A recent study funded by the Swine Health Information Center underscores the significant threat Japanese encephalitis virus (JEV) poses to the global swine industry. The study, led by Dr. Natalia Cernicchiaro at Kansas State University, in collaboration with USDA Agricultural Research Service scientists at the National Bio and Agro-Defense Facility, included a systematic literature review and meta-analysis on JEV vector and host competence. Key findings from experimental studies reveal that at least nine additional mosquito species can be potential vectors for JEV, nearly half of the mosquitoes exposed to JEV became infected, and that one in four infected mosquitoes can transmit JEV to hosts. Culex species of mosquitos may pose the greatest risk to humans and animals, including swine. Findings emphasize the need for robust surveillance and integrated mosquito management strategies for US pork producers.
The full report published by Parasites & Vectors can be accessed here.
Japanese encephalitis is an emerging zoonotic disease transmitted by JEV-infected mosquitos. It is considered a significant human and animal health threat. The virus is primarily maintained in its natural life cycle between mosquitoes and waterbirds, while occasionally spilling over into swine, horses, and humans. JEV infections in swine result in reproductive disease outcomes on sow farms, such as stillbirths, mummified fetuses, and abortions. While JEV has not been detected in the US, its recent spread globally, coupled with the presence of competent mosquito vectors and susceptible hosts in the US, elevates the risk of incursion.
Considering the recent expansion of JEV into mainland Australia and increased global research activity, this systematic review summarizes new experimental data on mosquito vector competence published between 2016 and 2023, building on a 2018 review previously published by the investigators. All reports included in the review were peer-reviewed literature and screened for relevance to vector competence, with a focus on JEV infection, dissemination, and transmission rates as the primary outcomes of interest. The study population was limited to mosquito vectors, and only experimental studies were eligible.
The updated meta-analysis revealed several crucial points for US pork producers and stakeholders to consider. First, the study found an overall JEV infection rate of 45.4% across 51 unique mosquito species, meaning that nearly half of the mosquitoes exposed to JEV in experimental settings became infected. This highlights the significant potential for virus amplification in mosquito populations around livestock, including pig farms.
The transmission rate across 30 experimentally tested mosquito species was 22.7%, indicating that roughly one in four of the tested infected mosquito species are capable of transmitting JEV to susceptible hosts, such as animals and humans. This underscores the importance of mosquito control measures in commercial swine operations to reduce the risk of an outbreak if the virus ever enters the country.
While vector competence for JEV varied by mosquito species, Culex mosquitoes exhibited the highest infection (51.9%) and transmission (27.8%) rates among all the mosquito species tested experimentally. These species are usually common in human and livestock settings, making them high-priority targets for surveillance and control.
The review identified an additional nine to 12 new mosquito species with demonstrated competence for JEV, expanding the list of potential mosquito vectors beyond those identified in the previous review. This continuous identification of new competent species emphasizes the dynamic nature of JEV epidemiology and the importance of ongoing systematic reviews to maintain up-to-date information essential for effective surveillance programs.
Data on which mosquito species are most likely to carry and spread JEV can help focus surveillance and control efforts on the species that pose the greatest risk. Some mosquito species can serve as early warning signals of JEV activity and may play key roles as primary or secondary vectors. However, infection rates alone are not enough, factors such as mosquito abundance, feeding habits, lifespan, and proximity to humans and animals are also important.
Understanding how efficiently mosquitoes spread JEV is essential for assessing the risk of the virus appearing in new areas. Identifying the species most capable of transmitting JEV allows for targeted control strategies to reduce infections and prevent the spread of the virus to vulnerable regions.
In their conclusion, the researchers state, “This review provides updated data not only on newly reported species showing competence for JEV but also on the level of competence observed in previously identified species. These findings offer valuable insights that go beyond what individual studies can provide, helping to synthesize the evidence base in a way that is accessible and actionable for policymakers, public health authorities, and disease modelers. Ultimately, the goal is to support evidence-based decision-making with the most current and comprehensive data available.”
If referencing this article’s findings, please cite the original study by Edache et al., 2025 published in Parasites & Vectors.
The Swine Health Information Center, launched in 2015 with Pork Checkoff funding, protects and enhances the health of the US swine herd by minimizing the impact of emerging disease threats through preparedness, coordinated communications, global disease monitoring, analysis of swine health data, and targeted research investments. As a conduit of information and research, SHIC encourages sharing of its publications and research. Forward, reprint, and quote SHIC material freely. For more information, visit http://www.swinehealth.org or contact Dr. Megan Niederwerder at [email protected] or Dr. Lisa Becton at [email protected].
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