Slow Diseases Caused by Conventional Viruses in Humans

Slow Diseases Caused by Conventional Viruses in Humans

Subacute sclerosing panencephalitis, progressive multifocal leukoencephalopathy (PML), and acquired immunodeficiency syndrome (AIDS) are the three slow diseases caused by conven-tional viruses in humans.

Subacute Sclerosing Panencephalitis

The subacute sclerosing panencephalitis is a degenerating disease of the CNS caused by persistent measles infection. It is a persistent infection by a variant measles virus that fails to complete its replication. The disease is characterized by the development of behavioral and intellectual deterioration and seizures after many years (mean incubation period is 10.8 years) of infection by measles. This is a serious and late neurological sequel of measles that affects the CNS.

The condition occurs in about seven in every one million patients. The condition is associated with the presence of an extremely high measles antibody titer in the blood and CSF. Inclusion bodies, which react with antibodies to measles virus, are present in the affected neurons.

Progressive Multifocal Leukoencephalopathy

Progressive multifocal leukoencephalopathy is a fatal demy-elinating disease of the white matter of the brain. The condition is usually fatal. It occurs primarily in persons with compromised cell-mediated immunity, such as patients with AIDS and those receiving immunosuppressive drugs and anticancer therapy.

JC virus or John Cunningham virus (JCV) is the causative agent of PML. The virus following the infection kills oligoden-droglia and causes syncytia in astrocytes. Reactivation of the virus in immunocompromised patients causes activation of latent virus, thereby causing the disease. Changes in mental status, alteration in the vision, and weakness are the initial clinical manifestations. The condition progresses rapidly to blindness, dementia, and coma. The patient usually dies within 6 months.

Laboratory diagnosis of the condition is made by PCR for viral genome in the brain tissue or CSF. Serum antibodies to JC are demonstrated in approximately three fourth of normal sera; hence serology is not useful. No specific antiviral treatment is available.

Acquired Immunodeficiency Syndrome

AIDS caused by human immunodeficiency virus has a long latent period. Hence, the disease is also considered as an example of slow disease with a progressive course and involvement of the CNS.