22 June 2010

Genome of human parasite throws up surprises

Agence France-Presse
Scientists have sequenced the genome of the body louse, offering insights into human biology and insect evolution that could help detach us from our inseparable, blood-sucking companions.
Male body louse with blood

Male body louse: the dark mass inside the abdomen is a previously ingested blood meal. Credit: Janice Harney Carr/U.S. Centres for Disease Control and Prevention

WASHINGTON: Scientists have sequenced the genome of the body louse, offering insights into human biology and insect evolution that could help detach us from our inseparable, blood-sucking companions.

The study, published in the Proceedings of the National Academy of Sciences, showed the louse had the smallest genome of any insect and very few genes related to light reception, odors and tastes.

The body louse has “the smallest number of detoxification enzymes observed in any insect,” researchers wrote, suggesting new repellants could one day help rid us of the tiny mites that have been our companions for millions of years.

Louse turned the course of history

“The ecology of lice is very, very simple. It either lives in your hair or on your clothing, and it has one type of meal, and that’s blood,” said University of Illinois entomology professor Barry Pittendrigh.

“So most of the genes that are responsible for sensing or responding to the environment are very much reduced,” said Pittendrigh, who coordinated the research of 28 institutions in the United States, Europe, Australia and South Korea.

Known to experts as Pediculus humanus humanus, the body louse has played its unsanitary part in history, blamed for spreading typhus and trench fever to Napoleon’s retreating army in Russia in 1812.

Completely dependant on humans for survival

“As an obligatory parasite of humans, the body louse is an important vector for human diseases, including epidemic typhus, relapsing fever, and trench fever,” the study said.

“Thus, the body louse genome project offers unique information and tools to use in advancing understanding of coevolution among vectors, symbionts, and pathogens.”

Completely dependent on humans for its survival, the louse will die if separated from its host for very long.

Genome will help to control louse

In turn a tiny microbe, the bacterium Candidatus Riesia pediculicola, lives inside it and produces pantothenate (Vitamin B5), an essential nutrient for its host’s survival.

The study also sequenced the genome of the microbe and pointed out that the research was key to understanding the co-evolution of disease-carrying parasites and their bacterial co-conspirators.

“Lice have been used to understand human evolution and migration. They’ve been used to estimate when we started wearing clothing,” Pittendrigh said. “The genome should also help us develop better methods of controlling both head and body lice.”

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