By: Sabrina Ahmed, PharmD Candidate c/o 2017

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One recent stride towards combating worldwide infectious disease has been in the improved surveillance of Japanese encephalitis in Asia, predominantly in South and South-East Asia. This potentially deadly virus is transmitted to humans via mosquito bites. The Japanese encephalitis (JE) virus is the leading cause of encephalitis in Asia with about 67,900 cases occurring each year.¹ The virus’s high prevalence in Asia is due to the abundance of flooded rice fields which can harbor large quantities of mosquitoes carrying the virus. While the most common hosts for JE are birds and pigs, humans can serve as hosts during periods of mosquito overpopulation. Most humans who contract the disease remain asymptomatic or experience mild symptoms. However, about 1 in 200 exhibit severe symptoms such as seizures, paralysis, high fever, and possible death concomitant with brain inflammation. The population affected by the virus is disproportionately young in age. Young children constitute the majority of the sufferers of JE due to their lack of immunity towards the virus, whereas older individuals are protected by their immunity attained from prior exposure..² Of the people who experience severe symptoms, as many as 20 to 30% may perish while 30% to 50% develop permanent neurological damage.³

There is currently no treatment for Japanese encephalitis but observation in the hospital setting is strongly recommended. Pain relieving and fever reducing medications can alleviate some of the symptoms but are ultimately not curative.⁴ So, preventive measures are particularly important. Modifying environments that mosquitoes carrying JE inhabit may serve as a viable option, depending on the methods employed. Typically, using mosquito nets and insect repellents is a relatively inexpensive and effective option to prevent infection. Conversely, chemical treatment of the rice fields, which act as breeding grounds for the mosquitoes, is costly and covers too large of an area to be a practical solution.² Health officials are still exploring for more effective alternatives.

The most integral and efficacious method for helping curb the spread of JE is vaccination. One type of vaccine for Japanese encephalitis is a live-attenuated formulation that is cheap but only available in China rendering it ineffective for worldwide use. There has been notable success, however, with the use of an inactivated version of the virus.² There are certain drawbacks to the vaccine, namely its cost and the need for two booster shots. Japanese encephalitis is most common in rural areas but the inhabitants of these areas may not be able to afford the vaccine or have enough access to health services to receive a vaccination.¹ In regard to travelers, the Advisory Committee on Immunization Practices recommends that travelers receive the vaccine if they plan to spend more than one month in an endemic region (can include rural and high-risk areas) during transmission season. The vaccine is not recommended for travelers staying for short periods of time in an urban area or when it is not primary transmission season.⁵

In spite of the shortcomings of the Japanese encephalitis vaccine, tremendous efforts have been made on a worldwide scale to increase immunization rates and to survey the disease. Indeed, these efforts have been moderately successful according to reports from the CDC in an article published in the Morbidity and Mortality Weekly Report (MMWR). These reports stated that public awareness regarding the severity of Japanese encephalitis and its status as a deadly disease has increased. In addition, data collection on the use of the vaccines in affected regions help evaluate the efficacy of these immunizations.¹ Limited resources and inadequate knowledge about disease burden prevent third world nations from fully utilizing the aforementioned preventive measures. Cooperation is critical; wealthier nations can provide support to poor endemic regions through “surveillance and vaccine introduction.”³

Out of the 24 countries at risk, 18 practice some form of surveillance. The extent of this surveillance, however, varies – from being conducted at a national level in some countries to only in high-risk areas in others. Furthermore, only 11 of these nations have an immunization program, seven of which employ either an  immunization program that spans the entire nation or all areas at risk, while the remaining four only immunize a fraction of at risk areas.³ As vaccination is the most effective preventive measure to control the spread of JE, it is imperative that more nations implement immunization programs. 10,426 cases of JE were reported from 19 of the 24 countries that had citizens who were at risk of contracting the disease. 95% of the cases originated in India and China; the remaining 150 cases were spread among the other countries.¹

The ramifications of this subpar surveillance are significant because even after immunization programs are implemented, undetected disease transmissions can occur. The number of cases reported is particularly troubling as well because the number falls well below the 67,900 cases estimated by the WHO. These thousands of unreported cases allude to inadequate surveillance. In fact, out of five nations to report no new cases of JE, three of them did not have a surveillance program in place. The disease could still be spreading, but because of the lack of surveillance programs in these nations, proper action to combat JE cannot take place. Consequently, the main concern for these nations according to the CDC is that “further progress toward [Japanese encephalitis] control requires increased awareness of disease burden at the national and regional levels…and international support for surveillance and vaccine introduction in countries with limited resources.”³ Advances in surveillance, more efficient usage of data to aid in immunizations, and a more thorough understanding of this virus have definitely improved the prospects of preventing disease transmission, but there are many obstacles left.³ Until we can properly educate the masses about the value of vaccines against Japanese encephalitis as well as fund vaccination programs in poorer countries, the JE will continue to threaten South and South-Eastern Asia.

SOURCES:

1. Japanese encephalitis: improved surveillance, immunization in Asia. American Pharmacists Association Web site. http://www.pharmacist.com/japanese-encephalitis-improved-surveillance-immunization-asia. Updated August 23, 2013. Accessed January 24, 2014.
2. Water sanitation health, water-related diseases: Japanese encephalitis. World Health Organization Web site. http://www.who.int/water_sanitation_health/diseases/encephalitis/en/. Accessed January 25, 2014.
3. Japanese encephalitis surveillance and immunization – Asia and Western Pacific, 2012. Centers for Disease Control and Prevention Web site. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6233a2.htm. Updated August 23, 2013. Accessed January 25, 2014.
4. Symptoms and treatment of japanese encephalitis. Centers for Disease Control and Prevention Web site. http://www.cdc.gov/japaneseencephalitis/symptoms/. Updated November 12, 2012. Accessed January 25, 2014.
5. Hills S, Weber I, Fischer M. Infectious diseases related to travel: Japanese encephalitis. In: CDC Health Information for International Travel 2014. New York: Oxford University Press; 2014. http://wwwnc.cdc.gov/travel/yellowbook/2014/chapter-3-infectious-diseases-related-to-travel/japanese-encephalitis. Updated September 18, 2013. Accessed January 31, 2014.

Published by Rho Chi Post