Bug of the Month: Rotavirus
Rotavirus is an important cause of diarrhea in young horses. (It's also a major cause of diarrhea in infants, but a different rotavirus is involved). Exposure to rotavirus is very common - most, if not all, horses are exposed to it early in life. Disease only occurs in foals, but not every foal that gets exposed becomes sick. Most often, rotavirus causes diarrhea if foals between 1 and 6 months of age, with most cases occurring between 1 and 3 months of age. Foals less than 1 month of age can be affected, but it's less common.
Foals become infected by swallowing the virus, which they usually pick up from the feces of other horses (including their mares) in their environment. The exact source of infection is rarely identified. It is likely that some healthy adult horses are the reservoirs and shed the virus in their manure.
Like other types of diarrhea, rotaviral diarrhea in foals can range from mild diarrhea alone to severe diarrhea with weakness, loss of appetite and dehydration. Colic can occur because of intestinal cramping associated with diarrhea. You cannot differentiate diarrhea due to rotavirus from other types of diarrhea by appearance alone. The diarrhea must be tested to identify the cause.
There is no specific treatment for rotavirus infection, but "supportive care" is often provided. One of the primary components of supportive care is fluid therapy, which may be needed for foals that start to become weak and dehydrated. Aggressive intravenous fluid therapy may be needed in some cases, depending on the severity.
Rotavirus vaccines are available in some regions, although there is limited evidence that they have much of an effect. Few people recommend vaccination. Rather, good attention to foal management practices, hygiene and early diagnosis of infected foals is the key. Foaling mares outside on pasture has been an effective practice in some outbreaks, presumably because there is less rotavirus contamination on pasture.
Image: Colourized TEM of rotavirus particles (source: CDC PHIL 173)
