Re: Arbovirus control of vectors

I pretty much agree with Richard Lampman's recent posting. Adulticiding
is not the first choice, but you wouldn't know if from reviewing the
1999 control programs. And even in 2000 aerial spraying for adult
mosquitoes was still widespread in New York.

I also agree with the philosophy and practice of integrated pest
management as ecologically sound and cost effective.
After listing some useful web-sites, R. Lampman goes on to provide a
lucid and orderly description of mosquito control.

It deserves a much wider audience.

However, my point was not only that adulticiding (a neologism I'm not
fond of) was generally inappropriate, but that the characteristics of
WNV as an infectious disease did not warrant the hype and aggressive
control programs. I have previously circulated my write-up explaining
why that is the case, but basically very few cases of mosquito bite
result in infection (and very few infections turn into illness, few of
which are serious). Moreover, West Nile accounts for only about 5% of
the deaths from mengingo-encephalitis in the NJ-NY-CT area, and the 1-5
deaths per year, pales besides the death rate from other diseases (e.g.
bronchitis, pneumonia, asthma) which hardly garner such attention.

I think that mosquito control is a good and necessary program for
communities that have large mosquito populations.
I think that IPM and habitat control are good ways of accomplishing
this.
I think that surveillance and monitoring are necessary parts, and that
local larviciding may be necessary.

But I don't think that West Nile has much to do with it. However, there
are other more serious mosquito-borne encephalitides such as Eastern
Equine which deserve public health attention (higher infectivity, higher
mortality, higher morbidity in survivors).

Michael Gochfeld

Richard Lampman wrote:
>
> I apologize for the first posting. As it was initially held up, I
> edited it substantially.
>
> The exchange about controlling arbovirus vectors has had several
> obvious misstatements and some of these seem to be polarizing people
> with different perspectives.
>
> First, mosquito abatement has been misrepresented as favoring adult
> control as the major line of defense. Many of the emails suggest the
> money for aerial spraying should be used for other more environmental
> efforts. There should be little argument on this topic because aerial
> spraying is usually held in reserve after the other methods fail. I
> think few would argue in favor of starting with aerial spraying. If
> you are dealing with groups dealing the the control of mosquitoes that
> feel adulticiding is the only approach available to protect people
> from WNV, then you should question their tactics. Adulticides are
> usually held in cases of emergency (indication of active urban cycles
> of transmission), or when larval control is not feasible in an area
> (usually due to inaccessibility or size), or if funds and expertise
> are inadequate to conduct a proper abatement effort. Please refer
> those groups to the IPM approach championed by many states like NJ,
> CA, FL, IL, TX, etc. (although there are cases where ULV spraying is
> appropriate and relatively safe).
>
> I recommend the following sites to Michael Gochfeld in order to see
> an integrated approach as proposed at Rutgers in New Jersey.
> http://www-rci.rutgers.edu/~insects/ipm.htm
> http://www.rci.rutgers.edu/~insects/bmpmcnj.htm#appendix
> http://www.rci.rutgers.edu/~insects/hisreas.htm
>
> Generally mosquito abatement requires - seasonally identifying and
> mapping larval habitats of target species in the area under
> consideration, seasonal surveillance of those habitats for larvae,
> breeding site sanitation and/or manipulation if the habitats produce
> the target species, and relatively target-specific biological
> larvicides if source reduction of breeding sites is not possible or is
> ineffectual. Synthetic chemical larvicides come next (a few of which
> are safe enough to be allowed to be present in drinking water).
> Larval surveillance at the sites gives you some idea of the efficacy
> of control efforts and adult surveillance gives you some idea whether
> you've identified the major sites. This is often a major problem
> (missing major breeding sites). Adult surveillance coupled with
> pathogen detection gives you an idea of relative risk. With WNV we
> also have natural sentinels, the Am. crow and other corvids, which
> indicate by an increase in mortality that WNV transmission is
> occurring in a general area. Whether number of dead birds per unit
> area per time unit can be used to estimate various levels of human
> risk, remains to be seen. Also keep in mind that it is very likely
> that the target vector species varies regionally and seasonally. If
> you have equine cases then you face a risk of transmission to humans
> (of course this also varies based on demographics of the area and time
> of the year and vector species involved).
>
> If, after all the other treatment options, you are left with an
> indication of active transmission in an urban area, then you are
> facing an emergency situation. Assuming you've kept the public
> informed and involved throughout the process, the adulticide option
> need to be considered (adulticides can be sprayed in a variety of
> ways, although the preferred method is by ULV). Adulticides, if used
> properly, can reduce the flying mosquito population which reduces risk
> of transmission. Mosquito abatement is an area-wide and area-specific
> problem. Although generalizations can be made about IPM strategies,
> they must be tailored to the physical, biological, ecological, and
> political characteristics and restraints within a specific PMU.
>
> Some people appear to have misread Dominick Ninivaggi's statements
> about mosquito control and concluded he promotes aerial spraying as
> the first line of defense. To me, he seems to agree that the
> non-pesticide techniques are the first line of defense, but pesticides
> should always remain a viable option. He's also addressing the
> chemophobia many show toward pesticides despite the overwhelming
> evidence of their safety. However, if used improperly (not following
> the label), they also pose a risk which is why pesticide applicators
> should always be licensed and should maintain a good, open to review
> record of pesticide use. Unfortunately, most problems with pesticides
> arise from operational issues. For example, I received a newsletter
> that said one east coast city changed spraying times from dusk and
> dawn to two hours on either side of midnight because they wanted to
> avoid times when people were outside. So, if they were targeting
> Culex pipiens, then they switched from spraying at periods of high
> flight activity to periods with relatively low flight activity,
> keeping in mind ULV adulticiding targets the vector on the wing.
>
> A second concept presented by some in this discussion is that states
> or communities are wasting money by trying to manage mosquitoes. This
> is a dangerous and poorly informed assumption. I look at WNV and see
> the potential for SLEV-type outbreaks (not to mention equine and avian
> epizootics). The statement that WNV is insignificant because it's not
> the major cause of meningo-encephalitis is truly without merit. That
> attitude is like
> saying we should not invest in studying tire defects because
> defective tires are not the major cause of car accidents. Such
> conclusions about arboviruses are based on a lack of knowledge about
> the history of mosquito-borne diseases in the US, mosquito biology,
> and mosquito
> IPM. The truth of the matter is that we have been losing expertise in
> medical entomology in the US because we have assumed vector-borne
> diseases are only important in tropical areas. We still seem to be
> enamored by the concept of a "silver bullet", except now it has
> shifted from the use of a pesticide to the use of a vaccine or
> antibiotic.
>
> In the absence of low-cost, readily available, efficacious, and
> low-side effect
> vaccines or antibiotics, vector management is the only practical
> alternative for protecting the population (Breeland et al. 1980).
> The rapid spread of WNV, the large number of birds infected with WNV,
> the ability to overwinter in northern and possibly southern areas,
> and the number of equine cases last year all of these tend to indicate
> a
> potential for human outbreaks in the future. The statement that we
> should ignore WNV until becomes a significant mortality factor
> among the elderly seems unduly callous. Furthermore, assuming it will
> be a minor problem reminds me of attitudes toward SLE in 1974, right
> before a
> major outbreak throughout much of the eastern US. Mosquito management
> of vectors does reduce risk and there are numerous examples throughout
> the US.
>
> Third, most mosquito abatement districts do maintain a record of
> mosquitoes caught in one or more types of traps or by dipping and
> they use this to monitor the effectiveness of their treatments,
> although this is not necessarily done in a standardized way or in a
> way that directly correlates to clinical cases. The efficacy of
> various treatments for different mosquito species have been
> well-demonstrated, although it is beyond the financial capability of
> most abatement groups to "scientifically" document the direct impact
> of each treatment on target and non-target species. However, the
> cornerstone of managing an arthropod-borne pathogen is surveillance.
> An active monitoring program of larvae and adults determines when,
> where, and how to treat. It also provides the ecological data to
> delineate the proper management strategies for different habitats.
> And, season-long surveillance detects failures in treatment
> interventions which may be due to operational problems, resistance,
> etc. If your area does not maintain records, then someone has missed
> a fundamental principle of IPM.
>
> Arbovirus transmission cycles are complex and are influenced by
> spatial and temporal differences in vector, host, and pathogen
> abundance, biology, and interaction with each of these components and
> with environmental variables. Furthermore, mosquito abatement is an
> area-wide and area-specific problem. Because of the complexity of
> arboviral encephalites there will probably never be a model that
> allows you to say X% of infected mosquitoes (or wild hosts) of a
> specific species will potentially result in Y% of human infections.
> That's why you have listserv subscribers that keep asking questions
> like "how many mosquitoes do you need before you do X intervention"
> and you end up getting an abundance of less than satisfying answers.
>
> This doesn't mean there hasn't been a considerable amount of study on
> the epidemiology of arboviruses. Take for example St. Louis
> encephalitis. I recommend reading St. Louis Encephalitis, 1980, ed.
> by T.P. Monath. There is a fantastic amount of data in this book (and
> occasionally West Nile virus is also covered). There are also
> examples in the book of cases where aerial ULV and
> adulticide spraying have successfully controlled vector species.
> One of the problems with vector management is that it optimally
> requires a leader that has a solid academic and research background in
> the biology of mosquitoes, population dynamics, field ecology,
> pathogen transmission cycles, biological and synthetic pesticides,
> etc. Typically, an entomologist is the last person on everybody's
> list. Let me give you an example. Several reports made it sound like
> the discovery of Cx. salinarius as a vector of WNV to humans was a
> new, unexpected development. Let's go back to a chapter from Monath,
> 1980.-- On page 316, Mitchell, Francy, and Monath make the following
> statement - "These data support our belief that, in the eastern US,
> Cx. salinarius and Cx. restuans play a role in enzootic SLE virus
> transmission second only to Cx. pipiens; in addition, Cx. salinarius,
> ... may be involved in transmission to man and in viral maintenance
> ..."
>
> Richard Lampman
> --
> Richard Lampman, PhD
> Research Scientist
>
> Medical Entomology Program
> Center for Economic Entomology
> Illinois Natural History Survey
> 607 East Peabody Drive
> Champaign, IL 61820
>
> Med. Ent. Program: 217-333-1186
> Office phone: 217-244-5631
> FAX number: 217-333-2359
> email: richlamp@uiuc.edu
> rlampman@denr1.igis.uiuc.edu
Received on Mon Jan 14 15:15:18 2002