There are many different strains of Salmonella and not all of them cause disease. Species which are harmful to domestic animals and humans include the following :
As a general rule strains of Salmonella that can attach to and invade the intestine lining (mucosa) and multiply in the hosts cells, and which are encapsulated or mucoid tend to be more harmful (pathogenic) than other strains. The ability of these "pathogenic" strains to invade the mucosa depends on the presence of pili or flagella. Some forms of Salmonella produce toxins as well as causing direct injury to the intestine wall. If the organisms get into the blood stream (called septicaemia) they can travel to other organs including the heart, kidneys, liver, spleen, lymph nodes or brain and cause serious disease and death. Similarly, the toxins can get into the blood (called toxaemia) and cause damage in other organs.
Infection is usually through direct or indirect ingestion of the organism from contact with animal faeces on animals or in the environment, or contact with contaminated food, water or objects (eg feeding bowls). Occasionally the infection can be transmitted by airborne spread.
A large number of Salmonella organisms need to be eaten because many are killed by acid in the stomach. Infected animals can shed the organisms in faeces or orally even if they do not show any signs of illness.
Salmonella dublin is transmitted from cattle to humans via contact with vaginal secretions
Predatory animals (eg cats) that kill and eat infected species (eg birds) are also at risk.
Young animals, animals with poor immune responses (natural or drug-induced), animals subjected to stress and animals suffering from malnutrition or obesity are at greater risk from exposure to Salmonella. Animals given oral antibiotics (eg ampicillin) may have lower resistance to Salmonellosis because the antibiotic alters the numbers of normal, protective bacteria in the gut.
In cats and dogs it has been estimated from tests that up to 36% of healthy dogs and 18% of healthy cats have Salmonella in their faeces, and the number of animals carrying the disease is thought to be higher than these findings.
Species commonly infected with Salmonella which may be of importance and risk to humans include :
Human workers most at risk to contract salmonellosis include :
Many animals can be infected with Salmonella but show no signs at all.. These present a real risk to humans especially young children who may handle infected pets eg terrapins and other reptiles. So basic hygiene is important when handling pets, cleaning out their environments or handling food and water bowls. Hands should always be washed thoroughly after handling pets and related objects.
When disease occurs the main signs are associated with gastrointestinal damage :
But other signs include
If the bacteria or toxins get into the bloodstream other signs may be seen according to the organs affected, for example :
Localised infections can occur in many tissues causing local abscesses or infection eg in bone Salmonella can cause osteomyelitis.
In young animals or animals infected in the uterus the signs may be :
Severe disease due to septicaemia or toxaemia is most likely to occur in very young animals, whereas gastrointestinal signs are more likely in adults. Animals that survive the acute stage of the disease and any septicaemia or toxaemia, may develop chronic disease with persistent diarrhoea , fever and weight loss.
In HUMANS the signs are similar and include :
Salmonella dublin is transmitted from cattle to humans and causes a cutaneous form of disease (dermatitis) with the formation of nodules and pustules
A real concern is the development of strains of Salmonella that are resistant to many antibiotics - eg Salmonella typhimurium DT104 which is present in people, cats and dogs and other species in the USA and UK.
Unfortunately, many animals will be positive for organisms but the Salmonella present may not be causing any clinical signs that the animal has. In addition, negative cultures may not mean that the animal does not have Salmonellosis - especially if there are large numbers of other organisms present as well. For this reason suspect cases should have samples tested every 2-3 weeks.
It is important that fresh samples are transported to the diagnostic laboratory correctly in Amies transport medium with charcoal.
*However - antibiotic use (especially chloramphenicol) should be reserved for animals with severe disease, and is not recommended for animals with gastrointestinal signs only - because of the risk of bacterial resistance developing.
The environment and objects should be disinfected with one of the following :
Updated October 2013