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Ecological changes have contributed to the emergence of kala-azar in some areas. Dams and irrigation projects create ideal conditions for sandflies to breed. Between 1966 and 1976, 29 cases of kala-azar from five districts in south Gujarat adjoining Tapi, Mahi and Narmada rivers were admitted to the Baroda Medical College (bmc ). The state had just introduced new irrigation projects (see box: Kala-azar in Gujarat ).
Epidemiological studies conducted by the bmc in 1977 reported that over 62 per cent of the cases of kala-azar were among agricultural labourers and farmers. Since 1976, however, there have been no references to the disease in health department reports. As malaria is endemic in the area and the epidemiology of kala-azar is quite complex, it is possible that deaths due to kala-azar are ascribed to malaria."Whether deaths are due to kala-azar or malaria, they get a single label of death due to malaria," Kalra said on July 7, 1998, at the National Conference on Health and Environment organised by the Delhi-based Centre for Science and Environment.
The lack of investigations after 1977 has proved to be a major impediment. Kalra says that the origin of cases of kala-azar that came up in Vadodara was not investigated, hence a great opportunity was lost to understand the transmission dynamics of the disease in an area that does not have ideal physical conditions for its spread. It is for this reason that it is difficult to say whether kala-azar could emerge at other irrigation sites.
Deforestation can also lead to the introduction of kala-azar in previously unaffected areas. Sub-Himalayan belts have reported sporadic cases of kala-azar. This defies a precondition for the presence of kala-azar: an altitude of less than 600 metres (m) above sea level. In Jammu and Kashmir, the disease has been detected at an altitude of 2,000 m, and in Himachal Pradesh at altitudes ranging between 300 m and 1,800 m. Nine cases were reported in 1989 and nine more in 1995 in Uttar Pradesh's Garhwal region.
All the above-mentioned areas have lost their forests. Deforestation causes increased contact between humans and sandflies as in the absence of wild animals, sandflies shift their attention to humans. Increased host-parasite contact in turn increases the rate of transmission, often leading to an epidemic.
This has been the case in Assam. The state's hospitals recorded 27 cases of kala-azar between 1974 and 1979. No investigation was conducted thereafter. At present, kala-azar is under control in Assam due to spraying of the pesticide dichloro diethyl trichloroethane ( ddt ). "But as soon as ddt is withdrawn, in all likelihood there will be a flare-up of kala-azar because it has not been eradicated; it is just simmering," Kalra says.