(Turkey coryza, Bordetella avium rhinotracheitis)
Avian bordetellosis is an acute upper respiratory disease characterized by high morbidity and usually low mortality. It primarily affects turkeys, and quail are also susceptible to infection. Infection has been documented in young chickens, but when experimental infections have been attempted, chickens have proved to be somewhat refractory. Mortality can increase and clinical signs can become severe if young turkeys infected with also become infected with Bordetella avium other agents such as Newcastle disease virus or when environmental conditions in turkey barns are less than optimal. Bordetellosis is a major initiator of colibacillosis, a secondary infection that is responsible for most of the mortality and severe clinical manifestations.
Bordetellosis has been identified in almost every area of the world where turkeys are intensively reared. Historically, it has been severe in focal areas and rare or subclinical in other locations where turkeys are reared intensively. The reasons for these epidemiological differences have not always been apparent.
Etiology, Transmission, and Pathogenesis: The causative agent is a gram-negative, nonfermentative, motile, small rod. The bacterium is best isolated from the anterior trachea; cultures taken from the sinuses frequently become overgrown with other faster replicating bacteria such as Proteus sp . There are two colony types of B avium ; after 25 hr incubation, one is large, dry, and serrate, and the other is small, smooth, round, and glistening. Other nonfermenters can frequently be isolated from the trachea, but the pathogenic B avium can be identified as producing small colonies that are nonfermentative with the bacteria able to hemagglutinate guinea pig RBC.
Bordetella avium is transmitted from infected turkeys by direct contact or by spreading the infection from one barn to another. There are also reports of infections being associated with contaminated drinking water, especially stagnant water that has inadvertently been given to turkeys. Water that has been allowed to stand in water lines may become contaminated with the bacteria, which subsequently infect susceptible turkeys.
The mechanism of pathogenesis of severe, complicated B avium infection is related to the ability of certain strains of the bacteria to cause deciliation and loss of mucous gland function of the tracheal epithelium. If there are additional stresses, secondary infection with Escherichia coli or other agents can occur. In many cases, turkeys infected solely with B avium do not develop secondary infections and recover without serious consequences. Damage to the tracheal cartilage with distortion and discoloration of the tracheal rings has also been reported. Some mortality has been caused by suffocation from tracheal collapse. Important factors involved in the ability of B avium to damage the tracheal epithelium include the ability of certain strains of the bacteria to adhere to the epithelium and to produce toxins, some of which appear to be similar to those from other Bordetella spp . Toxins and virulence factors associated with pathogenic strains of B avium include tracheal cytotoxin, dermonecrotic toxin, osteotoxin, and adherence factors associated with the pili and hemagglutinin.
Clinical Findings and Diagnosis: Clinical signs of uncomplicated B avium infection are sinusitis with a clear nasal discharge when pressure is applied to the nares, foamy eyes, and a characteristic snick or cough. Complicated disease can result in more exaggerated signs along with higher mortality. Bordetella avium alone does not cause airsacculitis.
Related factors that appear to affect the severity of disease include age of infection and presence of maternal antibody. The younger the age at infection, the more severe the disease. Because maternal antibody appears to reduce the pathogenic effects of early infection, it may be the most important factor in control.
Diagnosis of infection is confirmed by isolation of B avium on MacConkey's agar. Nonfermenting, small, slow-growing colonies from specimens from the anterior trachea are typical. Serology is also important, and both microagglutination and ELISA tests are available. The ELISA is preferred because it detects maternal antibody.
Prevention and Treatment: Vaccination with bacterins and a live, temperature-sensitive mutant vaccine has given mixed results depending on the age of the turkey and the method of administration. Vaccination is not widely practiced in turkey breeders, and the immunity that is passed to progeny comes from natural infections.
Treatment with antimicrobial agents has not been effective, even though B avium may be highly sensitive. The tracheal epithelium of the turkey is a difficult location to medicate even though blood levels of the antimicrobial appear to be adequate. Antimicrobial therapy may be helpful for secondary colibacillosis.
Prevention should include a good biosecurity program with rigorous cleanup and disinfection after field outbreaks. Bordetella avium is not transmitted to man.