Brucella canis in dogs – canine brucellosis symptoms

Overview

Brucella canis targets canine reproductive organs, but infection can also affect other organs. Reproductive problems are the most common manifestation. However, disease may remain hidden for years in a dog not used for breeding.

Dogs are the primary hosts specifically for Brucella canis. Brucella abortus and Brucella suis, for example, can also infect dogs, but this article concerns Brucella canis.

Brucella canis can also infect wild canids.

In northern European reports, findings have mainly involved dogs imported from endemic areas. A northern European record confirmed infection in a resident dog in 2008.

In 2013, an imported bitch introduced infection into a kennel. The bacterium is zoonotic, meaning it can pass from animals to people. However, a generally healthy person's risk of infection from a dog without symptoms is very low.

Causes

The bacterium persists inside cells and tissues

Once in the body, Brucella canis can survive inside cells and spread to lymph nodes, the spleen and liver. Reproductive targets include the uterus, placenta, testes, epididymides and prostate. In the pregnant uterus, bacteria multiply extensively and may cause foetal death.

Brucellosis can also cause early embryonic death, so the problem does not always appear as late-pregnancy abortion.

Bacteria usually begin appearing in the bloodstream 1–4 weeks after exposure. The blood bacterial burden usually decreases within 3–4 months of infection. However, bacteria can remain in blood for up to 18 months. Their presence may continue to fluctuate for years afterwards.

Reproductive fluids are major infection sources

The greatest transmission risk involves aborted foetuses, foetal membranes and uterine discharge. Bacteria are also shed in semen and male dogs' urine. Mating is an important route between dogs. Puppies can acquire infection from an infected dam.

Heavy shedding after birth or abortion can continue for several weeks. Hormonal changes during a season increase shedding. Bacterial numbers in male urine are generally lower than in semen.

Bacteria can enter through the oral or eye mucosa when a dog contacts fluids. Damaged skin can also provide an entry route. Contaminated surfaces may transmit bacteria between dogs. Brief, casual contact does not usually transmit infection easily.

Spread through small airborne droplets, or aerosols, has also been identified in kennel and laboratory environments.

Risk factors

Dogs used for breeding have the greatest opportunities for exposure. An untested dog entering a kennel may spread infection to others living there. Some preventive screening programmes focus particularly on imported dogs and breeding dogs from abroad.

Brucella canis is common in South and Central America and the USA. In Europe, infections have been identified in eastern Europe, Germany, Spain and Sweden, for example. Poor hygiene and uncontrolled breeding favour infection.

A spayed or castrated dog can also acquire infection and become ill. Exposure therefore does not require the dog itself to mate or give birth. Handling an infected dog's aborted foetuses or birth fluids also increases human exposure risk.

Breeders, vets and laboratory staff encounter these exposures at work. Reduced immunity in people may increase the possibility of more serious illness.

Typical symptoms

An adult dog may have few or no general signs for a long time. Abortion usually occurs around days 45–55 of pregnancy. However, pregnancy can end at other stages too.

• A bitch fails to conceive or pregnancies are lost.

• Stillborn puppies are delivered, sometimes alongside live puppies.

• A male dog's scrotum enlarges or becomes irritated.

• A male dog's fertility declines.

• Your dog moves painfully or has a sore back.

• An eye becomes inflamed or your dog squints.

• Your dog is subdued, loses appetite or develops a dry coat.

Inflamed testes may later shrink. Enlarged lymph nodes are a possible finding. Fever is not characteristic of canine brucellosis.

Eye signs may also include a small pupil. Infection in males is often easier to notice than in females because of visible scrotal changes.

Complications and consequences

Infection can damage organs beyond the reproductive system

Brucella canis can cause inflammation of the epididymis or prostate. A bitch may develop uterine inflammation. Disease can cause long-term fertility problems in both sexes.

Discospondylitis, inflammation of vertebrae and the disc between them, can cause back pain. Spinal or joint infection may also involve paralysis. Eye inflammation can be part of the infection's organ effects. Central nervous system signs are rare.

The kidneys can also be affected alongside the reproductive organs and spine.

Disappearing symptoms do not guarantee the infection has ended

Bacterial shedding may recur after medication ends. An infected dog may also have normally successful litters at times. Long-term carriage can therefore maintain transmission risk without visible disease.

Human Brucella canis infections are incompletely recognised because of symptom and testing limitations. A confirmed canine finding is therefore important for human infection control too.

Diagnosis at the vet

Routine blood tests may be normal

The vet considers reproductive problems, other signs and exposure opportunities when choosing tests. A routine blood count, blood biochemistry and urinalysis may be entirely normal. Antibody testing is the primary method for screening dogs without symptoms.

Antibodies usually develop 2–4 weeks after infection. In some dogs, this may take 2–3 months. An early negative antibody result therefore does not rule out recent infection.

Conversely, closely related bacteria can cause a false-positive antibody test. Confirmation may require several methods and repeat samples. Antibody methods include agglutination tests and ELISA.

Culture or PCR looks for the bacterium

Culture aims to identify the bacterium itself, while PCR identifies its genetic material. Samples may include blood, urine, semen or uterine discharge. Aborted foetuses and birth fluids may contain particularly large numbers of bacteria.

Detection can also be attempted in a tissue biopsy. Precise identification of Brucella bacteria can use molecular methods examining characteristics of their genetic material.

Bacterial numbers in blood and fluids vary, which may cause a false-negative result. Samples collected at several times improve the chance of detection. Infection in a carrier without symptoms may be particularly difficult to demonstrate because bacterial numbers are low.

Brucella canis grows slowly and requires specialist identification expertise. Sample handling accounts for staff exposure risk. Bacteria that die during transport or storage may not be detected by culture.

Treatment

Complete elimination of infection cannot be assured

No treatment is known to reliably eliminate Brucella canis infection completely. An antibiotic may settle symptoms while bacteria remain in the body. Bacteria persisting inside cells and tissues can later cause recurrence.

Some national guidance recommends euthanasia of infected dogs to prevent spread to people and other dogs. This recommendation also reflects that an absence of symptoms does not guarantee bacterial shedding has stopped.

If an infected dog is not euthanased

If the dog is not euthanased, spaying or castration and veterinary-planned antibiotic treatment are recommended. Surgery reduces reproduction-associated shedding but does not cure the infection. Medication often involves a combination of antibiotics.

No single reliably best antibiotic or treatment duration is known. Monitoring is long-term and may continue throughout life. Repeated tests monitor possible reactivation of infection.

Contact with other dogs is prevented to reduce transmission. An infected dog is not taken to shows or other dog events. Infection can still spread without mating after castration.

Prevention

Before breeding, antibody testing assesses infection risk in imported dogs and breeding dogs from abroad. A dog arriving from a high-risk area is tested before joining other kennel dogs. An infected dog is not used for breeding.

A testing interval of 6 months has been recommended for regular breeding-dog screening. Testing bitches before every mating is also recommended. Castration may reduce reproduction-associated spread but does not remove other exposure opportunities.

If infection is found in a kennel, dogs that have lived there or visited temporarily are also tested. Other kennel dogs undergo antibody testing at least twice. Environmental cleaning and disinfection also form part of control.

Routine disinfectants are effective against Brucella canis. Use protective gloves and hand hygiene when handling fluids and potentially infected material. Professional care may additionally require eye protection and protective clothing.

Important for dog owners

Tell the vet at first contact if Brucella canis is suspected. Record the country of origin, import date, matings, abortions and contact with other kennels. Bring previous laboratory results and medication details. Arrange sampling before handling or moving aborted foetuses or other potentially infectious material.

In some countries, vets and laboratories must report suspected or confirmed infection to an official vet. Under such reporting systems, the official vet passes information about confirmed infection to the relevant public-health doctor.

Compile a list of mating partners and other close canine contacts to plan investigations. Also record who has handled birth or abortion fluids. If a person seeks medical advice about possible exposure, mention the dog's suspected or confirmed Brucella canis infection.

Frequently asked questions

Can a healthy-looking dog carry Brucella canis?

Yes: an adult dog may have few general signs and infection can remain hidden for a long time. Even a normally successful litter is possible in an infected bitch. Outwardly good health therefore does not replace assessment of infection risk in a breeding dog.

Does brucellosis spread only through mating?

No: dogs can also be exposed through urine, birth fluids and contaminated surfaces. A castrated or spayed dog can also acquire infection and develop clinical illness. However, brief casual contact does not usually transmit infection easily.

Does a negative antibody result rule out infection?

Not always, because antibody development can take 2–4 weeks or even 2–3 months. Detection of the bacterium itself also varies with sampling time. The vet may therefore combine tests and collect further samples later.

Does castration eliminate infection?

No, although spaying or castration may reduce shedding and reproduction-associated spread. Bacteria can remain in cells and tissues elsewhere. Monitoring and contact management therefore continue after surgery.

Is the human infection risk high?

For a generally healthy person, the risk from a dog without symptoms is very low. Infection is nevertheless possible, particularly when handling reproductive fluids, aborted foetuses or stillborn puppies. Reduced immunity may increase the severity of human illness. The number of bacteria needed to infect a person is unknown.