There has been an increase in reports of dogs with Brucella canis in the UK since 2020, with several complex cases involving multiple dogs coming to light. Most are linked to imports of dogs from eastern Europe, but some reported cases have come from other countries and some have occurred in British-born dogs, albeit with some link to imported dogs.
In this environment, it is particularly important for vets to understand both the bacteria and the disease; the management and treatment options; the zoonotic risk; and their legal duty to report positive laboratory results to the authorities. Considering B. canis as a differential will enable vets to best advise both clients importing dogs from abroad and those who wish to breed dogs at risk of infection.
This article aims to outline the basics of brucellosis in dogs in the UK and point vets and owners to other available sources of information and advice.
Brucellosis in dogs
There are four Brucella species known to cause disease (brucellosis): Brucella suis, Brucella melitensis, Brucella abortus and Brucella canis (Carmichael and Greene, 2006). These bacteria are generally host specific, with the main hosts being pigs, small ruminants, large ruminants and canines respectively, but are able to cross to other species including humans. Most reported cases of brucellosis in dogs have been caused by B. canis and all cases detected in Great Britain to date have been caused by this species.
Most reported cases of brucellosis in dogs have been caused by B. canis and all cases detected in Great Britain to date have been caused by this species
The Brucella species adapted to ruminants are exotic to Great Britain and thus notifiable. Surveillance is in place (Holland, 2020) and suspicion of disease must be reported to APHA. Since April 2021 both direct and indirect detection of B. canis in a laboratory, for example not only by culture but also by serology, is also reportable and must be reported to APHA with a statutory requirement to provide additional information relating to the case.
B. canis is a Gram-negative bacteria first isolated in the USA in 1966; it was soon identified as a major economic risk to breeding kennels (Carmichael and Kenney, 1968). As seen with other Brucella species, B. canis is zoonotic and the first human case of brucellosis caused by it was identified in 1968. Human cases are rare; however, the pathogen is known to affect mainly domestic dogs and, less often, other canids such as foxes and coyotes.
Unlike the other Brucella species which are “smooth”, B. canis is “rough”. This description not only relates to their different appearance on bacterial culture media but also reflects significant differences in their surface antigens. This in turn impacts on the pathogenicity of B. canis in non-canine species and also means different serological tests are required to detect infection. Although B. canis is less zoonotic than the other Brucella species, it is still in the human pathogen hazard group three as assessed by the Advisory Committee on Dangerous Pathogens (ACDP).
Clinical signs in dogs
There are no pathognomic signs of brucellosis in dogs, and many infected dogs may be asymptomatic. Following a variable incubation period of at least two to three weeks, clinical signs can appear and symptoms can include abortion, stillbirth and prolonged vaginal discharge in females, and epididymitis, orchitis, painful urination, prostatitis, scrotal oedema and testicular atrophy in males. Infertility or failure to conceive is seen in both sexes. They may also present with lameness, particularly due to inflammation in the hindlimb joints (polyarthritis), lethargy, irritability and loss of appetite (Carmichael and Greene, 2006).
Clinical signs can appear and symptoms can include abortion, stillbirth and prolonged vaginal discharge in females, and epididymitis, orchitis, painful urination, prostatitis, scrotal oedema and testicular atrophy in males
B. canis is also a known causative agent of discospondylitis, which is the most common presentation of infection with B. canis after reproductive symptoms (Buhmann et al., 2019; Escauriaza et al., 2021). Less commonly, other varied and less specific signs such as uveitis can also be seen (Cosford, 2018).
Some infected bitches can give birth to seemingly clinically normal puppies that are themselves infected and can manifest the disease later in life.
Differential diagnoses can include other bacterial causes of infertility and abortions such as Streptococcus, Escherichia coli, Mycoplasma, Streptomyces, Salmonella, Campylobacter, etc; viral infections such as canine herpes viruses; and other rare parasitic causes of abortion in dogs such as Neospora and Toxoplasma.
In dogs infected with B. canis, large numbers of bacteria are shed in the first six to eight weeks following infection, commonly followed by intermittent shedding of the bacteria for their entire lives. The primary risks of spread are during mating and during contact with products of abortion such as the foetus, foetal membranes, placenta, etc, which poses a significant risk both to other dogs and to those handling them.
In utero transmission is common, and transmission through milk, blood, faeces and urine is also possible. Thus, care has to be taken in the handling and management of infected dogs to limit contact with other dogs and humans (Hensel et al., 2018; Buhmann et al., 2019).
The only reliable way to prevent the spread of infection from an infected dog is euthanasia of the infected animal.
Epidemiology of disease
B. canis has been reported worldwide and is considered endemic in southern USA and Central and South America (Buhmann et al., 2019).
A study by Buhmann et al. (2019) suggests that B. canis should be considered as a differential for reproductive disease and discospondylitis across the whole of Europe, after PCR-positive dogs were identified in Spain and Poland (and more rarely Italy and France) and seropositive dogs were identified from 13 of 20 European countries from which samples were tested. However, cases of B. canis appear to be on the rise across western Europe, stemming largely from the uncontrolled movement of dogs from eastern Europe where testing for B. canis is very uncommon. The Human Animal Infections and Risk Surveillance group (HAIRS) risk statement presents the high number of dogs legally imported into the UK from different countries.
Despite warnings that B. canis could be present in the UK following serological analyses in the early 1980s (Taylor et al., 1980), the first confirmed cases outside of quarantine establishments in Great Britain were two dogs in 2017. Both cases directly involved individual dogs that had been imported from eastern Europe (Morgan et al., 2017; Whatmore et al., 2017).
Another eastern European import was confirmed positive in 2018, and these cases were all that had been recorded until 2020. In June 2020, a fourth case was reported on a breeding site with a history of abortions. Multiple positive dogs were found, including both imports and British-born dogs. Spread between premises was identified, and significant human exposures came to light with public health authorities collaborating closely with APHA, as has been the situation with all subsequent cases. The index dog in this case was confirmed positive for B. canis by bacterial culture, the gold standard for diagnosis of this organism.
The fifth and sixth cases, again both involving multiple dogs, were identified in August 2020, and links to puppy imports from eastern Europe were found. There followed several reported suspicions and identified cases, with a total of 11 investigations being completed before the end of 2020 which resulted in 10 index cases being identified. During these investigations approximately 80 dogs were serologically tested, of which 49 were seropositive, with two index cases confirmed by culture.
As of mid-August 2021, there have been a further 19 investigations which resulted in 16 index cases being identified, 17 of 40 dogs tested being identified as serologically positive and four more index cases being confirmed by culture. This gives a total of 26 known cases and 66 seropositive dogs since June 2020.
There is currently no surveillance for B. canis infection in dogs and no mandatory pre- or post-import testing
There is currently no surveillance for B. canis infection in dogs and no mandatory pre- or post-import testing. Although the true prevalence of infection in the UK is not known, it is still considered to be rare in UK dogs, and significant efforts are being made to limit any onward spread from identified cases owing to their threat to public health.
In response to the earlier cases, a statement regarding the risk that B. canis presents to the UK human population was published by HAIRS in February 2021. A letter from the UK Chief Veterinary Officer was also published in February 2021 to “alert vets to this potential diagnosis, especially in imported dogs and recommend they use appropriate personal protective equipment when handling such animals” (Middlemiss, 2021).
Clinical diagnosis can be difficult due to the lack of pathognomic signs and the variable, sometimes very lengthy, incubation period.
In a laboratory, culture and PCR offer direct detection but they are more reliable when specific clinical samples – such as products of abortion or parturition, or synovial fluid from infected joints – are tested rather than blood samples. This is because sensitivity is relatively low in these tests, meaning a negative result from a blood sample does not guarantee absence of infection.
In a laboratory, culture and PCR offer direct detection but they are more reliable when specific clinical samples – such as products of abortion or parturition, or synovial fluid from infected joints – are tested rather than blood samples
Serology offers indirect evidence of the presence of the disease by detecting antibodies; however, these can take weeks or even months to form. There is a potential for false positives in the serology due to cross-reactivity, although the specificity of the serological tests used at APHA (RSA, SAT and iELISA) is high. Treatment with antibiotics and steroids prior to testing can also affect the sensitivity of the diagnostic tests, especially culture.
Different tests can be more useful than others at different times in the course of the disease and in different situations; the Great Britain National Brucella Reference Laboratory at APHA, Weybridge “recommends serological testing in most cases in order to obtain results with the most reliable sensitivity” (APHA, 2021). If B. canis can be isolated from samples, then whole genome sequencing is used to assist with epidemiological investigations. More information regarding this and other useful guidance for vets and owners of dogs suspected to be infected with B. canis can be found in this APHA guidance document.
Clinical signs in humans are similar to those seen with brucellosis caused by other strains of Brucella; however, there are currently no validated serological tests for B. canis infection in humans. If infection with B. canis is suspected, then this must be made clear to the medical services as the conventional serology for human brucellosis will not detect B. canis infection. Treatment with antibiotics, however, is much more effective than in dogs.
With assistance from APHA, public health authorities have tested all people identified as being at high risk of exposure to B. canis since the first case in 2020. So far no one has been diagnosed with brucellosis.
No vaccine is available against B. canis so prevention is key. Early identification of infected dogs and effective management of these cases is vital in controlling the spread of the disease. Screening can be difficult given the long and varied incubation periods but it is an essential tool. Screening should be encouraged for owners with dogs imported from countries where B. canis is more common and before breeding any dog that may have been in contact or previously bred with a high-risk individual.
No vaccine is available against B. canis so prevention is key. Early identification of infected dogs and effective management of these cases is vital in controlling the spread of the disease
Treatment and management
Once B. canis infection is confirmed in a dog, the recommended approach is euthanasia, especially where the animal is unwell. Treatment to a resolution whereby the animal no longer poses a risk as a source of infection to other dogs and people is very difficult, if not impossible, and cannot be verified (Santos et al., 2021).
For apparently healthy animals where the owner is reluctant to euthanise, then neutering (for entire dogs and bitches) with pre- and post-operative antibiotics – to protect veterinary staff by reducing shedding – can be employed, followed by regular testing. However, this should only be undertaken after a rigorous and documented risk assessment. Lifelong measures are also advised following neutering to reduce risk of spread.
Again, further advice for owners of dogs suspected of or diagnosed with brucellosis can be found in the APHA guidance document. A diagnosis of B. canis in a laboratory test is reportable to APHA or other relevant competent authorities and both owners and vets will be contacted by their local health protection team.
A diagnosis of B. canis in a laboratory test is reportable to APHA or other relevant competent authorities and both owners and vets will be contacted by their local health protection team
A diagnosis of B. canis in a laboratory test is reportable to APHA or other relevant competent authorities and both owners and vets will be contacted by their local health protection team.
In conclusion, brucellosis in dogs appears to be on the rise in the UK. Veterinary surgeons should consider the risk of B. canis infection when dealing with imported dogs, or dogs with signs consistent with the infection. They should take care to protect themselves from B. canis by wearing appropriate personal protective equipment when dealing with suspect cases, and undertaking robust risk assessments before conducting surgical procedures on suspect dogs (Boyden, 2021).
Veterinary surgeons should warn any lab or referral centre either receiving material from or taking over the care of a suspect dog of the potential zoonotic risks so appropriate risk management measures can be deployed.
Further guidance from APHA is available online, and from the Great Britain National Brucella Reference Laboratory at APHA.