There are no effective vaccines against Japanese encephalitis, but its spread can be controlled in India through vector management.
JAPANESE ENCEPHALITIS, or JE, has become endemic in many parts of the country, occurring repeatedly in epidemic form in many of themfor instance, in parts of Gorakhpur in northern Uttar Pradesh.
One can expect JE-type epidemics year after year in States where prolonged drought-like conditions are followed by heavy monsoons. This leads to intense breeding of mosquitoes, the vector of the disease. Such conditions had resulted in the first big epidemic of JE in 1957-58 in North Arcot district of Tamil Nadu, and subsequently in Burdwan and Bankura in West Bengal (1976), and in Tirunelveli in Tamil Nadu (1978), going by the investigations in which this writer participated. Since then, JE epidemics have been routinely reported in many parts of India.
In the recent past, there have been reports of meetings at different levels in the States as well as in the Union Health Ministry on managing the disease. Such meetings, which have become routine exercises for those dealing with earthquakes, floods, famine, terrorist attacks and the like, have become a common practice among the so-called think tanks under the Health Ministry too.
Whenever epidemics occur, questions are raised in Parliament, and a meeting of experts, many of whom have only a cursory understanding of JE, is arranged. Once the report of the expert committee is prepared and sent to the Ministry, the government behaves as if the epidemic has been overcome or has abated. It then proceeds to tackle newer problems that arise.Viral disease
JE, a viral disease, occurred for the first time in Japan in the 1940s, and hence the name. Grey herons were found to be the avian reservoirs of the JE-causing virus, and pigs the amplifiers. Unlike in India, where there are only stray and scavenger pigs, in Japan pigs are reared for meat in big farms. Japan developed a vaccine for pigs, and the infection died down in that country. The clinical infection pattern is well documented there and hence there has been no relapse.
It was reported for the first time in India in North Arcot district in 1954. The Culex vishnui group of mosquitoes, which includes Culex tritaeniorhynchus, are the recognised vectors. The disease is a killer unless treated in hospital early; survivors will be left with several neurological complications. It is mostly children who are affected.
The JE virus is one of 66 flaviviruses and belongs to the JE serocomplex, which is composed of flaviviruses such as the West Nile, Murray Valley encephalitis and Japanese encephalitis (WN-MVE-JE).
In India, there are pond herons and cattle egrets that share the same niche as grey herons. It has been found that pigs circulate high titres of the virus and are capable of infecting a large number of mosquitoes. Mosquitoes that pick up the infection are mainly zoophilic (that is, they prefer to feed on animals, including birds). The high cattle population in villages means an increase in the mosquito population there. The cattle can circulate the virus among them, but for too short a time and in too small a titre to play any significant role in the transmission. When the mosquito population increases uncontrollably under certain conditions, as when large waterbodies are formed after heavy rains, an odd mosquito among the tens of thousands of mosquitoes bites humans. The population pressure forces the mosquito to do so. If there are a hundred human cases of JE in a village, the victims would have got the infection from a hundred mosquitoes.
In diseases such as malaria and filariasis, a mosquito can pick up the infection from one human and transmit the infection to another, but this does not happen in the case of JE. After a blood meal, every mosquito vector of the disease must wait until one gonotrophic cyclethe process of blood feeding and egg maturation and laying, which takes 7-10 daysis completed before it can bite another human. The chances of the zoophilic vectors of JE transferring the infection from man to man are very remote.
It has been observed during JE epidemics that the infection in the human population dies down very soon. There is absolutely no use of carrying out vector-control measures at that juncture. Maybe thermal fogging in and around human habitations immediately after the first human case is diagnosed will help to some extent. But health departments have to do something to satisfy the public and their political masters after an epidemic has been detected. By then, the epidemic has died down, and everybody believes that their vector-control measures have helped in containing it.
A large number of papers are published in India year after year on one or other aspect of JE, its control, vectors, and so on. In the past 50 years, this writer has seen different diagrammatic depictions of the natural cycle of the JE virus, but they have all been created not for future reference, but to serve the vested interests of their authors.Vector proliferation
In India, where drought and floods occur periodically, occurrence of JE is an almost foregone conclusion. In scrub forests conducive to the nesting and breeding of Ardeid birds (belonging to the family Ardeida), heavy rains result in large water pools with algal growth. In peninsular India, one can find such waterbodies in large numbers; egrets and herons are seen nesting and feeding in them. These waterbodies simulate the conditions existing in paddy fields. They are ideal for the breeding of the JE vector. The mosquitoes, the avian hosts and the human victims in the adjacent villages with their cattle, poultry and pigs provide the deadly setting for an outbreak of JE.
The disease is also endemic in areas where paddy is cultivated, as this crop needs large amounts of water. Flooding of low-lying areas following unseasonal rains and cyclonic storms also leads to mosquitogenic conditions. Unusual weather conditions and sudden changes in the extent of waterbodies will also result in changes in agricultural practicesas had happened in Tirunelveli, Tamil Naduand animal husbandry practices, such as increased duck farming as in the Burdwan area. All these are factors conducive to vector proliferation. Nothing can be done by human bodies to change the natural process of vector proliferation or disease occurrence.
Let us see some past epidemics as examples. The area in North Arcot district where the first major epidemic of JE was discovered and investigated had suffered a prolonged drought from 1947 to 1957. This was followed by excessive rainfall in May, July and September, which flooded the fields and provided a tremendous impetus for mosquito breeding. The residents of the area had complained of an unusually large number of mosquitoes in the months following the rains. Most houses in the villages were mixed dwellings, and the preferred resting places of the vectors are cattle sheds. This was a significant factor in the occurrence of the JE epidemic in the area.
As for the outbreak of JE in Burdwan in 1978, the topography, climate, vegetation and sociological aspects played a major role. The first case of JE was noticed as early as 1973, and there were sporadic cases in 1974 and 1975 in the districts of Burdwan, Bankura and Hooghly. Pigs did not seem to play any amplifying role here. The epidemic season (January to April) coincided with the breeding season of birds, particularly immigrant birds. Viraemia was noticed in the fledglings of ducks. Ducks instead of pigs must have played the role of amplifiers since they were reared in very large numbers there.
In the Tirunelveli area (JE epidemic in 1978) there was a tremendous increase in mosquitogenic conditions following a 200 per cent increase in rainfall. Many low-lying areas remained flooded for months. There was also a tremendous increase in the area under paddy cultivation.
Research on methods of predicting a JE epidemic should be a continuous process in JE-endemic countries like India. There should not be a long-term objective as far as JE control is concerned.Vector control
The first priority should be to delimit areas where JE has been occurring in an epidemic form. This can be done using the data collected by the health departments of different States. The epidemiology has not changed and therefore attempts can be made to save human lives at the onset of a JE outbreak. Prompt hospitalisation is necessary. Supportive and symptomatic treatment can be given then. Efficient surveillance and prompt transfer of patient cases to hospital are necessary, as had been done in Vellore (where the Christian Medical College Hospital, or CMCH, and the District Health Office worked very hard) and in Burdwan (where local police outposts were motivated to transport patients immediately to the nearest hospital). Many lives were saved thus. Such a system should be developed in Gorakhpur and other areas that report hundreds of cases, including fatal ones, with regularity.
The animal husbandry, meteorology, agriculture and revenue departments should make coordinated efforts to contain the disease by sharing data to predict any unusual changes in the ecosystem. Data that are regularly collected in different districts were found to be of immense help to detect changes in the ecosystem. Since JE is a mosquito-borne disease, the data will give an indication of the likely build-up of the mosquito population. Not that any control measures against the larvicidal and adult vectors of JE will be practical because of the enormity of the problem. But one can predict with reasonable accuracy an impending epidemic of JE in some areas.
There have been some excellent studies in the recent past about delimitation of areas for forecasting and control of JE, based on data at the macro level. Even maps have been produced through satellite communication systems. Although this is a good effort, no validation of the data has taken place with any degree of accuracy to predict an epidemic. This effort should continue so that micro-ecological factors are also incorporated. This is not possible through satellite mapping. The maps produced may broadly indicate JE-endemic areas but not an area where an epidemic will occur; such information will help authorities take adequate control measuresnot necessarily against vectorsor precautionary measures.Vaccines
The first JE vaccine imported from Japan was one that was used to protect pigs in Japan. There were many problems with it, since the JE virus is different from the yellow fever virus. Efforts have been made by the government to produce an effective vaccine, first a three-dose one and then a single-dose one. But the question is which target population needs the vaccination. A universal single-dose vaccine that is safe and effective is the need of the hour.
On paper India has institutes where diagnostic facilities are available. In 1954, the Rockefeller Foundation established virus diagnostic laboratories with full facilities in many medical colleges in the country and trained their personnel too. By 1974, most of the laboratories had closed down for unspecified reasons. A few of the remaining ones are still doing excellent work (for example, the one at CMCH, Vellore).
Every district should have a unit to diagnose viral infections, which is possible thanks to the advanced technology that has made simplified techniques possible. This will help in prompt diagnosis of viral infections.
The next question is how many of the research institutions are really doing the job they are supposed to do. Many have said that rushing to investigate an epidemic is the job of the State governments, not theirs.
The annual report of a well-known institute noted that Gorakhpur had reported more than 2,000 cases with at least 400 deaths in 2007-08. This institute did isolate viruses from many samples. But the major work under the section JE is on molecular biological studies and characterisation of virus isolates (not the JE strain but the West Nile one). No studies were done on the vectors or their control.
Questions abound about the JE virus. Where did it come from? What happened to it in the inter-epidemic period? How was it introduced into an area? There are lots of theories, but no evidence. Nor is any long-term study planned by any of the research institutes. The only attempt to study the role of migrating grey herons in the Colair Lake area of Eluru district in Andhra Pradesh was terminated, and the personnel were transferred to investigate Kyasanur Forest disease; the results of the study are yet to be published.
Even if grey herons and some other Ardeid birds are infected, how is the infection transferred to their fledglings? The Laelaptid mites infesting the bird nests and feeding on the birds have not been studied conclusively. There may be other animals or birds involved in the natural cycle, and JE could most probably be a zoonotic disease. No work seems to have been done in this direction.
Even if vector control is not practical, investigation into the causes of the proliferation of mosquitoes in endemic areas is a possible proposition. There are district-level entomological units under the National Malaria Eradication Programme (of the National Vector Borne Disease Control Programme), but the majority of them exist only on paper or do not have any entomologists to man them. These should be converted into mosquito surveillance units, under the district health officers or any other authority. They should be fully equipped and their personnel trained to monitor vector populations.
This will greatly help in forecasting an epidemic. Once this is made possible, effective use of insecticidal residual sprays will help slow down transmission, provided they are done before the start of an epidemic. Cases of JE will still occur, but the intensity of the epidemic will be low and manageable. At least deaths can be prevented.
Dr P.K. Rajagopalan is former Director, Vector Control Research Centre, Puducherry, an institute of the Indian Council of Medical Research.