Biomedical Engineering Reference
In-Depth Information
strand of DNA. The synthesized strand of DNA is subsequently used as a
template to yield a double-stranded DNA molecule containing the genetic
information from the viral genome. Group VI viruses can integrate this
double-stranded DNA into the host genome. The Group VI viruses are
referred to as retroviruses.
The Group V viruses (Chapter 43), like the Group VI viruses, are single-
stranded negative sense RNA viruses. These viruses do not employ reverse
transcriptase. Instead, they use an RNA-dependent RNA polymerase, packaged
within the virus particle, to produce positive sense RNA, within the host cell.
The positive sense RNA is subsequently used to synthesize proteins.
Group VI viruses share their genetic legacy with the human genome.
About 8% of human genes are retroviral. Human DNA of retroviral
origin is referred to as endogenous retrovirus, or as a retroviral provirus.
Retroviruses in the external environment, capable of infecting eukaryotic
host cells, are referred to as exogenous retrovirus (i.e., a retrovirus that is
outside the gene).
Despite the legacy of retroviruses within the genome of eukaryotic cells,
there are only a few exogenous retroviruses that cause disease in humans.
The Group VI human pathogens are restricted to one class of retroviruses,
Class Retroviridae, and to two genera within this class: Deltaretrovirus and
Lentivirus.
Group VI, ssRNA-RT
Retroviridae
Deltaretrovirus
*Human T-cell lymphotropic viruses
Lentivirus
*Human immunodeficiency virus
Genus Deltaretrovirus contains four human T-cell lymphotropic viruses:
HTLV-1, HTLV-2, HTLV-3, and HTLV-4. Of these four viruses that infect
humans, only the HTLV-1 virus has been associated with human disease.
Infection with HTLV-1 greatly increases the risk of developing adult T-cell
leukemia/lymphoma, with about one out of every 25 infected individuals
eventually developing the disease. HTLV-1 has also been implicated as
a cause of a human myelopathic condition, tropical spastic paraparesis.
Although millions of individuals have been infected by HTLV-1, worldwide,
fewer than 2% of infected individuals will develop an HTLV-1-associated
myelopathic condition.
Genus Lentivirus contains the human immunodeficiency virus, which
produces HIV infection and the syndrome of associated diseases known as
AIDS.
Readers should not confuse HTLV-III, a virus discovered in 2005, and
which is not known at this time to produce disease in infected humans, with
an early name (long since abandoned) that was assigned to the HIV virus.
