Biosecurity
22 Aug 2025
Introduction
Fowl cholera, caused by Pasteurella multocida, is a significant disease in layer chickens across Australia and New Zealand. It affects both barn and free-range production, with free-range flocks at higher risk due to outdoor exposure. Outbreaks can appear suddenly and cause major losses, with the disease presenting as either an acute condition with sudden death or a more chronic form with ongoing health impacts.
How does it cause disease?
P. multocida enters through the mouth or respiratory tract, often from contaminated water, feed, or contact with carcasses. Once inside, the bacteria’s capsule and surface sugars protect it from the immune system, allowing it to spread rapidly through the bloodstream. This explains why birds can appear healthy one day and die suddenly the next.
In chronic cases, the infection localises in areas such as the wattles, joints, or respiratory tract. Some birds survive but remain long-term carriers, shedding bacteria back into the flock and restarting the cycle.
Clinical Signs
Sudden deaths with no warning signs (peracute form)
Swollen wattles, joint infections, or breathing issues in chronic cases
Reduced production in affected flocks
On post-mortem, signs may include petechial haemorrhages, necrotic areas in the liver, and caseous abscesses in tissues.
When do we see it?
Fowl cholera can appear at any stage in lay, but is most often seen in older flocks. The disease is strongly associated with multi-age sites and free-range systems where exposure to contaminated soil, water, or wild birds is common. Wet and muddy conditions increase survival of the bacteria and the risk of outbreaks.
Treatment and Control
Antibiotics such as sulfonamides and tetracyclines may reduce mortality but do not eliminate carriers, meaning outbreaks often reoccur. Resistance is currently low in Australia and New Zealand, but careful use is recommended.
Vaccination remains the best protection. Autogenous vaccines made from farm-specific strains are commonly used, although vaccine failures can occur if the strain changes. Consistent boosters and close matching of vaccine strain to field strain are critical.
Risk Factors
Free-range access and exposure to wild birds and waterfowl
Multi-age flocks that allow carriers to persist year to year
Poor drainage and muddy paddocks
Missed or mismatched vaccination programs
Carcass disposal and rodent activity acting as mechanical spreaders
Economic Impact
Fowl cholera can cause heavy losses. Mortality can be sudden and severe, with production drops following chronic outbreaks. Repeat outbreaks, treatment costs, and loss of bird productivity make it one of the more costly diseases in free-range and barn production.
To work on a prevention or vaccination plan, please reach out to the Hatch House Veterinarians through our contact page.
Written by Hatch House Senior Veterinarian
Alex-Kate Langfield BVetBiol/BVSc
