More than 1,100 people in the U.S. have been infected with the West Nile virus and at least 41 people have died, making this year’s outbreak of the mosquito-carried virus the largest since 1999, when the virus was first detected in the U.S., according to the Centers for Disease Control (CDC).
Of the 1,118 cases nationwide, 34 are in California, the CDC reported. At least one person in California has died from the virus.
Extreme summer heat likely contributed to the spike in cases because the warm temperatures speed up the life cycle of the mosquito so it can go from an egg to a biting adult in five days.
The virus spreads by the bite of an infected mosquito, which has fed on an infected bird; and from mother to child during pregnancy or breast feeding, officials said. It can also spread during blood transfusions, transplants, though those instances are "very low," according to the CDC.
It cannot spread through casual contact and is not airborne.
To cut down on the threat, several communities in the Bay Area are applying mosquito control products by helicopter to reduce the emergence of adult mosquitoes. Concord and the Palo Alto Baylands are among the neighborhoods getting the spray Thursday.
Watch: How to Protect Against West Nile Virus
Most people infected with the virus, about 80 percent, will not show any symptoms, according to the CDC. Up to 20 percent of those infected will have symptoms such as fever, headache, body aches, nausea and vomiting, and swollen lymph glands or a skin rash.
About one in 150 people infected will have to be hospitalized with severe symptoms, such as high fever, stupor, disorientation, tremors or muscle weakness.
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People typically develop symptoms within three to 14 days of being bitten by an infected mosquito.
There is no specific treatment for the virus, which usually goes away with rest and increased fluid intake, officials said. Milder cases of West Nile virus will improve on their own and do not necessarily need medical attention, though some people may choose to see their doctors, the CDC reported.
If you develop severe symptoms, such as unusually severe headaches or confusion, the CDC advises you seek medical attention immediately.
With the unprecedented number of cases come warnings from health officials to take extra precautions against possible infection by wearing long-sleeved shirts and pants when outdoors and use mosquito repellent, especially at dawn and dusk.
Officials also urge eliminating and avoiding standing water where mosquitos can lay eggs.
CDC: West Nile Virus Q&A
California’s 34 total cases were evenly split – 17 and 17 – between neuroinvasive, severe cases of the disease that affect a person’s nervous system, and nonneuroinvasive, less severe cases that do not show evidence of neuroinvasion, referred to as West Nile fever, the CDC reported.
The blood of 13 potential donors in California tested positive in preliminary tests when screen for the virus but showed no symptoms at the time they donated blood, according to the CDC.
Mississippi has the second-highest number of cases with 79, one of them fatal. Four states have reported more 65 cases within their borders.
