Wednesday, October 8, 2014

Birthplace of the HIV-1 pandemic


Fig.1. HIV-1 under electron microscope.

Like all gripping stories, the origin of HIV/AIDS is steeped in sex, a population boom, and a rapidly changing culture. A recent study in Science traced the source of the pandemic HIV-1 group M to Kinshasa, in what is now the Democratic Republic of Congo. The international team of researchers, led by Oxford University and University of Leuven, used archival HIV-1 strains and demographic data dating to the early 20th century. Researchers concluded that the “perfect storm” of factors -- including sharp urban growth, increased transportation, and changes to sex trade -- led to the global pandemic that has infected more than 75 million people.

The great leap

The jump from animal to human is a difficult journey for pathogens. Of the few diseases that transfer from animals to humans, even less become an exclusive human agent, passing only from human to human. Despite this, more than 75 percent of emerging human infectious diseases originated in animals. Faria et al. discovered that HIV-1 group M has close relatives in specific strains of simian immunodeficiency viruses (SIVs) local to the Kinshasa region. SIVs infect African non-human primates and most likely infected humans through hunting or consuming Bushmeat.

Like the other 12 known groups of HIV-1, group M might have fizzled out locally. However, the changing human habitat allowed for an exponential increase of infected people. Faria et al. focused not only on the evolutionary history of HIV-1 groups, but on their locations as well. The researchers sequenced HIV-1 strain collections and mapped those strains over time and space, tracking the disease along railways and waterways.  They compared archived strains of the pandemic HIV-1 group M and the non-pandemic group O from central Africa during the 20th century. Such collections allow for these "spatiotemporal" studies and show how one type of HIV-1 spread further than any of its relatives.



Fig.2. Kinshasa’s railway system connected it to Africa’s most populated cities (Photo: Atlas du Congo Belge et du Ruanda-Urundi, Gaston Derkinderen, Les Transport, Elsevier, Bruxelles, 1955).

 

Crossroads of disease and society

“We think it is likely that the social changes around the independence in 1960 saw the virus ‘break-out’ from small groups of infected people to infect the wider population and eventually the world,” co-author Dr. Nuno Faria said in a statement.

The railway system connected Kinshasa to the larger population centers of Brazzaville, Lubumbashi, and Mbuji-Mayi. By the late 1940s, more than 1 million people travelled through Kinshasa each year. Although that number dropped by 1960, secondary foci of HIV-1 transmission had already been established and provided a fertile breeding ground for a viral explosion.

In addition to increased transport and growing population, a large influx of male laborers eventually led to a roaring sex trade. Faria et al. believe that unsafe sex and use of unsterilized needles contributed to turning HIV into a pandemic as opposed to a localized outbreak. The original animal to human transmission exponentially increased in a small window during the colonial area due to this dangerous combination of factors.

This study was a unique cross between analyzing pathogen strains across time and space and understanding the social aspect of disease dissemination. HIV-1 group M is not alone in its birth of social and biological factors. Cholera, for example, kills over 100,000 people a year, yet proper water sanitation can effectively eliminate this water-borne illness from the region. The ability for a disease to survive and thrive is dependent upon its environment. With archived pathogen collections and demographic data, researchers can track a disease through its evolutionary and societal history. Faria et al. wish to apply this “viral archaeology” to other blood-borne pathogens with hopes of stopping a disease before it becomes a pandemic.

References:

Faria, N.R., Rambaut, A., Suchard, M.A., Baele, G., Bedford, T., Ward, M.J., Tatem, A.J., Sousa, J.D., Arinaminpathy, N., Pepin, J., Posada, D., Peeters, M., Pybus, O.G., & Lemey, P. (3 October 2014). The early spread and epidemic ignition of HIV-1 in human populations. Science, 34 (6205). Retrieved from: http://www.sciencemag.org/content/346/6205/56.full.

[HIV-1 under electron microscope]. Retrieved October 6, 2014, from: http://imgarcade.com/1/aids-virus-electron-microscope/.

University of Oxford. (2014). HIV pandemic’s origins located [Press release]. Retrieved from http://www.ox.ac.uk/news/2014-10-03-hiv-pandemics-origins-located.

Wolfe, N.D., Dunavan, C.P., & Diamond, J. (17 May 2007). Origins of major human infectious diseases. Nature, 447. Retrieved from http://www.nature.com/nature/journal/v447/n7142/full/nature05775.html.

Zoonotic Disease: When Humans and Animals Intersect. (2014). In Centers for Disease Control and Prevention online. Retrieved from http://www.cdc.gov/24-7/cdcfastfacts/zoonotic.html.




Glossary

Bushmeat
Meat from non-domesticated mammals, reptiles, amphibians, and birds hunted for food in tropical forests. Bushmeat often comes in the form of non-human primates.

1 comment :

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