Wet Weather to Blame for Record Numbers of West Nile Virus Mosquitoes
New York City’s health department found three times the average number of mosquitoes carrying the West Nile Virus in traps last month, with increasing wet weather to blame for the infestation.
The department counted 1,039 virus positive mosquitoes; typically the count is about 300.
“This year’s warm, wet weather may be contributing to these higher [West Nile virus] counts.” said Michael Lanza, deputy press secretary at NYC Health.
So far, 20 people across all five boroughs of New York City have tested positive for the virus, and 16 of these cases were of the neuroinvasive strain of WNV. Although rare, that strain can cause acute muscle weakness leading to flaccid paralysis in some cases, according to the Center for Disease Control. It can be fatal to people aged 50 and over or those with weakened immune systems, according to the World Health Organization.
West Nile Virus is commonly transmitted through the bite of infected mosquitoes or sometimes through blood transfusions if the donor is carrying the disease but does not have symptoms at the time.
Mosquitoes breed in stagnant water, and under ideal conditions of warm and wet weather, the development of a mosquito from egg to adult can be less than a week.
Despite a heat wave, NYC had the third wettest July on record, made worse in September by Hurricane Ida. It set a new hourly rainfall record, according to the National Weather Service.
The increase in West Nile Virus is also being seen in other states.
For example, Arizona has had the highest number of humans infected with the virus in the US as of October this year. Maricopa County was especially hard hit with 346 confirmed and probable human cases of the virus and 20 deaths this year, the highest in that state. Unlike New York, Maricopa’s climate tends to be dry and temperatures range between 40 and 106 degrees Fahrenheit throughout the year.
Colorado had the second highest number of cases in the country, according to the CDC. Typical weather in Colorado is more cold and dry throughout the year but the recent surge in average temperatures and precipitation in the summer are presenting ideal conditions for mosquito breeding, data by the National Weather Service shows. This has made West Nile Virus the leading cause of mosquito-borne disease in the U.S.
“We need to be on the alert for the potential of increasing mosquito populations,” said David Brown, technical advisor for the American Mosquito Association in California.
“If we do have more aquatic events that provide the water for mosquitoes, followed by warm temperatures, that really increases the opportunity for mosquitoes to emerge.”
The West Nile Virus originated in birds and can be found in 300 species of dead birds. Mosquitoes can carry the virus to other species after biting an infected or dead bird, Brown said.
“Since it is a bird disease, oftentimes warmer temperatures seem to enhance West Nile Virus within the bird population and the more it circulates within the bird population, the greater opportunity for it to go outside that cycle and can go into humans as well.” he said.
However, mitigation is possible. Biologists found that accurate weather forecasts can help improve contingency planning against the virus.
Public participation is crucial, city officials emphasize. This includes using EPA approved insect or mosquito repellent and disposal of containers that have standing water, which by itself is already a violation of the New York City code.
“Also, make sure windows have screens and make sure roof gutters are cleaned and drained properly.” Lanza said.
Nevada, which has similar weather conditions to Arizona, is a success story in controlling the virus spread. The state has one of the lowest rates of WNV activity across the US. The county has launched a Vector Control Program that focuses on outreach of public education on prevention methods and has a team of biologists and technicians who regularly collect samples from dead birds and mosquitoes to monitor the spread of the virus.
The record numbers of West Nile Virus mosquitoes in New York City gained national attention last month when Senator Chuck Shumer suggested the Environmental Protection Agency (EPA) intervene to “disperse the mosquito swamps”.
NYC Health sprayed pesticides between West 119th Street and West 53rd Street, last Monday and Tuesday, Lanza said.
Surveillance is also conducted by catching and testing mosquitoes from mosquito pools from 90 locations citywide.
