63 Historical Context

Zoonoses are a global problem. What occurs in one country can have a serious impact on the health of populations across the globe. Because of this, it is important that we understand the effects of zoonotic disease at local, national, and global levels, and ensure that we are able to develop interventions that allow collaboration between each of these contexts. AIDS (acquired immunodeficiency syndrome) is one of the best examples of a truly global zoonosis. We will begin by diving into the origins of the AIDS epidemic, how it has been addressed, and how it can serve as a model for what to do – and what not to do – when dealing with zoonotic disease. (NC)

In 1981, reports of young men in Los Angeles infected with Pneumocystis pneumonia began to capture the attention of doctors. This infection is common in individuals with weakened immune systems and very uncharacteristic of the male population that was reporting symptoms of pneumonia. Around the same time, clusters of men in New York City and San Francisco presented with Kaposi’s sarcoma, a cancer causing characteristic blotches on the skin of infected individuals. Interestingly, this disease is also common in individuals with compromised immune systems. All of these populations had something in common – they were men who had sex with men (MSM). This gave researchers an early hypothesis for how the disease was spread and who likely carrier populations would be. Soon after reports of these unusual infections, researchers identified human immunodeficiency virus (HIV) as the cause of the compromised immune systems exhibited by patients (Hidalgo et. al., 2000). (NC)

HIV-1 and HIV-2, the two main viral forms of HIV, have both been traced to primate populations in Africa. They are the result of viral mutations allowing a crossover event (trans-species transmission) that transmitted simian immunodeficiency virus (SIV) to human populations. HIV-1 has been found in virtually every country on the globe, and likely originated in chimpanzees in West-central Africa (Sharp and Han, 2011). Since HIV is known to spread through contact with infected fluids at mucous membranes, it is likely that a similar pathway allowed HIV to spread from chimpanzees to humans (WHO 2023). (NC)

The most common exposure to primate bodily fluids occurs in the context of bushmeat hunting (Sharp and Han, 2011). This practice involves the hunting and consumption of wild

animals. Although illegal or restricted in many parts of Africa, it can be difficult to enforce punishments on hunters. Additionally, for many Africans, bushmeat is an important part of life – hunters can sell their goods at markets to make a living, people can save money by hunting on their own instead of purchasing farmed foods, and individuals can connect with their cultural roots through traditional dishes (Tan 2020). (NC)

Bushmeat hunting and consumption slowed during the Ebola crisis in West Africa. Governments were able to successfully ban the consumption of wildlife and send a message to the public that engaging in those behaviors increased the risk of contracting Ebola. However, once the crisis was over, the prevalence of bushmeat consumption began to rise again (Tan 2020). This example demonstrates the difficulty of getting entire cultures to change their habits, even at the risk of severe disease. At least five instances of HIV-1 transmission from primates to humans have been identified, exemplifying the consequences that failure to communicate risk to the public can have (Sharp and Han, 2011). (NC)

HIV-1 subtype B is the major viral form present in European and American populations. Using preserved tissue samples and viral genome sequencing, scientists have been able to trace this subtype to a single African strain that spread to Haiti in the 1960s, and then onward to other Western countries, where it was finally detected in MSM populations (Sharp and Han, 2011). Over the course of the global HIV epidemic, 88.4 million individuals have been infected with HIV and 42.3 million have died from the virus or complications related to their immunodeficiency (WHO, 2023). (NC)

These high rates of infection have occurred in spite of scientific efforts to develop cures for the disease. Zidovudine, one of the earliest drugs developed to treat HIV, was effective until mutations in the virus allowed it to become resistant to treatment. HIV is a retrovirus – it contains an RNA genome that is synthesized into DNA in its host, and is then inserted into the genome (Hidalgo et. al., 2000). This process requires reverse transcriptase, an error-prone enzyme that converts the viral RNA into DNA. Its low fidelity, when combined with the short generation time of viruses, allows HIV-1 to evolve 1 million times faster than human DNA (Sharp and Han, 2011). This makes it incredibly challenging to develop a treatment for the virus that works in the long term. By 1996, scientists developed highly active antiretroviral combination therapy (HAART), a cocktail of protease inhibitors, reverse transcriptase inhibitors, and a double nucleoside backbone that works to prevent the replication of the HIV virus (Yeni, 2006). The use of HAART treatments caused the death rate of HIV patients to fall by 50-80% in just ten years. HIV is no longer a universally fatal catastrophic illness. In most cases, it is a manageable chronic illness (Delaney, 2006). Use of these drugs can reduce the viral load in HIV-positive patients, allowing increases in the number of CD4+ immune cells and limiting the ability to transmit infections to other individuals (Hidalgo et. al., 2000). Thus, the use of HAART treatments has had incredible effects on reducing the spread of HIV and improving the lives of those who are carriers. The U=U (undetectable=untransmittable) campaign has been instrumental in promoting the use of HAART and increasing the general population’s access to these drugs (Minnesota Department of Health, 2022). (NC)

Despite advanced treatments being available to reduce the spread of HIV, it still has high prevalence across the globe. The infection is very unevenly distributed, with many infected individuals living in low-income communities and developing countries around the world. As of 2023, 39.9 million people around the world live with HIV and almost two-thirds of that population is living in Africa (WHO 2023). (NC)