Salt Lake City mosquito population skyrockets after wet winter

What that means for malaria and West Nile virus risk in Utah.

It’s unlikely that anyone will catch malaria in Utah, even after the Centers for Disease Control and Prevention issued a health advisory last week because five people recently acquired the disease in the U.S.

But the state is still dealing with more mosquitoes than in recent memory, likely because of this year’s abundant snow and spring rain, which resulted in more standing water, an official with the Salt Lake City Mosquito Abatement District said, adding that abatement teams “have been very busy finding and treating mosquito sources.”

Just how many more mosquitoes are there? Salt Lake City’s population alone is nearly twice as high this year, when compared to the area’s average for the last five years, surveillance efforts indicate — and there’s still months to go in mosquito season.

(Salt Lake City Mosquito Abatement District) Salt Lake City's mosquito population is nearly twice as high this year, when compared to the area's five-year average.

How does malaria spread?

The type of mosquitoes that transmit malaria are called Anopheles mosquitoes, and in Utah, they are rare. Across the state, there are many species of mosquitoes, including a native species of Anopheles mosquitoes called Anopheles freeborni. But they present in low numbers, according to Greg White, the assistant director of the Salt Lake City Mosquito Abatement District.

For example, during a recent surveillance effort, the abatement district trapped 68,752 adult mosquitoes from 36 different spots across Salt Lake City — and only 25 Anopheles mosquitoes were identified.

“The chances of malaria transmission to humans is extremely low because the disease is not endemic in the state and it must be transported through an infected human traveler,” White said.

Malaria can cause fever, chills, headaches and vomiting, as well as seizures and even death in severe cases, according to the CDC. In 2021, an estimated 247 million cases were recorded worldwide in mostly tropical and subtropical climates, with about 619,000 resulting in death, according to the World Health Organization.

In order for malaria to spread locally, an infected person would have to be bitten by an Anopheles mosquito in Utah. That mosquito would then need to survive for about two weeks, long enough for the parasite that causes malaria to develop and migrate back to the insect’s saliva.

That same mosquito would then need to bite another human, passing on the disease, Hannah Rettler, a zoonotic and vector-borne epidemiologist with the Utah Department of Health and Human Services, said.

Though the Anopheles species has been detected in Utah since the early 1900s, to date, the state has not recorded any locally acquired cases of malaria, Rettler said.

“That being said, our DHHS team, along with our mosquito abatement districts, local health departments, and other partners are in regular communication to survey for any possible risk of disease transmission that may occur,” she said.

What if you plan to travel?

(Rick Egan | The Salt Lake Tribune) Chris Bibbs, with the Salt Lake City Mosquito Abatement District, picks up a trap to check the number of mosquitoes on Tuesday, Sept. 27, 2022.

It’s still important for people traveling to areas more commonly associated with malaria transmission to take the recommended malaria-prevention medication — for their protection, and to ensure that they don’t bring the disease back to Utah, said Nicholas Rupp, a spokesperson for the Salt Lake County Health Department. The CDC has a list of information travelers should know about malaria prevention.

The five cases reportedly caught in the U.S. this year were diagnosed in the last two months, according to the CDC. Four were acquired in Florida, and one was acquired in Texas.

There’s an average of seven cases of malaria recorded in Utah each year — all acquired through out-of-state travel, according to Rupp. That’s why he said it’s important to be on the lookout for symptoms after traveling, especially for those who do not take malaria-prevention medication.

The few Anopheles mosquitoes that do live in Utah typically bite in the early morning (from about 3-5 a.m.) and in the evening (from about 6-10 p.m.), Rettler said.

If you must be outside during those hours, consider wearing long-sleeved shirts, pants and closed-toe shoes, as well as wearing insect repellent with 20%-30% DEET, which is safe to use during pregnancy, Rettler said. Repellent is not recommended for children younger than 2 months old.

Whenever possible, wearing repellent and longer layers throughout the day is also genererally recommended to reduce exposure risk.

West Nile virus still a concern

(Rick Egan | The Salt Lake Tribune) Mosquitoes trapped by the Salt Lake City Mosquito Abatement District, in order to check the number of area mosquitoes on Tuesday, Sept. 27, 2022.

West Nile virus, the leading cause of mosquito-borne disease in the continental U.S., is a greater concern in Utah. It’s often reported each year in the Salt Lake Valley, though the CDC estimates that less than 1% of people infected with West Nile will develop a neuroinvasive disease, “which can result in debilitating long-term complications or death,” Rupp said.

In 2022, Utah saw five cases of neuroinvasive West Nile virus, none of which was fatal. In 2021, three people died from the virus in Utah out of 21 neuroinvasive cases.

An estimated 70-80% of West Nile infections are asymptomatic, according to the CDC. But symptoms can include fever, headache and body aches and typically appear within two to 14 days of exposure. Neuroinvasive infections may cause neck stiffness, disorientation, tremors, convulsions or coma. West Nile can’t be transmitted from person to person, and there is no treatment for an infection other than to treat symptoms.

That’s why it’s still important for people to minimize their exposure during mosquito season, which usually lasts from about spring to the beginning of fall in Utah, Rupp said. He advised people to clear rooftop gutters of debris, clean swimming pools often, cut tall grass short and ensure door and window screens are in good condition so mosquitoes can’t get inside.

Rettler recommended removing any standing water from your property, including from pet dishes, flower pots, buckets, tarps, and tires, where pools can form.

You can report bodies of stagnant water or spots thick with mosquitoes to your local mosquito abatement district. Visit umaa.org for a list of such districts.