Most people infected by the Japanese encephalitis virus do not develop any symptoms. However, approximately one in 200 infections result in severe brain inflammation.
Japanese encephalitis (JE) is a brain infection that infects both humans and animals. The disease is caused by a Flavivirus (a genus of viruses in the family Flaviviridae) that affects the brain, causing inflammation that is potentially fatal. Epidemics of encephalitis were described in Japan from the 1870s onwards. The JE virus was first isolated in 1935, and has subsequently been found across most of Asia.
Today, the JE virus is the leading cause of vaccine-preventable encephalitis in Asia and the western Pacific. The virus, which is commonly found in mosquitoes, pigs and wading birds, is transmitted to humans through a bite from an infected Culex tritaeniorhynchus or Culex vishnui mosquito.
Once a person is bitten by an infected mosquito and the virus enters the body, it travels to various glands where it multiplies. The virus can then enter the bloodstream and ultimately settles in the brain, where it causes serious problems. The World Health Organisation (WHO) estimates that there are approximately 50,000 cases of clinical disease per year with 10,000 deaths, predominantly in children.
How It Spreads
Mosquitoes that carry this virus circulate in a number of regions in Asia, including Japan, Korea, China, India, Thailand, Indonesia, Malaysia, Vietnam, Taiwan, and the Philippines. Circulation of the JE virus in Malaysia is linked to irrigated rice paddy fields and pig rearing. The flooding of the fields leads to a build-up of the mosquito population.
The mosquitoes act as a vector to circulate the virus and spread it to humans if they have bitten infected birds or pigs. These mosquitoes are most abundant during the warmest, rainiest months as these conditions are necessary for the mosquito breeding cycle.
Outbreaks In Malaysia
Major outbreaks of JE occurred in Langkawi in 1974 (10 cases, two deaths), Penang in 1988 (nine cases and four deaths), and in the Serian district of Sarawak in 1992 (nine cases, four deaths). In 1999, more than 50 people died and hundreds of thousands of pigs – the possible carriers of the infection – were culled after an outbreak in Perak and Negeri Sembilan.
This year, a total of 16 JE (as of June) cases have been reported nationwide since the start of the year, including four deaths, according to the Health Ministry.
Controlling The Disease
After the 1999 outbreak, the Health Ministry mounted a campaign to control the disease: 64,767 people were vaccinated, 150,000 farms and houses sprayed with insecticide, and an active programme of health education and social mobilisation were mounted in affected areas. The introduction of JE vaccination in July 2001 also reduced the number of JE cases in humans.
Signs And Symptoms
Most people infected by the Japanese encephalitis virus do not develop any symptoms. However, approximately one in 200 infections results in severe brain inflammation characterised by:
· Rapid onset of high fever
· Neck stiffness
· Seizures (fits)
· Spastic paralysis (inability to speak or control movement)
These symptoms begin to appear 6-15 days after being bitten by an infected mosquito. According to WHO, the case fatality rate can be as high as 60% among those with disease symptoms, and 30% of those who survive suffer lasting damage to the central nervous system.
There is no specific treatment for JE. Patient management focuses on supportive care (e.g. feeding, airway management, and anticonvulsants for seizure control) and management of complications. Fluids are given to decrease dehydration and medications are given to decrease fever and pain. Medications are also available to attempt to decrease brain swelling.
Patients in a coma may require mechanical assistance with breathing. The management of these cases is usually in the Intensive Care Unit (ICU).
Vaccination of high risk groups of the human population, e.g. pig farmers, people staying in or near the pig farms up to a radius of 2km and young children is recommended. Encephalitis occurs mainly in young children because older children and adults have usually been infected and are immune. A hospital-based surveillance system for JE in Sarawak from 1997-2006 found that 92% of 133 cases were children aged 12 years or younger.
Under the National Immunisation Programme, primary immunisations are administered to children in two doses given four weeks apart, followed by a booster after a year, and at three-year intervals after that. Newer vaccines will see children getting only two doses, one year apart. Take steps to avoid contact with mosquitoes.
Visitors to regions with high rates of JE or those living in the area should take personal protective measures to prevent mosquito bites, e.g. using insect repellent and/or mosquito nets, fixing wire netting at all windows and wearing long sleeved clothes/ trousers.
Another way of prevention is vector control against the Culex mosquitoes by fogging and larviciding, including destroying Culex breeding sites by land-filling and improving sanitation/drainage.
> Datuk Dr Zulkifli Ismail is a consultant paediatrician and paediatric cardiologist This article is courtesy of Malaysian Paediatric Association’s Positive Parenting programme. This article is supported by an educational grant by Sanofi-Aventis Malaysia. For further information, visit mypositiveparenting.org. The information provided is for educational and communication purposes only and it should not be construed as personal medical advice. Information published in this article is not intended to replace, supplant or augment a consultation with a health professional regarding the reader’s own medical care. The Star does not give any warranty on accuracy, completeness, functionality, usefulness or other assurances as to the content appearing in this column. The Star disclaims all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.