Health authorities in the US have issued an alert after multiple mosquitoes tested positive for a virus that can, in some cases, become life-threatening.
Mosquitoes are considered among the world’s most dangerous animals. The CDC says they contribute to hundreds of thousands of deaths each year through the transmission of diseases such as malaria.
Although malaria is the illness most commonly linked to mosquitoes, officials have also identified insects carrying another serious infection without showing signs of it themselves.
That disease is West Nile Virus, which is also spread by mosquitoes.
The CDC says most infected people do not experience symptoms. However, more severe illness can occur, especially in people with weakened immune systems and older adults. Possible symptoms include fever, headache, body aches, vomiting, diarrhea, and rash. In the most serious cases, the virus can affect the central nervous system and may prove fatal.
West Nile virus activity typically rises in the summer and into early fall, when mosquito populations are highest. Public health agencies say the best defense is to avoid mosquito bites by using insect repellent, wearing long sleeves and pants when possible, and removing standing water around homes where mosquitoes can breed.
Officials in Southern California are now dealing with a rise in positive detections after mosquitoes in 13 cities across Orange County, California, tested positive for the virus, according to the Orange County Mosquito and Vector Control District.
Figures show there were 38 positive mosquito samples in total. Of those, 15 were found in Fullerton, seven in Buena Park, three in Anaheim, three in Santa Ana, and two in Huntington Beach, according to the Daily Mail.
Single positive samples were also recorded in Westminster, Stanton, Seal Beach, Newport Beach, Garden Grove, Cypress, Costa Mesa, and Brea.
Speaking to KTLA, district officials said:
“We only treat when there is an abundance of mosquitoes and the presence of disease.
“Then that triggers us to go out with our trucks and knock down the adults [mosquitoes].”
Positive mosquito samples have also been identified in Ventura County, while Sacramento and Yolo counties have likewise reported detections.
State surveillance data show that West Nile activity has been building elsewhere in California as well, with mosquito samples reported in multiple counties across the state and no human infections reported yet this year. Health officials say that does not mean the risk is gone, because mosquito surveillance can move faster than human case reporting and risk can vary widely by neighborhood.
Most West Nile Virus infections do not cause noticeable illness, though some people develop symptoms similar to a fever or flu-like infection.
Roughly one percent of cases, however, can become much more severe.
These are known as neuroinvasive cases, meaning the virus is able to pass through the protective barrier between the bloodstream and the brain.
When that happens, it can spread into the meninges, the membranes that shield the brain and spinal cord.
This can lead to meningitis, a serious condition involving inflammation around the brain and spinal cord.
In the worst cases, severe complications can occur, including paralysis.
Health experts urge anyone with fever, severe headache, confusion, neck stiffness, weakness, or other serious symptoms after being bitten by mosquitoes to seek medical attention promptly, especially if they are older or have an underlying medical condition.