Colds and Coughs
Dr Peter Gillespie. BVSc MACVS.
Viral respiratory disease is the most common reason for coughs and colds and for poor performance in competition horses in New Zealand.
The early recognition of infections is important to ensure recovery is quick and uncomplicated.
The following two articles entitled "The Truth About Herpes And Horses" and "The Coughing Horse" provide an insight into the special characteristics of the Equine Herpes Viruses, especially the symptoms and the complications associated with infections. Other causes of respiratory problems are also discussed.
There are no magical cures for these viral infections. Treatment is based on a common sense approach outlined in what is known as the ‘Four Point Treatment Plan’
The Truth About Herpes & Horses
How often do we hear horse owners talk about ‘a virus’ being responsible for their horse’s poor performance during a race or an event. Are they accurate in their assessment or is the blame being laid unfairly?
There are many reasons for the so-called 'poor performance’. Musculo-skeletal injuries are by far the most common cause but viral respiratory infections justify their share of the blame.
The ‘viruses’ horse-owners usually refer to are members of the family of Equine Herpes Viruses that infect the respiratory system of horses. There are eight members of the family in total; five affect horses while the remaining three affect donkeys.
THE EQUINE HERPES VIRUS FAMILY
Abortions in late pregnancy
EHV4 is the most common herpes infection in New Zealand. Serological tests carried out on a cross section of the national horse population have shown it to be endemic. EHV1 is also prevalent though not as widespread as EHV4.
The respiratory disease caused by each is indistinguishable from the other so both viruses can be considered together.
Spread of the virus between horses is via nasal discharge or aerosol transfer. Contact between horses in either a herd or stable situation leads to cross infection. Upon entry to the nasal passages and throat, the virus incubates for between 5 to 7 days. During this time it multiplies and the symptoms associated with the infection begin to appear.
SYMPTOMS ASSOCIATED WITH EHV1 AND EHV4 RESPIRATORY INFECTIONS.
Fever – temperature increases above 38C
Nasal Discharge – initially clear and watery; may change to thick yellow muco-pus.
Mild conjunctivitis – discharge from the eyes.
Coughing – not always a feature.
Loss of appetite.
In some cases the infection is contained within the respiratory tract. While in others, the virus may spread throughout the body.
A common feature of both EHV1 and EHV4 infections is the development of a secondary bacterial infection after the initial viral phase. When this occurs, both the disease process and the recovery period are prolonged.
Equine Herpes Virus has the ability to establish a dormant infection in horses, in fact the majority of horses carry EHV4 in this form.
There are no symptoms associated with a dormant infection but when the horse is subjected to any form of stress, the infection can surface. Cases like this are common in practice – horses suddenly develop a stress – induced viral infection when there is no history of contact with infected horses. Usually these type of infections are associated with no symptoms other than the horse being slightly ‘off colour’ and performing below expectations.
The ability to exist in a dormant form is also the reason why an infected horse cannot develop a good post-infection immunity.
EHV has gained the reputation as the "Immune System Escape Artist". The dormant virus is able to move from cell to cell within the body thereby avoiding recognition by the body's immune defence mechanisms.
Because of the existence of the dormant form of the virus and the horse’s poor immune response, a horse can become reinfected after only a few months, a situation that can be both confusing and frustrating to owners and trainers.
There are four aspects to consider in the treatment of EHV infections.
Avoid undue stress
Treat the symptoms
Maximise immune competence
Minimise the chance of reinfection
The avoidance of stress is an important part of the treatment plan. It means total rest. In cases where there are no secondary bacterial complications, two weeks is usually adequate. When a course of antibiotic treatment is necessary to treat a secondary bacterial infection, three to four weeks rest may be necessary.
There are several products on the market that offer relief from the symptoms of coughing, nasal discharge and loss of appetite. They are all based on ammonium chloride and potassium iodide formulations. It is important to understand that these products do not represent ‘magical cures’. Used sensibly as part of the Four Point Treatment Plan, they definitely have a place in the therapeutic approach to viral infections.
The injectable immune stimulants such as Eqstim® are used to increase the activity of certain immune cells to fight infections. The results in cases of viral respiratory infections have been disappointing.
After the initial four week, two injection course, six monthly boosters are necessary to maintain an effective level of immunity. It is important to understand that even with vaccination, protection is incomplete. If re-infection does occur, the effect on the horse however is less severe and recovery is a lot quicker.
A vaccine is available in New Zealand that combines protection against both EHV1 and EHV4. Its use has become widespread because it represents the best method for the treatment and prevention of EHV infections.
Cases that are complicated by secondary bacterial infections usually require antibiotic treatment hence a veterinary consultation will be necessary.
To minimise the chances of re-infection, good stable hygiene is important. Equipment used on infected horses should be disinfected with an effective virus killing disinfectant such as Virkon® or Halamid® before being used on other horses.
In conclusion, the important point to remember with EHV infections is to diagnose the condition sooner rather than later and then avoid placing undue stress on the horse. If this is done, complications will be fewer, recovery quicker and the cost of treatment less.
The Coughing Horse
What should I do about my horse’s cough? This is a question I am frequently asked by concerned owners in my practice.
There is no straightforward answer to this question because a cough can be associated with a number of different conditions, some minor, others more serious.
We should start by defining what a cough is. Simply it is the sudden, noisy expulsion of air from the lungs allowing mucus and other material to be cleared from the airways. In horses it is an involuntary reflex, initiated by sensory cells located in the lining of the trachea and bronchi. These sensory cells are stimulated by irritation, hence they are often referred to as irritant receptors. Once stimulated, the receptors send messages along nerve pathways to the cough centre in the brain, which controls the muscles of the larynx and diaphragm as well as the intercostal and abdominal muscles.
Because the horse is an athletic animal, its lungs are extremely large. The volume of air inhaled with each breath is in the order of 6 to 8 litres for an adult horse. The trachea is also a large structure, extending the length of the neck from the larynx to past the first pair of ribs where it divides into the left and right bronchi. Lining the trachea and bronchi (and the smaller lower airways) is a membrane made up of microscopic, mucus producing cells with hair like projections called cilia. This muco-cilliary arrangement means the lining of the airway is always kept moist by a thin layer of mucus which is continuously being pushed forwards by the wave like motion of the cilia.
There are numerous causes of irritation and hence reasons why a horse starts coughing.
Occasionally a foreign body such as a stalky piece of hay or straw finds its way into the larynx or trachea. The horse usually distressed but the forcefulness of the cough is usually enough to dislodge the object.
This is probably the major cause of coughing in horses. There are several respiratory viruses that can affect horses but in New Zealand the most common are the two members of the Herpes family, known simply as Equine Herpes 1 (EHV1) and Equine Herpes 4 (EHV4). It is important to note that coughing is not always a feature of EHV infections, some horses show few outward signs other than a slight nasal discharge and a loss of appetite. Other respiratory viruses that can cause coughing include Rhinovirus and Equine Influenza.
These often follow a viral infection, in fact the two often overlap. Bacterial infections are usually associated with a thick nasal discharge and a productive cough. The infection may be isolated to the airways, or in more serious cases the infection may develop into pneumonia with involvement of the lung tissue. Two serious bacterial infections that affect young horses in particular are Strangles and Rhodococcus Bronchopneumonia. Bacterial infections can involve the guttural pouches causing a persistent cough and nasal discharge that does not respond well to antibiotic medication.
These are a common cause of coughing in horses. They are initiated by the inhalation of fungal spores or dust particles and result in a chronic inflammatory reaction in the lower airways. The cough is usually chronic due to the constriction of these smaller airways.
Lungworm can cause coughing in horses that are grazed with donkeys. The small lungworms live in the lower airways and are a source of irritation. Lungworms only grow to maturity and produce eggs when the donkey is their final host, hence horses with lungworm cannot infect other horses.
Roundworm infections can cause coughing in foals and weanlings due to the larvae migrating through the lung tissue as part of their life cycle.
EXERCISE INDUCED PULMONARY HAEMORRHAGE
Also commonly referred to as "bleeding from the lungs", this is a cause of coughing mainly in galloping horses. It has always been known that chronic lower airway infections play a significant part in the onset of this problem but new research has suggested that the transmission of shock waves from the forelegs through the chest wall and off the ribcage onto the lungs during galloping, also plays an important part.
Any horse that starts coughing soon after intense exercise should be scoped to determine whether there is blood in the trachea.
UPPER RESPIRATORY TRACT PROBLEMS
There are several clinical entities involving abnormal function of the upper respiratory tract that can cause coughing. The most common of these are Epiglottic Entrapment and Laryngeal Hemiplegia, both involving the larynx. Horses with these problems usually show other signs besides a cough, in particular abnormal breathing noises during exercise.
To enable effective treatment to be carried out, it is important that the cause of the cough be identified accurately. This involves a detailed veterinary examination beginning with an assessment of the horse's general health.
The presence of other coughing horses in the same stable or paddock maybe significant. Another important fact to consider at this stage is whether the cough is related to feeding or to exercise.
Listening to the chest with a stethoscope while the horse is standing quietly may reveal abnormal breathing sounds but these can be difficult to detect using this method. Examination of the throat, trachea and bronchi is possible using a flexible fibre-optic endoscope. This is a valuable aid to diagnosis especially when carried out immediately after exercise as it allows direct assessment of all these structures.
Another diagnostic test that can be carried out is a tracheal wash. A fine tube is passed through the endoscope into the bronchi and between 50 to 100mls of sterile saline is injected through the tube and allowed to mix with any fluid and cellular debris in the airways. The mixture is then drawn back into the tubing and sent away for laboratory analysis. The presence of bacteria, fungal spores, red blood cells, or inflammatory cells can be assessed.
Routine blood test can be useful to indicate the presence of infections (white cell count) and inflammation (fibrinogen) although these indicators are not specific for the respiratory system.
Once a diagnosis has been reached, the appropriate treatment programme can be started. Treatment can involve any of three options;
Good management practices that can be carried out routinely to help avoid coughing related problems include;
Avoid stabling in poorly ventilated stables. Muck out stables regularly. Ammonia from urine soaked bedding is a respiratory irritant.
Avoid feeding dusty or mouldy hay. Hay is best soaked for 15 minutes before feeding.
Feed low to the ground to allow natural drainage of the airways by muco-cilliary clearance.
Vaccinate all horses against EHV1 & EHV4 infections. Vaccines do not always prevent infections but they certainly reduce their severity.
Worm regularly, especially young horses and horses grazing with donkeys.
Keep horses warm, especially after exercising in cold or wet conditions.
Care needs to be taken during long float trips as this is when horses are most susceptible to respiratory infections.
The combined affects of close confinement, with other horses, increased body temperature, poor ventilation and the head being raised for prolonged periods, are all significant contributing factors.
There are several products available that can be useful in helping to treat and in some cases prevent coughs and colds. One of these is NASAL-EZE, an inhalation product with antibacterial, antifungal and nasal clearing properties. It can be used before transportation and anytime a horse is exposed to dusty or fungal spore conditions.
Products like VIREX Respiratory Relief are useful expectorants once a horse develops the symptoms of a cough or nasal discharge. They work by reducing the viscosity and enhancing the muco-cilliary clearance of the muco-pus that accumulates in the airways. They do not prevent a horse from becoming infected and they do not kill the viruses or bacteria that cause these problems. Despite this, their use is warranted in conjunction with the Four Point Treatment Plan. Following this plan gives the best chance at a rapid, uncomplicated recovery.
THE FOUR POINT TREATMENT PLAN
Avoid Undue Stress
Treat the Symptoms
Maximise Immune Competence
Minimise the Chance of Re-infection
Virex Respiratory Relief
Virex Respiratory Relief is 100% natural therapeutic product for horses to aid in the relief of symptoms associated with respiratory infections and irritations.
Viral respiratory infections are extremely common in horses. They are a major cause of respiratory disease and poor performance. They cause irritation and inflammation of the upper and lower respiratory tract, leading to the symptoms of nasal discharge, persistent cough and louder than normal respiration during exercise (‘thick winded").
Early recognition and treatment is important to ensure a fast, uncomplicated recovery. Two important points in the treatment program are the avoidance of stress (which means keeping the horse rested and warm) and the alleviation of the symptoms. This is where Virex plays an important part.
Virex works in 3 ways:
By reducing the viscosity of the mucus that blocks the airways.
As an expectorant.
As an anti-inflammatory.
The Liquorice Extract contains the natural anti-inflammatory Glycyrrhetinic. Acid which soothes the inflamed airways thereby reducing the frequency and intensity of coughing.
The Potassium Iodide and Anise Oil are both expectorants, while the ammonium chloride reduces the viscosity of the thick mucus secretions, allowing them to be cleared more effectively by muco-cilliary clearance.
Virex can also be used when other factors such as dust, allergies or bacterial infections cause irritation of the respiratory tract.
Virex contains no prohibited substances so it can be used before and during competition. It is palatable and easy to administer using the oral dosing syringe.
Virex is available in one and two litre sizes.
Available from all leading equestrian
and veterinary outlets,
or freephone 0800 864 000.
Nasal-Eze is a therapeutic product for horses where upper respiratory tract infections and irritations are a problem. It possesses antibacterial, antifungal and nasal clearing properties.
Nasal-Eze is a 100% natural product. It contains menthol and 4 volatile oils in an anhydrous base. The menthol gives a cooling sensation to irritated nasal membranes and also helps to clear the airways and bronchial passages.
Eucalyptus oil is a useful expectorant, increasing the amount of respiratory secretions while at the same time having an antibacterial effect.
Tea tree oil is also an antibacterial agent but has the added benefit of an antifungal action. It is able to maintain this activity in the presence of nasal secretions. It also has an anti-inflammatory action on the nasal membranes.
Oil of thyme has a significant antifungal effect due to its thymol content.
Pine oil possesses mild antiseptic properties.
These oils are formulated in a non-irritant anhydrous base that makes application to the inner nostril, easy and safe.
A liberal amount should be applied twice daily to the inside of each nostril.
It is also useful whenever horses are susceptible to respiratory infections or irritations. It should be used before transportation and anytime a horse is exposed to dusty or fungal spore conditions.
Nasal-Eze is available in 250gm and 500gm sizes.