A few words on HIV

The virus = HIV The disease = AIDS (Aquired Immunodeficiency Syndrome) First recognized clinically in 1981 By 1992, it had become the major cause of death in individuals years of age in the States. Human Immunodeficiency Virus (HIV)

Till Dec 2007: 25 million people died of AIDS (20 million in 2002) People living with HIV/AIDS in million Africa has 12 million AIDS orphans (2007) 8 out of every 1000 adults of age in the world population (2007; 1 out of 20 in Sub-Saharan Africa) HIV Statistics

The territories south to the Sahara. In the past the term ‘ Black Africa ’ has also been used to refer to the same region however today it is obsolete due to its ” politically incorrectness ” Sub-Saharan Africa

Species = HIV Genus = Lentiviruses Family = Retroviridae Lentiviruses have long incubation time, and are thus called “slow viruses”. HIV is a lentivirus

In 1986, a distinct type of HIV prevalent in certain regions of West Africa was discovered and was termed HIV type 2. Individuals infected with type 2 also had AIDS, but had longer incubation time and lower morbidity (# of cases/population size). HIV-1 and HIV-2

Primates: ~350 species and ~13 families The smallest living primate is the mouse lemur which weighs around 35g; the largest is the gorilla, weighing up to around 200 kg. Primates

Mouse lemur

Most primate species live in the tropics or subtropics, although a few, most notably humans, also inhabit temperate regions. Except for a few terrestrial species, primates are arboreal. Some species eat leaves or fruit; others are insectivorous or carnivorous. arboreal Arbor = tree in Latin Primates

Prosimians (Strepsirhines) Tarsiers New world monkeys (Platyrrhines) Catarrhines Gibbons Hominidae Old world monkeys Haplorhines = Higher primates = Monkeys+Apes The primate tree Great apes Apes

Prosimians

Hominidae is the primate family, which includes the extant species of humans, chimpanzees, gorillas, and orangutans, as well as many extinct species. The members of the family are called hominids. The family is also called “ great apes ”. Great apes

Originally non-human great apes were called Pongidae. However, this original definition suggests that Pongidae is a monophyletic family – which is not the case. Great apes

1990

Nature 1990 – Origin of HIV-1

1990

HIV and SIV tree based on maximum parsimony 1990

HIV-1 is most similar in sequence and genomic organization to viruses found in chimpanzees (SIVcpz). HIV-1 and SIVcpz evolutionary relationships

Five lines of evidence have been used to substantiate zoonotic transmission of primate lentivirus: 1. Similarities in viral genome organization; 2. Phylogenetic relatedness; 3. Prevalence in the natural host; 4. Geographic coincidence; 5. Plausible routes of transmission. Zoonotic transfer Zoonotic transfer: The transmission of a disease from an animal host to a human.

For HIV-2, a virus (SIVsm) that is genomically indistinguishable and closely related phylogenetically was found in substantial numbers of wild-living sooty mangabeys whose natural habitat coincides with the epicenter of the HIV-2 epidemic Zoonotic transfer of HIV-2 from SIVsm

Sooty mangabey

Close contact between sooty mangabeys and humans is common because these monkey are hunted for food and kept as pets. No fewer than six independent transmissions of SIVsm to humans have been proposed. Zoonotic transfer of HIV-2 from SIVsm

In the 1990 paper, the authors wrote: “It is not possible to conclude that SIVcpz was the precursor to HIV-1, if indeed infection ever passed in that direction” The origin of HIV-1 is much less certain.