Aliran Media Statement

"Japanese" Encephalitis: A Re-emergent Nightmare?

A cardinal principle of infectious disease control is that one should try to accurately identify the disease-causing organism, but even more urgently, the modes of transmission between host, vector, and human especially in the event of a hitherto unknown pathogen.

The current "JE" outbreak increasingly appears to be a replay of the misguided "Cox-Sackie" fiasco last year, which was plagued by a lack of clear-thinking, well-advised and decisive leadership.

Two main bodies of evidence have been adduced to presume that we are now faced with a principally JE outbreak:

1. the fact that the deaths, 48 at last count, were overwhelmingly clustered around pig-farms with the fatalities being largely confined to pig-farm workers (pigs are well-known to be a major reservoir of JE virus, as asymptomatic carriers)
   
2. many of the more recent fatal cases had tested positive for JEV antibodies (including IgM antibodies indicative of recent infection)
   

There is reason to be sceptical about these arguments. We should understand that the JE virus, even in "normal" times is seasonally endemic among pig populations, and people in frequent and close proximity with the infected animals, either residentially or occupationally, often get infected as well with mild or inapparent consequences. Infrequently, 5 per cent or less of these people may develop serious encephalitic illness with low to moderately high case fatality rates.

In short, a very low, seasonally recurring baseline frequency of JE fatalities has been the typical pattern. Furthermore, it means that people in the vicinity of pig-farms quite commonly have circulating JE antibodies, with corresponding seasonal IgM peaks. On top of this, in the wake of the publicity surrounding the "JE" outbreak this past month, many people in the affected areas have been vaccinated against the JE virus. Given all this, the fact that many of the more recent fatalities have tested positive for JEV IgM antibodies, at a time coinciding with a typical JE seasonal peak, offers no definitive proof that JE virus is the likely, sole or principal cause of death. Such serological "evidence" is even less convincing in the face of the recent mass immunisations against JEV particularly among the high-risk group.

The age spectrum of fatal cases is also puzzling: In Malaysia, JE fatalities are documented largely among young children, and in other countries, among elderly as well, but rarely among young adults. The fatalities in Perak and Negri Sembilan have largely been among young to middle-aged healthy adults. There are also conflicting reports that pigs have been dying as well - a highly unusual consequence of JEV infection.

What remains as a striking feature is the very tight association of fatalities with pig-farming occupations. What then can we make of the essential features of this epidemic?

· a very close association of fatalities with pig-farming occupations

· lack of widespread downstream occurrence thus far suggests that contact with raw pork (in food preparation or butchering) or consumption of cooked pork carries little risk (unless the latency period is of the order of months and the pig-farm associated deaths represent merely the early wave of the epidemic)

· possibility of a mutant strain of JE virus not excluded, with the resulting unusual clinical and epidemiological features

· a hitherto unidentified non-JE pathogen not excluded, this outbreak coming on top of a seasonal JE peak

· mosquito-borne transmission unlikely but not fully excluded (given the tight association with occupation, less so (or not at all?) with residents in looser proximity)

· oral-fecal transmission, or through inhalation, or contact with body fluids through broken skin not excluded

· possibility not excluded that some aspect of the ecology of pig-rearing (rather than a pig-infesting pathogen) being a culprit

Indeed the Ministry of Health, according to informed sources, has latterly come to the position that the current outbreak may not be solely a JE epidemic pure and simple. Nonetheless, it persists in calling it a JE epidemic in its public communiques, repeating its practice during the Sarawak outbreak of viral myocarditis. This is not just semantic or academic quibbling. Health personnel around the country, operating on possibly misleading assumptions may take wrong, potentially dangerous measures in attempting to contain the epidemic.

In view of all the above, the sensible measures that need to be taken now are:

· evacuate human populations from the vicinity of affected pig-farming areas

· destroy pig populations in the affected areas with compensation, proper disposal and disinfection of the pig- rearing areas

· spraying operations to destroy possible insect (mosquito) vectors

· look for evidence of pathogens other than JEV

· develop and refine clinical criteria for case identification to track the epidemic, while awaiting the development of serological or other tests if a novel pathogen is isolated and implicated

· continue epidemiologic surveillance to identify all new cases nation-wide, follow-up of infected or exposed persons; epidemiologic and ecologic investigations to clarify and confirm modes of transmission

· accurate, timely information to the public to allay anxieties and pre-empt civil disorder

· install early warning system for possible future outbreaks

George Orwell observed that in times of war, the first casualty often is truth. We should be wary that even more harm might come about through misguided, clumsy attempts to manage "the truth".


Dr Chan Chee Khoon (Epidemiologist)
Co-ordinator, Citizens' Health Initiative
Aliran Exco member
19 March 1999