Of mice and men

Till September 1994, plague was s 'upposedly a forgotten disease in India. It caught the country's medics aghast at their own ignorance. But after its outbreak, medical authorities have taken to pointing out that they had never claimed the disease had been eradicated from the country.

The bacterium which causes the disease, Yersinia pestis, is known to be endemic to a few pockets in Marathwada (Gujarat and Maharashtra), the Kolar district (Karnataka), southern Andhra Pradesh, north Arcot district (Tamil Nadu), Tehri-Garhwal (Uttar Pradesh), Himachal Pradesh, Kashmir and Madhya Pradesh. While the bacillus can survive independently for as long as 7 months, it lives longer in zootic carriers. In the known endemic regions, the most common carrier is the wild rat (Tatera indica).

The plague occurs when the rodents bring the bacilli, in sufficiently large numbers, close to human settlements. This may be due to sudden natural changes such as earthquakes or floods, which forces rats out of their natural habitat.

The transfer of the bacilli from rats to humans is a complex chain. The fleeing wild rats come in contact with their domestic cousins, the field or sewer rats (Rattus norvegicus), which transmit the bacilli to the house rats (Rattus rattus), who then transfer the bacilli to humans.

At each stage in its transmission cycle, the bacilli may get transferred directly through rat bites or through the fleas, Xenopsylla cheopis, X ast or X brasiliensis. The fleas live off the rats and infect them when they bite to suck the blood of their hosts. The internal environment of the flea is conducive to the proliferation of the bacilli.

An infected flea can live upto 3 days, and in frantic efforts to get rid of the plague bacilli, tries to release them through repeated excretion, regurgitation or vigorous biting of the host. Importantly, the domestic rats have less resistance to the bacillus than their wild cousins and die when infected with the microbe. Large-scale deaths of domestic rats, or "ratfall", is therefore, feared as a precursor of the plague. When the rats die, the fleas look for other hosts humans.

Three Delhi University entomologists, S S Sehgal, V Baweja and Manoj Kumar Nayak have carried out studies in the Marathwada region, indicating that the flea count had increased remarkably during the early '90s. In their paper published in the Indian Journal of Entomology in January this year, they suggested that the flea count per rat had crossed the danger mark of 5 long before the Latur earthquake last year. This suggests that other factors, including human-made ones, such as expansion of agriculture into the natural habitat of wild may have sparked off the cycle exploded into an epidemic at Beec Surat.

Also, the sarpanch of Killari vil close to the epicentre of the quake and near Beed, had bec-- worried over a noticeable increas the rat population in his area c1L. the past 6 months. This June, he - ac written about it to the state chief ister. When the first case of the was reported from Mamala village of Beed district, its sarpanch also ed several incidents of fleas humans.

Links between Beed and Surat The plague outbreak at Beed has generally treated as a consequer the Latur earthquake. A similar em, nation has been offered by the G government and official experts blame the floods earlier September in the river Tapi, flows through Surat. Another body of opinion has looked more at the possibility of the transfer of the plague to Surat from the Marathwada region through humans.

The initial instances are those of bubonic plague, in which the bacteria infect the lymph nodes of the human body. if untreated, this lymphatic Infection by the bacilli can cause fever and even death. The deaths in The Seed district have been diagnosed as being caused by bubonic plague. Further, the bacilli can break the confines of the lymph nodes, enter the bloodstream and reach the long tissue, causing pneumonic plague. Then, through their excreSons and exhalations, even humans become transmitters of the bacilli. Pneurnonic plague is believed to have caused the havoc in Surat.

There are those who plead for more cautious theorising. One of dwm is 0 Sanerii, professor emeritus in the Department of Social Medicine behru University, New Delhi, who 415"rees with the theory of the spread of the plague from Seed to Swat -By that reasoning, the entire owthquake-affected zone should love witnessed a plague outbreak," In argues. Similarly T Verghese, for- director of the NICD, has called a detailed examination of the .c structure of the bacilli. "Only this will give us definite Information how the bacilli may be evolving in India."