Unusual and severe lesions of proventricular dilatation disease in cockatiels (Nymphicus hollandicus) acting as healthy carriers of avian bornavirus (ABV) and subsequently infected with a virulent strain of ABV

Abstract

A flock of 14 apparently healthy cockatiels, purchased from a single aviary, was tested for the presence of avian bornavirus (ABV). Twelve birds were found to be intermittently shedding ABV, predominantly genotype 4. Four of the cockatiels known to be shedding ABV4 were subsequently challenged with the tissue culture derived, virulent M24 strain of ABV4. The challenged birds remained in apparent good health until day 92 when one was found dead. The remaining three birds began to exhibit severe neurologic signs, ataxia and convulsions on day 110 and were euthanized. On necropsy, all four birds showed mild proventricular enlargement. In contrast, histopathological examination showed unusually severe and widespread tissue lesions. These included massive lymphocytic infiltration and lymphoid nodule formation within and around the ganglia throughout the gastrointestinal tract. There were similar lesions in the medullary cords of the adrenal gland, heart, spleen, liver, kidney, lungs, pancreas, testes and ovary. Immunohistochemistry demonstrated ABV P antigen not only in the cells of the central and autonomic nervous systems, but also within the mononuclear cells infiltrating the various organs. Two healthy cockatiels, one of which was a known ABV carrier, were inoculated with uninfected tissue culture cells and euthanized on day 150. These birds showed no gross lesions of proventricular dilatation disease but had a mild lymphocytic infiltration in their liver, spleen, and kidneys. Prior infection with ABV did not therefore confer significant immunity on these birds, and may have resulted in increased disease severity following challenge.

Avian bornavirus in the urine of infected birds

“…IHC of a cockatiel experimentally infected with ABV, strain M24, genotype 4 clearly demonstrates the presence of BDVP in the kidney of an affected bird. 4 The presence of BDVP with cells and associated cellular debris within the tubular lumen is consistent with the presence of cell-associated viral shedding in the urine (Figure 3). …”

“…4 Virus escaping these cells would gain immediate access to the urine. Alternately, tubular cells shed in the lumen and excreted as urine could be a source of viral DNA.…”

“…IHC was performed according to the method described by Weissenbock using a polyclonal crossreactive antibody against recombinant borna disease virus polymerase protein (BDVP) on cockatiels in which the disease was induced. 4 …”

“…Multiple researchers have described the presence of ABV within the kidney, in Dovepress submit your manuscript | www.dovepress.com PDD-affected and ABV-infected birds via PCR and immunohistochemical staining. 4,5,9 Indeed, some have postulated that ABV may be transmitted via the kidney or urine. 5 Avian droppings consist of a mixture of feces and urine.…”

“…In fact, it commonly spreads to all the major organs, including heart, liver, adrenals, and the kidneys. 1,[3][4][5] Birds infected with ABV have an incubation period that may range from 20 days to several years. 6 For much of this time, the birds may appear healthy but shed the virus through their choana, nares, and droppings.…”