By Ethan Covey
Multiple members of a U.S. family that visited a network of caves in Costa Rica have tested positive for histoplasmosis, a fungal infection often caused by exposure to bird or bat droppings.
In total, 12 family members, living in three states, were suspected to have had the infection (MMWR Morb Mortal Wkly Rep 2025;74[17]:289-292).
During December 2024, 13 members of the family traveled to Costa Rica. While on their holiday, 12 of the family members visited Venado Caves, a popular tourist attraction in the area.
All the family members who visited the caves subsequently developed mild to moderate illness and reported having had direct contact with bat droppings while in the caves.
“This is an unusually high attack rate and may indicate that travelers were exposed to a large dose of Histoplasma spores in Venado Caves,” said lead author Ria R. Ghai, PhD, an Epidemic Intelligence Service officer at the National Center for Emerging and Zoonotic Infectious Diseases. “Travelers should be aware of the risk of histoplasmosis when considering touring caves inhabited by bats.”
The infected individuals ranged in age from 8 to 49 years. Five adults and one child sought medical care, and fungal antigen testing was performed for four family members. Among the family members who fell ill, one case of histoplasmosis was confirmed, eight were determined to be probable, and three were suspected. By 28 days after exposure, all 12 had recovered or were improving.
The Venado Caves have been associated with histoplasmosis, including a 1998-1999 outbreak that affected 51 people (Am J Trop Med Hyg 2004;70[4]:438-442), but Dr. Ghai said it is unknown whether exposures to Histoplasma are common or ongoing in the caves.
“It is possible that exposure is more common, and people who get histoplasmosis after visiting Venado Caves or other bat-inhabited caves are never diagnosed,” she said. “We know that people often do not get sick enough to go to healthcare providers, or if they do, they might be misdiagnosed and treated for viral or bacterial infections. It would therefore be helpful to understand in future investigations whether histoplasmosis infections from this cave or similar caves are uncommon or common but frequently missed.”
Dr. Ghai also noted that the relationship between infectious dose and severity of infection is not known for Histoplasma. “It would be helpful for future studies to investigate the potential for correlation,” she said.
The sources reported no relevant financial disclosures.
