Estimating dates using HIV evolution patterns

In this post we see how we can track mutation rates to estimate when people were infected with HIV and even when the virus first crossed over into humans.

HIV is an evolution machine

Its polymerase enzyme is pretty sloppy and has an error rate of about 1 mistake for every 10 thousand nucleotide bases copied.

For a virus with a genome about 10 thousand bases in length, that means that basically every time HIV replicates itself, it makes a mistake.

Sometimes these errors result in a defective virus, but sometimes they give the virus some new property its predecessor didn’t have, such as resistance to an antiretroviral agent (the drugs we use to treat HIV). The high mutation rate of HIV has also led to extensive worldwide diversity in the epidemic, leading to groupings of related viruses called clades that are named with the letters A through K, and sometimes with two letters where it looks like two clades have recombined into a spliced version of HIV. The different clades are shown in this phylogenetic tree. Also shown are how they relate to other immunodeficiency viruses that infect other primates, as well as how HIV (more precisely, HIV-1) is related to a distinct virus that also infects humans and causes AIDS, called HIV-2, which is mostly confined to west Africa.

This extensive diversity also makes it very difficult to develop an HIV vaccine.

Although the high mutation rate makes things difficult for scientific and medical advances in HIV, it does allow us to see evolution in action, and can lead to some pretty interesting discoveries.

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Friday coffee break

Coffee

Every Friday at Nothing in Biology Makes Sense! our contributors pass around links to new scientific results, or science-y news, or videos of adorable wildlife, that they’re most likely to bring up while waiting in line for a latte.

From Sarah: When scientific results have political implications, harassment of scientists is on the rise.

Climate science is just the tip of the iceberg. Seismologists are looking worriedly toward Italy, where six scientists were indicted and prosecuted for failing to adequately warn people prior to the 2009 L’Aquila earthquake, which killed more than 300 people. Given that timely earthquake prediction is currently impossible, it is unclear how any scientifically justifiable statement could be considered “adequate.” But whatever the outcome of the trial, the end result will almost certainly discourage geologists from making any public statement about future earthquake hazards, resulting in a less-informed and less-well-prepared public, more at risk from future earthquakes. [Link sic.]

From Devin: Spider silk contains chemical agents to defend against ants. The methods section of this paper gets pretty wild.

Spider webs are made of silk, the properties of which ensure remarkable efficiency at capturing prey. However, remaining on, or near, the web exposes the resident spiders to many potential predators, such as ants. Surprisingly, ants are rarely reported foraging on the webs of orb-weaving spiders, despite the formidable capacity of ants to subdue prey and repel enemies, the diversity and abundance of orb-web spiders, and the nutritional value of the web and resident spider.

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