Bovine adenovirus type 10: properties of viruses isolated from cases of bovine haemorrhagic enterocolitis

First DNA sequence proof for the occurrence of bovine adenovirus types 10 and 11 in continental Europe

Bovine adenoviruses (BAdV) are known to cause respiratory and/or intestinal disease in calves. Infection can manifest as acute outbreaks, but more often only sporadic cases occur. Here we describe the PCR detection and partial sequence characterization of several BAdVs found in sick or dead calves on different farms in Western Hungary. Intermittent diarrhoeal illnesses occurred after weaning among calves on several farms located up to 40 km apart. A high-sensitivity, broad-spectrum nested PCR, developed for the general detection of adenoviruses, gave positive results in four independent cases. Direct sequencing of PCR products showed clear results from only two samples, whereas sequences from the other two amplicons were mixed. Molecular cloning of these heterogeneous PCR products was performed to separate each DNA fragment therein. By sequencing several plasmid clones from both mixed samples, we were able to detect the simultaneous presence of two different BAdV types, namely types 6 and 10 classified into two separate (Atadenovirus and Mastadenovirus) genera. The sequence of one homogenous sample was identified as being derived also from BAdV-10, whereas the other sample contained a novel type, proposed to be BAdV-11. We demonstrated, for the very first time, the occurrence of the two latter virus types in continental Europe. Their appearance in Hungary marks a significant shift in the types of BAdVs actually circulating in the country. Considering the similarity of the pathological findings to those, attributed to BAdV-10 infections reported to date, the causative role of the viruses in these cases seems to be plausible. Phylogeny reconstruction further confirmed that BAdVs represent multiple genetic lineages.

Molecular characterization of a bovine adenovirus type 7 (Bovine Atadenovirus F) strain isolated from a systemically infected calf in Germany

Bovine adenovirus 7 (BAdV-7) is an unclassified member of the genus Atadenovirus with a worldwide distribution and has been reported to induce clinical disease of varying severity in infected cattle, ranging from asymptomatic infections to severe enteric or respiratory disease. In this study, we used next-generation sequencing to obtain the first complete genome sequence of a European strain of BadV-7, from pooled spleen and liver tissue obtained from a deceased newborn Limousin calf. Histopathological analysis and electron microscopy showing systemic lesions in multiple organs with intranuclear amphophilic inclusions observed in endothelial cells in multiple peripheral tissues. Virus isolation was readily achieved from tissue homogenate using bovine esophagus cells (KOP-R), a strategy which should facilitate future in vitro or in vivo BAdV-7 studies. Phylogenetic analysis of available genome sequences of BAdV-7 showed that the newly identified strain groups most closely with a recent BAdV-7 strain, SD18-74, from the USA, confirming that this newly identified strain is a member of the Atadenovirus genus. The fiber gene was found to be highly conserved within BAdV-7 strains but was highly divergent in comparison to Ovine adenovirus 7 (OAdV-7) (39.56% aa sequence identity). Furthermore, we report a variable region of multiple tandem repeats between the coding regions of E4.1 and RH5 genes. In summary, the presented pathological and molecular characterization of this case suggests that further research into the worldwide molecular epidemiology and disease burden of BAdV-7 is warranted.

Clinicopathological features of 11 suspected outbreaks of bovine adenovirus infection and development of a real-time quantitative PCR to detect bovine adenovirus type 10

CASE HISTORY

A retrospective study was conducted to investigate 11 outbreaks of presumptive fatal adenovirus infection diagnosed through two New Zealand diagnostic laboratories during 2014 and 2015. Outbreaks occurred in 6-12-month-old Friesian or Friesian cross cattle during autumn, winter and spring. Individual outbreaks were short in duration, with mortality rates ranging from 3/250 to 20/600 (1.2 to 3.3%).

CLINICAL AND PATHOLOGICAL FINDINGS

Clinical signs included severe diarrhoea, depression, recumbency, and death. Post-mortem examination revealed congestion and oedema of the alimentary tract and fluid to haemorrhagic intestinal contents. Histopathological lesions were characterised by congestion and haemorrhage of the alimentary tract mucosa, oedema of the submucosa, and mild interstitial inflammation in the kidneys. Large basophilic intranuclear inclusion bodies were identified in vascular endothelial cells of the alimentary tract in 11/11 cases and of the kidney in 8/9 cases.

MOLECULAR TESTING

A real-time quantitative PCR (qPCR) assay was designed to detect bovine adenovirus type 10 (BAdV-10) using hexon gene sequences available in GenBank. DNA extracted from a field case and confirmed by sequencing was used as a positive control. The qPCR had a reaction efficiency of 101% (R(2)=0.99) and the limit of detection was <10 DNA copies/reaction. The qPCR detected BAdV-10 in formalin-fixed paraffin-embedded (FFPE) tissue from 10/11 cases. DNA sequencing of PCR products from nine of these cases showed them to be identical to BAdV-10 sequences in GenBank. For the PCR-negative case, the PCR product had a hexon sequence 99% similar to bovine adenovirus Wic isolate Ma20-1, a close relative of BadV-10.

DIAGNOSIS

Bovine adenovirus type 10 was identified in FFPE tissues from cattle with histopathological evidence of adenovirus infection.

CLINICAL RELEVANCE

Bovine adenoviruses, and especially BAdV-10, should be considered in the differential diagnosis for acute enteric disease and death in young cattle. The qPCR detected BAdV-10 from FFPE tissue of cattle with suspected adenoviral infection diagnosed by histopathology. However results should be interpreted in light of clinical and pathological findings due to the possibility of adenovirus shedding by healthy cattle and the presence of pathogenic adenoviruses other than BAdV-10.

Detection of known and novel adenoviruses in cattle wastes via broad-spectrum primers

The critical assessment of bovine adenoviruses (BAdV) as indicators of environmental fecal contamination requires improved knowledge of their prevalence, shedding dynamics, and genetic diversity. We examined DNA extracted from bovine and other animal waste samples collected in Wisconsin for atadenoviruses and mastadenoviruses using novel, broad-spectrum PCR primer sets. BAdV were detected in 13% of cattle fecal samples, 90% of cattle urine samples, and 100% of cattle manure samples; 44 percent of BAdV-positive samples contained both Atadenovirus and Mastadenovirus DNA. Additionally, BAdV were detected in soil, runoff water from a cattle feedlot, and residential well water. Overall, we detected 8 of 11 prototype BAdV, plus bovine, rabbit, and porcine mastadenoviruses that diverged significantly from previously reported genotypes. The prevalence of BAdV shedding by cattle supports targeting AdV broadly as indicators of the presence of fecal contamination in aqueous environments. Conversely, several factors complicate the use of AdV for fecal source attribution. Animal AdV infecting a given livestock host were not monophyletic, recombination among livestock mastadenoviruses was detected, and the genetic diversity of animal AdV is still underreported. These caveats highlight the need for continuing genetic surveillance for animal AdV and for supporting data when BAdV detection is invoked for fecal source attribution in environmental samples. To our knowledge, this is the first study to report natural BAdV excretion in urine, BAdV detection in groundwater, and recombination in AdV of livestock origin.

Isolation of bovine adenovirus serotype 6 from a calf in the United Kingdom

Two viruses, designated 99-8130(C) and 99-8130(I), were isolated in calf testis cells from the colon and ileum, respectively, of a suckled beef calf which had developed dysentery and died. Electron microscopy indicated that the mean (sd) size of the viral particles, 83 (2.5) nm, and their morphology were consistent with their being members of the family Adenoviridae. They were confirmed as adenoviruses by PCR when products of the expected size (608 bp) were amplified from both isolates by using a primer pair specific for members of the genus Atadenovirus. A comparison of the sequence of a 567 bp segment of the 99-8130(C) amplicon with that of other prototype bovine adenovirus (BAdV) strains of atadenoviruses identified the isolate as BAdV serotype 6 (BAdV-6), which had 99.3 per cent and 100 per cent identities at the nucleotide and amino acid levels, respectively, with the prototype BAdV-6 strain 671130. A virus neutralisation test was developed and indicated a high prevalence of antibody to BAdV-6 in Northern Irish cattle. There was no evidence of adenoviral inclusions in tissues from the affected calf and no antigen was detected when the tissues were stained by an immunoperoxidase technique, using a homologous antiserum raised in rabbits. The two viruses were the third reported isolation of BAdV-6, and the first from a clinically ill bovine animal.

DNA sequencing and analysis of the right-hand part of the genome of the unique bovine adenovirus type 10

The prototype strain of bovine adenovirus (BAdV) type 10 and four additional isolates that were indistinguishable in serum-neutralization tests have been shown to have remarkable variation in their genome size and restriction maps. In the present study, more than 40 % of the DNA sequence of the BAdV-10 isolate with the longest genome was determined. A biased base composition resulting in low (<41 %) GC content was noticed. Analysis of the genes of the DNA-binding protein, 100K, 33K, pVIII and fibre proteins, as well as early regions E3 and E4, which are encoded by the genome fragment examined, confirmed that BAdV-10 is different from the other known BAdV types regarding its phylogenetic distance and the organization of its exceptionally short E3 region, apparently containing only two genes. A comparative analysis of the E3 and E4 regions of BAdV-10 with various animal adenoviruses revealed interesting features accounting for the very short genome of BAdV-10. In the examined BAdV-10 isolate, duplicated sequences were localized in and around the fibre gene. Since BAdV-10 appears to be pathogenic to cattle and is genetically distant from the other BAdVs, we suggest that BAdV-10 is not a genuine bovine virus, but has recently switched host and is now undergoing an adaptation process in its new host. In accordance with this hypothesis, the remarkable predominance of AT-rich codons along with the variable fibre gene might be signs of adaptation.

Isolation of a bovine adenovirus serotype 10 from a calf in the United States

Virus isolated from the lung, liver, kidney, and small intestine of a 3-month-old Holstein heifer with a clinical history of pneumonia and lesions in multiple organs was identified as an adenovirus on the basis of morphological and physicochemical characteristics. The adenovirus was determined to be a serotype 10 bovine adenovirus and represents the first reported isolation of this serotype in the United States. Inoculation of calves with this isolate resulted in mild to moderate clinical response consisting of fever, inappetence, increased respiratory rate, cough, and listlessness. Gross lesions were minimal in the respiratory tract and consisted of fibrin in the airways and small areas of consolidation in the cranial lobes of the lung. Mucofibrinous foci were present on the mucosa of the upper small intestine.

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.

Sequencing and phylogenetic analysis of the protease gene, and genetic mapping of bovine adenovirus type 10 define its relatedness to other bovine adenoviruses

The complete genome of a bovine adenovirus (BAV) type 10 isolate was molecularly cloned and partially sequenced. The encoded proteins were predicted by computer analysis of the DNA sequences of the ends or the entire length of the cloned viral fragments, and thus a rough genetic map was constructed. The protease gene of BAV-10 was completely sequenced and used in phylogenetic analysis. Based on the results of the phylogenetic analysis, and the location and presence of certain genes thought to be specifically characteristic of subgroup 1 or subgroup 2 BAVs, it could be concluded that, in spite of the striking similarity in certain biological properties, BAV-10 is not related to subgroup 2 BAVs as originally described. It does not however fit clearly into subgroup 1 either, the members of which show closer relationship with human adenoviruses. BAV-10 therefore should best be considered as the first member of a third subgroup of BAVs.

Sequence, transcriptional analysis, and deletion of the bovine adenovirus type 1 E3 region

The early 3 (E3) transcriptional unit of human adenoviruses (HAV) encodes proteins that modulate host antiviral immune defenses. HAV E3 sequences are highly variable; different HAV groups encode phylogenetically unrelated proteins. The role of the E3 region of many human and animal adenoviruses is unknown because the sequences are unrelated to previously characterized viruses and the functions of proteins encoded by these regions have not been studied. We sequenced a portion of the bovine adenovirus serotype 1 (BAV-1) genome corresponding to the putative E3 region. This sequence was substantially different from other adenoviral E3 sequences, including those of two other bovine adenoviruses. However, two regions of putative sequence conservation were identified. BAV-1 E3 sequences were identified in early and late transcripts, but, unlike HAV, introns were not detected in the E3 region transcripts. Like HAV E3, a majority of the BAV-1 E3 region was not essential for growth in cell culture, as demonstrated by the construction of a recombinant BAV-1 lacking 60% of the putative E3 region.