Collecting bat guano from caves in Southeast Asia is a centuries old practice that boosts crop yields. But a new study in Thailand shows the fertilizer may also carry coronaviruses, raising a quiet but urgent question: how do you keep people safe without shutting down a livelihood?
Researchers tested guano from 13 caves across Thailand and found betacoronaviruses in more than half of the samples. One cave alone contained five different viral strains. The bats themselves showed no signs of illness, but the dust from dried guano can hang in the air for hours. For the thousands of people who enter these caves each year to harvest guano, that dust is an invisible hazard.
Why cave dust is a problem for farmers and families
Bat guano is prized as a natural fertilizer across Thailand, Cambodia, Vietnam and other parts of the region. Farmers collect it from cave floors, often working without masks or ventilation. The study, led by researchers from Thailand's Chulalongkorn University and the U.S. Agency for International Development, found that the viruses detected were closely related to known bat coronaviruses. None were the viruses that cause COVID-19, but the genetic similarity shows that caves are mixing zones where new viral combinations can emerge.
The researchers focused on the moment when guano is disturbed. When people walk through a cave or shovel dried guano into bags, fine particles become airborne. Inhaling those particles is the most likely route of exposure. The study tested guano from caves used by both bats and people, and the results confirmed that viral material can persist in the droppings after the bats have left.
Simple steps that could cut the risk
The study did not stop at identifying the problem. It tested practical interventions. Researchers found that wetting guano before handling it reduced airborne particles significantly. They also recommended that collectors wear basic face masks and limit the time they spend inside caves during harvesting. Ventilation, where possible, also helped lower the concentration of viral particles in the air.
Local communities in Thailand have used bat guano for generations. The caves are often near villages, and the harvest provides income for families who have few other options. The researchers emphasized that the goal is not to stop guano collection but to make it safer. They worked with local health officials to design recommendations that fit the realities of cave work, not laboratory conditions.
A quiet risk that connects wildlife and daily life
The study adds to a growing body of evidence that human contact with wildlife, even indirect contact through waste, can carry disease risks. Bats are known reservoirs for many viruses, and their guano is a concentrated point of exposure. In Thailand, where caves are both ecological refuges and economic resources, the line between nature and livelihood is thin.
The researchers called for more monitoring of guano in caves across the region. They noted that the viruses they found are not an immediate threat, but the conditions for spillover exist. The study did not predict an outbreak. It simply showed that the risk is real, measurable and, with small changes, manageable.
