Spillover: Animal Infections and the Next Human Pandemic (48 page)

Other evidence hinted that it might be a retrovirus. This was new ground, but then so was AIDS. The only known human retrovirus as of early 1981 was something called human T-cell leukemia virus (HTLV), recently discovered under the leadership of a smart, outgoing, highly regarded, and highly ambitious researcher named Robert Gallo, whose Laboratory of Tumor Cell Biology was part of the National Cancer Institute in Bethesda, Maryland. HTLV, as its name implies, attacks T cells and can turn them cancerous. T cells are one of the three major types of lymphocyte of the immune system. (Later the acronym HTLV was recast to mean human T-lymphotropic virus, which is slightly more accurate.) A related retrovirus, feline leukemia virus, causes immune deficiency in cats. So a suspicion arose among cancer-virus researchers that the AIDS agent, destroying human immune systems by attacking their lymphocytes (in particular, a subcategory of T cells known as T-helper cells), might likewise be a retrovirus. Montagnier’s group began looking for it.

Gallo’s lab did too. And those two weren’t alone. Other scientists at other laboratories around the world recognized that finding the cause of AIDS was the hottest, the most urgent, and potentially the most rewarding quest in medical research. By late spring of 1983, three teams working independently had each isolated a candidate virus, and in the May 20 issue of
Science
, two of those teams published announcements. Montagnier’s group in Paris, screening cells from a thirty-three-year-old homosexual man who’d been suffering from lymphadenopathy (swollen lymph nodes), had found a new retrovirus, which they called LAV (for lymphadenopathy virus). Gallo’s group came up with a new virus also, one that Gallo took for a close relative of the human T-cell leukemia viruses (by now there was a second, called HTLV-II, and the first had become HTLV-I) that he and his people had discovered. He called this newest bug HTLV-III, nesting it proprietarily into his menagerie. The French LAV and the Gallo HTLVs had at least one thing in common: They were indeed retroviruses. But within that family exists some rich and important diversity. An editorial in the same issue of
Science
trumpeted the Gallo and Montagnier papers with a misleading headline:
HUMAN T-CELL LEUKEMIA VIRUS LINKED TO AIDS,
despite the fact that Montagnier’s LAV was
not
a human T-cell leukemia virus. Woops, mistaken identity. Montagnier knew better, but his
Science
paper seemed to blur the distinction, and the
editorial occluded it entirely.

Then again, neither was Gallo’s “HTLV-III” an HTLV, once it had been clearly seen and correctly classified. It turned out to be something nearly identical to Montagnier’s LAV, of which Montagnier had given him a frozen sample. Montagnier had personally delivered that sample, carrying it on dry ice during a visit to Bethesda.

Confusion was thus sown early—confusion about what exactly had been discovered, who had discovered it, and when. That confusion, irrigated with competitive zeal, fertilized with accusation and denial, would grow rife for decades. There would be lawsuits. There would be fights over royalties from the patent on an AIDS blood-screening test that derived from virus grown in Gallo’s lab but traceable to Montagnier’s original isolate. (Contamination from one experiment to another, or from one batch of samples to another, is a familiar problem in lab work with viruses.) It wasn’t a petty squabble. It was a big squabble, in which pettiness played no small part. What was ultimately at stake, besides money and ego and national pride, was not just advancing or retarding research toward an AIDS cure or vaccine but also the Nobel Prize in medicine, which eventually went to Luc Montagnier and his chief collaborator, Françoise Barré-Sinoussi.

Meanwhile the third team of researchers, led quietly by a man named Jay A. Levy in his lab at the University of California School of Medicine, in San Francisco, also found a candidate virus in 1983 but didn’t publish
until more than a year afterward. By summer of 1984, Levy noted, AIDS had affected “
more than 4000 individuals in the world
; in San Francisco, over 600 cases have been reported.” Those numbers sounded alarmingly high at the time, though in retrospect, compared with 30 million deaths, they seem poignantly low. Levy’s discovery was also a retrovirus. His group detected it in twenty-two AIDS patients and grew more than a half dozen isolates. Because the bug was an AIDS-associated retrovirus, Levy called it ARV. He suspected, correctly, that his ARV and Montagnier’s LAV were simply variant samples of the same evolving virus. They were very similar but not
too
similar. “
Our data cannot reflect a contamination
of our cultures with LAV,” he wrote, “since the original French isolate was never received in our laboratory.” Harmless as that may sound, it was an implicit jab at Robert Gallo.

The details of this story, the near-simultaneous triple discovery and its aftermath, are intricate and contentious and seamy and technical, like a ratatouille of molecular biology and personal politics left out in the sun to ferment. They lead far afield from the subject of zoonotic disease. For our purposes here, the essential point is that a virus discovered in the early 1980s, in three different places under three different names, became persuasively implicated as the causal agent of AIDS. A distinguished committee of retrovirologists settled the naming issue in 1986. They decreed that the thing would be called HIV.

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T
he next phase began, appropriately, with a veterinarian. Max Essex studied retroviruses in monkeys and cats.

Dr. Myron (Max) Essex, DVM, PhD, is not your ordinary small-animal vet. (Then again, this book is filled with extraordinary veterinarians who are keen scientists as well as caring animal doctors.) Essex is a professor in the Department of Cancer Biology at the Harvard School of Public Health. He worked on feline leukemia virus (FeLV), among other things, and cancer-causing viruses formed the broad frame of his interests. Having seen the effects of FeLV in wrecking the immune systems of cats, he suspected as early as 1982, along with Gallo and Montagnier, that the new human immune deficiency syndrome might be caused by a retrovirus.

Then something strange came to his notice, by way of a grad student named Phyllis Kanki. She was a veterinarian like him, but now working on a doctorate at the School of Public Health. Kanki grew up in Chicago, spent her adolescent summers doing zoo work, and then studied biology and chemistry on the way toward veterinary medicine and comparative pathology. During the summer of 1980, while still amid her DVM studies, she worked at the New England Regional Primate Research Center, which was part of Harvard but located out in Southborough, Massachusetts. There she saw a weird problem among the center’s captive Asian macaques—some of them were dying of a mysterious immune dysfunction. Their T-helper lymphocyte counts were way down. They wasted away from diarrhea or succumbed to opportunistic infections, including
Pneumocystis jirovecii.
It sounded too much like AIDS. Kanki later brought this to the attention of Essex, her thesis adviser, and together with colleagues from Southborough, they started to look for what was killing those monkeys. Based on their knowledge of FeLV and other factors, they wondered whether it might be a retrovirus infection.

Taking blood samples from macaques, they did find a new retrovirus, and saw that it was closely related to the AIDS virus. Because this was 1985, they used Gallo’s slightly misleading label (HTLV-III) for what would soon be renamed HIV. Their monkey virus would be renamed too and become, by analogy, simian immunodeficiency virus: SIV. The group published a pair of papers in
Science
, which had grown hungry for AIDS breakthroughs. This discovery, they wrote, could help illuminate the pathology of the disease, maybe even advance efforts to develop a vaccine, by providing an animal model for research. Only a single sentence at the end of one of the papers, a modest but pertinent comment dropped in like an afterthought, noted that SIV might also be a clue toward the
origin
of HIV.

It was. Phyllis Kanki performed the lab analysis of samples from the captive macaques and then made it her business to wonder whether the same virus might exist in the wild. Kanki and Essex looked at Asian macaques, testing blood samples from wild-caught animals. They found no trace of SIV. They tested other kinds of wild Asian monkey. Again, no SIV. This led them to surmise that the macaques at Southborough had picked up their SIV in captivity by exposure to animals of another species. It was a reasonable guess, given that the primate center at one point had a monkey playpen in its lobby, where Asian and African infant monkeys were sometimes allowed to mingle. But then which kind of African monkey was the reservoir? Where exactly had the virus come from? And how might it be related to the emergence of HIV?

“
In 1985, the highest rates of HIV were reported
in the U.S. and Europe,” Essex and Kanki wrote later, “but disturbing reports from central Africa indicated that high rates of HIV infection and of AIDS prevailed there, at least in some urban centers.” The focus of suspicion was shifting: not Asia, not Europe, not the United States, but
Africa
might be the point of origin. Central Africa also harbored a rich fauna of nonhuman primates. So the Harvard group got hold of blood from some wild-caught African simians, including chimpanzees, baboons, and African green monkeys. None of the chimps or the baboons showed any sign of SIV infection. Some of the African green monkeys did. It was an epiphany. More than two dozen of the monkeys carried antibodies to SIV, and Kanki grew isolates of live virus from seven. That finding too went straight into
Science,
and the search continued. Kanki and Essex eventually screened thousands of African green monkeys, caught in various regions of sub-Saharan Africa or held captive in research centers around the world. Depending on the population, between 30 and 70 percent of those animals tested SIV-positive.

But the monkeys weren’t sick. They didn’t seem to be suffering from immune deficiency. Unlike the Asian macaques, the African green monkeys “
must have evolved mechanisms
that kept a potentially lethal pathogen from causing disease,” Essex and Kanki wrote. Maybe the virus had changed too. “Indeed, some SIV strains might also have evolved toward coexistence with their monkey hosts.” The monkeys evolving toward greater resistance, the virus evolving toward lesser virulence—this sort of mutual adaptation would suggest that SIV had been in them a long time.

The new virus, SIV as found in African green monkeys, became the closest known relative of HIV. But it wasn’t
that
close; many differences distinguished the two at the level of genetic coding. The resemblance, according to Essex and Kanki, was “
not close enough to make it likely that SIV
was an immediate precursor of HIV in people.” More likely, those two viruses represented neighboring twigs on a single phylogenetic branch, separated by lots of evolutionary time and probably some extant intermediate forms. Where might the missing cousins be? “Perhaps, we thought, one could find such a virus—an intermediate between SIV and HIV—in human beings.” They decided to look in West Africa.

With help from an international team of collaborators, Kanki and Essex gathered blood samples from Senegal and elsewhere. The samples arrived with coded labeling, for blind testing in the laboratory, so that Kanki herself didn’t know their country of origin, nor even whether they derived from humans or monkeys. She screened them using tests for both SIV
and HIV. Despite one possible misstep involving a lab contamination, her team found what they had thought they might: a virus intermediate between HIV and SIV. With the code unblinded, Kanki learned that the positive results came from Senegalese prostitutes. In retrospect it made sense. Prostitutes are at high risk for any sexually transmitted virus, including a new one recently spilled into humans. And the density of the rural human population in Senegal, where African green monkeys are native, makes monkey-human interactions (crop-raiding by monkeys, hunting by humans) relatively frequent.

Furthermore, the new bug from Senegalese prostitutes wasn’t just halfway between HIV and SIV. It
more
closely resembled SIV strains from African green monkeys than it did the Montagnier-Gallo version of HIV. That was important but puzzling. Were there
two
distinct kinds of HIV?

Luc Montagnier now reenters the story. Having tussled with Gallo over the first HIV discovery, he converged more amicably with Essex and Kanki on this one. Using assay tools provided by the Harvard group, Montagnier and his colleagues screened the blood of a twenty-nine-year-old man from Guinea-Bissau, a tiny country, formerly a Portuguese colony, along the south border of Senegal. This man showed symptoms of AIDS (diarrhea, weight loss, swollen lymph nodes) but tested negative for HIV. He was hospitalized in Portugal, and his blood sample hand-delivered to Montagnier by a visiting Portuguese biologist. In Montagnier’s lab, the man’s serum again tested negative for antibodies to HIV. But from a culture of his white blood cells Montagnier’s group isolated a new human retrovirus, which looked very similar to what Essex and Kanki had found. In another patient, hospitalized in Paris but originally from Cape Verde, an island nation off the west coast of Senegal, the French team found more virus of the same type. Montagnier called the new thing LAV-2. Eventually, when all parties embraced the label HIV instead, it would be HIV-2. The original became HIV-1.

The paths of discovery may be sinuous, the labels may seem many, and maybe you can’t tell the players without a scorecard; but these details aren’t trivial. The difference between HIV-2 and HIV-1 is the difference between a nasty little West African disease and a global pandemic.

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D
uring the late 1980s, as Kanki and Essex and other scientists studied HIV-2, a flurry of uncertainty arose about its provenance. Some challenged the idea that it was closely related to (and recently derived from) a retrovirus that infects African monkeys. An alternative view was that such a retrovirus had been present in the human lineage
for as long as—or longer than—human time. Possibly it was already with us, a passenger riding the slow channels of evolution, when we diverged from our primate cousins. But that view left an unresolved conundrum: If the virus was an ancient parasite upon humans, unnoticed for millennia, how had it suddenly become so pathogenic?