Loss of absorptive capacity for sodium and chloride in the colon causes diarrhoea in Potomac horse fever.

The research article explores how Potomac horse fever, caused by the bacterium Ehrlichia risticii, leads to severe diarrhoea in horses. The study discovers that the diarrhoea results from the loss of the colon’s capacity to absorb sodium and chloride due to the bacterium.

Objective and Methodology

• The research aimed to uncover the mechanisms causing severe watery diarrhoea often associated with Potomac horse fever induced by the Ehrlichia risticii bacterium. The researchers specifically looked at the potential alterations in the transportation of sodium and chloride, colonic mucosa’s morphology and its cyclic adenosine 3′, 5′-monophosphate (cyclic AMP) content.
• The study examined ‘mucosa-submucosa sheets’ from the large and small colon of nine Ehrlichia risticii-infected horses and seven to nine uninfected horses. These tissues were set up in Ussing chambers, a laboratory tool, to measure the ‘short-circuit current’ and the ‘transepithelial 22Na and 36Cl fluxes’ which relate to sodium and chloride transport.

Findings and Conclusions

• The research found that while uninfected tissues could absorb both sodium and chloride, this capability was lost in the tissues infected with Ehrlichia risticii.
• In response to the agents bethanechol and histamine, both groups of tissues displayed a concentration-dependent increase in short circuit current. However, this response was significantly reduced in the infected horses.
• The study also recorded minor localized degeneration of colonic epithelial cells and the loss of microvilli from glandular epithelial cells in infected horses. Microvilli are microscopic cellular membrane protrusions that increase the surface area for absorption.
• Additionally, a noticeable increase in the content of cyclic AMP, an important cellular messenger, was observed in the colonic mucosa of infected animals.
• The study concluded that Ehrlichia risticii infection results in minute degeneration of epithelial cells and an increase in cyclic AMP in the colon. These anomalies are linked with diminished absorption of sodium and chloride that could potentially cause diarrhoea in horses.