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Brucellosis Updates and Information
Brucellosis is a contagious disease of livestock that also affects humans. The disease is also known as contagious abortion or Bang's disease in livestock. In humans, it is known as undulant fever because of the intermittent fever accompanying infection. It is one of the most serious diseases of livestock, because it spreads so rapidly and it is transmissible to humans.
Cause
The disease is caused by a group of bacteria known as Brucella. Within this group there are three species of concern: Brucella suis, which predominately affects swine and reindeer, but can also affect cattle and bison; Brucella melitensis, which principally affects goats but is not present in the United States; and Brucella abortus, which is the most common cause of brucellosis and mainly affects cattle. In cattle, the disease usually localizes in the reproductive organs or the udder. Bacteria are shed in milk or leave the body with the aborted fetus, the afterbirth, or with any discharges from the reproductive tract. Brucellosis is commonly transmitted by direct contact with infected animals. It is also transmitted to animals that come into contact with a contaminated environment. Aborted fetuses, placental membranes and/or fluids, and the vaginal discharge that persists for several weeks after an animal has aborted all carry the bacteria. The general rule is that brucellosis is carried from one herd to another by an infected or exposed animal. This occurs when a herd owner buys replacement cattle that have been infected or exposed prior to purchase.
Back to top of pageIncubation
The incubation period in cattle is quite variable, ranging from 2 weeks to 7 or 8 months or even longer. When abortion is the first sign observed, the minimum incubation period is about 30 days. Generally, cattle may be infected as calves but not show any signs of infection until they abort. Infected animals that don’t abort develop a positive reaction to the test within 30-60 days after infection, although some may not develop a positive reaction for several months.
Back to top of pageSymptoms
There is no sure way to detect infected cattle by their appearance. The most obvious signs in pregnant females are abortion, birth of weak calves, and vaginal discharge. Not all infected cows abort, but those that do usually abort between the fifth and seventh month of pregnancy. Even though their calves may appear healthy, infected cows continue to harbor and discharge infectious organisms and should be regarded as dangerous because they may not show any symptoms. Other signs include an apparent lowering of fertility with poor conception rates and retained afterbirths with resulting uterine infection.
Back to top of pageSurveillance
Two primary testing procedures are used to locate infection without having to test each animal in every herd. A milk test called Brucellosis Ring Test (BRT) is conducted in dairies two to four times a year by testing a small sample obtained from the creamery or farm milk tank for evidence of brucellosis. Milk from each cow in the herd is pooled and a sample is taken for testing. A suspension of killed Brucella organisms is added to a small amount of milk. If the test is positive, a bluish ring forms at the cream line as the cream rises. All positive herds are investigated. The second surveillance method is a blood test on all cattle more that two-years-old at slaughter (Market Cattle Identification [MCI] program). Numbered tags or backtags are placed on the shoulders of all cattle being marketed. Blood samples are collected at slaughtering plants. If a sample reacts to the test, it is traced by the backtag number to find the owner of the herd from which the animal originated. The owner is contacted by a State or Federal animal health official to arrange for testing of the herd. All of the eligible animals in the herd may be tested at no cost to the owner. In many areas, adult cattle are also subjected to blood tests upon change of ownership even if sold directly from one farm to another. The key to the MCI program is proper identification of all animals so they can be traced to their herds of origin. Backtags and other man-made identification devices are collected and sent to the State diagnostic laboratory along with matching blood samples to aid in identifying ownership of reactors.
Back to top of pagePrevention
The disease may be avoided by employing effective sanitation and management practices. Replacement animals should be obtained from brucellosis free herds and free areas. Cattle may be tested when purchased and retested after a 30-60 day isolation period during which they are kept separate from the remainder of the herd. This will allow detection of animals that were in the incubation stage when acquired. Heifers may be vaccinated when they are 4-6 months old. At this time a tattoo is applied in the ear. Currently, there is a cooperative State-Federal brucellosis eradication program to eliminate the disease from the livestock population in the United States. Like other animal disease eradication efforts, success of the program depends on the participation of livestock producers. The program’s Uniform Methods and Rules set forth the minimum standards for states to achieve eradication. States are designated brucellosis free when no cattle or bison are found to be infected for 12 consecutive months. California has been brucellosis free since 1997.
Back to top of pageHuman Health
Brucellosis in humans, known as undulant fever, usually develops like influenza but persists for several weeks or more. Farmers, ranchers, veterinarians, and packing plant workers are among the hardest hit because they come into direct contact with infected animals. The initial symptoms are fatigue and headaches, followed by high fever, chills, drenching sweats, joint pain, backache, and loss of weight and appetite. Death does not occur frequently, but the disease is too serious to be dealt with lightly. Rarely, if ever, does a human contract the disease from another human. Only 77 cases of human brucellosis were reported in the United States in 1990. There is no danger from eating cooked meat products because normal cooking temperatures kill the disease-causing bacteria. However, care should be taken when consuming raw milk products, which may contain the bacteria. Consumption of raw dairy products (those made from unpasteurized milk) and contact with infected animals remain the major sources of human infection with Brucellosis. People should take the precaution of disinfecting areas likely to become infected and keeping them clean. They should wear sturdy rubber or plastic gloves when assisting cows calving or animals that abort, and scrub well with soap and water afterwards. Prevention of cuts and the contamination of cuts should be addressed, as well as avoidance of contamination of the eyes with body fluids of animals. Exercise care in handling and disposing of placenta, discharges or aborted fetuses and avoid contact with tissues that could be infected.
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