Have a look at the following:
Miller,RA; Bronsdon,MA; Morton,WR (1990):
Experimental cryptosporidiosis in a primate model. J.
Infect. Dis. 161(2, Feb), 312-315.
<Cryptosporidium causes a disease in infant
macaques that is clinically, histologically, and
microbiologically indistinguishable from that seen in
young children. A reproducible experimental model of
cryptosporidiosis has been developed in pigtailed
macaques (Macaca nemestrina) and used to studied the
infectious dose of oocysts and the effect of inoculum
size on severity of disease. Inoculation with either
2 x 10(5) or 10 oocysts via nasogastric tube resulted
in clinical enteritis and the fecal passage of large
numbers of cryptosporidial oocysts in all four
primates studied. The size of the inoculum had no
apparent effect on the severity or duration of
disease. Rechallenge 2 weeks after resolution of the
primary infection demonstrated partial acquired
immunity. The small inoculum size coupled with the
passage of large numbers of oocysts contributes to
the highly contagious nature of cryptosporidiosis
among captive primates and may be relevant to the
epidemiology and control of cryptosporidiosis in
Finch,GR; Daniels,CW; Black,EK; Schaefer,FW;
Belosevic,M (1993): Dose response of cryptosporidium
parvum in outbred neonatal cd 1 mice. Appl. Environ.
Microbiol. 59(11, Nov), 3661-3665.
(Univ Alberta, Dept Civil Engn, Edmonton T6G
2E9, Alberta, Canada)
<Cryptosporidium parvum infectivity in a
neonatal CD-1 mouse model was used to determine the
dose needed to infect 50% of the population. The 50%
infective dose was estimated to be 79 oocysts. It was
observed that a mean oral inoculum of 23 oocysts
produced infection in 2 of 25 neonatal mice 7 days
postinoculation. All animals became infected when the
mean oral dose exceeded 310 oocysts per animal. The
dose response of C. parvum was modeled with a logit
dose-response model suitable for use in water
Blewett,DA; Wright,SE; Casemore,DP; Booth,NE;
Jones,CE (1993): Infective dose size studies on
cryptosporidium parvum using gnotobiotic lambs.
Water. Science. and. Technology. 27(3-4), 61-64.
(Moredun Res Inst, 408 Gilmerton Rd, Edinburgh
Eh17 7Jh, Midlothian, Scotland . Glan Glwyd Gen Hosp,
Cryptosporidium Reference Unit, Phls, Rhyl, Wales.
Lothian Reg Council, Dept Water & Drainage, Marine
Esplanade, Edinburgh, Scotland)
<Natural waterbourne transmission of
cryptosporidiosis was studied by a simulation using
low-level accumulative dosing. Gnotobiotic lambs were
fed on a diet artificially contaminated to a
predetermined level with cryptosporidium parvum
oocysts and the faecal output of cysts was measured.
Results indicate a minimum infectious dose as low as
Dupont,HL; Chappell,CL; Sterling,CR; Okhuysen,PC;
Rose,JB; Jakubowski,W (1995): The infectivity of
cryptosporidium parvum in healthy volunteers. N.
Engl. J. Med. 332(13, 30 Mar), 855-859.
(Dupont HL ST LUKES EPISCOPAL HOSP 6720
BERTNER AVE MCI-164 RM P153 HOUSTON, TX 77030 USA)
<Background. Small numbers of Cryptosporidium
parvum oocysts can contaminate even treated drinking
water, and ingestion of oocysts can cause diarrheal
disease in normal as well as immunocompromised hosts.
Since the number of organisms necessary to cause
infection in humans is unknown, we performed a study
to determine the infective dose of the parasite in
healthy adults. Methods. After providing informed
consent, 29 healthy volunteers without evidence of
previous C. parvum infection, as determined by the
absence of anti-cryptosporidium-specific antibodies,
were given a single dose of 30 to 1 million C. parvum
oocysts obtained from a calf. They were then
monitored for oocyst excretion and clinical illness
for eight weeks. Household contacts were monitored
for secondary spread. Reuslts. Of the 16 subjects who
received an intended dose of 300 or more oocysts, 14
(88 percent) became infected. After a dose of 30
oocysts, one of five subjects (20 percent) became
infected, whereas at a dose of 1000 or more oocysts,
seven of seven became infected. The median infective
dose, calculated by linear regression, was 132
oocysts. Of the 18 subjects who excreted oocysts
after the challenge dose, 11 had enteric symptoms and
7 (39 percent) had clinical cryptosporidiosis,
consisting of diarrhea plus at least one other
enteric symptom. All recovered, and there were no
secondary cases of diarrhea among household contacts.
Conclusions. In healthy adults with no serologic
evidence of past infection with C. parvum, a low dose
of C. parvum oocysts is sufficient to cause
infection. [References: 31]>
Rendtorff RC. The experimental transmission of human
intestinal protozoan parasites. II. Giardia lamblia
cysts given in capsules. Am. J. Hyg. 59:209-220, 1954.
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