Enlarge / This micrograph shows the presence of the fungal agent Blastomyces dermatitidis, 1978. (credit: Getty | CDC/Dr. Libero Ajello)

Toxic fungal spores wafting around a Wisconsin neighborhood—possibly spread by recent construction in the area—sparked an outbreak of rare infections that left one person dead, state health officials reported Friday in the Morbidity and Mortality Weekly Report.

In all, the outbreak cluster included five pet dogs and four people, with the onset of symptoms spanning from October 2021 to February 2022. While two of the cases in people were mild, the other two required hospitalization, including the fatal case. The five dogs were reported to have mild to moderate cases.

The outbreak was caused by the poorly understood fungus Blastomyces (B. dermatitidis and B. gilchristii), which lurks in moist soil and decomposing organic matter, such as wood and leaves, often near water. The Centers for Disease Control and Prevention estimates the fungus could exist throughout the eastern US, but its distribution is uneven. It’s often found around the Ohio and Mississippi River valleys and the Great Lakes. Parts of Wisconsin and Minnesota are considered hotspots.