Characterisation of hexon and fibre genes of a novel strain of adenovirus involved in epidemic keratoconjunctivitis

Genotyping of human adenoviruses circulating in Southwest India

Adenoviruses are found to be associated with a wide range of diseases in children and adults. There is little data available on the circulating serotypes of Human Adenoviruses (HAdVs) in the southwest region of India. In this study, we explore the molecular epidemiology of HAdVs circulating in southwest India. Twenty-three samples (Adenovirus PCR positive), collected between January 2011 and March 2013, have been typed based on the partial hexon gene sequence and phylogenetic analysis. The commonest serotypes were HAdV-3 and HAdV-2. The other serotypes were HAdV-7, HAdV-1, HAdV-8 and HAdV-40. Respiratory illness was the most common clinical manifestation of HAdV-3, HAdV-2 and HAdV-7 serotypes. HAdV-3, HAdV-7 and HAdV-8 were found to cause conjunctivitis, whereas HAdV-1, HAdV-2 and HAdV-3 caused encephalitis. In conclusion, this study documents the circulating HAdV strains and the epidemiology in southwest India. To the best of our knowledge, this is the first study on the molecular epidemiology of HAdVs in India.

Human adenovirus type 8: the major agent of epidemic keratoconjunctivitis (EKC)

Human adenovirus type 8 (HAdV-8) is the most common causative agent of a highly contagious eye disease known as epidemic keratoconjunctivitis (EKC). HAdV-8 strains have been classified into genome types HAdV-8A to 8K and HAdV/D1 to D12 according to restriction endonuclease analysis. This review focuses on the significance of HAdV-8 as an agent of EKC. Molecular analysis of HAdV-8 genome types HAdV-53 and HAdV-54 was performed to reveal potential genetic variation in the hexon and fiber, which might affect the antigenicity and tropism of the virus, respectively. On the basis of the published data, three patterns of HAdV-8 genome type distribution were observed worldwide: (1) genome types restricted to a microenvironment, (2) genome types distributed within a country, and (3) globally dispersed genome types. Simplot and zPicture showed that the HAdV-8 genome types were nearly identical to each other. HAdV-54 is very close to the HAdV-8P, B and E genomes, except in the hexon. In a restriction map, HAdV-8P, B, and E share a very high percentage of restriction sites with each other. Hypervariable regions (HVRs) of the hexon were conserved and were 100% identical among the genome types. The fiber knob of HAdV-8P, A, E, J and HAdV-53 were 100% identical. In phylogeny, HVRs of the hexon and fiber knob of the HAdV-8 genome types segregated into monophyletic clusters. Neutralizing antibodies against one genome type will provide protection against other genome types, and the selection of future vaccine strains would be simple due to the stable HVRs. Molecular analysis of whole genomes, particularly of the capsid proteins of the remaining genome types, would be useful to substantiate our observations.

Recombinant Adenovirus (AdV) Type 3 and Type 14 Isolated From a Fatal Case of Pneumonia

We report a fatal case of pneumonia apparently due to adenovirus infection in a 53-year-old male who had recently returned from Iraq. The isolate was identified by sequence analysis as AdV3 and AdV14. Based on restriction analysis (REA), the virus appeared to be a recombinant virus containing properties of both AdV3 and AdV14 rather than a coinfection with these two viruses.

Molecular typing of clinical adenovirus specimens by an algorithm which permits detection of adenovirus coinfections and intermediate adenovirus strains

BACKGROUND

Epidemiological data suggest that clinical outcomes of human adenovirus (HAdV) infection may be influenced by virus serotype, coinfection with multiple strains, or infection with novel intermediate strains. In this report, we propose a clinical algorithm for detecting HAdV coinfection and intermediate strains.

STUDY DESIGN

We PCR amplified and sequenced subregions of the hexon and fiber genes of 342 HAdV-positive clinical specimens obtained from 14 surveillance laboratories. Sequences were then compared with those from 52 HAdV prototypic strains. HAdV-positive specimens that showed nucleotide sequence identity with a corresponding prototype strain were designated as being of that strain. When hexon and fiber gene sequences disagreed, or sequence identity was low, the specimens were further characterized by viral culture, plaque purification, repeat PCR with sequencing, and genome restriction enzyme digest analysis.

RESULTS

Of the 342 HAdV-positive clinical specimens, 328 (95.9%) were single HAdV strain infections, 12 (3.5%) were coinfections, and 2 (0.6%) had intermediate strains. Coinfected specimens and intermediate HAdV strains considered together were more likely to be associated with severe illness compared to other HAdV-positive specimens (OR=3.8; 95% CI=1.2-11.9).

CONCLUSIONS

The majority of severe cases of HAdV illness cases occurred among immunocompromised patients. The analytic algorithm we describe here can be used to screen clinical specimens for evidence of HAdV coinfection and novel intermediate HAdV strains. This algorithm may be especially useful in investigating HAdV outbreaks and clusters of unusually severe HAdV disease.

Molecular typing of human adenoviruses by PCR and sequencing of a partial region of the hexon gene

Human adenoviruses (Ads) are responsible for a substantial disease burden. Type-specific identification of Ads can help guide therapeutic and disease prevention strategies and aid epidemiological investigations. Immunotyping of Ads by serum neutralization (SN) is laborious and time consuming and depends upon type-specific antisera that are in short supply. A rapid molecular typing assay based on polymerase chain reaction (PCR) amplification and sequencing of Ad hexon gene hyper-variable regions 1-6 (HVR(1-6)) known to contain type-specific epitopes was evaluated as an alternative to SN. Deduced amino acid sequences of HVR(1-6) obtained from all 51 currently recognized Ad prototype strains were well resolved, with the exception of types 15 and 29, which were identical. Of 192 temporally and geographically diverse Ad field isolates sequenced in this study, and 111 previously published sequences, all more closely matched their predicted prototype strains. Ads were also detected and correctly identified directly from 24 clinical specimens positive by culture or antigen detection. PCR and sequencing of HVR(1-6) offers a practical alternative to SN for typing most Ads and can be readily adapted for use in laboratories with molecular capabilities.

Heterogeneity of the fibre sequence in subgenus C adenoviruses

AIMS

To determine the nucleotide sequences of adenovirus (Ad) types 1 and 6 fibre genes; to clarify the molecular basis of the distinct haemagglutination properties of subgenus C Ads and their phylogenetic relations.

METHODS

Human Ad1 and Ad6 fibre genes were sequenced from genomic DNA by direct sequencing. Primer selection was based on alignment of the fibre gene of human Ad serotypes Ad2 and Ad5. Fibre based subgenus C specific polymerase chain reaction (PCR) was performed to check for deletions in field isolates of Ad6, as revealed by sequence analysis of the Ad6 prototype. A phylogenetic tree was constructed from the predicted amino acid (AA) sequences of the fibre gene of important Ads.

RESULTS

Ad1 and Ad6 comprise 1746 and 1584 nucleotides, encoding 582 and 528 AA, respectively. Ad6 showed deletions in motifs 15-17 (51 AA) of the shaft when compared with Ad1, Ad2, and Ad5. Subgenus C specific PCR with both prototype and field isolates also showed deletions in Ad6. In the shaft and knob, AA homology was 58.82-72.91% and 68.89-74.59%, respectively. The tail was 100% conserved. Phylogenetically, Ad1 and Ad6, including Ad2 and Ad5, formed a subgenus specific cluster, like other serotypes.

CONCLUSIONS

The fibre gene (including the knob region) of subgenus C Ads is heterogeneous, providing the molecular basis for lack of crossreactivity in the haemagglutination inhibition test. This heterogeneity could be helpful in fibre based genotyping of subgenus C field isolates. Phylogeny might be useful for subgenus specific identification of important field strains.

Serological and genetic characterisation of a unique strain of adenovirus involved in an outbreak of epidemic keratoconjunctivitis

AIMS

To characterise a novel strain of adenovirus (Ad) type Ad8 (genome type Ad8I) involved in an epidemic keratoconjunctivitis (EKC) outbreak in Hiroshima city using serological testing and sequence analysis of the fibre and hexon gene.

METHODS

A neutralisation test (NT) was performed in microtitre plates containing a confluent monolayer of A549 cells using 100 tissue culture infectious doses of virus and type specific antisera. The haemagglutination inhibition test was also carried out in microtitre plates with rat erythrocytes using four haemagglutination units of virus and twofold dilutions of serum. The fibre gene was sequenced by generating overlapping polymerase chain reaction products or by direct sequencing of genomic DNA. Primer selection was based on alignment of the fibre genes of human adenovirus serotypes Ad8, Ad19, Ad37, Ad9, and Ad15 available from Gene Bank.

RESULTS

The virus strain was specifically neutralised by anti-Ad8 antibodies, although there was a major crossreaction with anti-Ad9 antibodies. Haemagglutination was equally inhibited by anti-Ad8 and anti-Ad9 antibodies. The predicted amino acid sequences of the hypervariable regions (HVRs) of the Ad8I hexon gene showed higher homology with Ad9 (83.3%) than with Ad8 (62.0%). However, the Ad8I fibre knob was more homologous to Ad8 (94.4%) than to Ad9 (91.6%).

CONCLUSIONS

Ad8I is a unique strain of adenovirus because of its lower genomic homology with Ad8, major crossreactivity with Ad9 in NT, and mixed genetic organisation of HVRs of the hexon gene. These factors may have enabled the virus to circumvent acquired immunity, resulting in the outbreak.