Syed Akbar Hyderabad, May 30: Has the rabies virus in Andhra Pradesh mutated shortening the incubation period for development of full blown rabies symptoms? This question haunts scientists and doctors as quite a few number of recent rabies deaths in the State have occurred within a month of being bitten by rabid dogs. Usually the incubation (the period between dog bite and manifestation of symptoms) of rabies in human beings is sufficiently long, and often ranges between one and two years, though there are also cases of full blown rabies within six months of exposure to the virus. It is thanks to this long incubation period that most of the dog bite cases go unnoticed. But with rabies now being manifested between a fortnight and a month of being bitten by rabid dogs, many people feel that there's a spurt in rabies cases in the State. The rabies virus now circulating in India is of genotype-1 and many health experts in the country argue that the rabies virus is stable unlike the influenza virus or HIV. Some experts, however, feel that there has been some minor mutations in the virus. Unfortunately, both the claims are not backed by scientific studies. "Rabies takes its time before going from incubation to infection, so post-exposure rabies vaccinations tend to be effective at stopping the virus. We have found only one strain of rabies in India, though there may be some minor amino acid changes. But these changes are inconsequential," points out NIMHANS neurovirologist Dr SN Madhusudhana, who is also the WHO co-ordinator for rabies control. However, the argument that rabies virus, long thought to be stable, is capable of mutating to reduce the incubation period gained significance in the backdrop of a study by a team of American scientists in Arizona, which says if the genetic code of the rabies virus experienced enough changes, or mutations, its incubation time could be reduced dramatically. "We have no reports of the rabies virus undergoing mutations. It is a stable virus. There were deaths due to rabies and they still occur. You can say the virus has mutated if there were no deaths earlier," argues Dr Lalit Kant, former head of epidemiology and communicable diseases, Indian Council of Medical Research. No studies have thus far been conducted in the country on the shortened incubation period. In contrast, laboratory studies by the Centers for Disease Control and Prevention, USA, revealed that the rabies virus is capable of mutating. "If a rabies virus can mutate fast enough, it could cause infection within an hour or a few hours. That's entirely plausible," according to senior virologist Samita Andreansky. Dr H Poojani, senior scientist at the National Centre for Diseases Control, New Delhi observed though there's no evidence of the rabies virus taking to mutation, a thorough study need to be conducted to assess the problem. As many as 25,000 people die in the country every year due to rabies and about 1.5 crore people are bitten by various animals, mostly dogs. Ironically, India has just one centre - Pasteur Institute of India in Coonoor, to exclusively deal with rabies research and laboratory tests. Even the famous National Institute of Virology in Pune does not deal with rabies studies.