The Curse of the Pharaoh

Why do parasites kill their hosts? Surely if the host dies, the parasite is doomed itself and can’t propagate further? There is a hypothesis in biology that links the virulence of an infectious disease with how well the transmitter can live in the external environment.

Briefly put, it means that if a parasite can survive for a long time outside the host, the death of the host doesn’t necessarily mean the death of the parasite or at least the parasite’s offspring. For instance, roundworm eggs can survive in soil for years. Therefore, there is no reason why such a parasite would care to preserve the host but instead it would work as fast as possible to exploit it. This is called the ‘curse of the pharaoh hypotheses’ and it remains controversial.

Equally controversial is the origin of the name. In 1922 Lord Carnarvon and Howard Carter opened the Tomb of Pharaoh Tutankhamun which till today remains the only tomb of an Egyptian Pharaoh found intact. In 1923, Carnarvon died from blood poisoning probably caused by the infection of an accidental shaving cut on a mosquito bite wound. This led to the sensational story of the “Curse of Tutankhamun” which was supposed to fall upon whoever disturbed his rest. One hypothesis advanced was that Carnarvon had contracted a highly virulent and extremely long lived pathogen while opening the tomb, hence the name.

But why is this important now? As global temperatures rise, Siberian permafrost has started disappearing and species long locked underneath are surfacing. Scientists now regularly discover new species, including the famous giant viruses. To understand the significance of this, consider that HIV has only 12 genes and is about 120nm in size (1nm = 0.0000001 cm). In comparison, some of the newly discovered viruses are 1000 times larger and contain up to 2,500 genes.

Further, despite being frozen for thousands of years, some of these creatures never died. For instance, when a French team exposed the newly discovered Pithovirus sibericum (frozen for 30,000 years) to an amoeba, they immediately infected the cell, proving they were still virulent. Nobody has any idea what impact these viruses can have on our ecosystem or whether they could lead to diseases in humans.

Not surprisingly, one of the 3 groups of viruses discovered has been dubbed the Pandoravirus.

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1689335/pdf/9744106.pdf

[2] http://izt.ciens.ucv.ve/ecologia/Archivos/ECO_POB_2005/ECOPO6_2005/Kamo%20y%20Boots%202005.pdf

[3] https://en.wikipedia.org/wiki/George_Herbert,_5th_Earl_of_Carnarvon

[4] http://www.smithsonianmag.com/smart-news/microbiologists-keep-finding-giant-viruses-melting-permafrost-180956647/

[5] http://news.nationalgeographic.com/news/2014/03/140303-giant-virus-permafrost-siberia-pithovirus-pandoravirus-science/

[6] http://www.bbc.co.uk/programmes/b08bb9cy

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