West Nile Virus cases in Maricopa County in 2019 have spiked by more than 400% over last year, and public health officials are unsure why.
The West Nile virus is the most common mosquito-borne disease in the United States and arrived in the United States in the late 1990s and in Arizona in 2003. It’s not known how the virus was first introduced into the state.
Most cases occur during mosquito season, which runs from the summer through the fall.
Most people infected with it don’t feel sick and 1 in 5 don’t ever show symptoms. Only about 1 in 150 people infected will become seriously ill. Last year there were six deaths attributed to the virus, according to the Arizona Department of Health Services.
In 2018, there were a total of 24 cases of West Nile in Maricopa County and 27 statewide. So far this year, there have been 123 cases in Maricopa County and 126 statewide – and seven deaths.
Cases of West Nile Virus have not surpassed 110 since 2012, and the year with the most cases is still 2004 when there were 391 confirmed cases of the virus in the state. That was the first year the state began collecting data.
Jessica Rigler, assistant director for public health preparedness for the Arizona Department of Health Services, said the agency is exploring the potential causes of the increase, but an answer may elude them.
The agency is working on collecting data on potential cases and is also working with the Centers for Disease Control to try and better understand why there has been a spike in West Nile cases in 2019.
There currently isn’t a prevailing theory as to what has caused the sudden increase, but changes in rain patterns could have contributed to changes in the mosquito population, Rigler said.
Arizona has had more West Nile cases than any other state this year, according to Centers for Disease Control data.
The next highest number is 13 cases in California. Arizona accounts for 7 of the 11 West Nile deaths nationwide in 2019.
However, since most people do not present symptoms and many of the symptoms are “flu-like,” the data could be skewed as many people who have had the virus did not seek treatment, Rigler said.
Encephalitis, or inflammation of the brain, can be caused by the West Nile virus. While encephalitis is generally not life threatening, it can cause things such as seizures or memory loss in vulnerable people, such as the elderly or infants.
Another complication of West Nile virus that can impact the most at risk members of the population of the state is meningitis, an inflammation of the linings of the brain and spinal cord. Meningitis can be life-threatening, and symptoms include high fever, headache, confusion, disorientation, seizures and coma.
However, the percentage of the population that would experience the more serious symptoms of the virus is less than 1 percent, according to the CDC and ADHS.
Between 10 and 30 percent of the population is at risk of “flu-like” symptoms and the rest may get the virus and never know it.
While there is no medication or vaccine for the West Nile Virus, there are steps people can take to protect themselves.
The mosquitoes that are prone to carry the virus are more likely to come out at dusk or dawn, ADHS Director Cara Christ told the Mirror.
She suggested people wear long sleeves if possible and use protective bug spray.
So far in 2019, ADHS has trapped more than 17,000 mosquitoes across the state.
The large majority of the mosquitoes trapped and the mosquito pools found are in Maricopa and Pinal Counties, the areas where West Nile virus is the most prevalent.
Mosquitoes can lay their eggs in a standing body of water as small as a bottlecap, Rigler said. That’s why the agency is stressing the importance of eliminating any and all standing water you may have on or near your property.
Not overwatering your lawn and emptying and refreshing your outdoor pet water bowls are just two small ways you can minimize how and where mosquitoes can breed.
In 2019, 318 mosquito pools tested in Arizona have come up positive for West Nile virus.