Animal Waste, Water Quality and Human Health

128Animal Waste, Water Quality and Human Healthrecombinant Crypto. parvum surface antigen, but other trials evaluating vaccinationor colostral immunity did not consistently reduce shedding oocysts orreduce the severity of Crypto. parvum infection (Harp et al. 1989, Thompsonet al. 2008).Properly formulated vaccines have the potential to be valuable tools incontrolling leptospirosis in domestic animal reservoirs. The degree of protectionprovided by Leptospira vaccines is serovar-specific and has led to the use ofmultivalent vaccines with antigens from several serovars. However, some of themultivalent vaccines on the market have not been shown to provide long-lastingprotection against clinical disease or urinary shedding in cattle (Bolin & Alt2001). Other vaccines with Leptospira interrogans serovar harjo alone or incombination with serovar pomona have been shown to decrease urinaryshedding in cattle and are reported to decrease the incidence of leptospirosis inhumans in contact with the cattle (Mackintosh et al. 1980, Bolin & Alt 2001).Passive immunity is conferred to an animal by the uptake of specific antibodiesderived from another animal. As mentioned above, drinking the colostrum ofvaccinated dams is known to protect calves from diarrhoea-causing E. colistrains. Similarly, oral feeding of chicks with egg yolk derived from hensvaccinated against specific Salmonella serovars can provide passive immunityand reduce the likelihood of colonization by this pathogen (Cox & Pavic 2009,Rahimi et al. 2007). Antibody producing genes have also been cloned in toplants and “plantibodies” could potentially enjoy both prophylactic andtherapeutic use someday in the control of animal infections (Judge et al. 2004).Case Study 2: Vaccinating Water Buffaloes to Control Schistosoma JaponicaHuman schistosomiasis, or bilharzia, is a chronic parasitic disease that affects around200 million people in 76 countries and is second only to malaria in public healthimportance. There are three major types of schistosomiasis, of which only one,Schistosoma japonicum/S. Mekongi/S. malyayensis complex, is an importantzoonosis. This causes intestinal schistosomiasis and is found in Southeast Asia;around 40 reservoir hosts have been identified. Schistosomiasis is a water-basedinfection, contracted when free-swimming infective larvae (cercariae), released fromthe snail intermediate host, penetrate the skin. Infections can result in serious illnesscharacterized by hepatosplenomegaly and cerebral symptoms, and the disease isconsidered a major obstacle to economic development.Not all zoonoses are best tackled at farm level and before targeting pathogen loadreduction in the livestock host, it is necessary to fully understand the role of livestockin the transmission cycle. The presence of pathogens in animals and in humans tells