Shortterm infections

Viruses are the commonest causes of short-term infections and they infect the eye directly. It seems likely that host immune responses terminate infection. These infections do not usually cause long-term damage to the eye.

Picornaviruses cause acute hemorrhagic conjunctivitis, which is common in tropical and subtropical areas of the world with high humidity and high population densities. There have been two pandemics. Enterovirus 70 is the commonest cause, but coxsackie virus A24, poliovirus and adenoviruses are also associated with this disease.

Adenoviruses cause acute conjunctivitis and epidemic keratoconjunctivitis. They are the commonest cause of ocular infection in developed countries. Many adenovirus types have been isolated from the eyes of patients, and types 3, 7 and 10 predominate in the UK. Adenoviruses also cause ocular disease in developing countries: they have been isolated from patients with acute hemorrhagic conjunctivitis (see above) and they were the commonest cause of acute conjunctivitis in a study in Pakistan, where virtually all the isolates were type 8.

Ocular infection with enteroviruses and adenoviruses evokes the production of specific antibodies. Antibodies against eneteroviruses can neutralize virus infectivity, and antibodies against adenoviruses can fix complement. The roles of these antibodies in disease are not known.

Measles virus affects the conjunctiva and cornea of most, if nor all patients with measles. This usually resolves without damage to the eye. In parts of Africa, however, many children with measles subsequently develop corneal ulceration and postmeasles blindness. Although the roles of immune responses in measles are well defined, their importance in the development of postmeasles blindness is not known. Measles infection can reduce tear flow, and children who are severely ill are unable to close their eyelids, so that their eyes become more susceptible to secondary infection. Malnutrition and measles virus infection both cause immunosuppression. Vitamin A deficiency can lead to xerophthalmia, and traditional eye medicines can damage the eye. In some areas of Africa, children with measles often develop corneal ulcers caused by herpes simplex virus. This may result from direct infection of the eye or from reactivation of existing infection (see below).

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