Japanese Encephalitis, a viral disease that causes severe inflammation in the central nervous system, poses an increasing risk of emergence in the United States, according to a study led by Dr. Thomas Monath from Quigley BioPharma LLC. The study, published in the journal Viruses, highlights the potential consequences of the introduction of Japanese Encephalitis into America, including its impact on public health, agriculture, particularly the swine industry. The disease is transmitted by mosquitoes and primarily circulates in Asia and the Pacific, but the possibility of it spreading to the Americas has garnered attention due to its high mortality rate and neurological complications in survivors.
Dr. Monath and his colleagues explain that Japanese Encephalitis is spread by Culex mosquitoes, with pigs and wading birds serving as key amplifying hosts. Although humans are considered dead-end hosts (meaning they do not contribute to transmissison), the virus can still cause severe outbreaks, as seen in Asia, where Japanese Encephalitis continues to be a leading cause of viral encephalitis, causing significant fatalities each year. In addition, swine and horses are also affected, with the disease causing reproductive failure in pigs and neurological issues in horses. Dr. Monath noted, “The introduction of Japanese Encephalitis into the United States would pose a significant threat, not just to public health but to the agricultural sector, particularly the swine industry.” The disease’s potential to spread through local mosquito populations, along with climate change and increasing international trade, heightens the risk of an outbreak in America.
The possibility of Japanese Encephalitis invading the United States is further underscored by the recent spread of mosquito-borne viruses like West Nile, Zika, and chikungunya, which have already established themselves in the Americas. The geographic distribution of West Nile, which was first introduced in 1999 now includes virtually the entire continental United States, illustrating the potential for a repeat performance of the closely-related Japanese encephalitis virus. To illustrate the point, in 2022, the disease made its way to continental Australia, leading to multiple outbreaks and fatalities. This development prompted American authorities to assess the risk of Japanese Encephalitis introduction, particularly through infected mosquitoes or mosquito ova arriving via passenger aircraft or cargo shipments.
While the United States has not yet detected any cases of the disease, the presence of suitable mosquito vectors, such as Culex pipiens and Aedes albopictus, and the widespread distribution of both domestic and feral pigs make the country a receptive environment for the virus. The virus is shed by pigs in nasal/oral secretions and potentially can be transmitted directly between pigs without an intermediate mosquito vector. California, in particular, is considered at higher risk due to its proximity to international ports and its substantial pig population. “The risk of Japanese Encephalitis establishing in America is particularly high in regions where the ecological ingredients—Culex mosquitoes, avian hosts, and feral pigs—are prevalent,” Dr. Monath emphasized.
Despite the threat, there are preventative measures in place. The U.S. Food and Drug Administration has already approved a vaccine, IXIARO®, for use in humans. However, there is currently no licensed veterinary vaccine for swine in the United States. Pigs are a critical part of the virus’s transmission cycle, making them a key factor in controlling the spread of the disease. “The absence of a veterinary vaccine is concerning,” Dr. Monath explained, “especially given the role of pigs in amplifying Japanese Encephalitis transmission.” The study calls for additional public health measures, including enhanced mosquito control efforts around pig farms and preparedness for rapid vaccine deployment.
In Australia, the 2022 Japanese Encephalitis outbreak triggered emergency responses, including mosquito control in piggeries and vaccination of at-risk populations. The United States could face similar challenges if the virus were introduced. Agricultural authorities have begun preparedness activities to protect the swine industry, and human health measures are also in place, but experts warn that Japanese Encephalitis could become a significant public health emergency before these safeguards are fully effective.
Dr. Monath highlighted the importance of swift action in the event of an outbreak. “Rapid recognition and response are critical to preventing Japanese Encephalitis from becoming entrenched in the United States,” he said. “The risk factors are there, and the lessons from Australia should be taken seriously.” The study stresses the need for robust surveillance systems and diagnostic capabilities to detect the virus early, along with the development of new countermeasures, including antiviral drugs, an improved vaccine that provides long-term immunity in both humans and livestock and sufficient vaccine manufacturing capacity, which was a problem during the recent Australian outbreak.
As the global spread of mosquito-borne diseases continues to rise, the emergence of Japanese Encephalitis in America remains a real possibility. Ensuring that the necessary preventative measures are in place is essential to mitigating the potential impact of this deadly virus on public health and agriculture.
Journal Reference
Monath, T.P. “Japanese Encephalitis: Risk of Emergence in the United States and the Resulting Impact.” Viruses, 2024. DOI: https://doi.org/10.3390/v16010054
About the Author
Dr. Thomas Monath is an internationally known virologist and vaccinologist. He is especially well known for his work on viral encephalitis and viral hemorrhagic fevers. He has 40 years’ experience in senior positions in the biotechnology industry and played a leading role in the development of five vaccines now licensed against Ebola, dengue, Japanese encephalitis and smallpox and a veterinary vaccine against West Nile virus. Before joining industry, Tom served in the US Army and US Public Health Service for 24 years. He was Director, Division of Vector-Borne Viral Diseases at the Centers for Disease Control and Chief of the Virology Division at USAMRIID. Tom received his undergraduate degree and MD from Harvard and is trained in internal medicine. He has received many prestigious awards, including the Albert B. Sabin Gold Medal, and has served on numerous government and international committees on infectious diseases, biosecurity, WHO expert committees and the National Vaccines Advisory Committee (USA) and is Past-Presient of the American Society of Tropical Medicine and Hygiene. He has published over 450 scientific papers and 6 books on arboviruses and vaccine development.
