The Negative Effects Bat Guano Brings to Cannabis Cultivation

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Growing cannabis is not a simple task, and in some cases it can prove dangerous. A recent study published in the journal, Open Forum Infectious Diseases (1,2), disclosed the risks that come from utilizing bat guano as a fertilizer in cannabis cultivation. According to the study, “Histoplasmosis Associated With Bat Guano Exposure in Cannabis Growers: 2 Cases,” two men unfortunately passed away after coming into contact with the bat guano through inhalation. The two men succumbed to the fungal infection called histoplasmosis (1,2) which has a connection to bat and bird droppings, and use in cannabis growing. Bat guano has been promoted in some media as a “superfood” for cannabis because of its richness in nitrogen, phosphorus, and other organic compounds (2).

Histoplasmosis infections are more commonly found in the Mississippi and Ohio River valleys, as mentioned in Forbes (1). Histoplasmosis holds a death rate of 5-7% in hospitalized cases, and can affect 1-2 people per 100,000 annually in states that report cases (1,3). As noted in the abstract of the study, transmission occurs through inhalation of the spores when the fungus is disturbed (1). Often cases go undiagnosed and reported when those infected experience more mild cases, which was mentioned in a Centers for Disease Control and Prevention report from 2024 (3). The cases referred in the recent study took place in Rochester, New York. The bat guano fertilizer used was either wild-harvested or purchased commercially (1).

In the study (2), the first case reported was a 59-year-old man with previous heavy tobacco and inhalational cannabis use, rheumatoid arthritis on Adalimumab, and emphysema (1,2). It also mentioned that he recently underwent imaging which showed a laryngeal mass and was admitted for respiratory failure to Strong Memorial Hospital (Rochester, New York). A biopsy revealed yeast forms morphologically consistent with Histoplasma. The patient stated that he’d used bat guano as fertilizer for cannabis plants that he grew and subsequently smoked. He’d stated he’d purchased the bat guano online.

The second case (2) involved a 64-year-old man who was hospitalized for hypo-osmolar hyponatremia, weight loss of 35-pounds over several months, and a chronic cough. He also had prior aorto-bifemoral bypass surgery, tobacco, inhalational cannabis use, and alcohol use. He stated he had intended to collect bat guano accumulating in his attic due to a bat infestation, and use it to fertilize his cannabis plants, inspecting the guano on several occasions.

The study noted that neither federal agencies nor the New York State Department of Agriculture routinely test bat guano products for H. capsulatum, and noted the difficulty in culturing the fungus. It suggested risk mitigation strategies as a potential alternative, such as labeling products and raising public awareness of the potential hazards of collecting or utilizing bat guano fertilizers. It cautions that as home cultivation of cannabis increases, certain individuals, such as those who are immunocompromised, may be at more risk for contracting the disease and clinicians should include history of cannabis use and cultivation in their discussions with patients, which could also help with early diagnoses of histoplasmosis.

References

1. Sabaghi, D. How Bat Guano Turned Deadly for Two Men Growing Marijuana https://www.forbes.com/sites/dariosabaghi/2024/12/17/how-bat-guano-turned-deadly-for-two-men-growing-marijuana/ (accessed Dec 17, 2024).
2. Sudnik, P.; Passarelli, P.; Branche, A.; Giampoli, E.; Louie, T. Histoplasmosis Associated With Bat Guano Exposure in Cannabis Growers: 2 Cases https://academic.oup.com/ofid/article/doi/10.1093/ofid/ofae711/7917418 (accessed Dec 17, 2024).
3. Facts and stats about histoplasmosis https://www.cdc.gov/histoplasmosis/php/statistics/index.html (accessed Dec 17, 2024).