Todayโs path rounds are on ๐๐ก๐จ๐๐จ๐๐จ๐๐๐ฎ๐ฌ ๐๐ช๐ฎ๐ข!
๐๐ก๐๐ญ ๐ข๐ฌ ๐ข๐ญ?
๐๐ก๐จ๐๐จ๐๐จ๐๐๐ฎ๐ฌ ๐๐ช๐ฎ๐ข is a bacteria that is commonly found in the soil and in horse manure. It is considered a ๐๐๐๐ฎ๐ฅ๐ญ๐๐ญ๐ข๐ฏ๐ ๐ข๐ง๐ญ๐ซ๐๐๐๐ฅ๐ฅ๐ฎ๐ฅ๐๐ซ pathogen, meaning it needs to invade into host cells in order to survive.
๐๐ก๐จ ๐ ๐๐ญ๐ฌ ๐ข๐ญ?
This disease primarily affects horses, particularly 1-6 month old foals.
๐๐ก๐๐ญ ๐๐๐ฎ๐ฌ๐๐ฌ ๐ข๐ญ?
As mentioned before, R. equi is a soil borne bacteria, so typically foals acquire the disease from inhaling dust or ingesting dirt particles. Once the bacteria is within the foal, it gets engulfed by ๐ฆ๐๐๐ซ๐จ๐ฉ๐ก๐๐ ๐๐ฌ (the bodyโs major clean up cell). Normally when a macrophage eats a bacteria, the bacteria is enclosed in a storage unit called a ๐ฉ๐ก๐๐ ๐จ๐ฌ๐จ๐ฆ๐, which will fuse with a ๐ฅ๐ฒ๐ฌ๐จ๐ฌ๐จ๐ฆ๐ that contains a large number of toxic enzymes that destroy the bacteria. In the case of R. equi, however, the bacteria expresses a protein that prevents the lysosome from fusing with the phagosome, thus preventing the bacteria from getting destroyed. Crazy!
๐๐ก๐ฒ ๐ข๐ฌ ๐ญ๐ก๐ข๐ฌ ๐ ๐ฉ๐ซ๐จ๐๐ฅ๐๐ฆ?
Because R. equi survives within macrophages, the body canโt use that mechanism in order to kill the bacteria. Therefore, it has to use a different aspect of the immune system. In order to kill the bacteria, the body must now target the infected macrophages and destroy them. So, it employs a different type of cell called ๐ค๐ข๐ฅ๐ฅ๐๐ซ ๐ ๐๐๐ฅ๐ฅ๐ฌ, which identify infected macrophages and cause them to disintegrate.
However, this type of immune activity produces a lot of inflammation! Typically, areas where the macrophages are being destroyed form ๐๐๐ฌ๐๐๐ฌ๐ฌ๐๐ฌ, which is basically a soupy collection of immune cells in various stages of life and death. These abscesses are generally found in the lungs, intestine and occasionally in the growth plates of bones. Ultimately, this is what causes problems for the foal, by inciting a high fever, reducing lung capacity, causing gastrointestinal issues and generally making them feel pretty dumpy.
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐๐ข๐๐ ๐ง๐จ๐ฌ๐๐?
This disease should be suspected any time you have a sick foal with high fever and breathing issues. From that initial suspicion, a veterinarian might do an ultrasound or take an X-ray of the chest in order to visualize the abscesses. If the disease is in the intestine or bones, similar diagnostics can be used.
To definitively diagnose the disease, the veterinarian may do a ๐ญ๐ซ๐๐ง๐ฌ๐ญ๐ซ๐๐๐ก๐๐๐ฅ ๐ฐ๐๐ฌ๐ก, which is where they introduce sterile water into the lungs, then retrieve it to see what cells are hanging out in the lungs. When you look at the cells under a microscope, you can often see macrophages containing tiny dit dot bacteria, which is the Rhodococcus itself!
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐ญ๐ซ๐๐๐ญ๐๐? ๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐ฉ๐ซ๐๐ฏ๐๐ง๐ญ๐๐?
This disease requires intensive antibiotic treatment, because it is incredibly difficult for antibiotics to enter abscesses in order to do their job. However, most foals do recover from this disease and go on to live productive horsey lives! To prevent it, foals should be kept in well-ventilated, dust free areas and should be monitored closely for any signs of fever or respiratory issues.
๐๐ก๐จ๐ญ๐จ๐ฌ
1) An example of what you might see after a transtracheal wash. See all the little purple dots in the cell? Those are the bacteria!
2-4) Examples of abscesses in the lungs from R. equi.
5-6) Examples of abscesses in the intestine from R. equi.
7) A growth plate infected with R. equi, forming a large abscess within the bone! Ouch.
๐๐จ๐ฎ๐ซ๐๐๐ฌ
Maxie, G. Jubb, Kennedy and Palmerโs Pathology of Domestic Animals, Volume 2. Sixth Edition.
Rush, BR. Rhodococcus equi Pneumonia in foals. Merck Vet Manual 2014.
Photos 1-7 courtesy of Noahโs Arkive.
