Records and interviews show that Tempe officials knew encephalitis-carrying mosquitoes were breeding in huge numbers west of the downstream dam as far back as July. They knew the insects were proliferating to a lesser extent east of Town Lake's upstream dam, but elected to keep the information quiet.
Not only did Tempe fail to inform residents near the lake of the potential health hazard, the city did not directly alert residents to more than a dozen pesticide applications -- including malathion and a closely related chemical agent -- by a fogging apparatus leading up to the November 6 public opening of the lake.
Rather than publicly acknowledging the mosquito outbreak, Tempe officials -- including Mayor Neil Giuliano -- spoke of a breeding frenzy of midge flies near Town Lake. While nuisances, midge flies do not pose a public health threat.
Mosquitoes, however, can carry encephalitis, a disease that can cause death in children and the elderly.
Giuliano says he didn't know about the mosquito infestation downstream from Town Lake.
"Is there one?" he asked New Times.
Maricopa County health officials were well aware of the problem, as were several department heads in Tempe, including city engineer Howard Hargis and water management division manager Don Hawkes.
County environmental services director Al Brown says his staff worked overtime, weekends and nights to successfully abate mosquito infestations not only in the Salt River bed but in several other areas of the county.
"We made an extraordinary effort to go out there and get bugs," Brown says.
Brown said the county stepped up eradication efforts after mosquitoes were found to be carrying encephalitis -- particularly mosquitoes in the Salt River bed.
"It's the first time we have found Western equine encephalitis in the mosquito population in that area," Brown says.
Seven people contracted encephalitis in Arizona this year, including five in Maricopa County. Two cases were fatal. An 8-year-old Queen Creek girl who had suffered mosquito bites died of encephalitis on September 23. The second fatality is believed to be a Scottsdale man.
Craig Levy, who manages the state Department of Health Services' vector-borne and zoonotic disease section, wouldn't say on Monday whether laboratory tests have eliminated mosquitoes as the transmitter of the disease in the two fatalities. He provided general information about five of the encephalitis cases for which testing has been done. Mosquitoes have been definitively ruled out as the source in only one case, Levy says.
Tempe City Manager Gary Brown says it is not the city's responsibility to notify Tempe residents of the encephalitis-carrying mosquitoes -- or of the subsequent treatments. Brown says the city left notification to the discretion of the state health department.
"I have enough faith in the health department that if they felt there was a health risk, they would have notified people," Brown says.
The state health department did issue a September 1 press release warning of increased numbers of mosquitoes carrying the encephalitis virus in Chandler, Gilbert, southwest Phoenix and Tempe. The press release stated that mosquitoes carrying encephalitis are found almost every year in Arizona. The release stated that during the summer there was "significant increase" in the number of mosquitoes carrying the virus.
The release, however, did not identify any specific mosquito-breeding hot spots such as the areas east and west of Town Lake. Levy says the state did not identify specific breeding areas because officials wanted the public to take precautions regardless of where they lived.
Tempe community relations manager Nachie Marquez says the state never told the city that it should alert residents near the Salt River of the extraordinary high level of mosquito breeding.
She says "at no point" was Tempe "told it was a crisis nature and that you need to get specific information to the public."
Marquez says the city was taking steps internally to address the matter. The city, she says, asked the state health department and the county Environmental Services Department to write letters describing the seriousness of the situation. Those letters, she says, were forwarded to the U.S. Army Corps of Engineers as part of a city request for permission to clear mosquito-breeding habitat west of the dam.
The county Environmental Services Department and the state health department wrote Tempe in early September, detailing the extent of the mosquito outbreak.
"The area downstream of the Tempe Town Lake dam has become a potential health hazard, due to mosquito breeding activity in the area," stated a September 3 letter from John Townsend, vector control manager for the county Environmental Services Department.
"Arboviral sampling of the area has found the Western Equine Encephalitis virus present in mosquito samples collected from this area," Townsend wrote to Tempe city engineer Howard Hargis.
Four days later, Craig Levy of the state Department of Health Services wrote to Hargis, seeking the city's help in "addressing a mosquito breeding problem that is occurring in the Salt River Bed downstream of the Tempe Town Lake."
"Water that has been standing in the river channel is breeding mosquitoes, including the Culex species, which are potential vectors for encephalitis viruses. This problem is of even greater concern lately since the Western equine encephalitis virus has been isolated from mosquitoes collected in the same general area of Tempe in July and August," Levy stated in his September 7 letter.
Levy warned that "this virus can cause illness in both humans and horses."
Health officials recommended that Tempe channelize the river west of Town Lake and remove vegetation growing in the river bed. The vegetation -- mostly salt cedar -- is providing shelter for mosquitoes to breed in shallow ponds. The ponding is caused by steady flows from the city's street drainage system, which has an outfall immediately west of the downstream dam.
On September 9, Tempe asked the Corps of Engineers for permission to channelize the river bed and clear the salt cedar. The wetlands are not only breeding mosquitoes, but a variety of water fowl and migratory birds have been seen in the area.
The Corps of Engineers has not yet formally responded to the city's request, says Cindy Lester, who is with the agency's permitting section. Lester says the corps must first ask the U.S. Fish & Wildlife Service to make sure there are no endangered species that would be affected by the work Tempe wants to do.
Mosquitoes are vectors for the transmission of encephalitis from small creatures, usually birds and rodents, to humans. Birds that live near bodies of standing water are susceptible to encephalitis infection, according to the Mayo Clinic's Web site, HealthOasis. If a mosquito feeds on an infected bird, the mosquito becomes a lifelong carrier of the virus. The mosquito will transmit the infection to the next bird it feeds on, which will in turn spread it to more mosquitoes.
Although mosquito-borne encephalitis in humans is rare, it can be very dangerous. The risk of occurrence is highest during the warm months when birds and mosquitoes reproduce. There is no specific treatment for viral encephalitis.
Mosquito traps placed in the Salt River bed began turning up large numbers of encephalitis-carrying mosquitoes -- primarily Culex mosquitoes -- in July. Traps set one-eighth to a quarter-mile west of the downstream dam were capturing about 100 mosquitoes per night, says Rick Amalfi, laboratory director of Aquatic Consulting & Testing, which contracts with Tempe to monitor water quality in Town Lake and adjacent areas.
A half-mile downstream from the dam, the numbers soared -- 300 to as many as 900 mosquitoes caught in traps each night. Amalfi says the state-mandated alert level is 20 mosquitoes caught per night.
Amalfi, who conducted a survey of mosquito populations prior to the filling of Town Lake, says this year's mosquito population in the Salt River bed was about triple the year before. Amalfi says the heavy monsoon rains contributed to the growth of habitat suitable for mosquitoes. In addition, the steady flow from the Tempe storm drain is feeding water into the wetlands.
In contrast, the number of mosquitoes captured in traps directly adjacent to Town Lake was very low, typically about three a night, Amalfi says. The lake's depth -- ranging from five feet to 16 feet -- and concrete edge eliminate most mosquito-breeding habitat.
The infected mosquitoes breeding in the Salt River bed, however, can travel up to two miles in a night, Amalfi says.
The city and the county launched an aggressive mosquito-control operation last summer that lasted until early November.
More than 60,000 acres were treated with insecticides countywide.
County Environmental Services manager Al Brown says this is the first year that mosquitoes infected with Western equine encephalitis were found in the Salt River bed. He says their discovery could be the result of better testing, or possibly the presence of more birds attracted to the 2.2-mile-long Town Lake.
Residents near Town Lake should expect that pesticide applications will become routine.
"It is important to keep studying the mosquito population and applying pesticides as necessary," Brown says. "I don't see the problem going away. Is it going to become worse? I don't know."
Residents living near the lake were not formally notified by either the county or the city because the most toxic chemical used -- malathion -- doesn't legally require advance notice, officials say.
"Though not required, we discussed the issue of public notification during the planning phase of this work," says Tempe water management division manager Don Hawkes. "Our conclusion was that no notification was necessary."
Hawkes says the insecticide fogging operation -- malathion by the county and Anvil by the city -- did not come within 300 feet of any residences.
"The fogging was also done late in the evening or in the early morning with calm air conditions and when the majority of citizens were asleep," he wrote in an e-mail obtained under the state Public Records Act. "All this information contributed to our decision that public notice was unnecessary."
Maricopa County fogged the area on at least two occasions with malathion, says John Townsend, county vector control manager. The county also applied a larvicide -- Altacide -- directly to standing water in the river bed on two occasions. Altacide is a growth-hormone regulator that disrupts the evolution of mosquito larvae.
Tempe conducted numerous pesticide applications to control mosquitoes, as well as midge flies, in and around Town Lake and in the Salt River bed.
Between September 2 and 14, the city applied bacterial larvicides -- Vectobac and Vectolex -- directly into the lake and shallow pools both above and below the lake. The larvicides were spread at a concentration of 20 pounds per acre.
In October, the city switched to the larvicide Abate, which was applied at five pounds per acre to the lake and nearby shallow pools. The larvicide treatments cost the city approximately $68,000, city records indicate.
While the larvicides are effective in killing the insects before they become capable of flying, a different insecticide was employed to kill airborne mosquitoes.
Between September 2 and November 5 -- the day before the Town Lake dedication -- the city used pickup trucks to apply a fogging compound containing the pesticide Anvil. The pesticide was applied on 12 separate dates, including the four days leading up to the dedication.
City officials say the fogging applications cost $2.76 an acre. The city treated 500 acres of river bottom and Town Lake between the Hohokam Expressway and McClintock Drive 12 times since September, at a cost of about $16,560.
While city and county officials say malathion and Anvil are safe, environmental organizations have warned of potential dangers.
Malathion, an organophosphate insecticide, works by interfering with the central nervous system in insects -- and potentially humans. Although it is considered one of the less acutely poisonous of this family of pesticides, exposure to malathion can cause respiratory distress, headache, dizziness and nausea, according to a 1999 study by the U.S. Environmental Protection Agency.
Anvil's primary active ingredient is sumithrin, which is a synthetic pyrethroid insecticide generally considered to be less toxic than organophosphates. There are some indications that pyrethroids as a class may interfere with the immune and endocrine systems.
The use of malathion as a general treatment for encephalitis-carrying mosquitoes came under fire recently in New York, where mosquitoes were linked to the West Nile virus, which caused several deaths.
"Controlling Culex populations with . . . malathion is a strategy of last resort, when all other control possibilities have been exhausted and a public health emergency requires action," the New York Public Interest Research Group said on September 30. "It should not be the first or only line of defense."
Contact John Dougherty at his online address: [email protected]
