Pneumonia in foals is a major cause of foal death. It has been estimated by experts in foal diseases that up to 14% of all foals develop pneumonia and of these, the death loss may be as high as 45 to 50%. In those stables where Rhodococcus equi is the cause of pneumonia in foals, as many as 80% of these affected animals can die.
From February 19 through 23, 2006, I attended the Western Veterinary Conference at Las Vegas, Nevada, and was very fortunate to attend a two-hour class on Rhodococcus equi pneumonia in foals. The course was taught by Dr. Chaffin, a renowned expert on the disease. This was a very timely event for me, as every foaling season the phone brings me in contact with a number of horse breeders who are having a problem with this type of foal pneumonia.
Many stockmen realize that most cases of pneumonia can occur from inhaling pathogenic bacteria or developing the condition secondary to a septicemia, especially in the newborn foal. Poor passive immunity, hot/humid weather, chilling, overcrowding, exposure to a cold rain and poor ventilation with a high ammonia build-up are some of the common factors involved in the occurrence of pneumonia in the neonatal foal. It is very important that these foals should be kept under good sanitary conditions with adequate ventilation and protection from wet, chilly weather.
Transporting these foals during hot, humid weather should be avoided and, if necessary, should be done in well ventilated trailers during the coolest part of the day, which is usually during the nighttime hours. Overcrowding the trailer should be avoided at all costs. It has also been found that a selenium deficient, heavily parasitized foal is much more susceptible to pneumonia. The disease is likely to be more severe and of longer duration in these animals.
Researchers have found, from analyzing cases of bacterial pneumonia in young foals, that the causative bacteria are normal inhabitants of the horse’s upper respiratory tract, stomach or intestinal tract or they are contaminants from the foal’s environment. Such is the case of Rhodococcus equi, formerly named Corynebacterium equi, as it is found in the intestinal tract and manure of most herbivorous animals. It is also an inhabitant of the upper three inches of soil. Rhodococcus equi causes a very devastating and fatal form of pneumonia in foals from three weeks to six months of age.
Rhodococcus equi is found worldwide living in the top three inches of soil where it can possibly infect the foal as soon as it is born. The bacteria may be recovered from the feces of horses when they have reached three years of age. These older horses are immune to the effects of the bacteria.
The disease seems to be sporadic in occurrence at stables and farms; here today, gone tomorrow, but back again in the future. When it strikes, it may involve from 12 to 57% of the foal crop with foals less than 14 days old being very susceptible. On the other hand, the outbreak may often be less severe and affect only a few foals that may appear normal until most of their lungs are involved and they then die of pneumonia in a day or two.
Following a 10 to 25 day incubation period, the average case will exhibit a chronic purulent nasal discharge, increased respiration and heart rate plus an elevated body temperature. On the rare occasion, some foals will have a nonproductive cough and will exhibit no nasal discharge. The affected foal will take on an unthrifty appearance and, without adequate treatment, will die after several weeks or a month. Approximately 30% of these chronic cases will show distension of the hock, knee or fetlock joints with no evidence of lameness.
In these cases, the real damage is taking place inside of the body in the various organs. There will be abscesses in the lungs, lymph nodes, liver and in the walls of the intestines. Abdominal abscesses are common. These foals can also suffer occasionally from septic arthritis and osteomyelitis.
Many of these foals that recover, will stop growing and be scrawny, pot-bellied, long haired and generally just “poor doers.” Permanent pulmonary fibrosis with decreased lung capacity is often a problem in those who survive the infection.
Blood tests are of no value in the diagnosis of this disease. X-rays and sonograms of the thoracic areas of foals suspected with this disease are extremely helpful in its diagnosis. They are very useful in determining the presence of abscesses in the lung tissue of Rhodococcus equi patients. Ultrasound and x-ray of the infected abscessed lungs can also be used to monitor the progress of treatment in these foals.
Microbiologic culture is the best test to diagnose Rhodococcus equi infections. A tracheobronchial aspirate or wash is helpful to determine the cause of pneumonia and an appropriate antibiotic to be used on the microorganism.
Many owners and trainers who have gone through a session or two of the Rhodococcus equi pneumonia syndrome inform me that they can diagnose the condition just by noting the symptoms presented by the sick foal.
Erythromycin with rifampin is a very effective drug combination for the treatment of Rhodococcus equi pneumonia. In one case, 24 foals two-to-twelve weeks old were infected on one farm over a two year period of time. They were treated orally with this drug combination until two weeks after all clinical and lab tests were normal. Generally, this required four-to-twelve weeks of therapy. All 24 foals completely recovered and had normal growth rates.
Erythromycin with rifampin is administered to the foal at 15 to 25 milligrams per kilogram of the foal’s weight every 12 hours. The oral administration is a plus; however there are several drawbacks in the use of this treatment. On the rare occasion, this therapy has caused severe diarrhea, depression and hypothermia in the treated foal, necessitating the treatment be terminated. However, if this should happen there are other drugs that can be used.
Prevention and control of Rhodococcus equi infections on farms and stables is difficult at best. Remember the organism is shed in the feces of horses three years old and older, plus it grows or lives in the top three inches of soil. However, there are several things to be done which can decrease the incidence of pneumonia cases.
We know that foals maintained out of stalls are much less inclined to contract the disease. In prevention of this condition we know it helps to keep the foals away from other transient mares and horses. A third factor which seems to aid in the prevention of this disease is to decrease the population of the animals per square foot of paddock area.
Composting manure on those farms with a known high incidence of the disease seems to lower the number of cases.
Ultrasound, as mentioned before, is a very good tool in “spotting” individuals who are just developing the pneumonia. On farms with a high incidence of Rhodococcus equi infections, foals are scanned every two weeks after 30 days of age and treated immediately if the tests warrant it.
Hyperimmune plasma can be administered as a preventative measure. One liter is given to a foal one-to-three days of age. This is followed by a second liter at two weeks of age.
At the present there is no vaccine effective in preventing Rhodococcus equi pneumonia.
Rhodococcus pneumonia is much more prevalent than most livestock owners wish to believe. I am very sure that during each foaling season a large number of these cases, both in the acute and chronic forms, go undetected. A good number of horse owners call me every year wanting to know what to do about the problem which is costing them foals and money besides, so I know there are many more cases out there in the horse population that go undiagnosed.
If you think you have the problem, use this article as a guide and consult with a good equine veterinarian and you should not have to lose a foal with a Rhodococcus infection.