KATHMANDU, FEBRUARY 22
Encephalitis is inflammation of the brain caused by infection or altered host immune response. Although the cause is often unknown, more than 50 organisms have been identified. It has been postulated that more than half a million people in the world are affected every year. Along with other neurological illnesses, it is also the leading cause of disability and death in the world.
Japanese encephalitis (JE) is the most common laboratory confirmed encephalitis in Asia, including Nepal. It is caused by infection of the brain by the Japanese encephalitis virus (JEV). JEV is transmitted naturally between birds and pigs by Culex mosquitos. Collected rain water in the paddy fields during the monsoon provides a suitable breeding site for the female Culex tritaeniorhynchus mosquito, which transmits the JEV in humans. Pigs are important amplifier hosts for the virus. When the mosquito population becomes adequately high, JEV transmission spills over from the mosquito-bird-pig cycle into human populations through mosquito bite.
Approximately 99 per cent of the infected people do not show symptoms. Some may develop mild undifferentiated febrile illness. The illness predominantly involves the cerebral cortex, midbrain, pons and medulla oblongata regions of the brain. Typical abnormal movements of the limb occur if basal ganglia and thalamus regions are involved. The first prodromal stage of the illness is characterised by nonspecific febrile illness, coryza, nausea and diarrhoea. The second encephalitic stage presents with a headache, vomiting, reduction in consciousness, seizures, abnormal movements and increased tone of muscle or limb weakness. The typical JE features include a dull mask-like face, wide unblinking eyes, decreased voice, tremors and cogwheel type rigidity. Most deaths occur in this stage of illness. The third stage is the convalescent stage where patients show progressive improvement.
Currently there is no definite treatment. Intravenous immunoglobulin and Minocycline are potential adjunctive therapies. Plasma exchange therapy is useful in refractory cases. Approximately 25 per cent of the patients die and 30- 69 per cent have neuropsychiatric sequelae, which is why the disease is so devastating.
In Nepal, JE has been under constant surveillance by the government since 1978. Syndromic surveillance between 1978 and 2003 reported 26,046 suspected cases. After 2004, laboratory-based surveillance by anti-JEV IgM ELI- SA testing of the serum or cerebrospinal fluid began. Until 2015, of the 17,875 suspected cases, 17 per cent were JE. However, in endemic region, JE accounted for 50 per cent of all suspected encephalitis cases. Death was seen in 20-60 per cent. Most of the patients were children.
Although sporadic cases occurred throughout the year in endemic areas, epidemics occurred during the monsoon. In Nepal, three strains of JEV, namely Nep- 1/90, B- 2524 and B- 9548 have been isolated. The female Culex mosquito is the principal vector, and pigs, ducks and horses are confirmed natural reservoirs of JEV. The cost of medicine, hospital stay and loss of earnings have been reported at Rs 152,000 for those of moderate or severe neuropsychiatric sequelae, and Rs 70,000 for those with mild or no sequelae in government hospitals for all types of encephalitis.
Immunisation against JEV began in 1999 in humans and 2001 in pigs. JE vaccine is now included in the national immunisation schedule. The numbers of JE cases have steadily fallen since then. However, the findings of high anti-JEV antibody responses in almost half of the pigs and horses and a quarter of ducks tested in a recent sero-surveillance study among animal hosts for JEV suggest very high transmission in the environment, and human cases probably are contained by the vaccine. Therefore, sporadic outbreaks of JE will occur whenever there will be any lapse in the immunisation campaign.
The JE control programme in Nepal has been challenged in many areas. Most importantly the CSF sample collection rate is very poor.
Sample storage, transport and availability of skilled human resources have also been difficult. To improve surveillance, the Nepal National Committee on Immunisation Practices has recommended test samples collection after 10 days of the onset of symptoms, CSF samples from those who have received JE vaccination, monitoring evidence of waning immunity (for requirement of booster dose of JE vaccine), disability assessment in follow-up at six months and conducting plaque reduction neutralising tests for JEV in the National Public Health Laboratory. Training of healthcare providers to support people with encephalitis needs emphasis. JE vaccination coverage is still poor. Smartphones can also be used for vaccine reminders, especially during vaccination campaigns.
Between 2006 and 2015, in 83 per cent of suspected encephalitis cases, the cause was unknown. Their identification will be important to further reduce the burden of encephalitis in Nepal. Therefore, it is now time to screen for the entire spectrum of pathogens associated with encephalitis. One way forward, with limited resources, is to test initially for common known viruses and bacteria. Another way is create bio-banks of surveillance samples and test them where and when appropriate.
Improved insight into the specific organism and pathogen-specific clinical outcome of acute encephalitis in this region is essential to guide strategies for prevention and clinical management so that evidence-based public health actions can be planned and carried out. Antibody testing for autoimmune encephalitis could be also helpful.
The World Health Organisation is at the forefront in responding to the global challenges posed by encephalitis. Hence, an integrated one-health approach of efforts of clinicians, veterinarians and entomologists would be valuable to achieve better control of JE and other types of encephalitis.
A version of this article appears in the print on February 23, 2023, of The Himalayan Times.
