CORRESPONDENCE

Reactions to strangles vaccination

29 Adamson Street, Victor Harbor, South Australia 521 1

GS SEZUN

Dr H Smith (Aust Vet J 1994; 71:257) reported on the prevalence of systemic reactions to strangles vaccination, which included stiffness of gait, arthritis, fever, oedema of ventral abdomen and lower legs, founder, lameness, lethargy, respiratory signs, colic, ataxia, urticaria and failure to protect against clinical infection.

In late July/August 1992, a large Standardbred stud in northern Victoria had 5 of 120 weanlings with systemic reactions to their first strangles vaccination. Clinical signs, which were seen over the next few weeks, consisted of varying degrees of lethargy, stiffness, fever, lower limb oedema and ataxia. Two weanlings that were affected in the first week, also exhibited extensive and marked multiple sub- cutaneous abscesses on the neck, brisket and chest, each of which developed into a severe skin slough measuring about 200 to 300 mm in diameter - apart from injection site swellings. This type of information did not form part of the CSL data.

Clinical pathology gave a general picture of leucocytosis with a neutrophilia, low packed cell volume and haemoglobin, increased fibrinogen (1 weanling) and increased muscle enzymes (1 weanling). Equine viral arteritis (EVA) titres were not determined, although previous tests an the stud indicated that infection was endemic. One weanling had a faecal egg count of 840 eggs per gram. Presumably the skin sloughs were the final outcome of an immune-mediated vasculitis but probably not, by definition, a classical purpura haem- orrhagica reaction involving petechial haemorrhages.

Vaccination was performed by stud staff using multi-dose containers of vaccine administered into the neck muscle. No simultaneous injections were given.

The stud’s history in recent years (due to the Occurrence of clinical disease) suggests that endemic infection is present. Over the years there appears to have been a substantially higher prevalence of systemic reactions in horses on the stud than the figureof one reaction per 10 OOO doses reported by Dr Smith.

A further observation was that in October of the same year, a 23-year-old pregnant Standardbred mare developed a stiff hind limb gait and hind limb oedema ten days after a single strangles vaccina- tion. A rising EVA titre was demonstrated (1:48 initially increasing to 1:89 four weeks later). She also had a neutrophilia, increased muscle enzymes (CK at least 9955) and high protein and globulin.

Comments on the above situation would be appreciated, especially with regard to the significance of endemic infection. Is there a possible connection between sub-clinical EVA infection and sys- temic reactions to strangles vaccination?

CSL Limited, 45 Poplar Road, Parkville, Victoria 3052

HV SMITH

In reply to Dr Sezun, my review of reactions to strangles vaccination was completed before the six cases described in his letter were reported to CSL Limited. Multiple subcutaneous abscesses are unlikely to develop as an adverse reaction to strangles vaccine. Abscesses develop when pus forming bacteria are introduced concurrently with the vaccine or are seeded from the blood as a result of a bacteraemia. A variety of organisms, such as Streptococcus zooepidemicus, Staphlococcus aureus, Pseudomonas aeruginosa, Pasteurella sp, Cornyebacteriwn equi, can be responsible. Usually they are introduced by means of inadequately cleaned and sterilised equipment, but may also come from the skin or be carried by the blood from a distant focus in the body.

Multidose containers of vaccine, as used on this stud, are easily contaminated with microbial organisms or chemicals. Doses with- drawn after the seal has been punctured more than once may contain significant quantities of foreign material. These problems are avoided when injectable preparations ready for administration in single dose syringes are used.

Vaccination reactions are of two types; those caused by irritant properties of the formulation and those which are immunologically mediated. The former are usually local oedematous or granuloma- tous reactions to adjuvant or preservative, but can also be due to pH or osmolality of the preparation. Some adjuvants may be pyrogenic, for example, saponin. Irritant reactions are distributed through all classes of recipients. Immune-mediated reactions generally occur in animals which have received more than one dose of vaccine and may be either local or systemic. When immune-mediated reactions occur following a first dose of vaccine an incomplete vaccination history or sensitisation by some other means is the probable explanation. This could be through contact with an infected or carrier animal or allergy to one of the other components of the vaccine.

In the case discussed by Dr Sezun the stud had a history suggesting that both strangles and infection with equine arteritis virus (EAV) were endemic. Although vasculitis may be observed during the course of both diseases there is no evidence of an association between EAV and systemic reactions to strangles vaccination.

In a particular herd the reaction rate may be different from the average of 1 per 10 0oO doses sold because of differences in admini- stration of the vaccine, a different prior exposure to strangles, the vaccine or other environmental factors.

480 Australian Veterinary Journal Vol. 12, No. 12, December 1995