It is an age-old dance as a ground squirrel attempts to evade the rattlesnake's repeated strikes. A step is missed. Teeth sink in, delivering a full dose of flesh-dissolving venom - able to kill larger prey instantly.
Yet the ground squirrel leaps away to dance again another day.
Fairfield professor James E. Biardi explores venom resistance in ground squirrels in his recently published journal article. The research, funded by a UC Davis fellowship grant, may eventually lead to future venom treatments.
Biardi and his team found that the ground squirrel's protection against rattlesnake venom is highly specific. They were surprised that the ability to neutralize venoms - considered virtually identical - from two similar rattlesnake species differed significantly.
Furthermore, ground squirrels sampled from sites with higher rattlesnake density showed greater inhibition of venom activity - suggesting co-evolution.
"Understanding [resistance to venom in] ground squirrels... could potentially lead to better human treatments," said Biardi
About 125,000 deaths worldwide result from snakebites annually according to emedicinehealth.com.
Conventional antivenom consists of antibodies which attach themselves to venom molecules in order to disable them. Although antibodies are produced by the body as part of the immune response against specific disease-causing substances, it normally takes the body days to build a strong response.
Since this natural response is too slow, victims are routinely treated with antibodies from animal sources in cases of envenomation.
Generally, these antibodies are harvested from large animals (horses, cows, etc.) which have been injected with small doses of venom. However, Biardi said that antibodies are less effective against the rapid breaking down of tissues which are characteristic of rattlesnake venom.
Ground squirrel resistance is special because is innate. They constantly maintain high levels of proteins in their blood for immediate protection against venom, said Biardi. In other words, ground squirrels may hold the key to a potentially better alternative to antibodies for treating rattlesnake envenomation.
The activity of the venom was approximated using radioimmunoassays (RIA). This method involves venom which has been tagged with radioactive isotopes to distinguish it from test venom. Initially, tagged venom molecules are bound to antibodies.
Next, test venom - which has been mixed with ground squirrel blood plasma - is added to that solution.
Some of test venom particles may then steal antibodies from the tagged venom as they try to bind to the antibodies. To estimate venom activity, researchers measured the amount of unbound tagged venom. They then compare these numbers with those of samples from other sites along with venom alone as a control.
Researchers surmised that the ability of plasma proteins to protect ground squirrels from venom should correlate with how well the plasma proteins reduce the ability of the venom to steal antibodies.
Biardi admits however that RIA only gives indirect information about ground squirrel resistance. However, unlike earlier studies, this method avoids the "ethically not preferable" way of injecting the venom directly into the animals.
Blood samples were collected from live California ground squirrels which were sedated prior to collection. The squirrels were then released back into the site of capture upon recovery.
"There is still a lot to learn about [ground squirrels]," said Biardi, who intends to do further research involving ground squirrels and snakes in the future.