IN ANIMALS continued
CLINICAL DISEASE • Clinical salmonellosis is rare in dogs and cats, with most infections asymptomatic. Bacterial colonisation of dogs and cats is usually transient, with animals naturally clearing the infection over a period of weeks. • Clinical disease and shedding is more common in immunosuppressed dogs and cats, young animals, pregnant animals, those in crowded conditions, and those with underlying disease (such as neoplasia, diabetes mellitus, retroviral infection and immune-mediated conditions). 4 • Enteric manifestations of disease range from mild to severe and the character of the diarrhoea can vary (e.g. mucoid, watery, haemorrhagic) and is therefore not diagnostic. Septicaemia may occur with or without gastrointestinal signs and severely affected animals may develop septic shock. Dissemination of bacteria may rarely result in Salmonella seeding in distant organs with resultant organ dysfunction, even when enteric clinical signs are absent. • Animals with enteric salmonellosis should be provided with supportive care. Antimicrobial treatment is not indicated and may prolong shedding. Indiscriminate antimicrobial treatment may result in a subclinical infection becoming clinical. • Inappropriate use of antimicrobials to treat uncomplicated enteric salmonellosis is a societal risk as it leads to the development of resistance. DIAGNOSIS • Diagnostic testing was traditionally performed solely using faecal culture, however it has been mostly replaced by multiplex PCR screening, with culture performed on PCR-positive samples for antimicrobial susceptibility testing. The increased sensitivity of PCR may result in a diagnostic dilemma given the presence of asymptomatic carriers. • The significance of a positive result must be interpreted in the clinical context and with a healthy dose of scepticism, even in sick animals. Salmonella may be present in the faeces of animals with diarrhoea associated with another cause as concurrent illness may increase shedding in a subclinical carrier. • Regardless of its contribution to clinical disease in an individual animal, positive animals may be a source of infection for other animals and humans. • Antimicrobial resistant strains are documented in multiple species. These are not inherently more pathogenic but may pose problems in circumstances where antimicrobial treatment is required.
PREVALENCE AND RISK FACTORS • Globally, the prevalence of Salmonella carriage in dogs is reported to be between 0-44% (median, 4%; mean, 7.7%) with factors such as the study location and study population (sick versus healthy dogs, husbandry conditions etc.) significantly impacting prevalence. 6 In Australia, a published study of healthy dogs in Brisbane in 1969 reported a prevalence of 6.9%. 7 More recently, PCR analysis of faecal samples from dogs with diarrhoea in Western Australia demonstrated a prevalence of 8.3%. 8 • Reported global prevalence in cats varies from 0-13.6% (median, 2%; mean, 3.9%). 6 No published data is available on the prevalence of Salmonella in cats in Australia. • Consumption of raw food or treatment with antimicrobials have been identified as risk factors for shedding Salmonella in faeces. A study in Canada reported the odds of shedding Salmonella to be 23 times greater for dogs fed a raw food diet compared to those on standard commercial rations. 9 • Rural dogs are more likely to shed Salmonella than urban or suburban dogs, 6 and contact with livestock has been identified as a risk factor. Higher rates of infection have been identified in group-housed dogs, including greyhound breeding facilities. 10 Digitally colourised scanning electron microscopic (SEM) image depicting a number of Salmonella spp. bacteria (red) in the process of invading an immune cell (yellow) (Public Health Image Library, CDC)
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Companion Animal Zoonoses Guidelines 72
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