Photo credit Melissa Cantor, Penn State Extension
Cryptosporidium parvum (Crypto) is a protozoan species that invades the intestinal lining of calves (Thomson et al., 2017). Crypto is problematic because it causes watery diarrhea, dehydration and poor nutrient absorption in calves. It is the leading cause of diarrhea in neonatal calves 7 to 21 days of age (Urie et al., 2018) and the parasite is endemic on farms (Thomson et al., 2017). This article covers the parasitology of Crypto, management strategies to reduce pathogen load, and water sanitation strategies for calves.
How Crypto infects the calf
The parasite Crypto is transmitted via the fecal-oral route when the calf either ingests the oocysts in the feces or the calf consumes contaminated water (Cho and Yoon, 2014). Importantly, a calf can shed the oocysts up to a week after it recovers from diarrhea (Thomson et al., 2017). Once ingested, the oocyst is activated by the pH and temperature in the calf’s abomasum and four sporozoites are released (Thomson et al., 2017). Cryptosporidium parvum travels to the small intestine of the calf where the infection begins. Here, Crypto feeds itself using a special organelle extended into the host cell (Thomson et al., 2017). Because Crypto feeds on nutrients that were intended for the calf’s intestinal cells, poor nutrient absorption, poor growth, and reduced feed efficiency are typical for calves infected with the disease compared to non-infected peers (Harp and Goff, 1998; Thomson et al., 2017). Unfortunately for the calf, the parasite reproduces in the intestinal lining as well, re-infecting the calf through infection of neighboring cells, and starting the reproductive cycle again (Cho and Yoon, 2014). Thus, calves are susceptible in two ways, through the ingestion of feces shed by infected calves, and through re-infection in the lower gut by the parasite’s reproductive cycle. When Crypto is shed by an animal, the parasite is enclosed in an inactive, thick-walled oocyst (Harp and Goff, 1998). The oocyst’s shell is quite protective for this parasite, making it difficult to kill.
How to prevent Crypto infections
Sanitizing pens between groups of calves can help reduce pathogen loads but the type of disinfectant used is notable. Research has shown that Crypto is resistant to chlorine and iodine-based disinfectants (Harp and Goff, 1998). Crypto can also survive in extreme cold and warm temperatures. Boiling water at temperatures of 160 °F for three full minutes is required to destroy the oocysts (Fayer et al., 1996). Hydrogen peroxide-based disinfectants can kill Crypto, and a 3% Hydrogen peroxide solution is safe to use around calves (Thomson et al., 2017). Once a calf pen is emptied of soiled bedding, the pen can be sprayed down with a 3% hydrogen peroxide solution. It is important to remember that hydrogen peroxide at higher concentrations is more caustic and poses a risk to the farm staff handling the solution. Protective gear should be provided to staff. A hydrogen peroxide solution should be rinsed from metal surfaces after 10 minutes because it is an oxidizer and can cause rust. Allowing the pen to dry before returning calves to a pen is critical.
Crypto requires water to survive, which is why it thrives in humid environments like calf barns, but this can also be used against the organism. The easiest way to manage Crypto is to reduce parasite load by frequently removing soiled bedding from infected calf pens, and by cleaning bottles and buckets with very hot water followed by drying. The key here is to follow the hot water wash with drying because Crypto is vulnerable to desiccation, or dying out when moisture is removed from the environment (Harp and Goff, 1998). In addition to removal of soiled bedding, the isolation of sick calves away from healthy calves is also an important step in controlling Crypto. One tablespoon of diarrhea from a calf with Cryptosporidium parvum is enough to infect dozens of other calves if they consume it (Nydam et al., 2001). Having a dedicated, easy to clean area to house sick calves can help reduce the risk of disease transmission to other calves in the barn, regardless of the cause of diarrhea.
Diarrheic calves require supportive care
So now that we have described the parasitology and environmental management of Crypto, what can be done to manage it at the calf level? Crypto is a difficult species to manage in the calf because there are no effective treatments against it (Brainard et al., 2021). The best solution for calves with an active Crypto infection, much like any cause of diarrhea, is supportive care.
An effective supportive care plan for diarrheic calves involves providing rehydration solutions to them either by bottle, subcutaneously, or intravenously (Trefz et al., 2017). The herd veterinarian should work with calf producers to develop a care plan for producers to decide when diarrheic calves require rehydration solutions, and whether additional treatments are warranted. Cryptosporidium parvum is also zoonotic, meaning it is infectious to humans. Anyone treating or working with sick calves should always wear gloves, wash hands after calf handling even if wearing gloves, change and wash clothes soiled by calf diarrhea, and wash hands before eating.
A calf with diarrhea always needs access to clean drinking water because dehydration is the leading cause for death in diarrheic calves (Cho and Yoon, 2014). The dehydration status of a calf can be assessed by the following: pulling the skin on the shoulders to assess for elasticity, or skin tent, looking for recession of the eyes into the skull, feeling the calf’s extremities for warmth, checking the calf’s mucous membranes for dryness, and evaluating the calves for their ability to suckle and response to human presence, or attitude. A diarrheic calf that may not require oral rehydration solutions has tight skin elasticity that bounces back within a second, the eyes are flush with the skull, the ears are warm, the mucous membranes or nose and mouth are wet, the calf has a strong suckle, and the calf is responsive when approached (Figure 1 A). However, diarrheic calves can lose water quickly, so offering an oral rehydration solution to them is still valuable. A diarrheic calf with mild dehydration has a skin tent of one to two seconds, has at least 1 mm of eye recession, may have dry mucous membranes, and usually has a strong suckle; mild dehydrated calves need additional fluids, often provided by oral electrolyte solutions (Berchtold, 2009, a). Moderately dehydrated calves have a lingering skin tent of three to five seconds, at least 2 mm eye recession into the skull, and dry mucous membranes (Berchtold, 1999,a). Moderately dehydrated calves often present a weakened suckle and appear slightly depressed (Figure 1 B). A moderately dehydrated calf needs fluid therapy, but oral solutions may not be sufficient. These calves often need subcutaneous or intravenous fluids (Berchtold, 2009,b). Your herd veterinarian can help to decide what type of rehydration products are best for your operation. A severely dehydrated diarrheic calf has severe eye recession in the skull, a prolonged skin tent at the shoulders of six seconds or more (Berchtold, 1999,b), and usually these calves have cold extremities, a dry nose, and appear weak and depressed (Kells et al., 2020). Severely dehydrated calves require immediate intervention to survive (Figure 1 C). In summary, calves with Crypto experience diarrhea, and the best management strategy is to provide adequate rehydration and continued supportive care to keep diarrheic calves hydrated.
Figure 1. Examples of calves with different stages of hydration status. A well hydrated calf (Figure 1 A) has tight skin, is usually responsive to stimuli in their environment such as a human approaching them, and the eyes are flush with the orbit of the skull. A moderately dehydrated calf (Figure 1 B) has a skin tent of three to five seconds, a dry nose, and the eyes are notably recessed at least 2 mm into the orbit of the skull; this calf should receive oral fluids if suckling, or subcutaneous fluids. A severely dehydrated calf requires immediate care (Figure 1 C) and has a prolonged skin tent of greater than five seconds, the eyes are severely recessed into the orbit of the skull, and has cold extremities, a dry nose, and often is unresponsive to their surroundings; this calf requires an intravenous solution to correct metabolic acidosis.
Drinking water can be a reservoir for Crypto
Cryptosporidium parvum is also important to control in drinking water because it is zoonotic (Chalmers and Giles, 2010) and infected water sources have caused outbreaks in thousands of people (Chalmers and Giles, 2010). There is limited scientific research on the prevalence of crypto oocysts in calf water sources, but contaminated water sources have been identified as a likely source of infection on several operations (Cantor, unpublished). The UV light systems are the most effective sterilizer of water contaminated by Cryptosporidium parvum (Lacey, 2001), but this technology requires considerable investment and is not an economically feasible option for many farms.
There are many other options to render Crypto inactive in drinking water including boiling for 3 minutes at 160°F, using a filtration system certified to remove cysts from water at an absolute 1 micron rating, or the use of a water purifier such as reverse osmosis (Figure 2; CDC, 2023). Water filters are the cheapest option and may be economical for producers offering calves water from one source. There are three types of point-of-use water filters including particle, ion-exchange resin, or activated carbon (National Collaborating Centre for Environmental Health, 2006). Work with your local extension educator to find a filtration system that effectively filters out Crypto cysts from the water. Note that faucet-based carbon filtration systems are ineffective against filtering out Crypto because the pores are large enough for the small cysts to pass through. Filtering Crypto out of calf drinking water is important since this parasite thrives in water as a protozoan species.
Figure 2. Boiling drinking water for 3 minutes, using a filter ≤ 1 micron rating, or investing in a purifier, are all methods to sterilize water that is contaminated by Crypto. Figure reproduced for use from the Department of Health and Human Services, USA
In summary, Crypto is endemic and compromises calf growth, but the pathogen load can be managed to minimize the number of calves who get sick. Sanitation is key, and calf feeding equipment should be allowed to dry to kill Crypto. A frequent barn cleaning schedule is important to manage the pathogen load, including the use of a 3% hydrogen peroxide solution to sanitize hard surfaces, and allowing the pen to dry to break the reproductive cycle of this parasite. Calves sick with Crypto excrete large numbers of oocysts in their feces, so isolation of ill calves can reduce the risk of disease transmission. There are no approved therapeutic treatments for Cryptosporidium parvum in calves, but working with the herd veterinarian to build a strong supportive care plan can improve calf survival. Finally, if calves in your barn are struggling with Crypto, test the water source for this parasite. A water filtration system is a solution that can reduce pathogen load if the water source has a lot of Cryptosporidium parvum oocytes. It is also critical to remember that Crypto can cause disease in humans so appropriate protective strategies, such as wearing gloves should be used every time a sick calf is handled.
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