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‘Rattles’ is the name given to a lung infection (bacterial pneumonia) in foals caused by the bacteria Rhodococcus equi (R. equi). The disease is called ‘Rattles’ because of the rattling sound a sick foal can make while trying to breath with pus in the lungs.
The Rhodococcus equi (R.equi) is widespread in the foal's environment. The R equi organism is especially virulent and one of the first signs of the condition is a severe bronchitis that causes a rattling sound when the foal breathes. If not treated promptly, R equi causes large abscesses in the lungs and intestines and can be fatal and these abscesses are almost impossible to detect without tests like x-ray and ultrasound. It is among the top five most common equine diseases.
This bacteria is tough and can survive in soil. The foal becomes infected when it breathes in the bacteria in dusty environments. The foal is usually infected in the first few days of life. The foal does not show symptoms for several weeks to months after infection, therefore most foals are between 2-5 months of age when they become sick. This often coincides with summertime and the heat can significantly worsen the illness.
The first obvious symptoms are usually a cough and maybe discharge from the nose.
Many foals do not show any symptoms at all, but some foals can fail to gain weight or loose weight, spike a fever, go off their food, have trouble breathing and even die.
Not all foals will be infected, in fact many will not. It is not yet known exactly why some foals get sick and others do not but it is related to how the immune system is able to fight the disease.
Rattles is one on the most researched diseases in horses because of the significant effect it can have on foals being reared in intensive situations like the Thoroughbred breeding farms.
The bacteria rarely causes disease in the intestines or the abdomen (although it can occasionally – more on that later), it mostly causes disease of the lungs. Other bacteria can cause infections in the lungs, but Rhodococcus equi is the most likely suspect, especially in older foals on a farm with a history of Rattles.
Adult horses usually do not get R. equi infections because their immune system has developed the ability to fight the infection. Most foals do not develop this stronger immune system until they are older than 3 months of age.
Weak, lethargic behavior
Lack of appetite
Thick, nasal discharge containing pus
Once a property is contaminated, preventing the disease becomes a challenge, as the bacteria is in the soil and dust.
1. Minimizing contamination and exposure: Regular manure pick-ups and low stocking densities can decrease how much bacteria is contaminating the environment.
Keeping the foal in a ‘dust-free’ environment also helps. Many farms have day yards, where the Mare and young foal wait for vetting or other checks, in many cases in Australia these yards can be particularly dusty. Many farms have sprinkler systems in these yards keeping them damp, which is a good way to try suppress dust, however due to temperatures, this water evaporates very fast. There are other types of dust suppressors available, which do not evaporate and are harmless to animals, for example - EQUICLEAR. Research has found that foals confined to stables for the first 2-4 weeks of life are much less likely to develop infections. A ‘dust-free’ environment can be very challenging on large breeding farms, especially when the foals are born toward the end of a dry winter and spring when there is not much grass around.
2. Boosting the foal’s immune system: A plasma product has been produced that is rich in antibodies that help protect the foal against R. equi. The plasma is administered by a veterinarian, a bit like a blood transfusion, preferably when the foal is 24 hours old, and then 21 days later. There is some controversy as to how well the plasma works and whether it is worth the expense.
3. Early detection: Early detection means the foal can be treated before the disease gets serious, and which means shorter treatment times. Ultrasound is considered the cheapest and most effective screening test for the early detection of abscesses forming in the foal’s chest. Ideally the foals are examined every 2 weeks from 2 weeks of age.
Ultrasound can detect small abscesses on the surface of the lung.
Other tests that may be employed include:
Blood tests: The pus in the lungs causes a distinctive increase in the number of white cells in a foal’s blood. It also causes a large increase in an inflammatory protein called fibrinogen. White cell counts and fibrinogen levels are relatively cheap and useful for demonstrating the presence of infection, however there are other diseases that can also cause them to become elevated.
Lung washes: A tube is passed into the foal’s lungs and a sample of pus is collected and the type of bacteria is identified. This is a very useful test, but as you can imagine, it is a bit uncomfortable for the foal for a few minutes and if they are very sick it is not good to stress them further.
Radiographs (x-rays): X-rays are good at detecting abscesses in the lungs however they are more expensive and require the foal to stand very still.
Some recent large studies on farms in South America have shown that for small abscesses (< 2cm), antibiotic treatment may not be necessary. Foals that were not given antibiotics healed as quickly as foals that were administered antibiotics. For foals with large abscesses that are showing symptoms like coughing and weight loss, treatment involves daily administration of two different types of antibiotics as a paste into the foal’s mouth, for a period of between 1 to 6 months (until the abscesses have disappeared on ultrasound, then continue for several weeks afterward). The antibiotics are usually a combination of rifampin and one of erythromycin, clarithromycin or azithromycin. Erythomycin, clarithromycin and azithromycin can cause diarrhea in an adult horse if accidently ingested - sometimes severe and life threatening. Care must be taken to wipe away any antibiotics from the outside of the foal’s mouth so the mare does not accidentally ingest the antibiotic, either directly from the foal’s mouth or when it washes off in the drinking water.
Humans with immune deficiencies can also be susceptible R. equi infections.
When to Call the Vet
If your foal develops a cough that doesn’t go away after 1-2 days.
If your foal has a cough and a snotty (mucous and/or pus) nasal discharge.
If your foal is not interested in nursing or eating or has labored breathing (increased rate and effort of breathing).
If you are able to take the foal’s temperature, and it is greater than 39°C.