Why are there no human West Nile virus outbreaks in South America?

Identification of West Nile virus infection by anti-premembrane antibodies in Nicaraguan children prior to 2007-2009

Since its introduction to the Western Hemisphere in 1999 in New York City, West Nile virus (WNV) has spread throughout the continental USA and moved into Canada, Mexico, Caribbean, and Central and South Americas. While WNV has caused ~7 million human infections and >59,000 cases in the USA and >6,000 cases in Canada, only few human cases have been reported in Latin America. Due to the cross-reactivity of anti-envelope antibodies, the detection of WNV infection by serology to explore its epidemiology in Latin America, where multiple flaviviruses co-circulate, remains a challenge. Previously, we reported that anti-premembrane (prM) antibodies can distinguish between four flavivirus (WNV, dengue, Zika, and yellow fever viruses) infections. In this study, we examined 73 samples from 40 Zika cases from a pediatric cohort in Nicaragua using Western blot analysis and detected anti-prM antibodies to WNV in three participants in samples collected between 2016 and 2017, suggesting previous WNV infection prior to ZIKV infection. Analysis of available archived samples revealed anti-WNV prM antibodies in the earliest samples (2007-2009), which were further confirmed by plaque reduction neutralization test, suggesting that they were infected by WNV prior to 2007-2009. Our report of WNV infection in three Nicaraguan children, corresponding to a seropositive rate of 7.5%, highlights the transmission of WNV in humans in Central America prior to 2007. Future studies with improved serological tests for WNV surveillance in Latin America are needed to enhance our understanding of the epidemiology and transmission of WNV in the Western Hemisphere.

IMPORTANCE

Since its arrival to North America in 1999, West Nile virus (WNV) has caused multiple outbreaks in birds and humans, with thousands of human cases in the USA and Canada, whereas in Latin America, WNV has mainly been detected in birds and horses with few human cases. Due to cross-reactivity of anti-envelope antibodies among different flaviviruses, detection of WNV infection by serology to explore its epidemiology in Latin America remains a challenge. Previously, we reported that anti-premembrane antibodies can discriminate four flavivirus infections using Western blot analysis. Based on anti-WNV premembrane antibodies and confirmation by neutralization test, we report three Nicaraguan children with WNV infection, corresponding to a seropositive rate of 7.5%. Our findings underscore the transmission of WNV in humans in Central America and the application of improved seroepidemiological tools to address the knowledge gaps on the prevalence and distribution of WNV in Latin America and the Western Hemisphere.

Survey of West Nile virus infection in wildlife species in the Orinoquia region of Colombia

Studies focused on the epidemiological surveillance of arboviruses that cause potentially zoonotic diseases, such as dengue, Zika, or emerging viruses like West Nile virus (WNV), are critical due to their significant impact on public health. Although research on these infectious agents is increasing in Colombia, regions remain where the presence of zoonotic agents is still unknown. To address this knowledge gap, the present study aimed to investigate the current status of WNV circulation in wildlife in two municipalities of the department of Casanare (El Yopal and Paz de Ariporo) from the Colombian region of Orinoquia. Since the arrival of WNV in Colombia, reported in 2004, its detection has typically relied on antibody screening using ELISA. While informative, this technique needs to offer a sufficiently precise time frame to confirm active virus circulation. We employed a molecular approach to overcome this limitation, detecting WNV using qPCR, which provides greater specificity and a narrower time window. A total of 2,553 swab samples were collected from a broad sampling covering 142 birds, 19 mammals, and eight reptile species during 2023 and 2024 across four sampling events conducted during both the dry and wet seasons. The sampling included species with ecological or symbolic value to the region and those with economic importance, such as species used for human consumption (bushmeat). No evidence of WNV was detected in the evaluated species, indicating that these species were not infected with the virus during the sampling periods or that viral loads were below the detection threshold. Our results underscore the importance of further studies, including complementary diagnostic methods, such as antibody detection, to better understand the broader temporal infections and provide a more complete understanding of virus circulation.

Spatiotemporally Explicit Epidemic Model for West Nile Virus Outbreak in Germany: An Inversely Calibrated Approach

Since the first autochthonous transmission of West Nile Virus was detected in Germany (WNV) in 2018, it has become endemic in several parts of the country and is continuing to spread due to the attainment of a suitable environment for vector occurrence and pathogen transmission. Increasing temperature associated with a changing climate has been identified as a potential driver of mosquito-borne disease in temperate regions. This scenario justifies the need for the development of a spatially and temporarily explicit model that describes the dynamics of WNV transmission in Germany. In this study, we developed a process-based mechanistic epidemic model driven by environmental and epidemiological data. Functional traits of mosquitoes and birds of interest were used to parameterize our compartmental model appropriately. Air temperature, precipitation, and relative humidity were the key climatic forcings used to replicate the fundamental niche responsible for supporting mosquito population and infection transmission risks in the study area. An inverse calibration method was used to optimize our parameter selection. Our model was able to generate spatially and temporally explicit basic reproductive number (R0) maps showing dynamics of the WNV occurrences across Germany, which was strongly associated with the deviation from daily means of climatic forcings, signaling the impact of a changing climate in vector-borne disease dynamics. Epidemiological data for human infections sourced from Robert Koch Institute and animal cases collected from the Animal Diseases Information System (TSIS) of the Friedrich-Loeffler-Institute were used to validate model-simulated transmission rates. From our results, it was evident that West Nile Virus is likely to spread towards the western parts of Germany with the rapid attainment of environmental suitability for vector mosquitoes and amplifying host birds, especially short-distance migratory birds. Locations with high risk of WNV outbreak (Baden-Württemberg, Bavaria, Berlin, Brandenburg, Hamburg, North Rhine-Westphalia, Rhineland-Palatinate, Saarland, Saxony-Anhalt and Saxony) were shown on R0 maps. This study presents a path for developing an early warning system for vector-borne diseases driven by climate change.

Lessons Learned from West Nile Virus Infection:Vaccinations in Equines and Their Implications for One Health Approaches

Humans and equines are two dead-end hosts of the mosquito-borne West Nile virus (WNV) with similar susceptibility and pathogenesis. Since the introduction of WNV vaccines into equine populations of the United States of America (USA) in late 2002, there have been only sporadic cases of WNV infection in equines. These cases are generally attributed to unvaccinated and under-vaccinated equines. In contrast, due to the lack of a human WNV vaccine, WNV cases in humans have remained steadily high. An average of 115 deaths have been reported per year in the USA since the first reported case in 1999. Therefore, the characterization of protective immune responses to WNV and the identification of immune correlates of protection in vaccinated equines will provide new fundamental information about the successful development and evaluation of WNV vaccines in humans. This review discusses the comparative epidemiology, transmission, susceptibility to infection and disease, clinical manifestation and pathogenesis, and immune responses of WNV in humans and equines. Furthermore, prophylactic and therapeutic strategies that are currently available and under development are described. In addition, the successful vaccination of equines against WNV and the potential lessons for human vaccine development are discussed.

Antibodies from dengue patients with prior exposure to Japanese encephalitis virus are broadly neutralizing against Zika virus

Exposure to multiple mosquito-borne flaviviruses within a lifetime is not uncommon; however, how sequential exposures to different flaviviruses shape the cross-reactive humoral response against an antigen from a different serocomplex has yet to be explored. Here, we report that dengue-infected individuals initially primed with the Japanese encephalitis virus (JEV) showed broad, highly neutralizing potencies against Zika virus (ZIKV). We also identified a rare class of ZIKV-cross-reactive human monoclonal antibodies with increased somatic hypermutation and broad neutralization against multiple flaviviruses. One huMAb, K8b, binds quaternary epitopes with heavy and light chains separately interacting with overlapping envelope protein dimer units spanning domains I, II, and III through cryo-electron microscopy and structure-based mutagenesis. JEV virus-like particle immunization in mice further confirmed that such cross-reactive antibodies, mainly IgG3 isotype, can be induced and proliferate through heterologous dengue virus (DENV) serotype 2 virus-like particle stimulation. Our findings highlight the role of prior immunity in JEV and DENV in shaping the breadth of humoral response and provide insights for future vaccination strategies in flavivirus-endemic countries.

Assessing the risk of West Nile Virus seasonal outbreaks and its vector control in an urbanizing bird community: An integrative R0-modelling study in the city of Merida, Mexico

Urbanization is a global trend associated with key socio-economic issues, one of them being to control the transmission of infectious diseases to a urban fraction of the world's population that shall reach 68% in 2050. While urban growth has been shown to favor mosquito species responsible for the transmission of the West Nile Virus (WNV), a major human arbovirosis, the effects of concomitant changes in the host bird communities remain hard to anticipate albeit essential to quantify disease risk and to plan control initiatives. We developed a R0 modelling of WNV transmission in a urban bird community to assess the risk of outbreak in Merida, one of the cities with the highest growth rate in Mexico. The model was parameterized using ecological and epidemiological data collected over the past 15-years on the local vector, Culex quinquefasciatus, and avian community. We identified a 3-weeks summer period during which the vector population strongly amplifies the WNV enzootic transmission and lead to a significant risk of outbreaks in humans. Extensive sensitivity analyses showed that urbanization induced changes in the bird community could lead to an up-to 6-fold increase in the duration of the risk period, while the daily risk could rise by 40%. Interestingly, the increase in Quiscalus mexicanus abundance had 4-5 times larger impact than any other change in the bird community. In such a context, annihilating the current and future risk of WNV outbreaks in Merida requires reducing the mosquito population by 13% and up to 56%, respectively. This study provides an integrative assessment of the current and future risks of WNV outbreak in the fast urbanizing city of Merida, and points toward the implementation of epidemiological monitoring combined with preemptive measures targeting both C. quinquefasciatus and Q. mexicanus populations, as they are expected to have synergistic effects.

The Others: A Systematic Review of the Lesser-Known Arboviruses of the Insular Caribbean

The Caribbean enjoys a long-standing eminence as a popular tourist destination; however, over the years it has also amassed the sobriquet "arbovirus hotspot". As the planet warms and vectors expand their habitats, a cognizant working knowledge of the lesser-known arboviruses and the factors that influence their emergence and resurgence becomes essential. The extant literature on Caribbean arboviruses is spread across decades of published literature and is quite often difficult to access, and, in some cases, is obsolete. Here, we look at the lesser-known arboviruses of the insular Caribbean and examine some of the drivers for their emergence and resurgence. We searched the scientific literature databases PubMed and Google Scholar for peer-reviewed literature as well as scholarly reports. We included articles and reports that describe works resulting in serological evidence of the presence of arboviruses and/or arbovirus isolations in the insular Caribbean. Studies without serological evidence and/or arbovirus isolations as well as those including dengue, chikungunya, Zika, and yellow fever were excluded. Of the 545 articles identified, 122 met the inclusion criteria. A total of 42 arboviruses were identified in the literature. These arboviruses and the drivers that affect their emergence/resurgence are discussed.

Identifying and Managing Vector-Borne Diseases in Migrants and Recent Travelers in the Emergency Department

Purpose of Review

Recognition and treatment of neglected tropical and vector-borne diseases is paramount as travel and immigration resume after a brief lull during the COVID-19 pandemic. These patients often present initially to the emergency department, and increasing physician knowledge of symptoms and treatment can reduce morbidity and mortality. This paper aims to summarize typical presentations of common tropical diseases, both neglected and vector borne, and provide the emergency physician with a diagnostic pathway based on current recommendations.

Recent Findings

Co-circulation of ZIKV, CHIKV, and DENV is increasingly common in many countries throughout Caribbean and the Americas, requiring that patients be tested for each virus upon presentation. Dengvaxia is now approved as a vaccine against dengue in pediatric and young adult patients. A malaria vaccine, RTS,S/AS01, is currently in phase 3 trials and has been approved as a short-term vaccine by WHO for children in regions with high transmission risk after showing a 30% reduction in severe malaria. Mayaro is currently a neglected arbovirus that presents similarly to Chikungunya and is continuing to spread throughout the Americas at a rapid rate, gaining more attention after the 2016 Zika outbreak.

Summary

Emergency physicians should consider internationally acquired illnesses to appropriately identify which patients require admission among well-appearing febrile immigrants or recent travelers presenting to the emergency department. Identifying symptomatology and understanding the appropriate workup and treatment for tropically acquired diseases will assist in recognizing severe complications with prompt treatment.