Tuesday, March 18, 2008

OMG It’s Nature: Of Lizards & Lyme Disease

This is the first in a new series of post-headings: "OMG It's Nature". Originally, it was "OMG It's Freakin' Nature", but I withheld the "Freakin'" for those with more delicate sensibilities. These posts will focus on the natural goings-on in Santa Clarita.

I've decided to start with fence lizards, an oft overlooked but profoundly important part of SCV's native fauna. And they're scurrying around all over in the recent warm weather, so why not give them a shout-out? The story isn't a new one (the research I reference is nearly 10 years old), but it's one I like very much. In any case, I present to you the fence lizard (and ticks, bacteria, and rodents, too) and hope that the next time you see one, you'll exclaim "OMG It's Nature!"--in a good way.


There are plenty of animals that no one but the most ardent of tree-huggers wants to see in their yard: ants, skunks, rabbits, wasps, American Coots, etc… The list of animals we welcome with open arms is decidedly shorter, usually just some smallish birds and butterflies. To this list of beasts gleefully greeted by homeowners I propose an addition: the Western Fence Lizard (Sceloporus occidentalis). No, they don’t sing or flit about flowers, but they do help in the fight against Lyme Disease.

Western Fence Lizards (also called Blue-bellies) are exceedingly common, even in our own backyards. In recent weeks you’ve probably noticed them getting active again and scampering over fences, rocks, and paths. At this same time of year ticks also grow more active. I've had a couple of ticks myself, and they’re thoroughly unpleasant. Apart from the gross-factor (who likes having an invertebrate parasite stick its head in your bloodstream?) public health officials point to a long list of tick-borne diseases[1]. There’s Rocky Mountain Spotted Fever, Tularemia, Babesioisis, and--most infamously--Lyme Disease.

Lyme Disease is caused by a spirochete bacteria called Borrelia burgdorferi. Locally, it is the black-legged tick (Ixodes pacificus) that is responsible for passing on the spirochetes to the blood stream of their human hosts. When this happens, Lyme Disease follows.

Happily, we have Western Fence Lizards on our side. Not only do they eat ticks, but they cure the ticks that bite them of the Lyme Disease spirochete.

Indeed, when an immature tick (called a “nymph”) happens to bite onto a lizard for its blood meal, something remarkable happens. As the tick feeds, proteins in the lizard’s blood serum destroy spirochetes in the tick’s gut. Thus, when the tick is finished feeding and drops off the lizard, it is no longer a carrier of B. burgdorferi and won’t cause Lyme Disease in the next animal (including humans) that it bites.

The experimental support for this phenomenon is exceptionally strong. In a 1998 study by Robert Lane and Gary Quistad at UC Berkeley, 10 fence lizards were captured and brought into the lab[2]. The researchers placed 10 nymphs on each lizard. These nymphs were from a colony of ticks that were confirmed carriers of the Lyme Disease causing spirochete. After the ticks finished feeding on lizard blood, Lane and Quistad re-tested them for presence of the spirochete. Precisely 0% of the ticks were infected.

In a complementary experiment, the researchers dropped live spirochetes into blood serum drawn from lizards or mice. The spirochetes did just fine in the mouse blood, living for 2 or 3 days, but all of the spirochetes were destroyed after just one hour in culture with lizard blood serum. The protein responsible for destroying the spirochete seems to be present in other local lizard species as well, such as the alligator lizard[3].



Western Fence Lizards: not only are they fun to watch, their blood carries, in the words of Lane & Quistad, a "thermolabile Borreliacidal factor"! I'd look more excited if I had some of those.

As very common hosts of tick nymphs, Western fence lizards do us a great service in destroying the spirochetes responsible for Lyme Disease. Studies have begun to investigate how effectively lizards reduce the prevalence of the bacteria in ticks in the wild, and this work should be of great interest to those working in the fields of public health or epidemiology.

The Western Fence Lizard has a relatively small range—primarily just California, Oregon, and Nevada--so Santa Clarita is lucky to fall within this area. And since the lizards are doing so much for us, perhaps we should consider being a little more welcoming to the likable little reptiles. Rock piles for basking and abstaining from pesticides would be great. Keeping pet cats inside (have you ever noticed how many lizards cats take?) would be even better. I know that prioritizing wildlife over an exceptionally green lawn is decidedly unnatural for most Claritans, but it might be worth a try.

Now, just because we have lizards whose blood proteins destroy Lyme Disease spirochetes doesn’t mean we don’t have to worry about Lyme Disease. Infected nymphs and adult ticks will likely always be around, at least in small numbers. In California, there are new incidents of Lyme Disease every year, and it’s important to take the threat seriously. Still, it’s nice to know that our risk of the disease may be lessened by our friends, the fence lizards.


[1]Ticks, like mosquitoes, are shockingly good at spreading disease. Both of these bugs are essentially just biological syringes, and I’m sure mom warned you not to share syringes with your friends.
[2]Source: R.S. Lane & G.B. Quistad. 1998. Borreliacidal factor in the blood of the western fence lizard (Sceloperous occidentalis). Journal of Parasitology vol. 84, pp. 29-34.
[3]Source: M.M. Kuo, R.S. Lane & P.C. Giclas. 2000. A comparative study of mammalian and reptilian alternative pathway of complement-mediated killing of the Lyme Disease spirochete (Borrelia burgdorferi). Journal of Parasitology vol. 86, pp.1223-1228.

2 comments:

mike devlin said...

thanks for the lesson... one summer, my cousin was visiting from Philadelphia. He woke up one morning and half of his face was paralyzed. It seemed like he was giving every nasty looks. That night he took a trip to the ER and it took the doctors over four hours to figure out it was Lyme Disease. Common back there, but almost unseen in a given ER out here.

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