Brucellosis is a bacterial disease that causes significant reproductive losses in animals and is also an important zoonosis (can affect humans.) Brucellosis is caused by the closely related organisms that include Brucella abortus in cattle, B. melitensis (not present in the USA) in sheep and goats, B. suis in pigs, reindeer and caribou, and B. Canis in dogs. Abortion, inflammation of the placenta, and infection in the testicles are the most common symptoms: death is rare except in the fetus and neonate. Wildlife reservoirs are an ongoing problem found in bison, elk, feral pigs and European hares. There are also Brucella organisms isolated from many species of marine mammals, including pinnepeds (seals, sea lions and walruses) and cetaceans (whales, porpoises and dolphins).
Most species of Brucella can infect animals other that their preferred hosts if they come into close contact. Most of the common Brucellosis species are human pathogens that can cause serious, debilitating and chronic disease in several different organ systems. In the USA, B. suis has been eliminated from commercial pigs, and B. abortus is now considered eradicated from domesticated cattle. As a result, human brucellosis is rare in this country, usually caused by occupational exposure to infected animals or by the consumption of unpasteurized dairy products. While rare in the USA, the disease remains a common and very serious problem in some parts of the world.
Fortunately brucellosis is well controlled in most developed countries. Human clinical cases are still common in the Middle East, Asia, Africa, South and Central America, areas surrounding the Mediterranean and the Caribbean. For the purposes of this article, most of the remaining information relates to B. abortus, the organism found worldwide in cattle-raising areas, with the exception of Japan, Canada, some European countries, Australia, New Zealand and Israel. Although the USA has eradicated brucellosis from the existing domesticated cattle herd, it persists in wildlife hosts, particularly in the Greater Yellowstone area.
The disease is transmitted usually between animals by contact with the placenta, fetal fluids and aborted fetuses from an infected animal. Cattle are usually asymptomatic after their first abortion, but they can become chronic carriers and continue to shed the organism in milk and uterine discharges during subsequent pregnancies. Entry into the next host occurs by ingestion and through the mucous membranes, broken skin and possible intact skin as well.
Brucella species are also found in semen. Males can shed these organisms for long periods, even a lifetime although venereal transmission is actually uncommon for B. abortus. Brucella organisms have been detected in urine, feces, serum, saliva and nasal and ocular discharges. For the most part, these sources are relatively unimportant in transmission.
Brucella can also be spread on fomites such as feed and water. In the right conditions, of high humidity, low temperatures and no direct sunlight, Brucella can remain infectious for several months in water, aborted fetuses, manure, wool, hay, equipment (gynecological) and clothes. Brucella survives best below freezing temperatures.
Common sources of human illness is a result of contact with animal abortion products, ingestion of unpasteurized milk products and eating undercooked or raw meat products, contact with laboratory samples and accidental injection of live brucellosis vaccines. Treatment of human disease with antibiotics is usually straightforward, although long term treatment may be required. Human disease goes by the name Malta fever (where it was first recognized by British medical officers) or undulant fever (because of the tell-tale undulating fever commonly seen in the disease.) Brucellosis is also called Bang’s Disease, named for the man who first isolated the causative bacteria, and vaccination in cattle is commonly referred to as “bang’s vaccination.” The disease resembles a severe case of influenza, but it persists untreated for weeks to months. Initially symptoms include fatigue and headaches, followed by high fever, chills, sweats., joint pain, backache, lack of appetite and subsequent weight loss. Chronic infection may cause recurrent fever, joint pain and fatigue. Prior to the advent of pasteurization, raw milk was considered the prime source of brucellosis in humans. One study in California in 1994 suggests that in that state, brucellosis is likely still a food-borne illness from unpasteurized milk or cheese products from Mexico.
Prevention of human disease includes measures such as pasteurization of dairy products, and excellent hygiene in the handling of livestock birth products, performing necropsies or butchering an animal for consumption. Particular care is necessary in handling the products of abortion such as the fetus, afterbirth and fluids. Protective clothing is a necessity to prevent occupational exposure. Veterinarians and their assistants are at risk when handling Brucellosis vaccine, particularly the older Strain 19, but even the newer Strain RB51 vaccine is not without risk to humans. Anyone accidentally injected with Brucellosis vaccine, or exposed to the vaccine through abraded skin or mucous membranes of the eyes should immediately seek medical care. Such types of exposure to Strain 19 should be followed by administration of two antibiotics for a period of 3 weeks (doxycycline and rifampin.) People inadvertently exposed to RB51 should receive doxycycline alone for 3 weeks. Brucellosis vaccine for cattle is a restricted access vaccine in the US, and can only be administered by a licensed and federally accredited veterinarian.
Human disease is best prevented by controlling the infection in animals, thus the longstanding State and Federal cooperative attempt at Brucellosis eradication in the USA.
The disease in people is a very rare occurrence in the USA, with an annual occurrence of about 100 cases per year. However, there are some studies that suggest brucellosis is under diagnosed and under reported in this country.
Disease in cattle generally manifests as abortions, stillbirths and weak calves. Abortions usually occur during the second half of gestation, with initial exposure occurring anywhere from 2 weeks to 5 months prior to the abortion. Retained placenta may occur, and milk production may be reduced. After the first abortion, later pregnancies are usually normal, but the cows may still shed the organism and be a risk to other animals. Infertility in both sexes may occur; and swollen joints and arthritis may develop with chronic infections. Deaths are rare except for the fetus, and infection in nonpregnant animals is usually asymptomatic. The signs of B. abortus are similar in cattle, bison and water buffalo. Moose experimentally infected develop very serious systemic disease and die quickly.
Aborted fetuses and fetal membranes are all highly contaminated with the infectious organisms. Cows may lick those materials or the genital area of infected cows. Water and feedstuffs may also be contaminated and be a source of infection for other cows in the herd. With few exceptions, brucellosis is spread from one herd to the next via an infected animal. This may be the purchase of replacement animals or from infected wildlife mingling with the herd.
Presently, B. abortus is endemic in both bison and elk located in the Greater Yellowstone basin, and this has proved to be an ongoing problem with transmission of the disease to cattle herds in the area. Due to the behavior of bison vs. elk, there is greater danger from infected bison. They are more gregarious than elk, and tend to congregate together during calving time. This leads to exposure of larger numbers of the bison herd. Elk, on the other hand, tend to isolate themselves during calving time. Elk cows seek seclusion and are fastidious in removing all evidence of birthing, cleaning up the area by consuming afterbirth and fluids to avoid attracting predators. In the case of artificial elk feeding grounds, the risk of transmission to other members of the herd increases considerably.
Predators and scavengers such as coyotes, wolves, crows, vultures and bears are rarely infected, and not at high risk for shedding of the bacteria. However, these animals may mechanically drag infected tissues away from abortion sites and contaminate other areas with the organism.
In cattle, brucellosis can be diagnosed based on either bacterial culture from affected tissue (fetus, placenta, reproductive tract at slaughter or necropsy) or more commonly from serology (tests run on serum of the blood from the live animal.) These blood tests are used for a presumptive diagnosis or as a screening test for herds or individuals. Most cattle breeders will be familiar with these tests as a requirement for some shows or cattle sales, or for transport to another state. There is no practical treatment for infected cattle, and animals testing positive on a brucellosis test come under the jurisdiction of the state and federal governments.
Brucellosis was once widespread in US cattle herds. In 1934, the Federal and State governments began a Cooperative Eradication plan. In 1956, there were 124,000 infected herds found by testing. By 1992, this number was reduced to 700, and as of late 2009, all 50 states are now declared Brucellosis Free. (This designation relates only to cattle herds and is not affected by the presence of the disease in wildlife, except in those instances where domestic cattle are infected as a result of wildlife.) This success was accomplished by test and removal of infected animals, along with vaccination of replacement heifers. It is worth remembering that in the mid 70’s, there was a resurgence of brucellosis in the country’s cattle herds, with infections being found in 15 states that were previously declared free. With the apparent successful eradication of brucellosis in the nation’s cattle herds, USDA/APHIS/VS has developed a concept paper that provides an action plan to now reduce slaughter surveillance by 50%, eliminate the brucellosis ring test (a test performed 2-4 times per year on dairy bulk milk tanks, depending on the state’s brucellosis classification) and eliminate Federal funding for first-point test in low-risk states (states not bordering the Yellowstone area and Class-Free for 5 or more years). They would concentrate their efforts on eliminating the disease in wildlife.
There are presently no federal requirements for brucellosis testing in cattle crossing state lines. Such testing mandates are left up to the states. Some states require no brucellosis testing at all, while other states require all breeding cattle over a certain age to be tested prior to entry. Still other states require testing in cattle originating in states recently (less than 6 years) declared Brucellosis Class Free. The northernmost tier of states from North Dakota and east, including all of New England, Pennsylvania and West Virginia have maintained Brucellosis Class Free status for over 23 years. Wyoming, Idaho and Texas are relatively recent additions, and Montana just regained Class Free status in 2009.
There are two vaccines used to vaccinate for brucellosis in this country, the older strain 19, and the newer strain RB51. Strain 19 was notorious for vaccine reactions in cattle, (including vaccine induced abortions and localized swelling at the site of injection) human disease with accidental exposure, and difficulty in determining disease status due to interference with blood results. The newer Strain RB51 has virtually eliminated vaccine reactions and interference with blood testing, but it is still a problem if accidentally injected into humans.
Because brucellosis is now a very rare disease in cattle, most livestock operators do not bother with vaccination for brucellosis. The process of vaccination is unique for this disease. Only licensed and federally accredited veterinarians can administer brucellosis vaccine. Further more, federal rules dictate that the vaccine can only be given at less than 12 months of age unless specific dispensation is given for vaccination of older animals. The age of vaccination is also regulated on a state level, and certain states have more specific age guidelines, such as vaccination only between 4-8 months of age. Only females are vaccinated. All cattle vaccinated for brucellosis must be permanently identified as vaccinates by the application of a special tattoo in the right ear. This tattoo consists of a special veterinary shield V, followed by the last digit of the year of vaccination. Preceding the V is either the number 1-4 representing the quarter of the year the animal received the vaccination (in the case of Strain 19) or the letter R, representing a reduced dose (in the case of strain RB51.) Female cattle vaccinated as calves and identified with the appropriate tattoo are known as Official Calfhood Vaccinates (OCV). There is also a special tattoo or brand administered to so-called adult vaccinates, but again, this is only is very special circumstances and with appropriate state and federal permission and guidance. Cattle over 12 months of age that are vaccinated for brucellosis are known as Official Adult Vaccinates, but some states do not recognize this designation.
.The most critical application for Brucellosis vaccination for most members owning Highland cattle lies not in the animal’s risk for contracting the disease, but in selling the animal, particularly to the western states. As of this writing, at least 9 western states (including CA, ID, MT, NV, ND, OR, UT, WA and WY) require female cattle entering the state (except for exhibition) to be Official Calfhood Vaccinates. This requirement may carry over into breed sales and auctions; where the purchaser is unknown, and is a requirement for the National Highland Cattle Sale (and all other breed sales) that take place every year under the auspices of the National Western Stock Show.
The decision to vaccinate for brucellosis must be made with regard to future plans for the individual’s sales of breeding stock, both purebred and commercial. Bulls, steers, and usually slaughter heifers are exempt from vaccination requirements, but breeding heifers and cows are not. Top show females that could make a lucrative addition to a sale, may not qualify because their original owner did not routinely provide for brucellosis vaccination. While vaccination of heifer calves is an inconvenience requiring a licensed and accredited veterinarian, it is also a one-time event in each animal’s life, and never requires a booster. Failure to vaccinate females as calves may prove ill advised at a date much later in the cow’s life should the opportunity arise to sell that animal into a state requiring calfhood vaccination. .