Communicable Diseases

In low-income countries, waterborne diseases remain a major public health problem. Drinking water can be the direct cause of enteric infections, bacil-lary dysentery, and cholera. Standing water can also serve as the indirect cause through transmission of mosquito-borne diseases such as malaria and

Figure 12.2. Driving equipment is one of the serious hazards for children on farms. This girl is driving a tractor without rollover protection. One concern is how much training she has received about operating the tractor and whether she would be able to respond to an emergency. Judgment can play a significant role in appropriate responses in emergency situations; many researchers have questioned which tasks are the age-appropriate for children working on farms. (Photograph by William Bennett, Jr.)

Figure 12.2. Driving equipment is one of the serious hazards for children on farms. This girl is driving a tractor without rollover protection. One concern is how much training she has received about operating the tractor and whether she would be able to respond to an emergency. Judgment can play a significant role in appropriate responses in emergency situations; many researchers have questioned which tasks are the age-appropriate for children working on farms. (Photograph by William Bennett, Jr.)

filariasis. Water can also be the indirect cause of transmission of schistosomiasis, brucellosis, tularemia, hemorrhagic jaundice, and several other proto-zoal, bacterial, and viral infections (31,32).

Schistosomiasis affects individuals in rural areas who work either in irrigation ditches or freshwater fishing ponds. it is a blood fluke infection with adult male and female worms living within mesenteric or vesical veins of the host. Symptoms can be diarrhea, abdominal pain, hepatosplenomegaly, dysuria, urinary frequency, and hematuria. This parasitic disease is caused by infection with blood flukes belonging to the genus Schistosoma. The larval stages of the parasite develop in aquatic snails, emerge and penetrate the skin of anyone in contact with the water. untreated, schistosomiasis causes considerable pathology and can be fatal in chronic advanced cases (31-33).

As children in agricultural areas have daily contact with water in summer either through helping parents in agricultural work or playing (e.g., swimming) in the water, the risk of infection with schistosomiasis is extremely high. In many areas, a high proportion of children between the ages 10 and 14 are infected. An estimated 66 million children throughout 54 countries are affected by urinary schistosomiasis. Unfortunately, some environment modifications by human beings spread schistosomiasis rapidly. An extreme example is that in some villages around Lake Volta in Ghana the prevalence of the schistosomiasis among schoolchildren increased by more than 400% after the completion of the dam (31-33).

Between 1961 and 1964, the Akosombo Dam was constructed on the Volta River in Ghana, creating Lake Volta, one of the largest artificial lakes in the world. The Akosombo Dam and a nearby dam built in 1981 have dramatically changed the existing physical, biological, and socioeconomic environment of the people living above and below them. The construction of the dams and Lake Volta has created conditions suitable for explosive outbreaks of waterborne diseases, especially urinary schistosomiasis (31).

An epidemiological survey conducted before Lake Volta was constructed found that the prevalence of urinary schistosomiasis in schoolchildren in the riparian villages was 5.0%. A 1982 postconstruction survey at eight schools near Lake Volta revealed urinary schistosomiasis prevalence rates of 74.5% to 88.0% in schoolchildren, a substantial increase in schistosomiasis prevalence since the two dams were built. In addition to the infection of local children, several schistosomiasis cases have been identified among tourists who swam in Lake Volta (31).

Many regions in the world use raw wastewater for agricultural purposes. Raw wastewater has been associated with increased prevalence of helminthic infections among children in Morocco. In central Mexico there is a higher risk of diarrheal disease and a fivefold increase in risk of Ascaris lumbricoides infection among children as compared to areas where raw wastewater was not used. In Mexico, no association was found between raw wastewater use and Giardia intestinalis, even though children were found to have the highest prevalence of infection. The benefits of wastewater reuse in agriculture are limited by the hazards associated with the risk of transmission of pathogenic organisms from irrigated soil to crops, grazing animals, and humans (32-35).

Development of infrastructure for increased agricultural production in dry areas may lead to changes in the ecosystem that increase mosquito populations. Large-scale irrigation has often resulted in increased human malaria incidence, which leads to a need to aggressively address mosquito control. In studies of malaria prevalence in Laos during the dry season, 28% of villagers were infected with malaria. During the rainy season, 16% of villagers were infected with consistently high prevalence (40% among boys and 20% among girls) during the dry season among children under the age of 10 years (36,37).

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