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Attack of killer mutant microbes

They may not be the biggest killers, but animal plagues have gained cult status as one of the biggest threats to human survival, alongwith climate change and alien invasion.

health and fitness Updated: Feb 13, 2011 02:10 IST
Sanchita Sharma

They may not be the biggest killers, but animal plagues have gained cult status as one of the biggest threats to human survival, alongwith climate change and alien invasion. Malaria and tuberculosis have killed millions over centuries, but it’s swine flu, bird flu, SARS, Ebola and the-newest-bug-on-the-block, Congo haemorrhagic fever, that hog mindspace because they sweep through populations rapidly, sickening and killing a few hundreds within months, before disappearing to make way for a new wave of infection.

According to the World Health Organisation, a new disease emerges every four months, with poorer countries being the worst hit. What’s remarkable is that 61 per cent of all disease-causing microbes — viruses, bacteria and parasites — originate from animals, which transmit 75 per cent of all new human infections.

“A new infectious disease is born when infected animals live in close proximity to people, which makes it possible for a pathogen (infecting agent) to jump from animals to humans to mutate into a new pathogen that can be easily transmitted from person-to-person,” said Dr V M Katoch, director general, Indian Council of Medical Research.

Fewer new diseases emerge from developed countries because infections in animals are usually detected and contained before pathogens make the species jump. “The huge international trade in animal products for food, along with massive business and leisure travel across countries, can lead to new infections cause devastation across the world within weeks,” said Dr Delia Grace, veterinary epidemiologist, International Livestock Research Institute.

Blighted incomes

Besides causing disease and death, outbreaks — such as bird and swine flu — affect incomes of small farmers, who are
largely uninsured, and the food supply by prompting import bans and culling of millions of birds and animals. Animal plagues account for at least 16% of infectious diseases in poor countries, compared to just 4 % in rich nations.

“In India where people keep backyard poultry and cattle and buy and sell animals in village haats, resistance to safety checks is high even when there is a risk of infections because it affects income,” says Dr Katoch. India feeds over 1.12 billion people but has just 1,800 food safety inspectors, which shows there is more need for safety and regulation.

In the northeast, for example, the market has rapidly grown for the local inexpensive black and crossbred pigs kept in backyard pig farms. The result is infestations, with a 2009 survey reporting pig tapeworm – which can bury in the human brain and cause epilepsy -- in almost one in 10 pork samples.

Tracking trouble

“The most effective way to prevent outbreaks of exotic diseases is to detect infection in animals before it infects humans,” says Dr Grace. “In developing countries including India, 700 million people farm animals to feed their families and meet the rising demand for meat, milk and eggs among urban consumers, so food safety concerns are immense,” says Dr Grace.

"Since the bird flu outbreak, India has strengthened its active surveillance among animals and people with special focus on sharing safety information with farmers, traders and consumers," says Dr Katoch. But with the government still floundering to identify the animal source of the country’s first Congo fever outbreak, much more needs to be done before India can declare itself ready to swat away the new bugs in town.