Japanese encephalitis, a viral disease that causes severe inflammation in the central nervous system, is at increasing risk in the United States, according to a study led by Dr. Thomas Monath of Quigley BioPharma LLC. The study, published in the journal Viruses, highlights the potential consequences of the introduction of Japanese encephalitis to the United States, including its impact on public health, agriculture and, in particular, the pork industry. The disease is transmitted by mosquitoes and circulates mainly in Asia and the Pacific, but the possibility of its spread to the Americas has attracted attention due to its high mortality rate and neurological complications in survivors.
Dr. Monath and his colleagues explain that Japanese encephalitis is transmitted by Culex mosquitoes, with pigs and wading birds being the main amplification hosts. Although humans are considered dead-end hosts (meaning they do not contribute to transmission), the virus can still cause severe outbreaks, as seen in Asia, where Japanese encephalitis remains a leading cause of viral encephalitis, causing significant deaths each year. Additionally, pigs and horses are also affected, with the disease causing reproductive failure in pigs and neurological problems in horses. Dr. Monath noted, “The introduction of Japanese encephalitis into the United States would pose a significant threat, not only to public health but also to the agricultural sector, particularly the swine industry.” The disease's potential to spread through local mosquito populations, along with climate change and increased international trade, increase the risk of an outbreak in the United States.
The possibility of Japanese encephalitis invading the United States is further underscored by the recent spread of mosquito-borne viruses such as 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 recurrence of the closely related Japanese encephalitis virus. To illustrate this point, in 2022, the disease reached mainland Australia, causing multiple outbreaks and deaths. This development led US authorities to evaluate the risk of introduction of Japanese encephalitis, particularly through infected mosquitoes or mosquito eggs 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 albopictusand the wide distribution of domestic and wild pigs make the country a receptive environment for the virus. The virus is shed by pigs through nasal/oral secretions and can potentially be transmitted directly between pigs without an intermediate mosquito vector. California, in particular, is considered most at risk due to its proximity to international ports and its significant swine population. “The risk of Japanese encephalitis becoming established in the United States is particularly high in regions where green ingredients (Culex mosquitoes, host birds, and wild boar) are prevalent,” Dr. Monath emphasized.
Despite the threat, there are preventive measures. The U.S. Food and Drug Administration has already approved one vaccine, IXIARO®, for use in humans. However, there is currently no licensed veterinary vaccine for pigs in the United States. Pigs are a critical part of the virus 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 the transmission of Japanese encephalitis.” The study calls for additional public health measures, including increased mosquito control efforts on pig farms and preparation for rapid vaccine rollout.
In Australia, the 2022 Japanese encephalitis outbreak triggered emergency responses, including mosquito control in pigsties 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 pork industry and human health measures have also been implemented, but experts warn that Japanese encephalitis could become a major public health emergency before these safeguards are fully effective.
Dr Monath stressed the importance of acting quickly in the event of an outbreak. “Rapid recognition and response are critical to preventing Japanese encephalitis from taking hold in the United States,” he said. “The risk factors are there and the lessons from Australia must be taken seriously.” The study highlights 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 increase, the emergence of Japanese encephalitis in the United States remains a real possibility. Ensuring that necessary preventive measures are implemented is essential to mitigate the potential impact of this deadly virus on public health and agriculture.
Magazine reference
Monath, T.P. “Japanese encephalitis: risk of emergence in the United States and resulting impact.” Viruses, 2024. DOI: https://doi.org/10.3390/v16010054
About the author
Dr. Thomas Monath He is an internationally renowned virologist and vaccinologist. He is especially known for his work on viral encephalitis and viral hemorrhagic fevers. He has 40 years of experience in senior positions in the biotechnology industry and played a leading role in the development of five currently authorized vaccines against Ebola, dengue, Japanese encephalitis and smallpox, and a veterinary vaccine against West Nile virus. Prior to joining the industry, Tom served in the US Army and Public Health Service for 24 years. He was Director of the Division of Vector-Borne Viral Diseases at the Centers for Disease Control and Chief of the Division of Virology 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, biosafety, WHO expert committees, and the US National Advisory Committee on Vaccines. ) and is past president of the American Society of Tropical Medicine and Hygiene. He has published more than 450 scientific articles and 6 books on arboviruses and vaccine development.
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