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450 MIC Course: Medical Virology
Lecture Eleven
Viruses of Medical Importance
4- Human Immunodeficiency Virus (HIV) – part I
By
Dr. Mohamed A. Farrag
Assistant professor of Virology
Botany and Microbiology Dept., KSU
By the end of this lecture students should
Know the history of HIV/AIDS.
Have the knowledge HIV epidemiology and modes of transmission.
Learning outcomes
Recognize different symptoms associated with HIV/AIDS.
Be aware of different ways for prevention and control measures.
Before 1931, Congo: transmission of HIV from chimpanzees to humans, most
likely during “bushmeat trading” While hunting chimpanzees, hunters would
have come in contact with animal blood.
Historical Background
Before 1968, North America: a 16-year-old teenager, who never left the Midwest
and never received a blood transfusion.
1981, USA: 270 reported cases of severe immune deficiency among gay men (121
died) in USA. Patients presented with Pneumocystis carinii pneumonia (PCP) and
Kaposi’s sarcoma (KS).
1984, USA: there were 3,064 diagnosed cases of AIDS in the United States, 1,292
people died.
Historical Background
Hemophiliacs, who received contaminated blood transfusions.
Homosexual men, who reported higher incidences of the disease.
Heroin users, and people who used drugs via injection.
Haitians or people of Haitian origin, many cases of AIDS were reported in Haiti.
People were at Risk for HIV (Four-H club)
1995, USA: About 50,000 Americans died of AIDS-related causes. African-
Americans made up 49 percent of AIDS-related deaths.
Order: Ortervirales (5 Families)
Family: Retroviridae (2 subfamilies)
Taxonomy (ICTV, 2018)
Genus: Lentivirus
HIV-1, HIV-2
Subfamily: Orthoretrovirinae (6 genera)
Simian immunodeficiency virus
Bovine immunodeficiency virus
Feline immunodeficiency virus
Equine infectious anemia virus
HIV-1, HIV-2
Genome: RNA – single stranded – positive sense – Linear – non-segmented –
diploid – 9.3 kb long (each).
Capsid: complex (p24)
Envelope: Present Peplomeres (gp120)
Matrix protein (p17)
Viral enzymes: Reverse transcriptase Integrase - protease
Virus Morphology and Characteristics
Virion: Spherical – medium sized (100-150 nm in diameter)
Replication: Cytoplasm/nucleus
Virus Morphology and Characteristics
Virus Morphology and Characteristics
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5
Epidemiology and Transmission
According to WHO estimates, approximately 30 million people are estimated to have
died, while 35 million are living with HIV infection or AIDS.
Incidence and Prevalence of Infection
About 2.5 million new cases were estimated to occur globally during the year 2006.
Approximately 95% of all HIV infections have occurred in the developing world and
among young and middle-aged adults (i.e. sexually active).
Sub-Saharan Africa accounts for over 60% of the current cases of HIV infection and for
75% of the world’s HIV-infected women and children, although it contains only 10% of the
world’s population.
Asia accounts for over 20% of the world’s cases of HIV-1 infection, with over 6 million
cases as of the 2006. The majority of these have occurred in India.
Epidemiology and Transmission
Among the four genetic groups of HIV-1 (M, N, O, and P), group M viruses
dominate the pandemic.
This group is further divided into genetic subtypes or clades (A through D, F
through H, J, and K) based on nucleotide sequence differences.
While HIV-2 has remained largely confined to West Africa, HIV-1 has spread
throughout the world.
Epidemiology and Transmission
Group M viruses are responsible for the vast majority of HIV-1 infections.
in Cameroon, mixed infections were observed and included co-infection with two
subtypes within group M, co-infection with M and O viruses, and even co-infection
with HIV-1 and HIV-2.
Distinct subtypes or clades of Group M viruses have been isolated in geographically
distinct regions of the world.
In the United States, Europe, and Australia, subtype B is the predominant genotype.
Subtype A predominates in West Africa, subtype A and D in East Africa, and subtype C in
southern Africa.
Distribution and Geography
Sooty mangabey(SIVsmm)
Rhesus Macaques (SIVmac)
Gorilla(SIVgor)
Drill Monkey(SIVdrl)
Agile Mangabey(SIVagi)
Mandrill(SIVmnd 2 )
Chimpanzee(SIVcpz)
Red-capped mangabey(SIVrcm )
Epidemiology and Transmission A- Animal reservoir
Old World monkey cells cannot support infection with HIV-1 due to the species-specific
activity of the host protein TRIM5a, which targets the capsid protein of incoming virions
to inhibit viral replication.
HIV-1 is generally nonpathogenic in chimpanzees, and virus replication declines over time.
Similarly, human BST2 presented a barrier to the cross-species transmission of
SIVcpz to humans, which was overcome by evolution of the vpu gene of HIV-1.
Epidemiology and Transmission A- Animal reservoir