Brief Informational Sketches of Some Other Mastitis Pathogens

Kansas State University College of Veterinary Medicine
Mississippi State University College of Veterinary Medicine
Virginia-Maryland Regional College of Veterinary Medicine
Texas A & M University College of Veterinary Medicine.

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Calf Diarrhea Pathogen Information: Cryptosporidium parvum

Introduction: Cryptosporidium parvum can infect many species of mammals. Unlike many other diarrhea-causing pathogens, Cryptosporidia are not bacterial or viral, but coccidial protozoans.

Epidemiology: Cryptosporidia are found worldwide, particularly in young calves, which frequently harbor the organism without showing any sign of disease. Oocysts, the infective agent for Cryptosporidium parvum, can be found in the feces of calves as young as 5 days of age. Diarrhea due to Cryptosporidium Parvum typically occurs in calves between the age of 5 and 15 days. Calves with diarrhea due to Cryptosporidium parvum shed large numbers of infective oocysts in their feces. It takes very few oocysts to establish infection, and severity of disease is correlated with the number of oocysts ingested. Infection with the organism confers resistance to subsequent infection. Cryptosporidium parvum is not host-specific, may be carried by wild and domestic animals, and can infect humans.

Oocysts of Cryptosporidium parvum are resistant to most disinfectants and survive well in the temperature range 0-65 ° C (32-149 ° F). Numbers decrease in calf feces after 1 to 4 days of drying.

Zoonotic Risk: Cryptosporidium parvum infection is common in humans, and is a risk for any person who contacts animals or premises harboring the organism. People working with calves are at particularly high risk for cryptosporidial infection. Cryptosporidium parvum infection in humans is usually self-limiting but can be quite dangerous to people who are immunocompromised, such as the very young or elderly or those with illness or drug therapy that compromises the immune system.

Clinical Features/ Specifics of therapy: Diarrhea due to Cryptosporidium parvum is called cryptosporidiosis and most commonly occurs in calves 5-15 days old, often in conjunction with infection by other diarrhea causing agents, especially rotavirus and coronavirus. The diarrheic phase of the infection lasts for several days, commonly 6 to 10, regardless of treatment. Diarrhea due to Cryptosporidium parvum may be yellow or pale and watery, and may contain mucous strands. The most consistent early sign of cryptosporidiosis is anorexia. Because the infective agent destroys intestinal villi, cryptosporidiosis results in maldigestion and malabsoption, leading to the most marked clinical feature of the disease: profound weight loss leading to emaciation. It is important not to stop feeding milk to calves with cryptosporidiosis, as this may cause the animal to die from lack of caloric intake. Digestibility can be enhanced in affected calves by dividing the normal daily intake into smaller but more frequent feedings.

Diagnosis/Necropsy findings/Sampling Goals: Cryptosporidium parvum infection can be diagnosed by examination of feces for oocycts using a fecal smear or flotation. Special staining or special microscopic lighting may be necessary to visualize the oocysts.

At necropsy there will be dehydration and marked weight loss or emaciation, and possibly serous atrophy of fat. There is moderate enteritis with mucofibrinous exudate in the large and small intestine. It is common to also find other pathogens. Feces should be submitted for parasitology. Samples of jejunum, multiple sites of ileum, and colon should be preserved and submitted for histopathology.

Specific prevention measures/ Vaccination: Special attention should be paid to trying to limit the spread of this hardy organism on affected farms. Sick animals should be isolated as they shed high numbers of oocysts, and the caretaker of sick animals must be vigilant in order to avoid spreading the organism to other animals or humans. The use of calf hutches on dairy farms can diminish the severity of infection by decreasing the magnitude of calf exposure to oocysts. As mentioned above, oocysts are quite resistant to commonly used disinfectants. Freezing contaminated articles overnight will destroy oocysts.