In a new and alarming study, researchers at the University of Rochester, New York, have uncovered a troubling connection between the use of bat guano as a fertilizer for marijuana plants and the development of serious fungal lung infections, which can result in fatal pneumonia. The findings, detailed in a paper published in the Open Forum Infectious Diseases journal, highlight the dangers of using bat guano in the cultivation of marijuana and offer a stern warning to both recreational growers and commercial cultivators.
The case study centers on two men, aged 59 and 64, who tragically died after contracting histoplasmosis, a disease caused by the fungal pathogen Histoplasma capsulatum. This fungus is commonly found in environments with bat droppings, such as caves and attics, and can be inhaled when the spores become airborne. The study suggests that both men contracted the infection after coming into direct contact with bat guano while using it as fertilizer in their marijuana gardens.
As marijuana legalization has expanded across the United States, more people are engaging in home cultivation, sometimes even incorporating organic fertilizers like bat guano. The substance, which consists of bat droppings, has gained popularity due to its rich nutrient content—particularly its high levels of phosphorus and nitrogen, which are essential for plant growth. This organic fertilizer is often touted as the best option for cultivating marijuana, enhancing plant health and yield.
However, the tragic deaths of these two men serve as a stark reminder of the potential hazards associated with bat guano. While it is generally safe for most people to handle bat guano with appropriate precautions, it can harbor harmful fungal spores that are not readily visible and can pose significant health risks if inhaled. In the cases of the two men, both had come into contact with bat feces—one had collected it from his attic, while the other purchased a bag of it online. Both men, unaware of the risk posed by the fungus, unknowingly inhaled the spores while fertilizing their marijuana plants.
The symptoms of histoplasmosis in these cases were severe and similar in both men. Initially, they experienced a persistent cough, fever, and weight loss. Over time, the infection progressed, leading to respiratory failure as the fungus spread within their bodies. Histoplasmosis can cause pneumonia, and the fungus can also travel through the bloodstream to other parts of the body, potentially leading to organ damage. While the infection can often be treated successfully with antifungal medications, both men had underlying health conditions that complicated their recovery.
One of the men had emphysema, a chronic lung condition that impairs the ability to breathe, while both men were smokers, which further weakened their respiratory systems. These factors likely contributed to their inability to recover from the infection, underscoring the importance of considering an individual’s overall health when evaluating the risks of certain exposures.
Histoplasmosis is not a rare disease, particularly in areas where bat populations are common. The fungus thrives in environments contaminated with bat droppings and is often found in caves, old buildings, and other places where bats roost. However, it is not typically associated with marijuana cultivation or the use of bat guano as fertilizer. This makes the cases described in the study particularly unique, shedding light on an unrecognized risk for marijuana growers who may be unaware of the dangers posed by bat guano.
For the most part, the majority of people exposed to H. capsulatum spores will not develop serious illness. The body’s immune system can often suppress the fungus before it causes any significant harm. In fact, many people who are exposed to the spores will never show any symptoms at all. However, individuals with weakened immune systems—such as the elderly, those with pre-existing lung conditions like emphysema, and smokers—are at an increased risk of developing severe infections. In these individuals, the fungus can invade the lungs and spread to other organs, potentially leading to life-threatening complications.
The study’s authors caution that while the risk posed by bat guano is relatively low for the general population, it is critical for marijuana growers to be aware of the potential dangers. The researchers recommend that individuals avoid using bat guano as a fertilizer or, at the very least, take significant precautions to reduce the risk of inhaling harmful spores. This includes wearing protective masks, gloves, and other safety gear when handling bat guano, as well as ensuring proper ventilation to minimize the chance of inhaling airborne particles. Additionally, those handling bat guano should consider testing it for fungal contamination, particularly if they are using it in a large quantity or over an extended period.
Beyond these recommendations, the case study also serves as a broader reminder about the potential risks of handling organic materials without proper precautions. While fertilizers like bat guano are often marketed as natural and safe, they can harbor pathogens that pose significant health risks, particularly when inhaled. It is essential that individuals understand the potential hazards associated with such materials, especially when using them in enclosed spaces or without proper ventilation.
In light of the growing popularity of marijuana cultivation, both recreationally and commercially, this study also has important implications for public health and policy. As more states legalize marijuana and encourage personal cultivation, there is an increasing need for education about the risks associated with various cultivation practices, including the use of fertilizers. Marijuana growers should be made aware of the potential dangers of using bat guano, as well as the best practices for handling and applying organic fertilizers safely. Public health officials may also want to consider creating guidelines for safe marijuana cultivation to minimize the risk of fungal infections and other related health issues.
This case study also raises important questions about the intersection of public health, environmental factors, and the cannabis industry. As marijuana cultivation continues to expand, there may be a need for more research into the potential risks associated with growing the plant, particularly with the use of organic fertilizers. Understanding the full range of risks associated with marijuana cultivation—whether they are biological, environmental, or chemical—is essential for ensuring the health and safety of growers and consumers alike.
Reference: Paulina Sudnik et al, Histoplasmosis Associated With Bat Guano Exposure in Cannabis Growers: 2 Cases, Open Forum Infectious Diseases (2024). DOI: 10.1093/ofid/ofae711