Infectious colitis in foals and weanlings (Proceedings)
Diarrhea in young foals (< 1 month): 1) rotavirus; 2) Clostridial (difficile and perfringens); 3) Salmonella; 4) parasites (Strongyloides westeri); 5) cornavirus and 5) Cryptosporidium. Of these rotavirus, Clostridial spp. and Salmonella are the most common.
Diarrhea in older foals & weanlings:
Rotavirus, Salmonella & Clostridium spp. can still cause diarrhea in older foals and weanlings. Other differentials however should include: 1) Lawsonia intracellularis (Proliferative enteropathy) 2) other types of parasites (ascarids, small and large stronglyes).Rotavirus
Rotavirus diarrhea is probably the most common cause of neonatal diarrhea in many species. It is species specific. It is more common in young foals, but can affect any age foal (even up to 7-8 months of life). Simultaneous infections with other viruses (coronavirus) or bacterial pathogens can also occur (and also increase severity of clinical signs).
Foals become exposed to rotavirus through other shedding/infected foals, mares, or the environment (from fecal contamination of the environment). It should be noted that the virus is very resistant to a number of disinfectants, and only phenol products (not dilute bleach!) is effective.
Clinical signs: diarrhea (mild to severe), depression, anorexia, and fever. Colic may also occur and may initially be difficult to differentiate from a strangulating lesion. Loss of electrolytes can result in hyponatremia, hypochloremia, and hyper or hypokalemia. Metabolic alkalosis can also occur. Rotavirus affects primarily the epithelial cell of the villi tip in the jejunum and ileum. A lactase deficiency results, (and a lactose intolerance), resulting in malabsorption and osmotic loss of electrolytes. Water absorption may also be inhibited because the virus inhibits a Na-D-glucose transporter.
Electron microscopy will identify all the different serotypes of rotavirus, but requires 108 organisms/gm feces.
The ELIZA tests are widely used in human and veterinary medicine, and are rapid, highly sensitive and specific (Kallestad Pathfinder Direct Antigen Detection System; Premier Rotaclone Rotavirus EIA Diagnostic Kit; PorspecT Rotazyme EX Microplate Assay). The agreement between ELIZA and electron microscopy has been very good in human and equine rotavirus.
The latex agglutination (Meritec Virogen Rotatest) has been found to be more sensitive, but less specific when compared to electron microscopy.
Treatment covered at end of notes.
Prevention: There is a killed vaccine from Fort Dodge, with limited licensure (meaning that it is safe, does produce a humoral response) but efficacy is unknown. Labeled dose instructions include vaccination of the mare during gestation and 30 days prior to foaling to help produce colostral immunogloblins. Off label use could include vaccination of the mare after foaling, to help produce lactogenic immunity.
Clostridium difficile and Clostridium perfringens
Both Clostridial organisms can cause diarrhea in foals and adults. All Clostridial organisms produce exotoxins which can be very pathogenic.
Clostridium difficile produces several hydrolytic enzymes, and at least 5 toxic factors. Toxins A and B are the best described. Toxin A is an enterotoxin, and Toxin B is a cytotoxin. There are non-toxigenic strains of C. difficile, (25%) which are not pathogenic. C. difficile is highly associated with the use of antibiotics. However, it can also result in disease without antibiotic use.
Clostridium perfringens is categorized into types A-E, based on the expression of one or more lethal toxins and the combination of toxins to certain subsets. Types A and C are the most described pathogens in horses. Type C is the most severe (often fatal in young foals). Exact toxin is not as well worked out. Some labs will detect Enterotoxin unsure of the significance of this toxin.