The "other" side
Neil at nwjones.demon.co.uk
Wed Aug 2 13:46:43 EDT 2000
In article <3987D5F0.622 at mindspring.com>
cherubini at mindspring.com "Paul Cherubini" writes:
> Similarly, the NABA website
> http://www.naba.org/wnvirus.html is now making sensational,
> worrisome, scientifically groundless claim that the mosquito
> spraying over New York City represents:
> -"rather significant risks
> not only to humans but to non-target species" and could be
> -"devastating to butterflies and other non-target species,
> and frightening and potentially harmful to many humans"
I contend that the above is false logic and that small snippets
of an article have been knowingly taken and used to create a misleading
impression. Does anyone have evidence to the contrary?
Anyway here is the article concerned. Judge for yourselves whether the
learned author is a "scarmongering extremist" or is he applying his considerable
scientific knowledge to find a better solution that both satisfies
human needs and preservation of the environment.
The following article recently appeared in the Summer 2000 issue of
Public Panic over West Nile Virus
by Michael Gochfeld, Professor of Environmental and Community
Medicine at the Robert Wood Johnson Medical School and School of Public
NABA members, even those living far from New York, could hardly have missed
the news coverage of the great encephalitis outbreak (or "scare"). The
discovery in September, 1999 that a new viral encephalitis had appeared
in the New York Metropolitan area,fostered a media campaign as well as
some ill-advised control efforts. The virus, genetically very similar
to the West Nile Virus which is widespread in the Old World, caused more
than 50 documented cases of disease and about 7 deaths of humans (all of
people over the age of 60), as well as widespread mortality in crows and
sporadic mortality in other birds. West Nile Virus belongs to a large
group of arthropod-borne viruses (nicknamed ARBO viruses) which includes
many viruses that cause more familiar forms of encephalitis as well as
dengue fever and yellow fever.
As do other virus, ARBO viruses require a host, in which to live. The
primary hosts for the virus are referred to as reservoirs. Viruses are
sometimes spread from host to host by other animals, which are then
referred to as vectors. For West Nile Virus, mosquitoes are the vectors
and birds are the primary hosts, while humans are an alternate host. In
areas such as Africa, where the virus has occurred for years, most bird
species have developed resistance to the virus through the selective
elimination of susceptible individuals and the survival of those who
could resist the infection. This evolutionary process is similar to the
process by which mosquito populations build up resistance to pesticides,
or by which bacteria develop resistance to antibiotics.
Having studies ARBO viruses briefly in Trinidad many years ago, I have
a healthy respect for their potential impact. Nonetheless, it is
relatively difficult to contract an ARBO virus disease. These diseases
are not spread directly from person to person. Rather, a person has to
be bitten by an arthropod (usually a mosquito) that has recently bitten
an infected animal in whose blood the virus was already circulating.
Not only are humans not the primary host for this virus, but human are
probably not even a very good host. Based upon experience with other
West Nile Virus epidemics, we know that typically less than one
tenth of one percent of people bitten by infected mosquitoes develop
any clinical signs of disease, and of those who do develop disease
symptoms most do not develop the serious encephalitis manifestations.
However, up to 10% of those who actually develop encephalitis may
die of the disease.
It is clear that there is something particularly terrifying about
encephalitis that conjures up more frightful images than other more
common infectious diseases, such as influenza, which each year kills
more people than does encephalitis. Thus it is easy to understand why
the arrival of this West Nile-like virus caused such consternation
and alarm in the media and the public. However, in a city such as
New York, where more people die each day of respiratory diseases
such as asthma and tuberculosis than died in the entire two month
encephalitis "epidemic," it is surprising that there was such a
dramatic response among politicians and public health workers who
expressed an urgency to eradicate mosquitoes. Particularly fearsome
was the prospect that infected birds would soon be migrating and
spreading the virus.
Often, when people think of mosquito control, their first thought
is pesticide spraying -- what I call "quick Henry -- the Flit"
mentality (after a popular ad of 50 years ago). This is obviously
what politicians thought of first when West Nile Virus was discovered
in New York. Indeed, pesticide spraying can reduce local outbreaks of
mosquitoes temporarily, but populations recover quickly and over the
long term pesticide-resistance emerges. However, serious mosquito-born
e diseases, such as malaria, encephalitis and dengue, continue to
occur in many parts of the world, requiring public health officials
to develop effective means of reducing risks to humans.
The well-established public health techniques for preventing exposure
to mosquito-borne diseases include eliminating mosquito breeding
places or treating them to eliminate the larval mosquitoes, the use
of screens or netting in homes, the use of mosquito repellants,
reducing exposed areas of the body and reducing activities that
expose people to mosquitoes. The use of pesticides to eliminate
adult mosquitoes is a last resort and should be used only as an
interim measure when and where there are large infestations of
mosquitoes in close proximity to human populations.
Despite these recommendations from the Centers for Disease Control
and the World Health Organization, widespread spraying (termed
"broadcast" spraying) was conducted in the New York metropolitan
area -- even at a time when mosquito populations were declining
naturally due to cool weather. Pesticide advocates asserted,
incorrectly, that the pesticides used were innocuous to humans
and pets and ignored outcries about the harm to non-target species.
Advocates even pointed to the Monarch migration - the largest in
years - as evidence that the spray was harmless to butterflies.
Although reports of dead birds were widely publicized, no attempt
was made to document dead butterflies or other non-target insects.
Television coverage emphasized the spraying and reported where
spraying was being conducted, but rarely described all the
above-mentioned steps that homeowners could take to reduce
their contact with mosquitoes. There were impressive exceptions.
Union County, New Jersey took out a full-page advertisement in
the Newark Star Ledger explaining why it was not spraying and
clarifying the recommendations that empowered readers to act
in a way that reduced their risk of mosquito bites. Experts in
environmental medicine at our Environmental and Occupational
Health Sciences Institute concluded that the media coverage
of deaths and spraying actually distracted the public from
these effective measures and created the mistaken impression
that broadcast spraying was the first choice, the preferred
effective solution to West Nile Virus disease, and the only
thing that needed to be done.
In some counties, the finding of a single dead crow became a
sufficient stimulus for county-wide aerial spraying, ignoring
several important features of viral disease ecology,
avian ecology and pesticide science, and particularly ignoring
the rather significant risks of broadcast pesticide spraying
not only to humans but to non-target species that are of
economic, aesthetic and ecological importance. Moreover,
the investment in spraying diverted scarce funds from other
public health problems.
Although malathion (an organophosphate) and the synthetic
pyrethroids sumithrin (Anvil) and resmithrin (Scourge) have
relatively low toxicity to humans and other mammals and
birds, they are not innocuous or harmless. People can become
sick from exposure to these pesticides as well as from the
so-called "inert ingredients" in which they are applied.
This is particularly true when spraying is repeated.
Organophosphates such as malathion and pyrethroids reduce
the activity of the enzyme acetylcholinesterase which is
essential for normal nervous system function. This is the
mode of action by which these pesticides kill insects and
harm humans. For example, malathion is in the same class of
chemicals as the nerve gases such as sarin, and workers who
produce malathion or blend it into final products as well
as those who apply it, if not well-protected, can suffer
agitation, sleepy difficulty and weakness, as well as anxiety,
forgetfulness and depression.
Pesticides, even those with relatively low acute toxicity to
adults may be more problematic in young children, with
immature nervous systems, and in the elderly. It is also
a problem for those who have, or believe that they have,
unusual sensitivities to pesticides or other chemicals.
TV broadcasts cautioned listeners to remain indoors during
spraying, but the time of spraying at any one location could
not be predicted and many people could not remain indoors all
day on the announced day of spraying. Moreover, it is easier
to make a house mosquito-proof than spray proof. Indeed, it is
well-established that outdoor air pollutants tend to accumulate
at higher levels indoors than out.
The reason that my colleagues and I argued against broadcast
spraying are 1) in broadcast application most of the spray falls
on areas where the likelihood of mosquito-human contact
is low. Thus areas with few mosquitoes but many other non-target
species are sprayed, as are densely populated residential areas
where mosquito populations are low to begin with. 2) It is not made
clear to the public that these broad-spectrum insecticides kill many
other insects besides mosquitoes. These include economically valuable
insects such as honeybees, praying mantids and ladybird beetles as
well as conspicuous and attractive species such as butterflies.
Such insecticides also destroy innumerable less conspicuous insects
that are important components of biodiversity and are the food for
birds and small mammals. This, after all, was the message of Rachel
Carson's "Silent Spring" published in 1962, that even
her detractors recognize as one of the most influential books of the
In weighing the risks and benefits of mosquito control, we should also
consider the disease itself and the risk to the human population. The
media always paired the words "lethal" or "deadly" with "West Nile" or
"encephalitis," reinforcing in the publics mind the danger from the
disease. But it would be equally appropriate to characterize West Nile
Virus infection as "inapparent," "usually asymptomatic," or "occasionally
serious." Seven deaths in a population of over 10 million people
over a one month period is certainly tragic, but pales besides the
number of deaths from many other diseases that are addressed less
The only human epidemic of West Nile Virus infection that has been
well-studied occurred in Romania in the late summer of 1996.
The U.S. Centers for Disease Control and Prevention, certainly
the premier infectious disease control agency in the world,
assisted in the evaluation and control of that epidemic and
recently published a report in The Lancet, the leading British
In that epidemic an estimated 94,000 people were infected by the virus,
of whom about 400 developed clinically apparent encephalitis confirmed
by virological studies. Fifteen of those people, almost all over the
age of 65, died. Thus, even if one is bitten by an infected mosquito,
the risk of suffering disease is very low and the risk of dying much
lower. Moreover, in Africa where West Nile Virus has been recognized
for more than sixty years and where it is widespread, there have been
very few human epidemics. In fact, West Nile Virus infection is
characterized by its sporadic outbreak in humans, even in areas
where it is endemic in birds. This is likwise true of related
infections, such as St. Louis encephalitis and Easter equine
encephalitis, where 30 or more years may pass between human
outbreaks. A knowledge of these numbers is crucial in assessing the
risk-risk tradeoffs essential to public health decisions in this area.
Finally, emphasis has focused on dead birds, particularly dead crows.
Crows are among the most susceptible species to West Nile Virus in the
Old World and are obviously going to be a major reservoir for the virus
in the New World. The fact that West Nile Virus does not usually kill
the birds that carry it is one piece of evidence supporting the
hypothesis that it recently arrived in North America, where our
crows and other birds have yet to develop any immunity. However, in
order for the disease to be sufficiently widespread in the birds to
cause a number of bird deaths, and in order for there to be enough
infected birds to infect enough mosquitoes to produce an epidemic,
the virus had to be present in the bird population for many months,
perhaps even for years. In southern Europe the virus was present
for several years before the Romanian outbreak.
This means that the virus is probably already fairly widespread
in birds, not just in crows. Birds, including crows, range
widely and are not cognizant of county barriers. Thus a bird
that dies in county A today may have been infected in county B
last week. Thus, to base county-wide control programs on a single
dead crow is inappropriate.
It is interesting to contrast the experience and response in
New York versus that in New Jersey, which has a statewide
network of County Mosquito Control Commissions, established
long ago to control New Jerseys state "bird," the mosquito.
New Jersey has extensive experience in conducting surveillance
programs for viral encephalitis, including the strategic
placing of sentinel chickens in cages in area where mosquitoes
are prevalent. The chickens are then regularly tested for virus
activity. This surveillance program successfully reduced human
and equine infection by Easter equine encephalitis and St. Louis
encephalitis even though these viruses continued to be active in
Although New Jersey abandoned this program years ago because the
yield seemed to be low, it quickly re-instated surveillance when
news of West Nile Virus arrived. Moreover, the county Commissions
have been vigilant in keeping infestations of mosquitoes in check
through the use of Integrated Pest Management which reduces breeding
areas in proximity to human activities, introduces natural predators
to keep mosquito populations in check and uses judicious
spot-applications of larvicides. Spraying to control adult
mosquitoes is considered a last resort to be used only when
local infestations become a serious nuisance or health threat.
Local health officials, the media, and the public, need to be
aware of these facts and need to be reminded lest our vigilance
is reduced and serious disease outbreaks occur. The seductiveness
of aerial pesticide spraying, devastating to butterflies and
other non-target species, and frightening and potentially harmful
to many humans, should be the last, not the first, approach to
controlling disease spread.
West Nile Virus is likely to surface again this year, heralded
by dead crows and great fanfare, and the pressure to use broadcast
spraying may be powerful indeed. Improved surveillance will show
that the virus occurs over a much wider area than just the New
York metropolitan region. Spraying is likely to begin much earlier in
the season - June rather than August. If this happens, it is
likely that the impact on butterflies and other non-target
species will be severe.
Alternatively, public health agencies can focus on the
less flashy, but more effective,strategies for reducing
mosquito populations. Integrated Pest Management has been very
successful in reducing mosquitoes in New Jersey and elsewhere
where it has been tried. It can virtually eliminate the risk
of an ARBO-virus disease, without eliminating many other
valuable or aesthetically pleasing creatures and without
jeopardizing human health.
Neil Jones- Neil at nwjones.demon.co.uk http://www.nwjones.demon.co.uk/
"At some point I had to stand up and be counted. Who speaks for the
butterflies?" Andrew Lees - The quotation on his memorial at Crymlyn Bog
National Nature Reserve
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