Age, geographic, and temporal distribution of fecal shedding of Cryptosporidium parvum oocysts in cow-calf herds.
OBJECTIVE
To evaluate fecal shedding of Cryptosporidium parvum from California cow-calf herds with respect to age, geographic region, temporal effects, and association with watery feces.


METHODS
Cows and calves from 38 beef cow-calf operations.


METHODS
Fecal specimens were collected and examined for C parvum oocysts, using immunofluorescent microscopy. Associations between age, geographic region, month of collection, watery feces, and likelihood of shedding C parvum were evaluated.


RESULTS
3.9% of cattle were shedding C parvum oocysts. Prevalence of shedding among calves ranged from 0 to 13%, and was 0.6% among cattle > or = 12 months old. The odds of shedding C parvum among 2-month-old calves were 41 times greater than among cattle > 4 months old. The odds of shedding C parvum among cattle tested in May were 8.7 times greater than among cattle tested during June, July, or August. The odds of infected individuals having watery feces were 3 to 4 times greater than for noninfected individuals, but the etiologic fraction was only 8 to 9%.


CONCLUSIONS
Substantial fecal shedding of C parvum by cow-calf herds was limited to calves 1 to 4 months old, with low prevalence detected in older animals. Risk of contamination of watersheds with C parvum was limited to those periods when young calves were in the herd. Although the odds of having watery feces were greater for animals infected with C parvum than for noninfected animals, the low etiologic fraction suggests that most calves with watery feces were not infected with C parvum.
Atwill
E R
ER
Veterinary Medicine Teaching and Research Center, School of Veterinary Medicine, University of California-Davis, Tulare 93274, USA.
Johnson
E
E
Klingborg
D J
DJ
Veserat
G M
GM
Markegard
G
G
Jensen
W A
WA
Pratt
D W
DW
Delmas
R E
RE
George
H A
HA
Forero
L C
LC
Philips
R L
RL
Barry
S J
SJ
McDougald
N K
NK
Gildersleeve
R R
RR
Frost
W E
WE
D000367:Age Factors; D000818:Animals; D002140:California / Q000453:epidemiology; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology / Q000469:parasitology*; D003457:Cryptosporidiosis / Q000453:epidemiology / Q000662:veterinary*; D016785:Cryptosporidium parvum / Q000302:isolation & purification*; D005243:Feces / Q000469:parasitology*; D005843:Geography; D010270:Parasite Egg Count; D013997:Time Factors