If I were to describe a viral illness that infects people surreptitiously, lingers in their bodies for 10 years almost silently, is contagious throughout its silent years, and is uniformly fatal I would be describing a potential human extinction level pathogen. For the astute reader, it is obvious that what I am describing is the human immunodeficiency virus (HIV). For the reasons I enumerate below, I do not believe even this prolific killer has the capacity to cause and extinction level event.
A Snapshot of a Prolific Pathogen
When you look at HIV in terms of its global impact, it has a very impressive record. It has been the #1 infectious disease killer in the world, won major victories in every corner of the planet, made medical science turn on a dime to confront it, prompt society to explore sometimes taboo social mores, and elude—thus far—any and all attempts to cure or prevent it through vaccination, though one vaccine which reduced rates of acquisition by about 30% provides proof-of-concept that an efficacious vaccine may be possible.
But looking at its record in terms of the statistics and facts I just listed does not do this class A killer justice.
HIV as the Perfect “Form” of the Emerging Infectious Disease
When the infectious disease community discusses the need to better deal with emerging infectious diseases, exotic diseases like Hendra, Nipah, and chikungunya spring to mind. HIV is not one that makes the list in 2021. The general public, in many ways, views HIV as passé and a known quantity but, when looked at in the appropriate context, HIV is the emerging infectious disease par excellence, unequivocally demonstrates almost every attribute of this class of disease and dwarfs all other members of the category.
HIV is a zoonosis – an infection that originated in animals –that spilled into humans from other primate species: chimpanzees for HIV-1 and sootey mangabey monkeys for the less common HIV-2 strain. The precise manner in which this event occurred is something that is lost to history, but through genetic techniques it can be determined when and where this occurred.
Though HIV burst onto the infectious disease main stage in the early 1980s it was, like a small-town comedian, making important advances on second stages around the world since the early 20th century.
The way I explain HIV’s emergence is that it spilled into sentinel humans in Africa, such as bush meat hunters in Cameroon, but had a stultified spread. HIV was unable to make major inroads into the human population until aided and abetted by industrialization that allowed regular contact—especially sexual—between peoples in remote villages where HIV was present and burgeoning metropolitan cities. Even in this brief encapsulation of HIV’s emergence, the crucial actions needed to track emerging infectious diseases (the exotic infectious disease zebras as opposed to the ordinary horses whose hoofbeats we always hear when evaluating patients) become apparent. These include:
1. Understanding what infectious diseases are prevalent in animal species: Since almost all infectious diseases arise in animal species prior to infecting humans, it is important to know what is out there and will serve as the substrate for future human threats to health. Indeed, the entire “one health” movement, which seeks to meld human and veterinary health and epidemic intelligence, is devoted to this point. This is not a call for what was once derided as “viral stamp collecting” but a need to understand which minute proportion of the countless animal viruses that exist has the capacity to infect humans.
2. Monitoring sentinel populations: not every human has the same risk of acquiring novel infectious diseases. Just as not everyone skydives, not everyone hunts chimpanzees, works in an abattoir, goes spelunking, injects drugs, or works in a brothel. When an individual’s unique activities place them at the vanguard of what the human species does, they become the tip of the spear that first pokes into new microbial jungles. As such, these special populations are studied in detail in order to predict the next trend in microbial threats to humans as a whole.
3. The dynamics of social interaction can make or break a disease. If a disease is only present in an isolated society—say a remote village in the DRC—it may have little opportunity to spread beyond that population, especially if it is rapidly fatal and leaves little to no mechanism for widespread contagion to occur. However, if a contagious person has access to larger populations through buses, airplanes, trains, or crowded hospital waiting rooms, the microbe does too. This phenomenon is behind all the (mostly misguided) calls for travel bans, quarantines, vigilance at airports, and emphasis on travel history taking.
While HIV may be a staid representative of an established infectious disease and glossed over by those in the emerging infectious disease field, it can be viewed as, to use a Platonic metaphor, the “Form of the Emerging Infectious Disease” of which others are mere diluted versions.
Blood and Body Fluids
Generally speaking, if a microbe is spread through blood and body fluids it has a major problem it will always need to overcome: how to find easy access to new hosts. Unlike something that can spread through the air or through droplets in a sneeze, a virus like HIV requires close contact between individuals for transmission to occur because it is spread through blood and body fluids.
The ways in which humans exchange blood and body fluids are rather obvious: sexual intercourse, sharing of injection material, blood and blood product transfusions, breast-feeding, and in utero.
Again, the role of technological progress (i.e., blood transfusions) is something that viruses can exploit. HIV, with its long latent period, was able to contaminate blood banks before anyone even knew it existed. The latency period was also instrumental in allowing spread via the sexual route. Asymptomatic yet contagious vectors are a major boon for an ambitious infectious disease that is poised for world dominance.
Marginalized Populations
Who is first infected is almost as important how a person is infected. When the first victims of a disease are those that the world can empathize with, we are quicker to to action. When the first victims are far away, have special risk factors that are not seen as universal, or otherwise stigmatized, it may take longer for the world to notice and even longer for decisive action. All of this applied to the early years of HIV.
Though HIV was silently coursing through the African continent infecting many heterosexually, through birth, and through breast milk, it may have been hard to tease apart from the myriad other infectious diseases that perpetually plague those in non-industrialized settings. Indeed, there are early clues to HIV in African patient logs in certain areas in which mysterious opportunistic infections, a telltale sign of HIV-induced immune deficiency, were clustering.
The first descriptions of HIV occurred in men who had sex with men, injection drug users, Haitian immigrants, and hemophiliacs. Infectious diseases are taboo in many ways, even today, because of who they are thought to infect. When is the last time you say a hospital billboard advertising their infectious disease physician in a manner they do their dermatologists, surgeons, or oncologists? Any billboards that read “Got Hepatitis C, We Have Your Back?” in your hometown?
Such groups as those who doctors first diagnosed with HIV were not considered “mainstream” victims and therefore the outbreak response was slowed. This slowing did not affect all aspects of the management of the HIV pandemic and clearly does not characterize the rapid-fire discovery of the actual virus, the development of the test to diagnose it, and the elucidation of its transmission properties, all of which occurred in record time. The slowing was more of a general lassitude with which the general population and its leaders viewed the disease. Some of this is captured in the musical Rent. Yet, despite this general sentiment, HIV was subject to a travel ban by the United States until 2009.
HIV thrived on this neglect and even in the modern era, with our 5th generation HIV tests and robust anti-retroviral therapies can roar back when societal safeguards such as needle exchange for injection drug users are neglected. The 2015 Indiana HIV and hepatitis C outbreak is one powerful case to keep in mind in which then Governor Mike Pence had to be persuaded about the benefits of harm-reduction and clean needles.
Elusive Maneuvers
In the over 3 decades we have been actively battling this virus, the landscape has changed unrecognizable. HIV is no longer a death sentence, and a normal lifespan can be had if one is on treatment. HIV is a chronic infection that can be, in most cases, easily controlled with medication. Not only does treatment keep a person healthy, but one also becomes less contagious on treatment—treatment is prevention. Treatment can even render someone non-contagious, the U=Uparadigm (undetectable viral load means untransmittable virus sexually). There are even techniques that prevent people from acquiring HIV if they engage in behaviors that place them at risk, almost like pseudo-vaccines. Pre-exposure prophylaxis (PReP) — taking a daily antiviral pill or an injection every few months to prevent infection upon exposure — holds great promise, if implemented correctly, to changing how readily HIV can find new victims.
However, none of the above should be mistaken for a cure. There is currently no cure for HIV and no vaccine available. All attempts at a vaccine have fallen short and ingenious attempts to cure the infected with early treatment and other techniques have failed (save innovative and dangerous bone marrow transplants done for other reasons--the exception that proves the rule). Also, like any microbe, HIV can become drug-resistant if treatment is not judicious and these resistant strains can be transmitted rendering first line therapies ineffectual.
It Isn’t the One to Cause Human Extinction
With all the doom and gloom that is the HIV pandemic, it won’t be an extinction event for the human species for many reasons many of which I discuss above. Current treatment regimens, though not curative, are game-changers allowing a normal lifespan and even the ability for those with diagnosed HIV to give birth to uninfected children. A person with an undetectable viral load is unable to transmit the virus (U=U). Pre-exposure prophylaxis (PrEP) with antiretrovirals can prevent infection and long acting injectable antiretrovirals make treatment much simpler. In many important ways, becoming a diabetic is more life altering than becoming HIV positive (obviously one must ignore the social stigma in this calculation).
Human genetic variation also poses challenges for HIV as a proportion of the population is naturally resistant to infection. A specific human mutation (CCR5-Δ32), for which tantalizing hypotheses are devoted to, is present in a high enough frequency in certain areas of the world to provide a mechanism for the human race to survive HIV even if it were much more widespread. Ingenious physicians exploited the facts surrounding CCR5-Δ32 in the treatment of the Berlin Patient, Timothy Brown. His was the first of just a few durable cures of HIV to have been achieved and was accomplished via a bone marrow transplant for a concomitant leukemia containing the requisite mutation (though there is a hypothesis that a complication known as graft-versus host disease in which the transplanted bone marrow attack the recipient’s cells may be part of the actual curative process). Additionally, and even prior to the advent of therapies, mother to child transmission of the virus was never 100%.
While vaccine progress has been disappointing, there have been important advances. The most promising vaccine candidate today is the RV 144 vaccine (“The Thai vaccine”) that demonstrated a 31% protection rate in those vaccinated. While 31% isn’t perfect, it is substantial (compare it to the 2014-2015 23% efficacy of the seasonal influenza vaccine) and serves as the basis for newer vaccines.
HIV, like Ebola, is delimited in how it spreads. It is not measles. It requires close and intimate contact between individuals. Because of this limitation, behavior change is a key means to prevent infection. Countermeasures as simple as condoms, clean needles, limiting sexual partners—especially concurrent ones—and, in certain contexts, male circumcision (before sexual debut) can significantly make inroads into HIV’s spread.