The Arizona Department of Health Services reports that a woman died of the mosquito-borne illness today, Thursday. She was a senior citizen over 80 and lived around Phoenix. It was already known that the elderly and children are most at risk because of their less strong immune system.

Last year, around 120 people died of the virus, according to the U.S. Centers for Disease Control.

The season normally begins in April and lasts until September, but due to warm weather this year, the first cases of the West Nile virus have been reported as early as March 19.

The areas that favor mosquito population growth are standing waters, including swimming pools left abandoned. One way of counteracting the rapid spread of these mosquitoes is by inserting mosquito-fish populations into the water (which feed on mosquito larva).

According to UC Davis entomologist Bill Reisen, when the temperature increases from 60 to 90 degrees, the breeding cycle of mosquitoes decreases from ten to about four days.

West Nile virus was first spotted in New York in 1999 and has since spread westward, ultimately appearing in every state. Last year, the U.S. confronted with no less than 2,630 human cases.

The infection starts with one bite from an infected mosquito; for some people this could show no symptoms, while for others could manifest through fever, headache, chills, weakness and drowsiness. The most severe cases lead to meningitis or encephalitis, including low levels of consciousness and fatigue.