Date of download: 7/11/2016 Copyright © 2016 McGraw-Hill Education. All rights reserved. Different types of virus–host interactions: apparent (clinical disease), inapparent (subclinical), chronic, latent, occult, and slow infections. (1) Measles runs an acute, almost always clinically apparent course resulting in long-lasting immunity. (2) Measles may also be associated with persistence of latent infection in subacute sclerosing panencephalitis (see Chapter 40). (3) Yellow fever and influenza follow a pattern similar to that of measles except that infection may be more often subclinical than clinical. (4) In hepatitis B, recovery from clinical disease may be associated with chronic infection in which fully active virus persists in the blood. (5) Some infections are, in a particular species, always subclinical, such as eastern equine encephalomyelitis (EEE) in some species of birds that then act as reservoirs of the virus. (6) In human papilloma, the course of infection is chronic; when cervical cancer develops, the virus present is occult (not replicating). (7) Infection of humans with certain adenoviruses may be clinical or subclinical. There may be a long latent infection during which virus is present in small quantity; virus may also persist after the illness. (8) The periodic reactivation of latent herpes simplex virus, which may recur throughout life in humans, often follows an initial acute episode of stomatitis in childhood. (9) Infection may be unrecognized for long periods of time before it becomes apparent. Examples of such "slow" infections characterized by long incubation periods are scrapie in sheep and kuru in humans (thought to be caused by prions, not viruses). (10) In pigs that have eaten virus-bearing lungworms, swine "flu" is occult until the appropriate stimulus induces viral production and, in turn, clinical disease. (11) Lymphocytic choriomeningitis (LCM) virus may be established in mice by in utero infection. A form of immunologic tolerance develops in which virus-specific T cells are not activated. Antibody is produced against viral proteins; this antibody and circulating LCM virus form antigen–antibody complexes that produce immune complex disease in the host. The presence of LCM virus in this chronic infection (circulating virus with little or no apparent disease) may be revealed by transmission to an indicator host (eg, adult mice from a virus-free stock). (12) All adult mice develop classic acute symptoms of lymphocytic choriomeningitis and frequently die. (13) The possibility is shown of infection with an occult virus that is not detectably replicating. Proof of the presence of such a virus remains a difficult task that, however, is attracting the attention of cancer investigators (see Chapter 43). Legend : From: Chapter 30. Pathogenesis and Control of Viral Diseases Jawetz, Melnick, & Adelberg's Medical Microbiology, 26e, 2013 From: Chapter 30. Pathogenesis and Control of Viral Diseases Jawetz, Melnick, & Adelberg's Medical Microbiology, 26e, 2013