Strangles is an upper respiratory disease of the horse which most horse owners, even if they have not experienced an outbreak, will almost certainly have heard of.
Among horse owners, there is often a stigma attached to the disease and this can hinder quick diagnosis and effective control. However, strangles is not caused by poor horse husbandry or neglect – it is a respiratory infection.
Strangles is caused by a bacterium, Streptococcus equi, which is spread from horse to horse and via tools, equipment, tack, owners and their clothing. Shared water troughs are also a common source of infection.
In most cases, there are few complications from the disease and most horses make a full recovery. If a horse is affected and then recovers, immunity will usually last for approximately three to four years. A small number, about 5-10 per cent, of those affected will become carriers of the infection and intermittently shed the bacteria, infect other horses and cause future outbreaks. These carrier horses will usually not show any clinical signs to identify them as carriers.
Not all horses will show all the signs, but some of the following may be seen:
A less common form of the disease is seen when the horse shows only milder signs such as a raised temperature and loss of appetite.
Coughing is not usually a major feature of infection.
The signs seen and severity of infection are related to the health and inherent resistance of the individual rather than to the variations in the organism itself.
The diagnosis should be confirmed by growth and detection of the bacteria from a naso-pharyngeal (throat) swab taken from suspected animals. Swabs can also be taken from a discharging abscess. Blood samples can be taken from horses to see if they have been previously exposed to the infection. The blood sample does not indicate if the animal is affected by the disease at the time of sampling.
Transmission of strangles requires fairly close contact between infected and susceptible horses. Spread can also occur through shared water troughs and/or mechanical spread through personnel and grooming kit etc.
The incubation period, that is, the period between infection and signs being evident varies from seven to 14 days, though up to 21 days has been reported.
The main source of infection is carrier animals, but the bacteria can survive for long periods (up to nine weeks) on wood if conditions of temperature and humidity are optimal.
After infection, most animals will eliminate the bacteria fairly quickly, however, a significant proportion, perhaps 5-10 per cent may not eliminate the infection fully and become carrier animals. The infection often remains dormant in the guttural pouches (recesses in the throat) of these horses.
Good nursing care is the mainstay of strangles treatment:
The advice regarding the use of antibiotics in the treatment of strangles remains slightly controversial. Opinions vary but in certain circumstances, particularly those where horse welfare is severely compromised, antibiotics will be used. These will usually be given by injection as the affected horses often have difficulty eating.
Each situation will vary, but management of an outbreak on a yard is likely to involve the following: