Contagious abortion also called Brucellosis is an infectious disease caused by bacteria called Brucella (bru-CELL-a). Many different animal species and humans can become sick from this bacteria. Contagious abortion is primarily a reproductive disease in animals but it can also cause reoccurring fevers, arthritis or udder infection (mastitis).Contagious abortion can affect sheep, goats, cattle, pigs, horses, and dogs. It can also affect rats and wild animals including deer, bison, elk, moose, camels, water buffalo, and marine mammals.Contagious abortion causes reproductive problems (e.g. abortions, stillbirth and infertility) in most species of animals.
An incubation period is the interval of time between exposure to an infectious dose of organism and the first appearance of disease signs. The incubation period of contagious abortion in cattle and other animals is quite variable ranging from about 2 weeks to 1 year and even longer in certain instances. When abortion is the first sign observed, the minimum incubation period is usually about 30 days. Animals abort before developing a positive reaction to the diagnostic test. Other infected animals may never abort. Generally infected animals that do not abort develop a positive reaction to the diagnostic test within 30 to 60 days after infection although some may not develop a positive reaction for several months to over a year.
There is no cure for contagious abortion. Occasionally animals may recover after a period of time. Commonly the signs disappear and the animals remain with the disease. Such animals are dangerous sources of infection for other animals with which they associate. Since there is no cure the disease can be avoided by using proper sanitation methods. Proper herd management strategies can also help in the avoidance of the disease
- In animals Brucella (bacteria causing the disease) are usually spread through contact with infected birthing tissues and fluids (e.g. placenta, aborted fetuses, fetal fluids, vaginal discharges). Cows may lick those materials or the genital area of other cows or ingest feed or water contaminated with the disease-causing organisms.
- The bacteria can also be found in the milk, blood, urine and semen of infected animals.
- Animals can get the bacteria by ingestion (oral), direct contact with mucous membranes (eyes, nose, mouth) or breaks in the skin.
- Brucella can also be transmitted by contaminated objects (fomites) such as, equipment, clothing, shoes, hay, feed or water.
- Some animals are carriers; they will have the bacteria but show no signs of illness. These animals can shed the bacteria into the environment for long periods of time, infecting other animals in the herd.
- Herd owner buys replacement cattle that are infected or have been exposed to infected animals, animal tissues or animal discharges prior to purchase.
- The disease may also be spread when wild animals or animals from an affected herd mingle with contagious abortion-free herds.
Vaccination and control
- The contagious abortion vaccine is called RB51. RB51 works by producing an immune response that increases the animal’s resistance to the disease. The vaccine is a live product and must be administered only by an accredited veterinarian or State or Federal animal health official. Vaccination is not 100 percent effective in preventing contagious abortion it typically protects about 70-80 percent of the vaccinated cattle from becoming infected by an average exposure. For best results, female calves should be vaccinated when they are between 4 months and 1 year old.
- At the time of vaccination a sign should be made to the vaccinated cattle which identifies the animal as an “official vaccinate.” The sign identifies the RB51 vaccine and the year in which vaccination took place.
- Vaccination is an important tool in the control, management and elimination of contagious abortion. Every cattle owner regardless of location should discuss the advantages and disadvantages of vaccination with his or her veterinarian.
- Revaccination of female cattle at 3 to 5 year intervals is recommended. This gives much better protection to the herd.
- Maintaining closed herds
- recording individual animal identification and maintaining accurate records
- isolating and testing purchased additions as well as cattle re-entering the herd
The following programme can be opted when there is severe infection
- Success of the program depends on the support and participation of livestock producers. The basic approach has always been to vaccinate calves, test cattle and domestic bison for infection and send infected animals to slaughter.
- Depopulation of herds if funds are available may be used if herds are severely affected.
- Identification animals for tracing, surveillance to find infected animals investigation of affected herds and vaccination of replacement calves in contagious abortion-affected areas are important features of the program. An area is designated contagious abortion free when none of their cattle is found to be infected for 12 consecutive months under an active surveillance program.