Genera
Orthoretrovirinae (subfamily)
- Alpharetrovirus
- Betaretrovirus
- Deltaretrovirus
- Epsilonretrovirus
- Gammaretrovirus
- Lentivirus
Spumaretrovirinae (subfamily)
- Spumaretrovirus
Virion Properties
Morphology
- Consist of an envelope, a nucleocapsid, and a nucleoid
- Virus capsid is enveloped
- Virions are spherical to pleomorphic
- Virions measure 80-100 nm in diameter
- Surface projections are densely dispersed, small or distinctive glycoprotein spikes that cover evenly the surface
- The nucleoid is concentric, or eccentric
- Dimeric (monomers held together by hydrogen bonds)
- Unsegmented and contains a single molecule of linear
- -RT and a positive-sense, single-stranded RNA
- One monomer is 7000-11000 nucleotides long
- The encapsidated nucleic acid is mainly of genomic origin, but virions may also contain nucleic acid of host origin
- including host RNA and fragments of host DNA believed to be incidental inclusions
All retroviruses contain three large genes which are, reading from 5’ to 3’:
i. gag - contains information to direct the synthesis of internal virion proteins that form the matrix, the capsid and the nucleoprotein structures
ii. pol - contains information for the reverse transcriptase and integrase enzymes
iii.env - contains the information for building the surface and transmembrane components of the viral envelope protein.
Examples of Retrovirus
Human T-cell lymphotropic virus (HTLV)
There are four different types of human T-cell lymphotropic viruses:
HTLV-1 : HTLV-1 has an affinity for CD4+ T-cells and is associated with several types of disease states: Adult t-cell leukemia, tropical spastic paraparesis, uveitis, and dermatitis.
HTLV-2: HTLV-2 mainly infects CD8+ T-cells, but does not have any proven causative role in human lymphoproliferative diseases.
HTLV-3: HTLV-3 was originally isolated in association with AIDS. With further research, however, it was discovered that its pathogenic and genetic characteristics differed from those of HTLV-1 and HTLV-2.
HTLV-4: HTLV-4 has only been described in cases involving bushmeat hunters in Africa.
An infected T-Cell with HTLV-1(green)
Human Immunodeficiency Virus (HIV)
There 2 types of human immunodeficiency virus: HIV-1 and HIV-2. The new strain of HIV (HIV-2) discovered off the West coast of Africa is distinctly different than the original HIV-1 strain. While they have almost the same set of genes and very similar pathological effects, HIV-2 bears greater resemblence to the Simian Immunodeficiency Virus (SIV). HIV-2 is also less pathogenic than HIV-1.
The video below helps you know more about the life cycle of HIV:
Transmission
The source of infection is from bodily fluids of the carrier such as semen or blood.
HIV can be transmitted through:
- sexual activity
- sharing used needles or syringes
- mother-to-child transmission through childbirth or breast feeding
- receiving transfusions of infected blood, transplanted organs or donated sperm
Symptoms
Stages of HIV infection has been broken down into four steps:
A. Primary Infection
During stage 1, there is a short flu-like illness that is often mistaken for being nothing serious, thus diagnosis is frequently missed. This stage generally lasts for a few weeks, during which the immune system attempts to fight back by producing HIV antibodies and cytotoxic lymphocytes.
- swelling of the lymph nodes
- headache
- fever
- loss of appetite
- sweating
- sore throat
B. Clinically Asymptomatic Stage
Even though no symptoms are present, the virus is multiplying (or making copies of itself) in the body during this time. HIV multiplies so quickly that the immune system cannot destroy the virus. After years of fighting HIV, the immune system starts to weaken.
- Weight loss
- Fungal Nail Infections
- Repeated outbreaks of herpes simplex
- Personality changes
C. Symptomatic HIV Infection
It occurs when the immune becomes severely damaged by HIV. The body has been fighting back for years, the virus could mutate and become stronger and the T helper cells are dying off, with turnover rates failing to keep up.
- Severe weight loss
- Severe bacterial infections
D. Progression from HIV to AIDS
As the immune system becomes more and more damaged the illnesses that occur become more and more severe leading eventually to an AIDS diagnosis.
Kaposi's sarcoma (a skin tumor that looks like dark purple blotches)
- Shortness of breath and difficulty breathing due to infections of the lungs
- Dementia
- Severe malnutrition
- Chronic diarrhea
Treatment
Antiretroviral Drugs
Block the activity of one of the enzymes HIV needs to replicate inside human cells.
These drugs are:
- nucleoside reverse transcriptase inhibitors (NRTIs) / non-nucleoside reverse transcriptase inhibitors (NNRTIs)
-interfering with the action of reverse transcriptase. - protease inhibitors
- inhibit protease which cleaves the polyprotein to yield active virions - fusion or entry inhibitors
- prevent HIV from entering human cells
Treatment is most effective when at least two or three drugs are given in combination, referred to as highly active antiretroviral therapy (HAART). It can delay or prevent AIDS in HIV-infected people, thus extending their life.
Diagnosis
Specific tests include the following:
- Enzyme-linked immunosorbent assay (ELISA)
- Newer rapid screening tests
- Western blot