11/1/2022:  In 2020, GD found the Ornithobacterium rhinotracheale (O.r.) bacteria at two unrelated poultry farms, where a number of chicks had died of sepsis, which is an unusual clinical sign. These bacteria are known to cause respiratory problems, and an infection is generally only established upon slaughter. It is important to gain a good understanding of this new manifestation to enable prompt monitoring in case of mortality.

When serious signals are received from the field, involving the death of multiple chickens, the monitoring system is immediately on the alert for avian influenza (AI). Once this is officially suspected, there is often clarity within a few hours as to whether it is indeed avian influenza. In this context, it is also important to have good insight into any other causes of acute mortality. Ornithobacterium rhinotracheale (O.r.) is known as the bacteria that cause inflammation in the air sacs and lungs. It is generally only established upon slaughter, when residual signs are found in the form of cheesy clots. This results in increased rejects and is often an unpleasant surprise for the poultry farmer.

Sepsis due to O.r.

In May 2020, GD established unusual clinical signs in several flocks of broilers at two farms, which had no mutual epidemiological relationship. An infection with O.r. caused sepsis in these flocks. Upon pathological examination, we found an enlarged spleen and liver, but no abnormalities in the respiratory system. There was acute progress of the disease and increased losses. Remarkably, treatment with antibiotics resulted in a reduction in losses, while this generally has no effect on the respiratory form of O.r. There was no sign of other possible causes of sepsis, such as other bacteria, Clostridium botulinum and viruses including AI. At both farms, a subsequent flock once again suffered sepsis caused by O.r.

New insights

It was known from the literature that O.r. can occasionally cause inflammation in other organs or joints. However, sepsis without any respiratory clinical signs had not yet been reported. The examination of these cases provided us with reasonable evidence that these clinical signs were indeed caused by O.r. Globally, there has not been a great deal of research into the genetics of O.r. bacteria, though it was already clear that there are many genetic variants. In 2021, GD initiated an in-depth study into the relevant O.r. strains. The DNA study shows that the strains capable of causing sepsis are more strongly related to one another. Further analyses must provide more clarity on the exact genes that cause the clinical signs of sepsis. For the people in the field, it is important that O.r. is on their radar in case of acute mortality. So other causes (such as AI) can be excluded even more quickly and the actual cause becomes clear sooner.
 

Being alert to unusual causes of losses

Jeanine Wiegel: poultry veterinarian at GD

“We received a notification of a case of O.r. with unusual clinical symptoms. In addition, the bacteria had been found in organs other than the respiratory system. The classic form of O.r. will result in rejects on the slaughter line, but there are often no clinical signs in the broiler house. This form was a widespread problem some 15 to 20 years ago, but is much less common nowadays. These clinical signs, with animals dying, were really different. When within a short space of time, we also received a notification from a second farm on the other side of the country, this prompted us to take a closer look at sepsis and O.r.

We initially suspected a combination of infections or some other trigger for the clinical signs. We therefore examined a few animals from the affected flocks ourselves, using histological testing and bacterial cultures from various organs. We found O.r. mainly in the blood vessels. This was therefore indeed a case of sepsis caused by the O.r. bacteria.

As very little is known about the different O.r. strains, we conducted our own research into the genome in 2021. It would seem that the strains capable of causing sepsis are more strongly related to one another. We are currently looking into the underlying genetics. This is the type of research on which we spend more and more time, and developments take place very rapidly. We need to stay alert and determine which techniques are most suitable for each type of pathogen. In this study too, we used several methods.

These were not logical bacteria to find. An added complication is that you can easily miss O.r.; the bacteria are quickly overgrown by other types of bacteria and the laboratory circumstances are critical. It is therefore important that O.r. is on the radar as an option. We have not seen any other recent cases apart from the two farms we investigated as part of this case.

If poultry die, all the alarm bells go off. Once avian influenza is excluded, everyone is still curious as to the actual cause of the mortality. By investigating other causes carefully, we increasingly get insight into probable causes in the broiler house. This could avoid NVWA teams being put on standby unnecessarily. Due to the alertness to mortality, the current monitoring system works well for this manifestation of O.r.

O.r. sepsis should be part of the differential diagnosis

André Steentjes: poultry veterinarian at Veterinair Centrum Someren

“This case of O.r. sepsis truly surprised me. This poultry farm has a patio system, whereby the broilers are kept in different storeys. This allows for very effective ventilation and climate control. The outbreak here was therefore very remarkable, as disease caused by O.r. is generally related to the climate in the broiler house. All the alarm bells were sounded when a large number of chicks were found dead on one of the storeys. Rapid and great mortality can be a sign of avian influenza or botulism, for example. Luckily we were quickly able to rule that out. Immediately striking were the enlarged spleens of the chicks. Cultures taken from the spleens showed massive amounts of the Ornithobacterium rhinotracheale bacteria, without any sign of the typical cheesy clots in the chicks’ air sacs. The classic presentation of O.r. that we poultry veterinarians see, is of chicks with respiratory issues followed by increased mortality and rejects at the abattoir. However, the chicks at this farm all died acutely as a result of sepsis, on a single storey. A number of chicks also presented with unexplainable paralysis of the neck.

After contacting the Veekijker for poultry, we submitted chicks to GD for necropsy. Our compliments go out to the necropsy pathologists, who made the right call for further examination. A number of viruses were found, which suppressed the chicks’ immunity. The Marek’s disease virus was found in reasonably young broilers. Later, the type DV86 Gumboro virus was also found.

The chicks were probably immuno-compromised, which is why they were affected so much by O.r. There was no reason to consider climate problems in the broiler house or prior mucosal damage caused by other infectious agents. This farm pre-hatches its own eggs, after which the chicks hatch in the patio system. Thanks to effective cleaning and disinfection, in combination with starting in ovo-vaccination against Marek’s disease and Gumboro, the problems were soon under control.

In 2021, GD conducted further research into the O.r. strains involved, and plans to genotype the isolates found. The sepsis was seen at two separate farms in 2020. We want to know whether this was due to different O.r. strains. The ventilation systems did resemble one another. One of the farms simultaneously housed chicks of different ages, which could allow the introduction of O.r. via the ventilation air from older flocks to younger flocks. The same goes for the immuno-suppressant viruses. This could be the reason why the O.r. sepsis occurred in consecutive flocks.

My conclusion: in the event of acute losses, it is always important to submit a representative group of chicks for necropsy. And O.r. sepsis should certainly be part of the differential diagnosis, alongside avian influenza, botulism and Gumboro, especially if chicks are presenting with enlarged spleens.”