Critter Chemistry

October 13, 2004

The Stunning Saliva Of Shrews

Researchers are trying to unravel the mystery of the shrew's venomous brew

In the 1959 horror movie The Killer Shrews, giant shrews from an experiment gone wrong attack people stranded on an island during a hurricane. The giant shrews terrorize the castaways with sharp teeth, long claws, and poisonous saliva.

Surprisingly, the poisonous saliva is one of the few believable points of this movie.

SHREW SPIT Two compounds are thought to give Blarina brevicaudas saliva a little bite.

Photo by Daisuke Uemura

Venomous mammals are rare, but the North American short-tailed shrew, Blarina brevicauda, secretes venom from salivary glands in its lower jaw to paralyze prey.

The secret behind the shrews stunning saliva intrigues at least two research groups.

John M. Stewart, a biochemistry professor at Canadas Mount Allison University, Sackville, New Brunswick, has been studying B. brevicaudas venom for about four years. His team found a small, active peptide in the shrews venomous brew that theyve since synthesized and named soricidin, after the shrew family Soricidae.

Stewarts interest in shrew venom was sparked when a visiting postdoc, Karl Vernes, showed him a small groove in the outer side of a shrews lower incisor. Vernes explained that the groove is where venom is injected into the prey. Stewart wanted to know what the venom consists of but soon found out that the material had never been purified. He decided to pursue the matter.

Stewart is in the process of patenting soricidin for pharmaceutical and cosmetic uses. His group noticed that soricidin exhibits paralytic properties, making it potentially useful in treating migraines, myofacial pain, neuromuscular diseases, and even wrinkles. Imagine having a choice of shrew spit or Botox to achieve a more youthful look.

Meanwhile in Japan, Nagoya University chemistry professor Daisuke Uemura and research associate Masaki Kita recently published a paper on a completely different toxin they and coworkers isolated and characterized from tissue in the shrews mouth [PNAS USA, 101, 7542 (2004)]. The toxin, called blarina toxin, is a glycoprotein found in the shrews lower salivary gland.

Studying shrew saliva came naturally to Uemura and Kita. Their research, Uemura says, focuses on the identification of natural key compounds that control biologically and physiologically intriguing phenomena. Since mammalian venoms are rare, shrew saliva was a perfect candidate.

Blarina toxin, like soricidin, has some pharmaceutical possibilities. Uemura says blarina toxin may be able to lower blood pressure for the treatment of hypertension and Raynauds disease, a condition limiting blood circulation to the extremities.

Shrewsconcerned with eating and not with wrinkles or circulatory issuesuse poisonous saliva to paralyze prey. A shrew can then store captured prey for future feedings. Stewart observed that soricidin immobilized a mealworm for 15 days. Because the paralyzed prey is still alive, there is no worry about spoilage.

Short-tailed shrews, generally only 3 to 4 inches long, prey mainly on invertebrates, though they sometimes feed on small vertebrates and plants. They rarely prey on anything larger. Dragging large prey, such as an adult mouse, back to their nests would be inconvenient. As Stewart explains, It would be like parking a dead cow in your living room in case you got hungry during Seinfeld.

A shrew seems to be safe from its own venomous spit. Keith A. Carson, associate professor of biological sciences at Old Dominion University, Norfolk, Va., speculates that as long as the venom stays in the saliva, it should be destroyed by stomach acids and enzymes. Blarina toxin, for example, is a large protein and would be difficult to absorb through mouth tissues. However, if a shrew bit another shrew during a territorial fight, Carson suspects that the bitten shrew would succumb to the venom.

Although a shrew bite can mean the end for an earthworm, a juvenile mouse, or even another shrew, humans dont have much to fear. On the rare occasion a shrew bites a person, the wound may swell and be painful for a few days. Contrary to B-rated horror flicks, no giant shrews are going to cart you back to their living room for a Seinfeld snack.