Molecular Detection and Characterization of Avian Bornavirus

Proventricular dilatation disease (PDD) was first recognized during an outbreak among captive macaws in the late 1970s. The disease, also known as proventricular dilatation syndrome or macaw wasting disease can occur in any psittacine but the most commonly affected birds are macaws, cockatoos and conures. The disease causes inflammation of the central, peripheral and autonomic nervous systems, as well as weight loss associated with regurgitation and the passage of undigested food in the feces. Although a viral etiology for PDD has been suspected for almost 40 years, the etiologic agent of the disease was unknown until lately. Recently we cultured a novel bornavirus from brain tissue from birds clinically diagnosed with PDD. This finding supports data from other groups who, in 2008, identified bornavirus sequences among birds suffering from PDD. It was reported that more 60 percent of PDD affected birds were infected with the new virus, designated avian bornavirus (ABV). ABV is a negative sense, single stranded RNA virus related to Borna disease virus (BDV). ABV isolates differ dramatically from BDV isolates in their level of genetic variation. Using polymerase chain reaction (PCR) assays, we were able to detect ABV in feces and tissue of PDD birds. We also detected ABV shedding from clinically healthy birds housed in aviaries with no history of the disease. We also determined the complete genome sequences of eight North American ABV isolates. Genotyping indicates that the majority of North American ABV isolates are genotype 4. We found one ABV, genotype 1, which is the first complete sequencing of this genotype. Moreover, we found ABV genotype 2, isolated from an apparently healthy cockatiel with no PDD clinical signs. In order to investigate whether this genotype is avirulent, the virus was grown in duck embryo fibroblasts and inoculated into two adult cockatiels by the oral and intramuscular routes. One bird developed clinical signs on day 33 and was euthanized on day 36. The second challenged bird developed clinical signs on day 41 and was euthanized on day 45. On necropsy, the proventriculus of both birds was slightly enlarged and microscopic examination showed lesions consistent with PDD in the brain, spinal cord, heart, adrenal gland and intestine. A control, uninoculated cockatiel was apparently healthy when euthanized on day 50. ABV2 is now the second ABV genotype to be formally shown to cause PDD.