Prevention and Treatment of Respiratory Infections in Horses

Respiratory infections are the most common infectious diseases of horses. The acute infection in horses can sideline your horse anywhere from a week to a month. Worse yet, complications can have even more serious and long-lasting effects for your horse
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Respiratory infections are the most common infectious diseases of horses. The acute infection in horses can sideline your horse anywhere from a week to a month. Worse yet, complications can have even more serious and long-lasting effects for your horse

"No hoof, no horse" is a familiar saying, but "no lungs, no horse" is equally true. Respiratory infections are the most common infectious diseases of horses. The acute infection in horses can sideline your horse anywhere from a week to a month. Worse yet, complications can have even more serious and long-lasting effects for your horse.

The symptoms of respiratory-tract infection are hard to miss, and are the same for horses as they are for you. These include:

• Runny nose/nasal discharge-clear to yellow or white
• Often runny eyes or eye inflammation
• Cough-from dry to very moist
• Fever
• Depression/lethargy (seems sick)
• Poor appetite (both from feeling ill and throat pain)
• Changes in breathing pattern (normal respiratory rate is 6 to 8 breaths per minute)

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Respiratory Tract Invaders

There are several primary causes of respiratory tract infections. Identifying what's at the root of the horse's problem will make it faster and easier to get him into recovery and minimize the chance of any lasting damage. Here are some of the immediate considerations.

Bacteria: Strangles is the most well known bacterial respiratory tract infection. It usually remains confined to the upper portions of the respiratory tract (throat and local lymph nodes), but can sometimes also involve the lungs. At least 10% of strangles cases will end up with chronic infections in the guttural pouches.

A wide variety of bacteria can infect the lungs and cause pneumonia. In otherwise healthy adults, this usually occurs after the lung has been irritated by a virus infection, or in horses with weak lungs because of chronic allergic disease. Heavy exercise and shipping are also risk factors for developing bacterial pneumonia (and viral infections), because they cause a temporary weakening of the immune system. Both foals and aged horses, which have weaker immune systems, may be more susceptible to bacterial invasion of the lungs.

All-Too-Common Cold

  • Differentiating the cause of a respiratory infection (viral, bacterial, fungal, parasitic) will make it easier to treat.
  • Look for symptoms like those you'd see in a human: lethargy, runny nose, cough, fever, and loss of appetite.
  • Separate your sick horse from the rest of the herd as soon as you notice symptoms.
  • Keep an eye on other horses that have been exposed to the sick horse.
  • Avoid treating your horse with human cough and cold remedies.
  • Talk to your veterinarian about vaccinating your horse against several common causes of equine respiratory infections.

Viral: Myxoviruses cause the most uniformly severe viral infection in horses-influenza. As in people, influenza typically causes higher fevers and more lung damage, and has many potential complications. Horses are also usually sick for much longer with influenza virus than other viruses. Two to four weeks is not uncommon, sometimes even longer.

While flu takes the honors for severity, herpes virus in the form of rhinopneumonitis wins hands-down for how widespread it is. Once infected, the virus remains with the horse for life. Foals and aged horses are the most likely to have symptoms, which range from a slight snotty nose to a cold-like illness with fever and cough.

Once the immune system gets on top of the infection, the antibody response forces the virus to retreat to inside white blood cells in the lymphatic system. It avoids complete destruction by constantly mutating, but this mechanism also keeps the immune system constantly activated and on its trail.

Eventually, the horse and low levels of the herpes virus come to coexist-although stress or another infection may temporarily weaken the control the immune system has over it. When this happens, the horse may again show symptoms of respiratory disease or, at the least, will begin to shed the virus, exposing other horses to the disease even if he is not showing symptoms himself. Herpes virus can also invade other organs.

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Other Viruses
: Picorna, parainfluenza, corona, and adenoviruses can all cause respiratory disease in other species and are occasionally a problem for horses, especially foals. The symptoms are basically the same as for rhinopneumonitis. Equine viral arteritis is caused by yet another type of virus, the pestivirus. It is best known for causing abortion and severe leg/belly edema but may also cause respiratory symptoms.

Fungal: Fungal infections of the respiratory system are not as common as bacterial or viral, but they can occur. Horses on antibiotics for bacterial infections are more susceptible to fungal problems. Fungi may also take hold in the guttural pouches. The lungs of horses with chronic allergic lung problems may be more susceptible to fungal (and other) infections.

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Parasites: Larvae of roundworms migrate through the lungs. This can, and does, cause problems for foals as young as 2 months old. Viral or bacterial infections can occur on top of the damage from the parasites themselves. Between the ages of 1 and 4, the horse will build a sufficient immunity that this is no longer a problem, although aged horses with waning immune systems can again become susceptible.

Threadworms (strongyloides) can also be a problem for young horses. If these enter through the skin, they migrate through the lungs. Finally, although donkeys are more susceptible, horses can also become infested with a lungworm (dictyocaulus), a parasite that actually spends its adult life in the lungs, lays eggs that are coughed up and swallowed, then passed in the manure. With all of these parasites, it is the migration of the young larvae through the lung tissue that does the damage.

Complications
With adequate rest and good nursing, most respiratory infections resolve with no permanent damage. However, it's a mistake to take them lightly. Complications may occur in 10% or more of cases and include the following:

• Strangles infections can spread to internal organs, causing abscesses. An autoimmune reaction can also develop as a result of circulating bacteria and antibodies. This can cause severe leg swelling, which may cause the skin to actually break open and ooze, as well as kidney damage and laminitis.
• Both the strangles bacteria and respiratory viruses may invade the skeletal muscles, causing a very painful reaction with destruction of muscle cells. This can even cause death.
• Viruses may also seat themselves in the muscle of the heart. This is probably most common with influenza. Rhythm disturbances can result. The risk of heart involvement is one reason why horses with influenza should always be given a long rest period.
• The rhinopneumonitis/herpes viruses can also cause abortion or neurological disease.
• Damage to the lung from one type of infection, for example parasites or viruses, weakens the ability of the lung to resist other infections. Bacterial problems commonly develop on top of the original problem. Treating bacterial pneumonia with antibiotics to kill the disease-causing organisms also wipes out the normally present harmless ones that help keep fungi from growing there.

Treatments & Nursing
We all have memories of staying home from school with colds or flu when we were kids and the way our moms would take care of us. The basics of caring for a horse with a respiratory infection are very much the same.

Monitoring. As your horse's primary nurse, an important part of your job is monitoring. Record your horse's attitude, appetite, water consumption, temperature, and breathing rate twice a day.

The normal respiratory rate for horses is six to eight breaths per minute. Also watch for signs of shallow breathing or shortness of breath if moved (which also may induce coughing). Horses with pain in their chest will stand with their elbows turned outward and have very short, shallow breaths.

Also write down any changes in the character or intensity of a cough, changes in nasal discharge, leg swelling, and changes in urine or manure output.

By making yourself pay attention to these things, you'll notice changes early and can alert your vet.

Allergies, Infections, and the Environment

Although we tend to place respiratory problems into neatly separated categories of allergic (heaves, COPD), environmental irritants, and infections, the truth is that there is considerable overlap.

Studies have linked exposure to environmental irritants from bedding to both respiratory infections and inflammatory/allergic lung disease in stabled horses. Basically, anything that irritates the respiratory tract puts it at higher risk for all of these problems-including many irritants and even heavy exercise.

The respiratory tract is lined with a rich local immune system that keeps watch below the upper layers. When the system is healthy, there is a fine layer of mucus sitting on top of the respiratory lining cells. In the lungs, there are also special cells equipped with waving arms called cilia that sweep mucus, dead cells, organisms, small dirt particles, as well as plant particles, out of the organs. These layers prevent organisms from getting into the deeper tissues and keep the immune system cells from being constantly bombarded.

If an infection or irritation breaks down these outer barriers, the alarm bells go off in the immune system cells, which mount an immediate inflammatory response and, later, an antibody response. These antibodies allow the lungs to react more quickly and efficiently to infections with the same type of organisms. However, they can also cause allergic lung disease if an allergen happens to get through during the time of an infection. Conversely, the lung damage caused by allergies also weakens the outer defenses against infections.

Comfort care. Obviously you won't be riding this horse. He also needs to be protected from the antics or bullying of other horses. If the weather is nice, you can keep the horse in a paddock, but he should be protected from extremes of temperature. Keep him dry and do what you must to prevent chills.

If you need to keep the horse in a stall, it is very important that the barn be well ventilated. The horse can be protected from direct drafts, but the barn should not be closed up too tight. It's far better for the air temperature to be low but the air circulating freely, since this prevents the buildup of both infectious organisms and respiratory irritants. Paper- and wood-based bedding is preferable to straw.

Use common sense with blanketing and cooling. If the horse is shivering or the forecast calls for a sharp dip in temperatures overnight, apply a blanket. If the horse is sweating or blowing in summertime heat and has a fever, cool him down. Remember, too, that the horse may go from feeling feverish to feeling chilled, just like we do. In short, pay attention.

Take your cues from the horse with regards to how much pampering/hovering he wants. Just like people, some sick horses are comforted by a lot of attention, while others are irritated by it. It's no reflection on you how the horse reacts. Just respect his reactions and act accordingly.

Diet. As you know yourself, when you're sick, you don't always have much of an appetite. To make matters worse, throat inflammation often makes swallowing painful. The best, and most appealing, food for a sick horse is grass. The high moisture level helps keep him hydrated and makes it easier to swallow. It's also an excellent source of natural vitamin E, vitamin C, and antioxidant omega-3 fatty acids.

While grazing fresh grass isn't always an option-especially now that we're experiencing winter in many parts of the country-making meals wetter and softer is. Pelleted feeds can be soaked to a mash or soup consistency. Soaking hay for 20 to 30 minutes both softens it and removes surface dust/dirt. Grains can be mixed into some bran mash or beet pulp to make them go down easier. Don't panic if your horse's appetite is off, but do try to keep a fairly accurate record of how much the horse does actually eat. If appetite suppression is severe despite your best efforts, let your veterinarian know.

"Drink plenty of fluids" holds true for horses with respiratory infections, too. Make sure the horse has access to plenty of fresh water. If the horse is eating hay well, your target water consumption is at least 8 to 10 gallons a day. If the horse is on grass or not eating much hay, he should drink at least 4 to 5 gallons a day. Horses prefer water that is cool to tepid. Avoid extremes of both heat and cold. If the horse is not drinking well, alert your veterinarian.

Medications. The decision about using medications should be left to your veterinarian. Anti-inflammatories like phenylbutazone or flunixin meglumine (Banamine) are often recommended to control high fever and help reduce any throat pain. Antibiotics are not necessarily a must, but many vets will use them if symptoms last longer than a few days, if the nasal discharge changes from clear to white or colored, or if the lungs are obviously involved.

It's never a good idea to use human nonprescription cough syrups or cold remedies in horses unless you have the specific approval of your veterinarian. Decongestants are usually avoided in favor of keeping the secretions moving and thinned. Many decongestants can also cause excitement. Many also contain antihistamines, some of which are used in and safe for horses, others not. Even approved antihistamines may cause adverse reactions in individual horses, including either excitement or depression. Prescription human cough medications usually contain narcotics, which cause excitement in horses.

There is a wide assortment of nonprescription cough syrups and powdered supplements for horses. With a respiratory infection, the liquids are most appropriate. They usually are based on menthol and other aromatic oils. These help soothe the throat and also thin mucus. Expectorant ingredients might include iodides and glyceryl guiacolate. They offer some temporary cough relief but are actually most useful in keeping the mucus thinned and moving out freely.

Speaking of menthol and aromatic oils, rubs like Vicks Vaporub can be very useful. Apply liberally to the nostrils and throatlatch several times a day.

Preventing Spread of Infections

In an ideal situation, any horse new to the ranch/farm would be isolated for at least two weeks, and any sick horse would immediately be put in isolation with no contact with other horses. In reality, this is rarely possible, and even if it were, there's a good chance that the sick horse had a fever and was shedding viruses or bacteria before he even developed the red-flag warning signs of nasal discharge or cough.

If the worst case scenario happens and a horse in your barn comes down with a respiratory illness, involve your vet immediately. Some sanitation measures and precautions will depend on exactly what the problem is. In general:

• Horses turned out with, or in the stalls closest to, the sick horse are those at highest risk of also becoming sick.
• If facilities allow, separate horses into three groups-obviously ill, close contacts, little or no contact with the sick horse.
• Start taking temperatures of all horses twice a day. Horses that spike a fever (your vet will tell you how high) should be moved to the sick horse group immediately. Fever almost always occurs in advance of symptoms.
• Horses that show no fever or symptoms after the usual incubation period (again, your vet is your source of detailed information) can be moved to the healthy horse/no contact group.
• Turnout paddocks used by any sick horse should not be used for a healthy one until your vet gives you the okay. This will depend on the type of organism.
• Use separate tubs, buckets, halters, brushes, mucking equipment for infected horses.
• Use a disinfectant shoe/boot dip (available in farm stores) and a hand sanitizer after any contact with a sick horse or equipment used with a sick horse.
• Coveralls and head covering should be worn when working on sick horses or in their stalls. Leave these in the area of the sick horses.

Adequate Rest. Just like a human patient, the horse with a respiratory infection needs a comfortable place to rest. Equally important is not to try to put the horse back on a full work or social schedule too soon. You need to give his tissues time to completely heal. Wait at least a week after coughing has stopped and nasal discharge dried up before you turn the horse out with other horses or resume riding, two weeks for influenza. Gradually build back up to your previous work schedule.

Prevention
The single most important protection against respiratory infections is promoting a strong immune system in your horse through good management. Adequate intake of quality protein, vitamin C, vitamin E, and the trace minerals zinc, copper, and selenium (all three of those are commonly deficient) is critical.

Stresses such as shipping and heavy exercise are known to compromise the immune system, so always give the horse one or two days of rest after these. Deworm as needed to avoid having parasites sap the immune system.

Also very important is to do all you can to minimize exposure. High risk groups such as young horses, aged horses, and debilitated horses, should not be mixed with horses that do a lot of traveling. They may be harboring infectious organisms even if they are not showing symptoms themselves.

New horses should be isolated for two weeks whenever possible. If that's not possible, at least monitor their temperature twice daily. Be careful when away from home. Do not allow nose-to-nose contact with strange horses. Do not allow your horse to graze in areas where horses are heavily concentrated. Disinfect the walls and inner bars/doors/ledges of stalls at fair or show grounds before putting your horse in them, or put a muzzle on your horse if he's only going to be in there a short time. Use your own water and feed buckets. Never use communal watering troughs away from home. Don't allow your horse to touch, sniff, or lick walls and other surfaces at vet clinics, in commercial vans, or anywhere else away from home.

Vaccines are available for strangles, rhinopneumonitis, and influenza. But the bottom line is that none of them are 100% effective. They cannot substitute for a sound immune system and common sense in avoiding exposure. Speak with your vet regarding what vaccinations might be appropriate for your horse, a decision that is based to a large extent on risk of exposure.