Infectious Coryza (‘acute snot’ or simply Coryza) is a poultry disease caused by the Avibacterium paragallinarum bacteria. Coryza is mainly prevalent in tropical and subtropical countries but has been increasingly diagnosed in both commercial and backyard poultry in Europe over the past decades.
The main symptom of Coryza is an extremely rapidly developing inflammation of the frontal airways, particularly the paranasal sinuses. A combination with other bacterial or viral infections often results in exacerbation of the clinical symptoms. Nasal discharge, pulmonary constriction, ruffled feathers, swelling of the head (on one or both sides) and an increase in the number of affected animals and mortality is characteristic of such ‘double’ infection. Partially due to additional infections, mortality rates can vary from a few animals to double digit percentages. Coryza can also result in decreased egg production, of as much as 70 percent in some cases. Poorer hatching results may also occur. The severity of the clinical symptoms and the losses depends very much on the strain of bacteria present.
After recovery, and disappearance of all clinical symptoms, flocks remain contagious for the rest of their lives. These ‘carrier flocks’ form a risk for other farms in the vicinity. In order to prevent spread of the A. paragallinarum bacteria, hygiene measures must be taken in the event of a clinical outbreak, free range chickens must be contained indoors and all contacts informed of the situation. An early warning system (EWS) for Coryza was established in 2009 in order to enable nearby farms to take the necessary measures. The main method of controlling Coryza at a farm, following thorough cleaning and disinfecting, is to vaccinate any subsequent flocks for Coryza. The choice of appropriate vaccine depends on the A. paragallinarum serovar with which the flock is infected.
Two dominant serotypes
A number of genotypes are found both in commercial poultry farming and backyard poultry. There are two dominant serovars, which differ in terms of their pathogenic capacity. As of 2018, the A. paragallinarum bacteria has also been detected in flocks without any clinical symptoms. These animals are identified partly due to Coryza diagnostics being included in the respiratory package (a combination of PCR tests for the main respiratory pathogens). This may be a sign of frequent occurrence of carrier flocks. Alternatively, these flocks may be infected with a lower pathogenic A. paragallinarum strain. If the flock then becomes infected with another virus or bacteria, clinical symptoms of Coryza may still occur. Improved diagnostics and monitoring
The increased prevalence of Coryza in the commercial poultry sector has resulted in improved Coryza diagnostics. This bacteria can now be reliably diagnosed, after which we can determine the genotype and serotype. This allows us to monitor the situation in the field.
Anneke Feberwee, poultry veterinarian at GD
“Often milder strains of Coryza nowadays”
“We saw an increase in the number of clinical cases following the introduction of the Early Warning System (EWS) for Coryza in 2009. The turning point came last year. The number of clinical cases is on the decline but we are detecting more carrier flocks. Such carrier flocks may be flocks infected in the past, or those infected with a lower pathogen bacteria strain. These milder variants of Coryza may only become evident when a different type of pathogen occurs in the chicken. Together, they can then still result in a true Coryza outbreak. In the early years of the EWS, we were mainly seeing serovar A1, which were very virulent strains. More recently, the serovar C4 strain has been circulating. This serovar seems less virulent, resulting in the clinical symptoms also being more mild. We have however experienced a number of clinical outbreaks over the past year, though with only mild symptoms. This would be in keeping with the phenomenon of milder strains identified.
Any Coryza findings, reported by phone or during necropsy, are entered in the EWS in consultation with the veterinarian. This keeps the field informed of the outbreak. In the event of an acute clinical outbreak, whereby there is great risk for farms in the direct vicinity, everyone involved takes responsibility. This is particularly the case if there is a high density of poultry farms in the direct vicinity. During a serious outbreak, it is essential that free ranging flocks are immediately contained indoors. After all, the animals transmit large concentrations of bacteria during the initial outbreak phase. Due to that risk of infection, we always advise local free ranging farms to contain their poultry indoors. Strict hygiene measures are then taken in order to avoid transfer. It is sensible to vaccinate the subsequent flock for Coryza.
The EWS is extremely effective for the monitoring of Coryza, especially in the case of urgent and acute outbreaks, which carry a high risk of other farms becoming infected. Those involved are informed quickly, because notifications are communicated effectively, and veterinarians recognise their importance. Equally important is the monitoring of the various strains. Quicker tests are now available, which have made life easier for the sector. When an outbreak occurs, we conduct a molecular test to determine the genotype and the serovar. The genotyping test enables us to monitor the introduction of new strains. The serotyping test allows us to monitor the effectiveness of vaccination, and to continue to apply the most appropriate vaccination strategy.”
“Distinguishing between serovars is important in order to choose the appropriate vaccine to combat infectious Coryza”
Frank Westerbeek, poultry veterinarian at AdVee Dierenartsen, Ysselsteyn
“We need data for effective monitoring”
“Coryza is a disease which we would normally only occasionally encounter. I’ve recently been seeing increased numbers of clinical cases. These often concern clusters, whereby neighbouring farms are also involved. When clinical cases are detected at one farm, you can be more or less sure that there will be other cases in the neighbourhood. It’s very useful to be kept up to date on any outbreaks via the EWS. If the outbreak is local, I’ll call my colleagues, as mutual contact between veterinarians is just as important as the EWS. I myself always submit samples if I suspect Coryza. And when a notification from a farmer raises even the slightest suspicion of Coryza, I’ll plan my visit to that farm at the end of the day. You really don’t want to transfer this disease.
We sometimes see cases whereby a flock is not really developing well, and the loss percentage is a little higher than normal. I’ll then start my own bacteriological investigation, but if there are no useful results and the problem continues to linger to any extent, it’s time to submit samples to GD. The poultry sometimes turn out to be Coryza carriers. These animals do not display any symptoms, though such a subclinical case of Coryza can suddenly become clinical, with symptoms. This can happen, for example, following severe stress caused by a feed change or a case of infectious bronchitis (IB). Carriers make the whole situation complicated, and good consultation regarding the approach then becomes essential. You preferably want to dispose of a carrier flock more quickly than normal, while the new flock needs to be vaccinated. Luckily, poultry farmers are generally easily convinced of the necessity. As entrepreneurs, they are aware of how dramatic the consequences of Coryza can be, as they remember the cases a few years back. That’s always useful leverage as a veterinarian.
The GD respiration package is very useful, as it is low threshold and therefore quite readily deployed. However, farmers do sometimes struggle to determine which hens should be submitted. I therefore always advocate involving the veterinarian, so that the right hens end up at GD for pathological examination. Due to Coryza nowadays often taking a milder form, farmers are less likely to suspect this disease. And certainly if this is the first time they have been confronted with it. When losses increase and production decreases, poultry farmers would be wise to consult with their veterinarian. Increased awareness of Coryza would be useful, and the collaboration between consultants, poultry farmers, veterinarians and the Veekijker veterinarian is extremely important.”