What you need to know about Japanese Encephalitis

Annajarvis Pao *

Japanese Encephalitis (JE) vaccination at District Hospital, Churachanpur in July 2016 :: Pix - T Minlun Suantak

Introduction: Japanese Encephalitis is a mosquito borne viral infection caused by a virus belonging to the genus Flavivirus transmitted mainly by the vector Culex Tritaeniorhynchus in the most endemic region in Asia. It is a zoonotic disease infecting mainly animals and incidentally man. The initial viral replication occur in the local and regional lymphnodes and viral invasion of the central nervous system occur probably by infecting blood.

Global scenario: JE was first recognised in Japan in the late 18th century. During that time, JE was known as an epidemic in the East Asia, Japan, China and Korea. In the recent years, it has spread widely in the South East Asia and outbreak have considerable magnitude to have occurred in Thailand, Vietnam, India, Myanmar and Sri Lanka. As estimated 50,000 cases of JE occurs globally each year with 10,000 deaths and country wise data are not available due to lack of proper certified diagnostic centres and underreporting in most countries. The vast majority of cases occur among the children.

Indian scenario: It was first recognised in 1955, when cases from North Arcot District of Tamil Nadu and Andhra Pradesh were admitted in CMC, Vellore. Half of the population in the south India has neutralizing antibodies. So, for 26 states union territories have reported JE cases. However, the states reporting repeated outbreaks are South Central, Northern and NorthEast states of India. The population at risk is about 300 millions people of developing the disease.

As per 2014 data, 1657 cases of JE were reported in India with maximum number of cases from Assam(761). During 2006, 2832 cases occurred about 650 deaths at that time and in 2007, 391 cases reported in India and 92 deaths occurred. In 2015, 1500 cases was reported particularly in North East states of India. In Assam last year-304 cases has been registered with 1,256 cases of Acute Encephalitis Syndrome leading to over 200 deaths, according to the data from the health department. Manipur has seen a surge in the virus last year, recording 45 cases leading to three deaths according to Health Department.

Epidemiological features: JE infects several human, animals and birds host. It is evening and night time biting mosquitoes, a rice field breeding mosquito that feed outdoor and preferentially in the large domestic animals and water birds and only infrequently in human. Horses are the primary affected domestic animals of JE, though essentially a dead-end host. Donkeys are also susceptible. Pigs acts as an important amplifiers of the virus producing prolonged viremia which infect mosquito vectors.

In some places, up to 100% of pigs may be infected and the infected pigs do not manifest an outward system symptoms and does not suffer from the disease but allow manifold virus multiplication. The natural maintenance reservoir for the JE virus are aquatic birds( herons and egrets). Human are vulnerable to this disease and is a primary public health concern in Asia as it is transmitted by infected mosquito.

However, JE virus cannot be transmitted from human host to biting mosquito due to low viremia. So, man act as an accidental death end-end host and man to man transmission has not so far been recorded. Other subclinically infected animals which likely do not contribute to spread include cattle, sheep, goats, dogs, cats, chickens, ducks, wild mammals, reptiles and amphibians.

Transmision: It is very seasonal, in temperate zone of china, Japan, Korea, and northern areas of S.E Asia- Early autumn i.e., May to September. Northern India and Nepal- June to November. Southern India and Sri Lanka – September to January.

Clinical features: JE disease manifestation can be divided into 3 stages in human.

1. A prodromal stage: characterized by Fever, rigors, headache, nausea, vomiting which usually last for 1-6 days.

2. An acute encephalitic stage: begins by the third to fifth day. The symptoms include uncontrolled violent shaking of muscles, unconsciousness, coma, mask like face, stiff neck, muscular rigidity, tremors in fingers, tongue, eyelids and eyes, abnormal movement of limbs and speech impairment.

3. A late stage: characterized by the persistence of signs of CNS injury such as mental impairment, increased deep tendon reflexes, paresis either of the upper or lower motor neuron type, speech impairment, epilepsy, abnormal movement, behaviour abnormalities, paresis, paralysis and death.

Case fatality rates in human can reach 25% and 50% of cases result is permanent neurological damage, psychiatric disturbance, ataxia and catatonia.

In equine: Depression, fever, muscular tremors, photophobia, ataxia and incoordination .

In swine: Asymptomatic in adult pig and mortality rate is near zero in adult pig. Most common JE manifests as a reproductive disease and reproductive loss can reach 50-70%.There will be abortion in pregnant sows either still births or mummified foetuses and in boars, the number and motility of sperm is reduced. Mortality in non-immune, infected piglet can approach 100% if born.

Prevention and control: Sanitary measure –

1. Housing animals indoors in screened stabling can provide protection from mosquitoes especially during active J.E outbreaks and during peak vector activity usually dawn to dusk.

2. Vector control reduced transmission by spraying insecticides. All the villages reporting cases should be bought under indoor residual spray. The spraying should cover the vegetation around the houses breeding sites, animal shelters and area falling 2-3 km radius of the infected villages.

3. Use protective clothing, applying of mosquito repellent , installing mosquito nets and taking a shower after sweating will keep the pesky mosquitoes at bay.

4. If practical, swine should not be raised near horses and humans as well as in areas where rice cultivation is widespread.

Medical measures: Immunization of man, swine and equine, vaccination of swine prevent reproductive disorder and directly impacts JE viral amplification especially in enzootic areas. Vaccines also protects horses from clinical disease and possible outcome.