From SARS to encephalitis

First, there was SARS. Now, there’s encephalitis. Both diseases are caused by a virus. Both viruses are known to be harbored by certain animals. And both illnesses can be deadly.

Hong Kong authorities have already expressed alarm over the reported outbreak of Japanese encephalitis (JE) in Guangdong. Our local airport authorities have instituted procedures to sanitize planes coming from the Chinese mainland. The Philippine Olympic Committee has voiced its concern over the possible danger of JE to Filipino athletes who will participate in the SEA Games in Vietnam this December. And to add to these fears, our Department of Health has confirmed that there had been at least three cases of Japanese encephalitis in Tarlac.

So, what’s happening here? Doesn’t all these sound familiar? Is history repeating itself? Is this SARS, Part 2, but with a new virus and a new disease? Not quite. After all, unlike SARS, Japanese encephalitis is not a new disease. It is also not as communicable as SARS, and a vaccine against it is available.

But here’s what you need to know to avoid getting this potentially serious illness.

Overview

Japanese encephalitis is a disease that is spread to humans by infected mosquitoes. It is one of a group of mosquito-borne virus diseases that can affect the central nervous system and cause severe complications and even death. The disease is caused by an arbovirus (arbo is short for arthropod-borne virus). Like most arboviruses, it is spread by infected mosquitoes, specifically the Culex tritaeniorhynchus group, which breeds in flooded rice fields, marshes, and standing water pools in planted fields.

Thus, JE is found throughout the rural areas in Asia. It is a seasonal disease that usually occurs in the summer and fall in the temperate regions of China, Japan and Korea. In other places, disease patterns vary with the rainy seasons and irrigation practices.

Japanese encephalitis outbreaks are usually circumscribed and do not cover large areas. They usually do not last more than a couple of months, dying out after the majority of the pig amplifying hosts have become infected.

Countries which have had major epidemics in the past, but which have controlled the disease primarily by vaccination, include China, Korea, Japan, Taiwan and Thailand. Other countries that still have periodic epidemics include Vietnam, Cambodia, Myanmar, India, Nepal and Malaysia. Actually though, Japanese encephalitis is considered endemic in most of Asia, including the Philippines.

Transmission

Mosquitoes become carriers by feeding on domestic pigs and wild birds infected with the JE virus. The infected mosquitoes then transmit the JE virus to humans and animals during the feeding process. After infection, the virus invades the central nervous system, including the brain and spinal cord.

The JE virus is NOT transmitted from person to person. For example, you cannot get the virus from touching or kissing a person who has the disease, or from a health care worker who has treated someone with the disease. You also cannot get Japanese encephalitis from animals other than domestic pigs, or from insects other than mosquitoes. Only domestic pigs and wild birds are carriers of the JE virus.

The actual risk for someone living in an urban area or a traveler to Asia is really very small. After all, only certain mosquito species can spread the disease. Also, in areas infected with mosquitoes, only a small portion of the mosquitoes are infected with the JE virus. And of those persons who are infected by a mosquito bite, only one in 50 to one in 1,000 will actually develop the illness.

Signs And Symptoms

The majority of infections are subclinical, resulting in mild symptoms or no symptoms at all. It is estimated that, on average, only one in 300 infections results in symptomatic illness.

Symptoms usually appear within four-14 days after infection and are characterized by a flu-like illness, with sudden onset of fever, chills, headache, tiredness, nausea, and vomiting. In addition, gastrointestinal pain and dysfunction may dominate the early stage of the illness. After three-four days, signs of neurological involvement occur with a change in the level of consciousness, ranging from confusion to coma. Children often have seizures.

The illness can progress to a serious infection of the brain (encephalitis) and can be fatal in 30 percent of cases. Thirty to 50 percent of those who survive the disease will have serious neurological and psychiatric sequelae including brain damage and paralysis.

About 85 percent of cases happen in children less than 15 years old. Most deaths and residual neurological and psychiatric sequelae occur in children under 10 years of age. Infection during the first and second trimesters of pregnancy may result in intrauterine infection and abortion. Infections that occur during the third trimester of pregnancy have not been associated with adverse outcomes in newborns.

Diagnosis of Japanese encephalitis is mainly based on serological tests of blood and spinal fluid. Other diagnostic methods include the recently-developed dot-blot or immunoprecipitation IgM assays.

Treatment And Prevention

Currently, there is no specific treatment for Japanese encephalitis. Antibiotics are not effective against viruses and no effective antiviral drug has been discovered. The care of these patients centers mainly on the treatment of symptoms and complications.

Vaccination is the single most important measure to control Japanese encephalitis. Currently, there are three types of JE vaccines in large-scale use: mouse brain-derived inactivated vaccine, cell culture-derived inactivated vaccine and cell culture-derived live attenuated vaccine.

The mouse brain-derived inactivated JE vaccine is produced in several Asian countries. It is the only vaccine that is commercially available on the international market. The vaccine is used for adults and children over one year old. It is given subcutaneously in doses of 0.5 ml to 1 ml, the lower dose being for children one to two years old. Due to likely interference with remaining maternal antibodies, children are not usually vaccinated before they’re one year old. The recommended primary immunization schedule is three doses on days 0, 7 and 30 for those living in non-endemic areas. A booster dose may be administered at intervals of one to three years. Most Asian countries give two doses of the vaccine four weeks apart, with a booster after one year and every three years thereafter.

Controlled studies in two different endemic regions have shown that the JE vaccine is efficacious and without serious side effects for childhood vaccinations. The three-dose series of the vaccine prevents the disease in nine out of 10 people (90 percent protection). The JE vaccine is also indicated for travelers spending more than a month in rural parts of endemic areas during a period of transmission, as well as for those traveling less than one month, if the itinerary includes areas experiencing epidemic transmission and extensive outdoor activities, in rural areas. Actually, the risk to short-term travelers (less than a month) and those who confine their travel to urban areas and resorts is extremely low. These persons should not be routinely vaccinated.

Everyone should be advised to take precautions to reduce exposure to mosquito bites in endemic areas. The mosquitoes that transmit the Japanese encephalitis feed mainly outside during the cooler hours at dusk and dawn. Thus, people should minimize outdoor activities at these hours, use mosquito repellent on exposed skin, wear long sleeves and long pants in light-colored fabrics, and stay in air-conditioned or well-screened rooms, if possible. Those who travel to the rural areas should use a mosquito net and aerosol room insecticides. Sprays that contain deet can spare you a bite. Permethrin is a neurotoxin that is applied to clothing to kill bugs on contact.

So, unlike SARS, the prevention of Japanese encephalitis is much simpler: Just don’t get yourself bitten by a mosquito!