Animal Waste, Water Quality and Human Health

Zoonotic waterborne pathogens in livestock 129us little about disease epidemiology, but in the case of Schistosoma japonicum, there isstrong evidence that cattle and water buffaloes play an important role in the transmissioncycle. Historically, schistosomiasis was eradicated from Japan without medicalinterventions, with the switch from bovines to horses as draught animals consideredto have played a role in this. Field studies in China and elsewhere indicate animportant role for cattle and water buffaloes which shed hundreds of thousands ofeggs per day in their faeces. Water buffaloes spend most of their time in the waterand thus are constantly exposed to infected snails. The molecular biology of S.japonicum distinguishes between two main clusters: those from humans and bovinesversus those from domestic animals, again supporting the importance of bovines inhuman transmission. Mathematical models, parameterised by data collected from thefield suggest that water buffalo account for approximately 80% of transmission inChina and in their absence infection cannot be maintained. Finally, interventionstudies showed that if bovines are not treated for schistosomiasis along with humans,infection rates remain high.This assembly of independent evidence from different disciplines provides strongevidence that Schistosoma japonicum is a good candidate for livestock-basedinterventions to reduce risk to humans and this is now a component of most controlprogrammes. As for other complex diseases, current control of schistosomiasis takesan integrated approach with interventions targeting human behaviour; diseaseecology; management of bovines; and treatment of humans, bovines and some otheranimals. Praziquantal is an effective treatment for schistosomiasis and relativelyinexpensive. Although used in ongoing control initiatives, the need for repeatedtreatments and the possibility of development of resistance are impediments towidespread use. More recently there has been some success in the development ofsubunit vaccines: field trials in China show these are as effective as chemotherapy inreducing the infection rate in water buffaloes and could have an important role indisease control.A lesson from this case study is that while not all zoonoses are best or even usefullytackled at the farm level, when domestic livestock plays an essential role in transmission,then including livestock in integrated disease control programmes also is essential.Case Study 3: Vaccinating Cattle for E. Coli O157:H7Escherichia coli serotype O157:H7 was first recognized as a human pathogen in 1982,following a ground beef-associated outbreak of haemorrhagic colitis in Michigan (Rileyet al. 1983) and was subsequently associated with the haemolytic uremic syndrome(HUS) in children (Karmali et al. 1985). E. coli O157 produces Shigatoxins (a.k.a.Verotoxins) that enter the blood stream following damage to the large intestine andkill endothelial cells lining the small vessels in the intestine, kidney and brain(Karmali et al. 2009). HUS is characterized by kidney failure and haemolytic anemiaand has a mortality of up to 15% in young children (Gould et al. 2009).