Clostridia and Pasteurella Vaccination
The high prevalence of preventable diseases such as sheep scab, lice and CLD show that biosecurity measures on farms are inadequate on most sheep farms. With this in mind, it should be noted that there are highly efficacious vaccines available which can prevent outbreaks of diseases which otherwise may pose major endemic risks. The most effective and necessary vaccines used in sheep are clostridial and Pasteurella vaccines. Often these vaccines are combined.
Industry figures consistently show farmers spend £3.50 per ewe on vet and medicines every year. In the majority of flocks this kind of vaccination is necessary to prevent major economical lessons.
Clostridial diseases remain a serious threat to unvaccinated sheep; death occurs within hours of rapid bacterial multiplication and exotoxin production although lambs with tetanus can survive for several days. There are established vaccination protocols using toxoid vaccines which prevent all common clostridial diseases.
Initially, two vaccinations are given 4 – 6 weeks apart followed by annual vaccination 4 – 6 weeks before expected lambing date to ensure adequate accumulation of protective immunoglobulins in colostrum.
Lambs are vaccinated from 3 – 4 months old with the programme complete before weaning unless sold for slaughter before waning of maternal antibody at around 4 – 5 month old. All cases of clostridial disease are fatal despite treatment except for a small percentage of cases of malignant oedema (bighead) and blackleg that receive vet treatment during early stages of the disease.
The more common clostridial diseases are lamb dysentery, tetanus, pulpy kidney, black disease, blackleg, struck and braxy. Large losses can be experienced when sheep are not correctly vaccinated therefore it is surprising that in a recent study 20% of flocks in the UK are unvaccinated on a regular basis. Sporadic cases of clostridial disease may occur in the flock in those lambs which have received nil or inadequate specific antibody in colostrum due to various factors including individual ewes not correctly vaccinated, lack of colostrum in the ewe’s udder due to poor feeding/mastitis, large litter or alternative colostrum feeding from unvaccinated donors.
Types of Clostridial Diseases:
· Affected lambs are typically less than a week old. The lambs are typically found dead with no observed clinical signs.
· Affected lambs are typically 4 – 10 weeks old and are most commonly born to unvaccinated dams. Also it occurs when passive immunity has worn off in weaned lambs from 6 months old (when the lambs have not themselves been vaccinated).
· Major clinical feature s sudden death.
· Characteristically seen in unvaccinated weaned lambs during the winter months associated with ingestion of frosted root crops. Affected sheep are almost always found dead.
· Typically associated with migration of immature liver flukes during late summer/early autumn and can affect sheep of all ages if unvaccinated.
· Sheep are usually found dead.
· Entry of clostridia occurs through skin wounds, dog bites, shearing cuts, via contaminated needles, untreated umbilicus and trauma to the posterior reproductive tract during attempted dystocia correction.
· Affected sheep are dull, inappetant and have a fever (>41.0). Involvement of one limb results in sudden onset of severe lameness.
Malignant Oedema (Bighead)
· Typically seen in rams during late summer/early autumn when head butting is a common behaviour.
· Most obvious clinical sign is marked swelling of the head, particularly surrounding the eyes which forces closure of the eyelids.
· Lambs show hind leg stiffness and difficulty walking, leading to lateral recumbency, seizure activity progressing to opisthotonus and death from respiratory failure.
· Pasteurella haemolytica (previously P. haemolytica biotype A, now more correctly called Mannheimia haemolytica) is of considerable economic importance to the sheep industry as it causes septicaemia in young lambs, pneumonia in older sheep and mastitis in ewes.
· Bibersteinia trehalosi (previously P. trehalosi) causes septicaemia in 4 – 10 month old lambs. Systemic Pasteurellosis caused by B. trehalosi is the most common cause of sudden death in lambs between Aug-Dec in the UK.
· Prevention is best attempted using vaccines incorporating iron-regulated proteins. Since these iron-regulated proteins are antigenically similar they confer cross protection against other serotypes. Breeding ewes require a primary course of two injections 4 – 6 weeks apart followed by an annual booster 4 – 6 weeks before lambing.
· Lambs can be protected by two doses of vaccine administered from 10 day-old as colostral antibody does not interfere with the development of the active immunity. Alternatively, lambs can be protected against systemic Pasteurellosis by two doses of vaccine given 4 weeks apart with the second injection 2 weeks before weaning/sale.
· Vaccinations are advised to be administered to breeding ewes for clostridial diseases 4 weeks before lambing. It is also helpful to vaccinate the flocks as two separate groups, the later lambing group receiving the vaccine 7 – 10 days after the first group.
· It is important to ensure that the ewes are dry when injected, as if they are wet, can lead to contamination of the needle and abscess formation.