Rhodococcus Infects More Than Lungs
Rhodococcus equi is a bacterium that is an important cause of respiratory disease in foals. It typically causes numerous abscesses in the lungs, and it is an important cause of illness and death in foals from a few weeks to about six months of age. Infections of other parts of the body can occur, and these can cause serious problems because they can be hard to diagnose and hard to treat.
A recent study in the Journal of the American Veterinary Medical Association (Reuss et al 2009) described extra-pulmonary disorders (EPDs, disorders in parts of the body besides the respiratory tract). They studied 150 foals, and 74% had a least on EPD. These included:
- Immune-mediated synovitis (25%): This is a well-recognized problem where R. equi-infected foals get enlarged joints because of accumulation of excess joint (synovial) fluid. Fluid-distended joints can occur with joint infections, but with immune-mediated synovitis it's caused by the immune system alone. This typically does not result in long-term joint problems, although it's important to determine whether the foal has an infection which needs aggressive care, or just inflammation which is best left alone.
- Abdominal abscesses (17%): This is a very serious problem and abscesses in the abdomen can be very difficult to treat. These foals often die.
- Uveitis (11%): Inflammation of the eye, which can occur as a result of the immune response or infection.
- Septic synovitis (9%): As opposed to immune-mediated synovitis, this is an infection in the joint. This is very serious and can cause permanent joint damage.
- Pyogranulomatous hepatitis (11%): This is inflammation of the liver with abscesses and pus.
- Pleural effusion (3%): Accumulation of fluid between the lungs and body wall. This can be the result of severe lung disease.
- Meningitis (3%): Infection of the layer covering the brain, which is never a good thing.
Foals that had EPDs were more likely to die than foals with infections only involving the lungs, which isn't particularly surprising. In particular, the presence of uveitis, bloodstream infection, joint infection (not immune-mediated synovitis) and abdominal abscessation were associated with failure to survive.
