By Zachary D. Roberts
By Anna Merlan
By Jon Campbell and Laura Shunk
By Albert Samaha
By Amanda Dingyuan
By Anna Merlan
By Anna Merlan
By Albert Samaha
AIDS viruses have probably existed in many different animals for thousands of years, perhaps longer. Cows have been found with bovine immunodeficiency virus (BIV), while feline immunodeficiency virus (FIV) infects house cats, lions, cheetahs, and North American pumas. Many species of monkeys have now been found carrying SIV. (The fact that the virus is in so many simian species strongly suggests that it has circulated among them for a long time, whereas HIV only entered large human populations in the 1970s. That's one reason scientists are convinced the virus went from simians to humans, and not the other way around.) "The reservoir" of animal AIDS viruses, says Simon, "is unlimited."
So if such a vast ocean of immunodeficiency viruses has long existed, why did an epidemic happen only now? Why not during the slave trade, when millions of Africans were taken from the areas where both HIV-1 and HIV-2 originated? Here was a massive mixing of peoples, and the slaves were often raped, giving the virus ample opportunity to spread. And yet, no epidemic flared upor if one did, it was small, flickering out like the virus in the Norwegian sailor's family. On the other hand, two major AIDS epidemicsnot to mention the micro-epidemic of Group Ohave arisen in the past 70 years. This is what obsesses Marx: "Something that has to do with the 20th century has changed the ecology between SIV and HIV and has allowed these epidemics to occur. And we don't understand what that is."
A new book, The Riverby Edward Hooper, argues that the oral polio vaccine introduced SIV into humans, because some batches of the vaccine may have been grown in the kidneys of SIV-infected chimpanzees. "Plausible but improbable," says Ho. The chimps in that area are the wrong subspecies, and Los Alamos National Laboratory researcher Bette Korber will soon release findings that HIV very likely evolved into its modern form decades before the polio vaccine was invented. (Still, the remaining stock of the vaccine batches Hooper implicates will soon be tested.)
A more plausible idea is that blood transfusions and hypodermic needleswhich were often reused in Africa without being sterilizedboosted the evolution and spread of emerging HIVs, by giving these viruses more chances to adapt to human biology. And, of course, once the viruses had adapted, needles would help them spread, as they have among IV drug users throughout America.
But needles and transfusions probably aren't the whole story. After all, traditional African healers reuse blades to make medicinal incisions in their patients, and elders reuse knives for ritual scarification. What allowed a crossover virus to explode into an epidemic is almost certainly the cultural upheaval that has shaken Africa. Cameroon, a country smaller than Spain, has more than 200 indigenous languages. After World War I, colonial rule imposed just two national languagesEnglish and Frenchpermitting people who would never have intermarried, or even interacted, to do so. Roads, railways, and air travel allowed people to move and mingle more easily than ever before. And urbanization gathered huge numbers of people in one place, where poverty and the breakdown of traditional cultures led to industrial-scale prostitution. Early in the epidemic, it was noted that HIV cases clustered in the towns along Africa's trucking routes, because truck drivers frequented prostitutes.
Marx wants to understand as much as he can about the emergence of HIV, biologically and socially, in hopes of preventing the emergence of new viruses. Indeed, new microbes have already arisen. "Hepatitis C, there's no good explanation for the emergence of that virus," Marx says. "Where'd it come from?"
Where did viruses come from, period? HIV is a retrovirus, which copies its genetic code onto the DNA of its host. So perhaps, says Robert Gallo, co-discoverer of HIV, the virus started out as a kind of genetic messenger, transporting key segments of DNA among life's early organisms. "Did viruses play a role in evolution, perhaps a role in speciation or in embryonic life? Or did they start out as junk DNA with no purpose? What the fuck was their role? We don't know."
While HIV's history is fascinating, THE more urgent question concerns its future. The Hollywood scenario is that a deadlier or more transmissible AIDS "supervirus" might arise. "Unlikely," says Simon. Many scientists believe that it is in the best interest of a virus not to kill its host, so the virus may evolve into more benign strains. But it's also in the best interest of the virus to become more transmissible, in which case it doesn't matter if the virus kills its host because it will live on by spreading into new patients. Still, Simon had to screen many thousands of blood samples to find just five cases of the newest HIV-1 variant, Group N. Clearly, new crossover viruses are rare.
But they do occur, and even if they are not more virulent, they still pose problems. For one thing, they might escape detection on tests and so pass into the blood supply. They also might be able to evade drugs or a vaccine. Already, Simon and colleagues found that one HIV variant, subtype G, is resistant to at least two of the powerful protease inhibitors that have given patients in the West a new lease on life. Indeed, a "signature" of this subtype is a mutation which renders the drugs less effective.