Retroviridae

Host:
Virus infects vertebrates.

Description and Significance
A retrovirus is a genome virus that replicates by using a viral reverse transcriptase enzyme to transcribe its RNA into DNA in the host cell.
The DNA is then incorporated into the host's genome by an integrase enzyme.
The virus thereafter replicates as part of the host cell's DNA.

Genome Structure
The genome of retroviridae is dimeric, unsegmented and contains a single molecule of linear.
The genome is -RT and a positive-sense, single-stranded RNA.
Minor species of non-genomic nucleic acid are also found in virions.

Virion Structure
It consist of an envelope, a nucleocapsid and a nucleoid.
Spherical enveloped virion and measure 80-100 nm.
The virion RNA is 7 to 12 kb long, linear, single-stranded, non-segmented, and of positive polarity.

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When a retrovirus infects a cell:
- Its molecules of reverse transcriptase are carried into the cell attached to the viral RNA molecules.

- The reverse transcriptase synthesizes DNA copies of the RNA.

- These enter the nucleus and are inserted into the DNA of the host.

- These inserts are transcribed by the host's enzymes into fresh RNA molecules which re-enter the cytosol.

It injects its RNA into the cytoplasm of that cell along with the reverse transcriptase enzyme.

The cDNA produced from the RNA template contains the virally derived genetic instructions and allows infection of the host cell to proceed.

The virus that causes AIDS (Acquired Immune Deficiency Syndrome) is a retrovirus.

It is called HIV for human immunodeficiency virus.

Transmission

1.) Blood products

2.) Organ transplants

3.) Sexual intercourse

4.) Vertical Transmission

Clinical features

Primary infection

90% of patients develop a flu-like illness. Symptoms include, fever, night sweats, sore throat, lymphadenopathy, diarrhoea.

Asymptomatic phase

Of variable duration, from 2 to 10 years. Patients are clinically well, but infectious.

Prodromal phase

Insidious onset of a variety of prodromal disorders including weight loss, fever, persistant lymphadenopathy, oral candidiasis and diarrhoea. These symptoms precede the progression to AIDS.

Therapy

There is no effective vaccine available for HIV.

- Gene Sia