Practical and effective diagnosis of animal anthrax in endemic low-resource settings

Abstract

23Background: Anthrax threatens human and animal health, and people's livelihoods in 24 many rural communities in Africa and Asia. In these areas, anthrax surveillance is 25 challenged by a lack of tools for on-site detection. Furthermore, cultural practices and 26 infrastructure may affect sample availability and quality. Practical yet accurate diagnostic 27 solutions are greatly needed to quantify anthrax impacts. We validated microscopic and 28 molecular methods for the detection of Bacillus anthracis in field-collected blood smears 29 and identified alternative samples suitable for anthrax confirmation in the absence of blood 30 smears. 31 Methodology/Principal Findings:We investigated livestock mortalities suspected to be 32 caused by anthrax in northern Tanzania. Field-prepared blood smears (n = 152) were tested 33 by microscopy using four staining techniques as well as polymerase chain reaction (PCR) 34 followed by Bayesian latent class analysis. Median sensitivity (91%, CI 95% [84-96%]) and 35 specificity (99%, CI 95% [96-100%]) of microscopy using azure B were comparable to 36 those of the recommended standard, polychrome methylene blue, PMB (92%, CI 95% [84-37 97%] and 98%, CI 95% [95-100%], respectively), but azure B is more available and 38 convenient. Other commonly-used stains performed poorly. Blood smears could be 39 obtained for <50% of suspected anthrax cases due to local customs and conditions. 40 However, PCR on DNA extracts from dried skin, which was almost always available, had 41 high sensitivity and specificity (95%, CI 95% [90-98%] and 95%, CI 95% [87-99%], 42 respectively), even after extended storage at ambient temperature. 43 Conclusions/Significance: Azure B microscopy represents an accurate diagnostic test for 44animal anthrax that can be performed with basic laboratory infrastructure and in the field. 45When blood smears are unavailable, PCR using skin tissues provides a valuable alternative 46 for confirmation. Our findings lead to a practical diagnostic approach for anthrax in low-47 resource settings that can support surveillance and control efforts for anthrax-endemic 48 countries globally. 49 Author summary50 Anthrax, an ancient disease largely controlled in the developed world, is still widespread in 51 remote and rural communities of low-and middle-income countries where it affects human 52 and animal health, and livelihoods. To control anthrax effectively, detection and accurate 53 confirmation are important, but solutions need to be feasible for the most-affected areas 54 3 where resources and infrastructure are typically limited. To achieve this, we assessed a 55 newly proposed stain, azure B, for microscopic confirmation on animal blood smears, as 56 this method can be implemented in low-resource laboratories and in the field. Microscopy 57 using azure B was highly accurate compared to other recommended stains and has the 58 added advantage of being more readily available and convenient. However, blood smear 59 samples were unavailable for more than half of suspected case...

An Estimate of Global Anthrax Prevalence in Livestock: A Meta-analysis

“…An ongoing PCR test was produced for the quick identification of B. anthracis [16,20,38]. Field arranged blood smears were verified by microscopy using four recoloring strategies, including PCR trailed by Bayesian latent class investigation [39]. Samples were tested using a 31-marker multilocus variable-number tandem repeat analysis (MLVA) to identify different genotypes.…”

Participatory mapping identifies risk areas and environmental predictors of endemic anthrax in rural Africa

“…The NCA was chosen for our study as it is known to be hyperendemic for anthrax 4 , 17 , 20 . In addition, informal consultations we held prior to the study, as well as tailored data collection at the community and household level, indicated that local communities have a good understanding of the disease in humans and animals, and of practices around carcass and livestock management that increase risks, particularly in certain locations and periods of the year 24 .

Figure 1 Locations of participatory mapping.

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Development of a visible loop mediated isothermal amplification assay for rapid detection of Bacillus anthracis

“…Consequently, several nucleic acid-based assays targeting anthrax toxin genes have been optimized for the reliable, quick, specific and sensitive identification of organisms causing anthrax. However, these require expertise, expensive devices, heavy infrastructure laboratories and complicated protocols [9], thus are unsuitable for routine laboratories. The Loop-mediated isothermal amplification (LAMP) assay is preferred over other nucleic acid-based assays because it is fast, less labor-intensive and does not require any sophisticated equipment or skilled personnel, and is suitable for the applications at field level and routine laboratories [10].…”