The Rhode Island Department of Environmental Management discovered three isolations of West Nile virus in Rhode Island mosquito populations this year, said Al Gettman, mosquito abatement coordinator at the department. The virus was first detected mid-July during a routine weekly mosquito sampling in Westerly, Rhode Island and was followed by the discovery of virus-positive mosquito samples in Providence and North Providence July 30 and Aug. 20, Gettman said.
The presence of West Nile came as no surprise to Gettman and his colleagues, because it is generally found in the state annually.
The department also found two incidences of Eastern Equine Encephalitis - another mosquito-transmitted disease - in Tiverton, Rhode Island this summer. EEE is traditionally more rare than West Nile and has a much higher human mortality rate, Gettman said.
Despite the virus' presence in mosquito populations, there have been no West Nile cases in humans in Rhode Island this year, said Dara Chadwick, chief officer of health promotion at the Rhode Island Department of Health.
Brown students who recently participated in a three-day backpacking trip with Brown Outdoor Leadership Training armed themselves with bug spray and did not let the threat of West Nile keep them from participating.
"We had more pressing concerns, like bears," said BOLT leader Thomas Miotke '14.
Compared to a bear attack, the consequences of contracting West Nile virus are more subtle. About 80 percent of infected individuals do not display symptoms, according to the Centers for Disease Control and Prevention website. Mild flu-like symptoms are seen in around 20 percent of cases, while one in 150 people infected acquire serious symptoms including fever, convulsions and paralysis.
"When we get those positive results from the mosquito pools, it tells us that we need to make sure people are stepping up to protect themselves," Chadwick said. Prevention measures include limiting outdoor activity during sunrise and sunset, wearing long sleeves and pants, eliminating standing water and checking that screens are hole-free and effective, he said.
While the West Nile incidence rate in Rhode Island was not abnormal this year, the virus' presence nationwide was higher than average, Gettman said. West Nile incidence rate is the highest it has been since 1999 - 1,993 cases and 87 deaths have been reported this year, according to the Center for Disease Control website.
The winter was mild, which led to higher survival of earlier stages of mosquitos, Gettman said. He added that lack of rain during summer months could also have contributed to the increase of West Nile virus. Without rain to flush out the storm basins, standing water becomes more nutritious for mosquito larvae, Gettman noted.
To combat mosquito-borne diseases, the environmental management department purchases a "very environmentally-benign product" called Bti. This bacterium is targeted to underground water basins to reduce mosquito production, Gettman said.
"The product that's used is highly specific to killing only mosquito larvae," Gettman said. "It doesn't even kill closely related species."
West Nile arrived in North America in 1999 and "spread like wildfire," Gettman said. It is now firmly established across the country.
