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How did HIV start?

How did HIV start?

Understanding the evolution of HIV (Human Immunodeficiency Virus) involves tracing a complex timeline that spans continents and species. HIV-1, the virus most commonly associated with AIDS (Acquired Immune Deficiency Syndrome), and HIV-2 both have their roots in viruses infecting African primates, with HIV-1 originating from a chimpanzee subspecies and HIV-2 from the sooty mangabey, shedding light on the critical cross-species transmission events that have shaped the modern epidemic.

This article will navigate through the timeline of HIV’s emergence, highlighting key moments from its jump from animals to humans to its spread among communities. The journey not only uncovers the historical trajectory of the virus but also emphasizes the importance of understanding its origins to inform future prevention and treatment strategies.

Tracing the origins: Early clues and scientific investigations

HIV-1, the predominant cause of the global HIV epidemic, has its origins traced back to chimpanzees, revealing a complex journey of cross-species transmission. This virus is closely related to simian immunodeficiency viruses (SIVs) found in wild-living chimpanzees and gorillas in West Central Africa. Through four distinct lineages, HIV-1 emerged from SIVs, with at least one lineage involving gorillas. These lineages highlight the virus’s adaptability and the critical role of cross-species transmission in its evolution.

Origins and cross-species transmission:

  • Chimpanzee to human: HIV-1 originated from SIVcpz, found in chimpanzees. It has undergone three separate transfers to humans
  • Gorilla involvement: At least one or two transmissions of HIV-1 to humans may have involved gorillas, showcasing the complexity of its origins
  • SIV diversity: Over 40 species of African monkeys are infected with their own species-specific SIV, indicating a vast reservoir of these viruses

Genetic evolution and pathogenicity:

  • Chimpanzees acquired two distinct forms of SIVs, which recombined to create a virus leading to AIDS
  • The adaptation of monkey viruses first to chimpanzees and then to humans highlights the genetic changes crucial for understanding the pathogenicity of HIV

Epidemiological Insights:

  • The discovery that SIVcpz is pathogenic in its natural host challenges previous notions and provides insights into the virus’s impact on chimpanzee populations
  • Molecular clock analyses date the onset of the group M and O HIV-1 epidemics to the early twentieth century, offering a timeline for the spread of the virus among humans

This examination of HIV-1’s origins underscores the importance of understanding its evolution for developing effective prevention and treatment strategies.

The jump from animals to humans: The critical cross-species transmission

The critical jump from animals to humans marks a pivotal moment in the history of HIV, underscoring the complex interplay between species that led to the emergence of HIV-1, the virus responsible for AIDS in humans. This transition involved several key events:

Cross-species transmission events:

  • From monkeys to chimpanzees: The simian immunodeficiency virus (SIV) in chimpanzees is a hybrid virus, originating from two different viruses that jumped from red-capped mangabeys and greater spot-nosed monkeys into chimpanzees. This hybridization likely occurred as chimps consumed these monkeys, incorporating the viruses into their own genetic makeup
  • From chimpanzees to humans: The hybrid virus spread within the chimpanzee population before making the leap to humans, evolving into what is now known as HIV-1

Genetic evolution and diversification:

  • Following its transmission to humans, HIV-1 underwent significant genetic evolution, a process evidenced by the non-synonymous variants observed in viral genomes across different time points. This evolution played a crucial role in the virus’s adaptability and pathogenicity in humans
  • The recombination of various SIVs is believed to have facilitated the cross-species transmission and subsequent diversification of HIV-1, particularly within group M subtypes. This diversification was notably observed in Kinshasa in the early twentieth century

Implications of Zoonotic transmission:

  • The transmission of viruses from animals to humans is not unique to HIV but is a phenomenon observed in other diseases such as Ebola, Zika, and coronaviruses. Non-human primates (NHPs) serve as a reservoir for numerous pathogens, including retroviruses like SIV, that can jump to humans through activities such as hunting and butchering
  • Understanding the zoonotic origins of HIV, from SIVcpz endemic in West Central African chimpanzees to its global spread infecting over 33 million people, highlights the importance of studying cross-species transmission to prevent future zoonoses

This examination of the jump from animals to humans not only sheds light on the origins of HIV but also emphasizes the critical role of genetic evolution and human activities in the spread of zoonotic diseases.

The earliest known cases of HIV in humans

Time-stamped cases of HIV-2:

  • The time to the most recent common ancestor (tMRCA) for HIV-2 group A is estimated around 1932, with a possible range from 1906 to 1955
  • For HIV-2 group B, tMRCA is approximated to be 1935, with an earlier limit of 1907 and a later limit of 1961

Initial documented cases of HIV-1:

  • The first known case of HIV-1 in humans was detected in a male from Kinshasa, Congo, in 1959. This case underscores the presence of the virus in humans well before the global recognition of the AIDS epidemic
  • An adult Bantu male from Kinshasa, identified through the sample LEO70 in 1959, represents the earliest known sample of HIV-1, indicating the virus’s presence in the Democratic Republic of the Congo during that period
  • A Scandinavian man who had travelled to west-central Africa was identified in the 1960s as the first patient with HIV infection and AIDS, highlighting the disease’s existence outside of Africa at an early stage

Further historical cases and spread:

  • The Centers for Disease Control and Prevention (CDC) recorded the first 50,000 cases of AIDS from 1981 to 1987, with the subsequent 50,000 cases reported within a span of less than two years, between December 1987 and July 1989, signaling a rapid escalation of the epidemic
  • In 1978, a Portuguese man treated in London was confirmed to have HIV-2, marking a significant case in the disease’s history within Europe
  • The United States saw its first recorded case of AIDS with the death of Robert Rayford, a 16-year-old, in 1969, which retrospectively indicated that the virus had spread to North America earlier than initially thought
  • The earliest verified case of HIV comes from a 1959 blood sample of a man in Kinshasa, further confirming the virus’s existence in the human population during the mid-20th century

The timeline of HIV’s emergence in humans

The timeline of HIV’s emergence in humans is marked by pivotal events that have shaped our understanding and response to the epidemic. These milestones, from the initial reporting to groundbreaking medical advancements, provide a structured overview of the virus’s impact on society and healthcare.

  • 1981: The U.S. Center for Disease Control (CDC) reports the first cases of what would later become known as the AIDS epidemic
  • 1982: The CDC reports the first cases of AIDS in women and hosts the first conference to address the new epidemic
  • 1985: A landmark year with several firsts:
  • The U.S. Food and Drug Administration licenses the first blood test to detect HIV
  • The first International AIDS Conference is held in Atlanta, Georgia
  • The first cases of AIDS among children under age 13 are reported
  • Rock Hudson becomes the first major U.S. public figure to announce he had AIDS
  • Dwight Burk is born as the first child of a haemophiliac with AIDS
  • 1987:
  • The first panel of the AIDS Memorial Quilt is created
  • AZT becomes the first antiretroviral drug available to treat HIV
  • 1988: The first World AIDS Day is observed
  • 1992: Introduction of the first combination drug therapies for HIV
  • 2013: The first well-documented case of an HIV-infected child appears to be cured of HIV
  • 2019: The first living donor HIV-to-HIV kidney transplant in the U.S. occurs

This sequence of events, from the early reports in the 1980s to significant medical milestones in the 2010s, highlights the critical steps taken in understanding and combating HIV. The timeline not only reflects the scientific and medical community’s efforts but also underscores the societal impact, marking periods of fear, stigma, and eventually, hope.

Implications of understanding HIV’s origins

Understanding the rapid evolution of HIV is pivotal in grasping why combatting this virus presents such a significant challenge. Key factors contributing to this rapid evolution include:

  • Error-prone reverse transcriptase: Lacking proofreading activity, this enzyme introduces mutations during viral replication, contributing to the virus’s high mutation rate
  • Recombination: This occurs when viruses within a patient exchange genetic material. The impact depends on the viruses’ divergence
  • Short generation times: Accelerate the rate of viral evolution, leading to extensive diversity

This diversity hinders the immune system’s ability to eradicate the virus and complicates the development of effective drugs and vaccines. The challenge is underscored by the fact that few candidate vaccines have reached phase III trials, and none have shown efficacy. This situation is attributed to HIV’s ability to mutate rapidly, creating a “moving target” that eludes current vaccine development efforts.

Recent technological advances, such as next-generation sequencing (NGS), have provided deeper insights into HIV’s evolution, revealing:

  • High mutation rates: HIV exhibits the highest biological mutation rate known, with significant interpatient genome-wide nucleotide substitution rates
  • Unique recombinant forms (URF) and circulating recombinant forms (CRF): Arise from recombination events, complicating the viral landscape

These insights emphasize the need for a nuanced understanding of HIV’s origins and evolutionary mechanisms. Such knowledge is crucial for the development of targeted vaccines and therapies, addressing misconceptions, and formulating effective strategies for HIV/AIDS control and eradication.

Conclusion

Tracing the complex journey from HIV’s origins in African primates to its current status as a global epidemic illuminates not only the virus’s adaptability and resilience, but also underscores the critical importance of scientific inquiry in understanding zoonotic diseases. The shared insights from decades of research have not only mapped the historical trajectory of HIV but also laid the groundwork for future strategies in prevention, treatment, and possibly eradication. This narrative, woven through the article, highlights our collective challenges and triumphs in facing one of the modern era’s most formidable health crises. It underscores the necessity of embracing both the historical context and the evolutionary biology of HIV to navigate the path ahead effectively.

As we reflect on the significance of understanding HIV’s origins and its epidemiological journey, it becomes evident that this knowledge is pivotal for the ongoing fight against the virus. The implications extend beyond the realm of public health, touching on aspects of human behavior, societal norms, and international cooperation. The evolution of HIV serves as a stark reminder of the interconnectedness of humans and the natural world, emphasizing the need for vigilance, continued research, and a globally coordinated response to infectious diseases. It is through such comprehensive understanding and collaboration that we can hope to curb the impact of HIV and prepare ourselves for future challenges that may arise from our ever-changing relationship with the natural world.

Sources

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