Environmental Aspects and Features of Critical Pathogen Groups. Global Water Pathogen Project, 2018.
This chapter provides the reader with an overview of various environmental aspects and characteristics of critical pathogen groups (disease-causing microorganisms) associated with fecal wastes, sewage and water-related diseases including viruses, bacteria, protists and helminths.
The sources of these pathogens are primarily human feces but the reservoirs can be humans, animals or the environment itself. The handling and methods of human or animal waste disposal play a significant role in transmission of infectious diseases globally. The diseases caused by water-related pathogens range from mild gastroenteritis to severe diarrhea, dysentery, typhoid fever and hepatitis.
Some water-related infections have chronic sequelae. The risks of infection are dependent on specific characteristics of the pathogen including potency/infectiousness, concentrations in excreta, their ability to persist in the environment and resistance to sewage treatment.
Pathogen concentrations particularly viruses and bacteria in excreta and sewage is high, typically at concentrations of millions to billions of organisms. For pathogens transmitted via fecal-oral route, persistence in the environment is related to risk of host exposure and potentially disease.
Viruses, protozoan cysts and oocysts and helminths persist longer in the environment than vegetative bacteria. In contrast to other pathogen groups, all helminths have a distinct latency period in the environment and some require intermediate hosts to complete their life cycles.
In general, viruses, protists and helminths pose higher risks of infection (highly potent) than bacteria and resulting disease from ingestion of or contact with very low doses of the pathogen. In addition, the risks of infection by water-related pathogens are influenced by other environmental factors including their potential sources or reservoirs in the environment such as animal (zoonosis) fecal contamination, and their ability to be transported (e.g. vectors) in the environment to reach susceptible hosts.
Majority of the bacteria, protists and helminths are zoonotic pathogens. Vectors such as freshwater snails and rodents play an important role in transmission of infectious diseases caused by some protists (e.g. Leptospirosis) and most of the helminths.
Overall, water-related pathogens are one of the major contributors to the global burden of disease. Understanding how pathogens survive and move in the environment, their sources and transmission routes are crucial to developing effective interventions to reduce water-related diseases.