V Categories of waterborne disease organisms

Reports of case-studies as well as estimates of disease in local and regional populations provide us with patterns of disease that are subject to a variety of local environmental, societal, and biological influences. Environmental conditions are significantly influenced in turn by climate and human activities. All of these influences can be highly variable, resulting in very different patterns of disease burden among populations. Limiting discussion to the public health implications of waterborne zoonotic agents provides greater focus. Further limiting discussion to those agents that are emerging or are of renewed interest because they have resulted in increased disease burden provides even more focus. To select those agents for which a strategy can be developed for treatment or prevention, the impact of each agent must first be examined individually. The present section examines specific zoonotic agents from viruses to fungi, 210 Waterborne Zoonoses bacteria, protozoa, and helminths that pass in the faeces from an infected host to a susceptible host and are facilitated by waterborne transmission. BACTERIA Many bacterial zoonoses are known, but not many are known to be transmitted via water. The waterborne zoonotic bacteria are principally those shed in faeces by warm-blooded animals (birds and mammals), although some are also harboured by reptiles. Detection methods exist for the most important waterborne bacteria and are improving, but there is still good reason to use indicators of faecal contamination to monitor for water safety. This bacterial species is found in the colons and faeces of all warm-blooded animals. It usually occurs as a commensal, causing no disease. Until 1982, most of the known E. coli types that caused disease in humans were human-specific and not associated with other animal species. In that year, E. coli O157:H7 was incriminated in human illnesses and was shown to have a reservoir in cattle. This was the first recognition of a genre now called verocytotoxin-producing E. coli (VTEC), Shiga toxin-producing E. coli (STEC), or enterohaemorrhagic E. coli (EHEC). All of these are capable of causing severe disease in humans, although they are typically shed by healthy cattle and other species. Human-to-human transmission, both by contact and via water, is also known. Salmonella The chapter on Salmonella explores the traits of this genus. Although salmonellae typically do not multiply in the environment, they survive remarkably well under a variety of environmental conditions. The peroral infectious dose tends to be large, unless a vehicle more protective than …