Salmonella in Chickens: Zoonotic Risk, Pullorum and Prevention

Salmonella is divided into three clinically important groups in poultry: host-adapted pathogens (Pullorum, Gallinarum), and ubiquitous paratyphoid serovars (Enteritidis, Typhimurium, and hundreds of others).

• Paratyphoid serovars - environmental: S. Enteritidis and S. Typhimurium live in soil, rodent feces, wild bird droppings, and contaminated feed for months. They are introduced via contaminated bedding, feed, rodents, or wild birds and colonize the chicken intestine without causing disease.
• Transovarial transmission: S. Enteritidis uniquely colonizes the ovary and oviduct, contaminating eggs internally before shell formation. This is why even uncracked, clean-appearing eggs from an infected hen can contain Salmonella.
• Pullorum disease (NPIP reportable): S. Pullorum spreads vertically (hen to chick through the egg) and horizontally through feces. Chicks hatch infected or are infected in the hatcher by hatchmates. Strict NPIP testing has nearly eliminated Pullorum from commercial flocks but it persists in unmonitored heritage and backyard flocks.
• Rodent vectors: Mice and rats are highly efficient Salmonella carriers and shed massive numbers of organisms in feces. A single mouse nesting in a feed bin can contaminate an entire feed supply.

Salmonella in backyard flocks is usually diagnosed through surveillance testing, human illness investigation, or NPIP testing, not through flock clinical signs.

• NPIP testing for Pullorum/Typhoid: The Whole Blood Test (WBT) or Tube Agglutination Test (TAT) detects antibodies to S. Pullorum/Gallinarum. Required for interstate transport and exhibition in most US states.
• Fecal culture: Environmental swabs, cloacal swabs, or fresh fecal samples plated on selective Salmonella media identify colonizing serovars. PCR is faster and more sensitive.
• Chick mortality investigation: White pasty diarrhea and high mortality in chicks 1-3 weeks old is Pullorum until proven otherwise. Necropsy shows grayish nodules in liver, cecae, and lungs.

Paratyphoid Salmonella colonization in chickens is not treated. Treatment with antibiotics eliminates clinical signs in Pullorum/Typhoid but does not reliably clear the carrier state and is not the preferred management approach under NPIP.

NPIP approach to Pullorum/Typhoid: Positive reactors identified by WBT or TAT testing are culled, not treated. This is the regulatory approach in the US to achieve and maintain Pullorum-Typhoid Clean status.

Paratyphoid outbreak supportive care: In flocks with high mortality from paratyphoid infections (rare in adults), antibiotics (gentamicin, enrofloxacin, or trimethoprim-sulfa under veterinary guidance) can reduce acute losses. Long-term colonization is not eliminated.

Rodent control: Eliminating the rodent reservoir from poultry facilities is the most effective long-term control measure for paratyphoid serovars.

• Participate in the NPIP (National Poultry Improvement Plan). NPIP Pullorum-Typhoid Clean certification is required for flock exhibition and interstate transport in most states. Testing costs are minimal and provides important documentation of flock health.
• Eliminate rodent access to feed, bedding, and housing. A single mouse in a feed bin can colonize an entire flock with Salmonella within weeks.
• Collect eggs daily and refrigerate at 40F or below immediately. Wash hands after egg collection. Do not wash eggs unless visibly dirty, as washing removes the protective bloom that prevents bacterial penetration.
• Cook all eggs and poultry to 165F internal temperature. Never eat raw or undercooked eggs from any source, including backyard flocks.
• Supervise children handling live birds; ensure immediate handwashing. The CDC has linked numerous multistate Salmonella outbreaks specifically to backyard poultry contact by children.
• Quarantine new birds 30 days and consider fecal Salmonella testing before integrating into an existing flock.