RE: Arbovirus control of vectors

<x-charset iso-8859-1>Hindsight being 20/20, less adulticiding could probably have been done, but
we'll never know for sure. If I'm not mistaken, after we treated the "hot"
area in Queens (which had 30+ cases) human transmission essentially ceased
in the treated area. Now, perhaps it would have anyway, but transmission
did continue in other areas, and weather was suitable for further
transmission. That doesn't prove anything scientifically, but I think think
it's significant. In our county, we did relatively little adult control,
but we had data about our mosquito fauna, and no evidence of human
transmission.

Waiting until after human transmission starts before controlling vectors is
"closing the barn door...", and is a situation to be avoided. At that point
adult control might still be appropriate if further transmission is likely,
but much of the damage has already been done, since human cases are not
detected until some weeks after exposure. The ideal is to prevent exposure
by protective measures (screens, etc.) and by larval control. If that works
well, you might not see human illness, and people may wonder what the fuss
was about. SHould virus appear in mosquitoes, one should control them
before human exposure, realizing it will be impossible to know if zero, 1 or
dozens of illnesses will be prevented.

As far as risk perception, I find that residents of my county are very
intolerent of risk when it comes to mosquito-borne disease. In my
neighboring county, Nassau, there may be lawsuits filed over the 2 WNV
deaths there. While I do not care to comment on the merits of those cases,
they provide evidence that those families do not consider the deaths of
elders acceptable, and that they want accountability from the public health
community. My experience in dealing with the public and some polling data
suggest that this risk of contracting WNV is considered by most people in my
county as greater than the risks of mosquito control, although there is
strong opinion on the other side, of course. After all, WNV produces victims
in the here and now, while most of the risks alleged for pesticides involve
more subtle, long term effects. If you run the numbers for a town of
100,000 people, a Romania-like 4% infection rate translates into about 26
hospitalizations (using 1:150 ill/exposed) and 2-3 deaths (10% mortality).
WHile the media may have overplayed things a bit (OK, a lot)I can assure
you, this would not be acceptable were it to happen in my county.

The use of dead bird sightings as a surveillance tool itself creates
problems in terms of risk perception. We want the public to be concerned
enough to take the time to report dead birds, but yet not be too alarmed
when they see them. That's a subtle message to communicate to a mass
audience.

-----Original Message-----
From: Michael Gochfeld [mailto:gochfeld@eohsi.rutgers.edu]
Sent: Monday, January 14, 2002 7:47 PM
To: Dominick.Ninivaggi@co.suffolk.ny.us
Cc: rlampman@inhs.uiuc.edu; WESTNILEVIRUS-L
Subject: Re: Arbovirus control of vectors

I think I agree with you almost fully---but not quite on every point. For
example, the adulticiding in 1999 continued for weeks (sort of closing the
barn
door after the horse....)
I don't think it was always too late, given a roughly 2-3 week cycle time.

We are lucky that it was WNV rather than a really deadly ARBO virus, or for
that
matter rather than Dengue which may not be deadly but makes people wish they
were dead (or so patients told me).

And yes, I agree that it is ironic that instead of being relieved that it
was
WNV rather than the moderately more deadly SLE, the media reacted with
horror
stories about the alien invader. It certainly made good copy. But it
wasn't
easy to break into the press with stories about reducing breeding places.

Do you think that the lack of subsequent serious outbreaks (2000,2001) in
this
area was linked to aggressive mosquito control. WNV has a reputation in the
Old
World for shadow outbreaks in year 2 and then gradual disappearance, only to
reappear after intervals of several to many years.

As a former public health official I know how easy it is to be criticized in
retrospect for doing what seemed right at the time.

Michael Gochfeld

"Ninivaggi, Dominick" wrote:

> It is not fair to criticize mosquito control in general by pointing to
1999
> in NYC. That was a situation that hopefully will not be repeated again, at
> least not as long as we take the proper precautions. I was there when the
> initial situation was assessed in 1999. The adulticide response was
required
> because by the time it was realized that a mosquito-borne disease was
loose
> in a major metropolitan area, dozens of people were already hospitalized,
> there were fatalities, and the number of reported cases was increasing
> rapidly. At the time it was thought it was SLE, which has a history of
> large urban outbreaks. Given that it was too late for larval control
> (infected adults were flying), adult control was indicated, based on the
> information known at the time. It would have been great if NYC had been
> doing the things (surveillance, larval control) it does now, but that was
> not the situation in 1999. As more became known about the problem, it
> became possible to use the full range of modern mosquito control
practices,
> and the need for adulticide has decreased, as you've noticed. It is
unlikely
> that such widespread adult control will be needed in the future if proper
> vigilance is maintained. Still, scenarios may yet emerge where aerial
> application could be needed, although this would probably be in relatively
> small areas areas where ground application is not possible or likely to
> succeed, rather than entire townships or counties. We have such
situations
> in my county, for instance, where some areas that could harbor WNV are not
> accessible to ground ULV.
>
> We were very fortunate that the first exotic mosquito-borne arbovirus
known
> to reach our shores and establish itself was WNV and not something even
more
> lethal to humans. WNV demonstrates with certainty that these pathogens can
> arrive here and do very well, and there no reason to think it can't happen
> again. It would be wise to be better prepared so that the next "visitor"
> will not find such a hospitable new home and require such extreme
measures.
> Vilifying the people who went out and did something about the WNV problem
> and are trying to prevent the next such situation is not productive.
>
> -----Original Message-----
> From: Michael Gochfeld [mailto:gochfeld@eohsi.rutgers.edu]
> Sent: Monday, January 14, 2002 1:49 PM
> To: rlampman@inhs.uiuc.edu
> Cc: WESTNILEVIRUS-L
> Subject: 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
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Received on Tue Jan 15 10:44:13 2002