Homegrown weed lovers beware: there are some fertilizers that you should probably avoid. Doctors are warning people to steer clear of bat guano, a.k.a bat poop, after two cannabis growers contracted a fatal fungal infection linked to its use.
Researchers at the University of Rochester detailed the unusual infections in a case report published earlier this month. Both cases involved local men who developed a severe bout of histoplasmosis, likely contracted from bat guano they had used or intended to use as fertilizer for their cannabis crops. While exposure to bat guano isn’t a common risk for many people, the researchers note that it’s become a popularly advertised “superfood” for growing cannabis.
Histoplasmosis begins as a lung infection caused by inhaling spores of the Histoplasma fungus (typically the species Histoplasma capsulatum). These exposures don’t usually make people sick, but sometimes the infection can turn into relatively mild pneumonia, causing symptoms such as fever, cough, chest pain, and body aches. More rarely, the infection can linger in the lungs and become a chronic problem, or even spread to other parts of the body like the brain and cause serious, life-threatening illness. As is often true with fungal infections, chronic or severe histoplasmosis is more common in people with already weakened immune systems.
These infections aren’t contagious and can be only caught from environmental sources of the fungus. The fungus is primarily found in the central and eastern U.S., living in the soil. But Histoplasma fungi grow especially well in soil that’s been saturated with bird or bat droppings, and the fungi seem to naturally infect bats routinely, making the furry, flighted mammals an important vector of transmission. Outbreaks of histoplasmosis are often caused by disruptions of contaminated soil that kick up the spores in the air. But these latest cases appear to show that bat guano itself can be a deadly carrier of histoplasmosis.
The first victim, a 59-year-old man, had purchased bat guano online and used it to fertilize his cannabis. The second victim, a 64-year-old man, had recently discovered a “heavy bat infestation” in his attic, and he was hoping to use the bat guano as a fertilizer for his crops. Unfortunately, by the time the men had seen the doctors, their cases had gotten quite severe, causing other problems like secondary infections and sepsis. Despite treatment, they eventually died from complications of the infection. Both men had a history of other medical issues that may have made them more vulnerable to severe illness, such as emphysema or past heart surgery.
“Exposure to bat guano among cannabis growers appears to be a recent trend that can lead to histoplasmosis cases and outbreaks,” the researchers wrote in their paper, published in the journal Open Forum Infectious Diseases.
Histoplasmosis is a rare diagnosis (between 3,000 and 7,000 cases may occur annually in the U.S., according to the Centers for Disease Control and Prevention). But the researchers are worried that cannabis growers are likely in the dark about the potential dangers posed by bat guano. They note that guano is commonly touted online as a “natural superfood” for growing cannabis because of its richness in nitrogen and other compounds. But neither federal nor local agencies appear to currently test commercially sold guano for the fungus. And given that cannabis (and cannabis growing) is only expected to become more popular as legalization expands, the researchers argue that more should be done to educate people about this exposure risk and to keep fungus-tainted guano fertilizer away from customers.
“It is crucial to raise awareness among physicians and patients to reinforce personal preventive measures and establish timely diagnosis. Commercial biofertilizers containing bat guano should be tested for Histoplasma capsulatum before reaching the market,” they wrote. “If testing is not feasible, risk mitigation strategies should be implemented.”
English (US) ·