New Delhi, Sept. 18: Animal and human viruses have silently swapped genes in India for years and spawned a staggering diversity of new diarrhoea viruses against whom vaccines now under development might not work, scientists have said.
Genetic studies by researchers in Calcutta, Pune and Vellore have revealed that viruses from pigs, monkeys and cattle have exchanged genes with human rotaviruses that cause life-threatening diarrhoea in infants and children.
Rotavirus infections can cause severe diarrhoea and dehydration in infants and children. Doctors estimate that rotaviruses lead to two million hospitalisations and kill 450,000 infants and children worldwide each year, including 150,000 in India.
Several vaccines are undergoing clinical trials. These include two developed jointly by Indian and US scientists through a 16-year research effort.
Now, scientists are worried that the diversity of rotaviruses in India may pose a threat to the efficacy of vaccines in reducing the magnitude of the disease.
“From the point of view of vaccines, such diversity is not a good thing,” said Trailokyanath Naik, a virologist at the National Institute of Cholera and Enteric Diseases (NICED), Calcutta.
Naik has detected rotaviruses with genome segments from both pig and human viruses.
“The diversity of rotaviruses in India is far greater than anyone had imagined,” said Prof. Gagandeep Kang, from the department of gastrointestinal sciences at the Christian Medical College (CMC), Vellore.
She leads a team that has found rotaviruses with genes from bovine and human viruses. “For vaccines to be widely effective, they need to protect against diverse types. Studies to evaluate protection against multiple rotavirus types have not been done yet,” she said.
Gene swapping between animal and human rotaviruses occurs as a chance event when the viruses have infected the same cell in a human. The probability of this happening is high in India where people might often find themselves in close proximity to cattle, monkeys or pigs.
At the National Institute of Virology (NIV), Pune, a team led by Shobhana Kelkar has just shown that an outbreak of diarrhoea that occurred among tribal children was caused by a rotavirus created when a monkey virus exchanged genes with a human virus.
Growing evidence from the past five years indicates that the introduction of novel rotaviruses into humans from animals is likely to be a relatively common event in India, researchers from the CMC, NICED and NIV have said in the latest issue of the Journal of Infectious Diseases.
Scientists at the All India Institute of Medical Sciences, New Delhi, and the Indian Institute of Science, Bangalore, have collaborated with US counterparts in a government-supported programme since the early 1990s to develop vaccines against rotaviruses.
“When the vaccine effort took off, the assumption was that there were only five or six major strains of human rotaviruses. It’s clear now that there are at least 15 to 20 strains that commonly infect humans and cause diarrhoea,” Kang said.