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H.1 Water buffaloes in rice fields, Tamil Nadu, India
H.2 Household suffering from visceral leishmaniasis. North India
H.3 Use of rice fields as pasture land between cropping cycles, USA
H.4 Hoof prints in pasture lands providing breeding sites for floodwater mosquitoes, USA
H.5 Egrets in an irrigated rice field
Credit individual slides:
Robert Bos, Geneva
H.1
Food and Agriculture Organization of the United Nations
H.2
Professor Jim K. Olson. Texas A&M University
H.3, H.4
Danish Bilharziasis Laboratory
H.5
Slide H.1 Water buffaloes in rice
fields, Tamil Nadu, India
In most traditional agrarian societies, farm animals have an important role in the production process. They are a source of meat, milk products and energy. They also are an important factor in the local ecology, even a determining one in relation to endemic diseases.
First, they can serve as a reservoir host for certain disease causing organisms. The water buffaloes shown in these Indian rice fields could, were they working in the same environment in the Philippines, harbour Schistosoma japonicum, which causes the Asian form of schistosomiasis in humans. Its distribution is limited to the Philippines, parts of mainland China and a focus on the Indonesian island Sulawesi.
Pigs are amplifying hosts for the Japanese encephalitis virus and an essential ecological factor at the root of JE outbreaks. This explains the virtual absence of the disease from muslim countries such as Bangladesh, or from a country like Malaysia, where pig rearing by the Chinese population is spatially separated from the rice growing activities of the Malay.
Secondly, there is the more complicated role of cattle in the overall population dynamics of mosquito vectors and the transmission dynamics of diseases. Where mosquito species prevail with a preference to take blood meals from cattle (zoophilic species), the presence of cattle and its strategic location between breeding sites and human settlements will significantly reduce disease transmission risks. This approach is known as zooprophylaxis. If local mosquito species are less discriminate in the selection of their blood meal hosts, then the presence of cattle may in fact contribute to higher populations densities and higher transmission risks.
Where cattle plays an important role in diverting blood meal-seeking mosquitoes from human hosts, mechanization and the reduction of farm animals will have a dramatic impact on the human health status. A major malaria epidemic occurred in the Demerara River estuary in Guyana where after widespread mechanization of the agricultural sector, the local zoophilic vector, Anopheles aquasalis, found itself with only humans to trite.
PEEM reviewed the issue of livestock management and disease vector control at its tenth meeting in 1990; the technical discussion section of the meeting report can be obtained from the PEEM Secretariat, WHO, Geneva.
Reference:
PEEM Secretariat, 1991. Report of the tenth meeting of the joint WHO/FAO/UNEP Panel of Experts on Environmental Management for Vector Control (PEEM). Technical discussion: Livestock management and disease vector control. Document WHO/CWS/91.11, World Health Organization, Geneva
Slide H.2 Household suffering from
visceral leishmaniasis. North India
The proximity between humans and livestock is emphasized in this slide showing a kala-azar (visceral leishmaniasis) affected household in northern India. The local sandfly vector, Phlebotomus argentipes, is largely zoophilic, feeding on cattle. Locating cattle sheds away from human dwellings will lead to a significant decrease in health risks.
Slide H.3 Use of rice fields as
pasture land between cropping cycles,
USA
Slide H.4 Hoof prints in pasture
lands providing breeding sites for floodwater mosquitoes, USA
Psorophora columbiae, the flood water mosquito in the rice agro-ecosystems of the southern United States of America is an important vector of local encephalitis viruses. The Riceland Mosquito Management Program sponsored by the US Department of Agriculture has carried out in-depth research on agricultural practices and their ecological consequences for P. columbiae production.
Giving out rice fields as pasture land after harvesting the crop results in large numbers of hoof prints in the moist soil that provide suitable oviposition sites for this mosquito species.
The main malaria vector in sub-Saharan Africa, Anopheles gambiae, is often cited as being so versatile that it can even breed and complete its aquatic life cycle in water collections in hoof prints.
References:
Meek, C.L. and Olson, J.K., 1977. The importance of cattle hoofprints and tire tracks as oviposition sites for Psorophora columbiae in Texas ricelands. Environ. Entomol. 6:161-166
Welch, J.B., Olson, J.K. and Yates, M.M., 1986. Occurrence of Psorophora columbiae eggs in different field types comprising a Texas riceland agroecosystem. J. Am. Mosq. Control Assoc. 2: 52-56
Slide H.5 Egrets in an irrigated
rice field
Egrets and other birds can be reservoirs of viruses and transport them over large distances. Some ecologists have speculated that with global climate change, migratory birds may change their routes and may introduce arboviral infection in areas where they now do not occur.
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