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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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