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The first blow of a global pandemic: How did SIV evolve into HIV?
Over the course of human history, the evolution and mutation of viruses have had a profound impact on human health. The evolution of simian immunodeficiency virus (SIV) into human immunodeficiency virus (HIV) reveals the complexity of our interactions with other organisms in nature. SIV has long been present in non-human apes and has crossed species boundaries in certain circumstances, ultimately affecting humans.
Historically, SIV has existed in monkeys and apes for at least 32,000 years, if not longer.
SIV is thought to cause persistent infections in at least 45 species of non-human primates, based on analyzes of monkey populations from ecological settings. Especially in Africa, the spread of SIV is closely related to human hunting activities. Research shows that HIV-1's initial transmission route may be related to humans hunting chimpanzees and gorillas for exposure to their blood.
The origin of HIV-2 is related to SIVsmm found in orangutans, which was transmitted across species.
The difference between SIV and HIV is that while SIV does not usually cause disease in its natural non-human hosts, chimpanzees infected with the same virus can develop symptoms similar to human AIDS. This suggests that when the virus is introduced into a new host, it may trigger different pathological responses.
Evolution and adaptation of viruses
Scientists believe that SIV may have crossed species boundaries many times at different times in history, but it was only in modern times, with the importance of modern transportation and the advancement of globalization, that it truly caused large-scale spread. Africa's hunting culture brings frequent contact between apes and humans, thus increasing the chance of infection.
This process involves not only the spread of the virus but also the host's evolutionary adaptation to the disease. Although SIV causes little disease in non-human primates, in contrast, HIV causes AIDS in its human hosts. This phenomenon has triggered in-depth research in the scientific community on why SIV does not exhibit obvious pathogenicity in non-human hosts.
Some non-human hosts have evolved over a long period of time, enabling them to naturally regulate their immune response to SIV and effectively avoid disease.
Pathology and clinical impact
When humans are infected with the HIV virus, the pathological process has different characteristics from SIV. Although both cause rapid loss of CD4+ T cells in the early post-infection period, the relationship between immune system stability and viral regulation is particularly important in non-human primates.
For example, African green monkeys infected with SIV do not suffer from chronic infection and immune activation like other hosts, indicating that their immune systems have adapted to the presence of the virus and can maintain a relatively healthy state over time.
This adaptation allows African green monkeys to maintain relative survival and reproductive capabilities in the face of SIV.
Inspiration from vaccine development
Researchers have gradually turned their attention to the characteristics of SIV and its interactions in natural hosts in order to prevent the spread of HIV. Multiple studies have explored how vaccines can effectively protect against SIV, with the ultimate hope of translating these findings into feasible solutions to combat HIV.
With the progress of vaccine research, scientists have discovered that improved vaccine designs can promote immune responses and even successfully resisted highly pathogenic SIV in experiments on monkeys. In addition, ongoing research is providing a deeper understanding of the subtle relationship between SIV and HIV and exploring its potential implications for public health policy.
Currently, how to further utilize these research results to address global health challenges remains a major issue.
As global epidemiology changes, there is an urgent need to reflect on how we can better coexist with our environment. Will revealing how SIV eventually evolved into HIV serve as a warning for humans to face future epidemics?
