Deaths from the mosquito-borne illness have been growing recently. The Centers for Disease Control and Prevention (CDC) says as of September 21 that the virus has killed 21 people in 12 states this year. Nebraska registered its first death for the year on September 13; and on Friday, Los Angeles County in California reported its first West Nile virus fatality of 2021. RELATED: What Bit Me? Spot These 13 Bug Bites “West Nile virus can be a serious health threat to people who get infected,” warned Los Angeles County Health Officer Muntu Davis, MD, in a statement. The virus has no specific treatment or vaccine to prevent illness. While Arizona leads the country with 97 out of a total 479 West Nile disease cases nationwide, 83 cases have been found in Colorado this year, 48 in California, 38 in Nebraska, 26 in South Dakota, and 22 in North Dakota. While the disease currently appears to be spreading, CDC figures indicate that the situation is not worse than last year, when 664 cases and 52 deaths were reported across the country. The West Nile virus is transmitted to humans through a mosquito bite (although most mosquitoes do not carry the disease). Mosquitoes get the virus when they bite an infected bird. Crows and jays are the most common birds linked to the virus, according to Johns Hopkins Medicine. But at least 110 other bird species also carry the virus. It cannot be passed from one human to another as with COVID-19. Johns Hopkins adds that the virus occurs in late summer and early fall in mild zones but can be found year-round in southern climates. RELATED: Mosquito Bites That Spread Disease: Zika and More The disease typically produces mild flu-like symptoms, including fever, muscle aches, and tiredness. In some cases, especially in persons over 50 years old and those with chronic medical conditions such as cancer and diabetes, severe infection can occur and affect the brain and spinal cord causing meningitis (inflammation of the lining of the brain and spinal cord), encephalitis (inflammation of the brain), and paralysis. To help prevent getting the illness, the Los Angeles County Health Department advises people to regularly check for items that can hold water and breed mosquitoes, both inside and outside their homes, and to cover, clean, or throw out those items. “I encourage everyone to protect themselves from diseases spread by mosquitoes by using EPA-registered mosquito repellent products as directed, and wear clothing that covers your arms and legs,” said Dr. Davis.