Study suggests more mosquito vectors capable of spreading Japanese encephalitis virus

A recent systematic review by Kansas State University in collaboration with the United States Department of Agriculture (USDA) Agriculture Research Service on Japanese encephalitis virus (JEV) vector and host competence found that at least 9 additional mosquito species may be potential vectors for JEV.^1,2 The pathogen, which is transmitted via infected mosquitoes, affects many animals, including wild birds, horses, swine, and people.³

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“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 authors wrote in the study.¹ “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.”

According to the Swine Health Information Center (SHIC), although the JEV primarily circulates between mosquitoes and waterbirds, it poses a significant threat to human and animal health.² In swine, all ages are susceptible to the disease.3 Infected pigs can also pass the virus to mosquitoes.3 According to Iowa State University, JEV outbreaks in humans are often linked to areas where infected pigs and mosquitoes coexist.3 Other animals that may serve as reservoirs include snakes, lizards, many wild birds, and chickens.³

In swine, JEV can cause reproductive issues, including stillbirths and abortions. Although the virus has not been detected in the US, its global spread (including a recent expansion into mainland Australia²), along with suitable vectors and hosts in the US, increases the risk of entry.²

The recent systematic review, which received funding from SHIC, built on a 2018 analysis and included only experimental studies from 2016 to 2023. The review found that nearly half (45.4%) of 51 mosquito species tested experimentally became infected after being exposed to JEV. “This highlights the significant potential for virus amplification in mosquito populations around livestock, including pig farms,” wrote SHIC in a report.²

Additionally, the transmission rate for the disease across 30 experimentally tested mosquito species was 22.7%, meaning approximately 1 in 4 infected mosquito species could pass the virus to animals and humans. Among all mosquito species that were experimentally tested, the Culex species showed the highest rates of infection and transmission at 51.9% and 27.8%, respectively. According to SHIC, this mosquito species is commonly found in human and livestock environments, representing “high-priority targets for surveillance and control.”²

Moreover, the study identified 9 to 12 additional mosquito species beyond the initial potential mosquito vectors found in the previous review, that showed to be competent vectors for JEV.^1,2

The authors of the study noted that understanding mosquito abundance, host preference, longevity, geographical ranges, and co-occurrences with human settings or animal reservoirs are also important for determining JEV transmission and risk. “Moreover, data on JEV dissemination and transmission rates in vectors are crucial for assessing the risk of JEV introduction and transmission within new geographical areas previously free of the virus,” they added.¹

References

1. Edache S, Dixon AL, Oliveira ARS, et al. Mosquito vector competence for Japanese encephalitis virus: a systematic review and meta-analysis update. Parasites & Vectors. 2025;18(1):191. doi:10.1186/s13071-025-06843-7
2. SHIC-funded research reveals JEV threat remains high with mosquito control essential. Swine Health Information Center. News release. July 25, 2025. Accessed August 26, 2025. https://www.swinehealth.org/shic-funded-research-reveals-jev-threat-remains-high-with-mosquito-control-essential/
3. Japanese B encephalitis. Iowa State University. Accessed August 26, 2025. https://webhost-dev.cvm.iastate.edu/swine-disease-manual/index-of-diseases/japanese-b-encephalitis/#:~:text=Mosquitoes%20become%20infected%20by%20feeding,many%20wild%20birds%20and%20chickens.