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SALMONELLOSIS Note for Pet Owners:
This information is provided by
Provet for educational purposes only.
You should seek the advice of
your veterinarian if your pet is ill as only he or she can correctly advise
on the diagnosis and recommend the treatment that is most appropriate for
your pet.
Salmonella
can be transmitted to humans, and so this disease is a zoonosis. Proper
hygienic precautions should be taken after contact with animals which
could be carrying the disease, especially children and people with
impaired immune function. For practical purposes this means all pets and
domestic livestock as well as wild animals.
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Description
Salmonella poisoning (or salmonellosis) is one of the commonest forms of
zoonosis with infection being transmitted directly or indirectly from animals to
humans, or from infected food products (meat, eggs, dairy products) to humans.
Salmonellosis occurs in most countries and affects all animal species.
Cause
Th e cause of Salmonellosis are gram-negative, motile bacteria called
Salmonella which are part of the family Enterobacteriaceae, and are usually
found in the intestinal tract. These bacteria infect many species of animal
including amphibians, birds, mammals (including humans), insects and reptiles.
In addition, the organism can survive in the environment so in-contact objects,
bedding etc can carry them. However, the commercial heat-processing of foods
kills the organism.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 :
- Salmonella arizonae
- Salmonella choleraesuis
- Salmonella enteritidis
- Salmonella typhi and paratyphi (the cause of typhoid in humans - does
not affect animals)
- Salmonella typhimurium - the type most commonly isolated from humans and
animals
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
Breed Occurrence
There is no breed predisposition to infection, but animals kept in faecally
contaminated environments (eg farm livestock) or that eat faeces (coprophagia),
groom companions or share feeding and drinking bowls are at high risk to
contract the infection.
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 :
Birds
Cats
Dogs
Ferrets
Fish
Gerbils
Guinea Pigs
Hamsters
Horses and Ponies
Mice
Rabbits and hares
Rats
Reptiles
- Crocodilians
- Lizards
- Snakes
- Tortoises and Turtles
Agricultural Livestock
- Buffalo
- Camels
- Cattle
- Elephants
- Goats
- Pigs
- Sheep
- Pigs
Wild animals
- Amphibians
- Birds
- Hedgehogs
- Non-human Primates
- The quokka (Australian marsupial)
- Rabbits and Hares
- Raccoons
- Reptiles
- Rodents - mice , rats
Human workers most at risk to contract salmonellosis include :
- Animal handlers
- Butchers
- Food handlers
- Kitchen workers
- Veterinarians
Signs
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 :
- Diarrhoea - often watery and containing mucus
or blood
- Vomiting
- Inappetance
- Increased salivation (cats)
- Increased thirst
- Abdominal pain - all species but especially
horses (colic)
But other signs include
- High body temperatures
- Depression
- Dehydration
- Weight loss
- Weakness
- Shock
- Death
If the bacteria or toxins get into the
bloodstream other signs may be seen according to the organs affected, for
example :
- Brain
- Blindness
- Excitability
- Fits (seizures or convulsions)
- Flicking of the eye (nystagmus) - calves
- Staggering
- Paralysis of the hind legs
- Eye
- Conjunctivitis with enlarged lymph nodes
(in cats)
- Joints
- Arthritis in multiple joints - especially
in young animals that survive the acute stage of the disease
- Liver
- Lungs
- Cough
- Difficulty breathing (called dyspnoea)
- Nose bleeds
- Pneumonia - all species but especially
pigs
- Lymphatics
- Enlarged lymph nodes (with conjunctivitis
in cats)
- Skin
- Dark red to purple discolouration on
abdomen or ears (pigs) due to haemorrhages
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 :
- Abortion
- Weak offspring
- Death
Persistent vaginal discharges in bitches
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 :
- Abdominal pain
- Vomiting
- Diarrhoea
- Dehydration
- Fever
- Headaches, and eye pain
- Nausea
Salmonella dublin is transmitted from cattle to humans and causes a
cutaneous form of disease (dermatitis) with the formation of nodules and
pustules
Complications
Animals recovering from Salmonellosis shed organisms in their faeces for at
least 4-6 weeks, and this can start again if the animal is stressed - for
example if horses are transported.
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.
Diagnosis
Diagnosis of Salmonellosis is usually made by the identification of Salmonella
organisms in :
- Faeces
- Vomitus
- Swabs taken from the oral cavity
- Blood
- Synovial fluid from the joints
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.
Treatment
For acute, severe cases of Salmonellosis prompt treatment is needed to save the
animal, and a variety of therapeutic agents have been used including:
- Intravenous fluids - sometimes plasma
- Antibiotics* - for example chloramphenicol, trimethoprim-sulphonamide
combination drugs and amoxicillin.
- Lactulose
- Prostaglandin-inhibitors - may be effective when toxins are causing
increased fluid losses in the intestine
- A Salmonella antiserum containing antibodies is available against
some forms of Salmonella
*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 :
- Bleach
- Formalin (20%) - 1 hour
- Gluteraldehyde (2%) - 1 hour
- Ethylene oxide gas (equipment in veterinary facilities)
- Phenol-based disinfectants
or
- Autoclaved (equipment in veterinary facilities)
Prognosis
Poor for young animals with acute, severe infections and septicaemia or
toxaemia. Better for adult animals.
Updated October 2013
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