Zoonoses are diseases that can be transmitted from animals to humans. According to the Health and Safety Executive there are approximately 40 potentially zoonotic diseases currently identified in the UK and approximately 300,000 people in a variety of occupations which are potentially vulnerable to these zoonotic diseases.
The increased freedom of movement of animals across borders over the last 20 years, the increase in imported rescue dogs and effects of climate change have all contributed to significant changes in the distribution of infectious diseases across the globe. Therefore, the location of the UK as an island nation in the cooler climate of northern Europe is no longer a guarantee that many of these potential pathogens will be excluded from our animal populations.
In this article, we would like to highlight three zoonotic diseases that may occur in companion animals in the UK: leptospirosis, brucellosis and tuberculosis.
Leptospirosis is a zoonosis caused by spiral-shaped bacteria of the genus Leptospira (also referred to as leptospires), which may be either pathogenic or saprophytic. Hosts become infected either by contact of mucous membranes or broken skin with contaminated soil or surface water or alternatively by contact with the urine from infected animals.
There are over 250 known pathogenic serovars infecting a variety of species. Pathogenic leptospires belong to the sub-group Leptospira interrogans and non-pathogenic ones to the subgroup Leptospira biflexa. Antibody prevalence data indicate that dogs in Europe are mainly exposed to serogroups Icterohaemorrhagiae, Grippotyphosa, Australis, Sejroe and Canicola. The serogroup Grippotyphosa is common in continental Europe, but rare in the UK and Ireland.
Leptospirosis is more common in tropical areas of the world and is still uncommon in the UK. Clinical leptospirosis is common in dogs, but uncommon in cats. Both asymptomatic cats and dogs can shed leptospires in urine and pose a risk to humans.
In dogs, acute leptospirosis most commonly causes acute kidney injury (AKI) and liver disease; however, pulmonary disease and haemorrhagic disease may also occur
In dogs, acute leptospirosis most commonly causes acute kidney injury (AKI) and liver disease; however, pulmonary disease and haemorrhagic disease may also occur. Common haematological abnormalities include anaemia, thrombocytopenia and leukocytosis or leukopenia. Frequent biochemical abnormalities include elevated hepatic enzymes, urea and creatinine, as well as electrolyte disturbances. Urinalysis reveals isosthenuria in the majority of cases, with occasional hyposthenuria reported. Glucosuria, haematuria, pyuria and granular casts may be seen. Proteinuria of glomerular and tubular origin occurs in the majority of dogs.
The most useful diagnostic tests for canine leptospirosis are the microscopic agglutination test (MAT) to detect anti-leptospiral serum antibodies and the PCR for detection of leptospiral DNA.
Recent infection is best confirmed with MAT testing of paired serum samples, collected one or two weeks apart. A fourfold or greater rise in MAT is highly suggestive of leptospirosis.
Leptospires are generally detected by PCR in blood for the first 10 days after infection and thereafter in urine. The European consensus statement on leptospirosis in dogs and cats recommends PCR testing of both blood and urine collected before antibiotic administration in each dog with a clinical suspicion of leptospirosis, regardless of the duration of the clinical signs (Schuller et al., 2015).
The European consensus statement on leptospirosis in dogs and cats recommends PCR testing of both blood and urine collected before antibiotic administration in each dog with a clinical suspicion of leptospirosis
A clinical suspicion of leptospirosis can be confirmed post-mortem by applying PCR to renal tissue.
According to the European consensus statement, positive PCR on blood together with consistent clinical signs is highly suggestive of acute leptospirosis (Schuller et al., 2015). A positive PCR on urine indicates renal shedding, which can occur in both acutely infected animals and chronic renal carriers. Negative results on blood or urine do not rule out leptospirosis. PCR on urine is the test of choice to detect renal carriers.
It is important to highlight the recent increase in cases of Brucella canis infection diagnosed in the UK. B. canis is not considered endemic in the UK and historically it has only rarely been diagnosed in imported dogs. However, since summer 2020, the APHA has been notified of more than 40 cases of canine brucellosis. Almost all cases have been imported dogs, the vast majority from Romania.
Brucella canis infection in dogs is predominantly associated with reproductive failure, but other clinical signs include discospondylitis and uveitis. Infection can also be subclinical.
Diagnostic tests available in the UK are B. canis serum antibodies and PCR for detection of B. canis in EDTA blood, urine, semen, aborted material or swabs of presumed infected tissue.
Zoonotic infection with B. canis is infrequently reported in humans but may be underdiagnosed due to often vague clinical signs and lack of testing. Infected dogs pose a significant risk to owners, veterinary staff and laboratory staff processing pathology samples, particularly in individuals with certain underlying health conditions.
[Brucella canis] infected dogs pose a significant risk to owners, veterinary staff and laboratory staff processing pathology samples, particularly in individuals with certain underlying health conditions
In order to identify cases and minimise the risk of infection and transmission to other dogs or humans the following measures are recommended:
- Highlight risk to clients importing dogs from Eastern Europe (particularly Romania) or those travelling with their pets to this region
- Encourage potential owners to request pre-export testing and consider pre-breeding testing
- Highlight risk to the veterinary team and routinely record the origin and travelling history of dogs (and their parents) when they are registered and seen
Tuberculosis (TB) is an infectious disease caused by a number of different but closely related bacteria. Relevant members of the tuberculosis complex group include Mycobacterium tuberculosis, M. bovis and M. microti.
Mycobacterium tuberculosis causes over 90 percent of tuberculosis cases in people, but rarely infects other mammals, except for dogs. M. bovis is the main cause of tuberculosis in cattle. It can also infect various other mammals, including humans, dogs, cats, deer, llamas and pigs. M. microti causes tuberculosis in voles and cats, and disease in humans due to M. microti is incredibly rare.
Cases in small animals
Bovine tuberculosis in cattle and badgers receives the most attention from the veterinary profession in the United Kingdom. However, recent outbreaks in companion animals have raised the profile of tuberculosis in companion animals and other species.
For example, an outbreak of M. bovis infection was reported in a pack of English Foxhounds between 2016 and 2017 (O’Halloran et al., 2018). While the source of infection was uncertain, it seems likely that contaminated fallen stock carcasses were involved. One kennel worker was diagnosed with latent TB, potentially due to exposure to infected hounds and/or their contaminated food.
Another outbreak of M. bovis infection was reported in pet cats across England and Scotland associated with feeding commercial raw food between 2018 and 2019 (O’Halloran et al., 2020). Four owners and one veterinary surgeon were found to have a high likelihood of latent tuberculosis infection. One owner required treatment. Although it was not possible to conclusively demonstrate zoonotic origin for these infections, neither was it possible to eliminate the suspicion.
Intradermal tuberculin testing and interferon gamma release assays (IGRA) are at the forefront of bovine TB testing. The IGRA is showing promise for detecting mycobacteria in dogs and cats. Tuberculin testing is not thought to be useful in cats and is not often used in dogs.
Finding acid-fast bacilli confirms the presence of mycobacteria, but identification of the organism by culture or PCR is required to identify the organism and evaluate the zoonotic risk
To confirm mycobacterial involvement in dogs and cats, aspirates and/or biopsy samples of affected tissues should be stained with ZN stain. Finding acid-fast bacilli confirms the presence of mycobacteria, but identification of the organism by culture or PCR is required to identify the organism and evaluate the zoonotic risk.
General measures to minimise risk of transmission of these pathogens from animals to humans:
• Ensure appropriate testing is performed and PPE is used in suspected clinical cases
• Notify diagnostic laboratories clearly on submission forms of the suspected zoonotic disease when submitting samples to enable the laboratory staff to take appropriate precautions
• Ensure sample packaging is biosecure
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