The Louisiana Paper

    First, the exact question asked of the District was "Has the District used models to project the effectiveness of spraying [adulticiding] vs. not spraying?"  WE STILL WANT THE DISTRICT TO ANSWER THIS QUESTION.

    The important question is whether adulticide reduces transmission of WNV as compared to doing nothing or to treating with larvicides and using other methods only.  What is the decrease in effective WNV transmission when adulticide is used?  This paper cannot possibly answer those questions to address the effectiveness of adulticiding vs. not spraying, as it was not a comparative study.  It was not a study in any way, shape or form; there were no alternative approaches examined; there were no controls.  Rather this is a documentation of what one district did and the impacts upon that district.  The goal of the district was to prevent new WNV cases, yet they had no marker against which to gauge success or failure, there WAS NO COMPARISON OF TREATMENT METHODS, and there were no control areas for comparison.

    The Louisiana District's usual mode of yearly operation is to use heavy adulticide each year throughout mosquito season and only to use larvicide in roadside ditches.  They state that larval samples were collected from roadside ditches to determine population densities.  Counts were biased because samples were taken in areas were larvae were likely to be found.  Larval counts were used to determine areas requiring treatment and the effectiveness of treatment [with larvicide].

    In the presence of WNV aerial adulticiding took place regardless of mosquito population densities, whereas in other years without WNV decisions to treat were ordinarily made based on threshold levels derived from trap data.  The paper does say that increased amounts of adulticide were used because the WNV primary vector species exhibits chemical tolerance and that the District's reason for upping the dose of pesticide was based on unpublished data.

    There was no study done to look at transmission rates.  In fact, the only thing the District knows is that human cases of WNV peaked in July and then declined.  Transmission rates were never considered, nor were control methods compared.  In fact the strongest statement made anywhere in the article is in the summary, and all it says is "Examination of data from mosquito population monitoring suggests that vector control activities, which were initiated earlier in the year and were conducted more frequently than usual, effectively reduced mosquito populations well below the five year average."  The paper considers all vector control activities and not just adulticiding, as posed in the questions.  Of course if you step up the normal mosquito control activities 46% -450% the five-year average in population numbers should drop.  It then sums up that the rapid drop in human WNV cases suggests that vector control activities were effective in preventing human transmission of WNV.  It makes this leap in logic with nothing to compare that statement to.  It does not even mention the normal seasonal decline in population.

    What is evident from the paper is that increasing larvicide activity had a far more dramatic impact on reducing mosquito populations than did aerial adulticide spraying.  There was an 8-fold drop in larval populations with only an increase of 46% in larval treatment.  While aerial adulticide use increased 450% and at best reduced mosquito populations tenfold.  Or a 46% increase in larvicide had an 8-fold impact and a 450% aerial had at best a tenfold impact.    There is no way to truly separate out what portion comes from larviciding and what from adulticiding.  Even the District itself says that larviciding is far more effective.

    District officials did not answer the question as to whether it had done models to show effectiveness, and the paper they rely on does not even discuss spraying vs. not spraying.  The only thing it does show is that if you load up on aerial adulticide you will not reduce populations as effectively as does larviciding.  This is exactly what we have been saying, and as of now the District has not shown any evidence to the contrary.  This paper was the best that Vicki Kramer, head of the California Department of Health Services, Vector Borne Diseases Section, and the SYMVC District could produce to justify the use of urban adulticides.  This is shameful, and we still would like an answer to the question.  If all they can say is "no" then they should say "NO" -- they have no evidence, no models, no studies.