Page 660 - The Veterinary Care of the Horse

injections given 4 weeks apart. Foals can be vaccinated from 4 months of age. Horses in

high-risk situations (e.g. new horses regularly being introduced into the group, regular
VetBooks.ir attendance at competitions or being close to an outbreak of strangles) should be given
boosters every 3 months. Those in medium-risk situations (e.g. horses kept at home but with

occasional outings) should be vaccinated every six months.

If an outbreak occurs, any horse that has not had a booster within 3 months should be re-
vaccinated. Provided the last injection was less than 6 months ago, a single dose is sufficient.
Horses that are kept in a group with other horses that do not attend shows etc., are generally

low risk and may not need vaccinating. Pregnant or lactating mares should not be vaccinated,
and this vaccine should not be administered at the same time as other vaccines. Some horses

experience temporary swelling of the upper lip and muzzle following vaccination.
A new vaccine demonstrating more than 80% protection of horses has been developed

and is anticipated to be available in the UK in 2020. It can be given by the intramuscular
route.

In conclusion

Strangles can have huge cost implications as the activities of affected equine establishments
may be restricted for a considerable period of time. Early diagnosis and good management

are essential for prompt control of an outbreak.

PURPURA HAEMORRHAGICA

Purpura haemorrhagica is an immune-mediated condition that can develop as a sequel to
strangles and other respiratory infections including equine influenza, equine herpesvirus 1

and Rhodococcus equi. Occasionally it develops following a wound infection or without any
obvious cause. Very rarely it occurs after a strangles vaccination. The symptoms occur 1–4
weeks after the horse appears to have recovered from the original infection.

Causes

The disease is caused by an allergic reaction to the streptococcal or viral antigens which

circulate in the bloodstream. The blood vessels become inflamed and blood cells and serum
leak through the capillary walls into the tissues. All of the major organs, i.e. heart, lungs and
kidneys, may be affected.