Serologic evidence of West Nile virus and Saint Louis encephalitis virus in horses from Southern Brazil

Cross-protection against St. Louis encephalitis virus and Usutu virus by West Nile virus convalescent plasma

West Nile virus (WNV), Usutu virus (USUV), and Saint Louis encephalitis virus (SLEV) are emerging mosquito-borne flaviviruses within the Japanese encephalitis virus serocomplex. They share a similar transmission cycle between passerine birds and Culex spp. mosquitoes, and their spillover can cause neuroinvasive diseases among humans and animals. Individuals might be exposed to more than one of these viruses during their lifetime. Previously, we found that WNV vaccination protected mice from USUV disease, and sera collected from the WNV vaccinated mice cross-neutralized USUV in vitro. However, whether WNV convalescent (post-recovery) plasma cross-protects against heterologous SLEV or USUV infection is unknown. In this study, in vivo experiments were conducted to assess whether WNV human convalescent plasma and/or mouse convalescent serum afforded protection to mice against SLEV and USUV infection and neuroinvasion. First, we found that human and mouse WNV convalescent samples cross-neutralized USUV and SLEV in vitro. We then passively transferred human or mouse WNV convalescent samples into mice and challenged them with WNV, USUV, or SLEV. Both human and mouse WNV convalescent samples reduced WNV neuroinvasion and SLEV and USUV viremia during acute infection. Mouse WNV convalescent serum significantly reduced SLEV titers in the brain and showed a trend towards resulting in less inflammation in the brain. These findings helped to better understand the potential cross-protection among WNV, SLEV, and USUV, and identified cross-neutralizing antibodies as potential correlates of protection for individuals exposed to multiple flaviviruses, though protection was incomplete.

First Serologic Evidence of West Nile Virus and Usutu Virus Circulation Among Dogs in the Bulgarian Danube Region and Analysis of Some Risk Factors

This study aimed to assess West Nile virus (WNV) and Usutu virus seroprevalence among the dog population in the Danube region, Bulgaria, to confirm the results of ELISA by the virus neutralisation test (VNT), as well as to analyse several risk factors of seropositivity in dogs. To implement this, a total of 201 blood samples were collected from dogs in four districts bordering the Danube River. All the samples were tested for anti-WNV protein E antibodies using competitive ELISA. Neutralising antibodies against WNV and Usutu virus were tested in all the ELISA-positive samples. The results show a WNV seroprevalence of 45.3% (n = 91, CI = 36.45-55.59) by ELISA, whereas the virus neutralisation test indicated a seroprevalence of 21.9% (n = 44, CI = 15.91-29.39). Neutralising antibodies against Usutu virus were detected for the first time in Bulgaria, with a prevalence of 6% (n = 12, CI = 3.09-10.43). Compared to VNT, ELISA demonstrated 100.0% sensitivity and 70.1% specificity. The region (p < 0.0187), the district (p = 0.0258) and the ages of the dogs (p = 0.0180) were identified as statistically significant risk factors associated with WNV seropositivity. This study provides indirect evidence of WNV and Usutu virus circulation among dogs in the Danube region of Bulgaria, highlighting a potential risk for susceptible hosts in the area.

(Re)Emerging Arboviruses of Public Health Significance in the Brazilian Amazon

Brazil is one of the most important countries globally in regard to arboviral disease ecology and emergence or resurgence. Unfortunately, it has shouldered a majority of arboviral disease cases from Latin America and its rich flora, fauna (including arthropod vectors), and climate have contributed to the vast expansion of multiple arboviral diseases within its borders and those that have expanded geographically outside its borders. Anthropogenic landscape changes or human-mediated changes such as agriculture, deforestation, urbanization, etc. have all been at play within the country in various locations and can also be attributed to arboviral movement and resurgence. This review describes a brief history of landscape changes within the country and compiles all the known information on all arboviruses found within Brazil (endemic and imported) that are associated with human disease and mosquitoes including their original isolation, associated vertebrate animals, associated mosquitoes and other arthropods, and human disease symptomology presentations. This information is crucial as the Western Hemisphere is currently experiencing multiple arbovirus outbreaks, including one that originated in the Brazilian Amazon. Understanding which arboviruses are and have been circulating within the country will be pertinent as anthropogenic landscape changes are consistently being perpetrated throughout the country, and the occurrence of the next arbovirus epidemic will be a matter of when, not if.

Aedes-borne orthoflavivirus infections in neotropical primates - Ecology, susceptibility, and pathogenesis

Arboviral diseases comprise a group of important infectious diseases imposing a heavy burden to public health in many locations of the world. Orthoflaviviruses are viruses belonging to the genus Orthoflavivirus; this genus includes some of the most relevant arboviruses to human health. Orthoflaviviruses can infect several different hosts, with some species being transmitted in cycles involving birds and anthropophilic mosquitoes and others transmitted between mammals and mostly Aedes sp. mosquitoes. Some of the most important sylvatic reservoirs of orthoflaviviruses are non-human primates (NHPs). Many flaviviruses that infect NHPs in nature have the potential to cause epidemics in humans, as has been observed in the cases of Orthoflavivirus denguei (dengue virus - DENV), Orthoflavivirus flavi (yellow fever virus - YFV), and Orthoflavivirus zikaense (Zika virus - ZIKV). In this minireview, we discuss important aspects regarding history, ecology involving NHP, distribution, disease outcome, and pathogenesis of these three major orthoflaviviruses that affect humans and NHP and relate this information to the potential of using NHP as experimental models. In addition, we suggest some orthoflaviviruses that could be better investigated, both in nature and in experimental studies, in light of the recent revolution in molecular biology.

Serological Evidence of Exposure to Saint Louis Encephalitis and West Nile Viruses in Horses of Rio de Janeiro, Brazil

Infections with arboviruses are reported worldwide. Saint Louis encephalitis (SLEV) and West Nile (WNV) viruses are closely related flaviviruses affecting humans and animals. SLEV has been sporadically detected in humans, and corresponding antibodies have been frequently detected in horses throughout Brazil. WNV was first reported in western Brazil over a decade ago, has been associated with neurological disorders in humans and equines and its prevalence is increasing nationwide. Herein, we investigated by molecular and serological methods the presence of SLEV and WNV in equines from Rio de Janeiro. A total of 435 serum samples were collected from healthy horses and tested for specific neutralizing antibodies by plaque reduction neutralization test (PRNT90). Additionally, samples (serum, cerebrospinal fluid, central nervous system tissue) from 72 horses, including horses with neurological disorders resulting in a fatal outcome or horses which had contact with them, were tested by real-time reverse transcription-polymerase chain reaction (RT-qPCR) for both viruses. Adopting the criterion of four-fold antibody titer difference, 165 horses (38%) presented neutralizing antibodies for flaviviruses, 89 (20.4%) for SLEV and five (1.1%) for WNV. No evidence of SLEV and WNV infection was detected by RT-qPCR and, thus, such infection could not be confirmed in the additional samples. Our findings indicate horses of Rio de Janeiro were exposed to SLEV and WNV, contributing to the current knowledge on the distribution of these viruses in Brazil.

Retrospective Investigation in Horses with Encephalitis Reveals Unnoticed Circulation of West Nile Virus in Brazil

During these past years, several studies have provided serological evidence regarding the circulation of West Nile virus (WNV) in Brazil. Despite some reports, much is still unknown regarding the genomic diversity and transmission dynamics of this virus in the country. Recently, genomic monitoring activities in horses revealed the circulation of WNV in several Brazilian regions. These findings on the paucity of genomic data reinforce the need for prompt investigation of WNV infection in horses, which may precede human cases of encephalitis in Brazil. Thus, in this study, we retrospectively screened 54 suspicious WNV samples collected between 2017 and 2020 from the spinal cord and brain of horses with encephalitis and generated three new WNV genomes from the Ceará and Bahia states, located in the northeastern region of Brazil. The Bayesian reconstruction revealed that at least two independent introduction events occurred in Brazil. The first introduction event appears to be likely related to the North American outbreak, and was estimated to have occurred in March 2013.The second introduction event appears to have occurred in September 2017 and appears to be likely related to the South American outbreak. Together, our results reinforce the importance of increasing the priority of WNV genomic monitoring in equines with encephalitis in order to track the dispersion of this emerging pathogen through the country.

West Nile Virus in the State of Ceará, Northeast Brazil

In June 2019, a horse with neurological disorder was diagnosed with West Nile virus (WNV) in Boa Viagem, a municipality in the state of Ceará, northeast Brazil. A multi-institutional task force coordinated by the Brazilian Ministry of Health was deployed to the area for case investigation. A total of 513 biological samples from 78 humans, 157 domestic animals and 278 free-ranging wild birds, as well as 853 adult mosquitoes of 22 species were tested for WNV by highly specific serological and/or molecular tests. No active circulation of WNV was detected in vertebrates or mosquitoes by molecular methods. Previous exposure to WNV was confirmed by seroconversion in domestic birds and by the detection of specific neutralizing antibodies in 44% (11/25) of equids, 20.9% (14/67) of domestic birds, 4.7% (13/278) of free-ranging wild birds, 2.6% (2/78) of humans, and 1.5% (1/65) of small ruminants. Results indicate that not only equines but also humans and different species of domestic animals and wild birds were locally exposed to WNV. The detection of neutralizing antibodies for WNV in free-ranging individuals of abundant passerine species suggests that birds commonly found in the region may have been involved as amplifying hosts in local transmission cycles of WNV.