Q&AZ: Are rodents contributing to Arizona's increase in Valley fever cases?

Last year, Valley fever cases hit a record high in Maricopa County, where records show a 38% increase in cases from 2023 to 2024. This led many to question where the disease comes from.

Through KJZZ’s Q&AZ reporting project, one listener asked: Are rodents a contributing factor in the transmission of the illness?

Bridget Barker, a professor at Northern Arizona University, said although rodents are not the origin of the respiratory illness, they still play a role in transmissions.

Barker focuses her research on coccidioides — the fungus that causes Valley fever. The fungus, only found in North and South America, thrives in a desert environment.

Its main food source is animal-derived material, making habitats such as rodent burrows a breeding ground for the fungus.

“When we sample from rodent burrows specifically, we have a higher incident of the fungus present in those samples,” Barker said.

When the fungus runs out of food, it forms fungal spores.

“Those fungal spores then make their way to the surface of the soil, or maybe get concentrated in like rodent burrows, potentially, and then they can be inhaled by the next susceptible host," Barker said.

Any mammal can contract the disease. However, dogs are most susceptible to the illness because they sniff so close to the ground.

“Dogs are sniffing everything and potentially are then exposed to a lot of the fungal spores that are produced, and that’s what causes the infection,” Barker said.

Barker notes dosage as well as the potential host's immune system plays a role in the outcome of disease. Feeding your pet a healthy diet can help your pets overall well-being and immunity.

To further protect and prevent your animal from the illness, you can wet your soil, limit exposure outside on windy days, and avoid activities that stir up dust, such as digging.