Yersiniosis

The bacteria are widespread on soil, water and pasture. Carrier animals (including deer, birds, rabbits, pigs, cattle or sheep) shed the bacteria in their faeces. Deer become infected by eating or drinking contaminated material. There are three main types of these bacteria in New Zealand.

The disease is bought on by stress so is typically outbreaks are seen following weaning, transport, bad weather or underfeeding. For example deer being transported and off feed for several hours may be susecptible.

It typically affects young deer (four to eight months) during their first autumn/winter. They tend to go off food and stand alone, becoming dehydrated and weak. Diarrhoea causes staining of the hocks and tail, with diarrhoea colour changing from watery green through dark or bloody as the disease progresses. Acute cases may be found dead without any obvious clinical signs.

Infected deer with no major stressors will usually not present with the full-blown clinical symptoms and show only mild symptoms. They will shed the bacteria for some weeks or months however.

Yersiniosis disease outbreaks typically occur in young deer, with up to 20% of the mob affected.

It can be difficult to diagnose by looking at the visual symptoms. This is because it can be confused with other diseases like malignant catarrhal fever and leptospirosis. The best way to confirm the disease in a live deer is to culture a faecal sample.

In an outbreak it is too late to vaccinate so the best option is to treat all the mob (including the deer with clinical signs) with oral or injectable antibiotics. Fluids are effective if given early in the course of the disease. Sick animals benefit from sheltered housing.

A preventative approach is to vaccinate weaners with Yersiniavax®. Farmers need to decide whether a yearly vaccination programme is more cost-effective long term than treating outbreaks with antibiotics when/if they occur. For information on the product, click here >>

The vaccine has been used since 1994 and has shown good protection against outbreaks. Two doses are required three to six weeks apart. The timing of the first dose is critical. Ideally it should be done in the autumn before the risk of bad weather, and before young deer have been mobbed together. Vaccinating before weaning can be challenging but leaving deer unprotected until after the rut could lead to disease outbreaks. A veterinarian can help guide this decision based on previous history of disease, weaning and mating management, feeding levels and whether weaners are sold or retained. Vaccine will not stop all outbreaks but does decrease death rates in a mob.

Another prevention tool is to minimise stress for young deer. For example keep them well-fed and sheltered, avoid extended periods in the yard, treat for parasitism and ensure trace element levels are adequate.

To help manage this disease, create an animal health plan in consultation with a veterinarian.