Infectious coryza is an acute respiratory illness in chickens caused by the bacterium Avibacterium paragallinarum. The disease impacts the health and productivity of flocks worldwide, making proactive health strategies necessary to control its spread. Vaccination is a primary tool for preventing outbreaks and maintaining a healthy flock.
Understanding Infectious Coryza
The bacterium Avibacterium paragallinarum causes infectious coryza. Clinical signs appear rapidly after an incubation period of one to three days. Infected chickens show decreased activity, sneezing, and discharge from the nostrils and eyes. A distinct symptom is facial swelling, particularly around the sinuses below the eyes, which can become severe enough to prevent them from fully opening.
In laying hens, a drop in egg production of 10 to 40 percent is a common consequence. The disease spreads quickly through direct contact, airborne droplets, and contaminated water or feed. While chickens of all ages are susceptible, the disease’s severity tends to increase with age.
Antibiotics can treat symptoms of an active infection but may not eradicate the bacteria from the flock. This can create carrier birds that appear healthy but continue to shed the bacteria, posing a threat for future outbreaks. The existence of these carriers highlights the importance of prevention over relying on treatment alone.
Available Coryza Vaccines
Several types of coryza vaccines are available, falling into two main categories: inactivated (killed) and live attenuated vaccines. Each type stimulates an immune response in the chicken.
Inactivated vaccines contain killed Avibacterium paragallinarum bacteria and cannot cause the disease. They are administered by subcutaneous injection, often under the skin in the neck.
Live attenuated vaccines use a weakened form of the bacteria that provokes an immune response without causing significant illness. These vaccines are administered through drinking water or as an eye drop, which can be less labor-intensive than individual injections.
An important factor in vaccine selection is the serovar, or strain, of the bacteria. The three main serovars of A. paragallinarum are A, B, and C. For a vaccine to be effective, it must provide protection against the specific serovars prevalent in a geographic region. Using a vaccine that does not match the local strains can leave a flock vulnerable.
Administering the Vaccine
Proper administration is fundamental to a vaccine’s effectiveness, and the method depends on the type selected. Inactivated vaccines are given via subcutaneous injection to ensure a precise dose is delivered to each bird. Live vaccines offer more flexibility and can be administered by eye drop or through the flock’s drinking water system.
A vaccination schedule involves an initial dose for young birds at 3 to 5 weeks of age. A booster is administered about four weeks later, before the birds begin laying. This timing helps establish immunity before the stress of egg production, which can increase disease susceptibility.
Always follow the vaccine manufacturer’s instructions for correct dosage, storage requirements like refrigeration, and safe handling procedures. Deviating from these guidelines can render the vaccine ineffective or even harmful.
Minor, temporary side effects may be observed after vaccination. With injected inactivated vaccines, slight, localized swelling at the injection site is not uncommon. These reactions are typically mild and resolve on their own within a short period.