Nature Notes by Dr. Frank Lang

The flat bench just below the final itch to the summit of the Lower Table Rock trail in Jackson County, Oregon, is forested with a dense stand of stump-sprouted madrone trees. I often stop here on my wav to the top of the rock to catch my breath and look at large piles of sticks and branches scattered in the undergrowth that are the homes of dusky-footed woodrats,

Dusky-footed woodrats build homes of wood with multiple entrances and chambers. Like their real packrat cousin, the bushy-tailed woodrat, they add various items to their homes beside sticks and twigs. Woodrat houses are also home for many inquilines, animals occupying the home or nest of another. Spiders, springtails, centipedes, beetles of various kinds, sometimes frogs, salamanders, fence lizards, and other small mammals occupy woodrat homes.

Not only do dusky-footed woodrats share their homes with others, but they share their bodies as well. Duskyfooted woodrats are hosts to a horrific number of external and internal parasites. Some of them are enough to make the Marquis de Sade wince. Take warbles, for example: large, oozy, open, lumps that contain fly larvae. Larvae that may be 26 mm long, 12 mm in diameter and weigh nearly two grams. Larvae that slowly work their way out — ugh!

There is something else you or the Marquis won’t want to hear, either. Other parasites include fleas, mites, lice and ticks. Among the ticks are two that belong to genusIxodes, the Lyme disease vector. One tick, I. neotomae, sticks to woodrats and other small rodents. The other, I. pacificus, has more catholic tastes and bites other hosts, including humans. Among woodrats’ internal parasites are various roundworms, tapeworms, protozoans, and a spirochete, Borrelia burgdorferi, the cause of Lyme disease.

Discovery of the spirochete helps-explain some features of Lyme disease in the western United States, or at least in California. In the eastern United States 25% to 50% of the ticks are infected. In the west only 1% to 3% are infected, although there is some evidence this has been underestimated. We didn’t know why. Deer mice carry the parasite in the east. We didn’t know what the natural animal reservoir might be in the west. In California and likely Oregon, it turns out to be the poor duskyfooted woodrats, who infect each other via woodrat ticks. Only occasionally will I. pacificus ticks pick up the disease from woodrats and pass it on to humans: just often enough to transmit the disease to humans, but far too often for those who get the disease and let it go too long without proper treatment.

Another sink down whose drain Lyme disease goes are I. pacificus ticks that attach to reptiles like our western fence lizard and our alligator lizards. Ticks attached to them, not us. This means we don’t get the parasite because some factor in lizard blood kills the Lyme disease bacteria.

If bitten by a tick, carefully pull it straight out, by the head and not the abdomen, as soon as you discover it. Save the tick. If flu-like aches and pains soon follow and/or a strange round rash occurs, get to a physician with your dried-out tick. Treated early, antibiotics kill the Lyme disease parasite. Left too long Lyme disease is very difficult to treat and may lead to a human life of painful misery.

Don’t go out killing woodrats. lxodes pacificus apparently has a broad enough host range to shift to something else. A strategy that might work is to take advantage of the woodrat’s packrat habits. Dusky-footed woodrats might take home things like cotton soaked in a good tick killer. Not only might we get rid of Lyme disease in areas frequented by woodrats, ticks and humans, but we might make the woodrat’s life a little better in the bargain.

— Dr. Frank Lang

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