Cryptosporidium parvum is now recognized as a primary enteric pathogen in animals (Tzipori 1985a, Tzipori 1985b, Janoff and Reller 1987). The parasite is in the phylum Apicomplexa and part of the group of parasites commonly referred to as coccidia which include Cryptosporidium, Eimeria, Isospora, and Cyclospora (Fayer et al 1997). This parasite can be transmitted by the direct fecal-oral route or through ingestion of contaminated grain, milk or milk replacer or water (Kirkpatrick 1985). The primary environmental source of C. parvum ocysts for calfhood infection remains unidentified, but prompt removal of dairy calves from the dam and placement in a clean and sterilized calf hutch has resulted in low infection rates in calves (Dr. Jim Harp, personal communication).

The prepatent period for experimental infection in dairy calves, with an oral dosage of 107 oocysts per calf, was 4 to 5 days (Blewett 1989). Estimates of the prepatent period for natural infection range from 3 to 12 days (assuming exposure on the day of birth) (Anderson 1981, Blewett 1989, Xiao and Herd 1994). Estimating the prepatent period for natural infection is tentative since we do not know the initial time of exposure. It has been shown in gnotobiotic lambs that the fewer the number of oocysts ingested, the longer the prepatent period (Blewett et al 1993). Shedding of oocysts following experimental or natural infection ranges from 3-12 days (Anderson 1981, Blewett 1989), with recycling of shedding in small percentage of calves (Xiao and Herd 1994). The duration of diarrhea induced by experimental or natural infections can last for several days to 1-2 weeks (Blewett 1989). Clinical appearance of gastrointestinal infection in calves with C. parvum can range from asymptomatic shedding of oocysts to fulminating diarrhea, dehydration and death.

Calfhood infection with C. parvum is associated with clinical diarrhea. For example, one of the largest cross-sectional surveys to date on the shedding of C. parvum in beef calves found that the probability of having diarrhea among calves infected with C. parvum was 40% (78/194). In comparison, the probability of having diarrhea among calves not infected with C. parvum was 25% (313/1250) (National Animal Health Monitoring System 1994). Therefore, the risk of being diarrheic was 1.6 times ([78/194]/[313/1250]) greater for calves infected and shedding C. parvum compared to calves not shedding C. parvum. In southern Britain, the probability of having diarrhea among calves infected with C. parvum was 74% (85/115). In comparison, the probability of having diarrhea among calves not shedding C. parvum was 49% (329/678) (Reynolds et al 1986). Hence, risk of being diarrheic was 1.5 times ([85/115]/[329/678]) greater for calves infected and shedding C. parvum compared to calves not shedding C. parvum. In San Bernardino, California, the probability of having diarrhea among calves infected with C. parvum was 21% (20/95). In comparison, the probability of having diarrhea among calves not shedding C. parvum was 2% (8/405) (Sobieh et al 1987). Hence, risk of being diarrheic was 11 times ([20/95]/[8/405]) greater for calves infected and shedding C. parvum compared to calves not shedding C. parvum.

While asymptomatic and mild, self-limiting infections are common in immunocompetent calves, there are reported instances in which cryptosporidiosis has lead to severe diarrhea and subsequent death despite aggressive supportive care. Treatment for clinical cryptosporidiosis is limited to supportive care. Preventive measures on a dairy farm include general good management practices for raising healthy calves, such as adequate housing, disinfection of hutches between calves, handling sick calves last during feeding regimes, disinfecting feeding utensils between feedings, etc. We still do not have cost-effective, licensed antiprotozoal drugs for livestock infections. Products such as oral paromomycin and halofuginone lactate were effective in reducing the severity and duration of diarrhea associated with C. parvum infection (Fayer and Ellis 1993, Villacorta et al 1991), but their high cost and lack of federal approval prevents their use in the US. Moreover, the effectiveness of these and other antibiotics or vaccines for infection in calves has not been confirmed by clinical trials in the field. We evaluated two experimental products for their ability to reduce the period prevalence and clinical severity of cryptosporidiosis in calves on a California dry lot dairy (Harp et al 1996). One product, a preparation of lyophilized C. parvum oocysts, had shown clinical efficacy for experimental infection in calves. The other product was a lyophilized mixture of Streptococcus thermophilus, Bifidobacterium sp., and Lactobacillus sp. which when given orally had been shown to be protective for murine experimental infections. We found that both products were not successful in reducing the period prevalence or clinical severity of calfhood cryptosporidiosis in a commercial dairy environment. Colostral immunity was not protective for experimentally challenged calves (Harp et al 1989), but may help reduce infections caused by other pathogens and therefore lessen the clinical severity of calfhood cryptosporidiosis. Older calves appear to be less susceptible to experimental challenge compared to younger calves (Harp et al 1990).

Until we have effective vaccines and effective antibiotics to both prevent and treat this infection, good management practices will remain the cornerstone of an effective disease control program. Dr. Jim Harp, Agricultural Research Service, Ames, Iowa, offers several recommendations for preventing the spread of cryptosporidiosis on dairies: (1) provide a clean, dry area for cows to calve; (2) feed clean colostrum using a bottle and nipple that has been cleaned thoroughly with hot water and detergent; (3) provide clean, dry pens for calves and allow the pens to dry thoroughly between calves; and, (4) feed and care for sick calves last since you can easily spread the parasite from sick to healthy calves on your clothes or feeding utensils. With respect to beef cow-calf operations, we can help reduce the spread of this parasite between calves by avoiding overcrowding during the calving season and by preventing infected calves from defecating in the herd's watering source. One infected calf can shed billions of oocysts during the course of the infection, thereby quickly spreading the infection to the other calves through contaminated feed or water. In addition, Dr. John Maas, Beef Cattle Extension Specialist at UC Davis, suggests that a cow-calf herd health program needs to be in place which maintains healthy immune systems and minimizes diarrheal diseases. Such a program should include routine vaccination of all cattle for prevention of Bovine Virus Diarrhea (BVD), routine internal parasite control, and appropriate nutrient supplementation for the prevention of selenium and copper deficiency.

Rob Atwill, DVM, MPVM., PhD
Tel: 209-688-1731 ext 218
Fax: 209-686-4231
E-mail: ratwill@vmtrc.ucdavis.edu

References

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Blewett, D.A. 1989. Quantitative techniques in Cryptosporidium research, p. 85-95. In: K.W. Angus and D.A. Blewett (eds.), Proceedings of the 1st International Workshop on Cryptosporidiosis. Edinburgh, Scotland.

Blewett, D.A., S.E. Wright, D.P. Casemore, N.E. Booth, C.E. Jones. 1993. Infective dose size studies on Cryptosporidium parvum using gnotobiotic lambs. Water Sci. Technol. 27:61.

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