19 0 8 Disease Transmission in Water
source of pathogenic bacteria, viruses, protozoa, and
helminthes.
There are four ways by which water, or the lack of
it, may be associated with disease:
Waterborne diseases are caused by the ingestion
of water contaminated by human or animal feces or
urine containing pathogenic bacteria or viruses. The
diseases which can be transmitted include cholera,
typhoid, amoebic and bacillary dysentery, and other
diarrheal diseases. This list can be stretched to include
diseases which occur by the ingestion of a toxin pro-
duced by an organism growing in drinking water such
as toxins produced by cyanobacteria (Anonymous
2006a).
Water-washed diseases are caused by poor personal
hygiene and skin or eye contact with contaminated
water. They include scabies, trachoma, and flea, lice,
and tick-borne diseases.
Water-based diseases are caused by parasites found
in intermediate organisms living in water. They include
dracunculiasis, schistosomiasis, and diseases caused
by other helminths.
Water-related diseases are caused by insect vectors
which breed in water. They include dengue, filariasis,
malaria, onchocerciasis, trypanosomiasis, and yellow
fever.
Diseases may thus be transferred through water in
ways outside drinking (see Fig. 8.2).
In this chapter, we shall look at diseases transmitted
through drinking water, through recreational waters
such as swimming pools and through the eating of
aquatic invertebrates, shellfish, which ingest aquatic
microorganisms.8.1.1 Communicable Diseases Transmitted
Through Drinking WaterCommunicable diseases are those which are brought
about by microorganisms. Drinking-water-borne out-
breaks of any kind are particularly to be avoided
because of their capacity to result in the simultaneous
infection of a large number of persons and potentially
a high proportion of the community. Thus, in theFig. 8.1 Map showing
cholera-free zone in Malawi,
March 1974 (Note: The
cholera-free zone had piped
water, whereas other areas
obtained their water from
the river or well) (From Pineo
and Subrahmanyam 1975.
With permission)