Back to the West Nile Virus listserv archive.

Date: Wed, 13 Nov 2002
Posted by: Dominick Ninivaggi (Dominick.Ninivaggi@co.suffolk.ny.us)

As one who was there in NYC in 1999, I think the criticism about lack of efficacy measures is a bit off the mark. At that time, people were dealing with an entirely new situation in a jurisdiction that was unprepared to do such work. There was no baseline data, and barely enough resources to deal with the immediate problem. I believe the record does show that transmission to humans declined greatly, even ceased, after control was begun. Of course, perhaps it would have anyway, there's no way to know that. The situation in the Chicago area (transmission to hundreds of people, into October) this year provides an idea of what could have happened. We try do do efficacy follow-up whenever possible, but it's not a simple matter.

We have seen situations here on Long Island where WNV activity does appear to center around particular wetland areas. This does allow one to focus control efforts. However, we have also seen human cases appear to cluster in the highest, driest part of the county. I suspect this situation has something to do with this being a good area for the bird/mosquito cycle, despite the lack of obvious mosquito hot spots. Because WNV activity can be very widespread, figuring out how to identify high risk areas is very important, because you can't be everywhere.

I certainly hope CDC gets adequate funding to look into all these questions. We're trying to figure things out here, but it's not easy for an operational program to adequately address these questions.

Michael Gochfeld wrote:

Norman Robbins has posed some excellent questions, some of which are more easiliy answered than others.

Mosquito controllers have traditionally measured "knock down" efficacy of pesticides and application techniques. And in NJ, at least, some county mosquito commissions actually examine the species composition of live collections before and after spraying. This takes at least one trained person (doesn't need a PhD, a technician can do this).

It was appalling that in the 1999 NYC outbreak, there were NO reports of knockdown or efficacy, as if controllers were consciously avoiding it.

I think there are additional questions regarding serosurveys in both human populations and bird populations.

In a discrete area where a case has been identified, what is the proportion of seropositive humans within, let's say a km of an index case.

Does GIS mapping of cases reveal patterns that can point to particular ecosystems or sources of infection (i.e. around a pond).

Are there studies of avian populations in areas where WNV has not been recorded in humans (or dead crows), that can serve as baselines for future studies. There are statistical questions of how many negative birds one would need to accrue in order to state there has been no WNV activity in an area.

etc.

Michael Gochfeld

norman robbins wrote:

Dear West Nile List-Servers,

As a scientist, I am greatly disturbed to read lengthy discussions and CDC or State recommendations for WNv actions that often appear to be based mainly on opinion rather than citations of statistical validation. As much as one prefers prospective studies, could a thorough and sophisticated CDC retrospective analysis of activities (e.g. larviciding, adulticiding in 1999-2002) and resulting mosquito density and human disease, shed some light on questions we will once again be debating in the next few months?

I encourage List-servers to revise or expand the following list of questions in the hope that a collated version can be signed by you and sent to CDC advocating that they use resources to investigate these issues. My sense is that the CDC people are not at all resistant to undertaking this analysis -- they just need outside advocacy to gain the resources.

QUESTIONS FOR CDC TO INVESTIGATE BY ANALYSIS OF WEST NILE DATA TO DATE:

What is the STATISTICAL EVIDENCE AND PROBABILITY RANGE (not opinion) that:

1. larviciding (at WHAT intensity and frequency) reduces mosquito populations (by species)?

2. URBAN adulticiding (at what intensity, frequency, area and method) reduces mosquito populations, by species and for how long?

3. there are (or are not) acute or chronic human health effects of urban adulticiding in typical ULV amounts and frequency?

4. certain types of public messages or policies are more or less effective than others in reducing urban standing water (residential, public spaces, etc.)

5. one or another type of surveillance (dead crows, gravid or C0-2/light traps, virus-positive mosquitoes, etc.) predicts human disease with what kind of probability range.

6. both gravid and C0₂/light traps are desirable for human disease prediction.

7. there is some level of mosquito density which predicts risk of animal or human disease and calls for more aggressive mosquito management

Norman Robbins
Shaker Heights (OH) West Nile Task Force

-- 
-----------------------------------------------------------------------------------------------------------
WESTNILEVIRUS-L is an email discussion group for communication
and discussion about West Nile Virus, particularly regarding policy,
risk reduction and public education issues. It is moderated by
Dr. Lois Levitan at Cornell University's Center for the Environment.
To subscribe (or unsubscribe), send an email request to envrisk@cornell.edu.
Subscribers are encouraged to post to the group by sending an email to:
WESTNILEVIRUS-L@cornell.edu.  Please send only unformatted text,
without attachments.   Archives  are posted at: 
http://www.cfe.cornell.edu/erap/WNV/WNV-LArchiveIndex.cfm
------------------------------------------------------------------------------------------------------------