Overview of Waterborne Pathogens - Waterborne Pathogens: Detection Methods and Applications - page 26

the detection of any oocysts in a sample. There are no antibodies currently
available that can distinguish species differences on the oocyst wall sur-
face, 32 and thus genetic comparisons using molecular techniques become
important. Cryptosporidium hominis and C. parvum are the most commonly
detected in human clinical cases, 28 although several others have been shown
to infect humans. 35 Cryptosporidium hominis and C. parvum have dimensions
of 4.5×5.5µm and contain four sporozoites ( Fig. 2.7 , which also shows
the typical life cycle of this pathogen). Cryptosporidium parvum is the major
zoonotic species. It causes acute neonatal diarrhea in livestock and is a major
contributor to environmental contamination with oocysts. 28 The charac-
teristics of different Cryptosporidium species, including oocyst size, host pref-
erence and infection sites, have been reviewed by Smith and Nichols 28 and
we recommend both this review and an earlier one by the same author 37 for
further information on this pathogen.
2.3.2. Cyclospora
Cyclospora cayetanensis infect the intestines of humans, causing diarrhea in
both immunocompetent and immunocompromised hosts. Most cases of
disease occur in young children. No other hosts are known, and the life
cycle is not well characterized. It is known that excreted oocysts, 8 × 10 µm
in size, undergo a process of differentiation, called sporulation, in 7-10 days,
depending upon environmental conditions. The sporulated oocysts are
round, containing two sporozoites. Little information is available on the
prevalence of Cyclospora in water, though it is known to be spread world-
wide. Disease outbreaks associated with drinking water have been reported
in a hospital in the United States, in Nepal, and an estimated 200 people
were infected in Turkey in 2005. 21
2.3.3. Entamoeba
Entamoeba histolytica ( Fig. 2.8 ) is responsible for amoebic dysentery and coli-
tis. The pathogen may also spread to other organs in the body, e.g. the liver
or the brain, with possibly fatal results. Worldwide, an estimated 12% of the
population has been infected, though up to 90% of these will not show clin-
ical symptoms. Some studies have claimed infections in dogs, cats, pigs, rats
and cattle, whereas a 2008 report from the WHO reports humans as the sole
reservoir of this pathogen. This pathogen has a feeding, replicative tropho-
zoite of size 10-60 mm that can develop into a dormant cyst, of diameter
10-20 mm, under unfavorable conditions. Amoebic dysentery infects over
500 million people each year, resulting in approximately 100,000 deaths,