A feather disease in Senegal doves (Streptopelia senegalensis) morphologically similar to psittacine beak and feather disease.

The pathogenesis and epidemiology of a feather disease in wild Senegal doves (Streptopelia senegalensis) which is morphologically similar to psittacine beak and feather disease (PBFD) was investigated. Although the lesions in doves resembled PBFD there was little evidence for the presence of psittacine circovirus (PsCV). Haemagglutination activity (HA) using type A galah (Eolophus roseicapillus) erythro-cytes was not detected in feathers or livers of affected doves as would occur in PBFD. Low concentrations of HA excreted in the faeces of affected doves was not caused by psittacine circovirus (PsCV) because the antigen in faeces also caused haemagglutination of PsCV-insensitive type B galah erythrocyte and was not inhibited by anti-PsCV antibody. Similar HA of unknown cause was also detected in faeces from clinically normal Senegal doves. Anti-PsCV haemagglutination inhibiting (HI) antibody was not detected in the serum of affected doves or in the blood of 206 clinically normal wild Senegal doves or 17 captive columbid birds in close contact with a flock of psittacine birds that was known to be PsCV-infected. Senegal doves also failed to seroconvert after two inoculations with PsCV purified from the feathers of a PBFD-affected long-billed corella (Cacatua tenuirostris). The results indicate that the feather disease seen in feral Senegal doves in Perth is not due to PsCV although the possibility that it is due to another antigenically distinct circovirus was not eliminated.     

Circovirus-infected geese studied by in situ hybridization.

It has now been established that circovirus infection is common in farmed geese, but little is known about the clinicopathological significance of such infections. Ten clinically diseased geese suspected of being infected by circovirus were studied by in situ hybridization using a goose circovirus DNA probe. Circovirus DNA was demonstrated in the bursa of Fabricius (BF), spleen, thymus, bone marrow, liver, kidney, lung and heart, indicating that infection can be multisystemic. In some birds, virus DNA was present in very large quantities, most notably in the BF, liver and small intestine. With the exception of BF and thymus, there were no histological findings that would have suggested the presence of such quantities of circovirus DNA. In view of the very large quantities of virus DNA labelling present in some tissues, and by analogy to porcine circovirus type 2 infection and psittacine beak and feather virus infections, which are known to cause severe disease, and which have similar virus distribution to that found in our geese, it seems probable that the circovirus was important in the disease manifestations shown by the infected geese.     

A reovirus challenge model applicable in commercial broilers after live vaccination

The efficacy of live reovirus vaccines may be determined by challenge via the foot pad route 3 to 4 weeks after vaccination. Swelling and discoloration in the foot pad and shank are scored for a period of 14 days. The major disadvantages of this challenge model are the subjective judgement of gross foot pad and/or shank lesions, that it is very difficult to induce lesions in broilers, and that it causes animal suffering. Other reovirus challenge models are based on reisolation of the virus from different tissues or on scoring microscopic lesions in the tendons. Some disadvantages of these models are that they either cannot be used after vaccination with live reovirus because they cannot discriminate between vaccine and challenge virus or that the microscopic lesions scored need not necessarily be related to the challenge virus but may have been induced by other factors. Therefore, we have attempted to develop a reovirus challenge model that was an improvement on the existing ones, using isolation of reovirus from different organs followed by specific detection of the challenge virus with a monoclonal antibody that can discriminate between challenge and vaccine virus. The reovirus challenge model was examined in specific pathogen free (SPF) White Leghorn chickens and commercial broilers. In vivo studies were conducted to examine the efficacy of an attenuated reovirus vaccine in SPF White Leghorn chickens and commercial broilers with maternal immunity against reovirus. No challenge virus could be detected in any of the organs of the vaccinated chickens 3 and 10 days after challenge. In contrast, challenge virus could be isolated from the unvaccinated control group. At an increased challenge dose all unvaccinated challenge control birds were positive, while the vaccinated chickens were protected. It was shown that 1-day-old vaccination in the presence of maternal immunity was effective. It seemed that protection induced in broilers by the attenuated reovirus vaccine may not have been entirely humoral because in protected birds no antibodies against reovirus were detected by enzyme-linked immunosorbent at the time of challenge. Protection in these birds might therefore have been induced by cellular immunity.     

A disease complex associated with pigeon circovirus infection, young pigeon disease syndrome.

In order to collect more convincing data on the aetiological agent of young pigeon disease syndrome (YPDS), a comprehensive study was performed on pigeons in German lofts with or without outbreaks of YPDS. The investigations included examination of histories, clinical signs and pathology, as well as parasitological and microbiological analysis. Pigeons in their 4th to 12th week of life exhibited clinical signs at higher frequency and with greater severity than pigeons of other ages. Greenish liquid in the crop, proventriculus and ventriculus, and yellow fluid in the small intestine were seen more often in YPDS-affected pigeons. Escherichia coli and Klebsiella pneumoniae were isolated more frequently from these birds. Depletion of splenic and bursal lymphocytes was only seen in pigeons with YPDS. Inclusion bodies were present in various organs, especially the bursa of Fabricius. The genome of pigeon circovirus was detected in lymphoid tissues from all pigeons with YPDS. The results of this study indicate that YPDS is a multifactorial disease in which pigeon circovirus might be a crucial factor, possibly by inducing immunosuppression in infected birds.     

Hematology of vaccinated and non-vaccinated long-billed corellas following infection with beak and feather disease virus (BFDV)

The hematological characteristics of juvenile long-billed corellas (Cacatua tenurostris), with or without prior administration of a psittacine beak and feather disease vaccine, were studied for 97 days after experimental infection with beak and feather disease virus (BFDV). It was found that the pre-challenge hematological values were similar between vaccinated and non-vaccinated corellas. Most pre-challenge parameters were comparable to previously reported values of other cockatoos and psittacine birds. Significant differences were seen in both groups when comparing pre-challenge values with post-challenge values for total and differential leukocyte concentrations, but packed cell volume and total serum protein were not significantly affected by BFDV challenge.     

Development of novel real-time PCR assays for detecting DNA virus infections in psittaciform birds

Viral diseases of psittacine birds are detected presently by PCR. However, conventional PCR methods are not quantitative and the products can sometimes include non-specific products of the same size. To avoid these problems, real-time PCR assays based on the SYBR Green assay system were developed for the detection and quantitation of four virus diseases of psittacine birds: psittacine beak and feather disease, avian polyomavirus infection, psittacid herpesvirus infection, and psittacine adenovirus infection. Up to 1x10(2) copies of virus DNA were detected, indicating that these assays are as sensitive as conventional PCR assays. The assays are specific because they did not amplify any other pathogens including other viruses, bacteria, and fungi in psittacine birds. The assays measured successfully virus loads in clinical samples (blood, feathers, and tissues), showing that these specimens were suitable targets for the detection and quantitation of viral DNA in psittacine birds.     

Reovirus infection in two species of Psittaciformes recently imported into Italy

An outbreak of reovirus infection with high mortality in two groups of recently imported psittacine birds is reported. The disease in the two species involved, African grey parrots (Psittacus erithacus erithacus) and Australian king parrots (Alisterus scapularis), had differences in clinical presentation and gross lesions. Reovirus particles were observed by electron microscopy and ultrastructural examination of tissues, and two viruses were isolated in cell culture, one from each bird species. Both isolates were studied by cross-neutralization with antisera against reference avian reoviruses isolated from chickens and parrots, and were found to have the greatest similarity to viruses isolated from a budgerigar and a southern screamer.     

Beak and feather disease virus infection in cockatiels (Nymphicus hollandicus).

Psittacine beak and feather disease is known to occur in a wide range of psittacine species; however, there are no scientific or credible anecdotal reports of psittacine beak and feather disease occurring in the cockatiel (Nymphicus hollandicus) despite it being one of the world's most commonly kept companion bird species. Consequently, this has resulted in speculation that the species may have some innate resistance to beak and feather disease virus (BFDV) infection. To investigate this hypothesis we conducted a survey of cockatiels (n=88) at commercial aviaries to investigate whether BFDV infection occurs in cockatiels, and found that all birds were virus-free by polymerase chain reaction and haemagglutination assay and had no detectable antibody titre by haemagglutination-inhibition assay. In addition to this, we sequenced the genome of two BFDV isolates obtained from diseased cockatiel feathers and performed cross-reactivity assays using virus eluted from these feathers and sera from naturally immune psittacine birds. Serological cross-reactivity results and phylogenetic analysis of the nucleotide sequences indicated that the cockatiel virus isolates were serologically and genetically different to other BFDV isolates. This is the first paper to report evidence of an antigenically distinct BFDV in psittacine birds.     

Psittacine beak and feather disease infected cells show a pattern of apoptosis in psittacine skin.

Skin biopsies from 23 birds with psittacine beak and feather disease (PBFD) were examined by light and electron microscopy. Affected cells, preferentially found in the cell layers of the feather follicles, could be clearly identified by the presence of intracytoplasmic virus inclusion bodies. Ultrastructurally, the degenerative process in these cells was morphologically suggestive of apoptosis.     

Development of a blocking enzyme-linked immunosorbent assay for the detection of avian polyomavirus-specific antibodies

Avian polyomavirus, described originally as budgerigar fledgling disease virus, has been associated with devastating contagious disease outbreaks in budgerigar aviaries. At present, this virus affects a wide range of psittacine and non-psittacine birds worldwide, and the serum neutralisation test is used for the serodiagnosis of avian polyomavirus infections. A blocking enzyme-linked immunosorbent assay was developed for the screening of large numbers of sera collected from various avian species. The assay employs a monoclonal antibody directed against the major structural protein VP1 as a blocking antibody in a sandwich blocking procedure. Either purified avian polyomavirus particles or avian polyomavirus VP1 expressed in recombinant baculovirus-infected Sf9 cells were used as antigen. The specificity of the blocking enzyme-linked immunosorbent assay was evaluated by testing sera directed against mammalian polyomaviruses. Using sera obtained from chicken infected experimentally with avian polyomavirus and a collection of psittacine field-origin sera, a good correlation was observed between the results of the blocking enzyme-linked immunosorbent assay and the serum neutralisation test. However, the blocking enzyme-linked immunosorbent assay is more rapid and more economic. Both, avian polyomavirus particles and VP1 produced by recombinant DNA technology proved to be suitable antigens.     

Effects of experimental immunosuppression on reovirus-induced tenosynovitis in light-hybrid chickens

Groups of specific pathogen-free light-hybrid chickens which had been immunosuppressed either by surgical thymectomy (Tx) or surgical bursectomy (Bx) or cyclophosphamide (Cy) treatment or Tx plus Cy treatment (Tx + Cy), as well as intact (untreated) birds, were inoculated with graded doses of an arthrotropic avian reovirus at 1 day of age and observed up to 5 weeks post-inoculation (p.i.). Cy-treatment with or without Tx considerably increased the mortality, incidence of gross leg lesions and severity of microscopic lesions due to reovirus infection. The Bx group showed only a significant increase in mortality, and the Tx group response was generally similar to the untreated group. Dead birds showed hepatic necrosis, which in Cy-treated groups (Cy, Tx + Cy) was associated with calcification. Surviving Cy-treated birds had acute tenosynovitis characterised grossly by large amounts of serous exudate in leg tendon sheaths, and microscopically by a massive heterophilic but only mild lymphocytic infiltration of tendon sheaths. Tenosynovitis lesions in Bx birds were generally similar to those of the untreated chickens, i.e. grossly small amounts of yellowish brown gelatinous exudate and microscopically moderate chronic inflammatory changes in leg tendon sheaths. In Tx birds gross lesions were rarely seen and the microscopic lesions were often very mild. Reovirus could be recovered from cloacal swabs from untreated and Tx birds for 2 weeks, Bx birds for 3 to 4 weeks, and Cy and Tx + Cy chickens continuously throughout. Reovirus was isolated from tendon tissue of all Cy and Tx + Cy infected birds examined at 5 weeks p.i. and gross tenosynovitis lesions were seen in all birds. The virus was recovered from the tendons of only a proportion of the infected untreated, Tx and Bx groups, and overall more frequently from apparently normal birds. This was especially marked in the infected Tx group. Antibody responses as shown by gel precipitation and virus neutralisation were positive and similar in untreated and Tx birds, were delayed in the Bx group with the precipitation test only, and absent from most of the Cy and Tx + Cy birds. The results of these experiments indicate that recovery from reovirus infection probably involves both B- and T-cell systems but that the B-cell system is predominantly protective.     

Identification of a novel circovirus in Australian ravens (Corvus coronoides) with feather disease.

The complete genome of a novel Circovirus isolated from an Australian raven (Corvus coronoides) with feather lesions similar to those that occur in psittacine beak and feather disease is reported. Degenerate polymerase chain reaction primers were designed to amplify and sequence novel Circovirus DNA from affected feathers. Sequence analysis indicated that the tentatively named raven circovirus (RaCV) was 1898 nucleotides in size with two major open reading frames synonymous with other avian circoviruses, ORF C1 and ORF V1, likely to encode a putative capsid protein (Cap) and replicase-associated protein (Rep), respectively. In common with other circoviruses was the conservation of several nucleotide structures and amino acid motifs implicated in virus replication. Comparison with other members of the Circoviridae demonstrated that RaCV shares the greatest sequence homology with canary circovirus (CaCV) and pigeon circovirus (PiCV) and was more distantly related to the beak and feather disease virus, goose circovirus, duck circovirus and the two porcine circoviruses, PCV1 and PCV2. Phylogenetic analysis of the genome and the putative Cap and Rep proteins provided further evidence of the close relationship of RaCV with CaCV and PiCV.     

Experimental reproduction of psittacine beak and feather disease/French Moult

Nestling budgerigars and galahs and one-day-old SPF chickens were inoculated with an homogenate prepared from the feathers of a variety of birds with psittacine beak and feather disease (PBFD), and known to contain virus-like particles 20 nm in diameter. Uninoculated birds were included as in-contact controls and groups of birds were also inoculated with homogenate treated with ss-propriolactone to inactivate any virus present. Typical PBFD developed in many of the inoculated birds and in some in-contact controls but in none of the birds inoculated with inactivated homogenate nor in SPF chickens. It is concluded from these findings that PBFD is an infectious disease of viral aetiology and is identical to the disease in budgerigars commonly referred to as 'French Moult'.     

Comparison of three animal viruses with circular single-stranded DNA genomes

Summary No common antigenic determinants and no DNA sequence homologies were detected when three animal viruses, chicken anaemia agent (CAA), porcine circovirus (PCV), and psittacine beak and feather disease virus (PBFDV), all of which possess circular single-stranded DNA genomes, were compared. Negative contrast electron microscopy showed that PCV and PBFDV particles were 30% smaller than CAA particles and lacked the surface structure of CAA.     

Significance of paroviruses, entero-like viruses and reoviruses in the aetiology of the chicken malabsorption syndrome

Specific-pathogen-free White Leghorn chickens and commercial broilers were inoculated orally at 1 day of age with different intestinal preparations containing a chicken parvovirus, an entero-like virus associated with a reovirus from field materials, or the entero-like viruses and reovirus alone. Despite viral multiplication in inoculated birds, no clinical signs or growth retardation were observed in SPF and broiler chickens infected with the reo or parvo viruses. Abnormal faeces and reduction in weight gains were observed after infection with the field materials and the entero-like viruses. Some easily sedimentable particles could be involved with the entero-like virus in the aetiology of ranting syndrome. Proventriculitis was present in chickens inoculated with one of the field materials and with the entero-like virus isolated from that material. Specific-pathogen-free White Leghorn chickens were as susceptible as commercial broiler chickens to weight gain depression after oral inoculation with crude homogenates at 1 day of age.     

An outbreak of Pacheco's parrot disease in a psittacine bird collection and an attempt to control it by vaccination

An outbreak of Pacheco's parrot disease (PPD) is described in a psittacine bird collection of a municipal ornithological garden. A herpes virus was isolated and judged to be the causative agent from the mortality recorded. A formaldehyde/heat-inactivated experimental vaccine was prepared from polyethyleneglycol purified virus. The vaccine was locally and systemically well tolerated by all birds. Serocon-version was demonstrated by neutralization tests in most of the vaccinated birds of the genera Ara, Anodorhynchus and Probosciger.     

Diagnosis of psittacine beak and feather disease (PBFD) viral infection, avian polyomavirus infection, adenovirus infection and herpesvirus infection in psittacine tissues using DNA in situ hybridization

The evaluation of the usefulness of DNA probes in a diagnostic setting to identify nuclear inclusions in selected viral infections (psittacine beak and feather disease viral infection, avian polyomavirus infection, adenovirus infection and Pacheco's parrot disease) is reported. A DNA in situ hybridization method was used to detect viral nucleic acid in sections of paraffin-embedded tissues coming from birds naturally and/or experimentally infected. It is concluded that DNA probes used for polyomavirus (FN-19) and adenovirus (FN-23) are able to identify nucleic acid of each virus in the cells with nuclear inclusions, and when used for psittacine beak and feather disease virus (FN-8), and Pacheco's parrot disease virus (FN-49) are able to detect viral nucleic acid in cells with or without inclusions.     

Circoviruses: Immunosuppressive threats to avian species: A review

Circoviruses are small, non-enveloped, icosahedral viruses that are unique among animal viruses in having circular, single-stranded DNA genomes. Their genomes are also the smallest possessed by animal viruses. The circovirus family currently comprises three members, chicken anaemia virus, porcine circovirus, and psittacine beak and feather disease virus, with pigeon circovirus being classified as a tentative member. Infections with each of the four circoviruses are associated with potentially fatal diseases in which virus-induced damage to lymphoid tissue and immunosuppression are common features. Experience with other animal virus families suggests that additional animal species will be infected by, as yet undiscovered, circoviruses and that these may display similar tissue tropism and disease-causing potential. Recent reports describing the association of circovirus-like viruses with immunodeficiency-related diseases of geese and southern black-backed gulls suggest that circovirus infections of avian species may be more common than previously recognized, and prompt the question of whether novel circoviruses infect poultry to cause clinical and/or subclinical diseases that may be economically important. This review has three purposes. First, it is designed to summarize the currently available information about the classified circoviruses and viruses that are regarded as circovirus-like. Second, it aims to alert the readership to the possibility that other avian species, including commercial poultry, may be infected with novel circoviruses. Finally, possible methods for discovering novel circoviruses and for controlling infections by such viruses are suggested.     

Experimental studies on the aetiology of inclusion body hepatitis

Liver suspensions and an adenovirus isolated from typical cases of inclusion body hepatitis (IBH) were inoculated into specific pathogen free birds by a combined oral and intranasal route but no pathological changes resulted. Representative strains of 8 serotypes of avian adenoviruses from naturally occurring cases of IBH and non-hepatitis origins were inoculated intramuscularly into birds. The pathogenicity of these strains was studied and it was established that different strains produced different lesions; thus a diffuse and generalised hepatitis, diffuse and patchy hepatitis, focal hepatitis or no pathological changes were observed. In no instance were the lesions produced identical to those in natural outbreaks of IBH. Extra-hepatic haemorrhages were not seen in experimental birds and the inclusion bodies in their livers were consistently basophilic. Eosinophilic inclusion bodies, as seen in natural cases, were not identified in adenovirus-infected birds. Intramuscular inoculation of a reovirus isolated from a clinical case of IBH failed to induce liver lesions in birds and adenoviruses isolated from turkeys and adenoviruses and herpesvirus isolated from pigeons were also unsuccessful at producing hepatitis in fowl.