Mosquito spraying and public information

(Reference are current as of 8/29/18; of course, we are hoping that the state and County sites linked below will soon be updated so that we will have more data to study and share)

Don’t Spray Me! wishes to work factually and democratically to convey our negative view of pesticide spraying. We believe that the different levels of government should in turn work openly with citizens and taxpayers.

In its press releases about pesticide spraying, the Chester County Health Department says that it sprays “after exhausting all other available mosquito control strategies.” To us, this would mean at a minimum:

1) Reaching out to the County’s 73 municipalities to help them educate their residents about mosquito control, and to suggest the many precautions that residents should take in the regrettable case of airborne pesticide actually being disseminated in their community.

West Chester Borough and its citizens have dialogued exhaustively with the County Health Department and have taken on some of the needed education and outreach roles. We do not know that that has happened anywhere else in the County, except to some degree in East Bradford.

2) Larviciding (or helping municipalities to larvicide) pools of water and storm drains as needed to prevent the development of larvae from mosquito eggs there. This is the primary non-toxic mosquito control strategy.

DSM has had to file a Right To Know request with the PA Dept of Health asking when and where the County has conducted larviciding in West Chester Borough. The Health Department has said it either does not have records (2015-17) or does not have time (2018) to find out and has encouraged us to ask the State.

Furthermore, the County informs us of the general location of traps when it wishes to share high Vector Index readings or wishes to spray but not as a matter of course. Thus of the 31 mosquito traps set in the Borough, we have a general idea of where just 7* are. Therefore, we have no way to understand what role the readings from the other 26 traps played in the recent plan to spray much of the Borough — which Borough Council unanimously opposed (and which has not occurred).

According to the PA West Nile site, spraying has been conducted this year in 27 of the state’s 67 counties (as of Aug. 14; the chart is outdated). So are those 27 the only counties with supposedly high levels of risk for West Nile virus?

Not at all! According to “Recent West Nile Hot Zones in Pennsylvania in 2018” (also as of 8/14), 29 counties are described as: “There is no active county surveillance program in this county. DEP biologists do perform minimal surveillance in this county.” Of those 29 counties, 10 are said to be at “high risk” for WNV but they have not been sprayed. If WNV is such a crisis that in Chester County environmental and human health must be risked to broadcast pesticides in our communities, why do those 29 counties and especially the 10 “high risk” counties escape the same level of “treatment”?

The County justifies spraying on the basis of Vector Index scores. Although the math behind those numbers appears impenetrable to our statistician, the Vector Index level at which the County sprays municipalities varies widely, and some municipalities that have not been sprayed have higher Vector Indexes (per the information available online) than others that have been sprayed. How can there be such a discrepancy if the Vector Index is a reliable scientific tool?

And is it reasonable to think that WNV stops at municipal boundaries? Almost all of the County’s 24 untested municipalities are adjacent to municipalities with testing. For example, Parkesburg Borough (1.2 square miles) was sprayed on Aug. 9, but (as of 7/30/18) none of the 3 much larger adjacent municipalities was even being tested. Mosquitoes do know how to fly, and so do crows, the chief reservoir of the virus. But since almost no humans ever are aware of contracting the virus, what’s the big fuss anyhow?

If you wish to check the Vector Index for Chesco municipalities, see here. However, good luck in finding the levels for this month, as the posting stops as of 7/30/18. Since the County uses a 3-week window to justify spraying, that means that the public and elected officials have no online information to show any data that might underlie any recent spraying on the municipal level, nor any information either on the location of actual traps.

Citizens and their elected representative are being denied the information and data they need to form educated opinions in this important matter of environmental and human health (and the hundreds of thousands of taxpayer dollars being spent).

*8/30 just updated from 5 to 7 traps whose general locations we know in West Chester Borough, as we found out 2 more, in all:

• Greenfield Park
• College Avenue Pump Station (700 block of College Ave.)
• Everhart Park
• Kathy McBratnie Park
• Marshall Square Park
• 100 Block Magnolia Street
• 500 Block of East Miner Street

N.b. So 24 to go! Even if we knew precise trap locations, we wouldn’t publish them, because the Health Department fears interference with their traps and we don’t want to be blamed if there is any. And we do believe in valid data, when we can get it. Please note that where mosquitoes are trapped is not necessarily where they breed or spend most of their time.

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What is a Vector Index?

As of 2016, Chester County is using the Vector Index method of using mosquito data to predict the West Nile Virus threat to humans. Here is a summary from “2013 West Nile Virus in the United States: Guidelines for Surveillance, Prevention, and Control” at the CDC site, p. 18 (boldface added):

The Vector Index (VI) is an estimate of the abundance of infected mosquitoes in an area and incorporates information describing the vector species that are present in the area, relative abundance of those species, and the WNV infection rate in each species into a single index (Gujaral et al. 2007, Bolling et al. 2009, Jones et al. 2011). The VI is calculated by multiplying the average number of mosquitoes collected per trap night by the proportion infected with WNV, and is expressed as the average number of infected mosquitoes collected per trap night in the area during the sampling period. In areas where more than one WNV vector mosquito species is present, a VI is calculated for each of the important vector species and the individual VIs are summed to represent a combined estimate of the infected vector abundance. By summing the VI for the key vector species, the combined VI accommodates the fact that WNV transmission may involve one or more vectors in an area. Increases in VI reflect increases in risk of human disease (Bolling et al. 2009, Jones et al. 2011, Kwan et al. 2012, Colborn et al. 2013 in press) and have demonstrated significantly better predictive ability than estimates of vector abundance or infection rate alone, clearly demonstrating the value of combining information for vector abundance and WNV infection rates to generate a more meaningful risk index (Bolling et al. 2009). As with other surveillance indicators, the accuracy of the Vector Index is dependent upon the number of trap nights used to estimate abundance and the number of specimens tested for virus to estimate infection rate. Instructions for calculating the Vector Index in a system with multiple vector species present are in Appendix 2.

For the actual VI formula and a detailed example, see pp. 64-66 of the above Guidelines.