THE INTIMATE SPECIES
On February 2, 1921, Englishman Arthur Evelyn Liardet went into surgery. Liardet’s
symptoms were typical, but the surgery was not. At the time of the operation,
Liardet was seventy-five years old and complained of decreases in his physical and
mental energy. He had lost most of his hair and had developed wrinkle lines on his
face. In short, he was growing old.
Some years before that chilly day in 1921, Liardet had written to an up-and-
com-ing Russian surgeon practicing in Paris and offered his body for a unique
procedure. The surgeon, Serge Voronoff, claimed to offer nothing other than total
bodily rejuvenation—the elixir of life.
Serge Abrahamovitch Voronoff was born in Russia in 1866. At the age of eigh-
teen, he immigrated to France, where he studied medicine under the Nobel lau-
reate Alexis Carrel. Carrel had won his Nobel Prize in 1912 for surgical work on
blood vessels as well as the new methods of transplantation of both blood vessels
and whole organs. Carrel taught Voronoff surgery, undoubtedly impressing upon
him the excitement of science and the potential for discovery, particularly sur-
rounding the revolutionary new techniques of organ transplantation. In doing so,
he launched the career of the young, ambitious, six-foot-four Voronoff, described
in reports as magnetic and imaginative.
Following his studies with Carrel, Voronoff worked in Egypt for the Egyptian
king. Voronoff soon became fascinated with the eunuchs that were part of the
king’s harem. In particular, he noted that the castration they received seemed to in-
crease the speed at which the eunuchs aged. This observation was the beginning of
Voronoff’s obsession with a surgical answer to aging. Likely inspired by the pio-
neering work of his mentor and the excitement of the new surgical techniques,
Voronoff began to dabble in experimental transplantation. But he went beyond the
techniques that his mentor had perfected. In early experiments Voronoff trans-
planted the testicles of a lamb into an old ram, claiming that the transplant served
to thicken the ram’s wool and increase its sex drive. These early studies fore-
shadowed the work that would follow.
Some years later, on that cold February day in Paris, Liardet became one of
Voronoff’s early human experiments. Before Liardet was wheeled into the operating
room, a chimpanzee had been anesthetized using a specialized “anesthetizing box”
developed by Voronoff. The box served to protect the technicians from the massive
and potentially violent male chimpanzees, who would have certainly reacted
strongly to what was coming. Then Liardet was wheeled in on a gurney and placed
alongside the chimpanzee. The surgeons carefully removed a testicle from the
chimpanzee, cut it into thin slices, and grafted pieces onto the testes of Liardet.
The procedure, known in its day as the monkey gland operation, would go on to
become remarkably popular. By 1923 forty-three men had received testicles from
nonhuman primates, and by the end of Voronoff’s career, that number reached the
thousands. Although Voronoff had inherited a fortune as an heir to a vodka man-
ufacturer, he made more money operating on many of the most important men of
his day. Unverified but highly specific accounts point to Anatole France, a Nobel
Prize–winning French poet as one of his patients. Less reliable rumors suggest
Pablo Picasso might also have gone under Voronoff’s knife.
But to what end? Many of Voronoff’s patients swore by the procedure. Liardet
himself claimed to a New York Times reporter in 1922 that the procedure had been
a huge success. He showed the reporter his strong biceps while his wife nodded
knowingly by his side. Though the successes claimed by Voronoff and his patients
were certainly exaggerated, the underlying logic of the procedures remains open to
at least some scientific debate. Voronoff himself, as well as his procedure, even-
tually fell out of favor with the scientific community. By the time of his death in the
early 1950s, most considered him a quack, perhaps in part because of the extremes
to which he went. In the most dramatic of his experiments, he transplanted ovaries
from a human woman into a female chimpanzee named Nora. He then attempted
to inseminate her using human sperm!¹ Yet a 1991 editorial on Voronoff in the top
British medical journal The Lancet concludes with the following words: “Maybe
medical research councils should fund further research on monkey glands.”
For our purposes, the utility of the chimpanzee testicle transplants as the Viagra of
the roaring twenties, while interesting, is largely unimportant. What’s important
about the infamous monkey gland operation is that it provides one of the most
striking examples of how medical technologies have incidentally served to link hu-
mans (and sometimes animals) in ways that create new bridges for the movement
of microbes.
Given what we now know, the idea that we would consciously connect the
microbial worlds of humans and chimpanzees as Voronoff did would be unfath-
omable and unforgivable. Although there’s no straightforward way to confirm it in
the absence of specimens, Voronoff’s transplants almost certainly led to the trans-
mission of potentially dangerous viruses into humans who received these tissues.
Transplanting living tissue between very closely related animals eliminates all of
the natural “barriers to entry” that microbes face, and remains one of the riskiest
imaginable ways for a microbe to jump from one species to the next.
Yet Voronoff’s work, while certainly extreme, did not exist in a vacuum. The
explosion of medical technologies that has occurred over the past four hundred
years has provided new kinds of microbial connections between individuals. Trans-
fusion, transplantation, and injection, while some of the most critical tools for
maintaining human health, have also contributed fundamentally to the trans-
mission and emergence of pandemics. These technologies have connected us with
one another’s blood, organs, and other tissues in ways unprecedented in the his-
tory of life on our planet. They have served to make us, among other things, the
intimate species.
Before we dissect the role of medical technology in connecting our bodies and fa-
cilitating microbial transmission, it’s worth spending a moment to discuss this in
the context of the benefits of these technologies. Injections and immunizations as
well as transfusions and transplants are all technologies that have catapulted
medicine into the modern age.
Without blood transfusions, huge numbers of hemophiliacs, trauma victims,
and wounded soldiers would die. Transplants permit victims of leukemia, hepatitis,
and severe burns to live a normal life. And it is nearly impossible to imagine a
world without injections. The use of intravenous rehydrating fluids alone saves the
lives of millions of malnourished children and victims of diarrheal disease each
and every year. Injections also permit immunization, and to live in a world without
immunizations is to live in a world where smallpox threatens our day-to-day lives.
If smallpox had not been eliminated by immunization in the 1960s, it would prob-
ably be a worse plague today than it was then due to the same sort of hypercon-
nectivity discussed in chapter 6.
Examining the role that these medical technologies have played in the history of
epidemics does not argue against their utility in maintaining the health of our
species. Likewise, these arguments should not be interpreted as supporting the
hypochondriacal fears of the anti-immunizationists, whose rhetoric has been
soundly skewered in Michael Specter’s important book, Denialism, which brings to
a general audience years of research on the subject. Nevertheless, understanding
the ways in which the historical use of these technologies has connected human
populations is important in understanding why we are plagued with pandemics.
Rather than discourage us from using live-saving technologies, they serve to high-
light the need for maintaining vigilance in the way that we deploy them.
One of the clearest examples of how medical technology increases human micro-
bial interconnectivity is our use of blood. Historically, humans (and other animals)
rarely come into contact with one another’s blood. For the vast majority of our his-
tory since the advent of hunting, we’ve had more contact with the blood and body
fluids of other animals, through hunting and butchering. In the fifteenth century,
that would all change.
The first generally accepted attempt at a “blood transfusion” was given to Pope
Innocent VIII in 1492 and was described by the historian Stefano Infessura.² When
the pope went into a coma, the pontiff’s medical advisers sought to cure him by
feeding him the blood of three ten-year-old boys. At the time, there were no intra-
venous techniques, and both the pope along with the three donors, who had been
promised a ducat each, all died.³
Blood transfusions have advanced considerably since then. Today around
eighty million units of blood are collected every year worldwide. Blood transfusions
save countless lives. They also provide an entirely new form of connection between
human populations. When a unit of blood is transfused from individual to indi-
vidual, so too are the various viruses and other microbes present in that unit. The
proliferation of blood transfusions creates a novel route for the movement of mi-
crobes, sometimes providing a new route for microbes that already move in other
ways, as in the case of malaria. New connections made through medical tech-
nology can also provide transmission routes for agents that would otherwise never
have the potential to spread among humans and can be another way in which an
agent that we acquire from an animal can spread; otherwise, it might simply go ex-
tinct.
Blood transfusions are known to spread HIV and other retroviruses, as well as
hepatitis B and C, parasites such as malaria, and Chagas disease. Even prions like
variant Creutzfeld-Jakob (also known as mad cow disease), an infectious agent to
which we’ll return in the next chapter, can survive in blood bags, the plastic con-
tainers used to hold blood prior to transfusion.
The field of blood products has also advanced beyond single blood trans-
fusions that go from one person to the next. In the case of hemophiliacs, indi-
viduals lack particular blood factors that would normally allow their blood to clot, a
potentially life-threatening condition. In order to accumulate the missing blood fac-
tors in sufficient quantities to solve the problem, the appropriate components of
blood are often pooled from tens of thousands of donors. The consequences for
connectivity are substantial. A back-of-the-envelope calculation suggests that a per-
son living with hemophilia A in a city like San Francisco will inject themselves with
up to 7,500 doses of clotting factor VIII by the time that they’re sixty. That means
that this person will potentially have had contact with the blood-borne microbes of
2.5 million people during the course of their lifetime.
The good news is that many blood banks now screen for the usual suspects.
Blood infected with HIV, for example, will not get through the donation process.⁴
But this was not always the case. Perhaps not surprisingly, hemophiliacs who re-
ceive pooled blood products were among the first found to be infected with HIV in
the early 1980s. In the United States alone, thousands of hemophiliacs were in-
fected, and many of them died. Even now we can only screen for the microbes we
know. Undiscovered viruses, of which there are certainly many, move around daily
through blood products. And a new virus that entered into humans could easily
spread within the blood supply before we’d have a chance to stop it.
In terms of sheer number of procedures, blood transfusions trump organ trans-
plants by far. But while the number of blood transfusions will always be greater
than the number of organ transplants, the movement of an organ is a substantially
more dramatic biological event. Organ transplantation involves the movement of
blood as well as a large amount of tissue, so any microbes present in the blood or
the tissue being transplanted will move along with the organ into the recipient.
Organ donation risks the movement of all of the same usual suspects that will
transmit during a blood transfusion and then some. For example, in the case of ra-
bies, discussed in detail in chapter 5, I told you that rabies didn’t transmit from
human to human. To be slightly more exact, there have been no documented cases
of natural transmission of rabies from human to human. There have, however,
been a dozen or so well-documented cases of rabies moving from one person to
another. And every one of them has been due to a transplant with an infected
organ.
The majority of these cases of rabies transmission have been due to cornea
transplants, perhaps because the cornea is one of the only nervous system-related
tissues currently transplanted; and rabies is primarily a virus of the central nervous
system. In two fascinating cases, separate recipients from Texas and Germany re-
ceived organs infected with rabies. In both cases the deaths of the donors were
falsely attributed to drug overdoses, whose symptoms can sometimes mimic those
of rabies. Amazingly, both donors appeared to have died of fulminant rabies with-
out seeking medical care. It’s frightening to imagine that they reached that point in
the illness while moving about, conducting their normal day-to-day affairs.
Transplants can also transmit dormant stages of infectious diseases that can
flare up later. One particular species of malaria, Plasmodium vivax, whose Siberian
variant we discussed in chapter 1, has the capacity to stay latent, or dormant, in the
liver. During latency, there are no symptoms of the disease and, similarly, no
malaria parasites in the blood. But a liver transplant could potentially do the trick.
In one case in Germany, a twenty-year-old male who had emigrated from
Cameroon died of a brain hemorrhage and donated his organs. Among the recip-
ients was a sixty-two-year-old woman who needed the liver because of late-stage
cirrhosis. A full month after her organ transplant she developed a high-grade fever,
which was later diagnosed as vivax malaria and successfully treated. She had never
visited a tropical or subtropical area in her lifetime. But her liver had.
There’s another important rub to the problem of organ transplantation. While ob-
taining blood from donors is pretty simple, obtaining an organ is not. Rarely will
people living in the developed world who need a blood transfusion not get one, but
that is not the case with organ transplants. Currently in the United States there are
approximately 110,000 people on the waiting list to receive organ transplants, and
one of these people dies every ninety minutes.
The lack of organs available for transplant has caused surgeons to look for alter-
natives to human organs. Animals are an obvious choice. Clearly, the elective
transplantation of thousands of chimpanzee testicles into men for the purposes of
“rejuvenation” presents unacceptable risks. The real chance that a known or un-
known virus could enter into humans from such a closely related animal as a chim-
panzee would make the choice wrong even if the illness were life-threatening. But
there are other animals out there. For example, the organs of an adult pig are ap-
proximately the size and weight of an adult human’s, and while not without risk for
cross-species jumps, the risks are smaller than those for a chimpanzee.
In July 2007, Joe Tector, a pioneering transplant surgeon at Indiana University
School of Medicine, gave me a call. Tector had put together a team whose goal was
to genetically engineer pigs with organs that would be less likely to be rejected by
humans, a problem for surgeons to this day. Within five years he wanted to begin
transplanting pig livers into humans, and he wanted to understand the risks.
He explained that he didn’t want a rubber stamp scientist to simply tell him that
what he was doing was safe. He was looking for someone who loved finding new
viruses and was intent on discovering any possible risk associated with the work
he was doing. He spoke eloquently about his patients and how many of the people
on those waiting lists never received organs in time. He also spoke about the need
to determine that what he planned to do wouldn’t backfire, igniting a new pan-
demic in the human species. When Tector contacted me, I had already been inter-
ested for some years in xenotransplantation, the surgical term for the transplan-
tation of organs from one species to another. By the time I got off the phone, I was
hooked.
In the 1920s, following the time that Voronoff conducted his work in Paris, the
field of xenotransplantation went into a forty-year lull during which there were no
documented attempts. But in the 1960s work on xenotransplantation had a rebirth.
New antibiotics and immunosuppressive drugs provided hope for the success of
transplanting major animal organs into people who needed them. By dampening
the immune system, the immunosuppressive drugs could address the frustration
of organ rejection.
A series of high-profile operations brought major attention to the field through
the 1980s. One involved the famous Baby Fae, a twelve-day-old baby girl born
prematurely with a major heart disorder. She survived for eleven days on a baboon
heart. Another operation created a news flurry around Jeff Getty, a thirty-eight-
year-old man with AIDS. Getty received his diagnosis at a time when AIDS was still
called “gay cancer.” He went on to become a prominent activist who pushed for
access to care for AIDS patients and participated in numerous experimental trials,
including the one that led to his national notoriety. In the trial, he received a bone
marrow transfusion from a baboon with the hope that the natural resistance that
baboons have to AIDS would take hold in his body.
Getty’s experimental therapy ultimately failed, but it brought with it a national
debate about the potential that such transplants could transmit new and perhaps
unknown viruses to humans. Certainly, a transplant from a closely related species
like a baboon to a person with an already compromised immune system could be a
recipe for disaster. A person with a highly weakened immune system, as occurs in
late stages of AIDS, would provide an environment in which new viruses could bet-
ter grow and adapt.⁵ In the extreme, it could be a Petri dish for viral exploration into
a new and foreign land.
Fortunately for the success of Tector’s work, pigs are not as closely related to
humans as baboons are. Yet they are still mammals. As with other mammals (in-
cluding ourselves), they have many microbes that are still unknown. And some of
them undoubtedly have the potential to jump species. The real question then be-
comes what are the viruses that can jump and can they then spread from person to
person. The fact that one person might get a deadly virus is not the end of the
world, particularly if the person was about to die of liver failure. The real risk is if
that virus could spread.
In the small but active group that concern themselves with pig viruses, the
agent that has provoked the most worry is PERV, the porcine endogenous retro-
virus. Endogenous viruses like PERV are permanently integrated into the genetic
material of their hosts. Yet from time to time they emerge from the genes and go
on to infect cells and spread within the host’s body. As part of the actual genomes
of their hosts, endogenous viruses cannot currently be eliminated—hence the con-
cern that they could reemerge in humans following a pig transplant.
The eminent CDC virologist Bill Switzer, whom I’ve worked closely with for the
last ten years studying retroviruses, was one of the scientists to conduct the most
comprehensive study on PERV in xenotransplant recipients. Bill and his colleagues
studied specimens from 160 patients who had received pig tissues. Amazingly,
they found evidence of pig cells continuing to live in about 15 percent of the recip-
ients, even up to eight years after the transplant. Fortunately, they found no evi-
dence of PERV.
Whether PERV is the most important risk or not remains unknown. If it is, we
may not have much to worry about. Through our studies with Tector and other col-
leagues, we hope to determine what else may be in those pig tissues and what risks
those agents would pose. The decisions based on our research will not be easy
ones. As we’ll discuss further in chapter 9, even state of the art viral discovery right
now does not permit us to definitively determine all of the microbes in any sample.
Yet the costs of indecision are substantial. On one side are the transplant recip-
ients who die each day waiting for an organ. On the other is a small but important
risk of an epidemic in a much larger group. Is one life saved worth a species poten-
tially plagued?
We’ve been sticking ourselves with needles for a long time. The first evidence of it
comes from an unusual source—an iceman. On a sunny day in September 1991,
two German tourists hiking in the Italian Alps came across a corpse. The corpse
became known as Ötzi, after the valley in which he was discovered. Though initially
thought to have died recently, we now know that Ötzi lived 5,300 years ago.
Among the amazing elements of this discovery is the fact that Ötzi had tattoos.
In fact, this is the first evidence of tattoos in the world. Ötzi’s tattoos were located
on his lower back, ankles, and knee. X-rays of the mummy showed evidence that
the tattoos were positioned over spots where Ötzi had likely experienced pain due
to orthopedic maladies, leading some to speculate that the tattoos may have
served as a kind of therapy.
Whatever his reasons for having them, Ötzi’s tattoos, like any tattoo since,
represent risks. Tattooing, like a needle stick or an injection, involves blood con-
tact. And if the same implement is used multiple times on different individuals, it
can provide a bridge on which microbes can hop hosts.
Whether for tattoos, medicines, or vaccines, improperly sterilized needles can
play an important role in transmitting microbes. Widespread use of needles, as
with blood transfusions, provides an entirely novel route for microbes to move
around, allowing them to maintain themselves or spread effectively in humans in
order to survive and thrive.
Perhaps the most remarkable microbe we know of in the postinjection age is hep-
atitis C virus. HCV is a critically important virus that infects over one hundred mil-
lion people globally and more than three million new individuals each year. It also
kills through liver cancer and cirrhosis, causing over eight thousand deaths per
year in the United States alone. But it would likely kill precious few of those indi-
viduals if it weren’t for needles.
There is still a great deal that’s unknown about HCV. The virus itself was offi-
cially discovered in 1989, but it must have been in human populations for much
longer. My collaborator, the prolific Oxford virologist Oliver Pybus, has made
understanding this virus one of his many scientific objectives. Pybus utilizes the
tools of evolutionary biology and learns more each year about viruses through
computers than many others will in a lifetime of lab- or fieldwork. By using com-
puter algorithms to compare genetic information from distinct viruses as well as
mathematical modeling, Pybus has made some fascinating discoveries about HCV.
What we do know about HCV is that it’s on the move. During the past hundred
years, the virus has spread rapidly through blood transfusions, the use of unster-
ilized needles to deliver medicines, and through injection drug use. But genetic
analyses by Pybus and others have shown that the virus is somewhere between five
hundred and two thousand years old, so these contemporary technologies likely do
not tell the whole story. Essentially, it seems there were places, most likely in Africa
and Asia, where HCV existed on a much smaller scale prior to the massive expan-
sion that needles and injections permitted.
Since HCV is not effectively transmitted sexually or by normal contact between
people, other routes of transmission must somehow explain how it persisted many
centuries ago. The virus can be transmitted from mother to offspring, but that too
is an unlikely explanation since so-called vertical transmission is not particularly
efficient. Certainly, cultural practices like circumcision, tattooing, ritual scarifi-
cation, and acupuncture probably played a role. In an interesting twist, Pybus and
his colleagues have used a combination of geographic information systems (to
which we’ll return in chapter 10) and mathematical models of disease spread to
show that another possibility would be some kinds of blood-feeding insects. These
insects could have contributed to historical transmission by acting as natural con-
taminated needle sticks and carrying virus-infected blood from one host to the next
on their mouthparts.
Unsafe injection practices contributed to the spread of much more than HCV in
the twentieth century. In a series of thoughtful articles, the Tulane virologist Pre-
ston Marx and his colleagues have argued that injections helped launch the HIV
pandemic. Some mysteries still persist on the early spread of HIV. While the ge-
netic data points to an early twentieth-century jump of the chimpanzee virus that
would become HIV, understanding what sparked its true global spread in the
1960s and 1970s remains up for debate. For many scientists, the expanding air
routes discussed in chapter 6 are sufficient to explain this phenomenon. But Marx
and his colleagues add another potential cause.
The period that coincides with the global spread of HIV also coincided with a
dramatic expansion in the availability of cheap injection systems. Prior to the
1950s, syringes were handmade and relatively expensive. But in 1950 machines
began churning out glass and metal syringes, and in the 1960s disposable plastic
syringes became available. Effective ways to inject drugs and vaccines contributed
to the increased use of injections for medications and vaccines in the late nine-
teenth century. Often medical campaigns used the same unsterilized needle to
vaccinate hundreds or more individuals at a time, setting up unique conditions that
could potentially launch epidemics.⁶ An individual hunter who had been infected
with a virus from a hunted chimpanzee could theoretically transmit that virus to
many other individuals in just this way, the conditions under which Marx and his
colleagues think that the global launch of HIV began in earnest.
It’s important to note that Marx’s work is distinct from the oral polio vaccine hy-
pothesis for HIV origins that appeared first in a Rolling Stone article in 1992. Marx
and his colleagues suggest that unsafe injection practices helped to spread HIV;
they do not, however, argue that these techniques contributed to its introduction
from chimpanzees to humans. Alternately, the OPV hypothesis argued that since
oral polio vaccine was grown on fresh primate tissues HIV jumped directly from
such tissues to vaccines and spread as they were administered.
The OPV hypothesis is no longer taken seriously by the scientific community for
four primary reasons: (1) retrospective analysis of the original vaccine stocks
showed no evidence they were infected by the chimpanzee virus that seeded
human HIV; (2) genetic analyses suggest HIV has been around for roughly one
hundred years, far predating the period of OPV use; (3) the chimpanzee strains in
the region where the purportedly contaminated vaccine stocks were produced are
distinct from the chimpanzee virus that seeded HIV; (4) the pervasive human
exposure to these viruses through hunting and butchering of wild primates pro-
vides a more parsimonious explanation for the distribution of the multiple primate
viruses in the HIV family that have crossed into humans.
Further highlighting the end to the OPV debate in 2001, four separate articles
published in the leading scientific journals Nature and Science laid it to rest. Doing
so was important for a number of reasons, including the fact that the hypothesis
was misinterpreted in a way that severely compromised ongoing vaccine
campaigns, which use vaccines that are universally acknowledged as both safe and
effective. An accompanying editorial to the Nature articles sums it up well: “The
new data may not convince the hardened conspiracy theorist who thinks that con-
tamination of OPV by chimpanzee virus was subsequently and deliberately covered
up. But those of us who were formerly willing to give some credence to the OPV
hypothesis will now consider that the matter has been laid to rest.” More blunt
were the words of my colleague Eddie Holmes, one of the world’s most distin-
guished virologists, who said, “[The] evidence was always flimsy, and now it’s
untenable. It’s time to move on.”
While unsafe injections may very well have contributed to HIV’s spread, as they
did with HCV, they did not lead to its introduction. This, however, doesn’t mean
that we should ignore vaccine safety.
Right now around one in fifteen individuals reading this book are infected with a
virus that jumped into them from a monkey. To be more specific, if you’re one of
these individuals, you’re infected with SV40, a virus of Asian macaques, and you
acquired it from a contaminated vaccine.
During the 1950s and 1960s, poliovirus vaccines were grown on cell cultures
derived from macaque kidneys. Some of these kidneys were infected with SV40,
which then contaminated the vaccines. The results were dramatic.
In the United States alone, up to 30 percent of the poliovirus vaccines in 1960
were contaminated with the virus. From 1955 through 1963, roughly 90 percent of
American children and 60 percent of American adults were potentially exposed to
SV40—an estimated ninety-eight million people. And the virus is not a trivial one.
It causes cancer in rodents and can make human cells living in laboratory cell cul-
ture reproduce abnormally, a worrying sign that they may have the potential to
cause cancer.
The idea that more than half of the American population was placed at risk from
infection with a novel monkey virus had a notable effect on science, and epidemi-
ologists scrambled to determine if the individuals who’d received the virus had
cancer. Fortunately, while the evidence is still debated to this day, it appears clear
that SV40 did not pose a serious risk for cancer and, perhaps even more impor-
tantly, it didn’t have the potential to spread. We dodged a major bullet.
But because a single vaccine stock can be administered to thousands of indi-
viduals, we must remain vigilant. Contamination of a vaccine stock or multiple vac-
cine stocks can contribute to millions of infections with new viruses, just as we
witnessed in the 1950s and 1960s with SV40. This does not mean that vaccines are
not safe. They are! And they are essential to protect billions of people all over the
globe. Health monitoring and vigilance in vaccine production has also never been
greater. In a recent and important study, my collaborator Eric Delwart, a San Fran-
cisco–based scientist who perfects techniques to discover unknown viruses,
showed that some of these new approaches, which we’ll discuss in chapter 10, can
be applied to even further increase the safety of vaccines. The risks associated with
current vaccines are substantively less than the risks associated with the diseases
they protect against. Yet the risks are not zero. We must make sure that when we
knowingly connect animal and human tissues—particularly on an industrial
scale—we do so with the utmost care.
Since the 1920s when Voronoff conducted his monkey gland operations, our
planet has witnessed an explosion in the use of transfusions, transplants, and
injections. These wonderful technologies have helped rid us of some of our dead-
liest diseases. Yet they have also provided powerful new biological connections be-
tween individuals, which sometimes serve as an unwelcome by-product of these
beneficial tools. They provide bridges on which microbes can move, bridges that
did not exist until now. They pull humans together into a completely new kind of
intimate species, one unique to life on our planet and one that fundamentally
changes our relationship with the microbes in our world.
