Introduction: Medical Virology

Akram AstaniDepartment of Microbiology

University of Yazd

Basics of Virology

VIRUSES?

First document of a virus infection

Ruma

1.500 B.C.

1882 A. Mayer: transmission of tobacco mosaic disease by plant extract; pathogen can not be isolated

1892 D. Ivanofsky: agent of tobacco-mosaic disease is ‚non filtratable‘ and can not be propagated in culture medium

1898 M. Beijerinck: the pathogen can be propagated in live tissue

The pathogen is: ultrafiltratable does not replicate outside of live tissue ultravisible

‚Contagium vivum fluidum‘; later Virus (lat. poison)

History of Virology:discovery of viruses

1898: Loeffler and Frosch; foot and mouth disease virus (1. animal virus)

1901: W. Reed; yellow fever virus (first human virus)

1911: first discovery of a tumor virus (Rous Sarcoma Virus)

1915: discovery of bacteriophages (Twort; d‘Herelle)

1935: Crystallization of TMV (Stanley)

1949: propagation of Polio virus (Enders, Weller, Robbins)

1970: discovery of reverse Transcriptase (Baltimore, Temin)

1977: Last case of pox (Somalia)

1983: discovery of HIV

History of virology:some important milestones

Peyton Rous

Leading causes of death in 2008 (World Health Report):

Medical importance of viral diseases

World Deaths in millions % of deaths

Ischaemic heart disease 7.25 12.8%

Stroke and other

cerebrovascular disease 6.15 10.8%

Lower respiratory

infections 3.46 (Influenza) 6.1%

Chronic obstructive

pulmonary disease 3.28 5.8%

Diarrhoeal diseases 2.46 (Rotavirus) 4.3%

HIV/AIDS 1.78 (Africa: 20%) 3.1%

Trachea, bronchus, lung

cancers 1.39 2.4%

Tuberculosis 1.34 2.4%

Diabetes mellitus 1.26 2.2%

Road traffic accidents 1.21 2.1%

Measles: 1.4% (2000)

Two theories of viral origin can be summarized as follows:

May be derived from DNA or RNA nucleic acid components of host cells

may be degenerate forms of intracellular parasites.

Viral origin

Differences between viruses and bacteria

con. bacteria rickettsia chlamydia viruses

Obligat. Intracell. - + + +

Nucleic acid DNA and RNA DNA and RNA DNA and RNA DNA or RNA

Protein synthesis + + + -

Energy metabolism + + - -

Replication cell division cell division cell division Assembly

Sensitivity towards antibiotics + + + -

CHLAMYDIA: Obligate intracellular bacterial parasite which depends on eucaryotic cell for energy.

‚Frontiers‘ of Virology

Viroid Virosoids Prion

genome circular RNA ss RNA -

hosts plant plant, human human, animal

Example Coconut *Hepatitis D Virus Kuru Cadang Cadang

* Need a helper virus (HBV) to replicate