Tubercle bacilli have apparently not been 

 looked for on irrigated crops in the United States. 

 However, Sepp (154) states that several investiga- 

 tions on tuberculosis infection of cattle pasturing 

 on sewage-irrigated land have been carried out in 

 Germany. The investigators are in general agree- 

 ment that if sewage application is stopped 1 4 days 

 before pasturing, there is no danger that the cattle 

 will contract bovine tuberculosis through grazing. 

 In contrast, Dedie (39) has reported that these 

 organisms can remain infective for 3 months in 

 waste waters, and up to 6 months in soil. The 

 recent findings of atypical mycobacteria in intes- 

 tinal lesions of cattle with concurrent tuberculin 

 sensitivity in the United States may possibly be 

 due to ingestion of these organisms either from 

 soil or irrigated pastures. 



Both animals and human beings are subject to 

 helminth infections — ascariasis, fascioliasis, cysti- 

 cercosis and tapeworm infection, and schistosomia- 

 sis — all of which may be transmitted through sur- 

 face irrigation water and plants infected with the 

 ova or intermediate forms of the organisms. The 

 ova and parasitic worms are quite resistant to sew- 

 age treatment processes (IS?) as well as to chlori- 

 nation (22) and have been studied quite exten- 

 sively in the application of sewage and irrigation 

 water to various crops (125, 153, 187). 



The common liver fluke, Fasciola hepatica, the 

 ova of which are spread from the feces of many 

 animals, affects cattle and sheep (2, 169, 171) 

 commonly, in the United States, and man to a 

 lesser extent. The intermediate hosts, certain spe- 

 cies of snails, live in springs, slow-moving swampy 

 waters, and on the banks of ponds, streams, and 

 irrigation ditches. After development in the snail, 

 the cercarial forms emerge and encyst on grasses, 

 plants, bark, or soil. Cattle and sheep become in- 

 fected by ingestion of the grasses and plants, or the 

 water, in damp or irrigated pastures where vegeta- 

 tion is infested with metacercariae. Man contracts 

 the disease by ingesting plants such as watercress 

 or lettuce containing the encysted metacercariae. 



Ascaris ova are also spread from the feces of 

 infected animals and man and are found in irriga- 

 tion water (187). Cattle and hogs are commonly 

 infected, where the adult worms mature in the 

 intestinal tract, sometimes blocking the bile ducts. 

 Ascaris ova have been reported to survive for 2 

 years in irrigated soil and have been found on irri- 

 gated vegetables even when chlorinated effluent 

 was used for irrigation (61, 145). 



Schistosomiasis, although not yet prevalent in 

 the United States except in immigrants from en- 

 demic areas, should be considered for the future as 

 these individuals move about the country into irri- 



gated areas. The life cycle of these schistosomes is 

 similar to that of the liver fluke in that eggs from 

 the feces or urine of infected individuals are 

 spread from domestic wastes and may reach sur- 

 face irrigation waters where the miracidial forms 

 enter certain snails and multiply, releasing fork- 

 tailed cercariae. Although these cercariae may pro- 

 duce disease in man if ingested, the more common 

 method of infection is through the skin of indi- 

 viduals working in the infested streams and irriga- 

 tion ditches. Such infections are most common in 

 Egypt (70) and other irrigated areas where work- 

 ers wade in the water without boots. It is unlikely 

 that the cercariae would survive long on plants 

 after harvest. 



Little is known of the possibility that enteric 

 viruses such as polioviruses, Coxsackie, ECHO, 

 and infectious hepatitis viruses may be spread 

 through irrigation practices. Murphy and his co- 

 workers (118) tested the survival of polioviruses 

 in the root environment of tomato and pea plants 

 in modified hydroponic culture. In a second paper, 

 Murphy and Syverton (119) studied the recovery 

 and distribution of a variety of viruses in growing 

 plants. The authors conclude that it is unlikely 

 that plants or plant fruits serve as a reservoir and/ 

 or carrier of poliovirus. However, their findings of 

 significant absorption of a mammalian virus in the 

 roots of the plants suggest that more research is 

 needed in this area. 



Many other microorganisms than those specifi- 

 cally mentioned in this section may be transmitted 

 to plants, animals, and human beings through irri- 

 gation practices. One of the more serious of these 

 is vibriosis. In some cases, definitive information 

 on other microorganisms is lacking. In others, 

 such as the cholera organisms, while their signifi- 

 cance in other parts of the world is well estab- 

 lished, they are no longer important in the United 

 States. 



Direct search for the presence of pathogenic 

 microorganisms in streams, reservoirs, irrigation 

 water, or on irrigated plants is too slow and cum- 

 bersome for routine control or assessment of 

 quality. Instead, accepted index organisms such as 

 the coliform group and fecal coli (74), which are 

 usually far more numerous from these sources, 

 and other biological or chemical tests, are used to 

 assess the quality of the water.^ Two extensive in- 



^ For a more complete discussion, see Geldreich, E. E. 

 1966. Sanitary significance of fecal coliforms in the 

 environment. U.S. Department of the Interior. FWPCA. 

 Pub. WP-20-3. 



162 



