Canine brucellosis: key insights into a growing UK threat
Canine brucellosis is a zoonotic infection caused by Brucella canis, a gram negative intracellular bacterium. The infection is endemic in a number of countries, including much of eastern Europe. Although historically rare in the UK, data released by the UK government shows a steep rise in cases, with just three prior to 2020, and at least 107 since. Most of these cases have been directly imported into the UK from Eastern Europe.1
Brucellosis is a reportable disease with zoonotic potential and the implications of this growing threat should not be underestimated.
Clinical signs of canine brucellosis
- Neck or spinal pain (discospondylitis)
- Lameness due to osteomyelitis and polyarthritis
- Orchitis, epididymitis and scrotal oedema
- Discharge from penis / vulva
- Infertility or abortion
- Uveitis, corneal oedema, optic neuritis
- Lethargy
- Generalised lymphadenopathy
- Splenomegaly
In pregnant dogs, abortion may occur between days 45 and 59 of the first pregnancy following infection. Later pregnancies may reach full term, but pups often fail to thrive and may die soon after birth.
However, one of the challenges surrounding Brucella canis in dogs, is that many, if not most infected dogs are subclinical. Although these dogs may not be showing any signs of disease, they can still be infectious and there is a likelihood that they will develop clinical disease in the future.
Transmission
B canis is shed in all body fluids. It is largely a sexually transmitted disease, with mucocutaneous transmission via infected saliva, vaginal discharge, semen or aborted materials the main route of spread.
Vertical transmission to pups in utero or via infected milk is also possible, and it should be noted that even pups that appear healthy at birth may develop clinical disease later on.
Breeding facilitates transmission, but infection can also be transmitted between non-breeding dogs. This risk remains relatively low but is increased where there is prolonged contact.
Is Brucella canis zoonotic?
Brucella canis is a zoonosis. People who are at greatest risk of infection are those who come into contact with contaminated fluids, such as veterinary staff performing surgery, or laboratory staff. For most people, disease symptoms are relatively mild, and infection can be successfully treated with antibiotics. The consequences may be more serious in immuno-compromised individuals and a big concern is the risk of miscarriage in pregnant individuals.
It is thought that zoonotic transmission is not common even in endemic parts of the world, although infection levels may be under-reported.
What is the incubation period for brucellosis in dogs?
The incubation period is very variable. It generally ranges from two to four weeks, but can be as short as five days or as long as six months. The length of time between infection and the onset of reproductive signs is very variable.
How do you test for Brucella canis in dogs?
When it comes to brucellosis tests for dogs, there are several options. Owing to the zoonotic risk posed by canine brucellosis, samples from suspected cases should be handled with care and appropriate PPE should be worn.
- Serology
The Animal and Plant Health Agency (APHA) recommend serological testing in the majority of cases. Serology provides the greatest sensitivity but cannot distinguish between current or previous infection. It should be further noted that not all dogs produce detectable levels of antibodies, and this is especially true of puppies. Where there is strong clinical suspicion of disease in a dog with negative serology, further testing should be carried out.
- PCR
PCR tests lack sensitivity. There is a risk of obtaining false negatives and it is not usually recommended as a screening test. Veterinary surgeons should speak to their diagnostic laboratory for advice.
- Bacterial culture
Bacteriology can provide definitive evidence of disease.
Is Brucella canis notifiable?
All cases of B canis are notifiable, including both direct detection of the bacterium and detection or antibodies by serology. Reporting is via local APHA veterinary investigation centres.
Management of dogs with canine brucellosis
The management of individual animals with canine brucellosis is challenging, not least because of the emotional implications. Infection is lifelong in dogs and due to the zoonotic risk to people, euthanasia is usually the recommended course of action.
What about antibiotics for treating Brucella canis?
Treating B canis with antibiotics is not straightforward. B canis is in intracellular bacterium and can remain sequestered within cells for long periods. Even prolonged courses of antibiotics cannot guarantee successful treatment of infection. In addition, there is no test that can prove treatment success.
How about neutering?
As a predominantly reproductive disease, consideration is sometimes given to neutering. In cases where euthanasia is not carried out, neutering together with a prolonged course of antibiotics has been suggested. The use of pre-operative antibiotics decreases zoonotic risks to the surgeon and continued post-operative use reduces the risk of disease recrudescence due to physiological stress associated with surgery. While neutered dogs are less likely to spread infection, the risks are by no means zero.
Canine brucellosis: the challenges
With an influx of foreign rescue dogs in recent years, the threat of B canis is not going away any time soon. The disease is a particularly challenging one to manage….
- Infection can be subclinical
- Where clinical signs are present, they are variable and can be non-specific
- The incubation period varies widely and can be very long
- Diagnosis is not always straightforward, false negatives are possible
- Euthanasia is almost always the recommended course of action
At the moment there is no mandatory testing of foreign imports, so veterinary professionals should take care when handling these patients and wear appropriate PPE.
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