New World Screwworm: Fact Sheet & SHIC Article 6/10/2026 & USDA NWS Website & SHIC/AASV NWS Webinar (8/4/2026)
New World Screwworm: Fact Sheet & SHIC Article 6/10/2026 & USDA NWS Website & SHIC/AASV NWS Webinar (8/4/2026)
The Swine Health Information Center funded a study led by Dr. Angela Bosco-Lauth and colleagues at Colorado State University to evaluate the potential for Japanese encephalitis virus to affect US swine production. Researchers assessed the ability of US mosquito species to transmit the virus, examined how different JEV genotypes affect domestic pigs, and evaluated whether vaccination against JEV or the related West Nile virus could prevent infection. Results indicate that if JEV was identified in the US, there are mosquito species that can transmit JEV to domestic pigs. Vaccination, particularly against JEV, showed promise as a strategy to reduce infection and limit transmission and could be a useful tool producers could use to prevent an outbreak.
Find the industry summary for SHIC study #24-055 here.
Key Producer Outcomes:
JEV poses a risk to US swine herds
Although JEV has not been detected in the United States, its geographic expansion and recent outbreaks in countries including Australia and China highlight the importance of preparedness and prevention strategies in the US. Pigs are susceptible to JEV, can serve as an amplifying host for the virus JEV, and an introduction could create animal and public health concerns. The objectives of this proposal were to evaluate the competence of mosquitoes in the US to carry and transmit the virus, determine how different genotypes of the virus behave in domestic swine, and evaluate the potential for vaccination against either JEV or related West Nile virus to prevent infection in pigs. Understanding these various factors is essential to understanding JEV transmission risk and limiting potential outbreaks.
The study had four main objectives 1) evaluate vector competence of JEV genotypes I-IV in the three primary WNV mosquito vectors in the U.S.: Culex pipiens, Cx. tarsalis, and Cx. quinquefasciatus, 2) determine susceptibility and pathogenesis of JEV genotypes I-IV in domestic swine, 3) assess protective efficacy of vaccination using a commercially available equine WNV vaccine and an attenuated vaccine strain of JEV (SA-14-14-2) against JEV infection in domestic swine, and 4) evaluate cross-neutralization of porcine antibodies against JEV genotypes I-IV, WNV, and SLEV.
To address whether the three US mosquito species were competent vector transmit JEV, mosquitoes were fed spiked bloodmeals each containing one of the four genotypes (GI, GII, GIII, GIV) and tested for the presence and dissemination of the virus. The next step was to perform experimental infections in pigs approximately five weeks of age to determine how different genotypes behaved in pigs. Pigs were observed daily for lethargy, ataxia, fever and seizure. Sampling of whole blood and tissues at necropsy were performed for each pig. For the vaccination studies, pigs were vaccinated at five weeks of age and again at eight weeks of age. Blood was collected pre- and post-vaccination against either JEV or WNV and subsequently infected them with JEV genotypes 1 or 4 after vaccination. Pigs were challenged with JEV 14 days post-final vaccination.
US mosquitoes can be competent vectors for JEV transmission
The study determined that there are three major US mosquito species competent to transmit multiple JEV genotypes, including genotype IV, which has been associated with established transmission in Australia. Transmission rates varied between 0-20% in both Cx. pipiens and Cx. quinquefasciatus and ranging from 8-28% in Cx. tarsalis. The mosquito species evaluated are distributed across the United States, indicating that the potential for transmission is not necessarily limited to one geographic region.
These findings reinforce the importance of mosquito management as a potential component of swine herd protection. If JEV were introduced, reducing mosquito exposure could help limit opportunities for the virus to move between susceptible animals and mosquito populations.
Pigs are susceptible, even when clinical signs are limited
Researchers found that domestic pigs were susceptible to all four JEV genotypes evaluated. In experimentally infected weanling pigs, however, for all genotypes, clinical disease was minimal or absent, and viremia (virus in blood) was present in the first few days post-infection with rapid clearance. Animals experienced temporary increases in body temperature, but these were resolved within several days, and researchers observed no other obvious clinical signs.
Researchers were able to detect viruses from brain tissue during acute infection and from tonsil tissue at later time points post-infection. Examination of brain tissues identified lesions in some infected pigs despite the limited outward signs of illness.
These findings have important implications for disease preparedness. The absence of pronounced clinical signs does not necessarily mean infection has not occurred. The researchers noted that neonatal pigs and pregnant sows may be more likely to experience clinical disease than the young pigs evaluated in this study. Further work would help clarify the effects of JEV across different production stages and animal populations.
Vaccination demonstrates protective potential
JEV vaccination protected against clinical disease and prevented viremia in JEV infected pigs. WNV vaccination prevented clinical disease and reduced viremia in infected pigs compared to controls. Cross-neutralization assays confirm that antibodies against either JEV or WNV provide at least partial protection against infection with the heterologous virus.
Pigs receiving the experimental live-attenuated JEV vaccine developed neutralizing antibodies and were protected against clinical disease and detectable viremia following challenge with JEV. No adverse vaccine reactions were observed in the study animals.
Researchers also evaluated a commercially available inactivated WNV vaccine developed for horses. While this vaccine did not completely prevent JEV infection in pigs, it reduced the amount of virus detected in the bloodstream compared with unvaccinated controls. The findings suggest that vaccination against a related virus could offer partial protection under certain circumstances.
Antibody testing further demonstrated cross-protection between JEV genotypes I and IV and between JEV and WNV. Pigs exposed to either JEV genotype developed antibodies capable of neutralizing the other genotype and WNV. This cross-reactivity may provide some protection against related viruses, although it also highlights considerations for diagnostic testing.
Implications for pork producers
The research confirms a credible pathway for JEV introduction and transmission in the United States while also identifying potential tools to mitigate risk. US mosquito populations can transmit viruses, domestic pigs are susceptible, and infection may occur without pronounced clinical signs in young animals.
For pork producers, the results support maintaining awareness of emerging foreign animal diseases and considering mosquito control as part of broader herd health and biosecurity planning. Vaccination could also become a useful intervention if JEV were detected, with the study demonstrating strong protection from JEV vaccination and partial protection from WNV vaccination.
Proactive preparation is valuable even though JEV is not established in the US. Understanding transmission risks and potential prevention strategies gives producers and veterinarians a stronger foundation for responding to a possible introduction and protecting herd health.
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 https://www.swinehealth.org or contact Dr. Lisa Becton at [email protected].