A black fungus outbreak affected thousands of people in India when the country was battling a surge in COVID-19 cases last year. Researchers have now pointed out that the burning of cow dung is likely behind the epidemic.

Mucormycosis (CAM), more commonly known as black fungus, is a rare fungal infection caused by molds called mucormycetes. These molds can be found "throughout the environment," noted the U.S. Centers for Disease Control and Prevention. It can affect the sinuses or lungs when a person inhales fungal spores from the air, or the skin through injuries such as cuts or burns.

India saw a "disproportionate" increase in COVID-19-associated mucormycosis in 2021. The cases increased "sharply" in late April and it was declared an epidemic in May. By November, the country had recorded 51,775 cases of the illness, according to SciDev.net. However, what exactly caused COVID-19-associated cases has remained unknown.

"Most researchers consider the major cause of India's CAM epidemic to be the conjunction of the COVID-19 pandemic and associated corticosteroid treatment with the enormous number of Indians with diabetes mellitus (DM)," the researchers wrote in a paper published in the mBio, a journal of the American Society for Microbiology. "However, excess CAM cases were not seen to the same extent in the Western world, where diabetes is prevalent and corticosteroids are also used extensively for COVID-19 treatment."

The researchers then looked at other "important but overlooked" factors that were more specific to India. In particular, they hypothesized that the burning of Mucorales-rich cow excrement during the pandemic may have played a "key role" in the uptick in infections. Cow dung is widely used in India as a fuel and also to perform religious rituals.

"Incorporating cow excreta into daily life is a longstanding tradition in India, significantly more so than in the rest of the world," the researchers said, citing an increase in its use during the COVID-19 pandemic. "Even before the COVID-19 pandemic, several socio-cultural activities, including the burning of cow dung, and agricultural practices, like stubble burning, were possibly correlated with the high environmental loads of Mucorales, as biomass fires can disperse viable fungal spores."

This could then explain the "disproportionate case burden" of mucormycosis in India even before the pandemic, one of the paper's authors, Jessy Skaria from Houston, told SciDev.net.

Similar incidences were reported in some other countries as well. In Iran, for instance, there was also extensive burning of donkey dung during the pandemic, and the region also saw an "unusual" uptick in CAM cases.

"Verifying our hypothesis could have important implications for the prevention of CAM, and mucormycosis in general, in India and worldwide," the researchers wrote in the paper, titled "Are Unique Regional Factors the Missing Link in India's COVID-19-Associated Mucormycosis Crisis?"

"Further research in these directions would hopefully establish the role of herbivore dung in the causation of CAM and lay the foundation for initiating measures to reduce the incidence of the disease," they added.