Two deaths from the West Nile virus, a disease spread by infected mosquitoes, have been confirmed in El Paso, officials said Tuesday.

The patients were men in their 60s and 70s with underlying health conditions living on the East Side and the Lower Valley. El Paso’s public health department has reported six cases of West Nile virus this year, all of which have resulted in hospitalization.

“The community needs to take into account that for most people, a mosquito bite is a nuisance, but for others it can be very serious, particularly for those with medical conditions that impair their immune system’s ability to fight infection if the mosquito is carrying a disease like West Nile,” said City-County Health Authority Dr. Hector Ocaranza.

The majority of people infected with West Nile virus do not show symptoms. Those who do develop the illness show symptoms that can include fever, headache, body aches, nausea, vomiting and swollen lymph glands.

People over the age of 60 are at the highest risk of serious illness, as well as people with underlying health conditions, such as cancer, diabetes and hypertension. Other cases of West Nile virus in El Paso this year were found in patients ages 60 to 80, with and without underlying health conditions.

Why we might see more mosquitoes in fall

Annual cases of West Nile virus have fluctuated over the last decade. In 2021, El Paso reported 18 West Nile virus cases, two of which resulted in death.

The most common mosquitoes found in El Paso are Aedes aegypti, Culex quinquefasciatus and Culex tarsalis, said Doug Watts, a researcher at the Mosquito Ecology and Surveillance Laboratory at the University of Texas at El Paso.

The Culex genus mosquitoes carry two viruses found in El Paso: West Nile and St. Louis Encephalitis. El Paso’s Environmental Services Department found mosquitoes infected with St. Louis Encephalitis virus earlier this year, but there have been no reported cases of humans with the disease.

The mosquitoes that people are battling in and around their homes are most likely Aedes aegypti, Watts said. While this species is capable of transmitting zika, dengue and yellow fever, people have not contracted these diseases in El Paso, he noted.

Mosquitoes are seen as a summer nuisance, but rising temperatures caused by climate change could allow species like Aedes aegypti to remain active in the fall, grow in population and spread geographically, Watts said. Average September temperatures in El Paso have risen 5.1 degrees Fahrenheit since 1970, according to the research nonprofit Climate Central.

“This mosquito’s survival is almost totally dependent on temperature. If it doesn’t have a certain temperature, it isn’t going to survive,” Watts said. “Any increase in temperature is going to provide potential opportunity for this mosquito species to expand its range.”

In El Paso, Aedes aegypti adults typically lay their eggs in the fall when temperatures drop and those eggs hatch in spring. Females need blood to lay eggs, which could be driving those October mosquito bites, Watts said. Since this species lays eggs in water containers, Watts suggests that people routinely empty out their outdoor pet dishes and containers that collect rainwater.

Culex prefer laying their eggs on top of open pools of stagnant water, such as ponds, reservoirs and canals with low flow, Watts said. They hibernate in the winter, but warmer temperatures could also encourage them to remain active in the fall. The city puts biodegradable pellets, which are non-toxic to humans and animals, in mosquito breeding areas to block the development of larvae and pupae.