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Japanese encephalitis: a preventable cause of morbidity and mortality in the Asia-Pacific

Callum Narita, Editorials and Publications Team PMSA

Japanese encephalitis is an infectious disease endemic to South-East Asia and the Pacific region. The disease, caused by the mosquito-borne Japanese encephalitis virus, can result in headaches, fevers, rigors, and gastrointestinal upset, and potentially lead to encephalitis(1). Symptoms of this include behavioural and sensory change, confusion, seizures or neurological deficit. There is no cure for Japanese encephalitis, and supportive therapy is the only care that is currently recommended. The disease has a high morbidity and mortality rate: the case-fatality rate is estimated to be 10-30%, and the risk for persistent or permanent disability is as high as 50%(2).

The virus is present in most Asian countries, particularly those that border the Pacific Ocean(3). It also affects many Pacific nations, including Papua New Guinea, Timor-Leste and the Philippines. In Australia, Japanese encephalitis has been found in the Torres Strait Islands and Northern Queensland previously(4). Despite being localised to the Asia-Pacific region, the high population densities in the area result in 57% of the global population living in endemic countries(2).

However, what makes this disease unique is the presence of an effective vaccine(1). There are estimated to be fewer than 50,000 cases per year, regardless of the high proportion of the world population living in the endemic region(2). Unfortunately, the distribution of the vaccine does not cover all regions with Japanese encephalitis, and individuals in developing nations are at a greater risk as a result. There are significant proportions of Pacific populations who have no access to the vaccine, and are instead at the mercy of mosquito prophylaxis. There are currently no vaccination programs in Papua New Guinea, the Philippines, Cambodia, or Timor-Leste(2, 3).

Japanese encephalitis is a preventable cause of encephalitis, a condition that leads to significant morbidity and mortality. Whilst the Japanese encephalitis vaccine has assisted greatly in preventing many cases of the disease, there is still more work to be done to completely eradicate this condition. This is a disappointing example of the inequality of global healthcare, as the preventative measures for Japanese encephalitis are simple, yet not being utilised in the regions that are most in need of assistance. There is little reason that external organisations and countries are unable to assist in providing vaccines to these at-risk populations.

1. Misra UK, Kalita J. Overview: japanese encephalitis. Prog Neurobiol. 2010;91(2):108-20.

2. LaBeaud A, Bashir F, King CH. Measuring the burden of arboviral diseases: the spectrum of morbidity and mortality from four prevalent infections. Population health metrics. 2011;9(1):1.

3. Campbell GL, Hills SL, Fischer M, Jacobson JA, Hoke CH, Hombach JM, et al. Estimated global incidence of Japanese encephalitis: a systematic review. Bull World Health Organ. 2011;89:766-74.

4. Ritchie SA, Rochester W. Wind-blown mosquitoes and introduction of Japanese encephalitis into Australia. Emerg Infect Dis. 2001;7(5):900.

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