An overview to virology!

U luv ‘em

U hate ‘em

They make you sick

They make you scared

They make you work

U fight ‘em

Objectives

• To describe the classification of viruses.• To understand the spectrum of disease

caused by viruses.• To understand the public health

implications of viral infections.• To describe the pathogenesis of viral

infections.• To discuss the transmission of viral

infections.

What is a virus?

• Genetic material inside a protein coat.

• Very small 20 - 300nm.

E.coli 1000nm

Pox virus 300nm

Parvovirus 20nm

What else makes up a virus?

• A virus is an obligate intracellular parasite. It is completely dependent on living cells for replication and survival.

• Unlike other larger organisms, it contains either RNA or DNA. Never both forms of nucleic acid.

Viral structure.

• There are two basic shapes found in viruses:

• Icosahedral structure:

• Helical structure:

Viruses consist of the following components:

The genome. RNA or DNA.

The capsid

The matrix protein

The envelope

Glycoprotein spikesVarious non-structural

proteins

Viral classification.

• Type of nucleic acid:– RNA or DNA

• Number of strands of nucleic acid.

• Polarity of the genome.– Positive sense or Negative sense

• Shape of the capsid / nucleocapsid– Icosahedral or Helical

• Presence of an envelope

Virus

DNA

RNA

DS

SS

DS

SS

Non Enveloped

Enveloped

Enveloped

Non Enveloped

Non Enveloped

Enveloped

Non Enveloped

AdenoPapova

HerpesPox

Hepadna

Parvo

RetroArena

Reo

Para,Ortho etc

PicornaCalici

Nomenclature conventions:

• Family: ---viridae e.g. Herpesviridae

• Subfamily:---virinae e.g. alphaherpesvirinae

• Genus: ---virus e.g. Herpesvirus

• Species: --- e.g. Herpes Simplex virus

• Type: --- e.g. Herpes simplex virus type 1

Pathogenesis of viral infections:

• Localized:– Portal of entry is where the virus replicates

and causes disease.– There is seldom spread of the virus beyond

the localized area of infection– Short incubation period of 1-5 days.– Symptoms may be caused by the viral

replication or by the immune response to the virus.

Generalized infectionsPortal of entry

Migration to local lymph nodes

Primary viraemia

RES

Secondary viraemia

Target organs

Incubation period

14-21 days

Prodrome 2-3 days

Sick

How transmission happens:

• Inhalation

• Ingestion

• Direct contact with skin or mucous membranes

• Indirect contact - fomites

• Transplacental

• Organ transplant or blood transfusion.

Conclusion

• Small BUT:– Virulent– Dangerous– Major public health threats– Major public health disasters.