Breaking barriers by Natural selection, thanks to Global warming - Rise of Chondrostereum purpureum

The human race has survived many epidemics and pandemics including monekypox, COVID-19 respectively, that have emerged and redeemed throughout our history. If not for the past few decades, the last 3 years have very well taught us a lesson of messing with nature, when SARS-CoV-2 evolved and created chaos all around the globe. COVID-19 was a virus that crossed barriers and evolved from animals, being a zoonotic disease. Most of us know all about SARS-CoV-2 and its wonderful abilities, what we hardly know is the relationship of this virus to global warming. It is true that the rise in industrialization and other human-related activities has created a marked imbalance in the homeostasis of several environmental factors including temperature, weather, etc; and these might have even imposed conditions for the emergence of future coronavirus cycles. As heartbreaking and deadly the scenes due to COVID-19 were worldwide, it is even more shocking to not believe that our world is undergoing climate change at a rapid rate and that mankind is the only cause responsible for this. It is a fact that such pandemics, not just due to viruses, but also due to bacteria and fungi will be more frequent in the future and more severely impactful unless global warming is mitigated.

After a hectic few months, I came up with an interesting eye-opening topic for you all and decided to write an article on how a plant-based fungi that causes diseases in plants was transferred to humans. As surprising as it may sound, it is equally interesting to know about this fungi that breaks barriers by natural selection and has infected a person for the first time ever case in the world. I am talking about Chondrostereum purpureum, a fungus that causes silver leaf disease in plants, particularly plants of the rose family. It spreads by airborne spores landing on freshly exposed sapwood.

Fungi and their growth requirements:

Usually, fungi grow and thrive at colder temperatures. But owing to global warming and high temperatures, most fungi are growing at higher temperatures; including Chondrostereum purpureum that has been known to infect a plant mycologist in Kolkata, India. Few among the millions of fungal species on earth fulfill four basic conditions that are necessary to infect and invade human/animal hosts: First being high-temperature tolerance, followed by the ability to invade the human host, lysis and absorption of human tissue, and resistance to the human immune system. Now I can understand that this reminds you of the web series ‘The Last of Us’, but somehow there is a high chance that all that was depicted in the series will be the future of ‘all of us’. No pun intended. Considering the rate of global warming, that day is not far away.

First case of mushroom plant disease causing fungi seen in Human:

In Kolkata, in the beginning of April 2023, a 61 year old Plant mycologist was presented to the outpatient department with hoarsness of voice, cough, recurrent pharyngitis, fatigue, difficulty in swallowing and anorexia from the past 3 months. He had no history of diabetes, HIV, renal or any chronic disease, immunosuppressive drug intake, or trauma. CT scan revealed the presence of an abscess in his neck. The aspirated pus was sent for further identification, and none of the studies revealed its cause. The fungus could not be identified phenotypically and was thus sent to the “WHO Collaborating Centre for Reference & Research on Fungi of Medical Importance” in India, where it was identified as Chondrostereum purpureum by DNA sequencing. Another interesting thing about fungal infections is that a fungus or any antigen, when invading the body, is fought off by our immune system cells. Phagocytosis is the most common mechanism that can kill foreign antigens. However, in a few cases, if the fungi can escape the phagocytosis pathway and evade the host immune system, they can establish themselves as human pathogens, which is what happened in the abovementioned case. Those fungal species that are able to grow at 35–37 °C can become human pathogens or commensal flora. Such pathogens enter the human body through damaged skin and the respiratory tract and cause infection mostly in immunocompromised individuals, as seen in the case of Black fungus in COVID-19 immunocompromised patients throughout the pandemic.

Global warming and Natural selection helping pathogens cross barriers:

Cross-kingdom human pathogens, their potential plant reservoirs, and the environment altogether have important implications for the emergence of infectious diseases. An environmental gradient is a change in abiotic factors through space or time. Every continent on Earth has its own climate and a fixed environmental gradient. Every degree increase in the global warming average temperature reduces this gradient by about 5%, thereby disrupting the balance between the environment and nature. This increases the chance of the prevalence of fungal diseases. In the case of Chondrostereum purpureum, it took the benefit of adapting to a higher temperature by thermal selection. It is a fact that climate induces phenotypic responses as well as alters natural selection.

Moral of the article:

The emergence of SARS-CoV-2 or Chondrostereum purpureum should be considered a wake-up message for working towards a healthier environment on the planet. To mitigate global warming, decreasing deforestation, and worldwide greenhouse gas emissions, and controlling the transmission of pathogens, looking after risk factors of upcoming zoonotic spillovers, etc. needs to be worked upon. Apart from this, it is also important to spread knowledge about measures to protect natural niches and create and impose strong rules and regulations on people involved in wildlife and trade.

As often as it is said that 'Charity begins at home', helping overcome the ill effects of global warming is only possible when we act upon reducing manmade activities and protect the environment at an individual level. Let's take care of nature, so it takes care of us.

- Rachna Jadhav

@theresilientresearcher