Porcine Japanese Encephalitis

Porcine Japanese encephalitis (JE) is a significant viral disease that affects pigs and poses a considerable threat to the swine industry worldwide. The disease is caused by the Japanese encephalitis virus (JEV), a member of the Flaviviridae family. JE not only results in significant economic losses due to reduced productivity and mortality in pig populations but also raises concerns for public health due to its potential zoonotic transmission.

Cause and Effect

Porcine JE finds its origin in the transmission of JEV. The pivotal role of transmission is played by mosquitoes, particularly those from the Culex species, serving as primary vectors for the virus. These mosquitoes acquire the virus by feeding on infected birds, which serve as the natural reservoir hosts. Pigs function as amplifying hosts, contracting the infection through mosquito bites and subsequently developing viremia. This viremia amplifies the virus within their bloodstream, thereby elevating the potential for transmission to other susceptible animals. In rare instances, transmission to humans can also occur.

Fig. 1 Diagram of the transmission cycle of JEV in natural hosts.¹

Etiology

JEV is classified within the Flavivirusgenus, sharing lineage with notable pathogens such as the Zika virus, dengue virus, and West Nile virus. This virus presents as an enveloped, positive-sense, single-stranded RNA virus. Its predilection lies in the central nervous system, inducing inflammation of the brain (encephalitis) upon infecting individuals.

Fig. 2 Structure diagram of JEV under an electron microscope.²

Signs and Symptoms

The clinical manifestations of porcine JE exhibit variance contingent on the pig's age and the intensity of the infection.

• In piglets, observable indications encompass fever, anorexia, and lethargy. Additionally, neurologic symptoms like tremors, ataxia, and paralysis might manifest.
• Boars, in particular, can exhibit orchitis after a fever. Typically, one side of the testis becomes enlarged. A subset of afflicted pigs might experience testicular atrophy, rendering them incapable of breeding.
• Pregnant sows could undergo abortion, preterm delivery, or delayed parturition. In such cases, most fetuses tend to be stillborn or mummified. These instances might be accompanied by signs of fetal edema, meningeal congestion, subcutaneous edema, congestion of lymph nodes, as well as necrosis in the liver and spleen.

Is It a Zoonotic Disease?

Porcine JE is primarily a disease of pigs, but it is important to note that JEV can infect humans as well. However, human infections are relatively rare and usually occur in areas where the virus is endemic. Humans are considered incidental hosts, and transmission typically occurs through mosquito bites rather than direct pig-to-human contact. It is important to maintain proper precautions, such as mosquito control measures, to reduce the risk of zoonotic transmission.

Diagnosis of JEV

BioVenic provides customers with accurate and timely laboratory diagnostics solutions to help confirm the presence of JEV and rule out other potential causes of similar clinical symptoms. Laboratory diagnosis involves the detection of viral antigens or genetic material in pig samples, such as blood or tissue. We typically provide our clients with the following veterinary diagnostics development services,

• Japanese Encephalitis Virus Isolation
• Veterinary ELISA Development
• Veterinary PCR Kit Development

Treatment

Currently, there exists no targeted antiviral remedy for porcine JE. As of now, treatment primarily revolves around addressing symptoms through symptomatic interventions based on the presented clinical manifestations.

Fig. 3 Potential therapeutic targets for JEV.³

Prevention and Control

The prevention and control of JE are mainly achieved through vaccination and the implementation of vector control measures.

• Vaccination: Vaccination is considered the most effective measure to protect pigs from JEV infection. BioVenic can develop in-house vaccines for customers using inactivated or attenuated JEV strains. Pigs are usually vaccinated twice 2-3 weeks before the mosquito season begins.
• Vector control measures: Implementing vector control measures, such as mosquito control programs and proper waste management.
• In addition, regular screening of boars for semen quality and artificial insemination of sows with semen from uninfected boars can also have less impact on herd fertility.

BioVenic is recognized as the authority in animal diagnostics and we remain committed to advancing the understanding and management of porcine Japanese encephalitis. We support the diagnosis, prevention, control, and treatment of disease by actively exploring creative solutions. Please feel free to contact us for more details and discussion.

References

1. Roberts, Akanksha, et al. "Japanese encephalitis virus: a review on emerging diagnostic techniques." Frontiers in Bioscience-Landmark 25.10 (2020): 1875-1893.
2. Luca, Vincent C., et al. "Crystal structure of the Japanese encephalitis virus envelope protein." Journal of virology 86.4 (2012): 2337-2346.
3. Kumar, Sanjay, et al. "Molecular pathogenesis of Japanese encephalitis and possible therapeutic strategies." Archives of Virology 167.9 (2022): 1739-1762.