West Nile Fever

Researchers demonstrate the contribution of climate change to the spatial expansion of West Nile virus in Europe, a virus that constitutes a new public health threat in the continent. Their findings highlight a notable increase in the area ecologically suitable for the virus circulation since the beginning of last century and an increase in the human population at risk of exposure, due in part to climate change. In a study published this week in the journal Nature Communications, researchers from the Spatial Epidemiology Lab (SpELL, ) of the University of Brussels (ULB) and their collaborators demonstrate the contribution of climate change to the spatial expansion of West Nile virus in Europe, a virus that constitutes a new public health threat in the continent. Their findings highlight a notable increase in the area ecologically suitable for the virus circulation since the beginning of last century and an increase in the human population at risk of exposure, due in part to climate change. West Nile virus is an emerging pathogen in Europe and represents a public health threat in previously non-affected European countries. Occurring in a cycle involving transmission between bird and mosquito species, this virus can be transmitted to humans by mosquitoes and induce West Nile fever. While most human infections are asymptomatic, around 25% of victims develop symptoms such as fever and headache, and less than 1% develop more severe neurological complications that can lead to death. While climate change has been cited as a potential driver of the emergence of West Nile virus on the European continent, a formal evaluation of this causal relationship was lacking. In a study published in the journal Nature Communications, researchers from the University of Brussels (ULB) -- Diana Erazo and Simon Dellicour from the Spatial Epidemiology Laboratory -- and their collaborators investigated the extent to which West Nile virus spatial expansion in Europe can be attributed to climate change while accounting for other direct human influences such as land use and human population changes. To this end, they adopted a machine learning approach to predict the risk of local West Nile virus circulation given local environmental conditions. They subsequently unravelled the isolated effect of climate change by comparing factual simulations to a counterfactual where climate change had been removed. "Our results point towards a significant responsibility of climate change in the establishment of West Nile virus in the south-eastern part of the continent. In particular, we identify that current West Nile virus hotspots in Europe are most likely to be attributed to climate change" explains Diana Erazo, first author of the study and post-doctoral researcher at the Spatial Epidemiology Lab. "Our results also demonstrate a recent and drastic increase of the population at risk of exposure. While this increase is partly due to an increase in population density, we show that climate change has also been a critical factor driving the risk of West Nile virus exposure in Europe." Made possible by the collaboration of researchers with different expertise, the study is also the result of an interdisciplinary approach. "Our work illustrates how climate data could be effectively used in an epidemiological context by estimating the past and present-day ecological suitability of the virus, filling another analytical gap between climate science and epidemiology" says Simon Dellicour, supervisor of the study and head of the Spatial Epidemiology Lab. "With climate change emerging as a critical public health challenge, future work should explore the evolution of infectious disease distributions under different scenarios of future climate change to inform surveillance and intervention strategies."

Scientists have developed vaccine will protect farmed saltwater crocodiles from West Nile virus (WNV), providing economic and biodiversity benefits to northern Australia. A University of Queensland developed vaccine will protect farmed saltwater crocodiles from West Nile virus (WNV), providing economic and biodiversity benefits to northern Australia. Dr Jody Hobson-Peters from UQ's School of Chemistry and Molecular Biosciences said the virus, which is prevalent in high rainfall years, threatens the commercial viability of the $100million a year crocodile hide farming industry. "Crocs infected with the local strain of WNV, known as Kunjin virus, develop small skin lesions called pix, which renders their hide unsaleable," Dr Hobson-Peters said. "WNV infection can affect up to 30 per cent of croc hides, costing the industry as much as $10million in a single year. "If we were to experience consecutive years of high rainfall, the virus could render the crocodile farming industry unviable and threaten the current conservation model. "It would also disrupt an industry that contributes to Indigenous livelihoods and economic development opportunities in the Northern Territory and Far North Queensland." UQ's Professor Roy Hall said the vaccine is based on a benign 'Binjari' virus isolated from Australian mosquitoes and is the first of its kind to achieve proven safety and efficacy in crocodiles. "We have demonstrated that our vaccine induces a robust, immune response in vaccinated animals after two doses," Professor Hall said. "Crocodiles that received the vaccine developed strong protective immunity against WNV, without the virus replicating." UQ has received funding from the Australian Research Council to work with the Centre for Crocodile Research to assess the vaccine's long-term performance. Director of the Darwin-based Centre for Crocodile Research, Dr Sally Isberg said the surge in the wild crocodile population in recent decades was made possible by the farmed crocodile industry. "It's not just an economic threat we're facing -- croc farming has played a pivotal role in returning this apex predator from the brink of extinction over the past 60 years," Dr Isberg said. "The captive-breeding industry promotes sustainable practices and places an economic value on crocodiles, meaning communities living with or near crocs are more tolerant of their presence in waterways and are incentivised to protect their habitats. "As a result, other species that co-inhabit with crocs are protected, such as the brolga, jabiru and long-necked turtle." The research is published in npj Vaccines, and is an outcome of UQ's Dr Gervais Habarugira's PhD thesis. The team is working with the Australian veterinary vaccine company Treidlia BioVet, to develop a commercial version of the vaccine for wider industry use. UQ acknowledges the contributions of the Australian crocodile industry and biotechnology company Vaxine Pty Ltd.

A mosquito known only by its scientific name, Culex lactator, is the latest to establish in the Sunshine State, according to a new study. Another new mosquito species has made its way across the tropics into Florida, making a permanent home in at least three counties. Scientists are concerned because of the rate of new mosquitoes arriving in Florida and the potential for them to transmit mosquito-borne diseases. A mosquito known only by its scientific name, Culex lactator, is the latest to establish in the Sunshine State, according to a new study published in the Journal of Medical Entomology by faculty at the UF/IFAS Florida Medical Entomology Laboratory (UF/IFAS FMEL). This species was first discovered in Miami-Dade County in 2018 by UF/IFAS faculty while they hunted for other nonnative mosquitoes. Since then, thriving populations have been recorded in Miami-Dade, Collier and Lee counties. Scientists are concerned there hasn't been enough research on the species and their potential disease risk. "There are about 90 mosquito species living in Florida, and that list is growing as new mosquito species are introduced to the state from elsewhere in the world," said Lawrence Reeves, lead author of the study and an assistant professor and mosquito biologist at the UF/IFAS research center in Vero Beach. Mosquitoes are among the most studied insects because they can transmit diseases. However, there are large gaps of knowledge, said Reeves. "That's particularly true for species from the tropical forests, where mosquitoes are diverse and understudied," he said. "Introductions of new mosquito species like this are concerning because many of our greatest mosquito-related challenges are the result of nonnative mosquitoes, and in a case like this, it's difficult to anticipate what to expect when we know so little about a mosquito species." Globally, there are more than 3,600 types of mosquitoes. When a new mosquito is found in Florida, it could be any of these species. Reeves and his team used DNA analysis and other tools to not only discover they had found a new mosquito species, but to identify it as Culex lactator. Culex lactator is found in Central America and northern South America and is a member of the Culex group of mosquitoes. This group includes important species that transmit the West Nile and St. Louis encephalitis viruses, but it is unclear whether Culex lactator will contribute to the transmission of these viruses in Florida. Every year, Florida faces challenges from mosquito-transmitted diseases like West Nile virus, eastern equine encephalitis virus, dengue virus, chikungunya virus and others, explained Reeves. "It's too early to know whether Culex lactator will exacerbate these challenges, but the implications are often difficult to predict because not all mosquito species are equally capable of transmitting a particular virus or other pathogen," said Reeves. Each mosquito-borne virus is transmitted by only certain mosquito species, said Reeves. "We need to be vigilant for introductions of new mosquito species because each introduction comes with the possibility that the introduced species will facilitate the transmission of a mosquito-transmitted disease," he said. The initial specimens of Culex lactatorwere collected in 2018 from rural sites in southern Miami-Dade County, south of Florida City, followed by additional adult and immature specimens collected through 2022 in the same locations. Each set of mosquitoes were collected from traps set by associate professor Nathan Burkett-Cadena, doctoral student Kristin Sloyer and Reeves while looking for other recently introduced mosquitoes. In 2022, scientists with the Collier Mosquito Control District and Lee County Mosquito Control District found Culex lactator in their counties, indicating that Culex lactator has likely spread from its initial point of introduction. Currently, Culex lactator is known to live in Collier County -- south and west of Naples -- Lee County, west of Fort Myers, and in the Homestead area of Miami-Dade County, though it may have also spread elsewhere in the state, said Reeves. "Culex lactator is physically similar to mosquito species already known from Florida. It looks like other more common mosquito species," said Reeves. "Because of that similarity, the presence of Culex lactator in an area can be easy to miss." Reeves and his team stress it's important to monitor for Culex lactator as it is likely to spread within the state into areas that are environmentally suitable. Florida's proximity to the tropics and climate conditions make it ideal for nonnative mosquito species. Scientists are concerned about the rate and frequency of new species establishing in Florida. As many as 17 nonnative mosquito species are established in the state. Researchers stress that the detections of nonnative mosquito species are increasingly frequent, with 11 of 17 nonnative species first reported in the past two decades, and six of these 17 detected in only the past five years, said Reeves. The mosquitoes Aedes aegypti, Aedes albopictus, and Culex quinquefasciatus -- among the most important disease vectors in the United States -- like Culex lactator, are nonnative species, introduced from the tropics. "Climate change may improve the chances of tropical mosquito species becoming established once they make it to Florida if the state becomes warmer," adds Reeves. "Increasing storm frequency and intensity could also blow in more mosquitoes and other species from the Caribbean, Central America and elsewhere."