Letter: Adenovirus 19, a cause of epidemic keratoconjunctivitis, not acute hemorrhagic conjunctivitis

Suppression of Adenovirus Replication by Cardiotonic Steroids

The dependence of adenovirus on the host pre-RNA splicing machinery for expression of its complete genome potentially makes it vulnerable to modulators of RNA splicing, such as digoxin and digitoxin. Both drugs reduced the yields of four human adenoviruses (HAdV-A31, -B35, and -C5 and a species D conjunctivitis isolate) by at least 2 to 3 logs by affecting one or more steps needed for genome replication. Immediate early E1A protein levels are unaffected by the drugs, but synthesis of the delayed protein E4orf6 and the major late capsid protein hexon is compromised. Quantitative reverse transcription-PCR (qRT-PCR) analyses revealed that both drugs altered E1A RNA splicing (favoring the production of 13S over 12S RNA) early in infection and partially blocked the transition from 12S and 13S to 9S RNA at late stages of virus replication. Expression of multiple late viral protein mRNAs was lost in the presence of either drug, consistent with the observed block in viral DNA replication. The antiviral effect was dependent on the continued presence of the drug and was rapidly reversible. RIDK34, a derivative of convallotoxin, although having more potent antiviral activity, did not show an improved selectivity index. All three drugs reduced metabolic activity to some degree without evidence of cell death. By blocking adenovirus replication at one or more steps beyond the onset of E1A expression and prior to genome replication, digoxin and digitoxin show potential as antiviral agents for treatment of serious adenovirus infections. Furthermore, understanding the mechanism(s) by which digoxin and digitoxin inhibit adenovirus replication will guide the development of novel antiviral therapies.

IMPORTANCE

Despite human adenoviruses being a common and, in some instances, life-threating pathogen in humans, there are few well-tolerated therapies. In this report, we demonstrate that two cardiotonic steroids already in use in humans, digoxin and digitoxin, are potent inhibitors of multiple adenovirus species. A synthetic derivative of the cardiotonic steroid convallotoxin was even more potent than digoxin and digitoxin when tested with HAdV-C5. These drugs alter the cascade of adenovirus gene expression, acting after initiation of early gene expression to block viral DNA replication and synthesis of viral structural proteins. These findings validate a novel approach to treating adenovirus infections through the modulation of host cell processes.

Clinical and aetiological study of adenoviral conjunctivitis, with special reference to adenovirus types 4 and 19 infections

The clinical and aetiological findings are presented on 343 patients with clinical adenoviral conjunctivitis treated between July 1979 and July 1980 at 3 eye clinics in Sapporo. The age of the patients ranged from 12 days to 79 years, and the monthly incidence of the disease from 9 to 83, with clustering in the summer season. The aetiological diagnosis was established in 196 (57%) of 343 patients: adenovirus 3 in 24 cases; adenovirus 4 in 33 cases, including one case serologically diagnosed; adenovirus 8 in 124 cases; and adenovirus 19 in 15 cases. The different serotypes caused different clinical pictures. Adenovirus 19 conjunctivitis was more severe, with keratitis and preauricular lymphadenopathy more frequent than that of adenovirus 3 conjunctivitis. Adenovirus 4 conjunctivitis was generally similar to adenovirus 3 conjunctivitis. The clinical difference between the 2 groups adenoviruses 3 and 4, and adenoviruses 8 and 9, was statistically significant. Although in Japan adenovirus 8 was the most prevalent, adenoviruses 4 and 19 should be considered as causative agents of adenoviral conjunctivitis.