I’ve posted a couple of dozen articles on various chicken health issues and have been pecking my way, so to speak, through the list of respiratory infections. Coryza has been on the ‘to-do’ list, but managed to work its way to the top after I heard from Carol – one of the folks profiled in my series ‘Having Chickens Is A Great Way To Meet Your Neighbours; the bacterial pathogen had hit her flock, and hit a bit closer to home. I’ve never had, knock on wood, respiratory illnesses in my flock so I was interested in learning more.

“Over the past several months, three of my birds have suffered serious illness. The first was separated from the flock (something I do for all sick chicks), treated with a course of antibiotics, recovered and returned to the flock. Next, a hen that was hatched here in fall of 2018 followed the same pattern: except that she was treated with antibiotics, recovered briefly, but declined and died before being returned to the flock. The third and most recent, who was hatched here this August, was healthy and only sickened when introduced to the flock. I decided that, rather than have her treated, she should be euthanized and sent for a necropsy. She died before her appointment with the veterinarian. The necropsy indicated immediate cause of death as heart attack, but she tested positive for the bacterium responsible for Infectious Coryza.” – Carol

Infectious Coryza (I.C.) is an upper respiratory tract infection, usually resulting in acute and sometimes chronic, highly transmittable disease in chickens. The bacteria enter the body through the eyes or nares via direct contact with birds or their exudates in feeders and waterers (e.g. saliva, poop). An incubation period of 1-3 days is followed by rapid onset of the disease over the following 2-3 days with the whole flock potentially affected within 10 days.


  • Watery, pus-like discharge from eyes and nostrils
  • Swollen wattles and face
  • Sneezing, difficulty breathing, coughing
  • Weight loss
  • Decreased appetite
  • Loss in condition
  • Drop in egg production of 10-40%

Symptoms usually occur within 1-6 weeks after exposure, usually when new chickens (unknowingly recovered carrier birds) are introduced to a flock, and may last 2-3 weeks. Infection can spread slowly, with chronic disease affecting only a small number of birds, or rapidly, with a higher percentage of birds affected. Infection levels are high, but mortality rates can be low (up to 20%) in an otherwise healthy flock. Birds are more vulnerable if they already infected with other respiratory viral or bacterial infections

Diagnosis & Treatment

Your vet can do laboratory tests to diagnose the pathogen. As a bacterial infection there are antibiotics that can treat the symptoms, but as you can see from Carol’s experience that isn’t a cure. It is characteristic of I.C. that birds may respond to treatment, and then relapse at some point.


  • Stock Coryza-free birds on an all-in/all-out basis
  • Practice biosecurity between farms to prevent the spread of disease
  • Vaccines are used in areas of high incidence. Birds recovered from one strain are resistant to others

The good thing about I.C. is it only survives for 2-3 days outside the host and is easily killed by heat, drying and disinfectants. But what does that mean if your flock is already infected? Sadly, recovered birds remain carriers for long periods and may intermittently shed the bacteria when stressed. In short, assume your chickens that may appear healthy, once exposed to I.C., can potentially pass it on to other birds.

The Future Of A Flock With Coryza

As Carol discovered, once I.C. entered her flock her options were limited.

“The recommendation for dealing with the disease once it’s in your flock is “All in; all out”. So my choices are: either kill all remaining members of the flock or allow them to live as long as they happily can, then start again with an entirely new set of birds. I prefer the latter. I can’t see my way clear to wholesale slaughter. I also can’t add any new chicks – not even those hatched from my own flock.”   – Carol

She has a small flock, doesn’t show her birds and isn’t dependent on them for income. Carol has resigned herself to keeping a ‘closed flock’ – no one leaves and no new birds enter. It also means that she will still need to practice good biosecurity when visiting other folks with chickens, and conversely so will chicken keepers when they come to her property.

When Carol relayed her story I, of course, was curious about how Coryza might have infected her birds. She diligently went through her calendar and vet bills to try to reconstruct a timeline of her flock.

She got her first four birds several years ago. Within two months, two had died; the first presented with neurological symptoms. Another bird was added; it, too, subsequently died, also with neurological issues. She added a couple more birds and hatched her own chicks and things seemed to be okay until May, August and November 2019 when three birds presented with respiratory issues.

In hindsight, it’s apparent that the first birds she got were all infected with an unseen pathogen. The first seemed healthy, but quickly developed paralysis of her legs or wings – classic symptoms of Marek’s Disease. More generalized symptoms for the next two, one of which had been traded to another flock (and remains asymptomatic). The sole survivor, her rooster, appears healthy but it probably a carrier.

It is not as obvious as to when Coryza crept into her flock. The last spate of illnesses were all related to respiratory issues and the necropsy results didn’t indicate any signs of Marek’s. Without confirmation of cause of death with her first birds we can only surmise that a pathogen, likely Marek’s, has affected her flock and made vulnerable birds more susceptible to secondary infections like Infectious Coryza.

I think her experience is a sad reminder that we need to be diligent about biosecurity and quarantine. As an inexperienced chicken keeper, Carol purchased what she thought were healthy birds. She didn’t know when the first birds died, that she could have had them necropsied to find out what underlying issue was that affecting her flock. Now she’s aware and has sent one bird for necropsy (and will continue to do so with future losses) she’ll be better prepared to prevent transferring pathogens to another flock and how to support her remaining birds to bolster their immune systems, enabling them to be as healthy as possible, for as long as possible.

Other related posts of interest: Chicken Respiratory System 101; Respiratory Infections

3 comments on “Infectious Coryza

  1. Borden, Carol Ann

    Thanks Claire.

    Much appreciated.

    I’ll let you know results of future symptoms, necropsies – remainder of flock still surviving, , looks like two are now laying.



    Liked by 1 person

  2. Karen Reed

    Croyza has hit my flock. I introduced new chickens and in 10 days my original chicken were sick. I now have lost half of my flock, I have 6 in isolation and watching the remaining 6. I changed disinfectant to Virkon S. , stripped the coop sick chickens were in. Washed nest boxes & trays in bleach water. Then sprayed with new disinfectant, locked it up. All chickens in the well pen got an antibiotic injection. It’s awful to have to go thru this.

    Liked by 1 person

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