Salmonella Gallinarum is a bacterial pathogen that primarily impacts poultry, causing significant health issues. Understanding its nature is important for maintaining animal health in poultry operations and addressing challenges for producers globally.
What Salmonella Gallinarum Is
Salmonella Gallinarum is a non-motile, Gram-negative bacterium, a specific biovar within Salmonella enterica subspecies enterica serovar Gallinarum. It is highly host-specific, predominantly affecting chickens and other galliform birds, including turkeys, guinea fowl, and pheasants. This bacterium causes two distinct clinical forms: Fowl Typhoid (caused by S. Gallinarum biovar Gallinarum) and Pullorum Disease (caused by S. Gallinarum biovar Pullorum).
These two diseases are often grouped together as the Salmonella Gallinarum/Pullorum complex due to their similar characteristics and host adaptation. Fowl Typhoid affects older or mature birds, while Pullorum Disease is primarily seen in young chicks, often under four weeks of age. Both can lead to substantial economic losses in poultry farming through high mortality rates, reduced egg production, and decreased hatchability.
How It Spreads and What to Look For
Salmonella Gallinarum spreads through both vertical and horizontal transmission routes. Vertical transmission occurs when infected hens pass the bacteria directly to their chicks through contaminated eggs, a significant route for Pullorum Disease. Chicks hatching from infected eggs can then further spread the disease.
Horizontal transmission involves bird-to-bird contact, ingestion of contaminated feed or water, or exposure to contaminated equipment. The bacteria can persist in the environment for months, and wild birds, rodents, insects, and human visitors can act as mechanical carriers. Spread within a flock also occurs through fecal-oral contamination or cannibalism of deceased birds.
Clinical signs vary depending on the disease form and bird age. In Fowl Typhoid, seen in older birds, symptoms include dejection, ruffled feathers, loss of appetite, increased thirst, and yellow diarrhea. Affected birds may also appear pale with shrunken combs and wattles, show reluctance to move, and experience sudden death, with mortality rates ranging from 10-100%. Birds that recover can become chronic carriers.
Pullorum Disease, primarily affecting young chicks, presents with high mortality rates, especially in birds 2-3 weeks old. Affected chicks may huddle together, appear weak, have labored breathing, and exhibit white, pasty diarrhea that often causes fecal material to stick around their vents. Swollen joints and blindness have also been reported in some outbreaks.
Protecting Poultry Flocks
Diagnosing Salmonella Gallinarum involves laboratory tests to identify the bacterium. Veterinary professionals use methods such as bacterial culture from affected tissues or eggs, serology (blood tests) to detect antibodies, and PCR for confirmation. Early and accurate diagnosis is important for implementing effective control measures.
Preventing infections relies on comprehensive biosecurity measures. Strict hygiene practices, including regular cleaning and disinfection of poultry houses and equipment, reduce bacterial presence. Limiting access to the flock, quarantining new birds, and effective pest control programs for rodents and wild birds help prevent pathogen introduction. Sourcing healthy, certified Salmonella-free birds from reputable suppliers is a primary preventive step.
Vaccination plays a role in preventing and controlling the disease, particularly in areas where the disease is common. Both live attenuated vaccines, such as the SG9R strain, and killed (inactivated) vaccines are available. Live vaccines stimulate a strong immune response and provide long-lasting immunity, while inactivated vaccines reduce fecal shedding and decrease persistence in organs and eggs. Environmental management, including proper waste disposal and providing clean feed and water, also reduces bacterial load.
When an outbreak occurs, treatment with antibiotics can reduce mortality, but it may not eliminate the carrier state in birds. Responsible antibiotic use, under veterinary guidance, is advised. In severe outbreaks, culling infected birds is often necessary to prevent further spread and to remove carriers. Regular testing and monitoring of flocks, especially breeding flocks, identify and remove infected carriers, helping to eradicate the disease from commercial poultry populations.
Is There a Risk to Humans?
Salmonella Gallinarum and Salmonella Pullorum pose minimal risk to human health. Unlike other Salmonella serovars, such as S. Enteritidis or S. Typhimurium, which are commonly associated with foodborne illness, S. Gallinarum is highly adapted to avian hosts. While direct human illness from S. Gallinarum is rare, good hygiene practices are recommended when handling poultry or their products. Washing hands thoroughly after contact helps prevent pathogen transmission. Recent evidence suggests that in settings with close human-poultry contact, such as backyard operations, rare human infections may present as mild gastroenteritis, with potential for more severe disease in immunocompromised individuals.