Читать книгу Basic Virology - Martinez J. Hewlett - Страница 69

Persistent infections caused by some viruses can (rarely) lead to a neoplasm (a cancerous growth) due to continual tissue damage resulting in mutation of cellular genes controlling cell division (i.e., oncogenes and tumor suppressor genes). Examples include infections with slow‐transforming retroviruses such as human T‐cell leukemia virus(HTLV), chronic hepatitis B and hepatitis C virus infections of the liver, certain genital papilloma virus infections, and EBV infections. The latter require the additional action of auxiliary cancer‐causing factors (co‐carcinogens).

Autoimmune diseases such as multiple sclerosis (MS) are thought by many investigators to result from an abnormal immune response to viral protein antigens continually present in the body due to a persistent infection. Such persistent infections need not result in the reappearance of infectious virus. For example, infection with measles virus usually leads to rash and recovery, although portions of viral genomes and antigens persist in certain tissues, including neural tissue. The mechanism of this persistence is not fully understood, but it is clear that virus maturation is blocked in such cells that bear viral genomes, and viral antigens are present in reduced amounts on the cell surface. The presence of antigen leads to lifelong immunity to measles, but it can result in immune complications where the host's immune system destroys otherwise healthy neuronal tissue‐bearing measles antigens.

The fatal disease of subacute sclerosing panencephalitis(SSPE), which is a rare complication in children occurring a few years after a measles infection, is a result of such an autoimmune response. SSPE is a rare outcome of measles infection, but other severe sequelae of measles are common. One of the most frequent is damage to eyesight. The virus replicates in the host and infects surface epithelium, resulting in characteristic rash and lesions in the mouth, on the tongue, and on the eye's conjunctiva. Virus infection of the conjunctiva can clear, but movement of eye muscles in response to light, or in the process of reading, can lead to further infection of eye musculature, leading to permanent damage, which is why individuals infected with measles should be protected from light and kept from using their eyes as much as possible.