Small Mammals Can Be Reservoirs for a Life-Threatening Disease

The findings of this study are intended to inform health professionals about areas where disease may be caught locally.

Rodents are reservoirs of fungal pathogens. 

Because fungal infections are on the rise in the human population, it is critical for health officials to understand where these pathogens originate. 

A new study, published in Frontiers in Fungal Biology, has revealed that small mammals could act as a reservoir for these fungal infections. This implies that these rodents may act as reservoirs, dispersion agents, and incubators for emerging fungal pathogens.

“Our analysis, which specifically focused on lung pathogens that cause disease in humans, detected a wide range of fungi in the lung tissues of small mammals,” said Paris Salazar-Hamm, first author of this research, of the University of New Mexico.

“We found that many of the rodents we sampled from areas in the Southwestern US were harboring the type of fungi that can cause lung infections in humans, such as the fungus that leads to Valley Fever, a disease that typically causes flu-like symptoms and can be life-threatening.”

Animal to human jump

There has been a rise in reports of new human pathogens during the past four decades. Host jumps, like the virus COVID-19, have enabled fungi to evolve and diversify. In certain situations, this may boost their virulence, which may have an impact on humans.

“We wanted to understand if the fungal spores of respiratory pathogens reside in soils because they feed on dead and decaying plant matter, or if they are instead living within small animals and their spores are released into the soil after the rodents die,” explained Salazar-Hamm.

The researchers investigated fungal DNA in rodent lung tissues from museum specimens using next-generation sequencing, a process that allows for a quick assessment of the wide-ranging species of fungi.

“We detected the fungus Coccidioides, the cause of Valley Fever, in the lung tissues of animals from Kern County, California, and Cochise and Maricopa Counties in Arizona, areas that have high rates of this disease,” reported Salazar-Hamm.

“In addition, we detected sequences from Coccidioides in animals from Catron, Sierra, and Socorro Counties in New Mexico, which is the first time this pathogen has been detected in the environment in this region.”

“This is the first big study using next-generation sequencing to assess the fungi in the lungs of small mammals. Our results support the hypothesis that rodents could be a breeding ground for respiratory fungal pathogens,” she continued.

Monitoring the spread

The findings from this study hope to inform health officials where there is potential for disease to be acquired locally.

“Current forecasts of the distribution of Coccidioides, based on climate and soil conditions, predict that Valley fever will expand substantially northward and eastward over the next century as a result of climate change impacting environmental conditions. Our results will inform these modeling efforts by adding valuable information about animals as reservoirs for pathogens,” explained Salazar-Hamm.

Future studies hope to examine the health of the host animals and how this may impact the spread or virulence of the diseases.

“We were not able to assess the health of the mammalian hosts from which the lung tissues were acquired. Despite the presence of pathogens, it was impossible to say conclusively that there was disease,” said Salazar-Hamm.

“It would be interesting to further explore the impact of fungi on mammals. That effort would require more detailed information about the general health of the animal in question.”

Reference: “Breathing can be dangerous: Opportunistic fungal pathogens and the diverse community of the small mammal lung mycobiome” by Paris S. Salazar-Hamm, Kyana N. Montoya, Liliam Montoya, Kel Cook, Schuyler Liphardt, John W. Taylor, Joseph A. Cook and Donald O. Natvig, 26 September 2022, Frontiers in Fungal Biology.
DOI: 10.3389/ffunb.2022.996574