Waterborne transmission of Cryptosporidium and Giardia: detection, surveillance and implications for public health

Protozoan enteroparasites of the genera Cryptosporidium and Giardia have emerged over the past decades as major waterborne pathogens. Both parasites are among the major causative agents of gastroenteritis and nutritional disorders in humans, with tens of millions of new cases occurring every year. Although cryptosporidiosis and giardiasis are normally self-limiting in immune-competent individuals, both are potential severe, life-threatening diseases in immunecompromised patients. Both pathogens are transmitted via the faecal-oral route, with the consumption of contaminated drinking water and use of recreational waterways being significant avenues for acquisition of infection. Because infected humans and animals can seed enormous amounts of the transmission stages of these parasites (Cryptosporidium oocysts and Giardia cysts), both micro-organisms are ubiquitous in the aquatic environment. In addition, (oo)cysts may remain viable for several months under a range of environmental conditions, their small size allow them to pass through conventional water plant filters, both are resistant to disinfectants at the concentrations and exposure times commonly used, and have low infectious doses in humans. Taken together, these data indicate that Cryptosporidium and Giardia represent a significant threat to public health. Indeed an increasing number of waterborne outbreaks of cryptosporidiosis and giardiasis have been reported worldwide, with most cases occurring in the USA and UK. This situation has become a major concern for water utilities and sanitary authorities that are responsible for providing safe drinking water supplies for human consumption. In this chapter relevant aspects of the biology and epidemiology of Cryptosporidium and Giardia from the aquatic environmental perspective are discussed, including pathology, treatment, transmission dynamics, detection, prevention and control measures.