Bovine Brucellosis, also known as Brucella Abortus or Bang’s disease, is a devastating zoonotic disease that primarily affects ruminant animals such as swine, bison, and cattle. However, this disease is also transmissible to humans.
Brucellosis is one of the most serious and costly diseases that can affect both farmers and their cattle.
In humans, this disease is known as undulant fever because of the severe fever that comes and goes intermittently. It is also called Malta fever after the island of Malta where the first human was diagnosed with it.
This article will explain everything you need to know about Brucellosis as it is vital for every cattle owner to understand what Brucellosis is, what symptoms it causes, and how to test, diagnose, prevent, and treat it.
Table of Contents
Causes of Brucellosis
Brucellosis is an infectious disease that spreads rapidly. Brucellosis stems from three primary bacteria within the Brucella genus: B. suis, B. melitensis, and B. abortus.
B. abortus is most often seen amongst bison and cattle. B. melitensis also affects bison and cattle but is also frequently seen in swine and reindeer.
B. suis primarily affects goats, but is not as widespread, and has not been diagnosed in the United States.
Transmission of Brucellosis in Cattle
The bacteria responsible for Brucellosis is most often localized to the udder and reproductive organs in dairy cattle. These bacteria spread through milk and vaginal discharge of female cattle, as well as the expulsion of an aborted fetus or placenta in infected animals.
Transmission in cattle occurs when an infected member of the herd gives birth or aborts a fetus and other members of the herd come into contact with the infectious material left behind. It can be transmitted if a cow licks a contaminated area and then eats or drinks from a communal food or water source.
Brucella bacteria spreads quickly and easily through a herd.
It is often introduced for the first time by purchasing a replacement animal that carries the infection from another herd. It can also infect a Brucellosis-free herd when wild animals (or their excretions) come into contact with members of the herd out on pasture.
The incubation period of Brucellosis can range from 2 weeks up to a year, so it may not be readily apparent when and where Brucellosis came from.
Transmission to Humans
Human Brucellosis is most often caused by consuming raw milk or the ingestion of dairy products that have not undergone pasteurization. It can also be spread through ingesting meat that hasn’t been cooked properly.
Brucellosis can also spread through breathing in the bacteria. This most often occurs in slaughterhouses or laboratory settings where people can come into contact with significant amounts of the bacteria.
The third possible avenue of infection is through direct contact of membranes or skin wounds. Humans who handle newborn animals or the placenta and excretions after birth such as veterinarians, meat packers, and slaughterhouse workers are most at risk.
It is unlikely for humans to spread the infection to other humans, though a mother may pass along Brucellosis to a nursing infant. Human-to-human spread most often occurs through blood transfusion or organ transplants.
Risk Factors of Brucellosis
There are many ways to contract Brucellosis. The incidence of Brucellosis infection is higher in certain geographical areas, job industries, and products.
Areas that lack strong public health and animal health eradication programs have more cases of Brucellosis, though Brucellosis can still exist in places that have programs in place.
Some of the locations with greater Brucellosis cases in cattle are:
- Mediterranean countries
- Central and South America
- Middle East
- Caribbean islands
- Greater Yellowstone area in the United States
Certain products are more likely to spread Brucellosis and should be avoided.
- Raw milk cheeses
- Unpasteurized milk from cows, sheep, or goats
- Uncooked or undercooked meat from cows, sheep, pigs and goats
Certain occupations carry more risk of coming into contact with Brucella bacterial strains:
- Laboratory workers who handle Brucella bacteria strains
- Slaughterhouse workers
Symptoms of Brucellosis
While there are tell-tale symptoms of Brucellosis, it can still be difficult to determine because many of these symptoms can be attributed to several other types of illness.
The main symptoms of Brucellosis in cattle are:
- Slowing of milk production
- Weight loss
- Aborted fetuses
- Weak calves
- Uterine infection
- Retained afterbirth
- Arthritic, enlarged joints
It is not possible to tell that cattle have Brucellosis from the way that they look. It is often suspected when several members of a herd begin to deliver weak calves, or suffer pregnancy loss between the 5th and 7th month of gestation.
Cows may also be unable to become pregnant or suffer from delayed conception.
In cows who have given birth, milk production is reduced and may not be enough to sustain the calf.
It should be noted that even though the majority of cows either lose their pregnancy or birth weak calves, occasionally an infected cow can birth a healthy calf. This does not mean that the bacteria is not present – it still poses a danger to the herd and to human handlers.
Human Infection Symptoms
The symptoms in humans differ from cattle and other ruminants. Symptoms can come and go, and may last years or never go away.
According to the Centers for Disease Control and Prevention (CDC), the symptoms seen in humans infected with Brucellosis are:
- Muscle and joint pain
- Swelling of testicles or scrotal area
- Swelling of the liver
- Swelling of the spleen
Diagnosis of Brucellosis
There are several diagnostic tests available to diagnose Brucellosis in cattle.
Dairy cows have their milk batch tested during semi-annual tests. If Brucellosis is present in the herd, it will show up in the milk.
BRT testing is an economical way to test for Brucellosis in a dairy herd anytime Brucellosis is suspected. Samples of milk or cream are taken from every member of the herd and placed in a container with strained, dead Brucella organisms.
A blue color along the rim of the container is a positive result of the presence of Brucella.
For non-dairy cattle, routine blood tests are performed at auctions and livestock sales for Brucellosis. Blood tests are also performed in some states anytime transfer of ownership of cattle or bison occurs.
Cattle have USDA-approved approved backtags placed on them which can be traced back to the herd of origin. If a positive test happens at an auction or sale, the tag number can be traced and the herd owner notified of the presence of Brucellosis.
Additional testing is performed at no cost to the herd owner by public animal health officials to confirm the presence of Brucellosis within the herd. All cattle aged 6 months and older aside from spayed heifers and steers are required to be tested.
MCI testing is also conducted at slaughter on all beef cattle 24 months of age and older as well as 20 months and older for all dairy cattle.
Blood Agglutination Test
If a herd has been identified as having Brucellosis, blood agglutination tests can be performed on the herd to identify the members within that herd that have the bacteria.
Blood samples will be taken from each member of the herd and tested by a laboratory that can identify the individuals who are positive.
Brucellosis Card Test
This test can be performed in the field with results available within minutes. Kits contain everything necessary to test the blood from a single specimen.
Blood serum is placed on a white card and mixed with an antigen serum. After four minutes, the result can be read.
Diagnosis in Humans
Routine serological diagnostic tests for this animal disease are not recommended by the CDC for humans who have professions that place them more at risk.
Brucellosis infection has several symptoms that will be present in infected hosts. It is recommended to monitor for symptoms and if they are present, to seek medical treatment.
Prevention and Treatment of Brucellosis
There is no cure for Brucellosis in infected animals, although some animals may recover.
It is vital to practice safe management practices when purchasing new animals. Testing replacement animals and isolating them for at least 60 days and re-testing them is ideal to prevent the spread of Brucellosis.
Cattle that are located in areas with a high occurrence of Brucellosis should be given the Strain 19 or Strain RB51 Brucella vaccine. This vaccine is only available by veterinarians accredited by the USDA or through APHIS officials in the United States.
Strain RB51 is favored over Strain 19 as it eliminates the negative reactions associated with 19 postvaccination such as inflammation at the injection site and abortion of fetuses in pregnant cows. It also will not confuse the results on diagnostic tests because the antibodies will not be the same type as that produced by the bacteria.
Female heifers should be given the vaccine between 4 and 6 months of age. Once they are given the vaccine, they will have a tattoo placed on their ear to identify the year of the application of vaccine.
The Brucella abortus vaccine is not full-proof and is not 100 percent effective in prevention, but it does produce a bodily response and increase resistance to the disease. The vaccine has been shown to be 65 percent effective given average exposure.
Prevention and Treatment for Humans
In humans, prevention is key. Avoid unpasteurized milk and dairy products, and always cook meat to the proper temperature to reduce the chance of Brucellosis infection.
Good sanitation practices are one of the best methods of prevention.
For humans who are high-risk and regularly work with animal carcasses and excrement, it is vital to use proper PPE. It is important to not allow any open wounds to come into contact with potential bacteria.
Always monitor for Brucella symptoms and if present, seek medical treatment. Treatment usually involved antibiotics such as Doxycycline along with an antimicrobial taken for 21 days.
What to Do if Your Herd is Infected
It is vital to notify a public animal health official organization such as APHIS if Brucellosis is identified in your herd. They can help with the costs of additional diagnostic testing and will help you eradicate Brucellosis from your herd.
Specially trained professionals will help you locate the likely source of exposure and eliminate it.
Your herd will then be placed under quarantine and any exposed animals will only be allowed to move to slaughter. This condition will remain until no further members of the herd test positive.