Tuesday, January 29, 2013

DNA vaccine delivery system and Nef- Achilles heel

Greetings

     Recently had an argument (Not furious!!!) with one of my friends about topics chosen to blog and how it effects the readership. Our conclusion was, that if you write about very broad topics, in the way of a summary (Kind of blog review), the chances that the page will be read is high, than when you talk about a single article. This is simply because, most of the readers, reach a blog site, through search engines via keywords. And, Keywords are more in review compared to single paper talk. Its kind of the same scenario, about impact factor, used for journals.

    Before i get into the topic of the post, I want to make some points clear, especially for those who believe too much on impact factor for journals. The impact factor depends on number of citations a paper has received (Within 2 years of publication). For details on how it is calculated go here. As might be expected, journals that focus more on review will be cited more easily. This is possibly because, the matter is sometimes more digestible and well explained in comparison to the original papers. So they get easily cited. Moreover, impact factor is derived from the cited papers in a journal, and non cited are ignored. This means even if one paper is cited several times, but the rest is crap, you still get a pretty good impact factor.

   That ends the first part, that I wanted to say since a long time. The second part of the blog comes with two papers.
Photo 1: BD Soluvia 
Microneedle device
       The first study has to do with vaccines. Perhaps, what is the best strategy of vaccination? Live attenuated, Killed, Sub-component? Or the more sophisticated approach of DNA / RNA vaccines? While all the traditional vaccines have been good at some point, the long term effects have been variable. Many a times, vaccines has to be given repeatedly. That's where the idea of DNA vaccines come form. The recent success of mRNA vaccines against Influenza has brought in new hope. Read the story here.

    But more recently, the technique of delivery has also been researched under new light. for example the influenza vaccine delivery system. the 2 licensed mode of influenza vaccine delivery include intradermal vaccines using a microinjection system (BD Soluvia) and intranasal vaccines FluMist. That's one way of looking at it.

     Now what if i told you that scientists have one more possible armory, that combines the best of 2 worlds. On one way you have the potential DNA vaccine and on the other hand the elegance of a delivery system. That's exactly what the story is about. Researchers from MIT has developed a new type of vaccine-delivery film that holds promise for improving the effectiveness of DNA vaccines. This is a polymer film that gradually releases DNA coding for viral proteins. In a sense this polymer acts as an adjuvant that gives a controlled release. Given the promise of DNA vaccines this should be of great value. These polymer films are implanted under the skin using microneedles that penetrate about half a millimeter into the skin — deep enough to deliver the DNA to immune cells in the epidermis, but not deep enough to cause pain in the nerve endings of the dermis. Irvine (a senior author in this paper) says. “If you're making a protein vaccine, every protein has its little quirks, and there are manufacturing issues that have to be solved to scale it up to humans. If you had a DNA platform, the DNA is going to behave the same no matter what antigen it’s encoding”. For source and more information go here.

Fig 1: HIV-Nef. Source
   The 2nd paper is by Smithgall etal. The paper is titled "Effector Kinase Coupling Enables High-Throughput Screens for Direct HIV-1 Nef Antagonists with Antiretroviral Activity". The paper revolves aroud the factor nef, a culprit involved with HIV infections. Nef stands for Negative Regulatory Factor, which is expressed by most of the members of lentivirus group. The function is to increase the survival of infected T cells and for destruction of non-infected T cells (probably thorugh apoptosis). It accelerates the endocytosis of MHC class I molecules through the phosphofurin acidic cluster sorting protein 1 (PACS1)/phosphatidylinositol 3-kinase (PI3K)-dependent activation of ADP ribosylation factor 6 (ARF6)-mediated endocytosis. Reference. The point is, Nef is a key factor is bypassing the immune system control.

    The researchers were able to track the kinetics of nef by tagging with an enzyme Hck, which is activated by Nef in HIV-infected cells. High throughput drug screen was carried (with about 250000 compounds). A compound called B9 was identified, which inhibited the Nef activity strongly. In a series of experiment, they were able to pin down a important observation. B9 could prevent Nef dimerisation impairing its function in the viral replication process. Dr. Smithgall said "This pocket where B9 binds to Nef and where Nef forms a dimer indicates it's a hot spot, or Achilles heel, that could represent a new target for HIV drugs". For source go here.
ResearchBlogging.org
Peter C. DeMuth, Younjin Min, Bonnie Huang, Joshua A. Kramer, Andrew D. Miller, Dan H. Barouch, Paula T. Hammond & Darrell J. Irvine (2013). Polymer multilayer tattooing for enhanced DNA vaccination. NATURE MATERIALS : doi:10.1038/nmat3550



Emert-Sedlak LA, Narute P, Shu ST, Poe JA, Shi H, Yanamala N, Alvarado JJ, Lazo JS, Yeh JI, Johnston PA, & Smithgall TE (2013). Effector Kinase Coupling Enables High-Throughput Screens for Direct HIV-1 Nef Antagonists with Antiretroviral Activity. Chemistry & biology, 20 (1), 82-91 PMID: 23352142

Further Reading:
2. John L Foster and J Victor Garcia. HIV-1 Nef: at the crossroads. Retrovirology 2008, 5:84. Link

Wednesday, January 23, 2013

Culturomics- A Perspective

Greetings,

Fig 1: Core and variable components
of the human microbiome. Source 
     Give a moments thought to this. There are several set of organisms seen in association with humans as microbial flora. Much of the microbes have not been studied in detail, that is demanded by the science. Reason? its simply difficult to culture them in the laboratory. With the invent of DNA studies, a large number of bacteria have been studied with strategies such as the metagenomics. A detailed DNA analysis has also yielded insights into culturing bacteria's, that we are other wise unable to grow with common known set of laboratory conditions. In literature you would find a term "non-culturable bacteria". The term is often misleading to many students. The non cultivable conditions arise from our inability to grow them in artificial conditions rather than the microbes capability to grow. In the scientific writing it is often referred as VBNC (Viable but non-culturable) organisms.

    There is matter of interest here. Bacteria sure is capable of dividing (in other words reproducing). If i had to collect a few grams of urine sample from a normal person and plate it on all the available media, am probably going to end up with maybe 20 different types of organism. Or if am lucky enough, maybe a total of 50 species. But, guess what? There are at least another 1000 (probably one more zero), that is sitting in the sample not giving you a colony. But they have the capability to reproduce given the right conditions. That is the limit to Clinical Microbiology when it comes to culture. The effect is more greater when it comes to culturing bacteria from soil or other super microbe rich sources.

    Why am i boring you with the damn culture? After all we have PCR or DNA sequencing methods that can tell all the range of organism is there. Why culture? think about it for a minute and you have a set of answer. If you can grow the organism, you have to study and tease out its biology. DNA sequence and PCR (or other sophisticated methods to say) can tell you the gene part. As biologists, we are often interested in knowing the dynamics of the organism. And culture is a great way of doing it (Pls note, its not the only way).

    3 paragraphs of explanation to come to this one point of what am pointing towards. The post is all about "Culturomics". When I first heard this term, had the same reaction as you probably do. Yet another "Omics". But as I came to understand more and more what the idea seem to be, I begin to take a grasp of what exactly it is. But then am not a big fan of the "-omics" used for everything.

      Many a times crowning a title creates a confusion. Culturomics has two meanings. The first one is the field that focus on studies of linguistic and cultural phenomena (Link) and the second is one which focus on method of culturing bacteria (the focus is on improvising the culture technique).

    Culturomics is classically defined as "an approach allowing extensive assessment of the microbial composition by high-throughput culture". The definition is often seen ion contrast to metagenomics and possibly an alternative. An important digression here. Metagenomics is a sequencing approach (using pyrosequencing or 3rd generation sequencing methods) and aims to construct a map based on the DNA studies, whereas culturomics uses studies based on growth characters in artificial set of conditions.


Fig 2: Identification of bacteria in the human gut
by culturomics and metagenomics.
Source
    Alright. here's the paper that came first on the field that's worth a bit of discussion. This paper is by Lagier etal; In this study, stool samples from 3 people (2 lean African and one obese European), were analysed by 212 different culture conditions of culture. The study recovered 32500 colonies which was traced to 340 species of bacteria from seven phyla and 117 genera, five fungi, and a giant virus (Senegalvirus). Its not the recovery itself that am impressed about. Its the fact that 212 variety of conditions that then lead to recovery. A parallel meta-genomic approach was used for comparison, yielded 698 phylotypes, including 282 known species. By using a set of conditions they could culture out nearly half of the population that exists. That's mind blowing. So if you could get more conditions, probably they would get more. But for a start, it is massive step. Just make a note here that the metagenomics identifies probably about 50-60% of what is actually present. The Fig 2 from paper says it all.

    So what was the novel culture conditions that was brought in? It was use of rumen fluid and sterile fresh human stools. Selectivity in culture was tried by removal of E. coli by specific lytic phages, various antibiotic mixtures, heat destruction of non-sporulating bacteria, exotic range of selective media, amoebal co-culture. The selectivity gave a chance for other bacteria's that are more slow in growing (I call the shy growers) to get a hold and be cultured. But I could make a more general point here. The paper had concentrated more on culturing conditions very similar to native growing conditions. That makes sense. Perhaps we microbiologists should try to culture the microbe "in their conditions" rather than "our conditions".

     A very fine explanation on the use of culturomics and its contrast to metagenomics is published recently by G. Greub. The paper provides compelling evidence towards the new hot topic "Culturomics". But, I gave it some thought. We have been cultivating a variety of microbes in the lab. Though, Microbiologists have not successfully cultivated all the organisms, they aren't that bad too. Lets assume that we have not been able to grow a bacteria X, but happened to sequence its genome. And by bioinformatic approach, we concluded that the X is missing a pathway for making some important nutrient Y. Under normal culture conditions, the Y is not provided in the growth conditions. But if you substitute it, you now grow the bacteria X. This is not my naive approach. This method has been used for a longtime now, to culture organisms that were otherwise thought to be Non culturable. But they never gave this approach a entire field name, for it doesn't sufficiently represent a territory in itself (the way genomics, Proteomics etc do), and am little hesitant to call it with a suffix- "omics".

    But, perhaps right now this is a naive field and just begun to evolve. But whatever is the name is the take home excitement is that, we are now thinking of the classical microbiology culture once again, and trying to figure out how to grow the ones that are otherwise "shy growers". And an important point, this is a "Select in-out approach".


ResearchBlogging.org
Lagier JC, Armougom F, Million M, Hugon P, Pagnier I, Robert C, Bittar F, Fournous G, Gimenez G, Maraninchi M, Trape JF, Koonin EV, La Scola B, & Raoult D (2012). Microbial culturomics: paradigm shift in the human gut microbiome study. Clinical microbiology and infection : the official publication of the European Society of Clinical Microbiology and Infectious Diseases, 18 (12), 1185-93 PMID: 23033984

Greub, G. (2012). Culturomics: a new approach to study the human microbiome Clinical Microbiology and Infection DOI: 10.1111/1469-0691.12032

Monday, January 14, 2013

Antibiotic resistance- The basics

Greetings

    Infectious diseases represent one of the most important paradox. Most of the infectious diseases in immuno-competent individuals is caused by a small set of pathogenic microbes. The treatment is well defined in these set of organisms. However, even with well defined set of protocol to treat an infectious agent, the clinical care takers find it incredibly difficult to treat the organism. In this post, I want to elaborate on the issue of antibiotic resistance in context with treating bacterial infections.

    Antibiotic resistance can be classified into- Intrinsic and Acquired resistance. Intrinsic resistance refers to  non responsiveness to an antibiotic (usually a Subclass of drug) due to lack of target, that has been acquired by the organism as a part of its species character. Each species of interest is intrinsically resistant to a group of antibiotics. The intrinsic resistance for an organism is well characterized for clinically relevant species. A prior knowledge of this resistance pattern is important when treating a given infectious condition on a case by case basis. The Intrinsic resistance, though hampers the choice of antibiotics, isn't a significant chunk of problem because it is a non changing phenomenon (Not always the case).

     Acquired resistance represents, acquiring resistance to antibiotic through single or multiple changes that can be stably inherited from generation to generation. It can also be passed from one strain to another (or swapped in between genus). The patterns of resistance is not consistent at a global scale and the prevalent antibiogram has to be prepared locally. An antibiogram is a report that reflects the percentage of a given organism that is susceptible to each of the antimicrobial agents routinely tested.

Fig 1: Acquired resistance
      Its a common knowledge in clinical microbiology that the Gram negative infections are harder to treat, and highly resistance evolving type in comparison to Gram positive organisms. The question that is raised immediately is where does the resistance evolve from? The best explanation provided is natural selection. The normal mutation rate of the organism allows an occasional microbe to be generated that is resistant to the antibiotic. This population extends over a period of time replacing the original sensitive strain. Years of research and billions of dollars are pulled out to bring out an antibiotic. And the resistance is evolved, just like that (The sad part).

Fig 2: Resistome
Source
    The second most common mode of antibiotic resistance is through gene transfer. Many different antibiotics are inspired from nature. The antibiotics in use today are naturally existing compounds that is found in nature for thousands of years (Probably even millions!!!). Resistant genes are thus circulating in gene pool that has evolved. The genes just need to be transferred. The entire set of gene pool in a given bacterial community that can mediate resistance is referred as Resistome. The largest set of resistome, is probably Soil Microbiota.

    Understanding of mechanism of evolving resistance has some interesting set of implications. Irrespective of that the resistance is acquired through a mutation (slow ever evolving mechanism) or gene transfer (Rapid, leap in resistance) we can reverse the phenomenon, by removing the selective pressure. The genes are intact in a species and carried over for a long series of time over the generation only when there is a selective advantage of having it. That means, by the same mutation that brought in the resistance to an antibiotic, can also reverse it by another mutation. It can be stably inherited, if there is no selection pressure to keep the resistance gene. This is one of the central concepts of Antimicrobial Stewardship. Antimicrobial stewardship programs (ASPs) advocate for judicious use of available antimicrobials to preserve their usefulness.

Fig 3: Bystander effect.
        So far so good. But then, there is a third mode of antibiotic resistance that is not much discussed in the literature perhaps because of its undermined importance. This is called as Passive resistance or as i would like to call it more aptly, "Bystander Resistance". The idea is quite simple. Take this scenario. If there happens to be a sensitive organism in proximity to a resistant organism. Moreover the resistant bacteria secretes, an enzyme that mediates resistance, then the sensitive bacteria can benefit from bystander effect. I have explained this in Fig 3 to the left. For an argument on the bystander effect, go here. This phenomenon, though not convincing on the first look, is indeed shown to be true at least in one case. In Otitis media condition, Weimer etal; demonstrated that NTHi (nontypeable Haemophilus influenzae) provides passive protection for S. pneumoniae in vivo through production of β-lactamase.

   That leads to a question someone asked me. If organism is in CNS and sensitive to a particular drug, but you cannot use it, because the antibiotic cannot penetrate the Blood-Brain-Barrier, then the resistance will be called as? (By the way, crossing BBB has to do with lipid solubility of the drug). According to me the question is baseless. This is a case where the bacteria enjoys the privilege of site, where the antibiotic cannot reach, rather than anything from the part of microbe. So its not resistance at all. I suppose that clarifies.

      So I can summarize, there are 3 modes of bacterial resistance- Intrinsic, Acquired and Passive resistance. The resistance mechanism under each can be classified as follows

Intrinsic
  • Impermeability to the drug
  • Absence of target site
  • Lack of enzymes to convert the Pro drug to the active form
Acquired
  • Alteration in anti-microbial target
  • Reduction or nullifying cell permeability to drug penetration
  • Decreased uptake of antibiotic by expression of efflux pumps
  • Production of an enzyme that inactivates the drug
  • Production of an alternate pathway that bypass the action of drug
  • Biofilm formation
Let me talk some basic ideas and concepts under each.

Changes in outer membrane permeability:

       This was early recognized early in history of antibiotic development that natural penicillin was effective only against Gram positive organism but not against Gram negative bacteria which is attributed to the impermeability of the outer membrane. Mutations in specific porins, formation of biofilm and large size of the drug with respect to the channels of influx also contribute significantly to resistance mechanism.

Inner membrane impermeability:

       Many drug molecules bind to a transporter molecule (E.g.: Anionic transporter in aminoglycoside) which subsequently is transported to the cytoplasm across the membrane by a proton motive force (PMF). The PMF that is required for substrate transport into the cell is often mutated in resistant strains. This generally is seen after a stepwise mutation in chromosome.

Promotion of antibiotic efflux:

     The drugs that are used may not reach optimal intracellular concentrations which are due to active efflux the drug. The process is usually due to acquiring of a new protein that is plasmid encoded and hence easily transmitted. This mechanism is also possible owing to a chromosomal mutation which is well noted in 4 genes-PenA, PenB, PonA and mtrR that encode increased expression of an efflux pump. Such an active efflux system is well studied in E.coli against norfloxacin.

Alteration of target:

     Resistance to various different antimicrobial agent is mediated this mechanism. The resistance is usually acquired through a single step or multistep mutation in chromosome or a plasmid that is expressive. The target may be modified in enzyme binding site (e.g.: Rifampicin resistance), Receptor mutation (e.g.: MRSA due to PB2’) or ribosomal targets (e.g.: Macrolide resistance). The change is mostly due to a chromosomal mutation or in some instances through recombination.

Bypass of antibiotic inhibition:

      This mechanism though not common is of importance as it creates very stable auxotrophic mutants. The organism by mutation loses some gene activity which encoded for a protein that was a target for the drug. The new variant is unable to synthesize the compound and becomes dependent. This may affect virulence in a few scenarios.

     The above described mechanism reflects a broad way of defining the resistance mechanisms that an organism is able to use in an unpredictable format. In any given organism multiple mechanisms may exist in co-existence can lead to pan-resistant (e.g.: Pan-drug resistant Acinetobacter, PDRA), multidrug resistant (e.g.: Multidrug resistant Enterococci, MDRE), extremely resistant (e.g.: Extremely drug resistant Mycobacterium tuberculosis, XDRTB) or super resistant types (e.g.: Super drug resistant Enterococci, SDRE).


ResearchBlogging.org
Forsberg KJ, Reyes A, Wang B, Selleck EM, Sommer MO, & Dantas G (2012). The shared antibiotic resistome of soil bacteria and human pathogens. Science (New York, N.Y.), 337 (6098), 1107-11 PMID: 22936781.

Khadem TM, Dodds Ashley E, Wrobel MJ, & Brown J (2012). Antimicrobial stewardship: a matter of process or outcome? Pharmacotherapy, 32 (8), 688-706 PMID: 23307518.    

Wednesday, January 02, 2013

The birth story of HIV

Hello,

    First of all, Let me Wish a happy new year to all the readers. Its now almost an year, since i have been blogging. And, I can say, to date its been a good experience. I have often posted here, with most happenings in field of research, and sometimes posted more of like a mini-review or rather a snapshot of some data. Today, i decided to make an exception. I thought i had tell you the story of HIV. By story, I don't mean that am going to take you for a ride. I will still stick to science.

   In the 1980's when the first cases of HIV was published, it was thought to be something of rare phenomenon. The disease was strange. It broke the immune defense code of the body leaving it susceptible even to the most simple microbes. And the people infected where men who had sex with men (MSM). And to this day, the etiological agent is one of the most studied and feared infection. So How did it all begin?

Fig 1: Origins of human AIDS viruses
Source
     The Origin of HIV is a big debate. Multiple theories had popped up and some of the theories were competing with each other. However, to date this issue of why has not been resolved fully (Though, Hunter's theory is most accepted and seems to fit the explanation). But, it is now almost beyond a doubt that, the HIV is a derivative of SIV. In simplest words "Daddy of HIV is SIV (simian immunodeficiency viruses)". SIV is a infection found in the monkey group. Almost more than 40 different SIV has been implicated to have crossed the species barrier. Depending on the monkey origin a suffix is used to denote their primate species of origin (e.g., SIVsmm represents sooty mangabeys). As you can see from the figure, there are a variety of HIV that has originated from various sources. And the SIV represents an array of virus and not just a single virus.

     So, i just am intrigued. Who's the grandpa here. In other words, SIV is evolved from? Of course, there is no link of interest to medicine by knowing this. But, yet just as matter of making the story go more alive. The SIV of interest seems probably a hybrid!!! The origins of SIV that lead to HIV traced by a great deal of molecular work . The following is the speculation (With molecular evidence). The first is a virus from Red Capped Mangabey and the other is a virus from Spot Nosed Guenon. Both virus together created a genome hybrid which was stable and turned to evolve to modern day SIV that parented the HIV!!!

    So how did the HIV enter human territory? Seems to be a simple question. At first people were tempted to say zoonotic. That sets a stage for theories- The Polio vaccine theory, Contaminated needle theory, Colonialism theory, Conspiracy theory and Hunter theory. Lets see what each mean.

Photo 1: Edward Hooper
Polio Vaccine theory:

      Oral polio vaccine (OPV) AIDS hypothesis states that an experimental polio vaccine called CHAT, developed at the Wistar Institute in Philadelphia, initiated the Aids pandemic by introducing SIV from the common chimpanzee into some of the million Africans who were given the vaccine between 1957 and 1960. The theory was highly criticized after it made in the form of a book by Edward Hooper (The title of book is "The River"), the main proponent of this theory. The idea was the SIV was introduced into humans with OPV (It was sometimes referred as Hilary Koprowski's vaccine) which was prepared by using kidney cells of infected chimps.

   The theory has multiple flaws. Dr Koprowski testified that primate material used in the vaccine came from Asiatic monkeys, but Hooper reacted "I have individual testimony from three or four people that these chimps were used, the kidneys were excised from these chimps and sent back not only to Philadelphia where Koprowski was working but also to Belgium where they were used in cell cultures." Moreover, Dr Harry Hull, head of the WHO's polio eradication programme says "It also does not make sense in that there were other children who received this vaccine who didn't contract it - so the question is why would it just be the children in the Congo and not elsewhere?". For source and more information go here. Clearly the theory is incomplete or totally wrong. By 2001 Nature and science had published the lack of conclusive evidence. Multiple studies have failed to confirm presence of viral elements specially SIV in the vaccines that has been used. But in 2003, Hooper springs back in action with some new findings. The findings said "In 1950s, virologists in South Africa were using African green monkey cells to amplify the Sabin vaccines, while their colleagues in French West Africa and French Equatorial Africa were apparently using cells from baboons (and perhaps other species, too) to amplify the Pasteur Institute vaccines of Pierre Lepine. In Stanleyville, they had the Lindi chimpanzees". Source.

Contaminated Needle Theory

Photo 2: Preston Marx
Source
    The theory was led by Preston Marx, a virologist in primate research. The theory believed that re-use of unsterile needles, as practiced in Africa in the mid-50s could have spread HIV from person to person. The theory does explain how the HIV might have spread without sexual contact but fails to grasp the origin. The idea sprung from his research findings that the mangabey blood samples tested positive for SIV and that the blood samples from a few of the villagers contained both HIV and SIV genes. As far as research has supported this has been probably a great mode of enhanced transmission but probably origin is blurred. This finding of SIV in villagers blood is better explained with the hunter's theory.

      The main blow to the theory was molecular clock predictions. The prediction was that AIDS would have emerged as a global pandemic in the 1960s as opposed to the 1980s. Ya, at times predictions means nothing. Cause the theory predicts the origin of HIV within ten years of Korbers’ genetic prediction favoring a range from 1915-1941. Impressive!!

Other Competing Theories:

    The Colonialism theory supported by Jim Moore took into consideration the overcrowding, poor sanitation and assumes had first caused immunodeficiency. This allowed time for SIV to become HIV . The spread was enhanced through prostitution. The conspiracy theory or sometimes called as genocidal theory posed in 1985 by Soviet official, Valentin Zapevalov. The theory was believed by many and was thought that it was an artificial creation for biowarfare use. It was further believed that the virus was propagated by small pox vaccine and (or) Hepatitis vaccination trials. These theories doesn't hold much water and lacks some solid evidence back up.

Photo 3: Dr Robert Gallo
Source
Hunter's theory:

    More famously known as the "Cut hunter theory", was laid down by AIDS researcher, Dr. Robert Gallo. The theory suggests that the SIV virus which circulates in African monkey population, was transferred to the people, who hunted the monkeys for their meat (Bushmeat hunting). The virus subsequently was ingested, mutated and emerged as HIV. This gives a chance to explain new strain types emerging and also explains Anti-SIV titers sometimes seen in the village population even to date. The virulent HIV-1 is most possibly derived from the SIV-cpz (Chimpanzee strain) and HIV-2 from SIV-sm (Sooty mangabeys strain). The theory is further supported by many molecular evidence studies and to date has explained most of the observations made in HIV epidemiology.

      So much so for the theories on HIV origin. HIV is a pandemic and has been one of the greatest challenges to the Infectious science. But how as it come to spread to the whole world? The first answer of interest came to be known as "Patient zero".


Photo 4: Gaetan Dugas
Source
      Let me cut the story in short. When a epidemiological investigation was launched to trace source of HIV infections, a large cluster, was seen. The analysis somehow showed a central player with multiple sexual contacts. On deep analysis, he was shown to be the source. The character here is Gaetan Dugas and became infamous as Patient Zero or the index case. It was hypothesized that he had carried the virus from Africa and introduced it to the western world. When he learnt of his disease, (as literature says) he continued to deliberately infect other people, to an estimated 250 people!!! At the time the disease became famous as Gay cancer.

     The story suggests that the evolution of HIV is at about 1950's. But then studies have demonstrated conclusive evidence pointing to existence of HIV strains as early as 1930. This means there is someone before Gaetan to have spread this infection across African regions. By comparing a very large set of HIV isolates, from historical samples a genetic family tree was constructed. The estimates is that the origin dates back to something like 100 years. The best estimates of HIV entering human population is 1908, but it can be as far as 1884.

   So if I can rebuild the story in short it would be something like this. A hybrid SIV circulates in the monkey population. Through a hunter the virus passed on to local human population in western Africa. It slowly spread around through needles and sexual contact which was picked up by exogenous population. The virus transfers through index cases into the western world and spreads through multiple sexual partners throughout the world. Mean while, the virus mutates and evolves establishing itself and come to be the pandemic problem.

ResearchBlogging.org
Auerbach DM, Darrow WW, Jaffe HW, & Curran JW (1984). Cluster of cases of the acquired immune deficiency syndrome. Patients linked by sexual contact. The American journal of medicine, 76 (3), 487-92 PMID: 6608269


Further Reading:

1. Aids and the Polio Vaccine. Link
2. Worobey etal. Direct evidence of extensive diversity of HIV-1 in Kinshasa by 1960. Nature 455, 661-664. Link