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Researchers Decipher Genome to Fight Ticks

(CN) - The fight against Lyme disease received boost as a team of 93 researchers from 46 institutions around the world announced Tuesday that they had mapped the genome of a blacklegged tick.

With the tick genome decoded, researchers can "begin to hack their system and write a counterscript against them," the team's head, Catherine Hill of Purdue University, said in a statement.

Primarily funded by the National Institute of Allergy and Infectious Diseases (NIAID), the research appears in the online, open-access journal Nature Communications.

"Ticks spread more different kinds of infectious microbes to people and animals than any other arthropod group," so the importance of the work cannot be exaggerated, NIAID director Anthony Fauci said in a statement,

"The spiral-shaped bacterium that causes Lyme disease is perhaps the best known microbe transmitted by ticks; however, ticks also transmit infectious agents that cause human babesiosis, anaplasmosis, tick-borne encephalitis and other diseases," Fauci added. "The newly assembled genome provides insight into what makes ticks such effective disease vectors and may generate new ways to lessen their impact on human and animal health."

About 2.1 billion DNA base pairs make up the tick genome, but the researchers said they managed to determine the order and sequence of about two-thirds of it.

"We determined the sequence for 20,486 protein-coding genes," Hill said, "of which 20 percent may be unique to ticks."

"Those tick-specific genes are like guideposts that say 'start here' as we look for new ways to counter infectious ticks," Hill added.

Unlike other blood-feeders like mosquitos, Hill said ticks are unique in that they have more proteins devoted to consuming, concentrating and detoxifying iron-rich food.

Other genes code for proteins that help ticks concentrate the blood and rapidly excrete excess water that accompanies large blood meals.

To accommodate a 100-fold increase in total body size during blood feeding, researchers said the ticks rely on a different set of genes that let them quickly expand their stiff outer coats.

Other peculiarities of the tick's lifestyle reflected in the genome include genes associated with the multifaceted sensory systems that the parasite uses when "questing" for a host during each of its separate blood-feeding stages.

Compared with mosquitoes, ticks appear to have fewer genes used to detect hosts, and, unlike a mosquito's "smell" receptors, ticks may use "taste" receptors to locate their food sources.

In an effort to explain variations in Lyme disease, which is carried by ticks and causes illness if it's not caught before the chronic stage, researchers examined ticks from five states in the Northeast and Midwest and three in the South.

There were 22,014 confirmed human cases of Lyme disease reported in the United States in 2012.

Some have speculated that ticks in the Northeast and Midwest spread the bacteria that cause Lyme disease more easily than those in the South, but the genetic analysis showed that there is only one species of I. scapularis.

The subtle genetic differences that researchers did detect, however, may help explain some of the variance in the ability of populations to transmit disease and, therefore, affect disease prevalence, Hill said.

Hill admitted to a grudging admiration for her eight-legged subjects.

"I find them almost endearing in the way they stick so firmly to the business of parasitizing their hosts," Hill said in a statement. "They are persistent and resilient. In a way, our team took a page from the tick's book in working together over so many years until we achieved our goal."

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