In 2009, PREDICT, a project that aimed at the detection of the emergence of zoonotic viruses was launched by the United States Agency for International Development. Zoonotic viruses are those that pass from animals to humans and can be sources of potential pandemics. During its first decade of activity, the project discovered at least 931 different viruses and provided assistance to 60 countries in order to strengthen the global defence mechanism against the threat of zoonotic diseases. The scientific journal The Lancet stated that it was unfortunate that the programme was cancelled only a few weeks before the breakout of the novel coronavirus, SARS-CoV-2.
How does the environment work on the virus?
According to a report published by the World Health Organisation (WHO), there are certain fronts where climate change can influence the spread of viral diseases. In 2018, an article published in the journal Nature indicated that 30% of all emerging diseases from the previous decade had been transmitted by vectors (the overarching term for mosquitoes, flies, birds, fleas, lice etc.).
When the phenomenon of climate change was first proposed by scientists, widespread concerns were raised about its implication on the spread of arboviruses. Arboviruses are viruses that are carried by arthropods like mosquitoes, midges and ticks. Experts are of the opinion that while changes in temperature and rainfall are central factors in making new territory hospitable to an invading arbovirus, many other forces are also significantly engaged in the emergence of new viral patterns. The European Society of Clinical Microbiology and Infectious Diseases has summarised the relationship between climate change and virus mutation. It stated that as a result of climate change, sudden changes in the temperature are witnessed and also there are frequent occurrences of extreme weather events like drought, flood, hurricane etc. This is an ideal breeding ground conducive to virus modification and for growth of infectious diseases. This happens because of the alterations in average temperatures, humidity levels, vegetation quality and the ensuing large-scale movement of animals inevitably results in changes in the arthropod distribution patterns.
The WHO in its website has published an essay titled ‘Climate change and human health’. The essay states, “Infectious agents vary greatly in size, type and mode of transmission. There are viruses, bacteria, protozoa and multicellular parasites. Those microbes that cause ‘anthroponoses’ have adapted, via evolution, to the human species as their primary, usually
In contrast, non-human species are the natural reservoirs for those infectious agents that cause ‘zoonoses’. There are directly transmitted anthroponoses (such as TB, HIV/AIDS, and measles) and zoonoses (e.g., rabies). There are also indirectly-transmitted, vector-borne, anthroponoses (e.g., malaria, dengue fever, yellow fever) and zoonoses (e.g., bubonic plague and Lyme disease).
Experts are of the opinion that the destruction of ecosystems, demolishing of forests and other human transgressions on the natural environment could increase the risk of transferring viruses from animals (also wild ones) to people. A study published in Nature stated that the degraded habitats breed more viruses that can infect humans. Researchers at the United States Agency for International Development have determined that nearly 75% of all new diseases, emerging or re-emerging, affecting humans at the beginning of the 21st century are zoonotic. In the same context, the Centre for Disease Control and Prevention (CDC) in the United States estimated that three out of every four new or emerging diseases originate with animals.
How the virus works on a human body?
The functioning of different viruses inside a patient’s body is comprehensively explained by Dr. Siddhartha Mukherjee, an American-Indian physician and author. He has stated in his article title ‘How the coronavirus behaves inside a patient?’ published in The New Yorker that the examination of several viruses including the ones that cause AIDS, SARS and smallpox suggest a more complex view of the disease, its rate of progression and strategies for containment. He stated, “In the nineteen-nineties, as researchers learned to measure how much H.I.V. was in a patient’s blood, a distinct pattern emerged. After an infection, the virus count in the blood would rise to a zenith, known as ‘peak viremia’, and patients with the highest peak viremia typically became sicker sooner; they were least able to resist the virus.”
Dr Mukherjee refers to the research by Rik de Swart, a virologist at Erasmus University, in Rotterdam that states the strongest association between the intensity of exposure and the intensity of subsequent disease is seen in measles. In a conversation with Dr. Mukherjee, Swart had stated, “In measles there are several clear indications that the severity of illness relates to the dose of exposure. And it makes immunological sense, because the interaction between the virus and the immune system is a race in time. It’s a race between the virus finding enough target cells to replicate and the antiviral response aiming to eliminate the virus.”
It can be said that the changes in infectious disease transmission patterns are major consequences of climate change. Experts feel that the underlying complex causal relationships have to be examined and the resultant information should be applied to predict future impacts and subsequently their modes of treatment.