Phylogeny Friday - 9 June 2006


You may have thought that Orin Scrivello was the worst dentist ever. Well, have I got a story for you. This dentist isn't a sadist, and his follies were far from intentional. But the implications of his conduct greatly affected the lives of at least five of his patients. This week's Phylogeny Friday is story fit for CSI. Learn about the dentist, the virus, and his patients below the fold.

The story revolves around Dr. David Acer, a Florida dentist who died in 1990 from complications of AIDS. Dr. Acer's death would have been far from remarkable at the time -- the AIDS epidemic was quite visible by the late 1980s, and one death earned no more attention than any other. Dr. Acer's story, however, extends beyond his private life and into his practice. You see, Dr. Acer had multiple patients that had been diagnosed as infected with HIV within a couple of years of his death.

Many of the infected patients showed no risk factors associated with HIV infection. One elderly woman (hardly the at risk type that Tara described) had been married for more than 25 (her spouse was HIV negative), had never used intravenous drugs, never had sex with any at risk individuals, and never received a blood transfusion. Another patient was not an intravenous drug user, had no history of transfusion, and all recent sexual contacts were HIV negative.

A phylogeny created using DNA sequences of the HIV virus taken from the dentist, patients, and other individuals within a 90 mile radius is shown below. Note the cluster containing sequences from the Dentist, Patient A, Patient B (the elderly woman), and Patient C (the second patient described above).


The sequences in the boxed cluster differ by an average of 3.4%, consistent with HIV strains obtained from a single person or HIV strains from individuals who share a common source of infection. The genetic relatedness of the strains, along with other corroborating evidence, presents a strong case that the dentist somehow transmitted the virus to multiple patients. Subsequent analyses revealed other patient to whom the dentist transmitted HIV, though not all of the Dr. Acer's HIV positive patients obtained the virus from the dentist (e.g., Patient D).

To the best of my knowledge, no one has yet to present a clear picture of how the dentist transmitted the virus to his patients. It is possible that he sustained small abrasions while operating on patients which allowed his blood to enter the patients' mouths. Even though we lack a clear mechanism, the evidence strongly supports the hypothesis that Dr. Acer is the source of some of his patients' HIV infections.

Some news outlets expressed skepticism regarding the conclusions reached by the CDC. A response to the news coverage surrounding the investigation can be found here.

Centers for Disease Control. 1991. Update: Transmission of HIV infection during an invasive dental procedure. MMWR 40(2): 23-27, 33.

Ciesielski et al. 1992. Transmission of human immunodeficiency virus in a dental practice. Ann. Intern. Med. 116(10):798-805.

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According to information in Duesberg papers 4 % of the population is hiv positive obtaining their seropositivity naturally due to perinatal tranmission. This is how, Duesberg explains the Kimberly Bergalis case. Presumably, 4-6 people in a practice of 1000 plus patients of Dr. Acer is merely reflecting this natural occurring phenomena. Perhaps this can be taken into meaningful discussion.

By McKiernan (not verified) on 09 Jun 2006 #permalink

I'm not an expert on the science here, but I recall this case from when it first became news back in the early-90's.

It was very controversial (for a number of reasons, political as well as scientific) and if I'm not mistaken the conclusions reached by those CDC studies have been called into question. This may not be the best example of a phylogentic analysis success story, and I'm not sure those of us on the pro-evo side of he debate should be eager to cite it as such.

Still, as I said, I'm not an expert, and my memory is a little unclear on the case. Just a red flag...

By Red Right Hand (not verified) on 10 Jun 2006 #permalink

The controversy surrounding this case was generated by the news media and was probably unfounded (see the link at the end of the entry).

This may not be the best example of a phylogentic analysis success story, and I'm not sure those of us on the pro-evo side of he debate should be eager to cite it as such.

I don't present evidence for the sake of some non-existent debate. This is educational. Those that want to learn may learn. Those that don't, live in ignorance. This is an excellent example for which to teach evolutionary biology.


Duesberg is inconsistent in his claims.
He cites CDC statistics for a figure of approximately 1 million people infected with HIV in the US ~ 0.4%. He also claims that HIV is predominantly transmitted perinatally and that it is equally distributed between the sexes. He can't have it both ways. The CDC figures show HIV infection occurs primarily within risk groups such as homosexual men and intravenous drug-users. If you accept the figure of 1 million then you also have to accept that the majority of these are in one or more risk group. If the majority of this 1 million are in specific risk groups it is completely nonsensical to claim that they were infected perinatally. If you read Duesberg's writings you will see that he frequently changes his story depending on the point he is trying to make.

In Duesberg's "statistical" analysis of the Bergalis case he does the same thing. Out of a randomly chosen 1000 you would expect approxiamtely 4 to be HIV posistive. You would also expect those 4 to be homosexual or intravenous drug-users.

However, Kimberly Bergalis was not a male homosexual and did not take drugs. If you randomly selected 1000 white female non-drug-users you would not statistically expect any of them to be HIV positive. Duesberg hopes that you don't notice this statistical slight of hand.

Duesberg also makes other false claims. He has claimed in his book that Bergalis was perfectly healthy until she took AZT. This is not true. Bergalis had a CD4 count of less than 50 and PCP before she took AZT.

There are also many other cases where phylogenetic analysis has been used to determine transmission pathways.

Molecular evidence of HIV-1 transmission in a criminal case

Figures 1 and 2 show more phylogenetic trees.

By Chris Noble (not verified) on 13 Jun 2006 #permalink