Brucella ovis

Overview

Cause

Brucella ovis

Description

Brucella ovis infection causes disease and infertility in sheep. The prevalence of infection can be high if the disease is not controlled. Merinos show a lower incidence of disease compared to British breeds and crossbreds.

Where the disease occurs

Brucellosis of sheep has been reported in most major sheep-producing regions of the world and is present in Australia, New Zealand, the United States, South Africa and Europe (excluding the United Kingdom).

The disease in animals

The consequences of infection in a flock are largely seen in rams. The first sign of disease in a ram is a marked deterioration in the quality of the semen. Acute oedema and inflammation of the scrotum may follow. A mild systemic reaction, including fever and depression may be noticed. After about nine weeks after infection, palpable lesions develop in the epididymis and tunica of one or both testicles. Affected rams have normal libido but reduced fertility to complete sterility. When the number of affected rams in a flock is greater than about 10%, the fertility of the flock is appreciably decreased.

There are usually no clinical signs in the ewe but in some flocks infections causes abortion or the birth of weak or stillborn lambs, associated with a placentitis.

How the disease spreads

The infected ram is the source of infection and perpetuates the disease in a flock. The excretion of B. ovis in the semen of infected rams is thought to continue indefinitely until the testicle becomes completely fibrosed. The main method of transmission is from ram to ram via the ewe's vagina during the mating season. During the non-breeding season spread can occur between rams when mounting each other or licking each other's prepuce.

Infection in ewes is short-lived but will persist in a few animals. Nevertheless, spread between ewes has not been noted. Lambs born to infected ewes and drinking their milk do not become infected.

The organism can survive on pasture for some months but this is not important in the spread of the disease.

Diagnosis

The palpation of both testicles from behind will detect the lesions associated with brucellosis. Blood samples may be collected for a complement fixation test (CFT). Where lesions are present in rams, sterile samples of epididymis, accessory glands and testicle can be taken at post-mortem for bacterial culture. Semen samples collected by electro-ejaculation can be examined for semen quality or cultured.

Control of the disease in animals

Owners of commercial flocks should purchase rams from studs that are accredited under the Ovine Brucellosis Accreditation Scheme. Good management of the rams will keep the disease at a low level. Good fences are important in keeping neighbouring rams out. Virgin rams and those known to be free of infection should be kept separate from older rams or those suspected of being infected. All rams should be palpated every six months and those with palpable lesions of the reproductive organs should be culled. Individual treatment is not seen as an option. Vaccination is practiced in other countries but not in Australia.

Ovine brucellosis accreditation scheme

A voluntary Ovine Brucellosis Accreditation Scheme is administered by Biosecurity Queensland.

Responsibility for meeting the conditions of the scheme rests with the owner of the flock and an approved private veterinary practitioner. Owners are required to meet all veterinary and laboratory costs and to pay an accreditation fee to Biosecurity Queensland.

Flock owners must abide with the rules of the scheme with regard to flock management and biosecurity, testing requirements and purchase of stock. Two negative blood tests of all eligible rams at 60-day intervals are required for accreditation. Re-accreditation is required annually or biennially, depending on the time the flock has been accredited. If infection is detected in the flock, accreditation is withdrawn until all reactors are removed and the flock tested back to accreditation standards.

For more information, please contact Biosecurity Queensland or your veterinary practitioner.

Can people get the disease?

This form of brucellosis does not affect people.

Last updated 13 April 2016