A QUANTUM OF SCIENCE
Are HIV rates in the US substantial enough to merit a policy of circumcision?
Following evidence of the protective effect against HIV infection, recent news articles report that the CDC is mulling the idea of endorsing circumcision for all male infants born in the United States. But will it have that much impact?
First, the science: how does circumcision prevent HIV infection? HIV infections occur when the virus gains entry to cells by binding to a protein called CD4, found on the surface of cells. Cell types rich in CD4 are thus easier targets for a successful HIV infection. One such cell type is the Langerhans cell, a part of the primate epidermal tissue related to defending the body against invading microbes. As it happens, primate foreskin is rich in Langerhans cells, meaning plenty of CD4 protein for the AIDS virus to bind to and invade the body. By removing the foreskin through circumcision, an easy point of entry for the virus is blocked.
(Interestingly, CD4-rich Langerhans cells are found in human foreskin and vaginal tissues, but not in oral or rectal tissues. This suggests that HIV infections use a different biochemical route when introduced into the body through those tissues.)
The idea of reducing the risk of contracting HIV through circumcision is far from new. In 1987 a letter was published in the New England Journal of Medicine suggesting exactly that, and studies done in the last fifteen years bear out that theory. While the methods used and areas studied (largely in Africa) varied, the conclusions were so striking that in at least one case a circumcision/HIV infection study was halted years early so the findings could be considered for public policy discussions. Depending on the area studied and the risk factors of those involved in the study, HIV infection rates were found to be as much as 50% lower among circumcised African men than their intact counterparts. Various attempts have been made to expand the conclusions of individual studies through meta-analysis papers and their conclusions found an even greater protective effect of circumcision when those studied were from high-risk populations.
So why not support a policy of encouraging circumcision in the United States? The same studies being reviewed by the CDC have some counterindications that are well worth considering in any kind of policy discussion.
First, the benefits of circumcision are greatly enhanced among high-risk populations. This means that for the average American man (whose risk is far, far lower than the average African man) the benefits are considerably lessened. This could well have something to do with the fact that an estimated 79% of American men are already circumcised – though as rates of circumcision have fallen to around 65% in the most recent surveys, that number is now trending downward. Secondly, use of barrier protection is far more prevalent in America among all demographics, another factor that reduces the positive impact of circumcision protection. Another risk factor related to the need for additional preventative measures against HIV infection – the rate of STDs causing lesions or ulcers, such as herpes or syphilis, which help HIV enter the body during sexual contact – is lower in America than in most African nations, and treatment for those afflictions is considerably more available. Finally, almost all the research done in this area has been performed in Africa. This means there is a possibility that things could be different among Caucasian populations, simply because they are biochemically distinct from non-Caucasians.
The need for additional research is clear. Until scientists can repeat the highly successful African studies in America, Europe, or ideally both – since circumcision is much less common in European nations than in America – the benefits of circumcision for Western populations will remain a question too open for a substantive policy debate to take place.
For more information:
CDC mulls routine circumcision of infants to reduce spread of HIV (NY Daily News, 25-Aug-09)
Circumcision and heterosexual transmission of HIV infection to men. (Fink, 1987)
Comparative investigation of Langerhans' cells and potential receptors for HIV in oral, genitourinary and rectal epithelia. (Hussain, 1995)
Male circumcision and risk of HIV infection in sub-Saharan Africa: a systematic review and meta-analysis. (Weiss, 2000)
Male circumcision for HIV prevention in young men in Kisumu, Kenya. (Bailey, 2007)
Langerhans cells.
© AQOS / P. Smalley (2009)
Reproduction with attribution is appreciation
Tuesday, August 25, 2009
Thursday, August 20, 2009
Comets: Interstellar Johnny Appleseeds?
A QUANTUM OF SCIENCE
Are comets the disseminators of the seeds of life?
It was January 2, 2004. The NASA space probe known as Stardust passed through the tail of the Wild-2 comet, five years after the craft was launched on its mission to collect interstellar dust and particle samples from the tail, or coma, of the comet – particles that might well come from beyond Earth’s solar system. A specially-designed collector called an extra low density aerogel was used to capture the particles, and the probe’s camera took high-resolution images of the comet’s nucleus.
On January 15, 2006, the Stardust probe returned to Earth. A sonic boom and a fireball heralded its return over Utah’s Great Salt Lake desert. It was travelling at almost 29,000 miles per hour – the fastest re-entry speed into Earth's atmosphere ever achieved by a man-made object.
Since then, scientists in the Stardust Mission of NASA’s Jet Propulsion Laboratory have been hard at work analyzing the microscopic dust and particles it collected on its seven-year, three billion mile journey. And the results of that analysis are breathtaking.
Some things were expected. Silicate crystals had been predicted based on spectroscopic observations, but their presence confirmed not only those predictions but also the belief that the comet contained matter from outside the solar system.
Even more exciting, organic materials were detected. Astrobiologists have long been aware of aliphatic hydrocarbons (long chains of carbon and hydrogen) diffused throughout space, but the hydrocarbons found in the coma of Wild-2 were much longer than standard interstellar chains, indicating greater complexity. Methylamine and ethylamine, while simple molecules, were an exciting find as well because the nitrogen they contain is essential for life.
But on August 16, 2009, Dr. Jamie Elsila of NASA's Goddard Space Flight Center in Greenbelt, Maryland announced something astonishing. Scientists analyzing the Stardust samples had detected the presence of glycine, the simplest amino acid – and one of the critical building blocks of almost all life on Earth.
Rigorous testing was required in order to confirm this result. Every effort was made to ensure that "earth grime" did not contaminate the samples. The Johnson Space Center in Webster, Texas maintained the comet particles (it is also the home of most of the moon rocks recovered by the Apollo missions) and over 150 scientists from some of the most prestigious laboratories in the world helped with the analysis.
Among the tests they performed as confirmation of the results was an isotopic analysis. Isotopes of an element contain different numbers of neutrons than the most common version of that element, and the prevalence of different isotopes of a given element are well characterized. Using that information, scientists were able to confirm that the isotopic prevalence found in the glycine detected in the comet particles was not terrestrial contamination.
Where did the glycine come from, then? Theories abound, but the one with the greatest antiquity is the theory of panspermia (also known as exogenesis). First proposed in ancient Greece, many respected scientists since the Renaissance have expressed support for the idea that life came to Earth from outer space. This is one of the core areas of study in the field known as astrobiology, a multidisciplinary science that has existed formally since NASA established the first astrobiology program in 1960. Combining physics, astronomy, chemistry, biology and even more specialized sciences, astrobiology concerns itself with the study of the origin, evolution, distribution, and future of life in the universe.
The presence of even the simplest amino acid in the tail of a comet is a profound piece of evidence supporting the idea of panspermia. If this theory is correct, comets might well be the Johnny Appleseeds of the universe, slowly sowing their seeds of complex pre-biotic molecules throughout the galaxy – and suggesting that life on other worlds may be far more common than scientists once thought.
For more information:
NASA article on the discovery
http://www.nasa.gov/mission_pages/stardust/news/stardust_amino_acid.html
SCIENCE Magazine article on Wild-2 analysis (2006)
http://xray.physics.sunysb.edu/research/pdf_papers/2006/sandford_science_2006.pdf
More on the Wild-2 comet
http://en.wikipedia.org/wiki/Comet_Wild_2
More on Panspermia
http://en.wikipedia.org/wiki/Panspermia
More on Astrobiology:
http://en.wikipedia.org/wiki/Astrobiology
© AQOS / P. Smalley (2009)
Reproduction with attribution is appreciation
Are comets the disseminators of the seeds of life?
It was January 2, 2004. The NASA space probe known as Stardust passed through the tail of the Wild-2 comet, five years after the craft was launched on its mission to collect interstellar dust and particle samples from the tail, or coma, of the comet – particles that might well come from beyond Earth’s solar system. A specially-designed collector called an extra low density aerogel was used to capture the particles, and the probe’s camera took high-resolution images of the comet’s nucleus.
On January 15, 2006, the Stardust probe returned to Earth. A sonic boom and a fireball heralded its return over Utah’s Great Salt Lake desert. It was travelling at almost 29,000 miles per hour – the fastest re-entry speed into Earth's atmosphere ever achieved by a man-made object.
Since then, scientists in the Stardust Mission of NASA’s Jet Propulsion Laboratory have been hard at work analyzing the microscopic dust and particles it collected on its seven-year, three billion mile journey. And the results of that analysis are breathtaking.
Some things were expected. Silicate crystals had been predicted based on spectroscopic observations, but their presence confirmed not only those predictions but also the belief that the comet contained matter from outside the solar system.
Even more exciting, organic materials were detected. Astrobiologists have long been aware of aliphatic hydrocarbons (long chains of carbon and hydrogen) diffused throughout space, but the hydrocarbons found in the coma of Wild-2 were much longer than standard interstellar chains, indicating greater complexity. Methylamine and ethylamine, while simple molecules, were an exciting find as well because the nitrogen they contain is essential for life.
But on August 16, 2009, Dr. Jamie Elsila of NASA's Goddard Space Flight Center in Greenbelt, Maryland announced something astonishing. Scientists analyzing the Stardust samples had detected the presence of glycine, the simplest amino acid – and one of the critical building blocks of almost all life on Earth.
Rigorous testing was required in order to confirm this result. Every effort was made to ensure that "earth grime" did not contaminate the samples. The Johnson Space Center in Webster, Texas maintained the comet particles (it is also the home of most of the moon rocks recovered by the Apollo missions) and over 150 scientists from some of the most prestigious laboratories in the world helped with the analysis.
Among the tests they performed as confirmation of the results was an isotopic analysis. Isotopes of an element contain different numbers of neutrons than the most common version of that element, and the prevalence of different isotopes of a given element are well characterized. Using that information, scientists were able to confirm that the isotopic prevalence found in the glycine detected in the comet particles was not terrestrial contamination.
Where did the glycine come from, then? Theories abound, but the one with the greatest antiquity is the theory of panspermia (also known as exogenesis). First proposed in ancient Greece, many respected scientists since the Renaissance have expressed support for the idea that life came to Earth from outer space. This is one of the core areas of study in the field known as astrobiology, a multidisciplinary science that has existed formally since NASA established the first astrobiology program in 1960. Combining physics, astronomy, chemistry, biology and even more specialized sciences, astrobiology concerns itself with the study of the origin, evolution, distribution, and future of life in the universe.
The presence of even the simplest amino acid in the tail of a comet is a profound piece of evidence supporting the idea of panspermia. If this theory is correct, comets might well be the Johnny Appleseeds of the universe, slowly sowing their seeds of complex pre-biotic molecules throughout the galaxy – and suggesting that life on other worlds may be far more common than scientists once thought.
For more information:
NASA article on the discovery
http://www.nasa.gov/mission_pages/stardust/news/stardust_amino_acid.html
SCIENCE Magazine article on Wild-2 analysis (2006)
http://xray.physics.sunysb.edu/research/pdf_papers/2006/sandford_science_2006.pdf
More on the Wild-2 comet
http://en.wikipedia.org/wiki/Comet_Wild_2
More on Panspermia
http://en.wikipedia.org/wiki/Panspermia
More on Astrobiology:
http://en.wikipedia.org/wiki/Astrobiology
© AQOS / P. Smalley (2009)
Reproduction with attribution is appreciation
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