Environmental Engineering Reference
In-Depth Information
TAble 6.7
Valid Named Species of
Cryptosporidium
Species
Host
Cryptosporidium baileyi
Chicken
Cryptosporidium felis
Domestic cat
Cryptosporidium meleagridis
Turkey
Cryptosporidium muris
House mouse
Cryptosporidium nasorum
Fish
Cryptosporidium parvum
House mouse
Cryptosporidium serpentis
Corn snake
Rat snake
Madagascar boa
Cryptosporidium wrairi
Guinea pig
Source:
Adapted from Fayer, R. et al., in
Cryptosporidium
and Cryptosporidiosis
, Fayer, R. and Xiao, L.,
Eds., CRC Press, Boca Raton, FL, 1997, pp. 1-41.
Cryptosporidium
is one of several single-celled protozoan genera in the phy-
lum Apicomplexa (all referred to as coccidia).
Cryptosporidium
, along with
other genera (
Eimeria
,
Isospora
, and
Cyclospora
) in the phylum Apicomplexa
develop in the gastrointestinal tract of vertebrates through all of their life
cycle—in short, they live in the intestines of animals and humans. This micro-
scopic pathogen causes a disease called
cryptosporidiosis
. The dormant (inac-
tive) form of
Cryptosporidium
is an
oocyst
, which is excreted in the feces (stool)
of infected animals and humans. The tough-walled oocysts survive under a
wide range of environmental conditions. Several species of
Cryptosporidium
were incorrectly named after the host in which they were found; subsequent
studies have invalidated many species. At the present time, eight valid spe-
cies of
Cryptosporidium
(see
Table 6.7
) have been named.
Upton (1997) reported that
Cryptosporidium muris
infects the gastric glands
of laboratory rodents and several other mammalian species but was not
known to infect humans (even though several texts state otherwise).
C. par-
vum
, however, infects the small intestine of an unusually wide range of mam-
mals, including humans, and is the zoonotic species responsible for human
cryptosporidiosis. Upton observed that, in most mammals,
C. parvum
is
predominately a parasite of neonate (newborn) animals. Even though excep-
tions occur, older animals generally develop poor infections, even when not
exposed previously to the parasite. Humans are the one host that can be
seriously infected at any time in their lives, and only previous exposure to
the parasite results in either full or partial immunity to challenge infections.
Oocysts are present in most surface bodies of water (e.g., lakes and riv-
ers) across the United States, many of which supply public drinking water.
Oocysts are more prevalent in surface waters when heavy rains increase
runoff of wild and domestic animal wastes from the land, or when sewage
