West Nile Virus Hits Biggest Urban Areas of the US

West Nile virus-positive mosquitoes have made their first appearance of the season in New York City as Los Angeles County health officials have reported the area’s first human case of the year, as the virus continues to make an appearance around the country.

The Centers for Disease Control’s (CDC) recent Morbidity and Mortality Weekly Report notes that the United States has seen 13 human cases of West Nile virus thus far in 2017 as of June 10, 2017, while this time last year, there were 38 human cases reported across the country. Of the cases reported thus far this season in the United States, 6 individuals have had the more severe neuroinvasive form of the illness, while 7 have had a less severe nonneuroinvasive infection. As state and local health officials around the country work to monitor and control the mosquito populations — particularly the Culex species — that transmit West Nile virus to humans, birds, and farm animals, the CDC notes that the virus is a seasonal public health issue for most of the United States each summer.

On June 19, officials from the New York City Health Department reported the first detection of West Nile-infected mosquitoes of the season in the city. The infected insects were discovered in a surveillance site in Staten Island, and belonged to the Culex pipiens species. However, there have not yet been any reports of human cases of West Nile in New York City or upstate New York so far this season. In a recent press release, the department noted that it currently operates 60 mosquito surveillance sites and 120 surveillance traps across the city’s 5 boroughs, and plans to add more monitoring traps. In addition, the city is targeting marsh areas and other bodies of standing water with larvicide to kill mosquito larvae before they can mature and spread the virus.

“There are simple precautions you can take to protect yourself and your family from mosquito bites when outside,” said the city’s health commissioner, Mary T. Bassett, MD, MPD, in a recent statement. “Wear insect repellent and cover your arms and legs, especially at dawn or dusk. Additionally, remove standing water from items that might harbor mosquitoes, including buckets, planters or any other containers that might be outdoors. Call 311 for any standing water you cannot manage yourself.”

In Los Angeles County, the Department of Public Health announced its first human case of West Nile virus of the season on June 15, 2017. The case involved an elderly resident of San Gabriel Valley who was hospitalized in March. The cause was recently confirmed by the California Department of Public Health to be West Nile. This is the second human case of the virus in California in 2017, and each of 10 has reported presence of West Nile-positive mosquitoes or dead birds. The CDC notes that although serious illness can occur in people of any age, those over 60 years are at greatest risk of developing severe West Nile symptoms.

“There is currently no vaccine or treatment for West Nile virus,” said Los Angeles County health official Jeffrey Gunzenhauser, MD, MPH, urging the use of insect repellants containing DEET when outdoors. “Elderly persons and other people with weak immune systems are at highest risk of developing severe illness.”

In the Midwest, Indiana’s State Department of Health announced on June 16, 2017, the state’s first 2 confirmed human cases of West Nile virus, in Hamilton and Lake counties. Surveillance efforts have also detected West Nile-positive mosquitoes elsewhere in the state. “Unfortunately, West Nile disease is a common occurrence in Indiana during mosquito season,” said Jerome Adams, MD, MPH, Indiana’s health commissioner. “When we find evidence of the virus in multiple counties, that means the risk is starting to increase statewide.”