Earliest case of HIV shows virus' origin

0 Comments | Insight on the News, March 9, 1998 | by Ruth Larson

Scientists are discovering much about the origin of the virus that causes AIDS, although a cure remains elusive. Recent findings indicate that HIV evolved in Africa during the 1950s, and has diversified over the years.

Researchers have found what they believe is the earliest known case of the human immunodeficiency virus, or HIV, in plasma from an African man who died in 1959. Their molecular sleuthing has provided a glimpse at the earliest origins of the AIDS epidemic that has infected an estimated 30 million people around the world.

According to Thufu Zhu of the University of Washington in Seattle, HIV probably originated in the late 1940s or early 1950s. "This is a decade or two earlier than previous estimates of the introduction of HIV-1 into the human population," he told the Fifth Conference on Retroviruses and Opportunistic Infections, recently convened in Chicago.

Zhu now believes that all strains of HIV evolved from a single introduction of the virus into humans rather than from repeated transmissions from animals to humans, as some scientists had speculated. His findings have been published in the current issue of the journal Nature.

Researchers examined 1,213 blood samples gathered in Africa between 1959 and 1982. The HIV-1 virus was positively identified in just one sample, drawn in 1959 from a man who lived in Leopoldville, Belgian Congo -- now Kinshasa, Republic of Congo. The patient was suffering from symptoms that seemed to resemble sickle cell anemia, a hereditary blood disease.

The plasma sample had degraded during the course of 39 years, but scientists were able to isolate four small fragments of two viral genes. "This is, to date, the oldest known HIV case," says David Ho, director of the Aaron Diamond AIDS Research Center at New York's Rockefeller University, who coauthored the study.

Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, says the discovery was unlikely to help individuals now infected with HIV, but it could help researchers predict future evolutions of the virus. "We might learn where the virus could be 20 or 30 years from now," Fauci says. "It gives us a fuller picture by enabling us to project how the virus changes over time."

Although scientists had previously estimated the rate at which the virus had evolved, "what wasn't known was the very first case in humans, when the virus was first injected in the human species," says Fauci. "It's fortuitous we had this specimen to examine, so that we're able to close the loop on that 'missing link."'

Scientists compared the 1959 HIV sample to a current HIV sample, to measure the evolution of the virus. HIV mutates quickly, changing about 1 percent of its genetic material each year. Researchers have identified 10 distinct subtypes, identified with the letters A through J. Type B is most common strain in the United States and Europe, while Type D is most common in Africa.

Using the analogy of an HIV "family tree," with each of the 10 branches representing a different strain, the 1959 HIV is located near the trunk, where types B and D branch off. "The diversification of HIV-1 in the past 40 [to] 50 years portends even greater virol [variety] in the coming decades, and underscores the need for continued surveillance," Zhu and his colleagues wrote in Nature.

Their research also refutes earlier theories that HIV was responsible for AIDS-like syndromes that were recorded in Europe during the 1930s. Several years ago, British researchers reported that a sailor from Manchester, England, had died of AIDS in 1959. But Ho's research found evidence that the sample had been contaminated by HIV long after the man died.

The study did not explore how AIDS spread from Africa and became a worldwide epidemic. However, the researchers speculated that the virus may have been transmitted by unsterilized needles used in vaccination programs.