All Roads Lead to Spraying?

    During the August 9, 2007 meeting of the Sacramento City Council, District Manager David Brown minimized the importance of Washington, D.C.'s decision not to spray adulticides but instead to use sensible control methods for WNv by saying that D.C. does not have the "encephalitis mosquito" and thus implied that the D.C. region has an easier time managing the virus than we do in our supposedly more harsh region. Not only is this statement misleading, but it is also a contradiction to what Brown had been saying for years were the primary mosquito species carrying WNv. The fact is even though D.C. is a region with a much more hospitable climate to mosquitoes carrying WNv, officials there are able to handle the issue without spraying but instead with sensible control measures. We give details below, highlighting several policy justifications of local vector control officials, questioning some of their assertions, and discussing relevant facts associated with WNv and the species responsible for the spread of the virus.  

THE OFFICIAL REASON TO SPRAY:  In the formal answers to questions submitted at the August 23, 2005 forum in the Davis City Council chambers, in order to justify aerial spraying Brown had said that "the biological reason behind this spraying technique is that the mosquitoes that transmit WNv (Culex pipiens and Culex quincifaciatus) primarily feed on birds and are considered primary vectors of WNv within the bird population, additionally acting as bridge vectors to humans or other mammals." See more questions from that forum and our responses here.

NOTE: There is no mention of Culex tarsalis in any portion of the official responses in that forum. That is, this large panel of local experts and officials was apparently completely unaware of Culex tarsalis at the time. However, two years later at the 8/09/07 meeting Brown characterized Culex tarsalis as the primary threat. Also, a search of the CDC database turns up no mention of a species Culex quincifaciatus. One with a similar name, Culex quinquefasciatus, is considered one of the "two least efficient laboratory vectors" in a 2002 study by some UCD researchers. In that study Culex pipiens is characterized as one of the "most efficient laboratory vectors."

QUESTIONS: Since this was two weeks after Sacramento had been sprayed aerially with adulticides, we question whether Sacramento was sprayed partially because of an imaginary mosquito Culex quincifaciatus, or because of a very inefficient vector, Culex quinquefasciatus? If these local experts and officials are this uninformed about the species of mosquitoes in this area, are they also uninformed about the safety and efficacy of adulticiding?

THE OFFICIAL REASON FOR AERIAL SPRAYING: In order to justify aerial spraying of urban areas District Manager Brown has repeatedly claimed the biggest problem is the back yards in this district. The mosquitoes in our urban back yards are indeed Culex pipiens, sometimes known as the "sewer mosquito" or the "house mosquito." Brown and others claim that the only way to reduce their numbers quickly enough is by indiscriminate aerial spraying because truck spraying or backpack spraying won't work since these methods cannot reach back yards. 

WHY BROWN ARGUES WE MUST SPRAY EVEN THOUGH D.C. DOES NOT: In the August 9, 2007 Sacramento City Council meeting, when asked about the decision in Washington, D.C., of not spraying adulticides, District Manager Brown said the following: "I think what is important to note with that process is that at least at this point there's never been a need to try to perform adult mosquito control because of the risk.  We have more than one species of mosquito here in Sacramento and Yolo County. We have literally hundreds of mosquitoes throughout the United States. Two of the primary mosquitoes that are very efficient vectors of West Nile virus reside here in Sacramento County, called Culex pipiens and Culex tarsalis. Culex tarsalis in fact has been identified as the encephalitis mosquito here in California. It happens to be the most dominant mosquito that we have here in Sacramento County. In Washington, D.C., they do not have Culex tarsalis, and they have not seen the risk levels increase to where there's been a need to perform adult mosquito control activities."

NOTE: Suddenly a species that was previously unknown to the experts on the Davis panel in 2005, including David Brown, Culex tarsalis, is now the "encephalitis mosquito" and is the purported reason we must spray. Brown claims that since D.C. does not have this species, it is not imperative for D.C. to spray, as it is for us. Brown did not seem troubled that the main species he now offers up to justify the spray, Culex tarsalis, became known to local experts only after they had first sprayed Sacramento. Also, these statements invariably begin with the assumption that adulticide spraying is effective and completely ignore the evidence about how ineffective it actually is.

QUESTIONS: So, Washington, D.C. has an easier time of it than we do in our  harsh region because they do not have the "encephalitis mosquito," Culex tarsalis?  But is this really the case? Please see the comments by our entomologist below (indented), as the situation is very much the other way around relative to climate, extant mosquito species, and risk. Also, what about Culex pipiens? We have supposedly been spraying indiscriminately in Sacramento urban areas because of this species. Does D.C. not have this threat either?

FACT: Culex tarsalis is much more abundant than Culex pipiens in California, outnumbering it 9 to 1 in some situations. Culex tarsalis is suspected to be the main vector that has transmitted WNv in California.  However, Culex tarsalis is the mosquito playing a major role in the virus' rural amplification in birds but not urban, so what sense does it make to spray urban areas if the main threat is Culex tarsalis?

FACT:  A very inconvenient truth:  The D.C. Arbovirus Surveilance and Response Plan for 2004 says "Multiple mosquito genera have been identified in the District as carriers of West Nile virus and malaria.  The Department of Health has made a commitment to identify and test mosquitoes for diseases that may threaten the public health and safety of the residents and visitors in the District.  Culex pipiens is the predominant carrier of the West Nile virus in the Washington, D.C. area" (emphasis ours). So, while D.C. does not have Culex tarsalis, it does indeed have the species Culex pipiens that supposedly justifies the indiscriminate aerial spraying of urban areas here.  Beyond that, however, the D.C. area has several potent vectors that are much more likely to transmit to people than either Culex tarsalis or Culex pipiens and a humid climate that prolongs the survival of mosquitoes and promotes the transmission of the virus.

FACT:  When we look at what happened at the local public meetings to date and compare the climates of D.C. and Sacramento in more detail, this bizarre web actually gets even more tangled.  In a letter to the Sacramento City Council after having viewed the tape of the August 9, 2007 meeting, our entomologist, who has extensive experience in different areas with mosquito control, including the Choco Province of Columbia (for malaria control), and is knowledgeable about mosquito control around the world, writes:

"Members of the Sacramento City Council,                                      
    Though I am not a resident of Sacramento, but rather a resident of Davis, still I hold an exceeding interest in the Sacramento City Council proceedings concerning the aerial spray applications by the SYMVCD, purportedly to abate the transmission of West Nile virus. Statements entered into the record by Glennah Trochet, David Brown and David Tamayo leave me appalled and affronted both for the inaccuracy of some and the implications of others.   
    Mr. Tamayo made a claim to your council that open public meetings of the SYMVCD had been abandoned due to lack of participation. This claim is an outright falsity. The last public workshop, held on Jan 12, 2006, was well attended and the presentation made by Mr. Steven Zien had drawn so many questions from the participants that my scheduled presentation on risk/benefit analyses was rescheduled by Chairperson Parella to be given at a workshop devoted to risk/benefit analyses scheduled for Feb. 14, 2006. This public meeting was canceled without explanation.

    It troubles me greatly that until now the public has not been informed of the lack of any scientific assessment of the exposure risks from aerial ULV applications of pyrethrum and piperonyl butoxide. We are, indeed the unwitting (and I, for one, unwilling) subjects in a great experiment. In this case, so far, there hasn't been any scientific assessment performed of either the exposure risks from the insecticide or the actual extent of the transmission of the virus. [emphasis added]                                                                   

    In spite of this appalling failure, even to make a measurement of the human exposure risks, Dr. Trochet claimed to your council that she knew the exposure was so slight that she deemed it not cost efficient to make such a study. How, pray tell, does the good doctor know the exposure was so slight if it was never measured? Whose standard of cost efficacy is the doctor employing? The one Union Carbide utilized at Bhopal?            
    Mr. Brown made a number of claims to your council in response to comparisons of Washington DC where the problem of WNv has been managed without insecticide applications such as this aerial spray. Two of these are distinctly false. The DC area actually experienced a more severe outbreak than the 2005 Sacramento outbreak. 11 people died from WNv in the DC area in 2002. Mr. Brown claimed the transmission had never been critical enough to "require" spray activities. 
    He went on to claim that DC lacks one of the two potent vectors we have here, Culex tarsalis, and that's why their control efforts are easier. In fact, we lack several potent vectors that the East coast has to contend with such as Aedes solicitans, that are much more likely to transmit to people than either Culex tarsalis or Culex pipiens.  But more importantly, our climate is hostile to the transmission of this arbovirus where the more humid climate of DC promotes it.  This has to do with the relatively low survivorship of mosquitoes in arid and semi-arid habitats such as ours, and the length of time required for the incubation of the virus in the mosquitoes. Only one in a thousand will live long enough to transmit the disease in our climatic conditions.  
    What is stunning to me about Mr. Brown's statement is the contrast to prior claims that we must employ aerial spray because the vectors, Culex pipiens, are canopy feeders and ground spray won't work. When presented with the remarkable efficacy of Culex pipiens control with exclusively larval control methods by Washington DC, Mr. Brown is suddenly aware of the actual principal vector, Culex tarsalis. It must be noted that this mosquito is associated with irrigated agriculture, and all reasonable control measures would be most effectively applied in rural settings and not aerial spray over suburbs and residential neighborhoods. It also should be noted that the abundant breeding of this mosquito brings an exponentially increasing number of new adult mosquitoes into our communities each day that will not have been effected by the spray in any way.         
    In fact, there are a number of superior larval control measures that are not being employed by SYMVCD. Researchers with CIB in Medellin, Colombia are maintaining a recently isolated culture of Bacillus thuringiensis ser H14 that is much more infective in Culicines and persists with ongoing populations in the manner of classic bio control. They are also collaborating with the Pasteur Institute on cultures of Lagenidium giganteum, natural California isolate, which show the same properties of establishing ongoing populations. In Oaxaca, Mexico, malaria, dengue and yellow fever are being controlled utilizing Mermithid nematodes in the genus Romanomermis that also establish ongoing populations.       
    If SYMVCD deemed fit to establish a similar culture facility here in Sacramento it would add to the local economy as well as provide a safer measure of mosquito control for our communities. But even more significantly, these measures would fit the type of control the best scientific models designate as effective, while the aerial applications being utilized have not been proven effective or even tested for their safety."                        
Jim Northup                                                                    

QUESTIONS:  A number of vexing questions arise:
We consider these questions to be very troubling. The chief of the Vector-Borne Disease Section of the Department of Public Health has a PhD in entomology from UC Berkeley, and there are PhD entomologists on the Board. These scientists either know or should know there is no evidence to justify adulticiding. Is it really the case with our vector control and public health officials that "all roads lead to spraying?" We have seen other instances suggesting facts and science may not drive this matter for local officials.  Instead, officials seem to be implementing unsupported, ineffective, and even harmful policies, relying on specious claims to justify them.