An Unwelcome Gift from Gorillas

July 3, 2015

By Medical Discovery News


You probably know that Acquired Immunodeficiency Syndrome (AIDS), which has affected 79 million people and killed 39 million since 1981, is the result of Human Immunodeficiency Virus (HIV). What you may not know is that there are several different types of this virus and they did not all come from the same source, making the search for HIV’s origins lengthy and complicated.

There are four groups of HIV-1: M, N, O, and P. Each of them was transmitted between African primates as simian immunodeficiency viruses (SIVs) before infecting humans, and each crossed species to humans independently. More than 40 African primates carry SIVs, which emerged up to 6 million years ago. It is likely that transmission to humans has occurred many times when hunters where exposed to the blood and tissues of infected animals. However the isolation of humans in Africa limited the spread of SIVs that crossed into humans until the last century.

It was not until modern travel allowed infected humans to move from the bush to cities and from there to other cities and countries that an HIV strain such as M took hold among humans, leading to a global pandemic. Group M causes more than 90 percent of AIDS cases and currently affects 40 million people worldwide. We already know that it came from chimpanzees in southern Cameroon. Group N also came from chimpanzees, but has infected less than 20 people.

Group O has infected about 100,000 people in Cameroon, Chad, Gabon, Niger, Nigeria, Senegal, and Togo. Although anti-retroviral drug combinations have made HIV infections survivable, many in Africa and the developing world do not have access to these treatments. Group P has only been isolated from two people. The origins of groups O and P were previously unknown, but now their source has been definitely confirmed: gorillas.

Scientists gathered fecal samples from western lowland, eastern lowland, and mountain gorillas, screening them for SIV antibodies and genetic information. Despite testing many wild troops of gorillas throughout Cameroon, Gabon, the Democratic Republic of Congo, and Uganda, the virus was identified at only four sites. Two strains of SIVs from southwestern Cameroon resembled HIV Group P and one from central Cameroon resembled Group O.

Not only does this data prove that gorillas were the immediate source of groups O and P, but the genetic information revealed that the viruses originated through a cross-species transmission from chimpanzees to gorillas. These are the same chimpanzees that infected humans, leading to groups M and N. Chimpanzees and gorillas share the same habitat, so the virus could have infected a gorilla if it bit a chimpanzee with SIV or was exposed to its blood or tissues.

Understanding the origins of HIV in humans is crucial if we want to prepare for additional viruses, especially SIV variants, entering the human population in the future, which will remain a risk as long as humans continue to hunt and eat primates.

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The Birth of Ebola

May 1, 2015

By Medical Discovery News

Colorized micrograph of Ebola by Dr. F.A. Murphy

For most Americans, the Ebola scare seems to have come and gone, but that doesn’t mean the outbreak is over in Africa or that we’ve seen the last of the virus, especially considering its history. Scientists believed that Ebola is relatively new as far as viruses go – only 10,000 years old. However, ancient animal bones show that Ebola appeared between 16 and 23 million years ago, perhaps even earlier.

The Ebola virus was discovered in 1976 during two outbreaks in what was then called Northern Zaire (now the Democratic Republic of the Congo) and Southern Sudan. The outbreaks were actually caused by two different strains of the Ebola virus named Zaire and Sudan, with 90 and 50 percent mortality rates respectively. Since then, three other strains have been identified: Tai Forest, Bundibugyo, and Reston, which is the only one that doesn’t affect people. Overall, there have been 27 outbreaks, but the current outbreak that started in March 2014 is by far the worst, infecting almost 25,000 people and killing over 10,000, thereby making it the world’s first Ebola epidemic.

Ebola is a member of the filovirus family, which also includes the Marburg virus discovered in 1967. Filoviruses are zoonotic, meaning they replicate in other animals, their natural reservoirs, before transmitting to humans. The Ebola virus’s natural reservoir is African fruit bats, so it can transfer to humans who come into contact with an infected bat or another species that has been infected, such as chimpanzees, antelope, and porcupine. Then the virus can spread from person to person.

New research into the origins of filoviruses shows that they have evolutionary ties that go back millions of years. Scientists tracked the viruses’ origins by looking for pieces of their genetic information in fossilized animal bones. While using the bones to study the genomes of ancient voles and hamsters, they found the same pieces of the viruses’ genetic material in the same locations in both rodent species. This suggests that the viruses have existed at least as long as the two species have.

Given the billions of bases each animal has in its genome, it is highly unlikely that these fragments of viral genetic information would have been inserted in exactly the same locations during different infections. Scientists therefore concluded that the virus had infected a common ancestor of these two rodents sometime before the Miocene Epoch, 5-23 million years ago, around the time the great apes arose. Furthermore, the viral genetic elements more closely resemble Ebola than Marburg, meaning the two viruses had already diverged from each other. Sometime before then, the two viruses shared a common ancestor that has not yet been identified.

This means that these viruses have been coevolving with mammals for millions and millions of years, much longer than previously believed. An understanding of the origins and evolution of filoviruses could help us better prevent outbreaks of them and hopefully even create a vaccine that would be effective against all of them.

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