West Nile virus is the most common and serious vector-borne disease in California, according to the California Department of Public Health. There have been more than 7,500 human cases and over 300 deaths reported in the state since 2003.
It is typically spread to people during the summer and early fall when the mosquitoes that carry the virus are most active. Experts previously told The Bee this season could be worse than before due to lowered immunity and the winter storms that created a climate ripe for the pests.
No human cases have been reported so far in 2023, but there are at least 84 mosquito samples, including reported infections in Yolo, Placer and Sacramento counties, The Bee previously reported.
Here’s what you need to know about West Nile virus:
How is it contracted?
Ronald Owens, a spokesman for the California Department of Public Health, said the increasing numbers of mosquitoes heightens the risk of virus transmission to humans.
“West Nile Virus is common in the United States, especially in California, and is a problem that is here to stay. The best way to prevent (it) is to protect yourself from mosquito bites,” Owens said in an email to The Bee.
Aside from mosquito bites, the virus can also be contracted through:
- Blood transfusions
- Organ transplants
- Mother to baby during pregnancy
Why do mosquitoes carry the virus?
The main species of mosquitoes in the U.S. that carry the virus are Culex pipiens, Culex tarsalis, and Culex quinquefasciatus.
“These mosquitoes can get West Nile Virus by feeding on the blood of a bird that is infected with (it) and then spread the virus to humans or other animals the next time they bite,” Owens said.
What are the symptoms?
Owens said about 80% of people (about four out of five) who are infected with West Nile virus don’t have any symptoms and most likely don’t know they have been infected with West Nile virus.
However, symptoms can include and are not limited to:
- Skin rash
- Nausea and vomitting
- Headaches and body aches
“Symptoms usually develop 3 to 14 days after being bitten by an infected mosquito,” Owens said. “Most symptoms usually only last a few days, although fatigue and weakness can last for weeks or months after being sick.”
How serious is it?
Owens said less than 1% of people (about 1 out of 150) will become very sick.
According to recent data, West Nile virus infected at least 209 Californians and killed 15 residents last year.
“In these cases, the virus affects the brain and/or nervous system and can cause encephalitis or meningitis,” Owens said.
Other severe symptoms can include but are not limited to:
- Vision loss
- Muscle weakness
“These symptoms may last several weeks, and effects on the brain and nervous system may be permanent,” Owens said.
How can you prevent it?
Owens said that individuals should protect themselves against mosquito bites and West Nile virus by practicing the “Three D’s” below:
- DEET – Apply insect repellent containing DEET, picaradin, oil of lemon eucalyptus or IR3535 according to label instructions. Repellents keep the mosquitoes from biting you.
- DAWN AND DUSK – Mosquitoes usually bite in the early morning and evening. It is important to wear proper clothing and repellent if outside during these times.
- DRAIN – Mosquitoes lay their eggs on standing water. Eliminate all sources of standing water on your property by emptying flower pots, old car tires, buckets, and other containers.
This story was initially revealed June 27, 2023, 9:18 AM.