Strangles

To limit the spread of infection it is important to isolate a horse immediately at the first sign of illness; obtain a veterinary diagnosis if strangles is suspected; ascertain what other horses the infected horse has been in contact with and quarantine them for a week to 10 days.

Strangles is one of those diseases that can spread panic around the equine community, even though it is also one of the few diseases that many Australian horses are regularly vaccinated against. Such is the fear of this disease that a recent (and incorrect) rumour of infected horses in WA caused many events to be cancelled and clinicians to postpone their visits to the state. Though not normally deadly the disease is highly contagious, and acute. It is easily spread by direct exposure, so bio-security and isolation of an affected horse are the most effective ways to prevent it spreading.

Outbreaks of strangles occur occasionally all around Australia. Mostly it’s considered a ‘nuisance’ disease, though it is notifiable in Victoria, NSW and South Australia - meaning that any outbreak must be reported to veterinary and government authorities. An outbreak in an area with a high population of horses could severely disrupt equestrian activities, therefore broadcasting the presence of the disease, and practicing good bio-security for containment and prevention, are vitally important.

An upper respiratory infection in horses, strangles is caused by the bacterium Streptococcus equi, which in nature resembles strep throat in humans. Not usually life threatening, strangles is occasionally fatal in young and old horses, though the animals die from toxic shock in response to massive infection, rather than the disease itself. Usually, however, it is an acute and debilitating illness and its highly contagious nature gives it the potential to cause havoc in the equestrian world, particularly during breeding and competition seasons.

SYMPTOMS
The initial symptoms can be very subtle, so those who know their horses well and are in the habit of doing regular monitoring of an animal’s vital signs at every feed are more likely to catch the early indication that all is not right. The most common symptoms are a lack of appetite, depression, fever (above 39°C; normal body temperature is 37.9°C), listlessness, and swelling of the lymph nodes in the throat area.

Once established, the symptoms of strangles include a copious creamy discharge from the nostrils, enlarged lymph nodes (glands) under the jaw, and an elevated temperature. Abscesses may also occur in the lymph nodes in the back of the throat, though these are not outwardly visible or accessible to treat. These abscesses contained within the lymph nodes can cause difficulty in breathing and swallowing due to swelling in the throat area, exacerbated by the copious nasal discharge. Often they will burst, which brings relief to the horse, pain-wise, though the bacteria-laden pus is extremely contagious. The immune system of most healthy horses will then fight off the infection. In a minority of cases the infection can progress to the lungs, where a large number of abscesses may form, causing pneumonia, and occasionally, death.
Strangles is spread rapidly by direct contact with an infected horse, through coughing and nasal discharge, or via contaminated feed or water buckets. It is spread indirectly through contaminated utensils, buckets, rugs, feed bins, and human hands or clothing. The incubation period is one to three weeks, after which the disease symptoms will run for 7 to 10 days. Bacteria may be shed in the nasal discharge of infected horses for several weeks after the clinical signs have disappeared. The symptoms may persist for weeks. In some horses, infection of the upper respiratory tract will involve infection of the guttural pouch and these horses are likely to become long term chronic carriers of the bacteria and are a significant source of bacterial infection of susceptible horses.

CARE OF A STRANGLES PATIENT
If strangles is suspected, a veterinarian should always be called, even in states where the disease is not notifiable as the illness can be severe and can lead to complications. Diagnosis made from the classic symptoms of swollen lymph nodes under the jaw, nasal discharge and fever will be confirmed in a laboratory, which may take a couple of days.
It is very important to isolate a horse immediately at the first sign of illness, and to obtain a veterinary diagnosis if strangles is suspected. It is also very important to try to ascertain what other horses the infected horse has been in contact with, and quarantine them for a week to 10 days to limit the spread of infection. It’s possible that a young horse introduced to a property may come down with the disease, but to have caught it from a carrier among the resident horses. All horses that travel to public places, for example competition horses, should be vaccinated regularly to reduce the possibility of them being carriers.

Good nursing, combined with efforts to drain the abscesses are the best options for treatment. Stringent biosecurity should be practiced at all times; for instance, leave the sick horse until last so there is less chance of spreading germs to the others, and wear disposable gloves whilst tending the horse and handling it’s rugs, buckets, etc. Everyone in contact with an infected horse should disinfect hands, clothing and footwear each time they have been in contact with the animal.

Hot compresses applied to swollen lymph glands may accelerate the drainage of unburst abscesses. Hot water bottles, snap-freeze packs, or old soft-gel human-use injury packs can be used. Wheat bags are not recommended due to the possibility of transmitting bacteria. The pack should be held against the abscess several times a day, if possible. Lymph nodes beneath the jaw (sub-mandibular) may swell to the point of bursting, either outside the body, or internally, which usually relieves the horse’s pain. Wounds and draining pus should be cleansed often with warm salty water, followed by a diluted iodine solution. Wear gloves and safely dispose of all infected material, then hands and arms can be disinfected using either an iodine, or chlorhexidene based disinfectant. Equipment and the area in which the horse is being treated should be considered contaminated.  It is not advisable for people treating horses with strangles to handle other horses subsequently.

If the pharyngeal lymph nodes at the back of the throat, which are not accessible to lance, are so swollen that the horse is having difficulty breathing, consult the veterinarian as a matter of urgency. These horses must be kept as calm and cool as possible, as their respiratory capacity is severely diminished. The vet may perform a tracheotomy, or lance the abscesses from the outside at the base of the swelling. This will quickly relieve symptoms of respiratory distress.
While the horse is in the acute stage of the disease, carers should watch for signs of difficulty in breathing such as heaving, and a spread stance with a lowered head. Also watch for signs of shock, increased temperature and swelling in the abdomen or legs, which may be indications of secondary infections. In these cases, the vet will prescribe antibiotics.

A sick horse should be kept comfortable: not too hot and not too cold, but protected from the elements, and from stress. Horses respond well to quiet, sympathetic care, and attention. A feverish animal is better off with the option of a shelter, but no rug. Feed from the ground to encourage drainage of the lymph nodes, and dampen feeds and hay to avoid the inhalation of dust and microbes, which could exacerbate breathing problems. A small amount of apple juice or molasses mixed in the feed may encourage eating, so long as the horse is not at risk of laminitis from the increased sugar.

After a strangles outbreak, contaminated pasture should be rested for at least four weeks so that drying and ultraviolet light can kill off the organism. Stalls and tie-up areas should be washed down with hospital-grade disinfectant, as should headstalls, buckets, brushes, rugs, etc. Rinsing feed and water buckets in gravity-fed communal water sources or piped water courses on the property can spread the disease very efficiently. It is vital to disinfect, wash, and rinse all buckets (including their handles), containers, brushes, towels etc, and to wash hands (without touching taps), in separate water sources such as a plumbed sink, where the germs cannot be spread. It may be preferable to set up a washing area nearby, such as a large container or drum containing chlorinated water, where washing and rinsing of all infective material can take place immediately and as a matter of course, and the water emptied daily into a sewerage system.

BASTARD STRANGLES
The strangles bacteria can be treated with antibiotics, but many vets avoid this, as most horses recover uneventfully. Occasionally, however, surviving bacteria may lead to internal secondary infections that are more serious and more difficult to treat. Abscesses can occur in the lungs, internal organs, or the brain; these secondary infections are known as ‘bastard’ strangles. Very rarely, when abscesses occur in the lymph nodes of the chest or abdomen, if these abscesses rupture this can cause a massive shock response, and the horse can die. Fortunately, many cases of strangles can be avoided by following an annual vaccination schedule. The strangles vaccine Equivac 1 and Equivac 2, which also includes the tetanus vaccine, are available at feed stores and saddlers, and can be administered by the owner, or a veterinarian. Immunity is rather short-lived, but vaccination is worthwhile as it helps reduce the number of horses infected, and decreases the severity of the disease for those that do contract it. Horses on large agistment properties, or living or congregating where many horses come and go, such as at competitions, are particularly at risk and vaccination is highly recommended.

The primary vaccination involves three intra-muscular injections at two-week intervals; an annual booster maintains immunity. Stallions should be given a booster vaccination before commencing stud duties, and brood mares should receive a booster in late July to provide immunity to newborn foals, until they are old enough to be vaccinated at three months.
To prevent strangles outbreaks, best-practice bio-security should be maintained at all times. New arrivals to a property should be isolated from resident horses for at least 14 days, with double fencing between paddocks to prevent nose-to-nose contact. Wash hands between handling horses, do not share tack or grooming equipment, and ensure each horse has its own feed and water containers.

Prevention is paramount, as strangles is highly contagious and therefore spreads quickly. Unfortunately diagnosis, which currently takes place in a laboratory, takes time. The University of Maine, USA,  recently won a US$500,000 grant to develop a new and inexpensive diagnostic field kit for strangles, which, when it becomes available globally, will save valuable time and expense in detecting and isolating the disease. In-field diagnostic kits -such as this will be a boon in the fighting and prevention of strangles and other serious equine diseases.

Dr James Gilkerson
A graduate  from the veterinary faculty at The University of Sydney, James has been involved in equine infectious disease research for nearly 20 years. He is currently an Associate Professor in Veterinary Microbiology and is the Director of the Equine Infectious Disease Laboratory at Melbourne University.