Although the parasite Cryptosporidium was first identified at the beginning of the 20th century by physician-parasitologist Ernest Tyzzer, it was not until the 1980s before these intestinal protozoa were recognized as an important pathogen impacting cattle and human health globally. It is now known that there are over twenty species of “crypto.” Still, Cryptosporidium parvum is the species that exhibits widespread prevalence in US calf herds and remains a significant manure pathogen and cause of pre-weaned calf diarrhea.

Neonatal calves, particularly in dairy or calf ranching settings, are most susceptible to C. parvum and herd outbreaks usually occur in calves less than a month old, with some displaying clinical signs of diarrhea as early as three to five days old. Calves infected with Cryptosporidium parvum can be healthy or develop severe scours. Infected animals shed large numbers (1 x 1010) of infective eggs called oocysts in feces, rapidly contaminating the housing environment and exposing other calves. Ingestion of higher doses of oocysts is usually associated with more severe diarrhea and higher calf morbidity.

There are currently no licensed treatments for “crypto” in the US. Hence, interventions for sick calves with C. parvum-related diarrhea aim to improve calf hydration with electrolytes and fluids and ensure adequate energy and nutrition to fight off the infection. Individual cases of calf diarrhea and outbreaks attributed to C. parvum have high morbidity, are usually self-limiting, and typically do not result in significant herd mortality. However, sick calves with “crypto” experience poor growth pre-weaning. Studies have found that calf body weight lost during bouts of neonatal diarrhea is not regained in the six months following infection, suggesting that the impact of Cryptosporidium parvum on the calf-raising industry may be more significant than previously thought. Negative impacts in the pre-weaning period due to C. parvum, like some other manure pathogens that impact neonatal calves, result in economic losses related to:

Short-term costs:
• Diagnostics
• Supplies for supportive care
• Increased labor to manage individual cases and outbreaks
• Reduced pre-weaned calf growth

Long-term costs:
• Increased age at calving or time to slaughter
• Reduced future milk production for dairy replacements

When neonatal disease monitoring and diagnostics are included in a calf health management plan, it is common to find co-infection of C. parvum with other neonatal enteric pathogens, such as bovine rotavirus A and coronavirus. In a recent summary report from the Texas A&M Veterinary Diagnostic Laboratory (TVDL), which included 1,088 manure

and tissue samples from dairy and beef calf diarrhea cases in Texas between 2019-2023, 43% of samples tested positive for Cryptosporidium. Of those samples that tested positive for Cryptosporidium, 44% also tested positive for co-infection with either bovine rotavirus A, coronavirus, or both viral pathogens.

Proactive approaches include implementing farm-specific neonatal calf biosecurity plans with your herd advisors to identify and reduce risks of spreading Cryptosporidium parvum within your herd. Some key considerations for devising an internal biosecurity plan aimed at preventing neonatal disease outbreaks from “crypto” should address the following:

1. How is the workflow for feeding and calf care organized? Feeding and working calves from the youngest to the oldest is ideal since the older calves may shed C. parvum but not become sick, unlike the youngest calves, which are more susceptible to clinical disease. Handling any sick calves with scours last may help to prevent spread.

2. How frequently are you evaluating the cleanliness and hygiene of the calves? Consider doing routine hygiene checks on calves to aim for having 90% of the herd clean. Dry and clean bedding and lowering housing density can go a long way in preventing calves from becoming clinically sick.

3. Do you have the appropriate sanitizing chemicals for addressing C. parvum? Are staff trained in SOPs for pre-weaned calf housing hygiene? Research has indicated that some hydrogen peroxide and chlorine dioxide formulations may kill the infective oocysts of C. parvum. Still, these agents are only effective at certain concentrations and with adequate contact time. Check with your veterinarian and follow chemical manufacturer product labels carefully. Thorough cleaning and washing of debris, manure, and bedding before application of disinfectants is recommended.

4. How clean are maternity pens, and are calves being removed in a timely fashion? Like other pathogens that cause scours, Cryptosporidium parvum is present in the manure of healthy cows at calving. Expedient removal of calves and maternity pen cleanliness is important to minimizing fecal-oral perinatal transmission.

5. When did you last review your neonatal calf nutrition and feeding plan with your nutritionists and calf feeding team? Ensuring neonatal calves receive adequate dietary energy may limit the severity of sickness when they face elevated exposure rates to Cryptosporidium in the environment. In one study where pre-weaned calves were challenged with C. parvum, those on higher nutritional planes of milk replacer had diminished severity of disease, improved feed efficiency, and growth rates.

Pre-weaned calves are considered the most vulnerable life stage on farms and ranch operations since they are the most sensitive to pathogen density. In the case of parasites, where exposure rates are very high in early life, environmental biosecurity and housing are critical elements for minimizing their spread. The parasite is very difficult to remove from surfaces, as the oocysts have a tough outer wall, which enables the parasite to survive for months in moist conditions and makes it difficult to kill.

Additionally, the zoonotic potential for transmission of Cryptosporidium parvum to humans makes this parasite a risk for calf caretakers. Anyone handling calves with “crypto” should have adequate personal protective equipment (PPE) and be educated about risks. Optimizing biosecurity practices to include worker training and hygiene is an important part of everyday Cryptosporidium biocontainment.

REFERENCES:
Adkins, P. R. (2022). Cryptosporidiosis. Veterinary Clinics: Food Animal Practice, 38(1), 121-131.
Barnhardt, T. R., & Raabis, S. M. (2024). Biosecurity Strategies for Optimization of Calf Health in North American Beef and Dairy Operations. Veterinary Clinics: Food Animal Practice. Ollivett, T. L., Nydam, D. V., Linden, T. C., Bowman, D. D., & Van Amburgh,
M. E. (2012). Effect of nutritional plane on health and performance in dairy calves after experimental infection with Cryptosporidium parvum. Journal of the American Veterinary Medical Association, 241(11), 1514-1520.
Rideout, H., Cook, A. J., & Whetton, A. D. (2024). Understanding the Cryptosporidium species and their challenges to animal health and livestock species for informed development of new, specific treatment strategies. Frontiers in Parasitology, 3, 1448076.
Rodriguez, C. (2024, Aug). Summary of Calf Diarrhea Multiplex Results from Texas Cattle, 2019-2023 – Texas A&M Veterinary Medical Diagnostic Laboratory. Texas A&M Veterinary Medical Diagnostic Laboratory. https://tvmdl.tamu.edu/case-studies/summary-of-calf-diarrhea-multiplex-results-from-texas-cattle-2019-2023/