Parascaris Equorum Infection in Foals
Dr. Melissa Mazan
Verminous pneumonia is a term for inflammation of the lung caused by parasites. The presence of the parasites is extremely irritating to the lung, and sets up a strong inflammatory and immune reaction. In foals, the culprit in cases of verminous pneumonia is the ascarid worm called Parascaris equorum. History of responding well to antibiotics – only to relapse.
The diagnosis of verminous pneumonia is increasingly rare today, but still exists where there are groups of foals with inadequate deworming. Those who stop deworming their foals generally encounter this problem.
Ascarids can also cause colic in foals, primarily because they obstruct the passage of food and fecal material. P.equorum is a roundworm – one of the ascarids. Most foals have some ascarids in their gastrointestinal systems at some time between two months and 24 months of age, but most horses develop a strong protective immunity against ascarids by 12 to 24 months of age.
Ascarids are incredibly tough creatures. Their eggs have a thick shell that allows them to survive despite dry, hot or cold conditions for up to eight years. The shells are also sticky, so they get all over any environment that a foal has been in – they stick to water buckets, fences, and stall walls – in short, anything that a foal might like to chew on or lick. So, you're pretty much guaranteed that if foals have been on a property in the past few years, that property contains an infective dose of ascarid eggs.
P. equorum, similar to other ascarids, has what is termed a direct life cycle, meaning that they have only one host – the horse. The adults live in the gastrointestinal system of the horse and lay eggs that are shed in the manure. The eggs are then ingested by other foals, and enter the gastrointestinal system. The larvae, or immature worms, emerge and migrate through the liver and then to the respiratory system. They spend some time in the bronchi (breathing tubes) and trachea, where they elicit a tremendous inflammatory response. At a certain point of maturity, the foal coughs up the larvae, swallows them, and the worms then set up housekeeping as adults in the gastrointestinal system.
What to Look For
Elevated respiratory rate
Failure to put on weight at a normal rate
Rough hair coat
Pendulous abdomen (haybelly)
Lack of appetite or not nursing
Roundworms in the manure.
Mild, moderate, or severe colic
Pawing, rolling, getting up and down
Lying on their back
Your veterinarian will take a careful medical history, and will want to know exactly when and with what product your foal was last dewormed. He will also want to know when, how often, and with what antibiotics your foal has already been treated, and the length of time the foal improved before relapse. Tests may include:
Fecal analysis. Keep in mind that the ascarids may be doing considerable damage to your foal even before the worms are laying eggs – and in this case, the fecal analysis may be negative.
Physical examination. Your veterinarian will pay particular attention to the respiratory tract.
Complete blood count (CBC) and chemistry profile. With parasitic infections, certain white blood cell levels may be elevated. On the chemistry profile, there may be elevations in the globulins and fibrinogen, that reflect both an inflammatory and an immune response, and there may also be elevations in the liver enzymes, reflecting the pathway of the parasite through the liver.
Endoscopic exam of respiratory system.
Chest x-ray. This will show signs of a bronchopneumonia – inflammation of the airways and air sacs.
Transtracheal aspirate. Fluid may be aspirated from the lungs, especially if the foal has a history of relapsing after treatment with antibiotics. This aspirate is examined under the microscope (cytologic evaluation) and will also be cultured it to see if there is a concurrent bacterial infection.
A nasogastric tube may be passed if colic is suspected. In severe cases of ascarid impaction, worms may come out of the nasogastric tube.
Rectal examination. Foals are generally too small to perform a rectal examination, although a 7-month-old may be large enough for a veterinarian with a thin arm and small hand to palpate.
Ultrasound. If your foal is too small for rectal palpation, then your veterinarian may choose to examine the abdomen using ultrasound. The ultrasound will then let your veterinarian determine if there is distended small intestine, or a large amount of free fluid in the abdomen.
Abdominocentesis or belly tap. In this procedure, your veterinarian removes a small amount of fluid from around the intestines. Analysis of this fluid will help to determine if there has been any compromise to the intestinal wall. If there has been damage to the intestinal wall, then the amount of protein and cells in the fluid may increase.
The treatment for verminous pneumonia of foals is effective deworming. It is important to keep in mind that your foal probably also has a heavy load of parasites in the intestinal tract, and that these parasites are more likely to cause an obstruction if they are rapidly killed. This is more likely to happen with an effective dewormer such as ivermectin, or one that rapidly paralyzes worms, such as piperazine.
If your veterinarian suspects that your foal has a heavy worm burden, then he will often choose to deworm first with a less effective dewormer, to induce a slow kill of worms, and follow up with a dewormer such as ivermectin. He will also often choose to give mineral oil via nasogastric tube prophylactically, in order to help any worm obstruction to pass more easily.
If the primary cause of pneumonia is a P.equorum infection, then the pneumonia should go away with deworming. If a secondary bacterial pneumonia is firmly entrenched in the lungs, then a course of antibiotics may also be necessary.
In some cases, treatment for ascarid impaction is surgical. It is important to discuss the pros and cons of surgery with your veterinarian. Intestinal surgery in foals is more fraught with complications and difficulties in foals than it is in older horses. Foals are more apt to develop adhesions after intestinal surgery – this refers to the propensity of foal intestines to stick permanently to each other after they have been handled in surgery. Adhesions can often result in further signs of colic, as they cause the intestines to kink and effectively create an obstruction. Intestinal surgery is usually quite expensive as well.
It is important to notify your veterinarian immediately if you see any signs of colic in your foal. Early treatment may be able to ward off a colic surgery. Monitor your foal carefully for any signs of colic after deworming – your veterinarian should be notified immediately if you see any such signs.
Follow your veterinarian's instructions carefully if your foal is being given antibiotics. It is important to administer the full course of antibiotics even if the signs of pneumonia are gone. Monitor your foal for any continuing signs of pneumonia – especially nasal discharge, fever or cough.
Deworm your foal regularly, but always under the supervision of your veterinarian. If you begin to deworm your foal no later than every 4 to 6 weeks, then you will break the ascarid worm cycle.
If your foal is 3 months old or older, it is especially important to deworm under a veterinarian's supervision. There could be an ascarid impaction lurking that could result in catastrophic colic for your foal.