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1. Re-emergence of yellow fever in the neotropics — quo vadis?

   https://doi.org/10.1042/ETLS20200187  

   Sacchetto, Livia; Drumond, Betania P.; Han, Barbara A.; Nogueira, Mauricio L.; Vasilakis, Nikos (December 2020, Emerging Topics in Life Sciences)

   Low, Jenny (Ed.)

   Yellow fever virus (YFV) is the etiological agent of yellow fever (YF), an acute hemorrhagic vector-borne disease with a significant impact on public health, is endemic across tropical regions in Africa and South America. The virus is maintained in two ecologically and evolutionary distinct transmission cycles: an enzootic, sylvatic cycle, where the virus circulates between arboreal Aedes species mosquitoes and non-human primates, and a human or urban cycle, between humans and anthropophilic Aedes aegypti mosquitoes. While the urban transmission cycle has been eradicated by a highly efficacious licensed vaccine, the enzootic transmission cycle is not amenable to control interventions, leading to recurrent epizootics and spillover outbreaks into human populations. The nature of YF transmission dynamics is multifactorial and encompasses a complex system of biotic, abiotic, and anthropogenic factors rendering predictions of emergence highly speculative. The recent outbreaks in Africa and Brazil clearly remind us of the significant impact YF emergence events pose on human and animal health. The magnitude of the Brazilian outbreak and spillover in densely populated areas outside the recommended vaccination coverage areas raised the specter of human — to — human transmission and re-establishment of enzootic cycles outside the Amazon basin. Herein, we review the factors that influence the re-emergence potential of YFV in the neotropics and offer insights for a constellation of coordinated approaches to better predict and control future YF emergence events. 

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2. Landscape-scale analysis of raccoon rabies surveillance reveals different drivers of disease dynamics across latitude

   https://doi.org/10.1371/journal.pntd.0013581  

   Michalska-Smith, Matthew; Craft, Meggan E; Davis, Amy J; Gilbert, Amy T; Chipman, Richard B; Kirby, Jordona; Nelson, Kathleen M; Ma, Xiaoyue; Wallace, Ryan; Miller, Grace; et al (September 2025, PLOS Neglected Tropical Diseases)

   Rayner, Simon (Ed.)

   When raccoon rabies first invaded the mid-Atlantic United States, epizootics were larger, longer, and more pronounced than those in its historic, more southern, range, suggesting a North-South gradient in disease dynamics. In addition, due to higher raccoon densities and concentrated feeding sources, urban areas might sustain larger epizootics, suggesting an urban-rural gradient might likewise influence dynamics. Here we leverage long-term surveillance data on raccoon rabies, collated by the Centers for Disease Control and Prevention, United States Department of Agriculture, and state and local public health agencies to better understand the role of latitude and urbanness for raccoon rabies epizootiology. Our analysis utilizes surveillance data from the 20 states composing the raccoon rabies enzootic area across 2006–2018. We identified effects of latitude and human population density (a proxy for urbanness) on the county-level probability of detecting raccoon rabies. We find that: 1) in the northeastern US, more samples are submitted in the summer, and more positive results are obtained, albeit with a lower likelihood of a given sample being found to be rabid, while these trends are independent of season at southern latitudes; 2) the association between urbanness and risk of rabies cases varies across latitude, with greater rabies presence in rural vs. urban counties in the south and a more consistent risk across urbanness in the north; and 3) the most consistent predictors of raccoon rabies detection are spatiotemporal effects, suggesting that recent detection of cases in a county or its neighbors are more informative of raccoon rabies dynamics than are general metrics like latitude and urbanness. Statistical and spatial long-term studies like these not only can improve understanding of wildlife disease patterns but can help guide public health and wildlife management efforts in areas most at risk for raccoon rabies virus infection. 

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3. Culicoides-Specific Fitness Increase of Vesicular Stomatitis Virus in Insect-to-Insect Infections

   https://doi.org/10.3390/insects15010034  

   Rozo-Lopez, Paula; Drolet, Barbara S (January 2024, Insects)

   Messenger, Louisa Alexandra (Ed.)

   Vesicular stomatitis virus (VSV) is an arthropod-borne virus affecting livestock. In the United States, sporadic outbreaks result in significant economic losses. During epizootics, Culicoides biting midges are biological vectors and key to the geographic expansion of outbreaks. Additionally, Culicoides may play a role in VSV overwintering because females and males are capable of highly efficient venereal transmission, despite their relatively low virus titers. We hypothesized that VSV propagated within a midge has increased fitness for subsequent midge infections. To evaluate the potential host-specific fitness increase, we propagated three viral isolates of VSV in porcine skin fibroblasts and Culicoides cell lines. We then evaluated the viral infection dynamics of the different cell-source groups in Culicoides sonorensis. Our results indicate that both mammalian- and insect-derived VSV replicate well in midges inoculated via intrathoracic injection, thereby bypassing the midgut barriers. However, when the virus was required to infect and escape the midgut barrier to disseminate after oral acquisition, the insect-derived viruses had significantly higher titers, infection, and dissemination rates than mammalian-derived viruses. Our research suggests that VSV replication in Culicoides cells increases viral fitness, facilitating midge-to-midge transmission and subsequent replication, and further highlights the significance of Culicoides midges in VSV maintenance and transmission dynamics. 

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4. Higher West Nile Virus Infection in Aedes albopictus (Diptera: Culicidae) and Culex (Diptera: Culicidae) Mosquitoes From Lower Income Neighborhoods in Urban Baltimore, MD

   https://doi.org/10.1093/jme/tjaa262  

   Rothman, Sarah E; Jones, Jennifer A; LaDeau, Shannon L; Leisnham, Paul T (December 2020, Journal of Medical Entomology)

   Andreadis, Theodore (Ed.)

   Abstract The temperate United States has experienced increasing incidence of mosquito-borne diseases. Recent studies conducted in Baltimore, MD have demonstrated a negative relationship between abundances of Aedes albopictus (Skuse) and Culex mosquitoes and mean neighborhood income level, but have not looked at the presence of pathogens. Mosquitoes collected from five socioeconomically variable neighborhoods were tested for infection by West Nile, chikungunya, and Zika viruses in 2015 and 2016, and again from four of the neighborhoods in 2017. Minimum infection rates of pooled samples were compared among neighborhoods for each year, as well as among individual blocks in 2017. West Nile virus was detected in both Ae. albopictus and Culex pools from all neighborhoods sampled in 2015 and 2017. No infected pools were detected in any year for chikungunya or Zika viruses, and none of the target viruses were detected in 2016. Infection rates were consistently higher for Culex than for Ae. albopictus. Minimum infection rate was negatively associated with mean neighborhood income for both species in 2015. Although earlier work has shown a positive association between block-level abandonment and mosquito abundance, no association was detected in this study. Still, we demonstrate that viral infection in mosquito pools can differ substantially across adjacent urban neighborhoods that vary by income. Though trap security and accessibility often inform city sampling locations, detecting and managing arboviral risk requires surveillance across neighborhoods that vary in socioeconomics, including lower income areas that may be less accessible and secure but have higher infection rates. 

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5. Ecology and geography of Cache Valley virus assessed using ecological niche modeling

   https://doi.org/10.1186/s13071-024-06344-z  

   Muller, John_A; López, Krisangel; Escobar, Luis_E; Auguste, Albert_J (June 2024, Parasites & Vectors)

   Abstract BackgroundCache Valley virus (CVV) is an understudiedOrthobunyaviruswith a high spillover transmission potential due to its wide geographical distribution and large number of associated hosts and vectors. Although CVV is known to be widely distributed throughout North America, no studies have explored its geography or employed computational methods to explore the mammal and mosquito species likely participating in the CVV sylvatic cycle. MethodsWe used a literature review and online databases to compile locality data for CVV and its potential vectors and hosts. We linked location data points with climatic data via ecological niche modeling to estimate the geographical range of CVV and hotspots of transmission risk. We used background similarity tests to identify likely CVV mosquito vectors and mammal hosts to detect ecological signals from CVV sylvatic transmission. ResultsCVV distribution maps revealed a widespread potential viral occurrence throughout North America. Ecological niche models identified areas with climate, vectors, and hosts suitable to maintain CVV transmission. Our background similarity tests identifiedAedes vexans,Culiseta inornata, andCulex tarsalisas the most likely vectors andOdocoileus virginianus(white-tailed deer) as the most likely host sustaining sylvatic transmission. ConclusionsCVV has a continental-level, widespread transmission potential. Large areas of North America have suitable climate, vectors, and hosts for CVV emergence, establishment, and spread. We identified geographical hotspots that have no confirmed CVV reports to date and, in view of CVV misdiagnosis or underreporting, can guide future surveillance to specific localities and species. Graphical Abstract 

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