A Misdiagnosis of Japanese Enchephalitis

In the last few months of 1998 a disease killed a few farm workers in Malaysia. Because of the symptoms the disease displayed, health authorities in Malaysia thought they were dealing with an outbreak of Japanese Enchephalitis (JE) which infects a few dozen people each year. Indeed, an analysis of blood and cerebro-spinal fluid showed the presence of antibodies to JE. Health authorities therefore focussed their prevention efforts on fogging the breeding places for mosquitoes known to carry the disease, and innoculating people at risk. However, the disease continued to spread. By April 1999 nearly a hundred people had died of the disease, which by this time is presumed to be an entirely new virus that pigs pass to humans.

Evidence of this being a new disease included...

that it affect pigs which JE rarely does.
that it affects people in close contact with pigs rather than people in close contact with mosquitoes
that it kills adult humans which JE rarely does
the cinching evidence was that no live JE virus could be cultured from the blood of victims who displayed JE antibodies

How is it that authorities spent months in a fruitless effort to prevent the wrong disease? First, the disease symptoms were like JE, but this provides only a superficial relationship, as many other viruses cause enchephalitis-like symptoms. Second, the presence of JE in the blood of victims is highly probable in a region where much of the population carries JE antibodies.

In conclusion the authorities used a prior hypotheses highly focussed on JE, while the evidence with which they tested the hypothesis had such a broad likelihood of occurrence that it wouldn't rule against this hypothesis. The outcome of a wrong diagnosis was pre-ordained.

Note:

That the cinching evidence involved an inability to culture the cause from the blood of victims shows the importance of Koch's postulates in demonstrating causes of infections.