Hippopotamus movements structure the spatiotemporal dynamics of an active anthrax outbreak

Stears, Keenan; Schmitt, Melissa H.; Turner, Wendy C.; McCauley, Douglas J.; Muse, Epaphras A.; Kiwango, Halima; Mathayo, Daniel; Mutayoba, Benezeth

doi:10.1002/ecs2.3540

Cited by 11 publications

(18 citation statements)

References 59 publications

(83 reference statements)

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“…Herbivores are likely to die of anthrax within a few days to a week of a lethal exposure (Easterday et al, 2020; WHO, 2008). Although B. anthracis can infect a wide range of host species, a single outbreak typically involves one to a few species, while other susceptible species remain unaffected or marginally affected (Beyer & Turnbull, 2009; Driciru et al, 2020; Stears et al, 2021).…”

Section: Introductionmentioning

confidence: 99%

Environmental drivers of biseasonal anthrax outbreak dynamics in two multihost savanna systems

Huang

Kausrud

Hassim

et al. 2022

Ecological Monographs

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Environmental factors are common forces driving infectious disease dynamics. We compared interannual and seasonal patterns of anthrax infections in two multihost systems in southern Africa: Etosha National Park, Namibia, and Kruger National Park, South Africa. Using several decades of mortality data from each system, we assessed possible transmission mechanisms behind anthrax dynamics, examining (1) within-and between-species temporal case correlations and (2) associations between anthrax mortalities and environmental factors, specifically rainfall and the Normalized Difference Vegetation Index (NDVI), with empirical dynamic modeling. Anthrax cases in Kruger had wide interannual variation in case numbers, and large outbreaks seemed to follow a roughly decadal cycle. In contrast, outbreaks in Etosha were smaller in magnitude and occurred annually. In Etosha, the host species commonly affected remained consistent over several decades, although plains zebra

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Section: Introductionmentioning

confidence: 99%

Environmental drivers of biseasonal anthrax outbreak dynamics in two multihost savanna systems

Huang

Kausrud

Hassim

et al. 2022

Ecological Monographs

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“…Zebras in this system move 13 to 16 kilometers per day on average (depending on the season and whether they are members of a migratory or non-migratory herd; [ 30 ]), blurring the lines between where higher risk behaviors occur and where disease mortalities are detected. Although little is known about post-exposure behaviors in wildlife, anthrax infected hippos in Tanzania showed no changes in their movement patterns in the days leading up to mortality [ 68 ].…”

Section: Discussionmentioning

confidence: 99%

A framework for integrating inferred movement behavior into disease risk models

et al. 2022

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Movement behavior is an important contributor to habitat selection and its incorporation in disease risk models has been somewhat neglected. The habitat preferences of host individuals affect their probability of exposure to pathogens. If preference behavior can be incorporated in ecological niche models (ENMs) when data on pathogen distributions are available, then variation in such behavior may dramatically impact exposure risk. Here we use data from the anthrax endemic system of Etosha National Park, Namibia, to demonstrate how integrating inferred movement behavior alters the construction of disease risk maps. We used a Maximum Entropy (MaxEnt) model that associated soil, bioclimatic, and vegetation variables with the best available pathogen presence data collected at anthrax carcass sites to map areas of most likely Bacillus anthracis (the causative bacterium of anthrax) persistence. We then used a hidden Markov model (HMM) to distinguish foraging and non-foraging behavioral states along the movement tracks of nine zebra (Equus quagga) during the 2009 and 2010 anthrax seasons. The resulting tracks, decomposed on the basis of the inferred behavioral state, formed the basis of step-selection functions (SSFs) that used the MaxEnt output as a potential predictor variable. Our analyses revealed different risks of exposure during different zebra behavioral states, which were obscured when the full movement tracks were analyzed without consideration of the underlying behavioral states of individuals. Pathogen (or vector) distribution models may be misleading with regard to the actual risk faced by host animal populations when specific behavioral states are not explicitly accounted for in selection analyses. To more accurately evaluate exposure risk, especially in the case of environmentally transmitted pathogens, selection functions could be built for each identified behavioral state and then used to assess the comparative exposure risk across relevant states. The scale of data collection and analysis, however, introduces complexities and limitations for consideration when interpreting results.

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“…anthracis transmission in the NCA, movement of infected wildlife and scavengers acting as carriers of B. anthracis spores could represent an additional mechanism contributing to our observations [57, 58]. Further comparative genomic studies across wider areas will be essential for elucidating the geographical scales at which transmission occurs.…”

Section: Discussionmentioning

confidence: 99%

Population genomics of Bacillus anthracis from an anthrax hyperendemic area reveals transmission processes across spatial scales and unexpected within-host diversity

et al. 2022

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Genomic sequencing has revolutionized our understanding of bacterial disease epidemiology, but remains underutilized for zoonotic pathogens in remote endemic settings. Anthrax, caused by the spore-forming bacterium Bacillus anthracis , remains a threat to human and animal health and rural livelihoods in low- and middle-income countries. While the global genomic diversity of B. anthracis has been well-characterized, there is limited information on how its populations are genetically structured at the scale at which transmission occurs, critical for understanding the pathogen’s evolution and transmission dynamics. Using a uniquely rich dataset, we quantified genome-wide SNPs among 73 B. anthracis isolates derived from 33 livestock carcasses sampled over 1 year throughout the Ngorongoro Conservation Area, Tanzania, a region hyperendemic for anthrax. Genome-wide SNPs distinguished 22 unique B. anthracis genotypes (i.e. SNP profiles) within the study area. However, phylogeographical structure was lacking, as identical SNP profiles were found throughout the study area, likely the result of the long and variable periods of spore dormancy and long-distance livestock movements. Significantly, divergent genotypes were obtained from spatio-temporally linked cases and even individual carcasses. The high number of SNPs distinguishing isolates from the same host is unlikely to have arisen during infection, as supported by our simulation models. This points to an unexpectedly wide transmission bottleneck for B. anthracis , with an inoculum comprising multiple variants being the norm. Our work highlights that inferring transmission patterns of B. anthracis from genomic data will require analytical approaches that account for extended and variable environmental persistence, as well as co-infection.

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Hippopotamus movements structure the spatiotemporal dynamics of an active anthrax outbreak

Abstract: Mutayoba. 2021. Hippopotamus movements structure the spatiotemporal dynamics of an active anthrax outbreak.

Cited by 11 publications

References 59 publications

Environmental drivers of biseasonal anthrax outbreak dynamics in two multihost savanna systems

Environmental drivers of biseasonal anthrax outbreak dynamics in two multihost savanna systems

A framework for integrating inferred movement behavior into disease risk models

Population genomics of Bacillus anthracis from an anthrax hyperendemic area reveals transmission processes across spatial scales and unexpected within-host diversity

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