Introduction

• Rice is a staple food in many Asian countries, and over 90% of the world’s rice growing area is in Asia.
• In India, 43.28 million hectares of cultivable land is under rice cultivation.
• Unfortunately, agricultural practices involved in rice cultivation have led to the generation of a phenomenal increase in number of mosquitoes.
• Lowland or irrigated rice cultivation enhances population development of many mosquito species, many of which transmit human diseases.
• Favorable breeding habitats of pests and vector mosquitoes are inundated ricefields and other associated aquatic habitats in riceland area.

Mosquito-borne diseases associated with riceland agro-ecosystem:

• Mosquito larval control in irrigated paddy fields is a problem of a completely different magnitude from that in other habitats, because of the enormous breeding surface involved.
• The two most important vector-borne diseases associated with rice cultivation are Malaria and Japanese encephalitis (JE). Malaria problem with regard to rice cultivation has been extensively reviewed in past.
• Some of the early epidemiological observations resulted in the regulation or prohibition of rice cultivation within a certain distance from human settlement.
• In China, the malaria vectors Anopheles sinensis and An. anthropophagus and in Indonesia, An. aconitus breed principally in paddy fields. In Africa, increase in rice cultivation provide perennial breeding sites for An. gambiae (especially, in West Africa) and An. arabiensis. A shift in the mosquito fauna in favor of vector species was associated with rice irrigation in Kenya. In Gambia and Kenya, peaks of vector population were regularly associated with the weeks following transplantation.
• In India, malaria had not been a major problem in rice cultivation areas except in Pattukotai taluka, Tanjore district, Tamil Nadu. It was found that the defective and untidy irrigation that led to the establishment of vector species. Outbreaks of malaria are generally associated with preferential vector breeding habitats available in riceland area. It has been clearly shown that resurgence was not linked to agricultural practices. In the past few decades, malaria, on account of rice cultivation, has been diminished.
• In India, rice fields provide breeding habitats for Culex species and twenty Anopheline species of which some are of major importance.
• An.culicifacies in Nilgiris districts of Tamil Nadu, An. philippinensis and An. annularis in Bengal are known to breed extensively in Paddy fields.

JE, a fatal zoonotic viral disease, unlike malaria, is very closely associated with rice cultivation. Extensive outbreaks of this disease continue to occur in Southern and South-East Asian countries, most notably in India, Nepal, SriLanka, Burma, Thailand and Vietnam.

• In India, frequent JE outbreaks have been recorded in Andhra Pradesh, Assam, Bihar, Goa, Karnataka, Manipur, Tripura, Nagaland, Tamil Nadu, Uttar Pradesh, West Bengal and Pondicherry. Many Mosquitoes, which preferentially breed in rice fields, have been incriminated as vectors. So far, JE virus has been isolated from 16 mosquito species.
• n India, the influence of rice irrigation and vector abundance in relation to the incidence of JE has been analyzed in the Gorakhpur district of Uttar Pradesh, and Mandya district of Karnataka. Predominantly, the occurrence of JE was closely associated with high vector densities, breeding in the fields or the canal system. The highest numbers of JE cases were observed shortly after the mosquito densities peaked. In addition, Mandya district in Karnataka is found to be endemic to JE due to extensive rice cultivation.
• Approximately 1.9 billion people currently live in rural JE-prone areas of the world with majority of them in China (766 million) and India (646 million).
• 700 million children under the age of 15 years reside in JE-endemic areas.
• According to recent estimates, 1,025,000–1,080,000 km of land is irrigated in JE-prone areas. Currently 180–220 million people are living in proximity to irrigation or rice-irrigation schemes in the JE-endemic regions, and thus, are at risk of contracting the disease.