Coryza
Coryza is akin to a common cold in chickens, but with markedly more dire effects.
Coryza is an upper respiratory infection caused by a bacterium. It is highly contagious, with morbidity as high as 50% and mortality as high as 30%.
The facts:
What is it? An upper respiratory infection.
Causative agent: A bacterium called Avibacterium paragallinarum.
Disease onset: 2-3 days, symptoms begin.
Disease duration: 2-3 weeks or longer depending on the severity and if other disease agents are present, such as other bacteria or viruses.
Morbidity: Can be as high as 50% and is highly contagious.
Mortality: Can be as high as 30%.
Signs: Malodorous eye and nose discharge, facial swelling, sneezing, labored breathing, loss of appetite, diarrhea, loss of egg production, and lethargy.
Treatment: Antibiotics. In the U.S., antibiotics must be prescribed by a veterinarian who already has a relationship with the client.
The scoop:
The A. paragallinarum is a gram-negative rod-shaped bacterium that can only be diagnosed positively if a veterinarian takes a sample from a sick bird and runs some laboratory tests. This bacterium is microaerophilic, meaning it can survive in areas with little oxygen available, such as water or feces. It isn’t yet clear how long this organism lives in the feces, so the main documented source is from water and carrier birds. This bacteria lives in chronically ill chickens or chickens that appear healthy but are carriers of the disease due to previously encountering it.
Click here to get this information as a Coryza Flock File pdf.
Transmission takes place when an unaffected bird encounters an affected bird via direct contact, airborne droplets, or from contaminated drinking water, feed, or bedding. Carriers of A. paragallinarum are frequently spreading bacteria in their environment. A recovered bird must always be considered a reservoir for the disease because they will continue to shed bacteria throughout their life despite remaining asymptomatic.
This bacterium can be carried by wild birds, so high-risk areas should have netting covering the chicken run to reduce the interactions between species. Wild birds may carry coryza on their bodies but most likely are not true carriers of the disease. This means they haven’t contracted it but can easily carry it from flock to flock. Birds are more susceptible when they are already fighting off some other illness. Similarly, once a bird has this disease, they are more likely to fall prey to a secondary infection. Mortality rates due to secondary infections are higher than in coryza alone.
The only certain way to control the spread of coryza is to avoid keeping a flock of differently aged birds, referred to as an “all-in/all-out” farm management system. The chicken coop then has a chance to be thoroughly disinfected and go without housing birds temporarily between batches. This practice lets the bacteria die, having no viable host, and effectively halts the spread of the disease. A. paragallinarum can only survive two to three days outside of the bird and is easy to kill. This form of prevention is useful on a large, commercial scale where farmers frequently change birds for meat or egg production but can be difficult to implement on a smaller scale. Most cases of coryza occur in backyard flocks because the same birds can stay on the farm for many generations.
Birds are more susceptible when they are already fighting off some other illness. Similarly, once a bird has this disease, they are more likely to fall prey to a secondary infection. Mortality rates due to secondary infections are higher than in coryza alone.
If a farm has a history of coryza, then vaccinations can be used for disease prevention in any new-coming birds. Vaccines offer a controlled exposure to the bacteria, giving the bird a type of protective immunity against coryza. Exposing the chicken’s immune system to a small amount of the bacteria gives it a chance to safely practice its response. This allows the chicken to mount not only a quicker response when it encounters A. paragallinarum again but a more effective one as well. Each bird will need two shots several weeks apart for the vaccine to be effective. However, vaccinations are only recommended for large flocks and can only come from a veterinarian.
Vaccinations are quickly becoming more of a problem than a solution. People usually try to buy vaccinations online, which are often fake or not the correct vaccination for the problem. In addition, Sherrill mentions that “Coryza vaccinations are only meant for large flocks. It can be impossible to dilute vaccinations to safe levels for individual birds in small flocks.”
Early treatment is key to flock health. Any bird presenting the above symptoms should be isolated immediately, and the rest of the flock needs to be closely monitored for outbreaks. For a small flock, monitoring your birds and supportive treatment is the only real option. Speak to a veterinarian prior to administering any medications. Not only can coryza be misdiagnosed, but the needless overuse of antibiotics can lead to antibiotic-resistant superbugs.
Coryza vaccinations are only meant for large flocks. It can be impossible to dilute vaccinations to safe levels for individual birds in small flocks.
Dr. Sherrill Davison
Those at risk for contracting coryza are the very stressed birds, older birds, weak birds, or birds with weakened immune systems. There is some debate in the science community on whether coryza affects only chickens, or if other birds can contract it as well. Regardless, the same or a very similar disease is seen in turkeys, pheasants, quail, and guineas, however, these diseases don’t transmit to humans. Humans can still eat the meat or eggs from infected birds without fear of contracting the disease.
Biosecurity is exceedingly important when it comes to flock safety. To help prevent the disease, remember to quarantine new birds and not share equipment. In addition, if visiting another flock of chickens, you’ll need to take appropriate steps to not bring anything back to your bird. If your flock has coryza, you’ll need to tell your chicken-owning friends. Furthermore, you will not be able to sell birds from your property unless you cull your current flock, sanitize, and start with new stock. For backyard flocks that are pets, the disease is manageable. Contracting coryza does not mean you need to cull your flock unless you intend to sell birds in the future.
For backyard flocks that are pets, the disease is manageable. Contracting coryza does not mean you need to cull your flock unless you intend to sell birds in the future.
Coryza is akin to a common cold in the chicken world, however, it has markedly more dire effects. The mortality rate of coryza alone isn’t very high, but it opens the door to secondary infections. The disease also affects the marketability of a flock and their quality of life while sick. Vaccines are effective for large flocks and can be costly. Rest assured that for the majority of small backyard flock owners, chickens fully recover and continue on to live a good life.
All information in this article has been vetted for accuracy by Dr. Sherrill Davison, Poultry Specialist at University of Pennsylvania School of Veterinary Medicine.
Originally published in the October/November 2019 issue of Backyard Poultry and regularly vetted for accuracy.
