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A novel strain of adenovirus has been isolated from a 25 year old male patient in Japan suffering from severe clinical manifestations of epidemic keratoconjunctivitis (EKC). The novel causative agent, strain M86, showed similarities with two other adenoviruses: type 11 (Ad11) and type 35 (Ad35).
Although Ad11 infrequently causes keratoconjunctivitis, Ad35 and the new strain M86, have never before been reported as ocular pathogens. Analysis of M86 at a molecular level using restriction endonuclease showed that it might have evolved from the recombination of the two parent viruses Ad35 and Ad11.
The fibre knob of M86, used to attach the virus to a specific cellular receptor on conjunctival or corneal cells, was found to have 99% homology with Ad11. The hexon protein of M86, the antigen against which antibodies are raised to neutralise the infectivity of adenoviruses, was found to be partly homologous to Ad35 and partly to Ad11; the hypervariable regions (HVRs) of the hexon protein were 100% homologous to Ad35 in HVRs 1,2,3, and 6 and to Ad 11 in HVRs 4 and 6.
The mixed antigenic characteristics of a virus strain like M86 may enable it to circumvent existing immunity. This is important since it can enable the non-ocular adenoviruses to become ocular pathogens, which in the future might be responsible for outbreaks of EKC.