Florida Farm and Feed

Is it really an epidemic? Will Aerial Spraying be Worthwhile?

West Nile Virus: not a "deadly epidemic"

It would be unfair to downplay the seriousness of a severe infection of West Nile Encephalitis. It is reported to be a painful disease that can be debilitating if not fatal.

Fortunately, it is extremely unlikely that you or any member of your family will get sick and die from WNV, even in areas where it is endemic. While determining any one person's risk level is difficult, it is important to point out the range within which uncertainty exists. Some of the evidence available for understanding the risks of illness from the bite of a WNV-infected mosquito follows.

West Nile Virus was first identified in the United States during the summer of 1999 when a large number of birds were found dead in the New York City area. Out of a population of more than 7 million, 62 people -- or less than .0009% -- became ill with the virus, and 7 died (1 in 1 million).
The median age of the people who became ill was 68 years. The seven who died ranged in age from 68 to 87 years of age.
Of these seven, one had HIV and 3 were on immunosuppressive drugs for cancer.
By comparison, more than 2,000 New Yorkers died from the flu in 1999.

In 2000, one 82-year-old man from Little Falls, N.J. died from WNV. The victim had an undisclosed pre-existing medical condition "that probably contributed to his death as well," said Dr. Eddy Bresnitz, a New Jersey epidemiologist and assistant Health commissioner.

The New York City Department of Health Bureau of Communicable Disease's Questions and Answers About West Nile Fever answers the risk question this way:

Q: If I live in an area where birds with West Nile Fever have been reported, and I am bitten by a mosquito, am I likely to get sick?
A: No. Even in areas where mosquitoes do carry the virus, very few mosquitoes -- perhaps only one out of 1,000 -- are infected. The chances that any one bite will be from an infected mosquito are very small.

Q: But if I am bitten by an infected mosquito, won't I get sick?
A: Probably not. Even if you are bitten by an infected mosquito, your chances of developing illness are roughly one in 300.

From these statistics we can conclude that if 1 in 1000 mosquitoes in an area with WNV are carriers, and your chances of getting sick from a bite from an infected mosquito are 1 in 300, then a bite from 1 in 300,000 mosquitoes could make you ill.

A New York City Health Department survey of blood samples taken from people who lived in northern Queens, the epicenter of the 1999 outbreak, showed that 19 out of 677 tested positive for the virus. But none had become seriously ill, and all either reported no symptoms or mild illness, such as a low-grade fever. The survey concluded that between 1.2 percent to 4.1 percent (between 533 and 1,903 people) of the 46,000 residents in that three-square-mile area had been infected. Of the infected group, four people in the sample had non-specific aches, pains or fever.

WNV was first identified in the Boston area in July 2000 when a dead crow was found near Willow Pond. As of mid-November, a total of 448 birds had died in Massachusetts due to infection from the virus, and one horse had developed severe neurological disease. There were, however, no reported cases in Massachusetts of human infection.

In a story about the psychological impact of the outbreak, the Boston Globe (8/20/00) put the risk of West Nile infection in perspective: "Based on current information on casualties, the odds of an American dying of this summer's most dreaded virus are roughly 1 in a million, the statistical cutoff point for saying something has almost no risk at all."

Michael Gochfeld, Professor of Environmental and Community Medicine at the Robert Wood Johnson Medical School and School of Public Health writes: "In weighing the risks and benefits of mosquito control, we should 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 public's 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 beside the number of deaths from many other diseases that are addressed less aggressively.

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 assisted in the evaluation and control of that epidemic and recently published a report in The Lancet, the leading British medical journal.

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, most over the age of 65, died.

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 likewise true of related infections, such as St. Louis encephalitis and Eastern 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.

Why all the spraying?

Webster's New World Dictionary defines 'epidemic' as "prevalent and spreading rapidly among many individuals in a community at the same time; widespread," and 'deadly' as "causing death or likely to cause death."

As we have seen from the available data, West Nile Virus can hardly be considered a "deadly epidemic." So what's behind the big push to spray where the virus shows up?

The Centers for Disease Control recommend spraying under certain circumstances in their guidelines for surveillance, prevention, and control of WNV. Their mission is "To promote health and quality of life by preventing and controlling disease, injury, and disability." They tend to focus more on the disease agents, not the possible effects of the 'cure' -- spraying and larvicides -- on human health, ecosystems, and lobsters.

The focus needs to be on why the spraying is even being considered in the first place: to reduce the incidence of West Nile Virus carrying mosquitoes, one would hope. Amazingly, there is no scientific evidence that demonstrates a decrease in human mortality from WNV after a spray program, or even a long-term reduction in the number of mosquitoes. Rates of kill for mosquitoes at over 80%, as claimed by New York officials during their spray campaign, are based on speculation: a kill rate of around 30% is probably more accurate according to other experts. It is estimated that for every 1,000,000 droplets of spray released to kill mosquitoes, only one droplet lands on a mosquito. It takes 2-3 droplets to kill the mosquito.

Naled

Naled (trade name Dibrom) is an organophosphate with many of the same characteristics and concerns as malathion. Naled can cause cholinesterase inhibition in humans: that is, it can overstimulate the nervous system causing nausea, dizziness, confusion, and at high exposures, can cause respiratory paralysis and death. One of the byproducts of degradation of Naled is dichlorvos, another registered organophosphate. This compound is of toxicological concern.

Researchers at the Cornell University Program on Breast Cancer and Environmental Risk Factors in New York State review several studies on dichlorvos. In one study female mice that were fed high doses of dichlorvos over a long time had a higher frequency of stomach cancers than untreated mice. High doses of dichlorvos fed over two years caused an increase in the number of male rats that had pancreatic tumors and leukemia. A higher number of leukemia cases were reported in one study among male farmers who used dichlorvos for more than ten days per year, compared to those who had not used dichlorvos. A higher number of childhood brain cancer cases were reported among families that used dichlorvos than among families that did not.

The pesticide trichlorfon is a common ingredient in the mosquito pesticide dibrom (naled). In one study, trichlorfon was found to cause a "severe reduction" in brain weight (and shape) in test animals exposed. The timing of exposure to the developing offspring appeared to be the key factor in determining neurological damage (known as the "critical brain growth period"). It occurred when the chemical was administered between 40-50 days gestation for the guinea pig which scientists say correlates with the brain growth spurt period for the animal.

Russian scientists studied the growth rates of fish called Bream (Abramis brama) after exposure to the dibrom/naled contaminant dichlorvos. The first major effect detected was a significant reduction in the growth rates of the fish. Researchers believe it may be due to the subtle neurotoxic actions of the pesticide and its effects upon the areas of the brain involved in feeding or food search mechanisms.

Naled is characterized as very highly toxic to bees and aquatic invertebrates. It is moderately to highly toxic to fish and slightly toxic to upland game birds and waterfowl.

There is potential for chronic risk from Naled to estuarine invertebrates.
http://www.meepi.org/wnv/overkill.htm

Though the environmental impact of WNV spray operations in the Tri-State area over the past two years has yet to be fully tallied (and no official Environmental Impact Statement has yet been issued!), these pesticides are known to severely impact many aquatic species and nontarget insects.

There is a pending lawsuit regarding the impact of these pesticides on the widespread die-off of crabs and lobsters in Long Island Sound.

Thousands of fish, lobsters, birds and beneficial insects like butterflies and bees were killed by the spraying. Our waterways were polluted. Even the Connecticut Sea Grant (Sea Grant is a Federal Agency which sponsors regional projects on coastal marine problems usually tied with industry)notes with alarm that pesticide spraying is implicated in the lobster die-off.

Repeated spraying has severely impacted vital ecosystems, and the offspring of mosquitoes that survived the spray are likely to now be growing increasingly resistant to the pesticides applied. The use of pesticides is being planned again, without justification, and despite the fact that, historically, West Nile epidemics throughout the world have subsided and vanished on their own. Last year, we saw only a handful of cases, mostly centered in Staten Island in a city of more than 8 million people. Indications are that the public health "threat", if there ever was one, is over.

http://www.nospray.org/

Update August 17, 2001:

For the third year in a row, West Nile Virus has again been detected in the United States--in larger numbers and over a wider range than in previous years at the same point in the season. However the epicenter of WNV activity seems to have moved south. Since it is not known whether to credit ecological factors for this shift or considerable efforts at mosquito prevention and control, "mosquito hygiene" remains the key message--ie, reduce or eliminate mosquito breeding sites!

Three humans have been confirmed as WNV-positive thus far this year in the US. Two of the 3 people are from Madison County, Florida. The first, a 73-year old man, became ill in mid-July, a few days earlier than the first human onset last year and more than a month earlier than the first human onset in 1999. A 64-year-old woman has also been confirmed to be infected. The third, a 73-year-old woman, is from Richmond County (Staten Island), NY and had onset of illness on July 26.

Twenty-three infected horses as well as 32 birds of several species have also been detected in Florida. A horse from Pennsylvania has also tested positive.
http://www.cfe.cornell.edu/erap/WNV/

Update August 18,2001: A woman who lived near downtown Atlanta has died of the West Nile virus, the first reported death from the disease outside the Northeast since the virus emerged on the East Coast in 1999.

The reason that my colleagues and I argued against broadcast spraying [of mosquito adulticide pesticides] 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 20th century. 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 public's 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 aggressively.

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 medical journal.

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 likewise 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.
http://www.cfe.cornell.edu/risk/WNV/WNVScienceRefs3.html

Howard, John J. and JoAnne Oliver. 1997.
Impact of Naled (Dibrom 14) on the Mosquito Vectors of Eastern Equine Encephalitis Virus.
Journal of American Mosquito Control Association 13(4):315-25.

Abstract: In central New York, aerial mosquito adulticide applications have been used in response to eastern equine encephalitis (EEE) outbreaks and have targeted the swamp habitats of the primary enzootic vector of EEE virus, Culiseta melanura (Coquillett). The organophosphate insecticide naled (1, 2, dibromo-2, 2-dichloroethyl dimethyl phosphate) has been the insecticide of choice in this region. This study reports on analyses of 11 years (1984-94) of mosquito collection data from Cicero and Toad Harbor swamps in relation to applications of naled.

Naled applications were successful in achieving short-term reductions in mosquito abundance.

However, despite repetitive applications, populations of the primary vector of EEE virus, Cs. melanura, have increased 15-fold at Cicero Swamp. Preventive applications had no noticeable impact on the enzootic amplification of EEE virus, and isolations of virus following preventive applications have resulted in additional spraying.

The possibility that applications of naled contributed to increased populations of Cs. melanura discredits the rationale that preventive applications of naled reduce the risk of EEE.

Authors are with New York State Department of Health, SUNY-College ESF, Syracuse 13210, USA. See Moore (1998) for critique of this study.

http://www.cfe.cornell.edu/risk/WNV/WNVScienceRefs3.html

THE FMCA'S ACCEPTED PRACTICES ARE:

1. Control by insecticides. It is the FMCA's policy to use only those approved insecticides that scientific data show are effective and safest for humans and wildlife, as approved by the EPA and FDACS.
As a routine practice, larviciding is preferred to adulticiding where feasible; however, it is recognized that local circumstances might make this procedure impractical. In order to avoid or delay insecticide resistance, synthetic organic pesticides used as adulticides shall not be used as larvicides. For the same reason, every effort must be made to avoid the use of organic pesticides for the destruction of newly emerged adults over extensive areas at the breeding site when these chemicals normally are used for adulticiding.

2. Source reduction. Typically, water management is the preferred method of source reduction for control of freshwater and salt marsh mosquitoes. However, federal and state regulations must be followed before any water management activity is initiated in any wetland.

3. Other methods. When biological or other methods that might be more compatible with the environment are shown to be effective and economically feasible for the control of mosquitoes and other arthropods of public health importance, these shall be used as the principal control agents or integrated control options. The above-mentioned FMCA goals, principles and accepted practices are consistent with those of the PESP program by encouraging non-chemical control measures when possible and reducing pesticide use/risk where practicable.
http://www.floridamosquito.org/

Spraying could make the problem worse

Spraying pesticides for mosquito control may be worse than ineffective, it may even make the West Nile Virus situation worse. There are several reasons for this.

First, spraying can increase mosquito populations by killing off natural predators (fish, other arthropods, birds, etc.) of the mosquitoes and their larvae, thereby removing natural checks on population levels. A 1997 study looked at trends in populations of Culiseta melanura, the mosquito primarily responsible for transmitting eastern equine encephalitis (EEE) among birds.

Over a period of eleven years, Cicero Swamp in central New York state was sprayed fifteen times with the insecticide Dibrom (naled). Instead of declining, the population of Culiseta melanura grew fifteen-fold during this period. The study suggests that the pesticides may have altered the ecological balance of the swamp, killing organisms whose presence would ordinarily help limit the mosquito population.

Second, as ecologist Garret Hardin puts it "every biocide selects for its own failure." This means that mosquitoes can and will become resistant to chemical efforts to destroy them. Overuse of pesticides may create resistant super-mosquitoes that require ever increasingly toxic chemicals to kill them.

Also, toxic chemicals may be leaving mosquitoes that are sprayed but not killed in an immuno-compromised state, thereby allowing them to accumulate and spread more WNV than healthy mosquitoes. "Every time a mosquito spray plane or truck sprays these proven genetically damaging pesticides over the area, they are very likely increasing the amount of subtle genetic damage in the mosquito population, and hence, increasing the number of mosquitoes with genetic flaws which could in theory, allow the encephalitis virus to take hold and grow more rapidly," speculates pesticide researcher Richard Pressinger.

Walter Tabachnick, director of the Florida Medical Entomology Laboratory, disputes this theory: "To my knowledge there is no information that indicates sublethal doses influence movement (of WNV within a mosquito's body). This too seems unlikely to me to have any major role in mosquito biology and disease epidemiology."

Clearly, more research is needed on this question. Dr. Ray Parsons, who heads the Harris County Mosquito Control Division in Houston, has observed that malathion may actually aggravate Culex, causing an increase in aggressive biting behavior for an hour or two after spraying.

Finally, the public living in sprayed areas may feel a false sense of security. If they feel that fewer WNV mosquitoes are around, they may be less likely to use other proven measures to prevent mosquito breeding on their property and bites to themselves.
http://www.naba.org/wnvirus.html

Although little is known about the long-term effects of mild or repeated contact to organophosphates, indications are mounting that exposure--from residues in food and drinking water and from use in homes and schools--can damage the nervous and immune systems, particularly in infants. Acute overexposure causes flu-like symptoms, and longer-term problems include impaired vision, anxiety, restlessness, insomnia, headache and emotional instability.

Many claims that OP exposure led to long-term health problems have ended up in court in this and other countries. The chemicals have also been implicated as contributing to the mysterious, debilitating symptoms known as Gulf War Syndrome.

In many cases, OP residues are not detectable once foods reach consumers. However, the chemicals are prevalent enough that most people are exposed daily to a couple of these chemicals through their food--especially if the individuals are eating fresh or processed fruits and vegetables. It is hardly news that pesticide residues exist in food.

Over the years, the U.S. Environmental Protection Agency has allowed thousands of uses of pesticides on food crops, concluding that the benefits outweighed the risks. And the nation's food supply is reputedly the safest in the world.
http://www.ecologic-ipm.com/latimes.html

Mosquito Spraying to Control Eastern Equine Encephalitis Debated New York --
The Syracuse Post-

Standard carried an editorial on March 25, 1998 about efforts to control disease carrying mosquitoes by spraying local wet lands: It is disturbing news, indeed, to learn that the aerial pesticide spraying over Cicero Swamp actually may be defeating its own purpose.

A new study by state Health Department scientists indicates that the population of the Eastern equine encephalitis-carrying mosquitoes that live in the swamp has grown 15-fold since the spraying began in 1984. By any calculations, that figures to raise the risk of someone getting bitten and infected by the sometimes-deadly virus, which is why the spraying began.

Though Onondaga County health officials maintain that spraying is the best method to combat the insects and that they have no plans to change the spraying policy, that policy ignores what the study suggests is happening. Dr. David Ackman, director of the Bureau of Communicable Disease Control, said current practices won't be abandoned based on one study. He further questioned whether any follow-up studies or policy reviews are necessary.

At the least, this study demands another look at the effectiveness of spraying pesticides in our swamps, if not warranting an end to the current practice altogether. The spraying reportedly made the population of the disease-carrying mosquitoes skyrocket because it also killed off its chief competition for food, only at a greater rate.

The disease-carrying mosquito, the Culiseta melanura, was able to rebound immediately after most of the aerial sprayings because it breeds twice a year while its counterpart, the Culiseta mortisans, breeds only once per year. So the melanura had little competition when feeding off the swamp's bird population. It increased its population 15-fold while the Culiseta mortisans declined more than 80-fold during the study period. The scientists who conducted the study say they are certain about their findings, not hesitant. That should be enough for a cautionary response, to say the least.
http://tarlton.law.utexas.edu/dawson/theme/ilnes_98.htm

Here are steps you can can take around the house

• Get rid of any unnecessary items on your property that can hold stagnant water, such as old tires.
• If you use old tires for farming or gardening, drill holes in them and empty them regularly.
• Empty water from buckets, toys, and containers, and store them in places where they will not collect rain.
• Make sure your drydocked boats' drain is open so as not to collect rainwater and/or make sure that the cover is tight and has no standing water pockets.
• Keep your canoes and kayaks stored upside-down.
• Drill holes in the bottoms of recycling bins and any other containers that must be kept outdoors.
• Drain the water from bird baths, fountains, wading pools, plant pots and drip trays twice a week.
• Check for other ways water may be collecting around your house, such as puddles beneath air conditioners.
• Clean out your gutters and fix gutters that sag or do not drain completely.
• Check for areas of standing water on flat roofs.
• If you have a swimming pool, outdoor sauna, or hot tub, make sure rainwater does not collect on the cover.
• Clear vegetation and trash from any drains, culverts, ponds or streams on your property so that water drains properly.
• Keep grass cut short and trim shrubs to minimize hiding places for adult mosquitoes.
• Eliminate standing water in your basement.
• To minimize the likelihood of being bitten inside your house, make sure window and door screens fit properly and replace outdoor lights with yellow "bug lights."
• To avoid being bitten outdoors, wear hats, long sleeves and long pants in the evenings, when mosquitoes are most active.
  http://www.meepi.org/wnv/overkill.htm