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Date: Fri, 25 Oct 2002
Posted by: Michael Gochfeld (gochfeld@eohsi.rutgers.edu)

R.Lampman identified some issues regarding WNV risks.

UPFRONT I will say that we are now doing adequate research with serosurveys of human or avian populations. It is not difficult to figure out what to do, but there doesn't seem to be interest in investing in the studies. There is urgent need, I think, for a followup on cases to establish sequelae rates and seriousness. Issues of alternative modes of transmission need to be sorted out, but shouldn't detract from a focus on the natural or sylvan cycles.

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The case fatality rate for identified cases of West Nile Meningo-encephalitis, has been between 5 and 15% in most outbreaks, both in the Old World and the New.

There is actually quite a bit of serosurvey information from the Old World in the wake of epidemics, showing a high degree of antibodies (up to 100% in some villages). It's not definite that these are all protective against future outbreaks.

The case fatality rate can be confusing, because it depends not only on the virulence of the infection, but on the way cases are diagnosed. If there is a high index of suspicion then more cases with headache and fever will get tested, and some of these will be mild West Nile encephalitis, that will raise the number of cases and therefore lower the case fatality rate.

The case fatality rate in 2002 in the U.S. seems to be lower (5% or less), probably because of this heightened index of suspicion. But it would be nice to know.

Another point that Lampman and others have been emphasizing is that we know very little about the sequelae among those who recover from acute WNV infection. He mentions one case, but I am sure that is too low. Remarkably there is no formal followup, although the director of CDC assured me they are planning a followup now.

In looking at sequelae it is important to distinguish the impairment such as motor weakness, which follows the acute infection, but improves gradually over months and the permanent residual damage. The information from 1999 is that many of the cases took many months to get better and some weren't completely better after 12 months. But information on permanent sequelae is still elusive.

Are there lessons from comparison with other ARBO virus diseases. Probably, but each has unique features which change over time as WNV has revealed in the Old World.

Eastern Equine Encephalitis which kills 30-50%, attacks children preferentially, and has a very high rate of sequelae (not just motor, but cognitive), is clearly a more severe disease, but not necessarily a more severe public health hazard today (Richard and Dominick have both pointed this out). Those of us who remember the 1950's when EEE was a major public health concern (at least in New Jersey), are relieved that it seems to have gone underground (at least for the past generation). When I was in charge of ARBO virus surveillance for NJ in 1980, EEE was still a memory, and SLE was of greater concern. We operated a mosquito surveillance/sentinel chicken program which was maintained, not to mention a statewide mosquito control endeavor making use of many new techniques, including integrated pest management. Some years later, as the public health memory of both EEE and SLE waned, surveillance funding waned as well. .

EEE has moved from devastating concern to oddity. I am willing to predict that WNE will do the same, but not before it has wreaked hazards with humans, birds (and mosquitos too).

Michael Gochfeld

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