Overview of Waterborne Pathogens - Waterborne Pathogens: Detection Methods and Applications - page 25

with water treatment failure, in developed countries, including the United
States, 22,23 the UK, 24 Australia 25 and Sweden. 26 If ingested, this pathogen
can cause acute self-limiting gastroenteritis, cryptosporidiosis in immuno-
competent hosts, and potentially fatal protracted disease in immunocom-
promised ones. Research into this pathogen intensified in the 1980s after
its association as a major opportunistic pathogen in patients with AIDS. 27
There is no recognized safe and effective treatment for human cryptospo-
ridiosis. 28
In the developing world, persistent diarrhea, caused by agents such as
Cryptosporidium , accounts for 30-50% of mortality in children under 5 years
old, and it is estimated that 250-500 million cases of cryptosporidiosis occur
each year. 22 In the developed world, cryptosporidiosis presents a high risk
mainly to the very young, the elderly, and immunocompromised individuals,
and it accounts for most gastrointestinal disease outbreaks where water sup-
plies are chlorinated. The unreported rate of disease from Cryptosporidium
in England alone has been estimated at >60,000 cases per year, 29 with tap
water being the most common risk factor in recorded cases. Cryptosporidium
is particularly problematic to the water industry since it is resistant to both
environmental stress and standard chlorination disinfection procedures and
can survive for up to 16 months in water. 30 Additionally, these organisms are
ubiquitous in the environment and have an extremely low infectious dose.
For some C. parvum isolates, one of the human pathogenic species, fewer
than 10 oocysts can be required to cause infection. 31,32 This number should
be compared against the billions of oocysts that an infected host could shed
during an episode of infection. 28 During a clinical infection, a calf may shed
around 10,000 million oocysts, which would provide enough parasites to
infect the whole human population of Europe.
In addition to the risk of disease, Cryptosporidium has a significant eco-
nomic impact. For example, a Cryptosporidium contamination in the water
supply for Sydney, Australia cost US$45 million in direct emergency mea-
sures 33 despite no recorded increase in the cryptosporidiosis case rate. Med-
ical expenses and the cost of lost productivity for the Milwaukee outbreak,
which was the largest documented outbreak with over 400,000 people
infected, were estimated at US$96 million. 34 There are also substantial eco-
nomic costs involved in upgrading water treatment plants to deal with the
issue of Cryptosporidium .
Not all of the >20 Cryptosporidium species, and more than 44 genotypes,
are pathogenic to humans. Given this fact, it is clear that species identifica-
tion is an essential characteristic to assess the public health risk arising from