How the myth of Patient Zero unraveled

According to genetic research, HIV-1 did not originate in a laboratory. Its origin lies in multiple independent transmissions of a simian immunodeficiency virus from non-human primates to humans. The pandemic group M originates from a virus strain found in a subspecies of chimpanzees.

The southeastern region of Cameroon is considered a likely area for the crucial transmission event. During hunting and processing of wild meat, infected blood could enter the human bloodstream through small injuries. In rare cases, the virus adapted to humans through mutations. Of the four human lineages that emerged, group M in particular developed efficient transmission between humans.

The virus spread along waterways to Léopoldville, now Kinshasa. The city grew into a significant commercial, administrative, and transportation center under Belgian colonial rule. Rail connections and shipping brought many people from rural areas to the city.

Several factors facilitated the spread there. These included significant demographic inequalities, sexually transmitted diseases with mucous membrane lesions, and medical campaigns with insufficiently sterilized syringes and needles. This unintentional transmission in medical facilities accelerated the early spread of the virus.

Gaëtan Dugas was diagnosed with Kaposi’s sarcoma in 1980 and assisted in the early investigations of the US health authority, the CDC. He provided the names and contact information of more than 72 people from his sexual network. Due to this detailed information, he was at the center of a contact diagram.

In internal documents, Dugas was referred to with the letter O for “Out of California”. Later, the O was read as the number zero. The media and the book publication And the Band Played On, which appeared in 1987, reinforced the false narrative of a single starting point.

A 2016 study published in Nature, led by Michael Worobey and involving historian Richard McKay, analyzed historical blood samples, as well as a sample from Dugas from 1983. His virus was not at the origin of the North American lineage, but within an already diverse branch of subtype B.

The oldest known evidence includes the samples ZR59 and DRC60. ZR59 dates back to 1959 and was taken from an adult man in Léopoldville. DRC60 is a lymph node sample from a woman from the same city, taken in 1960 and preserved in paraffin.

The genetic distance between the two samples shows that HIV-1 was already significantly diverse at that time. Using molecular dating, the common ancestor of the current Group M was dated to the period between 1908 and 1920. Approximately 1920 is considered the most likely time.

After the independence of the Democratic Republic of Congo in 1960, specialists from French-speaking countries, including Haiti, worked on building state structures. Phylogenetic analyses trace the virus strain, later designated as subtype B, from Kinshasa to Haiti around 1967.

According to reconstructions, the virus reached the United States around 1971 from Haiti. New York became an early center. The subtype was circulating in San Francisco around 1976. Thus, the virus was already widespread in several cities years before Dugas was diagnosed.

The reconstruction shows how problematic the search for a single guilty person is. Such narratives promote stigmatization and distract from social, political, medical, and ecological conditions.

Genetic family trees, archived samples, and historical data allow for a more precise view of epidemics. They show that pathogens can spread unnoticed over long periods, and that early case networks do not automatically reflect the origin of an epidemic.