Salmonellosis

This fact sheet was updated on 11/4/2020.

Other names: Paratyphoid, Pullorum disease, Fowl typhoid

Cause

Salmonellosis is caused by bacteria from the Salmonella genus, or group. There are more than 2,000 different species or subspecies of Salmonella that have been found across many species of animals, including pets, livestock, captive reptiles, fish and birds, and wildlife.

Significance

Salmonellosis is one of the most widely distributed zoonotic diseases. Salmonella commonly infect the intestinal tract, but can also be found in urine, blood and other body tissues. Infected animals typically have diarrhea but some animals, like reptiles, may be asymptomatic carriers, showing clinical signs and posing serious potential for spreading of the disease. People can contract salmonellosis by direct contact, exposure to contaminated feed, bedding or materials, oral ingestion or inhalation of aerosolized fluids.

During the winter months, songbirds are particularly at risk (songbird fever) when Salmonella are shed through sharing of bird feeders causing large-scale mortality events. Humans, house cats, and birds of prey that are exposed to sick and dying songbirds at feeders, or contaminated bird food can become infected with salmonellosis.

Species Affected

Birds, mammals and reptiles are all susceptible to salmonellosis. As with many infectious diseases, the young and those with suppressed immune systems are at greater risk.

Songbirds can become infected when they congregate at high densities at feeding sites and come in contact with infected birds or contaminated food or water.

Distribution

Salmonellosis occurs worldwide and is most prevalent in areas of intensive farming.

Transmission

Salmonella bacteria are shed in the feces of infected animals. The bacteria are transmitted by direct contact with infected individuals or by ingestion of food or water contaminated with feces from an infected bird or mammal. Many species or subspecies of Salmonella can persist for long periods of time in the environment (up to 9 months in soil and in stagnant water).

Once ingested, Salmonella replicates within and damages the intestinal lining of its host. The infection can progress when the bacteria enters the blood stream and infects multiple organs (septicemia), which can cause more severe clinical disease and result in death. The young, the old and the immunocompromised are at greatest risk of developing these severe infections. 

Carrier animals appear clinically normal, but intermittently shed Salmonella in their feces.

When birds are confined in close quarters, the bacteria can be transmitted via inhalation. In poultry, eggs can become infected with the bacteria, though this mode of trans-mission is not known to be significant in wild birds. 

Clinical Signs

Clinical signs of Salmonellosis include dehydration, lethargy, weakness, rapid breathing, diarrhea, ruffled feathers, swollen eyelids, loss of appetite, weight loss, shivering, and eventually coma and death. Neurological signs such as loss of coordination and tremors may also be observed. Salmonella can also cause abortions.

Infection with Salmonella can lead rapidly to fatal illness, chronic infections that may or may not have clinical signs, or an asymptomatic carrier state. Factors such as age, stress level, and species of the bacteria influence the severity of clinical illness.

Diagnosis

To diagnose salmonellosis, Salmonella bacteria must be isolated from infected tissues, though gross signs at necropsy can result in a presumptive diagnosis.

Treatment

There is no treatment for salmonellosis in wildlife populations.

Management

To prevent outbreaks of Salmonellosis, wildlife and farm animals should not be allowed to mix. Feed and water supplies should be protected from fecal contamination. Contaminated buildings, equipment or materials should either be disinfected or disposed of. Personal hygiene can protect from human infection. Handwashing and avoiding eating and drinking while handling live or dead wildlife is recommended. Hunters are reminded not to shoot or consume sick animals and wear personal protective equipment when handling game. Fully cooking the meat to an internal temperature of 165oF will destroy the bacteria.

Bird feeders should be cleaned regularly with soap and water followed by a solution of 10% bleach and water (9 parts water: 1 part bleach). Feces and discarded seed should be removed from the ground. Removal of bird feeders for 2-3 weeks may help reduce songbird transmission during out breaks. Individuals who handle bird feeders should adopt the same safety measures as hunters and others handling wildlife.

Suggested Reading

Images

Esophageal nodules from Salmonellosis in a grosbeakYellow, cheese-like nodules in the esophagus of an evening grosbeak caused by salmonellosis. Photo courtesy of USGS by J. Christian Franson