Water Quality Management - River Dynamics and Integrated River Management - page 597

on providing better access to safe water supply. Types of waterborne and water-contact diseases are first
reviewed. Then means of monitoring possible pathogen contamination and human health risk are discussed.
Finally, methods to reduce pathogen loads reaching rivers are described.
9.4.1 Water-Contact Diseases and Indicator Organisms
9.4.1.1 Types of Diseases
Five categories of parasitic organisms infective to man are found in water: bacteria, protozoa, worms,
viruses, and fungi (Fair et al., 1971, p. 283). Some of these complete their life cycle by passage through
an intermediary aquatic host; others are merely transported by water from man to man. Masters (1991,
p. 108) further details the disease producing organisms that grow and multiply through an intermediary
aquatic host as follows:
¾ Bacterial causes of cholera, bacillary dysentery, typhoid, and paratyphoid fever
¾ Viral causes of infectious hepatitis and poliomyelitis
¾ Protoza which cause amebic dysentery and giardiasis
¾ Helminths (parasitic worms) which cause schistosomiasis and dracontiasis (Guinea worm)
The intestinal discharges of an infected individual, a carrier, may contain billions of these pathogens,
which, if allowed to enter the water supply, can cause epidemics of immense proportions. Carriers may
not even necessarily exhibit symptoms of their disease, which makes it even more important to carefully
protect all water supplies from any human waste contamination (Masters, 1991, p. 108).
Giardia cysts and Cryptosporidium oocysts passed through feces of carriers pose an unusual threat to
surface waters and even to municipal supply systems. Both of these are diarrheal diseases that can result
in death. They can be carried by wild animals as well as humans, may survive for months in the environment,
and are not easily destroyed by disinfection. In particular, dozens of species harbor Cryptosporidium
oocysts, including mammals (e.g., cattle, horses, rodents, deer, dogs, cats, kangaroos), birds, reptiles, and
fish. As such, there are many routes for this parasite to enter the environment, including natural runoff
(non-point sources), runoff from agriculture, effluents from industries such as meat processors, wastewater
effluents, and combined sewer overflows (Clancy et al., 2004).
Schistosomiasis is the most common water-contact disease in the world, affecting approximately 160
million people, and causing more than ten thousand deaths every year, mainly in sub-Saharan Africa
(WHO, 2004). Schistosomiasis is spread by free swimming larva in water, called cercaria , which attach
themselves to human skin, penetrate it, and enter the bloodstream. Cercaria mature in the liver into worms
that lay masses of eggs on the walls of the intestine. When these eggs are excreted into water, they hatch
and have only a few hours to find a snail host in which they develop into new cercaria . Cercaria exerted
by snails, then, have a few days to find another human host, continuing the cycle. Continuation of the
cycle requires continued contamination by schistosomiasis carriers in water that are still enough to allow
snails to thrive. The effects of schistosomiasis can be controlled by monthly injections.
Shellfish can become toxic because they concentrate pathogenic organisms in their tissues, making the
toxicity levels of the shellfish much greater than the levels in the surrounding water (Davis and Masten, 2004,
p. 268). Diseases that can be transmitted through shellfish harvested from or stored in sewage—polluted
water include typhoid, paratyphoid, bacillary dysentery, and infectious hepititus.
9.4.1.2 Indicator Organisms
The specific identification of pathogenic bacteria as pollution indicators would require extremely large
samples and a wide variety of media and methods to exclude all the various pathogens that could be
present (Clark et al., 1977, p. 259). To sample and measure for all these pathogens would be expensive if
not impossible (i.e. measurement protocols have not been developed for some pathogens). Further, the