Brucella canis: The emergence of Brucella canis as a public health threat in Europe

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The emergence of Brucella canis as a public health threat in Europe: what we know, and what we need to learn

Published 2 November 2023

Djokic, V. et al. (2023) The emergence of Brucella canis as a public health threat in Europe: what we know, and what we need to learn. Emerging Microbes & Infections, 12 (2), no.2249126.

This paper provides an overview of the current understanding of Brucellosis canis infection in dogs and humans and points out current gaps in knowledge. It proposes a range of future steps needed to identify the risks of human infection, and the diagnostic and management strategies needed for infected pet and kennel dogs.

The paper starts by providing an overview of geographic spread of cases and provides a table of European incidents of B. canis infection, although it notes that because of the lack of systematic surveillance it is likely that not all cases are detected or reported.

There is a comprehensive section reviewing diagnostic testing for B. canis, including methods of isolation and identification, noting that “This is followed by information on molecular detection (PCR) and indirect detection methods (serology).

The section on serology reviews the range of different tests available and includes a summary table detailing the platform, antigen and method as well as providing evidence on the diagnostic performance (sensitivity and specificity) where possible. Although they emphasise that “it is impossible to present a complete picture within a summary as, for example, the selection criteria used to select the samples for validation has a big impact on the outcome” (p. 10). They note that the interpretation of serological results requires an understanding of epidemiological context (e.g. estimated prevalence) and risk factors such as clinical and travel history, and opportunity for transmission. They also note that there is no international scientific community consensus on serological testing strategies according to the stage of infection.

The following section reviews the current evidence on the risk that exposure to B. canis poses for human health. This concludes that “Based on current data, without reliable diagnostic tools, it is estimated that B. canis has a low zoonotic risk” (p. 14).  However, they note the factors such as the non- specific symptoms of the disease and absence of reliable diagnostic tools leave unanswered questions about the prevalence and severity of human infection.

In the section on treatment authors note that there are currently no preventive treatment options available, and that the “treatment of infected dogs is a debated issue as antimicrobial therapy does not guarantee B. canis elimination, with relapses of infection frequently reported in addition to the risks related to the development of antimicrobial resistance” (p. 15).  However, they acknowledge that attempts to treat may be the first choice for owners who see their dogs as family members, and that antimicrobial treatment, combined with neutering, may represent the only alternative to euthanasia. However, it is noted that in vitro susceptibility studies that suggest that tetracyclines, aminoglycosides, and fluoroquinolones possess bactericidal activity against B canis, particularly in combination, do not always translate into efficacy of treatment in vivo and the frequency of relapse is considered high, although precise data on this is lacking.

While neutering removes the predilection sites for infection and prevents reproductive transmission the authors acknowledge that there is currently a dearth of evidence on the impact of neutering on disease progression, non-reproductive transmission, and the level of risk for veterinary surgeons carrying out the surgery.

They suggest that dog owners who opt for treatment should be “clearly informed on costs, duration (weeks) and possible inconvenience (relapses and repeated treatments) related to the therapy and the necessary follow-up of laboratory investigations to monitor the efficacy of therapy” (p. 16).

The paper concludes with the discussion of the management of B. canis infection in dogs in the light of current knowledge.

Scenario 1: Individual dog as a house pet

For this scenario, the authors start by clarifying that “currently the isolation of B. canis strain is the only unequivocal proof of infection (with or without clinical symptoms) but that “dogs with compatible clinical symptoms and at least positive serology or PCR may be considered as infected, beyond reasonable doubt, especially if epidemiological links with infected dogs are highlighted” (p. 19).

They also point out that for animals that test serologically positive, “multiple criteria have to be taken into account to determine whether the dog can be considered as infected or false positive” noting that uncertainty about the true infection status creates additional management issues. Further guidance regarding the interpretations of infection status is provided in Table 4 in the paper.

The authors then discuss appropriate diagnostic testing and the interpretation of results for pet dogs before making separate recommendations for the management of dogs with suspected and confirmed infection with B.canis.

Scenario 2: B. canis infected kennels

The authors start by defining a B. canis positive kennel as one with at least one confirmed infected dog (isolation or PCR positive) or at least two reproductively active animals with confirmed serological positive response. They then provide recommendations to mitigate the risks of B. canis in both breeding kennels and adoption kennels including appropriate testing before introduction and sale or adoption.

The authors conclude that new epidemiological and experimental studies are urgently needed and include, amongst others, the following suggestions:

  • To fill the surveillance gaps, representative epidemiological surveys in Europe would be required to assess the prevalence of the disease.
  • Further investigations should be undertaken into
    • The epidemiological significance of non-reproductive contact routes of transmission between dogs.
    • The effect of gender and neutering on the infectiousness and susceptibility of dogs.
    • Whether puppies and asymptomatic dogs transmit the disease?

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