Health officials typically see the highest number of West Nile cases in August and September. But warmer, wetter-than-average conditions projected for September and October could keep mosquito populations active later into the fall, extending the period of highest risk, especially for states like Arizona, Colorado, New Mexico and Utah.
West Nile virus often flies under the radar. According to the New Mexico Department of Health public health veterinarian, about 80% of people infected never develop symptoms.
Arizona, Colorado, and Utah have seen the numbers of West Nile virus grow rapidly, with Arizona reporting 82 cases and five deaths. Nevada, Idaho, and Wyoming have reported one case each and New Mexico four. California and Texas have the highest cases in the country outside of the Mountain West.
Of those who do get sick, roughly one-in-five experience what’s known as West Nile fever — a relatively mild illness that can look like many other viruses,” said Dr. Erin Phipps, a veterinarian with the New Mexico Department of Health.
Symptoms can include headache, body aches, fever and GI issues, and most people recover without medical care. The most serious concern, however, is a small fraction of infections — less than 1% — that become “neuroinvasive,” affecting the nervous system.
Those cases can lead to meningitis, encephalitis, seizures, confusion, loss of coordination, coma and even death, with many survivors facing long-term complications, she said.
People with weakened immune systems are at higher risk for severe illness. That includes those with chronic conditions like diabetes, and people taking steroids or biologic medications that suppress immune function.
Phipps said recent studies show B‑cell-modulating drugs, in particular, can impair the body’s ability to fight off West Nile infection.
Patients should not change or stop medications without talking to their doctor, Phipps said. Instead, they should focus on prevention:
- Wear an EPA-approved insect repellent DEET, picaridin, or oil of lemon eucalyptus
- Use long sleeves, long pants and loose-fitting clothing to reduce bites
- Limit time spent outside at dawn and dusk
While dogs and cats are more threatened by heartworm disease, which can also be spread by mosquitoes, horses are highly vulnerable to West Nile. A West Nile vaccine for horses is available and should be part of routine spring shots.
With several years of above-average human cases in New Mexico, officials are watching closely as climate and monsoon patterns shape yet another mosquito season.
