STRANGLES VACCINATIONS PART TWO (II)

STRANGLES

Many of you will be aware from recent media reports that strangles is with us again. An unfortunate number of you have known for more than six months! Those with studs and spelling complexes will no doubt be receiving questions from worrying clients. For your own and your clients information, here are the facts of the disease:

BACKGROUND OF STRANGLES

Strangles infection is always around. If we haven't had it recently, we are going to get it soon!! It is highly infectious, spreads very rapidly and affects all ages and types of horses.

CAUSE OF STRANGLES
The disease is caused by the bacteria Streptococcus Equi only. Other Strept. Organisms such as Strept. Zooepidmicus and viruses may infect secondarily but only the one organism causes the disease. There are no recognised strains of Strept. Equi but the organism is enclosed in a capsule which may vary slightly and this may be the cause of the apparent variation in signs and infectvity recorded at various times and places.

The organism can survive in damp, mild conditions such as stables for up to 12 months and in open areas has been shown to survive for up to four months.

SPREAD OF INFECTION
The organism is spread in nasal discharges, either by direct contact between horses or by contamination of drinking water, tack, rugs, grooming utensils, stomach tubes and personal. Symptoms generally show first in young animals and then spread to older members of the population. Affected animals (carriers) may continue to excrete the organism for up to three (3) months, after apparent recovery.

SIGNS OF INFECTION
The first signs are lack of appetite, depression and a high temperature. This is rapidly followed by localisation of the organism in the pharyngeal, mandibular and sub-manibular lymph nodes causing the characteristic swellings and abscesses under the throat and jaws. Many will also have nasal discharges.

Very occasionally the organism spreads via the lymphatic system to affect other lymph nodes inside and outside the body. (The so-called 'bastard' strangles). This particular type of strangles can be particularly difficult to diagnosis and treat as all abscess formation can be within the abdomen. These horses so affected may die or become chronic 'poor doers'.

DIAGNOSIS OF STRANGLES

In the early stages of an infection the only sure means of diagnosis is by needle drainage of abscesses and laboratory culture of the organism. Once the infection is established within a herd, diagnosis becomes all too easy on the basis of symptoms alone.

TREATMENT OF STRANGLES

There are two schools of thought regarding treatment:

NO ANTIBIOTICS
Allow abscess development to occur and abscesses either allowed to drain naturally or are opened with a scalpel and swabbed out with disinfectant.

ANTIBIOTICS
All affected horses are treated with antibiotics. I believe this is only an option is all horses temperatures are taken daily and any horses with elevated temperature (greater than 40°c) are put straight onto a course of procaine penicillin. It is the experience of many that use of antibiotics after abscess formation has occurred will only prolong the presence of abscesses and may encourage the development of 'bastard strangles'.

Each situation is different but generally I would recommend allowing abscess formation and discharge to take its natural course without antibiotic treatment. Occasional individuals with discharging abscesses and persistent high temperatures may require short-term therapy with procaine penicillin.

PREVENTION OF STRANGLES

Many of you may have experienced disappointment with the results of vaccination. Put simply: vaccination is not always effective but often the natural infection does not confer any immunity on individual horses (some horses in this outbreak have been infected up to three times). I do urge you most strongly to please continue to vaccinate your horses. While it may not always be effective, I firmly believe it does reduce the number of cases you will see and the severity of the infection. Vaccination cannot cause the infection, neither can it cure it.

The biggest problem with vaccination is that it cannot be relied upon alone. You must still continue the strictest standards of hygiene when moving from infected to non-infected horses and if at all possible, all infected horses should be isolated: preferably for as long as possible (3 months) after signs have subsided. I know that this is often not practical but if infected horses are allowed to run with non-infected horses the disease will continue to spread regardless of vaccination.

Vaccination must be done effectively. Always ensure that the manufacture's instructions are followed and that vaccines are kept in the refrigerator.

Each year all foals over three (3) months of age should be given an initial course of three doses of vaccine into the muscle of the neck, chest or rump two (2) weeks apart. All older horses of unknown vaccination status will require the same initial course. In subsequent years a single annual booster dose only is required, preferably just prior to the breeding season.