As the number of mosquitoes that have tested for West Nile virus grows, health officials warn people to “take this treat seriously” because the risk of human infections is nearly five times higher than in previous years.

New York City Health Commissioners warned residents to take steps to avoid contacting the illness, which is transmitted through mosquito bites. In order to avoid the contamination with the virus, people are advised by the authorities to avoid exposure at dusk and dawn, when mosquitoes are most active. Wear insect repellent containing permethrin or DEET on top of clothing and wear long sleeves and pants while outdoors.

The symptoms of the infection can have three different stages in humans, from unnoticeable symptoms to symptoms similar with those of flu. The final stage can lead to loss of consciousness. The West Nile virus can seldom lead to meningitis or death.

Earlier this month, health officials from Los Angeles, Orange, Riverside, San Bernardino, San Diego, gathered  in Garden Grove to announce that the region experiences a resurge of West Nile virus an to warn people to “take this threat seriously,” as Gerard Goedhart, district manager of the Orange County Vector Control District, said, quoted by the Los Angels Times.

Over the past two years, the virus has been responsible for hundreds of deaths in the United States. In 2004, Southern California experienced 710 human West Nile virus cases and 21 people died.