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Letter to the Editor - The Fight Against Japanese Encephalitis in South Asia

Laxmi Vilas Ghimire
Institute of Medicine, Katmandu, Nepal

Letters to the Editor are accepted from any reader, and may address any topic dealing with science or undergraduate issues. They are published at the editor’s discretion. To submit a Letter to the Editor, please write to eic@jyi.org.

To the Editor—

Prem Yadav, a 35-year from Rautahat came to the district hospital to get treatment for his five-year-old son, who had had a high-grade fever for the last three days. In the last 12 hours, the child had had seizures and lost consciousness. Prem was anxious and worried. His memory was still fresh of his daughter who had died of a similar sickness two years back. Prem also said that many of the children in his village had a similar illness and some had died already.

This is true of most of the Terai districts of Nepal. Children suddenly become sick as the monsoon season begins and a large number die before they realize that Japanese encephalitis is the culprit.



Every year, as soon as the monsoon begins, Nepal's farmers (about 90% of the total population) begin busily transplanting the paddy in the paddy fields. The sun tans their skin heavily. At the end of the cultivation, they celebrate the end of hard work, hoping for a better harvest. However, after the celebration, when the tan still has not faded away and their hope, joy, and festive moods prevail, epidemics always sweep the region. Tens of thousand fall sick and thousands die. This is the Japanese encephalitis (JE) epidemic, which has for decades been the scourge of Nepal's farming people.

The Virus

Japanese encephalitis is a zoonosis caused by group B arbo virus (a flaviviridae) that is transmitted by culex mosquitoes. As the name suggests, this epidemic was recorded every year in Japan between 1873-1968 (see Figure 1 for the history of JE). At present, the disease is wide-spread, with 40,000 - 50,000 cases globally each year. This year, over 11,000 people – between 20 and 40% of those who are infected - will die of the disease and 9,000 will be disabled. Most of these cases will involve children. Of those who survive, 50% will develop long-lasting neurological disabilities.

Fortunately, JE has recently become a vaccine-preventable disease.

Geographical Distribution and Epidemiology

Each year, cases of JE are reported in Nepal, India, Sri Lanka, Burma, Thailand, Cambodia, Vietnam, Malaysia, and Singapore (see Figure 2 for the geographical distribution of JE). Most cases involve children age three to six and more than 85% of cases are found in children under the age of 15. Most adults in heavily-infected areas develop natural immunity due to sub-clinical infections.



Mosquitoes, notably the Culex tritaeniorhynchus and Culex vishnui, carry the virus. The mosquitoes breed in pools of stagnant water, such as rice fields which provide the most suitable habitat and is readily available in rainy season. The density of mosquitoes increases rapidly between July and October, when the fields run dry.

The epidemiology of JE involves a complex relationship between climate, entomology, human behavior, and virus and host factors. The principal hosts of the virus are wild and domesticated animals while humans are infected by the bite of infected mosquitoes. Humans are the 'dead-end' hosts since normally, they do not have sufficiently high or prolonged viraemia to transmit the virus further. Interestingly, mosquitoes prefer to feed on animals over man.



Pigs, the principal animal reservoir, do not manifest any overt symptoms of illness when infected, but circulate the virus so that other mosquitoes get infected and transmit the virus to man (see Figure 3 for epidemiology of JE virus). Thus, pigs are considered 'amplifiers' of the virus. Besides pigs, poultry and ducks are natural hosts of JE virus. However, no man-to-man transmission has been recorded so far.

Clinical Features and Complications

The overt cases represent the tip of iceberg as the ratio of symptomatic to apparent symptomatic infection is 300:1. The incubation period of the virus is 5 - 15 days. The symptomatic cases may occur with sudden onset of a high-grade fever with headache and malaise, which is followed by a rapid rise in temperature to 38 - 40.70C, neck tenderness and rigidity, projectile vomiting, focal CNS signs, altered sensorium, and convulsions progressing to coma. Mortality may peak as high as 58% or more. In as many as 30% of cases, neurological signs may become stationary, leading to long-term disabilities like paralysis, ataxia, abnormal movements, memory loss, aphasia and abnormal emotional behavior.



Once a person gets JE, there is no specific treatment except symptomatic support with antipyretics and maintenance of fluid and electrolytes. Therefore, it is the prevention that needs more focus, particularly, through vector control and vaccination.

Japanese Encephalitis in Nepal

In Nepal, the disease is known as "the visitation of the Goddess of the Forest." Local people believe the goddess visits the villages when she is angry and can even ruin the village. Therefore, when people start having fevers, they sacrifice a hen or goat to make the goddess happy, as there is widespread belief that she wants animals and hen.

Terai, the southern part of Nepal, is annually hit especially hard by the JE epidemic as it is a hyper-endemic region. In addition, Terai is affected by health conditions like arsenic in drinking water and recurrent epidemics of plagues and typhoid. With the introduction of JE epidemics in Nepal, every year, thousand of people are affected and hundreds have lost their loved ones. Twenty-four districts of Terai and inner Terai, which harbors 12.5 million people, are affected by JE. There has been a constant rise and fall of cases along with several outbreaks.



Terai has a very high incidence of JE due to the extensive paddy plantations, which serve as the best habitat for mosquito breeding. Pig and duck/poultry farming is also common there and many unvaccinated people live in the endemic area. This year alone, 1879 people were affected and 298 died of JE, accounting for 15.9% of all mortalities.

This year, the World Bank made available Rs.130 million (about US $1.5 million) to vaccinate 275,000 people. Yet, the government was unable to supply enough vaccines to the areas at risk.

"Due to delay in tender processes and some other technical difficulties, we could not supply the vaccine on time,” Dr. Hari Nath Acharya, the health ministry spokesman, said easily when asked why vaccines were not available on time despite the available financial aid.

Japanese Encephalitis and Future

Japan has begun to control its JE epidemics using widespread vaccination of children between 3 and 15 years old and by controlling the vector population. However, Napel faces many challenges in its attempt to do the same. Large populations of people living in Nepal are uneducated and have very little knowledge of the disease and proper health practices. Therefore, increased public awareness and taking preventive measures are crucial to curbing this national epidemic. As vaccinations are not included under the Extended Program on Immunization (EPI), the lack of manpower and follow-up for the vaccination program would result in lower than expected efficiency.



Since there is no specific treatment for the disease, prevention is the principal aim of the control process. Effective methods of vector control could include thermal fogging with ultra-low-volume insecticides (e.g. malathion and fenitrothion), spraying vegetation, homes, breeding sites and animal shelters. Such spraying has proved very effective in many districts.

Currently, all individuals living in the Terai area are recommended for vaccination. Nepal uses live attenuated BHK-vaccine from South Korea while in India, the killed 'mouse brain' vaccine is widely used. For primary immunization, the government recommends two doses of 1 ml each subcutaneously at an interval of 7 to 14 days. A booster dose of 1 ml should be given after a few months time (before one year) for full protection.



The Nepal Pediatric Association (NEPAS) has recommended that the JE vaccine be included in the list of essential vaccines for which home production has been started. In addition, the government of India has intensified mosquito control measures and distributed 200,000 mosquito nets. There is also a program to improve the surveillance and control of three vector-borne diseases - malaria, JE and kala-azar - through bilateral and regional collaboration among four countries: Bangladesh, Bhutan, India and Nepal.

"An Anti-Japanese Encephalitis immunization campaign, along with awareness programs, have been initiated following the spread of the disease," says Krishna Gopal Sinha, the District Public Health Officer at Kailali district, one of the worst-hit districts. "Due to the free treatment facility and the immunization drive, the impact of the disease in the district has been minimized significantly."



"People were vaccinated against the disease for the first time four years ago," says Dr. Mahendra Bahadur Bista, director at the Epidemiology and Disease Control Division. "The Chinese government had provided the vaccine free of cost for 225,000 people."



"The disease has not been seen in those who were vaccinated," adds Dr. Bista. "The Chinese vaccine has a success rate of 98.4 per cent. The government has launched programs like spraying insecticides to kill mosquitoes that transmit the deadly disease, immunize children and distribute mosquito nets at affordable prices. Based from last year’s experience, the government had already initiated process to procure vaccines for encephalitis for the next year."

Deadly JE, which rears its ugly head every year with the monsoon, can be controlled. Concerted efforts from different sectors, including the government and regional alliance, could soon bring JE under control, allowing south Asia along with Nepal, to fight for other health-related problems in the near future.

Prem Yadav's son lived, after 5 days unconscious and 15 days in the hospital.

References

WHO, vaccine preventable disease surveillance Bulletin, vol 9, no 39, Oct 3, 2005.

Tiroumourougane, S. V. , Raghava P., and Srinivasan, S. Japanese viral encephalitis. Postgrad. Med. J., April 1, 2002; 78(918): 205 - 215.

Tom Solomon, Nguyen Minh Dung, Rachel Kneen, Mary Gainsborough, David W Vaughn, Vo Thi Khanh. Japanese encephalitis, J Neurol Neurosurg Psychiatry 2000; 68:405-415.

Kir C. India, Nepal Fight Outbreak of Japanese Encephalitis. 14 September 2005, VOA Special English Health Report.

Park K. Park's textbook of preventive and social science. Jabalpur, India, 18th edition, 2005.