Japanese B Encephalitis is a viral disease transmitted by the bite of an infected female Culex mosquito. Over 50,000 cases are reported to occur each year. The disease is found in over 25 countries throughout the world, mainly in South East Asia as can be seen from the following list of endemic countries; Australia, Bangladesh, Bhutan, Brunei, Cambodia, China, Hong Kong, India, Indonesia, Japan, Korea, Laos, Malaysia, Myanmar (Burma), Nepal, Pakistan, Philippines, Russia, Singapore, Sri Lanka, Taiwan, Thailand, Trust Territory, Vietnam, Pacific Islands. The majority of cases these may occur within rural areas of the endemic countries and especially in regions where pig farming is found. While transmission can occur in urban areas, this is uncommon.
Patients with Japanese B Encephalitis usually present symptoms within a week or two after being bitten by an infected mosquito. They will usually develop distinct symptoms of a ‘flu like’ illness with muscle pains and headache. Following this initial phase, patients frequently present with vomiting and diarrhoea. These early gastrointestinal symptoms are then followed by more severe neurological signs as the virus effects the patient’s brain tissue. Seizures and paralysis are then seen, and the condition carries a mortality rate of between 10% to 40%. In up to 80% of those who survive, there may be residual neurological findings. This is not a pleasant disease and it causes many deaths each year in the endemic countries.
Avoiding Japanese Encephalitis
There is no specific form of therapy against Japanese B encephalitis and so the best way of avoiding the disease is to ensure that those at risk are as well protected against the disease as possible. This protection takes two forms; general protection against mosquito bites or specific vaccination against the disease. As with many arboviral (arthropod borne viral) diseases the main protection rests in taking all possible care against being bitten. The mosquitoes which transmit Japanese B Encephalitis tend to bite mainly in the evening time though day biting in shady areas may also occur. In regions of the world where Japanese B occurs the transmission of both malaria and dengue fever are usually reported. Avoiding all mosquito bites is essential.
There is a vaccine to help avoid Japanese encephalitis which can be used in those at high risk. The vaccine is given on four occasions (days 0, 7-14, 28 and a final vaccine after 1 year). This should give a 2 to 3-year protection against the disease. It is suggested that cover for up to 3 months can usually be achieved by giving the vaccine on two occasions (day 0, 7-14).
However, in the early 1990’s a number of reactions were associated with the vaccine, making it unacceptable for widespread use in the short-term traveller and so, it is only recommended for those felt to be at significant risk. This is usually only those who will be visiting or living in the infected regions of an endemic country, those mentioned earlier in this leaflet, for more than 2 to 4 weeks. An exception to this general rule may be for those travellers who will be highly exposed to mosquitoes in high-risk rural regions during exploration trips or extensive trekking holidays.
Book your appointment today or contact us to find out if you require the Japanese B encephalitis vaccine with our full pre-departure health screening service.