FIG. 23.10

Did an HIV-positive dentist spread the AIDS virus to his patients?

BACKGROUND In the late 1980s, several patients of a Florida dentist contracted AIDS. Molecular analysis showed that the dentist was HIV-positive.

HYPOTHESIS It was hypothesized that the patients acquired HIV during dental procedures carried out by the infected dentist.

METHOD Researchers obtained two HIV samples each (denoted 1 and 2 in the figure) from several people, including the dentist (Dentist 1 and Dentist 2), several of his patients (Patients A through G), and other HIV-positive individuals chosen at random from the local population (LP). In addition, a strain of HIV from Africa (HIVELI) was included in the analysis.

RESULTS Biologists constructed a phylogeny based on the nucleotide sequence of a rapidly evolving gene in the genome of HIV. Because the gene evolves so quickly, its mutations preserve a record of evolutionary relatedness on a very fine scale. HIV in some of the infected patients—patients A, B, C, E, and G—were more similar to the dentist’s HIV than they were to samples from other infected individuals. Some patients’ sequences, however, did not cluster with the dentist’s, suggesting that these patients, D and F, had acquired their HIV infections from other sources.

CONCLUSION HIV phylogeny makes it highly likely that the dentist infected several of his patients. The details of how the patients were infected remain unknown, but rigidly observed safety practices make it unlikely that such a tragedy could occur again.

FOLLOW-UP WORK Phylogenies based on molecular sequence characters are now routinely used to study the origin and spread of infectious diseases, such as swine flu and Ebola.

SOURCE Hillis, D. M., J. P. Huelsenbeck, and C. W. Cunningham. 1994. “Application and Accuracy of Molecular Phylogenies.” Science 264: 671–677.