Female gluttony blamed on male tick

A certain species of tick has learned the secret to staying slim–by remaining virgins. Female ticks who mate will drink 100 times their weight in host blood, whereas virgins aren’t so gluttonous says a University of Alberta researcher who has discovered a protein that may offer clues to a $10 billion global tick problem.

“What happens is that a female will remain attached to a host, eating slowly and waiting to be fertilized,” said Dr. Reuben Kaufman from the U of A’s Faculty of Science. “If she does copulate, the seminal fluid contains an engorgement factor protein which acts as a signal to tell her to complete engorgement. Within 24 hours of copulation she will increase another 10 times her unfed weight.”

Female ticks require six to 10 days to engorge fully. The feeding cycle consists of three phases: a preparatory phase when she attaches herself to the skin; a slow phase, during which the female feeds to 10 times her unfed weight and the third phase after copulation when the female increases her weight a further 10-fold. The virgin tick, however, rarely exceeds the critical weight necessary for laying some eggs.

Kaufman and Brian Weiss, who was a doctoral student in the Department of Biological Sciences at the time of this research, produced a protein–recAhEF– from feeding-induced genes in the male gonad of the African cattle tick. This research is published in the latest issue of the Proceedings of the National Academy of Sciences journal. By injecting that protein into virgin ticks they could stimulate the tick to grow to full engorgement. Armed with that knowledge, the researchers then immunized a rabbit against recAhEF and found that about 75 per cent failed to feed beyond the critical weight, whereas mated ticks feeding on a normal rabbit engorged fully.

“We want to use these proteins as a basis of a vaccine,” said Kaufman. “If we can vaccinate cattle against this protein, or voraxin as we have called it, then they would be significantly protected against ticks. Not only would it control the tick problem–which is a $10 billion problem globally–but it would inhibit the disease ticks transfer as well.

“Ticks affect the growth of calves and they affect milk production, even with minor infestations.”

Currently, the major control mechanism used to treat ticks is pesticides, which often come with ecological problems and may affect the meat, said Kaufman.

Kaufman’s research was funded by a Natural Sciences and Engineering Research Council of Canada (NSERC) grant.