Chicken anaemia virus inoculated by the oral route causes lymphocyte depletion in the thymus in 3-week-old and 6-week-old chickens

There have been many reports of the severe clinical disease and pathology seen in young chicks that have been vertically infected with chicken anaemia virus (CAV). The disease is characterized by anaemia, and atrophy of the thymus and bone marrow. However, while it has been suggested that horizontally acquired infections of older birds are common, to date there has been no description in the literature of the pathology of this type of infection. In the present study, 3-week-old and 6-week-old chickens were infected by the oral route, as is likely to occur naturally, and a wide range of tissues were examined immunocytochemically for the presence of CAV antigen. Histological examination was carried out on the thymus, spleen and bone marrow of all birds, and on all other tissue samples in which CAV antigen was found. CAV antigen and associated pathological change were detected in the thymus of both 3-week-old and 6-week-old birds. However, CAV antigen was rarely found in other tissues, which is in contrast to what is found in birds infected when 1-day-old. In particular, very few infected cells were found in the bone marrow. Anaemia and bone marrow atrophy, which are typically found in chicks infected vertically or when 1-day-old, did not develop in the 3-week-old or 6-week-old birds. The findings of this study show that CAV is capable of infecting thymocytes of older birds, in contrast to previous belief, and that it is associated with lymphocyte depletion. There was only limited evidence of viral replication in the other tissues examined.

Evaluation of polymerase chain reaction and dot blot hybridisation tests in the diagnosis of pigeon circovirus infections

Polymerase chain reaction (PCR) and dot blot hybridisation (DBH) tests for detecting pigeon circovirus (PiCV) DNA were developed and evaluated using tissue samples obtained from diseased and clinically normal pigeons, which originated in Belgium and Northern Ireland. When PCR product was visually detected, the limit of detection of the PCR test was 31 fg, while that of the DBH was 1.6p g. For evaluation purposes, the results of the PCR and DBH tests, performed with DNAs extracted from samples of bursa of Fabricius (BF), were compared with those of in situ hybridisation (ISH) and histology. In 32 samples tested by all four tests, 27 (84%) were positive by PCR, 24 (75%) were positive by ISH, 20 (63%) were positive by DBH, and 13 (41%) were positive by histology. Additional PCR testing showed that in some disease-affected birds, PiCV DNA could be detected in a range of tissues including thymus, spleen, liver, kidney and brain. The PCR detection of PiCV DNA in BF samples from clinically normal birds indicated that PCR can detect infections in the absence of disease, a finding that mitigates against its use as a disease diagnostic. In addition, nucleotide sequence determinations indicated that PCR test performance was adversely affected by the sequence diversity exhibited by selected PiCVs. The application of the DBH test to dilutions of test samples indicated that the BF from some diseased pigeons contained very large amounts of virus DNA, as much as 10(13)genome copies/g tissue, and suggested that this test may be a convenient method of providing a semi-quantitative estimate of virus load.

Detection of circovirus infection in pigeons by in situ hybridization using cloned DNA probes

Degenerate primers were designed based on known sequence information for the circoviruses psittacine beak and feather disease virus and porcine circovirus and applied by polymerase chain reaction (PCR) to known virus-infected bursa of Fabricius (BF) from a pigeon. A 548-bp DNA fragment was amplified and shown to be specific to a novel circovirus, named pigeon circovirus (PiCV), and was used to produce sensitive and specific probes for detection of circovirus DNA by in situ hybridization (ISH). Using ISH on BF from 107 pigeons submitted for necropsy, infection was detected in 89%, compared with a histologic detection rate of 66%. Using the ISH technique, infected cells were also found in liver, kidney, trachea, lung, brain, crop, intestine, spleen, bone marrow, and heart of some birds. Large quantities of DNA were present in some of these tissues, and in the absence of BF, liver in particular is identified as a potentially useful organ to examine for presence of PiCV. This high prevalence of infection in diseased birds is noteworthy, emphasizing the need for studies to determine the precise role of this virus as a disease-producing agent.

Examination of adenovirus-types in intestinal vascular endothelial inclusions in fatal cases of enteric disease in cattle, by in situ hybridisation

There have been occasional reports in the literature of a severe naturally occurring enteric disease of cattle in which adenoviral inclusions were found in intestinal vascular endothelium. Bovine adenovirus type 10 (BAV-10) was identified by in situ hybridisation (ISH) in the inclusions of all 13 such cattle detected in Northern Ireland [Smyth, J.A., Benkö, M., Moffett, D.A., Harrach, B., 1996. J. Clin. Microbiol. 34, 1270-1274]. The present paper describes ISH examination of the vascular endothelial inclusion bodies in a further seventeen cattle with enteric disease, from Canada, Great Britain, Italy and The Netherlands. BAV-10 was identified in the inclusions of ten cases, and Subgroup 2 BAVs in six cases. BAV-10 was identified in cattle from Canada, The Netherlands and Great Britain. This is the first recognition of BAV-10 infection outside Northern Ireland and New Zealand. The results also show that at least two adenovirus serotypes may induce inclusion bodies in intestinal vascular endothelium of cattle. It will, therefore, be difficult in the short term to develop a simple test to allow diagnosis of this form of adenoviral infection in living animals, and thus to determine the relationship between it and clinical disease.

Bovine viral diarrhoea virus infection in bone marrow of experimentally infected calves

Colostrum-deprived calves were inoculated with either a field isolate of bovine viral diarrhoea virus (BVDV) containing cytopathogenic (CP) and noncytopathogenic (NCP) biotypes or with only the NCP biotype. Paraffin wax-embedded sections of bone marrow from these calves, examined by means of an immunoperoxidase method, showed BVDV antigen in megakaryocytes and myeloid cells. Infection of such cells may play a role in the pathogenesis of thrombocytopenia, leucopenia and neutropenia, as reported in cattle infected with BVDV.

Bovine adenovirus type 10 identified in fatal cases of adenovirus-associated enteric disease in cattle by in situ hybridization

A severe, naturally occurring enteric disease of cattle in which adenovirus inclusions are present in the intestinal vascular endothelium has been recognized in several countries; three different adenovirus serotypes have been isolated from affected animals. An in situ hybridization technique for the detection of bovine adenoviral DNA was developed and applied to tissue from 13 cattle in Northern Ireland diagnosed to have the disease. Bovine adenovirus serotype 10 (BAV-10) was identified in the vascular inclusions of all cattle, providing strong evidence that adenoviral enteric vascular disease in cattle is associated with this serotype. The existence of BAV-10 has only recently been recognized. The first molecular biology-based technique for the diagnosis of BAV-10 infection is described. The animals in the present study are the first in which BAV-10 has had a confirmed role in a pathologic process.

A sequential histopathologic and immunocytochemical study of chicken anemia virus infection at one day of age

Detection systems for chicken anemia virus (CAV) antigen in paraffin sections were evaluated. Mouse monoclonal antibodies to CAV used in conjunction with an avidin-biotin-peroxidase-complex detection system gave best results. Immunoreactivity of CAV was markedly affected by fixation. Fixation in neutral buffered formalin for 6 hours gave best results. Use of decalcifying fluid containing formic acid eliminated immunoreactivity of CAV, whereas use of an EDTA solution did not. In a sequential study, CAV antigen and lesions were first detected in bone marrow, thymus, and spleen at days 3-4 postinoculation (PI). Subsequently, antigen and/or cells containing nuclear inclusions were found in many tissues, but usually within lymphoid tissue therein. Thymus, spleen, bone marrow, proventriculus, and ascending duodenum contained most antigen. No antigen was detected after 26 days PI. The results indicated that CAV replicates in thymic lymphoblasts, intra- and extra-sinusoidal hemocytoblasts, and reticular cells, with consequent lymphocytic depletion of the thymic cortex and hypoplasia of the bone marrow, and that CAV antigen is widely distributed in the body.