Japanese encephalitis, a mosquito-borne illness endemic to the Philippines and which is fatal in nearly 3 out of 10 severe cases, may be on the rise, a World Health Organization (WHO) report said, after the discovery last year by Chinese researchers that the current vaccine may not be effective against a re-emerging strain of the virus.
Three billion people are at risk from Japanese encephalitis, the WHO report said, with an average fatality rate of 3 out of every 10 patients who exhibit severe symptoms, which affect about one out of every 250 people who contract the illness. There are about 68,000 severe cases of Japanese encephalitis worldwide annually, most in Asia.
The WHO also said that nearly all survivors of the illness may experience permanent effects, with 30 to 50 percent of those who survive left with severe permanent disabilities. About 20 percent of victims experience convulsions, cognitive, and language problems, while 30 percent may suffer from motor deficiencies. Other survivors may suffer less severe learning disabilities or behavioral problems.
Japanese encephalitis is a mosquito-transmitted disease carried by the Culex tritaeniorhynchus, a mosquito endemic to tropical and sub-tropical countries like the Philippines.
The disease is present in all regions of the Philippines, as well as throughout most of Asia.
The WHO said that children below the age of 15 are most susceptible to the disease, with children younger than four years being nine times more likely to be infected with Japanese encephalitis than older children. About 15 percent of Japanese encephalitis cases are adult victims.
The most recent case of Japanese encephalitis in the Philippines was a 52-year-old man in Davao City in July 2016. Davao City Health Officer Dr. Josephine Villafuerte said the patient survived, but now suffers from neurological diseases, including memory lapses.
Japanese encephalitis is considered incurable, but can be prevented through vaccination and mosquito abatement procedures. A WHO-recommended vaccine was licensed for use in the Philippines in 2013, and is part of the Department of Health’s vaccine program for school-aged children, similar to programs in other countries.
New strain emerging
However, researchers in China discovered last year that the current vaccine might not provide protection against an emerging strain of the Japanese encephalitis virus.
A team led by Dr. Liang Guodong, from the Chinese Center for Disease Control and Prevention in Beijing discovered that the rarest of the five known Japanese encephalitis genomes, called G5, has been found with increasing frequency since it reemerged in South Korea in 2009. The genome was first identified in 1951, but had not been detected again for more than 50 years.
The present vaccines are based on the more common G3 genome, and provide adequate protection against the G1 to G4 varieties of the virus. However, the researchers discovered that only 35 to 65 percent of patients
developed antibodies to the G5 strain after being vaccinated.
The researchers’ findings were published in PLOS Neglected Tropical Diseases.
While they pointed out that the number of G5-strain Japanese encephalitis infections is not known yet, they recommended that health officials increase their vigilance and testing of possible Japanese encephalitis cases, even those that are considered mild, to determine the extent of the new strain to help development of a new vaccine.
MICAH YVANA M. VARDELEON