Foal Pneumonia

Source :  Equine Research Centre

© Dorothy Woodward

Foals that acquire Rhodococcus equi (R.equi) pneumonia can die an untimely death by slow suffocation. R.equi lives in the soil and manure on farms and can be a persistent contaminant that becomes impossible to eradicate. It affects foals between one and five months of age. Since the foal continues to nurse and maintain body weight and appears healthy, this disease often goes unnoticed until it has progressed significantly. It is
expensive to diagnose and treat.

Foals that survive R.equi may have a slight decrease in overall performance, particularly racing; however, thanks to the work of Dr. John Prescott, Jun Ren, and a team of researchers at the University of Guelph, a vaccine may become available for R.equi in the near future.

Over the past 20 years, Dr. Prescott has contributed to the understanding and treatment of R.equi. He first became interested in R.equi pneumonia when he did a case study as a veterinary student at the University of Cambridge. When he came to work at the University of Guelph he encountered a number of cases and found there had been no treatment developed for the disease.

Farmers were worried about their other foals but it seemed that few were investigating the cause or treatment. Dr. Prescott began to work on the antibiotic susceptibility of the pathogen, and the testing of various drugs. He developed the regime currently practiced to treat foal pneumonia, saving many foals as a result of this research; however, the new concern is that the organism will eventually become resistant to
antibiotics. On some farms, according to Dr. Prescott, it already has. This drives the need to develop a vaccine against it.

R.equi is an organism that thrives wherever there is horse manure, heat, and dust. The bacteria are inhaled and cause an inflammation of the lung tissue. The lungs become filled with macrophages, which are cells produced by the immune system to digest and kill harmful bacteria. In the case of R.equi, the macrophages ingest the bacteria but are unable to kill it. In fact, the bacteria multiply inside the macrophages, killing them in the process. Large abscesses develop in the lungs; the foal, as a result, slowly suffocates.

The first part of Dr. Prescott’s research is to understand how R.equi survives in the body. Some of the methods that the macrophages use to kill harmful bacteria actually help
R.equi to grow. By identifying which genes are most important to the survival of the bacterium inside the macrophage Prescott believes the harmful genes can be altered, taking away their ability to grow. This may become the basis for producing an effective vaccine.

The second part of the work being done in the laboratory is to investigate why foals get R.equi pneumonia. During the course of his Ph.D work, Dr. Steve Giguere discovered that the organism actually caused changes to the foals immune systems to enhance its own survival. Another obstacle to fighting off R.equi is the fact that foals, not adults, contract the disease.

Although it is not clear why, the immune system of young mammals has a tendency to only release antibodies to fight disease. Antibodies are ineffective at killing bacteria that reside inside macrophages. The fact that young animals do not use macrophages as a defense has led some researchers to take the position that it would be impossible to vaccinate a foal by three weeks of age. To fight off this disease, the foal’s immune system must be coaxed into producing a response, allowing macrophages to kill the organism.

Work going on in the laboratory suggests that it is possible to produce a vaccine that will be 100 percent effective in preventing R.equi pneumonia in foals, eliminating the
need for the lengthy and expensive treatment that exists today.

PRECAUTIONS
To reduce levels of bacteria on the farm, manure should be regularly disposed of and measures should be taken for controlling dust in areas where the foals are kept.

To decrease the chance of inhaling the bacteria, loafing paddocks should be well grassed, preventing them from becoming infected dust bowls.

Foals should be housed in wellventilated, dust-free areas.

Any foal found to have R.equi should be immediately isolated and special precautions should be taken to dispose of soiled bedding to prevent spreading the organism.

On endemically infected farms, administration of hyperimmune plasma can reduce illness caused by this organism.

Foals should ideally be born in January when conditions limit the growth of the organism.