More Like this

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

   https://doi.org/10.1002/ecm.1526  

   Huang, Yen‐Hua; Kausrud, Kyrre; Hassim, Ayesha; Ochai, Sunday O.; Schalkwyk, O. Louis; Dekker, Edgar H.; Buyantuev, Alexander; Cloete, Claudine C.; Kilian, J. Werner; Mfune, John K.; et al (April 2022, Ecological Monographs)

   Environmental factors are common forces driving infectious disease dynamics. We compared inter-annual and seasonal patterns of anthrax infections in two multi-host 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 inter-annual variation in case numbers, and large outbreaks seemed to follow roughly a 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 (Equus quagga) became relatively more dominant. In Kruger, turnover of the main host species occurred after the 1990s, where the previously dominant host species, greater kudu (Tragelaphus strepsiceros), was replaced by impala (Aepyceros melampus). In both parks, anthrax infections showed two seasonal peaks, with each species having only one peak in a year. Zebra, springbok (Antidorcas marsupialis), wildebeest (Connochaetes taurinus) and impala cases peaked in wet seasons, while elephant (Loxodonta africana), kudu and buffalo (Syncerus caffer) cases peaked in dry seasons. For common host species shared between the two parks, anthrax mortalities peaked in the same season in both systems. Among host species with cases peaking in the same season, anthrax mortalities were mostly synchronized, which may imply similar transmission mechanisms or shared sources of exposure. Between seasons, outbreaks in one species may contribute to more cases in another species in the following season. Higher vegetation greenness was associated with more zebra and springbok anthrax mortalities in Etosha, but fewer elephant cases in Kruger. These results suggest that host behavioral responses to changing environmental conditions may affect anthrax transmission risk, with differences in transmission mechanisms leading to multi-host biseasonal outbreaks. This study reveals the dynamics and potential environmental drivers of anthrax in two savanna systems, providing a better understanding of factors driving biseasonal dynamics and outbreak variation among locations. 

   more » « less
2. Variation in herbivore space use: comparing two savanna ecosystems with different anthrax outbreak patterns in southern Africa

   Huang, Y.-H.; Owen-Smith, N.; Henley, M.D.; Kilian, J.W.; Kamath, P.L.; Ochai, S.O.; van Heerden, H.; Mfune, J.K.E.; Getz, W.M.; Turner, W.C. (January 2023, Movement ecology)

   Background The distribution of resources can affect animal range sizes, which in turn may alter infectious disease dynamics in heterogenous environments. The risk of pathogen exposure or the spatial extent of outbreaks may vary with host range size. This study examined the range sizes of herbivorous anthrax host species in two ecosystems and relationships between spatial behavior and patterns of disease outbreaks for a multi-host environmentally transmitted pathogen. Methods We examined range sizes for seven host species and the spatial extent of anthrax outbreaks in Etosha National Park, Namibia and Kruger National Park, South Africa, where the main host species and numbers of cases differ. We evaluated host range sizes using the local convex hull method at different temporal scales, within-individual temporal range overlap, and relationships between ranging behavior and species contributions to anthrax cases in each park. We estimated the spatial extent of annual anthrax mortalities and evaluated whether the extent was correlated with case numbers of a given host species. Results Range size differences among species were not linearly related to anthrax case numbers. In Kruger the main host species had small range sizes and high range overlap, which may heighten exposure when outbreaks occur within their ranges. However, different patterns were observed in Etosha, where the main host species had large range sizes and relatively little overlap. The spatial extent of anthrax mortalities was similar between parks but less variable in Etosha than Kruger. In Kruger outbreaks varied from small local clusters to large areas and the spatial extent correlated with case numbers and species affected. Case numbers of secondary host species with larger range sizes were positively correlated with the spatial extent of outbreaks in both parks. Conclusions Our results provide new information on the spatiotemporal structuring of ranging movements of anthrax host species in two ecosystems. The results linking anthrax dynamics to host space use are correlative, yet suggest that, though partial and proximate, host range size and overlap may be contributing factors in outbreak characteristics for environmentally transmitted pathogens. 

   more » « less
3. Coalescence modeling of intrainfection Bacillus anthracis populations allows estimation of infection parameters in wild populations

   https://doi.org/10.1073/pnas.1920790117  

   Easterday, W. Ryan; Ponciano, José Miguel; Gomez, Juan Pablo; Van Ert, Matthew N.; Hadfield, Ted; Bagamian, Karoun; Blackburn, Jason K.; Stenseth, Nils Chr.; Turner, Wendy C. (February 2020, Proceedings of the National Academy of Sciences)

   Bacillus anthracis , the etiological agent of anthrax, is a well-established model organism. For B. anthracis and most other infectious diseases, knowledge regarding transmission and infection parameters in natural systems, in large part, comprises data gathered from closely controlled laboratory experiments. Fatal, natural anthrax infections transmit the bacterium through new host−pathogen contacts at carcass sites, which can occur years after death of the previous host. For the period between contact and death, all of our knowledge is based upon experimental data from domestic livestock and laboratory animals. Here we use a noninvasive method to explore the dynamics of anthrax infections, by evaluating the terminal diversity of B. anthracis in anthrax carcasses. We present an application of population genetics theory, specifically, coalescence modeling, to intrainfection populations of B. anthracis to derive estimates for the duration of the acute phase of the infection and effective population size converted to the number of colony-forming units establishing infection in wild plains zebra ( Equus quagga ). Founding populations are small, a few colony-forming units, and infections are rapid, lasting roughly between 1 d and 3 d in the wild. Our results closely reflect experimental data, showing that small founding populations progress acutely, killing the host within days. We believe this method is amendable to other bacterial diseases from wild, domestic, and human systems. 

   more » « less
4. Inferring epidemiological parameters under an infectious phylogeography model with visitor dynamics

   https://doi.org/10.64898/2025.12.16.25342415  

   Soewongsono, Albert C; Thompson, Ammon; Landis, Michael J (December 2025, medRxiv)

   During an outbreak, infectious disease can spread among populations through host movement, potentially fueling local outbreaks with their own epidemiological dynamics. However, it is difficult to know how often infections between populations are transmitted by diseased travelers infecting healthy residents when abroad, rather than by diseased residents infecting healthy travelers, who later return home with the new pathogen. In this paper, we introduce a phylogeographic model where pathogens spread through visitor dynamics, whereby hosts “visit” other populations for short trips before returning home. To do so, we used the stationary properties of an epidemiological compartment model with visitor dynamics to construct an approximation that is statistically accurate and computationally tractable for phylogenetic modeling. We applied our model to empirical infection data and travel statistics from the European SARS-CoV-2 pandemic. Inference under our model suggests that, in the early stages of the outbreak, SARS CoV-2 was more often “pulled” into new countries by returning travelers than “pushed” into new countries by visitors from the source country. Estimates of host movement–related parameter values under our visitor model suggest that competing migration models, with trips of indefinite length, may underestimate the magnitude of outbreaks caused by visitors. This study emphasizes the importance of carefully incorporating host movement dynamics into such models. Significance StatementViral infections can spread among distinct locations by human travel. Being able to identify the source of a local outbreak – whether triggered by infected visitors or individuals returning home – is crucial. Here, we designed a phylogenetic model for modeling infectious disease transmission in spatially structured populations, explicitly accounting for realistic host movement. By accounting for “short trips”, our model can help inform travelrelated strategies for containing outbreaks. 

   more » « less
5. Transient disease dynamics across ecological scales

   https://doi.org/10.1007/s12080-021-00514-w  

   Tao, Yun; Hite, Jessica L.; Lafferty, Kevin D.; Earn, David J.; Bharti, Nita (May 2021, Theoretical Ecology)

   null (Ed.)

   Abstract Analyses of transient dynamics are critical to understanding infectious disease transmission and persistence. Identifying and predicting transients across scales, from within-host to community-level patterns, plays an important role in combating ongoing epidemics and mitigating the risk of future outbreaks. Moreover, greater emphases on non-asymptotic processes will enable timely evaluations of wildlife and human diseases and lead to improved surveillance efforts, preventive responses, and intervention strategies. Here, we explore the contributions of transient analyses in recent models spanning the fields of epidemiology, movement ecology, and parasitology. In addition to their roles in predicting epidemic patterns and endemic outbreaks, we explore transients in the contexts of pathogen transmission, resistance, and avoidance at various scales of the ecological hierarchy. Examples illustrate how (i) transient movement dynamics at the individual host level can modify opportunities for transmission events over time; (ii) within-host energetic processes often lead to transient dynamics in immunity, pathogen load, and transmission potential; (iii) transient connectivity between discrete populations in response to environmental factors and outbreak dynamics can affect disease spread across spatial networks; and (iv) increasing species richness in a community can provide transient protection to individuals against infection. Ultimately, we suggest that transient analyses offer deeper insights and raise new, interdisciplinary questions for disease research, consequently broadening the applications of dynamical models for outbreak preparedness and management. 

   more » « less