Tyagi B K
Centre for Research in Medical Entomology, 4-Sarojini Street, Chinna Chokkikulam, 625 002, Madurai, India.
Acta Trop. 2004 Jan;89(2):227-39. doi: 10.1016/j.actatropica.2003.09.016.
Recently, there has been a resurgence of malaria in several parts of India, and the Thar Desert in north-western India, is currently suffering from the impact of repeated annual epidemics. Nearly all malaria epidemics in the Thar Desert have come about with the progression of canal-irrigation work, particularly the massive Indira Gandhi Nahar Pariyojana (IGNP). Therefore, the Thar Desert provides an excellent model for understanding the underlying factors responsible for the exacerbation of malaria, pathways of evolution of the epidemics, succession in anopheline fauna, changes in the vector breeding and feeding preferences and, most importantly, the possible repercussions of mismanagement of irrigation systems. Before the initiation of canalised irrigation only Anopheles stephensi, breeding exclusively in household and community-based underground water reservoirs, and transmitting malaria at a low level, was prevalent in the interior of the Thar Desert. Since the 1980s, extensive irrigation with water from three different canal systems has altered the desert physiography, vector preponderance, distribution and vectorial capacity, whilst triggering the emergence of Plasmodium falciparum-dominated malaria in the virgin levees of the Thar Desert. The major objective of bringing the Himalayan waters to the xeric environment of the Thar was to transform it into verdure through growing irrigation-intensive crops like paddy, groundnut, cotton, mustard, wheat and sugarcane, besides providing drinking water to the desert dwellers. The change in crop pattern, retention of high surface moisture, and excessive canalisation rife with mismanagement of irrigation water have attracted several anophelines, including Anopheles culicifacies, which were earlier unknown in the desert. Thus, A. culicifacies has penetrated into the interior of the Thar Desert, along with irrigation and is now established in vast areas covered by the IGNP project. The distribution of P. falciparum-dominated malaria in the Thar Desert is more or less synchronous with the spread of IGNP-related irrigated agriculture and of A. culicifacies.
最近，印度多个地区疟疾疫情有所反弹，印度西北部的塔尔沙漠目前正遭受连年反复疫情的影响。塔尔沙漠几乎所有的疟疾疫情都随着运河灌溉工程的推进而出现，尤其是大规模的英迪拉·甘地运河项目（IGNP）。因此，塔尔沙漠为理解导致疟疾加剧的潜在因素、疫情演变途径、按蚊种类演替、病媒繁殖和觅食偏好变化，以及最重要的灌溉系统管理不善可能产生的影响，提供了一个绝佳的范例。在运河灌溉开始之前，只有斯氏按蚊在塔尔沙漠内部普遍存在，它仅在家庭和社区的地下蓄水池中繁殖，并以较低水平传播疟疾。自20世纪80年代以来，来自三个不同运河系统的大量灌溉改变了沙漠地貌、病媒优势、分布和传播能力，同时在塔尔沙漠的新垦堤岸引发了以恶性疟原虫为主的疟疾疫情。将喜马拉雅山的水引入干旱的塔尔沙漠的主要目标，是通过种植水稻、花生、棉花、芥菜、小麦和甘蔗等灌溉密集型作物，将其变成绿洲，同时为沙漠居民提供饮用水。作物模式的改变、高地表湿度的保持以及灌溉水管理不善导致的过度渠化，吸引了包括库氏按蚊在内的几种按蚊，而库氏按蚊此前在沙漠中并不为人所知。因此，库氏按蚊随着灌溉进入了塔尔沙漠内部，如今在IGNP项目覆盖的广大地区已稳定存在。塔尔沙漠中以恶性疟原虫为主的疟疾分布，或多或少与IGNP相关灌溉农业和库氏按蚊的传播同步。
