A new study by the Centers for Disease Control and Prevention in the United States says that the West Nile virus is the main cause of the spread of viral diseases by insects.

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This summer has brought a flurry of warnings about cases of mosquito-borne diseases, including malaria, dengue fever and eastern equine encephalitis.

But West Nile virus, which is primarily transmitted by the bite of an infected mosquito, remains the leading cause of viral diseases spread by insects, known as Viral diseaseIn the continental United States, according to a report It was published by the US Centers for Disease Control and Prevention on Thursday.

The report summarizes the number of West Nile virus infections and other viral diseases that occurred across the United States in 2021.

Forty-nine states and the District of Columbia have reported more than 3,000 cases of the viral illness that occurred locally—2,911 of those cases were West Nile virus. A total of 2,099 people infected with West Nile virus have been hospitalized, and 227 people have died.

Nationally, the incidence of neurogenic West Nile virus disease, meaning that the infection affected the nervous system, was the highest since 2012 at 0.6 cases per 100,000 people, largely due to the outbreak in Arizona.

In 2021, three Arizona counties—Maricopa, Pima, and Pinal—reported more than half of all neuroinvasive cases identified in the country. The jurisdictions with the highest number of West Nile virus cases were Texas with 130, Colorado with 101, California with 96 and Nebraska with 69.

West Nile spreads as well Mosquitoes bite infected birds and then humans, which makes bird and mosquito populations an important part of public health surveillance for disease. Mosquito is The most dangerous animal in the world Because it spreads diseases such as malaria, dengue fever and West Nile, killing more people than any other creature.

Although West Nile virus was the most common cause of neurodegenerative viral disease in the United States in 2021, as in previous years, another disease – caused by Lacrosse virus It continues to be the most common cause of ARV in children, according to a new CDC report.

In 2021, 40 cases of lacrosse virus disease were reported in eight jurisdictions – Illinois, Indiana, Michigan, North Carolina, Ohio, Tennessee, West Virginia and Wisconsin – and 35 of those cases were among children. All 40 people were hospitalized, but none of them died of the disease.

“Although case numbers vary by year, virus, and geographic region, arboviruses continue to cause significant morbidity rates in the United States. Climate, animal hosts, vector abundance, and human behavior are all possible factors,” the CDC researchers write in the new report. It can affect when and where an outbreak occurs.”This complexity makes it difficult to predict future locations and timing of cases and underscores the importance of surveillance to quickly identify outbreaks to guide public health prevention efforts.”

As of Thursday, few deaths from the West Nile virus have been reported across the United States, including in the United States. Illinois, Nebraska And Colorado. total 247 cases in West Nile have been reported to the CDC this yearand this number is increasing.

Historically wet winters, and now hotter summers, are resulting in “very significant” warning signs of West Nile virus in the western US, according to public health and mosquito control experts, suggesting that residents should take care to avoid mosquito bites.

people can Reducing the risk of infection with West Nile virus And other mosquito-borne diseases Use insect repellent and wear long-sleeved shirts and long pants to ward off mosquito bites.

“The number of mosquitoes hatched after the spring snowmelt is overwhelming in many states, whether it’s Colorado, Utah or California,” Daniel Markowski, a technical advisor for the American Mosquito Control Association, said earlier this month.

He said many areas are starting to see West Nile virus in mosquitoes, which means “you’re in the right temperature, the right number of mosquitoes, and the right time of year to have a local outbreak.”

on 1 in 5 people is infected with West Nile virus He may have a fever along with other symptoms, but most people do not have symptoms. About 1 in 150 infected people develop a severe or sometimes fatal disease that affects the central nervous system, such as encephalitis, which causes inflammation of the brain, or meningitis, which causes inflammation of the membranes that surround the brain and spinal cord.

CNN’s Meg Terrell contributed to this report.