Overview of Waterborne Pathogens - Waterborne Pathogens: Detection Methods and Applications - page 8

In general, the focus is on those pathogens for which the route of disease
transmission occurs through ingestion of water. This chapter is divided into
sections according to the main categories of pathogens.
Environmental Persistence
Environmental persistence refers to the length of time a pathogen is able to sur-
vive in the environment and retain infectivity.
Host-dependent pathogens gradually lose viability and the ability to infect
after they are shed from a host. Pathogens with low persistence are unlikely to be
spread by drinking water since they would be nonviable or noninfectious by the
time they were able to reach a new host. Some waterborne pathogens are capable
of growth in water. For example, Legionella , Vibrio cholerae and Naegleria fowleri
will grow in warm water that contains relatively high amounts of biodegradable
organic carbon, which can occur in some surface waters or water distribution sys-
tems. Other pathogens, e.g. norovirus (NoV) or Cryptosporidium , are unable to mul-
tiply in water but are robust enough to survive for a considerable length of time.
The persistence of pathogens in water is influenced by many factors, includ-
ing temperature, exposure to sunlight (UV) or certain chemical conditions (e.g.
salinity or ammonia), all of which could inactivate pathogens and result in set-
tling or interaction with sediment in surface waters.
In this chapter and the WHO list, the persistence in water is defined as short
for survival periods of less than one week and moderate for times between a
week and a month, with high persistence being assigned to those pathogens
capable of survival in the environment for periods of greater than one month.
Microbiology Definitions
Virus: Viruses are the smallest of the microorganisms, typically 20-300 nm, and the
only living organisms not to have a cell membrane; they consist of a small amount
of nucleic acid (DNA or RNA) coated with and protected by a layer of protein.
Bacteria: Bacteria are prokaryotic microorganisms with a typical size of a few
micron; prokaryotes are cells with little intracellular organization that reproduce
asexually via cell division to give two daughter cells.
Protozoa: Protozoa are a diverse group of unicellular eukaryotic organisms,
including sporozoa (intracellular parasites), flagellates (which possess tail-like
structures for movement), amoeba (which move using temporary cell body pro-
jections called pseudopods) and ciliates (which move by beating multiple hair-
like structures called cilia).
Helminth: Helminths are worms, with the name coming from the Greek word
for worm.
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