New viruses on the prowl

Humans have exposed themselves to a host of new viral diseases by playing around too much with the environment

Published: Wednesday 15 September 1999

 The deadly Ebola virus: natur outbreaks of previously unknown viruses is increasingly being reported from several parts of the world. The us Centers for Disease Control and Prevention ( cdc ) in Atlanta, Georgia, has identified 50 new viruses that cause illness among humans. One reason for this is the rampant human infiltration into virgin forests -- a result of the rising human population that is adding to the pressure on natural resources all the time. This brings humans in contact with new viruses all the time. International travel has also exposed populations across the world to a host of previously unknown viruses.

"The moment humans interfere with nature, viruses start breaking out," warns Pradeep Seth, head of the department of microbiology at the All India Institute of Medical Sciences ( aiims ), New Delhi. He adds that human encroachment into animal territories due to indiscriminate developmental and infrastructural activities accelerates the risk of more lethal outbreaks.

In recent years, many complicated and deadly viruses have been found in human populations in India, transmitted directly or indirectly by human intervention. "The Kyasanur forest disease, named after the forest where the disease broke out in the Shimoga district of Karnataka, is a clear example of human interference with nature," says Seth. When the forest was cleared, ticks belonging to the arbovirus family, which were present in the rodents and monkeys, were passed on to humans, leading to several casualties.

The Ebola virus that struck Congo in 1995 is suspected to have spread from forests. In April 1999, two infants in Hong Kong were infected with a new bird flu virus that differs from the deadly bird flu virus that killed six people in the territory in 1997. A two-year-old boy recently died in Hong Kong from severe complications arising from an intestinal virus called Eterovirus 71. After a routine check at a farm on Quemoy island in Taiwan in May, officials from the agriculture department found a new strain of virus that causes the foot-and-mouth disease. Two animals checked in a second farm also tested positive for the virus. Due to fear of the disease spreading to the main island, Quemoy authorities ordered the destruction of the farm's 45 cattle. Apparently, none of the cattle showed any symptoms.

Scientists at cdc report that a new virus, called Nipah after the area where it first broke out in Malaysia, claimed around 100 lives. The virus is carried by pigs and has never been seen in humans earlier. Since it was first detected in 1998, it has greatly devastated the us $395 million pig farming industry of the country. Pork sales slumped by 70 per cent. So far, there have been 221 reported cases of Nipah and 850,000 pigs have been slaughtered since the outbreak. Controlling the disease is becoming more complicated. Scientists fear the virus would spread to other animals, making it difficult to keep it under control. "Viruses constantly mutate. A new, more lethal mutant resurfaces all the time. This is the process of virus evolution," says Sudhanshu Vrati, principal research scientist at the National Institute of Immunology.

The Nipah outbreak in Malaysia is said to have catalysed from an outbreak of a strain of the flavivirus that causes Japanese encephalitis, a disease that leads to inflammation of the brain. It is also transmitted from pigs to humans by mosquitoes. However, the deadlier Nipah was found to be involved. Studies by cdc revealed that the rna sequence of the virus is closely related to the deadly Hendra virus, which was first isolated in 1994 in Brisbane, Australia, where it killed 14 horses and a trainer. " rna viruses replicate at a rapid pace. Once they enter the brain, they start replicating and cause severe illness," says Vrati.

V Ramalingaswami, former director general of the Indian Council of Medical Research, makes an interesting observation: "Old viruses re-emerge because of the ecological conditions that may be conducive to viral attack." In India, Japanese encephalitis was first discovered in 1955. There were a few outbreaks. However, it has lately assumed serious significance and is associated with high mortality. "Sporadic cases have broken out and it is now a major public health issue," adds Ramalingaswami.

By Lian Chawii

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