Control of Viral Infections

Control of Viral Infections

	Control of Viral Infections Chemicals are most widely used to treat DNA virus infections of the conjunctiva and cornea of the eye. The agents used are pyrimidine analogues that are incorporated into viral DNA and prevent replication and transcription. These compounds (except acyclovir) are incorporated into cellular DNA hence their use is restricted to the poorly vascularised surface ofthe eye. In practice 0.1 % 5'-iodo2'-deoxyuridine, an analogue of thymidine, improved healing in 72% infections with herpes simplex type vaccinia and adenoviruses.
In serious infections as herpes virus type 1 (causing encephalitis) or vaccinia viruses analogues of cytidine (cytosine arabinoside) or adenosine (adenine arabinoside) may be used. These chemicals are extremely poisonous and can be used only where death is the likely alternative. Another anti-viral compound is amantadine used for type A-influenza virus infections. The drug was licensed by Food & Drug Administration, U.S.A. in 1966. Another drug vidarabine has been in use since 1977 for herpes zoster (shingles) and encephalitis (brain disease) due to herpes simplex virus. A recently developed chemical, and licensed in 1985 acyclovir or zovirax, properly known as 9-(2 hydroxye-thoxymethyl) guanine has proved the best antiviral agent. Like other pyrimidine analogues it is a topical ointment, effective against acute infection with herpes simplex viruses
In an infected cell, acyclovir requires viral thymidine kinase to attach the phosphate groups necessary for DNA synthesis of the virus. Thus, chemical is toxic only for infected cells. This agent is effective against corneal eye infections, cold sores and the life threatening generalised infections as those treated with immunosuppressions and transplant surgery or cancer therapy. Other drugs are idoxuridine (developed in 1964) and trifluridine for herpes infection.

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