Occurrence: Worldwide.   Species affected: Chickens and turkeys   Age affected: All.

Causes: Gram-negative, non-sporulating rod shaped bacterium, Ornithobacterium rhinotracheale. Recently isolated, formerly known as a Pasturella-like organism, Kingella or Taxon 28.

Effects: Broiler breeders (24-52 weeks of age) show slightly increased mortality, decreased feed intake, mild respiratory signs, decreased egg production, poor egg shell quality and decreased egg size. In young chickens, coughing, sinusitis and sometimes respiratory distress and oedema of the head are seen, leading to increased mortality and higher condemnations at processing.

The bacterium Ornithobacter rhinotracheale (ORT) was only identified in the 1990’s, but has received much attention since then. Twelve different serotypes of ORT are known. The disease is an acute, contagious respiratory disease of chickens and turkeys. Early research has suggested that the organism is not a primary pathogen and can unfold its pathogenic properties only in association with primary pathogens. However, these results have been disputed, especially through experience in the field with turkeys.

The course and duration of the disease depend on such factors as climate, stocking rate and other simultaneous infections.

ORT is often isolated from chickens without obvious clinical signs. Clinical signs are coughing, nasal discharge and sinusitis. Sometimes there is respiratory distress and oedema of the head. In broiler breeders, clinical signs are usually observed early in the production period and consist most importantly of a decrease in egg production of 2-5%, lower egg weight and poor eggshell quality. In broilers, ORT symptoms occur between oedema, depression, increased mortality and low growth. Increased slaughterhouse condemnations may occur.

At postmortem, clinically diseased birds may reveal various gross lesions including rhinitis, sinusitis, tracheitis, airsacculitis, pneumonia, pericarditis and arthritis. Foamy or cheesy exudate in the air sacs is often seen as an indication for ORT.

In vitro, ORT bacteria grow slowly and need special growth conditions such as 5-10% CO2. ORT may therefore easily be overgrown by other bacteria that are present, such as E. coli. Suspected chickens should therefore be sampled early in the disease. The addition of gentamicin and polymyxin to the medium contributes to a more selective isolation of ORT.

Amoxycillin and doxycyclin are most effective drugs, but resistance often occurs. In the late 1990’s, an inactivated vaccine was developed against ORT. Offspring from broiler breeders vaccinated against ORT have shown increased resistance to the disease for up to three weeks of age.

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