Ornithobacterium rhinotracheale: the current status

G. van den Bosch

Intervet International bv, Bacteriological Research, Wim de Körverstraat 35,

P.O. Box 31, 5830 AA Boxmeer, The Netherlands

Proceedings of the 24th Technical Turkey Conference  p1

Introduction

Ornithobacterium rhinotracheale is a slow growing, pleomorphic, gram-negative, rod-shaped, relatively new bacterium associated with poultry diseases. Before 1994, the bacterium was named Pasteurella-like, Kingella-like or Pleomorphic Gram-Negative Rod (PGNR) and also the name TAXON 28 was used. Currently the bacterium is often referred to as ORT.O. rhinotracheale can cause acute highly contagious diseases in poultry. The severity of clinical signs, duration of the disease and the mortality rate are extremely variableand are influenced by many environmental factors such as poor management, inadequate ventilation, high stocking density, poor litter conditions, poor hygiene or concurrent infections. O. rhinotracheale can be associated with high economic losses in poultry due to an increase in mortality rates and condemnation rates, a drop in egg production or a decrease of the performance results. The presence of O. rhinotracheale in commercial poultry and also in wild birds has been shown to be worldwide,meaning that there is a broad potential reservoir. All over the world, maternally derived antibodies against O. rhinotracheale can be detected in eggs and day-old birds. Several surveys showed that the vast majority of turkey flocks in Europe, Africa, North and South America and some Asian countries have been in contact with O. rhinotracheale. O. rhinotracheale has been isolated from many bird species such as chicken, chukar partridge, duck, goose, guinea fowl, gull, ostrich, partridge, pheasant, pigeon, quail, rook and turkey. However, many of the infections, caused by O. rhinotracheale, are not recognised as such either because the causative agent can not be isolated or because investigators are not aware of the possibility that O.rhinotracheale can cause infections other than the more well-known respiratory ones.

O. rhinotracheale infections.

The characteristic features of an O. rhinotracheale infection include relatively mild respiratory signs in young birds. These symptoms start with sneezing and are accompanied by a slightly increased mortality and a poor performance. At post mortem examination, foamish, white, “yoghurt like” exudate can be seen in the air  sacs, commonly accompanied by unilateral pneumonia. These symptoms can disappear within one week but can also be deteriorated by succeeding infections with other pathogens and through that may not be recognised as an O. rhinotracheale infection anymore. O. rhinotracheale also can cause sudden deaths in young birds through infections of the brains and the skull, featuring totally weakened skull-bones. This kind of O. rhinotracheale infection can be seen with or without the above mentioned respiratory symptoms. Especially when older birds are involved, the  economic losses of O. rhinotracheale infections can turn out to be considerable. In turkeys of 12 weeks of age or older, O.rhinotracheale can cause acute pneumonia with mortality rates of up to 50%. Another kind of O. rhinotracheale infection in older turkeys causes paralysis through arthritis, osteitis and osteomyelitis, commonly showing a purulent, slimy exudate in the joints of the lame birds. O. rhinotracheale infections in turkey breeder birds leads to slightly increased mortality, a drop in egg production and a decrease in the egg quality. However, these kind of infections seldom will be recognised as an O. rhinotracheale infection. Early experiments showed that the disease could be evoked by aerosol administration of O. rhinotracheale butonly as a secondary infection after the administration of viral primers such as Turkey rhinotracheitis virus or Newcastle Disease virus. However, it has been proven thatsome strains of O. rhinotracheale induces the above mentioned infections without priming. Nevertheless it is clear that some viruses have a strong aggravating effect on O. rhinotracheale infections and it is shown that bacteria such as Escherichia coli and Bordetella avium can also trigger O. rhinotracheale infections. In fact, respiratorysymptoms in poultry, including O. rhinotracheale infections, is influenced by a complex of factors such as stress, inadequate ventilation, poor hygiene, high ammonia levels and the type of secondary infection.

Diagnosis

The clinical signs and post-mortem lesions of the different O. rhinotracheale infections are not sufficiently specific to be diagnostic. Respiratory diseases in poultry are so complex that the respiratory signs caused by O.rhinotracheale can easily be confused with those caused by viral infections or by infections of e.g. E. coli orRiemerella anatipestifer. Joint infections, caused by O. rhinotracheale, also result in signs similar to those caused by other bacteria e.g. E. coli, Staphylococcus aureus or Streptococcus feacalis. Brain infections are most of the time not even noticed as possible cause of death and therefore easily misinterpreted. Many factors can interfere with the diagnosis of O. rhinotracheale infections. For instance, O. rhinotracheale normally only can be isolated in an early stage of the infection, the recovery of O. rhinotracheale infections in a late stage will often fail. Also, after an O. rhinotracheale infection, other potential pathogenic bacteria can induce secondary infections and, because these bacteria will survive longer and will grow more readily, they often will be designated to be the causal agent of the infection.In field studies, using a sensitive immuno-histochemical coloration for confirmation of O. rhinotracheale infections, it was found that O. rhinotracheale was the cause of 70% of the cases with respiratory symptoms in broiler chickens, while through  acteriology and/or serology only 30% of the cases could be connected to O.rhinotracheale. Lately, also joint-infections in turkeys are regularly found to be O. rhinotracheale infections, but most of the time only after immuno-histological confirmation. Antibodies can be detected by an ELISA shortly after the start of a field infection and titres will peak between 1 to 4 weeks post infection. Because titres decline rapidly after peaking, serum samples for flock screening should be taken frequently. The serotype specificity of the ELISA is a disadvantage but commercial ELISA’s are available with which most serotypes can be detected.

Epidemiology

The investigation of the epidemiology of O. rhinotracheale is hampered by the difficulties found in culturing O. rhinotracheale from infected organs, the brevity of the serological responses after an O. rhinotracheale infection and the complexity of the infections in which O. rhinotracheale can be involved. It has been proven that transmission of O. rhinotracheale is possible not only horizontally through aerosols but also vertically through the egg. Because eggs are sent all over the world, these findings make it more easy to understand the relative rapid, world-wide spread of O. rhinotracheale infections in the commercial poultry world during the lastdecade. Relationships are seen between the geographic origin of the O. rhinotracheale isolates and their serotype. From the eighteen serotypes, serotype A is predominant among the chicken-isolates (96%) and the most frequent (54%) among the turkey isolates, which are more heterogeneously divided. Up to now there is no explanation for these differences in distribution but it has been shown that serotype A and C strains from chickens and serotype B, D and E strains from turkeys have a similar virulence for both chickens and turkeys. So there is no indication of any hostspecificity of the serotypes. A possible explanation may be found in the different breeding practices in the chicken and turkey industries.

Treatment with antibiotics

The treatment of O. rhinotracheale infections with antibiotics is very difficult because of the inconstant sensitivity of the strains. It has been proven that O. rhinotracheale is able to acquire resistance easily against antibiotics such as doxycycline, enrofloxacin, flumequine, lincomycin, trimethoprim+ sulphonamide and tylosin. The sensitivity pattern depends on the source of the strain and on the routine use of antibiotics on the poultry where it is isolated. Successful antibiotic treatments of O. rhinotracheale infections through water medication were reported with chlortetracycline and amoxicillin. Also injections with tetracyclines and penicillins were found to be effective in some cases. However, it should be emphasised that for successful  treatment an investigation of the sensitivity pattern of the isolated strain is needed.

Control measures

O. rhinotracheale bacteria can cycle and recycle from farm to farm and from house to house. t O. rhinotracheale infections appears to have become endemic and can effectnewly introduced stock, especially in multiple age farms and in areas with an intensive poultry production. Therefore it is important to clean and disinfect housesthoroughly between stocks. Disinfectants that are based on different organic acids such as formic and glyoxyl acids and disinfectants that contain aldehydes were found to readily inactivate O. rhinotracheale, in vitro.

Vaccination

Vaccination of turkey broilers with autogenous bacterins successfully reduced the number of outbreaks of O.rhinotracheale infections in the field. A problem in turkeysis that repeated infections caused by other serotypes regularly occur during the rearing period . Although there is proof for a degree of cross-protection between some serotypes of O. rhinotracheale, it still means that vaccination of turkeys should be performed using several serotypes in the vaccine and that vaccines with a long-lasting efficacy should be used. This also applies to autogenous vaccines.Maternally derived antibodies, which can be found in almost all flocks, can have a negative influence on the vaccination of one-day-old birds against O. rhinotracheale.Vaccines in potent (oil) adjuvants are needed to break through this barrier, but it is well known that only the vaccination of one-day-old birds with this kind of vaccines already can have negative effects on performance. The best results in young birds are obtained by the vaccination of breeder flocks. This induces the maternally derived antibody levels in their progeny resulting in significant protection up to 3-4 weeks of age against experimental challenge. In field trials, the vaccination of breeders also significantly reduced the number of O. rhinotracheale isolates and outbreaks in their progeny. To protect birds at older ages, vaccination should be started at 2-4 weeks because infections do occur at all ages. Live vaccination is feasible but up to now no non-virulent strains of O. rhinotracheale have been found that could be used for this purpose.

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