are greatly needed to quantify anthrax impacts. We validated microscopic and molecular methods for the detection of Bacillus anthracis in field-collected blood smears and identified alternative samples suitable for anthrax confirmation in the absence of blood smears. We investigated livestock mortalities suspected to be caused by anthrax in northern Tanzania. Field-prepared blood smears (n = 152) were tested by microscopy using four staining techniques as well as poly-merase chain reaction (PCR) followed by Bayesian latent class analysis. Median sensitivity (91%, CI95% [84–96%]) and specificity (99%, CI95% [96–100%]) of microscopy using azure B were comparable to those of the recommended standard, polychrome methylene blue, PMB (92%, CI95% [84–97%] and 98%, CI95% [95–100%], respectively), but azure B is more available and convenient. Other commonly-used stains performed poorly. Blood smears could be obtained for <50% of suspected anthrax cases due to local customs and condi-tions. However, PCR on DNA extracts from skin, which was almost always available, had high sensitivity and specificity (95%, CI95% [90–98%] and 95%, CI95% [87–99%], respec-tively), even after extended storage at ambient temperature. Azure B microscopy represents an accurate diagnostic test for animal anthrax that can be performed with basic laboratory infrastructure and in the field. When blood smears are unavailable, PCR using skin tissues provides a valuable alternative for confirmation. Our findings lead to a practical diagnostic approach for anthrax in low-resource settings that can support surveillance and control efforts for anthrax-endemic countries globally.
Bibliographical noteFunding Information:
O. R. Aminu was supported by grants from the Bill & Melinda Gates Foundation (Program for Enhancing the Health and Productivity of Livestock, project reference ID 1083453). T. Forde was supported by a Marie Sk?odowska-Curie Individual Fellowship (659223), a fellowship from the Natural Sciences and Engineering Research Council of Canada (PDF-471750-2015), and a Biotechnology and Biological Sciences Research Council (BBSRC) Future Leader Fellowship (FORDE/BB/R012075/1). The work was also supported by the Wellcome Trust through a Springboard award (SBF002\1168) to T. Lembo by the Academy of Medical Sciences. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.We are grateful for all the support received for this research, including from the NCA commu-nity. We thank the Ngorongoro District Council (District Veterinary Officer and District Medical Officer), Ngorongoro Conservation Area Authority (NCAA), Tanzania Wildlife Research Institute (TAWIRI) and members of our field team?Sabore Ole Moko, Sironga Nanjicho, Alutu Masokoto, Godwin Mshumba, Kadogo Lerimba and Paulo Makutian. We are also grateful to the Directorate of Veterinary Services, Ministry of Livestock and Fisheries, and Ministry of Health, Community Development, Gender, Elders and Children. We thank Daniel Bailey of Public Health England, Salisbury for sharing cap and lef primer sequences. We are grateful to Richard Reeve of the Boyd Orr Centre for Population and Ecosystem Health, University of Glasgow for useful discussions on improving the statistical analysis.
© 2020 Aminu et al.