A Mosquito-Free Summer
New York City Region - 1999
Summer 1999
The primary vector for West Nile virus was said to be mosquitoes, but record-low mosquito populations existed in the NYC region during the summer of 1999, as that period was regarded as a mosquito-free summer due to the lengthy drought. Mosquito larvae require standing water, plus 10 to 14 days, to mature into adults, which in turn, require the absence of predators such as dragonflies, birds and bats. Clearly, mosquitoes hardly existed at all until a month after the human epidemic began. First significant summer rain was 8/14/99. It takes 10-14 days for larvae to hatch into adult mosquitoes. (ref) Many citizens did not see a single mosquito until just after the NYC emergency aerial malathion application program ended. When the epidemic began, the media gave the impression that the common house mosquito population had exploded during the summer.
The WNV is said to be carried by the Culex Pipiens species, as if this unsourced phrase explains the contradictions inherent in the "mosquito-free summer". Any blood-sucking animal can transmit WNV, as seen in the list below. In nearby Connecticutt, where (unlike in New York) mosquitoes are counted and analyzed for encephalitis arboviruses, WNV was not searched for until after the 1999 epidemic began, and then was found in only 2 of over 45,000 mosquitoes tested, 1 Culex and 1 Aedans (see Connecticut mosquito surveillance). Quantitative data regarding the concentration of WNV in the infected mosquitoes is entirely lacking.
Pre-Epidemic Article: 1998
-- The New York Times, 8/10/98"Two mosquitoes in particular -- the salt-marsh variety and a similar freshwater type -- thrive in wet-dry cycles like those that characterized the early summer in this region, said Dominick Ninivaggi, the vector control superintendent in Suffolk County on Long Island. The common household mosquito known as culex has also been more abundant than usual this year [1998], but although these insects have made the summer a misery for some residents, none carry disease."
An inquiry to Mr. Ninivaggi produced no reply regarding actual numbers re culex. Search for actual numbers is ongoing. Does he mean more abundant than other mosquitoes, which were almost zero? Or does he mean more abundant in absolute numbers? The phrasing is not Mr. Ninivaggi's. "None carry disease" is a strange statement in retrospect from 1999.
Pre-Epidemic Article: 1999
"A Mosquito-Free Summer" -- The New York Times, 8/7/99Note: Crows were dying since June from WNV encephalitis. Human WNV seropositives first onset was 8/4/99 (NYCDOH, 5/2000).
According to The New York Times, 8/7/99:
"That silence is the sound of a mosquito-free summer. 'Last year I was playing connect the dots with the mosquito bites on my legs,' said 12-year-old A. J. De Marco of New Canaan, Conn., as she and her campground cronies captured and then released Leppy the leopard frog. 'I'm usually covered, but now all I have is scratches from climbing the mountain.'"
"Truth be told, the season is not quite mosquito free. There have been scattered swarms of the salt-water mosquitoes that breed in coastal marshes whenever high tide comes. But the far more common species that blanket inland areas each year are largely missing."
"In Connecticut, scientists found an average of 250 mosquitoes a week in each of their 37 traps during last July; this July, it was about 75. On Long Island, Suffolk County's mosquito catch for the entire month of July was 6,152 -- compared with 27,161 last summer. In Monmouth County, N.J., mosquito-watchers counted 1,711 in traps last month, about a fifth of the typical July yield over the previous six years."
"'It's been, probably, the quietest summer we've had in years,' said Martin Chomsky, superintendent of the Monmouth County Mosquito Extermination Commission. 'I would say that this is a record year in terms of the lack of freshwater mosquitoes.'"
"Gardeners are going outside without bug nets. Summer people are eating dinner on the deck."
"'I was very prepared with the itchy stuff, the calamine and Caladryl, and we haven't had to use it,' said Clara D'Angelo, the nurse at Camp Waneeshi in Salt Point, N.Y., where 90 Girl Scouts pitch tents each night. 'I'm well prepared for mosquitoes that don't exist.'"
""Scientists say the phenomenon is simple: 'If you understand that mosquitoes need water,' said Wayne Crans, director of Mosquito Research and Control at Rutgers University, 'no water, you're not going to have mosquitoes.'"
Epidemic Declared 9/4/99
The Mosquito Picture Abruptly Changes
Though there was no rain in time to bring about the maturation of mosquito larvae, The New York Times presents a new mosquito image:
"They added, however, that the area's relatively wet spring and hot, dry summer had been ideal for the mosquito species that carries St. Louis encephalitis in the Northeast, Culex pipiens." -- The New York Times, 9/4/99
"People in other parts of the city and nearby Westchester County have no particular reason to worry, experts said, because the type of mosquito that carries the virus, Culex pipiens, typically flies less than a mile in its lifetime. [...] Fewer than 1 in 1,000 Culex pipiens mosquitoes carry the disease, and most people who contract the virus do not develop symptoms." -- The New York Times, 9/8/99
"A disease spread by mosquitoes that favor the polluted waters of storm drains and other urban vessels, St. Louis encephalitis has largely been concentrated in the cities of Florida, Texas and the Midwest. Edward D. Walker, an associate professor of entomology at Michigan State University, said its arrival in New York is curious, and could reflect either new behavior by one species of mosquito, Culex pipiens, or new migration patterns by its southern sister, Culex quinquefasciatus." -- The New York Times, 9/10/99
"The most likely vector, the Culex pipiens mosquito, is found virtually everywhere in the metropolitan area." -- The New York Times, 9/11/99
"Since Sept. 3, officials in New York City have investigated 108 possible cases of St. Louis encephalitis, which is spread by a species of mosquito called Culex pipiens. [...] Experts noted that the Culex pipiens mosquito typically flies less than a mile in its lifetime and that the closest place with a confirmed encephalitis case was the South Bronx, at least 5 miles south of the Westchester County line." -- The New York Times, 9/21/99
"Ms. Smith of the State Health Department said the mosquitoes that carry St. Louis encephalitis and West Nile viruses, the Culex pipiens, are generally active from dusk to dawn. But another type of mosquito known to carry the West Nile virus, the Aedes vexans, is also active during the day, she said." -- The New York Times, 9/26/99
"NEW HAVEN - This time a prolonged drought produced a large supply of the northern house mosquito, Culex pipiens, which happens to be particularly efficient at transmitting certain viruses from birds to humans. This mosquito likes stagnant water with rotting leaves that help provide abundant food for its larvae. Storm-sewer catch basins are favorite habitats; in New York City, nearly every street corner is a potential breeding pool. Although frequent rains normally flush out the pools, low rainfall concentrates the food for the mosquito larvae and generates adult mosquitoes by the thousands. [...] The spraying program the city has now undertaken is probably reducing the overall number of mosquitoes (as well as many other insects), but its effectiveness in reducing the risk of disease cannot be evaluated because we don't have any estimates of how many Culex pipiens there were." -- The New York Times, 9/28/99.
During the summer of 1999, New York had less than "low rainfall" and according to pre-epidemic articles, personal interviews and experience, there was no evidence of mosquitoes.
One post-epidemic article (NYT, 9/10/99) describes a diminishment in mosquito New York populations.
"Dr. Varuni Kulasekera, a mosquito researcher with the American Museum of Natural History who specializes in medical entomology, was summoned as the sleuth. On her first visit last December, she found thousands of mosquitoes in the sewers, but by June, the population had dwindled to three or four beneath each manhole cover, she said." Note: no rain occurred after June and until after the epidemic began. First rain (1.14 inch) occurred August 14th.
New York City had no virus/mosquito surveillance system, however, WNV was found in a mosquito pool in a Greenwich County, Connecticut surveillance station, in 0.006% of mosquitoes tested (1 culex and 1 aedes mosquito out of 45,391 tested). This is over 600 to 2,400 times less than in humans from northern Queens, which tested at approximately 1-4% seropositive for WNV. This percent is 18,000 to 72,000 time less than the WNV positive incidence in the NYC region's crow population because, since 1/3rd of the crow population was estimated to have been killed by WNV in New York during June/July (categorized as unconfirmed), then at least 33% of the crow population was WNV positive.
A Wide Variety Of WNV Carriers
Though Culex Pipiens is often portrayed as the mosquito with a unique relationship with WNV, this is not so. An overview of West Nile Virus disease and WNV vectors is presented online by virologists Zdenek Hubálek and Jirí Halouzka of the Academy of Sciences, in the Czech Republic. The following is their arthropod vector table, reformatted:
Isolations of West Nile Virus From Hematophagous Arthropods Type Species Number Countries Mosquitoes Culex antennatusa 6 Egypt, Madagascar Culex decens group 8 Madagascar Culex ethiopicus 1 Ethiopia Culex guiarti 1 Côte d Ivoire Culex modestus 3 France, Russia Culex neavei 4 Senegal, South Africa Culex nigripes 1 Central African Republic Culex perexiguus 1 Israel Culex perfuscus group 3 Central African Republic, Senegal Culex pipiensa 7 South Africa, Egypt, Israel, Romania, Czechland, Bulgariab Culex poicilipes 29 Senegal Culex pruina 1 Central African Republic Culex quinquefasciatusa 7 India, Pakistan, Madagascar Culex scottii 1 Madagascar Culex theileria 4 South Africa Culex tritaeniorhynchusa 3 Pakistan, India, Madagascar Culex univittatusa 51 Egypt, Israel, South Africa, Madagascar Culex vishnuia group 6 India, Pakistan Culex weschei 1 Central African Republic sp. 3 Egypt, Algeria, Central African Republic Coquillettidia metallica 1 Uganda Coquillettidia microannulata 1 South Africa Coquillettidia richiardii 5 South Russia, Bulgariab Mansonia uniformis 1 Ethiopia Aedes aegyptia 1 Madagascar Aedes africanus 1 Central African Republic Aedes albocephalus 35 Madagascar Aedes albothorax 1 Kenya Aedes cantans 7 Slovakia, Ukraine, Bulgariab Aedes caspiusa 1 Ukraine Aedes circumluteolus 2 South Africa, Madagascar Aedes excrucians 1 Ukraine Aedes juppi+caballus 1 South Africa Aedes madagascarensis 1 Madagascar Aedes vexans 3 Senegal, Russia Anopheles brunnipes 1 Madagascar Anopheles coustani 1 Israel Anopheles maculipalpis 1 Madagascar Anopheles maculipennis 3 Portugal, Ukraine Anopheles subpictus 1 India sp. 1 Madagascar Mimomyia hispida 8 Senegal Mimomyia lacustris 4 Senegal Mimomyia splendens 6 Senegal sp. 2 Senegal Aedeomyia africana 1 Senegal Soft ticks Argas hermannia 3 Egypt Ornithodoros capensisa 5 Azerbaijan Hard ticks Hyalomma marginatum 5 Astrakhan, Azerbaijan Hyalomma detritum 1 Turkmenistan Rhipicephalus turanicus 1 Azerbaijan Rhipicephalus muhsamae 1 Central African Republic Amblyomma variegatum 1 Central African Republic Dermacentor marginatusa 1 Moldavia aExperimental transmission of the virus also demonstrated. bDetected in mosquitoes by immunofluorescence assay.
Media Misrepresentation: 2000
NYC's Channel 4 spent 30 minutes, a WNV special, explaining the threats of the epidemic (August 10, 2000, 5:30pm). Misrepresentation, under-representation of the contrary theories, timidity, ignorance, and bias were present.
It ended with a pro/con discussion between two "experts" on the issue of spraying. The con (a Ph.D., biologist) was dreadful even for a plant, refusing to speak and waving every question over to the Westchester Health Commissioner. The interviewers told the biologist that he was very quiet and asked if he would he like to say something. He just wagged his head with a goofy smile.
Clearly misrepresented was the weather for 1999, and by implication, mosquito populations.
Twice, experts stated (paraphrased here) that "WNV epidemics follow a pattern of drought followed by heavy rain, as happened in Europe, Asia, and NYC 1999." Rain implies mosquito populations. Drought means few mosquitoes, and drought was the New York weather during the summer of 1999. According to La Guardia Airport weather station report, precipitation leading up through the human epidemic's first onset of 8/4/99, at the epidemic center, can be listed as follows:
LGA Weather Data -- Existing Rain: Summer of 1999 Month Day MaxTmp AvgTmp Precip Comment May 1 66 57 0.00 May 5 62 57 0.56 May 7 60 57 0.22 May 8 63 58 0.15 May 19 66 62 2.00 May 23 64 62 0.34 May 24 67 64 1.14 Jun 21 68 64 0.21 Late June, bird epidemic begins - Dr. Charos, Layton, McNamara Jun 29 91 84 0.15 Jul 1 78 74 0.52 Jul 15 Apex of bird epidemic - Dr. Charos Aug 1 First human case, determined later by CDC analysis Aug 5 89 80 0.29 Aug 11 85 79 0.38 Aug 12 First recognized human case - CDC Aug 14 86 79 1.14 Aug 20 77 69 0.65 Aug 21 64 62 0.10 Apex of human epidemic - CDC Aug 26 78 74 2.58 Sep 1 Epidemic area investigated for mosquitoes and open water - NandoTimes 12/5/99 Sep 3 Giuliani declares epidemic, pesticide program - NYT Sep 7 0.54 Sep 10 0.54 Sep 15 0.47 Sep 16 4.63 Thus, between 5/25/99 to 8/13/99 there was a total rainfall of about 1.7" in 11 weeks (including mini-rain, like 0.03") with many dry intervals of high evaporation rate (indicated by wetbulb, not shown herein). Thus there existed "record-low" mosquito populations, and a "mosquito-free summer", as of 8/7/99, per quotes of NYT article of that same date.
There was no "drought followed by heavy rain." A drought existed from 5/25/99 through 8/13/99, i.e., through much of the human epidemic (first seropositive onset: 8/4/99).
First significant rain was 8/14/99. Add 10 days to find 8/24/99, which is the first day for significant adult mosquito populations. It takes 10 days minimum for larvae to produce adult mosquitoes.
Throughout the summer, rain was sporadic and record-low, temperature was record-high, and evaporation rates were high, the worst possible weather for mosquitoes.
Mosquito Eradication Programs: Ineffective
Much has said about mosquito control programs (pesticides) with regard to the WNV virus and malaria. From an environmental view, it is unfortunate that such programs exist at all. Regardless, according to the experts, they may be useless:
1) "'The general perception is that mosquito-borne diseases ought to be eradicable,' said Harold Varmus, director of the National Institutes of Health, 'and they have not proven to be so. And not only have the mosquitoes not been eradicated, but some of these diseases they carry are resurgent. They have come back from a fairly low ebb.' In response to this rebounding threat to public health, the National Institutes of Health and the World Health Organization are planning a long-range research effort, while the World Bank is seeking support for a 30-year plan to battle malaria, but the obstacles strike many as nearly insurmountable. An effective malaria vaccine, long a goal, seems years away, and no one talks about trying to eliminate malaria-carrying mosquitoes anymore. Like Aedes aegypti, the Anopheles mosquito rapidly developed resistance to insecticides like DDT. Eradication, as one World Bank official said, 'has become a dirty word.'" -- The New York Times, 8/24/99. 2) "Given the lack of knowledge about what conditions set off the virus's spread to people, spraying near spots where birds died, the major response so far, is akin to shooting at an assailant in the dark, many scientists say. 'But at least it give you something to do,' said Dr. Vincent Deubel, a virologist at the Pasteur Institute in Paris who has studied West Nile outbreaks for 15 years." -- The New York Times, 8/8/2000 3) "Although the reasons for the failure of [vector-borne disease control programs] are complex and not well understood, two factors played important roles: 1) the diversion of financial support and subsequent loss of public health infrastructure and 2) reliance on quick-fix solutions such as insecticides and drugs."
Duane J. Gubler, Centers for Disease Control and Prevention, Fort Collins, Colorado, USA
Resurgent Vector-Borne Diseases as a Global Health Problem
Emerging Infectious Diseases, Vol. 4 No. 3, July-September 1998Mosquito-fear should be eliminated. We should stop poisoning the environment (and ourselves) and support mosquito predators, such as spiders, dragonflies, and bats. Bat rabies fear is unfounded because, with all the opportunities that bats have to spread rabies (a highly arguable disease paradigm according to the study of Pasteur's lab notes by Michael Geison) the number of human rabies in the U.S. is between 0 and 1 per year. Window screens are 100% effective. Soybean oil is claimed to be an effective natural repellant. Note: Deet repellants, distributed by NYC, can be dangerous.