What are Vaccinations?
Prevention is ultimately better than cure and vaccinations play an important role in preventing disease in horses. Vaccinations are used to:
• reduce the risk of a disease outbreak occurring
• reduce the spread of disease in the event of an outbreak
• decrease the severity of illness in affected animals. Vaccinations are available for a number of diseases that affect horses in the UK.
Some of these diseases can be fatal. The most important vaccinations that are applicable to all horses are those for tetanus and equine influenza. Vaccination against other diseases may only be appropriate for horses that travel overseas or are used for breeding. The principle of all vaccinations is to initiate a course of injections followed by booster doses at specific intervals, the frequency of which depends on the type of vaccine and the immunity provided.
The cost of routine vaccinations for tetanus and influenza is not covered by insurance policies. However, vaccinations are relatively inexpensive given the expense involved in keeping horses and they can save lives as well as avoiding large veterinary bills.
Horses are the most susceptible of all domestic animals to tetanus due to the environment they live in and the frequency with which they are injured.
Tetanus is a disease caused by the bacterium Clostridium tetani which is found in the soil. The bacterium also lives in the horse’s gut which presents no risk to the horse as long as the gut remains healthy. The bacterium can be passed out of the gut and deposited within the horse’s faeces. Tetanus becomes a problem when the bacterium enters the body via a wound. Even the smallest wounds can allow the bacterium to enter the bloodstream, for example, a common site of infection is a puncture wound to the sole of the hoof. Infection can also occur via the intestines if a horse eats contaminated soil or faeces. Newborn foals can be infected by the bacterium via the navel (umbilicus).
Wounds offer the bacterium a perfect environment for survival as it does not require oxygen, enabling the bacteria to multiply anaerobically in the damaged tissues at a rapid rate. A poisonous neurotoxin is produced which then targets the nervous system.
The incubation period of tetanus is between 7-21 days. The nerves controlling the muscles of the body are attacked by the toxin causing the initial signs of the disease followed by a progressive deterioration.
The clinical signs include:
• Stiffness in the head and limbs
• Progressively worse muscular spasms in the limbs with the horse reluctant to move
• Muscle spasms in the head and neck with the horse not able to eat or chew properly (hence tetanus may also be referred to as ‘lockjaw’)
• Flaring of the nostrils
• The horse exhibits a startled, wide-eyed expression due to facial muscle spasms.
• Erect ears
• The tail is held out straight
• Prolapse of the third eyelid (a membrane positioned at the inner corner starts to extend across the eye)
• The animal’s reflex reactions to sudden movements, light or noise become hypersensitive
• Exacerbated spasms and convulsions will cause the horse to collapse in the later stages of the disease followed by death due to respiratory failure from paralysis of the breathing muscles.
Once clinical signs of an infection are exhibited by the horse urgent veterinary attention is essential. Approximately 90 percent of horses that become infected with tetanus will die. If the disease is diagnosed in the early stages, treatment is aimed at destroying the bacteria to prevent any further production of the toxin. If the horse is able to eat, food should be positioned at a height which is easier for them to consume and help encourage the horse to continue eating. In advanced stages of the disease the chances of recovery will be minimal, and euthanasia is often advised to prevent any further suffering.
Prevention Tetanus can be easily prevented by establishing and maintaining an effective vaccination programme. The initial course consists of two primary injections four to six weeks apart. The first booster injection must be administered within 12 months of the second primary injection. Subsequent boosters are normally administered every two years – but ensure you check with your vet as products can vary. Tetanus vaccines often give rise to a reaction (swelling) that will disperse in a few days. If you have any concerns, contact your vet.
Vaccinated pregnant mares should be provided with a tetanus booster four to six weeks pre-foaling. This increases the antibodies available in the colostrum (first milk), which will provide the foal with a degree of maternal protection for approximately 6-12 weeks. To supplement this, newborn foals can be given.
A tetanus antitoxin soon after birth to provide temporary cover for three to four weeks. A regular vaccination programme can be initiated from approximately three to four months old. Further advice can be sought from your veterinary surgeon.
Unvaccinated horses that sustain a wound will need a tetanus antitoxin injection to provide temporary protection. The antitoxin will last three weeks, after which time the horse is no longer protected. Horse owners who do not vaccinate their horses should not rely on the antitoxin to provide protection as cuts that go unnoticed could become the site of infection. Puncture wounds may be difficult to spot yet provide a perfect environment for Clostridium tetani to thrive. In addition to vaccination, good hygiene and management will help in minimising the risk of infection. Regular inspection of your horse for cuts and grazes, particularly puncture wounds to the feet, will assist in detecting potential sites where tetanus may enter. Any wounds should be cleaned immediately to remove dirt and soil and a vet called if necessary. Yards, stables and paddocks should be kept clean, safe and clear of any items that may cause injury such as barbed wire, corrugated sheets or nails.
Equine Influenza, most commonly referred to as flu, is a highly contagious viral disease of the respiratory tract. The virus can be spread via the airborne route by an infected horse, via direct contact or indirectly by handlers. The incubation period for the disease is between one to five days. This is why an influenza outbreak can quickly spread in unvaccinated horses.
The clinical signs of influenza include:
• The sudden onset of a dry, harsh cough which can continue for two to three weeks and potentially persist for longer
• A rise in temperature for one to three days of up to 41°C (106°F) often goes undetected until the horse begins to cough
• A nasal discharge that is initially clear but becomes thick and purulent
• Loss of appetite
• Lethargy The disease can debilitate a horse, leaving it susceptible to secondary infections such as bronchitis and pneumonia. Such infections are particularly worrying in young foals or elderly animals and those with a pre-existing respiratory disorder.
Permanent lung damage is a risk to unvaccinated horses resulting in the potential loss of their previous athletic ability.
It is important to consult your vet, and in cases where flu is suspected, it is likely a swab will be taken to confirm the diagnosis. There is no direct treatment that can be used against the virus. Instead, like people, horses will require rest in order to recuperate. The environment the horse is kept in should be as dust-free as possible to ensure the respiratory system is not further compromised.
It can take several weeks for the horse to recover and return to full health. It is important to seek your vet’s advice before returning your horse to work. Prevention Vaccination remains an important practice in efforts to prevent an outbreak of flu; in an unvaccinated population there will be an almost 100 percent infection rate. Estimates suggest that less than 40 percent of the equine population in the UK are vaccinated against influenza. Flu is an adaptive virus, and has evolved to gradually alter through a process known as antigenic drift. Your vet will be best placed to advise on the most current vaccine available.
The vaccination programme begins with a series of injections administered over the first year, which is then continued by annual boosters.
First Vaccination – Start
Second primary Vaccination First booster injection – 4 to 6 weeks later
Annual booster – Six months later Within 365 days of the previous injection
Annual booster vaccinations are required to maintain cover against the virus. It is imperative not to allow the booster to lapse because even being one day late can result in the initial vaccination programme having to be restarted, which will be costly for the owner.
In addition, there is also the option of having a combined vaccine of tetanus and equine influenza; speak to your vet for further details.
Upon the vet’s arrival to vaccinate the horse ensure you have the horse’s passport available so the injection can be correctly recorded. Vaccination and Rules for Competition If you decide to compete with your horse it is important to check with the appropriate governing body’s rulebook on their vaccination requirements. If your horse does not meet their requirements it is likely that you will not be allowed to compete.
EVA – Equine Viral Arteritis
The variety and severity of clinical signs of EVA vary widely. Infection may be obvious but there may be no signs at all. Even when there are no signs, infection can still be transmitted and stallions might still ‘shed’ the virus, ie excrete it in their semen. These stallions are known as ‘shedders’ and pose a significant risk of disease transmission if undetected. In pregnant mares, abortion may occur. EVA may, occasionally, be fatal.
The main signs of EVA are fever, lethargy, depression, swelling of the lower legs, conjunctivitis (‘pink eye’), swelling around the eye socket, nasal discharge, ‘nettle rash’ and swelling of the scrotum and mammary gland.
Infection can be transmitted between horses in any of the following ways:
direct transmission during mating;
direct or indirect transmission during teasing;
artificially inseminating mares with semen from infected stallions or which has been contaminated during semen collection or processing. The virus can survive in chilled and frozen semen and is not affected by the antibiotics added;
contact with aborted fetuses or other products of parturition;
via the respiratory route (eg via droplets from coughing and snorting).
The shedder stallion is a very important source of the virus. On infection, the virus localises in his accessory sex glands and will be shed in his semen for several weeks, months or years – possibly even for life. The fertility of shedder stallions is not affected and they show no clinical signs but they can infect mares during mating, or through insemination with their semen. These mares may, in turn, infect other horses via the respiratory route.
The main ways of preventing EVA are vaccination, particularly for stallions and teasers, and the establishment of freedom from infection before breeding activities commence.
Establishing freedom from infection
This involves checking the disease status of breeding stock before commencing breeding activities each year. Veterinary surgeons should take blood samples from horses for testing in a laboratory to detect the antibodies that the horse generates in response to infection with the virus. The horse also generates antibodies in response to vaccination against EVA.
The laboratory detects both the presence and the level of antibodies in the blood (‘serological testing’).
If antibodies are not present (‘seronegative’), the horse is not infected and breeding activities may begin.
The presence of antibodies (‘seropositive’) may be the result of:
In mares, a rising level of antibody in two or more sequential samples indicates active infection and the mare should not be used for breeding activity. A stable or declining level indicates previous infection or vaccination and the mare can be used safely for breeding activity.
A stallion who is shedding virus in his semen is always seropositive, but a seropositive stallion is not necessarily a shedder. Therefore, if a stallion returns a seropositive result, it is important to establish whether he is a shedder before use for breeding activities.
Routine vaccination against EVA is particularly recommended for stallions and teasers. In the UK, routine vaccination of mares is not recommended, and emergency vaccination might only be considered in exceptional circumstances involving widespread disease outbreaks.
One vaccine, Equip Artervac (Zoetis), is available in the UK and the last available licensed batch of this vaccine expired on 26th November 2017. Due to unforeseen circumstances, Zoetis advises that it does not expect a new batch of vaccine to be available until sometime during 2018 and a precise date cannot currently be predicted. This will result in a supply gap and there is no satisfactory alternative vaccine to source and use.
This positive status cannot be differentiated from positive status caused by infection. It is essential, therefore, for breeding and export purposes, to be able to demonstrate that the horse is positive because of vaccination and not infection. This is done by blood testing before vaccination to show that the horse was previously seronegative and keeping a record of the test result, certified by a veterinary surgeon, preferably in the horse’s passport. The vaccine should not be administered until the blood test result is available.
Veterinary advice should be sought on the timing and administration of the vaccine. The current datasheet requirement for the only inactivated vaccine against EVA used in Europe presently is for 6 monthly (not annual) boosters.
All vaccinations (primary course and booster doses) must be recorded in the horse’s passport, by the veterinary surgeon who administered the vaccine. Details should include the date and place where the vaccine was given, and the name and batch number of the vaccine.
EHV -Herpes 1 and 4
Equine Herpesvirus – EHV
Equine herpesvirus is a common virus that occurs in horse populations worldwide. The two most common types are EHV-1, which causes respiratory disease in young horses, abortion in pregnant mares and paralysis in horses of all ages and types, and EHV-4, which usually only causes low-grade respiratory disease but can occasionally cause abortion.
Following first infection the majority of horses carry the virus as a latent (silent) infection that can reactivate at intervals throughout life. EHV-3 is a venereal disease that causes pox-like lesions on the penis of stallions and the vulva of mares (Equine Coital Exanthema) and EHV-5 is a virus that is currently associated with unusual sporadic cases of debilitating lung scarring (Equine Multinodular Pulmonary Fibrosis) in adult horses.
EHV abortion can occur from two weeks to several months following infection with the virus, reflecting either recent infection or recrudescence (re-activation) of latent infection in a carrier horse. Abortion usually occurs in late pregnancy (from eight months onwards) but can happen as early as four months.
Respiratory disease caused by EHV is most common in weaned foals and yearlings, often in autumn and winter. However, older horses can succumb and are more likely than younger ones to transmit the virus without showing clinical signs of infection. It is the continual cycling of EHV respiratory disease in young horses and the periodic reactivation of latent EHV in older horses that maintains the risk of EHV abortion in pregnant mares and EHV neurological disease in horses of all types and ages.
Although EHV-1 may cause outbreaks of abortion, particularly in non-vaccinated mares, EHV-4 has only been associated with single incidents and is not considered a risk for contagious abortions.
Occasionally, EHV-1 can cause paralysis, which ranges in severity from a mild incoordination of the hindlimbs to quadriplegia (total paralysis where the horse is unable to stand). The most important risk factors for this form of disease include animals greater than 5 years of age, season (autumn, winter and spring when animals are more likely to be stabled or UV light levels are low) and perhaps the strain of virus involved. However, although so-called ‘neurological’ strains have been identified, paralytic signs are seen with both these and ‘non-neurological’ strains, so this differentiation cannot be relied upon.
Therefore, characterising EHV-1 on the basis of the ‘neurological’ strain marker is not considered useful and control measures should be adopted consistently irrespective of the strain of EHV-1 involved. Clinically, the onset of paralysis may be sudden, with no prior clinical signs of respiratory disease and usually occurs in the second week following infection.
The above are different viruses but there is another prevalent reason you would advocate using isolation procedure and this is with Ringworm. It is a highly contagious disease and needs thought procedures put in place when it appears in a yard or establishment.
What is Ringworm?
Dermatophytosis, also known as ringworm, is one of the most common skin issues that affect horses. Higher incidents are seen more frequently in hot, humid climates but can be seen in colder, dryer climates. It can occur at any time of the year but more frequently seen in the warmer months. It has a unique appearance of circular lesions with a crusty layer of build-up and hair loss in the area. Ringworm is not caused by a worm but by a fungus. There are antifungal medications you can get from your veterinarian once a diagnosis is confirmed.
Prognosis of recovery is drawn out, but good. Ringworm can affect horses in any environment, any age, and at any place on the body. It is known by appearance of circular, crusty lesions located anywhere. Variable degrees of pain are seen with ringworm so treatment should be started as soon as possible to offer your horse relief.
Symptoms of Ringworm in Horses
Symptoms you may see in your horse include:
Ring-shaped lesion (although it can appear in other shapes too)
Round, bald patches
Affected skin dry and scaly
Size of lesions vary
Usually not associated with itchiness
There are 2 types of fungi that can cause ringworm in horses: Microsporum and Trichophyton. Both of these infect the skin and the hair. The incubation period is long compared to other organisms; it can be months from when the spore is deposited on your horse’s skin before symptoms may appear.
Causes of Ringworm in Horses
For ringworm to infect the skin, the skin has to be damaged or rubbed to allow the fungi to make it past the protective layer of skin. The fungus weakens the base of the hair shafts causing the hairs to break off. The fungi produce spores resistant to environmental conditions making them very difficult to get rid of.
They can remain in the area for months to years and cause re-infection of the same horse or others as well. Spores can survive in and on many type materials including in the stable and on fencing.
Diagnosis of Ringworm in Horses
While it can affect any aged horse, it is more commonly seen young horses under the age of 5. Older horses usually develop immunity to ringworm but infection can occur. Ringworm is not necessarily itchy or sore despite its scaly, thickened appearance. Lesions appear with a characteristic look of circular patches of hair loss and skin change. Lesions are most commonly seen where the tack rubs and at the saddle and girth areas, but also on the face. By physical examination alone, your veterinarian will have a good idea if your horse is suffering from ringworm or not.
However, for a definitive diagnosis, he/she may want to perform a DTM culture. Dermatophyte Test Medium (DTM) is a selective medium used to grow and isolate pathogenic deratopytic fungi, such as the ones that cause ringworm. The veterinarian will collect a sample from the suspected area on your horse and apply it to the culture. Cultivation of the fungi on the medium can take up to 14 days. If there is no growth after the allotted time, then it is considered negative for ringworm.
Treatment of Ringworm in Horses
There are multiple options for treating ringworm in horses. Your horse’s sex, breed, age, and pregnancy status will be considered by your veterinarian when she is choosing a course of treatment. Since the fungi do infect the skin, she may prescribe oral antibiotics. However, some antibiotics cannot be given to pregnant mares so other options may need to be considered. Treatment topically is beneficial since fungi also affect the superficial layer of skin and hair.
Medicated shampoo and sprays with antifungal medications in them are helpful. In some cases, a secondary bacterial infection will develop and will also need to be treated. Your horse’s environment should also be treated for ringworm. Disinfectants should be used in and around his stall and your stable. Be sure to also clean his tack and grooming kit and anything else you may use on him.
Ringworm can be spread by direct contact so you should keep your infected horse away from the others and an isolation procedure needs to be put into place. Also, if putting outside, keep him in an area he can be quarantined to.
Recovery of Ringworm in Horses
Ringworm is zoonotic, meaning you can contract it from your horse. When treating him and dealing with him in any manner, be sure to clean your personal protective equipment and employ appropriate hygiene habits. Getting rid of ringworm can be a long process but it is necessary for the health of you and your horse.
The lesions may take a while to heal even after it is no longer considered contagious. The skin has to clear and the hair has to regrow meaning it can take weeks to months. While it may not look pretty, just know your horse is on the mend and considered healthy.
The Complete BHS veterinary manual.
The BEF Guidelines, which was put together with the British Veterinary Association
HBLB codes of practice 2019
Article by Sam Goss BHSI/PCCHL5. MSc Coaching Science
Tel: 07875 311983