The Little Tick That Will Let You Find New Friends
We’ve known about Lyme for many decades now. So why is everybody so concerned this year?
For sportsmen and folks that spend time in the outdoors, Lyme disease has long been a concern. Knowing what to look for and how to prevent these little critters from doing damage to the human body is important.
The reason I am bringing the issue up is two-fold. This year it looks like a reflex storm for the ticks that act as hosts for Lyme and with the discussion regarding deer in the city limits of Jamestown at the forefront, this may be another reason to get off our butts and finally do something.
It’s no big secret that deer over the past several years are becoming a problem for city residents. I would like to ask the “powers to be” this: What is it going to take to seriously do something about the overwhelming deer population in the city limits?
With summer just starting and local schools winding down, students are out and about. It’s not a stretch to see that deer-human conflicts could be an issue. Just as important is what we can’t see, the black-legged tick that carries Lyme. It’s my hope that once folks learn how Lyme is carried and how it can happen anywhere to anyone, maybe, just maybe, they will understand the serious situation we are in.
Two factors in particular seem to be making it easier for the tick that carries Lyme, the American black-legged tick (Ixodes scapularis) and in Europe, its cousin, the castor bean tick (I. ricinus) to spread the disease. One is an explosion in the populations of the creatures on whose blood it likes to feed. The other is global warming. Both, of course, are humanity’s fault. Ticks feed entirely on blood. They need a bloodmeal to graduate from larva to nymph and from nymph to adult — the three stages of their life cycle. Females must take a third bloodmeal to lay eggs. All this usually happens in about the space of two years.
When they hatch (usually) in late spring, tick larvae are tiny — no bigger than the period at the end of this sentence. These newborn ticks are programmed to toddle out to the end of a blade of grass and wait there, squatting with their upper legs outstretched — something scientists call “questing.”
When a suitable animal — usually a small rodent or bird — ambles close enough by, the tiny larva grabs hold. After burrowing through some fur or hair, the tick latches into a nice patch of skin, saws through flesh, inserts its straw-like mouthtube, and starts sucking away on blood. Once it has gulped down this first bloodmeal, which takes a few days, the tick drops to the ground, ready to molt into the next stage of its life cycle: a nymph.
For Lyme transmission, this first bloodmeal is critical. A larval tick isn’t born carrying the Lyme spirochetes. It needs to pick up the bacteria from the host it feeds on. Only then, after reawakening as a hungry new nymph, can the tick pass Lyme on to the next host it feeds on.
So, what are those typical hosts? In the popular imagination, deer are practically the mascot of Lyme’s seemingly freak emergence in fact, most folks call it (I. scapularis) the “deer tick.” And indeed, the deer population has exploded in the last few decades, after nearing extinction in the 19th century.
Deer are indeed a favorite blood source for adult female ticks. A single deer might feed 100 adult ticks, which drop off and lay as many 3,000 eggs each.. But deer are usually much too big for larvae and nymphs to grab hold of which is why they’re not the real culprit for the spread of Lyme.
Research suggests that white-footed mice are more important numerically. Basically, mice are a fantastic host for both the tick and the bacteria that causes Lyme.
White-footed mice infect 75 percent to 95 percent of larval ticks that feed on them. Deer infect only about 1 percent. So, while deer are key to helping the adult ticks get the blood they need to reproduce, it’s mice that are crucial in helping the disease-causing bacteria spread to infant ticks.
One big reason is simply that white-footed mice are sloppy groomers. Most mammals will claw, bite, or lick ticks off their bodies while scratching or cleaning themselves, often killing the tick in the process. But scientists sometimes find a few dozen ticks latched onto a single tiny mouse.
The Lyme transmission cycle goes like this. A nymph or adult tick that has already picked up Lyme disease bites an animal. It takes a few weeks for the bacteria to reproduce in the animal’s bloodstream enough for it to become infectious. Any larval ticks that then bite that critter will pick up the disease, passing it on after they in turn molt into nymphs.
Whether the Lyme bacteria keep spreading therefore depends a lot on when each generation of larval ticks is feeding. If larvae happen to feed at the same time as newly emerged nymphs what biologists call “synchronous feeding” they’re less likely to pick up the infection, since the bacteria won’t have had enough time to reproduce inside the mammal hosts.
But if newly hatched larval ticks feed much later than the nymphs (“asynchronous feeding”) they’ll be more likely to pick it up and to transmit it the next season as nymphs.
After lying dormant for winter, adult ticks emerge in the spring, find a bloodmeal, probably a deer, and lay their eggs; those start hatching in midsummer. In the American Midwest, these newborn larvae often fail to find a bloodmeal before chilly fall weather forces them into dormancy for the winter.
When they wake again in the spring, two things will happen. First, they’ll be feeding on hosts early in the season, weeks before these animals have become infectious. Second, there’ll be relatively fewer nymphs around to infect new hosts. And thus, the chain of transmission gets broken.
In the American northeast, however, the autumn weather stays warm long enough that a higher percentage of newborn larvae manage to feed, molt and spend the winter as dormant nymphs. When they come out of hibernation, they’ll have time to bite and infect new animal hosts well before the next generation of larvae can hatch and feed.
This, scientists think, is one factor explaining why Lyme plagues New England residents more than it does American Midwesterners.
The mean temperature for October in the U.S. Northeast has risen an average 0.1 degree Fahrenheit (0.06 degrees Celsius) each decade during the last century according to the National Centers of Environmental information. The upper Midwest, where synchronous feeding occurs, in theory has been warming at the same rate as the northeast, and in some places even faster. However, it’s still much colder there. For instance, in eastern-central Minnesota, the state’s Lyme epicenter, October’s temperatures have averaged 45.9∂F since 2000, compared with the New York Hudson Valley’s 51.3∂F.
Admittedly, climate is probably not the whole story. For instance, it doesn’t explain why ticks feed synchronously in both frigid Minnesota and the much more temperate UK. And unfortunately, it’s nearly impossible to know what larvae are up to for sure, because they’re too tiny to track in the wild.
But if the theory is right, places where Lyme has been relatively muted up to now could be in for trouble.
What all this means for people is still pretty simple: The best protection against Lyme is not to get bitten. The next best defense is nipping the problem in the blood-filled bud. Since it can take a while for the spirochetes to travel from the tick into the new host’s bloodstream, removing a tick within 24 hours of its attaching dramatically slashes your chances of getting Lyme.
The trouble is, while you might think you’re good at plucking off ticks after a stroll through some underbrush, the ones you find are probably adult ticks. About the size of a match head and as big as a pea once engorged with blood they’re relatively easy for vigilant humans to see and feel.
Nymphs, though, are roughly half the size of adults, about the size of a poppy seed. Tiny enough to pass for a smallish mole or freckle, they’re far harder to find than adults are; no surprise, then, that most human Lyme infections come from nymphs. All you can do is to take precautions against getting bitten, search for ticks thoroughly, remove them carefully if you find them, and look out for Lyme symptoms afterwards.
It’s important that anybody that spends time in the outdoors understands the signs for Lyme, what look for and the proper way to handle them.