Retroviruses

Retroviruses have been studied more than any other group of viruses because of their unique features and the diseases they cause. 

Properties 

·         Polyhedral capsids
·         Spiked envelope 80-120nm in diameter
·         Two identical molecules of positive, single-strained RNA
·         Reverse transcriptase dsDNA from ssRNA.
·         Formation of long terminal repeats before provirus DNA inserted into host genome
·         Gag, pol, env genes some regulatory genes, some oncogenes
·         Gag – group-specific antigen
               ·         Virion core (capsid protein)
·         Pol – polymerase (reverse transcriptase)
            ·         RNase H
·         Env - envelope
·         Tumour-forming
     ·         Transducing
     ·         Cis-activating
     ·         Trans-activating (HTLV)
·         Non-tumour-forming
     ·         Lentiviruses
     ·         HIV
Human T-lymphotrophic virus 1 (HTLV-1)

Human t-lymphotrophic virus 1 caused adult acute t-cell lymphocytic leukemia, a cancer in humans. HTLV-1 is transmitted via sexual intercourse, blood transfusion, and contaminated needles. An ELISA can reveal infection with HTLV. As with many viral diseases, there is no specific antiviral treatment. Infections are chronic, and the long-term prognosis of patients are poor.
Stages of HIV infection

Stage 1: Primary HIV infection
Stage 2: clinically asymptomatic stage
Stage 3: Symptomatic HIV infection
Stage 4: Progression from HIV to AIDS

http://www.avert.org/stages-hiv-aids.htm
(details of the stages)
Antiretroviral therapy

Nucleoside reverse transcriptase inhibitors
1.      AZT (azidothymidine)
2.      3TC (lamivudine)

Non- nucleoside reverse transcriptase inhibitors
1.      Efavirenz
2.      Nevirapine

Protease inhibitors
1.      Indinavir
2.      Ritonavir

Combination therapy to combat resistance

AIDS therapy

1.      Immunomodulation
-          Enhancement of immune system through treatment with interleukin-2. (inform cells to work harder)

Flaviviridae

Most togaviruses and flaviviruses are transmitted by arthropods and these viruses are designated as arboviruses.

Arbovirus (insect-borne viruses)
-          Flaviviruses à falviviridae

Flaviviridae
-          Flavivirus (yellow fever, dengue, west nile)
-          Hapacivirus (hepatits C)

Properties

Picture
1.      Enveloped (icosahedral)
2.      Positive single-stranded RNA viruses
3.      Tightly appressed capsids (like shrink wrapping)
4.      3’ polyadenylated tail and 5’ cap
5.      Cytoplasmic replication (perinuclear)
6.
      3 structural proteins


 

 

Dengue

Picture
1.      Most important arbovirus presently
2.      Non-fatal dengue fever
3.      Usually fatal dengue haemorrhagic fver
4.      4 distinct serotypes DEN-1, DEN-2, DEN-3 and DEN-4

 

Dengue fever

1.      Several asymptomatic infections
2.      Acute infection resulting in fever, severe headache(frontal), retro-orbital pain, nausea and vomiting
3.      Sever muscle and bone pain
4.      Sever arthralgia (joint swelling- mainly back) à break bone fever
5.      Maculopapular rash before recovery

Dengue hemorrhgic fever/ dengue shock syndrome

Picture
Dengue hemorrhagic fever is a more serious disease caused by reinfection with the dengue virus, and it involves a hyperimmune response. Inflammatory lymphokines released by activated memory T cells cause rupture of blood vessels, internal bleeding, shock, and possibly death.

Yellow fever

Another flavivirus causes yellow fever, a disease involving degeneration of the liver, kidneys, and heart, as well as massive haemorrhaging. Haemorrhaging in the intestines may result in “black vomit and liver damage causes jaundice.

Incubation period: 3-6 days
Flushing of head and neck, conjunctival injection, strawberry tongue