Japanese encephalitis virus (JEV) poses a significant threat to the global swine industry. According to a recent study led by Natalia Cernicchiaro at Kansas State University in collaboration with USDA Agricultural Research Service scientists at the National Bio and Agro-Defense Facility, nine additional mosquito species have been confirmed as potential vectors for the virus.
Japanese encephalitis is an emerging zoonotic disease transmitted by JEV-infected mosquitos. The Swine Health Information Center (SHIC) funded this systematic literature review and meta-analysis on JEV vector and host competence that adds to the knowledge of this significant human and animal health threat.
“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,” the researchers explain. “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.”
Transmission Risk Grows
The results reveal that 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 published by Parasites & Vectors emphasize the need for robust surveillance and integrated mosquito management strategies for U.S. pork producers.
While JEV has not been detected in the U.S., its recent spread globally, along with the presence of competent mosquito vectors and susceptible hosts in the U.S., elevates the risk of incursion, SHIC reports.
The virus is primarily maintained between mosquitoes and waterbirds, but occasionally spills over into swine, horses and humans. In swine, JEV infection results in reproductive disease outcomes on sow farms, such as stillbirths, mummified fetuses and abortions.
The updated meta-analysis revealed several crucial points for U.S. 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. SHIC says 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 rates at 51.9% and transmission at 27.8% 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,” SHIC reports.
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,” SHIC says.
Where Should We Focus Effort?
Data on which mosquito species are most likely to carry and spread the virus can help focus surveillance and control efforts on the species that pose the greatest risk, SHIC says. Some mosquito species can serve as early warning signals of JEV activity and may play key roles as primary or secondary vectors. However, researchers say 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,” SHIC adds. “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.”
