ABSTRACT

Viruses may infect animal, plant, and bacterial cells. Viruses that infect each of these groups of organisms are, in general, quite distinct, such that animal viruses are not capable of infecting plants and vice versa. Essential features of viral replication and pathogenesis are that viruses, though they can remain active outside a cell, must gain entrance to a host cell in order to replicate. Though viruses are exceedingly small, they express multiple antigens on these various surfaces with which the immune system may interact. Herpes simplex virus causes recurrent superficial ulcerations of mucous membranes and a devastating form of meningoencephalitis. Cytomegalovirus infections range from asymptomatic to a syndrome resembling mononucleosis. Polyoma virus is a potentially oncogenic DNA virus that can cause chronic viral infections associated with immune-complex formation. Influenza viruses are major world-wide pathogens of man and other animals. Most serious infections in man are produced by influenza A and influenza B.