By Dr. Max Thornsberry, Milk Specialties Global Animal Nutrition
Cryptosporidiosis (or crypto) is caused by the protozoan parasite Cryptosporidium parvum.
Crypto and coccidiosis are caused by similar parasites; both disease organisms utilize the cells lining the digestive tract to reproduce. Many different species of Coccidia affect different portions of the digestive tract. Typically, the most severe coccidiosis parasites infect cells lining the lower portion of the small intestine and the upper portions of the large intestine in cattle. Coccidia have a very complicated lifecycle.
Calves typically pick up Coccidia oocytes by lying in feces or wet bedding, and then grooming themselves by licking the hair on their legs, thighs, and hips. Keeping bedding dry and feces removed is essential to coccidiosis control. Many calf raisers do a good job of keeping bedding clean and dry during the milk replacer portion of calf management, but aren’t nearly as aggressive in managing the environment of weaned calves. It is not unusual to find weaned calves standing in mud, wet feces or wet bedding. In my 30 years of clinical veterinary practice, it is the weaning period where coccidiosis rears its ugly head.
Crypto has a similar lifecycle to coccidiosis, but the reproductive stages do not enter the intestinal cells. Oocysts are consumed in dirty, wet, poorly bedded environments and immediately begin to reproduce using the outside surface of the cells lining the small intestine. This reproduction does not usually destroy the intestinal cell, but it does destroy or severely damage the surface of the cells. Crypto reproduces much more quickly than coccidiosis. Symptoms may develop as soon as five to seven days of age.
Because of the damage to the absorptive surface of intestinal cells, these cells do not absorb nutrients and fluids from the lumen of the intestine as effectively as they do if not damaged. The infected animal can shed oocysts as soon as three to five days following initial infection and continue to shed oocysts for 10 to 14 days. An infected calf re-infects itself and all pen mates exposed to its feces. Crypto is not inactive in cold temperatures. Infectiveness is greater during warm seasons, but crypto, unlike coccidiosis, can be a major disease condition during cold winter months.
Because crypto organisms do not typically destroy their host cells, a crypto infection rarely leads to little if any blood in the diarrhea. Depending on the number of crypto organisms present in the small intestine, symptoms can vary from a simple loss of appetite, to mild diarrhea, to severe, watery diarrhea and debilitation. Feces typically are pasty to thin, the color of milk or milk replacer, with or without mucus, and usually devoid of blood.
If a concurrent infection with another pathogen occurs, blood may be present in the stool. Concurrent infections are made more significant by the presence of crypto. To complicate the matter, crypto is contagious to humans, especially those humans that are on immune-suppressing medications or those with compromised immune systems. Leukemia patients, cancer therapy patients, patients treated for lupus, rheumatoid arthritis, or severe allergies are particularly susceptible to crypto infection contracted from cattle.
Crypto is very difficult to diagnose. Oocysts are not readily identified until the lifecycle is almost completed at 12 to 14 days. Intermediate life stages can sometimes be identified on histopathological examinations of the small intestine of dead calves. PCR testing procedures may also assist in diagnosis. Two types of oocysts are produced:
A thick-walled oocyst that can be detected in a fecal microscopic examination
A thin-walled oocyst that often “hatches” in the intestines to immediately re-infect the calf, making recovery more prolonged
There is no effective treatment for crypto. The use of amprollium and sulfa combinations have been said to provide clinical improvement, but this is difficult to assess since the disease is self-limited to about three weeks. If the calf environment is not kept clean and dry, it is possible for calves to continuously re-infect themselves for several weeks, exhibiting a pasty scours the entire period of time they are consuming milk replacer. It is these poorly managed systems of calf rearing that would benefit from using an electrolyte with thickeners. This process should slow passage of the pasty stool, improving the nutritional status of a crypto-infected calf by providing damaged intestinal cells with additional electrolytes and glucose energy.
Since there are no known treatment options for crypto, prevention of this disease is vital, but difficult.
Calves must be born into a clean, dry environment. Newborn calves lick and suck on the legs, udder and abdomen of their dams. If these surfaces are contaminated with crypto oocysts, the disease will begin at birth.
Calf hutches, pens and stalls must be steam-cleaned to kill crypto oocysts. No known disinfectant will destroy viable crypto oocysts. As soon as newborn calves are placed into a hutch, pen or stall, they lick and suck all exposed surfaces as they explore their new surroundings. This is the most likely source of crypto oocyst infection.
Calves must be maintained on clean, dry bedding. Crypto oocysts thrive in wet conditions, feces and any wet environment. Keep bedding free of feces, and especially, keep bedding dry. Prevent fecal contamination of feed and water.
Any calf with symptoms of crypto should be isolated from pen mates. Nose-to-nose contact should be prevented.
Research indicates the best treatment is energy. Keep feeding the calf.
The question is often asked if good colostrum management will help a crypto problem. The simple, short answer is “yes.” Although direct antibodies against crypto are rarely found in lactating cow colostrum, antibodies against other typical causes of calf diarrhea will definitely lessen the severity and duration of crypto-induced scours. Crypto is an opportunist disease. Its severity is compounded by concurrent intestinal disease of another unrelated pathology.