Overview of Waterborne Pathogens - Waterborne Pathogens: Detection Methods and Applications - page 32

Toxoplasma has been found worldwide, with prevalence, based on sero-
logical studies, among adults in the United States and the UK estimated as
being around 30%, and in continental Europe, about 50-80%. Although
drinking water is recognized as a transmission route for this pathogen, there
are limited studies on the prevalence in water supplies, or the impact of
water treatment processes, possibly due to challenges in pathogen detection.
For more information, we recommend two recent reviews. 51,53

2.4. HELMINTHS
Helminth comes from the Greek word for worm, and while worms
in general infect large numbers of people and animals worldwide, the only
two worms that have drinking water as a major mode of transmission are
Dracunculus medinensis and Fasciola ( Table 2.4 ).

2.4.1. Dracunculus medinensis
This worm, a member of the phylum Nematoda, is commonly known as
a guinea worm. Major efforts to eradicate this disease, which is known to
have a huge economic and health impact, have reduced the incidence from
3.3 million cases in 1986 to only 3190 cases in 2009. The disease is geo-
graphically restricted to sub-Saharan Africa and mainly occurs in rural areas
that lack a piped water supply. It is easily prevented by filtration to remove
the Cyclops , which are the waterborne hosts of the larvae. When Cyclops are
swallowed, the larvae are released in the stomach penetrating the intestinal
wall and inhabiting the cutaneous and subcutaneous tissue. Here the larvae
grow into worms, where the males reach 25 mm in length and the females
can reach 700 mm. When ready, the female emerges from a blister or ulcer
to release a large number of larvae into the water. Mortality is rare but com-
plications can lead to disability.

Table 2.4 Overview of waterborne helminths

Relative
infectivity

Persistence
in water

Resistance to
disinfection

Route of
transmission Pathogen Disease

Dracunculus
medinensis

Dracun-
cliasis

High Moderate Moderate Ingestion

Fasciola spp. Fasciolasis Unknown Moderate High Ingestion

Schistosoma
spp.

Schistoso-
miasis

High Short Moderate Skin contact

Source: Adapted from the WHO list.