Salmonella is a notifiable disease under the Act on Zoonoses and veterinarians should report cases to the Board of Agriculture and to the concerned county veterinary officer.
Infections caused by Salmonella spp are common in cats worldwide with the exception of the Nordic countries (Sweden, Norway, and Finland) where the incidence is low.
Transmission of disease
Salmonella is a group of gram-negative bacteria of the family Enterobacteriaceae. Salmonella is mainly an intestinal pathogen, but can also cause systemic disease and can then be isolated from blood and various organs.
Salmonella mainly infects people via food. Cats can become infected if contaminated raw material in the feed is inadequately heated. Food produced in Sweden rarely causes salmonella infection in animals or humans.
Some small birds are infected with salmonella and when large numbers of small birds in late winter and early spring gather around bird tables they may facilitate the spread of infection. Birds suffering from malnutrition after a long winter may die from the infection. Live or dead birds, such as passerines, and bird faeces may be a source of infection both for cats and dogs. Since the first observed outbreak in 1999, salmonella infection has been detected frequently in cats during late winter-early spring. It is not unusual for both cats and wild birds to become infected with Salmonella Typhimurium at this time of the year.
Pathogenesis and clinical symptoms
Several different virulence mechanisms have been identified in salmonella bacteria and the pathogenicity may vary between different serotypes. Pathogenesis studies performed in cats are missing, but studies in other animals have shown that Salmonella spp. can attach to and invade intestinal epithelial cells and thereby cause enteritis with subsequent diarrhoea and/or systemic infection. Systemic infection may also develop without previous gastrointestinal symptoms.
Salmonella bacteria may persist for a long period of time in intestinal epithelium and lymph nodes. Faecal excretion is usually continuous during the first week and then becomes intermittent. The period of excretion is usually 3-6 weeks, but there are occasional reports of longer excretion time. Up to 115 days have been reported in cats.
The bacteria can also persist in phagocytic cells in intestinal lymph nodes, liver and spleen. This may explain why reactivation of infection can be seen in some individuals in, for instance, immunosuppression or different states of stress.
The severity of clinical symptoms of salmonella infection in cats varies. Asymptomatic infection is common, as are mild clinical symptoms such as minor rise in temperature and inappetence.
In more severe cases, high fever (often above 40ºC), inappetence, vomiting, diarrhoea, and abdominal pain can be seen. Diarrhoea can range from mild to watery or mucous to very severe and blood streaked. Affected cats may rapidly become dehydrated, and in severe cases life-threatening septicaemia and endotoxemia may develop. In rare cases the infection may spread to different organs. With or without concurrent or previous gastrointestinal symptoms- even symptoms such as pneumonia, meningitis and abortion - may be seen, depending on which organs are affected.
Diagnosis is made by bacterial culture from fresh faeces. In case of sepsis, blood culture may be necessary for detection.
Currently there are no strict guidelines or rules for follow-up samples to show freedom of infection in cats. For cats, most follow-up samples have been taken about 3-4 weeks after the initial diagnosis. There is always a risk of false negative result since salmonella can be excreted intermittently, particularly in the later stages of infection. The highest probability of finding salmonella in faeces is by sampling in the acute stage of the disease.
Cats usually recover spontaneously from uncomplicated acute diarrhoea caused by salmonella. Cats that suffer a more serious gastroenteritis may need supportive care, including fluid therapy.
Antibiotics are not indicated except as a supportive treatment during a short time for life threatening symptoms, shock, and in case of sepsis.
Antibiotic treatment may prolong the excretion time in faeces. The risk selecting for antibiotic resistance should also be considered. The prognosis for cats with uncomplicated salmonella infection is generally good. In sepsis cases the outcome could be less favourable.
General hygiene advice on salmonella infection in cats
• Careful hand washing after cleaning the litter tray and handling of the sick cat, or its excretions. The cat should not be on the dining table, the kitchen sink, in the pantry or other areas related to food. Wash the cat´s dishes separately with a separate brush/cloth.
• Salmonella positive cats should not be allowed in areas where animal feed for other animals is stored, or in barns or stables. The actual risk of transmission is however not known.
• To keep the cat indoors after clinical symptoms have been observed may be indicated for various reasons. The owner will be able to observe the cat´s status and possible need of further treatment and prevent further spread.
• It usually takes a high infection dose for symptoms of disease to occur. Susceptibility to infection varies and small children, elderly people, and persons with impaired immune defence may be more susceptible to infection. It is therefore justified to discourage close interaction between cats and children.
• Do not forget to take hygiene measures to prevent infection from for example small birds and bird tables. Careful hand washing is recommended after tending to bird tables. The ground beneath bird tables may be heavily contaminated and small children should not play in the immediate vicinity of feeding areas for small birds.
• The best way to prevent infection with S. Typhimurium in cats is to keep them away from bird tables. It may be difficult to completely prevent a cat from catching and eating birds, especially since sick birds are easier prey than usual.
• If there are several pets in the household, be extra careful with hygiene as long as there is an infected cat in the household. This applies even if the other animals do not show symptoms.