Biliary is one of the most common serious illnesses in South African horses. Vets call it equine piroplasmosis, or equine babesiosis, and it is caused by tiny parasites that live inside a horse's red blood cells.
The parasites are spread by ticks, which are found across much of the country. As a result, a large proportion of South African horses are exposed to biliary at some point in their lives, and most owners will deal with it sooner or later.
This guide provides general information only. Biliary can become life-threatening, so always contact your vet if you think your horse is unwell, and ask your vet for advice on tick control in your area.
What Causes Biliary?
Biliary in horses is caused by two different blood parasites:
- Theileria equi, previously known as Babesia equi. This is the more common of the two and usually causes the more severe disease.
- Babesia caballi, which tends to cause milder illness.
Both parasites invade and destroy red blood cells. This leads to anaemia, fever and, in many cases, yellowish discolouration of the gums and eyes. Horses can be infected with one or both parasites.
How Biliary Spreads
Biliary is spread mainly by ticks. When an infected tick feeds on a horse, the parasites pass into the horse's bloodstream. Several tick species found in South Africa can transmit the disease, including the red-legged tick and the bont-legged ticks.
The parasites can also be passed directly in blood, for example through needles or equipment used on more than one horse, or through a blood transfusion. This is one reason needles and syringes should never be shared between horses.
Ticks are most active in the warmer, wetter months, so cases tend to increase in spring and summer. Biliary can occur at any time of year, however, especially in warmer parts of the country.
A few other points worth knowing:
- Biliary in horses does not affect people.
- Horse biliary is caused by different parasites from the biliary that affects dogs. Your horse cannot catch it from your dog, or the other way round.
- Horses do not spread biliary to each other through normal contact. Ticks or blood are needed to pass it on.
Signs of Biliary
Biliary can range from mild to severe. Some horses only seem slightly off colour, while others become seriously ill within a day or two. Watch for:
- Fever, often well above the normal range
- Dullness, lethargy and a reluctance to work
- Reduced appetite, or leaving feed
- Pale, yellow or orange-tinged gums and inner eyelids
- Dark yellow, orange or reddish-brown urine
- Faster breathing and a raised heart rate
- Swelling of the lower legs or along the belly
- Constipation or colic-like discomfort in some horses
- Weight loss and poor performance in longer-standing cases
A normal adult horse's temperature is usually between about 37.5°C and 38.5°C at rest. Taking your horse's temperature is one of the quickest ways to tell whether something is wrong, so keep a digital thermometer in your first-aid kit and get to know your horse's normal reading.
Biliary can look similar to other illnesses, including African horse sickness, which can also cause a fever and swelling. Only your vet can tell the difference, so call them rather than trying to work it out yourself. Our guide to African horse sickness explains the warning signs of AHS.
Diagnosis and Treatment
Your vet will usually confirm biliary by examining a blood smear under a microscope or by sending a blood sample for laboratory testing. Blood tests also show how anaemic the horse has become, which helps your vet decide on treatment.
Treatment usually involves prescription medication to kill the parasites, together with supportive care such as rest, fluids and good-quality feed. Severely affected horses may need to be hospitalised, and some need a blood transfusion.
The medicines used to treat biliary can have side effects, including sweating, diarrhoea and colic-like signs. They should only be given by your vet or under your vet's direct instructions. Never treat a horse with medication meant for dogs or cattle.
Most horses recover well when they are treated early. Afterwards, the body needs time to replace the lost red blood cells, so recovery can take several weeks. Bring your horse back into work gradually and follow your vet's advice on when it is ready.
Carrier Horses
Many horses that recover from biliary remain carriers. They look and behave normally, but low levels of the parasite stay in their blood, and ticks that feed on them can pick it up and pass it on. Horses infected with Theileria equi often remain carriers for life.
In South Africa, carrier horses are common and usually live normal lives. Some carriers become ill again when they are stressed, unwell, travelling or working very hard, so it helps to know your horse's history and to watch for early signs at these times.
Carrier status matters most if your horse may ever be exported. Many countries do not accept horses that test positive for piroplasmosis, so horses intended for export need testing well in advance. If export is a possibility, talk to your vet early.
Tick Control: Reducing the Risk
There is currently no vaccine against biliary in horses, so controlling ticks is the main way to reduce the risk.
- Check your horse every day. Ticks prefer warm areas with thin skin. Check in and around the ears, under the jaw, along the mane, at the base of the tail and under the dock, between the hind legs, around the sheath or udder, and on the lower legs and heels.
- Remove ticks promptly and properly. Use fine-tipped tweezers or a tick remover to grip the tick as close to the skin as possible, then pull steadily. Avoid squeezing the tick's body or twisting it off roughly. The sooner a tick is removed, the less opportunity it has to pass on infection.
- Use a tick-control product registered for horses. Sprays, pour-ons and wipes are available. Choose a product registered for use on horses, follow the label exactly and ask your vet which option suits your horse and area. Some products made for cattle or dogs can be dangerous to horses.
- Manage your paddocks. Keep grass short where practical, clear long grass and bush along fence lines and remove piles of rubble or old material where ticks shelter.
- Think about other animals. Cattle, dogs and wildlife can bring ticks onto your property. A tick-control plan that covers the other animals on the property helps reduce overall numbers.
- Check new arrivals. Inspect new horses carefully for ticks before they join your herd, and treat them if needed.
Daily grooming is the perfect time to check for ticks. Our guide to grooming a horse covers a simple routine and the other health checks to do while you brush.
Biliary and Buying a Horse
If you are buying a horse, ask the seller whether it has had biliary, how it was treated and whether it has had any repeat episodes. A single past case is not unusual in South Africa and is not necessarily a reason to walk away, but repeated episodes are worth discussing with your vet.
If you plan to compete abroad or might export the horse in future, ask your vet about testing as part of the pre-purchase examination. Our step-by-step guide to buying a horse explains how vetting fits into the process.
Frequently Asked Questions
Is biliary contagious between horses?
Not through normal contact. Biliary needs a tick, or a transfer of blood such as a shared needle, to pass from one horse to another. A carrier horse can, however, be a source of infection for ticks that then feed on other horses.
Can a horse get biliary more than once?
Yes. Horses can be reinfected, and carrier horses can become ill again, particularly when they are stressed, travelling or unwell for another reason.
Is there a vaccine against biliary in horses?
No vaccine is currently available for equine biliary. Regular tick checks and a sensible tick-control plan are the best ways to reduce the risk.
Is horse biliary the same as biliary in dogs?
No. The two are caused by different parasites. You cannot catch biliary from your horse, and dog tick-control products should not be used on horses unless they are specifically registered for horses.
When are ticks at their worst?
Tick numbers usually rise in spring and peak in the warmer, wetter months. In the warmer parts of the country, ticks can be a problem for much of the year, so keep up daily checks even in winter.
Stay Ahead of Ticks
Biliary is common in South Africa, but daily tick checks, a sensible tick-control plan and a quick call to the vet when your horse seems off colour make a real difference.
Keep your vet's number handy and learn your horse's normal temperature. You can find equine vets and health services on Trot's veterinary and equine health listings, and our guide to the cost of owning a horse explains why it pays to budget for vet bills.
