New infectious diseases are a sign of how the world is changing, say experts. The more we change the environment, the more we disrupt ecosystems and provide opportunities for diseases to emerge.
Deforestation and human-animal conflict
Clearning of forests may bring wildlife out of the forest to nearby human settlement. ,amu viruses exist harmlessly with their host animals in forests because the animals have co-evolved with them. But humans can become unwitting hosts for these pathogens when they venture into or change forest habitat and come in contact with the host animals directly or indirectly.
New infections can spread rapidly in big cities as population density is higher – people are packed tightly, breathing the same air and touching the same surfaces.
Wildlife trade
Wildlife trade increases the chances of human-animals contact, putting humans at the risk of contracting diseases. For instance, SARS was linked to wildlife trade and eating of wildlife. People who handle, killed and sold wild animals made up early 40% of the first cases. Poorly regulated wet markets (a market selling fresh meat, fish, produce and other perishable goods) and illegal wildlife trade offer a unique opportunity for viruses to spill over from wildlife hosts into the human population. Bird flu’s – H7N9 and H5N9 – too originated in wet markets.
Mobility of people
Increased movement of people, faster transport and international travel and greater inter-connectivity among megacities pose greater risks of disease transmission.
Climate change
Climate change is altering the way animals live and eat. For instance, unusually heavy rains may create favorable environments for bats hosting the virus to reproduce and multiply. Similarly, food scarcity brought about by drought, may lead to more bush meat hunting, raising the risk of outbreaks such as Ebola.
In the American Southwest, years of drought led to a boom in rodent populations as predators suffered. This led to the deadly hanta virus outbreaks in 1993.
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