28 December 2022

4 minute read

By: Global Ag Media

North America

In February 2022, an outbreak of Japanese encephalitis in Australia drew the attention of pork producers, veterinarians, animal and public health government officials, and allied industries around the world. In the US, the pork industry began monitoring Australia’s situation and response, ramping up preparedness activities immediately. Some of these efforts were shared during a symposium held in October, hosted by the Center for the Ecology of Infectious Disease at the University of Georgia, sponsored in part by the Swine Health Information Center. 

Of those attending virtually or in person, 30 were with USDA-affiliated agencies and Michael Neafsey, One Health Coordinator for USDA APHIS, was an invited speaker. He said the likelihood of JEV being found in the US is low, however, taken seriously by his agency. If established, substantial human and animal health issues along with significant economic impacts are expected outcomes. As with West Nile virus, eradication would be difficult if not impossible if JEV becomes established. Neafsey said the most likely mechanism for JEV introduction and establishment of infection would be through infected mosquitoes and expressed concern about delayed recognition of infection in livestock due to the disease’s non-specific presentation.

Neafsey outlined USDA APHIS Veterinary Services feral swine sample collection programs and pre-existing relationships with local resources as key to JEV surveillance efforts. Veterinary Services staff also have pre-established communications chains.

If suspected, JEV diagnosis will come from virus isolation and molecular tools, according to Dr. Neafsey. This process will include sequencing for detection and differentiation of flaviviruses. The National Animal Health Laboratory Network along with the National Veterinary Services Laboratories in Ames, Iowa, and Plum Island, New York, will be instrumental in detection of JEV, should there be an incursion.

Existing USDA response frameworks include FAD preparedness which Dr. Neafsey said have been used to successfully detect, control, and contain diseases for many years. FAD response plans provide disease specific information and response strategies. Dr. Neafsey said USDA’s JEV disease response strategy is under review and has been removed from the agency’s website as it was outdated.

In conclusion, Neafsey outlined USDA response goals which are to detect control and contain FAD outbreaks as quickly as possible, eradicate the FAD using strategies that stabilize animal agriculture, the food supply, the economy, and protect public health and the environment. Goals also include providing science and risk-based approaches and systems to facilitate continuity of business for noninfected animals and noncontaminated animal products.

Examining JEV Introduction Risk in the US

Natalia Cernicchiaro, Kansas State University, presented information on the risk of introduction of JEV in the continental US. She noted that the US shares similar climate and environmental conditions with countries where JEV is epidemic, that the US has competent vectors and hosts, and that there has been increased travel and trade to and from JEV-affected regions. These characteristics, along with the lack of active JEV surveillance in the US, make this region at risk to a JEV incursion.

This risk assessment addressed:

• Probability of entry
• Probability of transmission
• Probability of establishment
• Extent of spread
• Likelihood of persistence
• Impact of disease

Based on the risk assessment, aircraft and cargo ships were the most likely pathways of JEV introduction via infected adult mosquitoes. The probability of introduction of JEV through infected adult mosquitoes via aircrafts was deemed very high whereas the probability of entry via ships/containers was considered of low to moderate risk. Although the probability of transmission was deemed of variable risk, the probability of JEV establishment in the US is considered negligible. This is due to low availability of amplifying hosts (pigs) and the limited contact rates between infected mosquitoes and hosts in airports and seaports, areas at high risk of introduction of infected vectors.

Presently, Cernicchiaro and her team are reassessing pathways and noted the need to re-consider vector-free transmission, which has been suggested due to some experimental circumstances. Their work now includes study of the role of domestic and feral pigs and redefining regions of introduction, adding ecosystems and information on distribution and density of commercial and feral pig populations. Their work will be ongoing due to changing conditions including population growth, urbanization, increased animal movement, climate effects, and habitat modification. Changes in their model assumptions will likely lead to changes in introduction probability.