Recently, I read that India has just reported the outbreak of a deadly form of encephalitis among adults in Siliguri, West Bengal (BMJ, 2001; 322: 693). Outbreaks of illnesses in India aren't unusual. What caught my eye was the fact that the scientists studying this outbreak realised that it was caused by a strange form of measles. Even more worrying, this was a strain of measles that couldn't be contained by vaccination. India is one of the many countries that believed it had herd immunity against measles through widespread vaccination coverage. At first, the authorities believed they were faced with an epidemic of celebral malaria or Japanese encephalitis. Instead, to their surprise, tissue samples taken from victims and examined at the National Institute of Virology in Pune showed an antibody 'signature' of measles. Furthermore, the antigen of the measles virus was present in samples of brain tissue of two of the victims. Other tests have also confirmed that the encephalitis was due to measles. This illness didn't resemble measles. There was no rash, and it presented with weird symptoms. Unlike the ordinary variety, which only kills highly undernourished children, this disease, which affects the brain, lungs or kidneys, is highly fatal. The outbreak in February of this year killed at least 28 people. This new strain is also highly contagious. The infection spreads through droplets in the air breathed out by people during terminal phases of the illness. Consequently, two doctors and five nurses numbered among the victims. "This doesn't look like a one time event," said Dr T. Jacob John, a leading Indian virologist, formerly with the Christian Medical College in Vellore. "India may even have had early warnings.
"Those early warnings came in the form of three small outbreaks. Two years ago, five adults in Bombay suffered acute kidney failure and neurological symptoms. Four of the five died. Although none of the victims had a rash, when they were examined by a team from the National Institute of Virology, the measles virus was isolated. In 1998, two highly fatal outbreaks of encephalitis occurred among children under 12 in three states of India. Again, in these cases, the cause was put down to a measles virus.
Perhaps the most frightening aspect of the outbreaks, as far as the virologists are concerned, is the likelihood that mutant strains like these don't respond to vaccination. "In those previous outbreaks, immunisation seems to have failed to protect against this virus," admitted Dr Nirmal Kumar Ganguly, director general of the Indian Council of Medical Research. The other worry is that it can be caught so easily. The present outbreak was only contained by barrier nursing and quarantine like measures.
The National Institute of Virology worries that this new type of disease may signal that measles is reemerging despite the vaccination programme and that an epidemic may be on the cards. The news has sent the virologists scurrying into the laboratory to carry out genetic studies on the new strain.
What none of the Indian scientists seem to realise is that vaccination was the probable cause of this disaster. It never fails to amaze me when scientists of this calibre fail to make the mental leap between mutation of viruses and vaccination. We all know that viruses and bacteria are smart. When you wipe out too many of a certain strain through indiscriminate use of antibiotics, stronger and more virulent mutant strains emerge. Microbes are the ultimate Terminator cyborg. You shoot them down and after a short interval, they stand up again but this time angrier, better armed and more deadly than before. What India is experiencing may be yet another microbe backlash against vaccination. All we may have accomplished with the measles vaccine is to trade a relatively benign illness for an invariably fatal one.