It's a Tick's Life
by Jake Farley
For our readers who love to spend time outdoors, ticks are indeed the enemy. In this case, a little knowledge can be a good thing.
All ticks in New Jersey are hard ticks with a two-year lifecycle. These include deer, Lone Star and wood (dog) ticks. This two-year lifecycle is important in the transmission of Lyme Disease and also in maintaining the Lyme Disease cycle in the wild.
The spirochete, Borrelia burgdorferi, causes the disease and, according to Webster, a spirochete is “any of an order (Spirochaetales) of slender spirally undulating bacteria."
Deer ticks, lxodes scapularis, need three hosts in order to take a blood meal at each stage in their metamorphosis. The larva need it for nutritional development and to help them molt; nymphs need it to molt to adults; and adult females need blood for egg production. Males don't take big blood meals because they don't need it. The current thought on adult males is that they attack but are not good vectors of Lyme Disease.
Here's how these blood suckers operate:
Adults over-winter and take a blood meal in March and April and lay eggs which hatch in August, the peak season for uninfected larva. The larva take a blood meal, then are finished for the year and burrow down to over-winter. If they happen to have fed on infected white-footed mice they pick up the spirochete, and when they emerge as nymphs the following May, June and July, they are infected.
The infected nymphs take a blood meal, again on mice, which helps infect new mice. So when larva hatch in August, there's a good chance they'll feed on infected mice. This is how the two-year life cycle maintains the disease: two generations living, feeding, ingesting and transmitting the spirochete simultaneously.
Meanwhile, nymphs molt into adults in late fall. The adult female stays active from October to December as long as it's warm. The adults we see in the spring have over-wintered without a blood meal in the fall, so they are hungry and looking.
Infection rate of ticks: 49.3% of adults, 25% of nymphs, 1% of larva.
Sean Healy, entomologist with Monmouth County Mosquito Commission, tick-borne disease program, collects deer ticks and tests them. His research involves looking for the DNA of the pathogen in infected ticks that are dead or alive. (See list of Labs.) With dead ticks, the whole tick is needed to detect infection. Healy says it takes at least 24 hours for the spirochete to replicate inside the tick and move from the mid gut to the salivary gland, then transmit to a human.
How to identify:
The adult female deer tick is the easiest stage to identify, but the characteristics become hard to see when it's engorged. The female has a tear-drop shape with an almost solid black dorsal shield near the head, surrounded by a reddish-orange abdomen. (The abdomen appears to be on its back.) The dorsal shield is a hard plate and does not expand. In males, it covers the entire back. The female dog tick has mottled brown and white markings on the dorsal shield.
Good tick habitat exists in most hardwood forests, which are everywhere in DIG IT! territory. Ticks like brushy understory that enables them to “host seek and quest." They climb on shrubs and low-lying vegetation along the edges of trails and paths with their legs outstretched and wait for a host to brush by, whether deer or human. A male only attaches to a host to wait for a female or just to be moved to another place. Mating occurs on a host, like a white-tailed deer. “If you're a tick, the best place to find a mate is on a host," says Healy.
Desiccation is a major cause of tick mortality. Rain keeps vegetation and leaf litter moist‚ perfect tick habitat. Even so, ticks don't hide on dry days or wet. They host seek regardless of the weather.
“In early spring we deal with infected adults that over-wintered. By late May, and June and July when the nymphs are out, fewer ticks are infected, but they are much smaller and harder to find so they remain attached longer and, if they are infected, cause disease. Lyme Disease peaks in New Jersey and corresponds with peak deer tick nymph activity," Healy says.
So what good are ticks? Whether you believe in creation or evolution or both, then one must think there is a reason for ticks. The answer: they help keep the rodent population down.
More than the usual tips:
Self: Wear something slick - no fleece.
Take a shower and scrub your entire body to dislodge unattached ticks. Then, run your hand smoothly over your skin to feel any new bumps - it could be a tick!
The yard: Clear out vegetation along edges. Clean out leaf litter. Problem areas in most yards are at the edge where the lawn meets the woods. It's good habitat for preferred hosts, such as mice, chipmunks, deer.
Clothing: With their hard protective shell, ticks survive a washing machine and, often, a dryer, but if you dry your clothes long enough and hot enough, you'll kill them.
DIG IT! asks: “After a tick becomes embedded in a human -- or dog -- how soon does it start to become engorged? To know this would enable the host to gauge how long the tick has been in its skin."
Healy answers: “Of course there is no simple answer to this. Regression equations based on scutal index (body length/scutal width); have been developed to help determine the duration of attachment for nymphal and adult female lxodes scapularis ticks. But these are not easy to do without microscopes and the technique is still an educated guess at best. There are many factors that further complicate this.
"I. scapularis nymphs usually feed between 3-5 days until fully engorged. Adult I. scapularis females feed 7-10 days until fully engorged. On top of this, virgin females are not able to enter the rapid engorgement phase that occurs in the hours just before detachment. Yes, how long a tick has been attached is a very important risk factor in determining the likelihood that transmission of a pathogen has occurred. Transmission (for B. burgdorferi) studies with I.scapularis nymphs did not show transmission after 24 hours of attachment; half of the nymphs transmitted after 48 hours and all of the nymphs transmitted after 72 hours of attachment. In adult I. scapularis similar studies showed no transmission after 36 hours of attachment; half of the adults transmitted after 48 hours and all of the adult I. scapularis transmitted after 120 hours or greater of attachment.
"A study published in 2001 in New England Journal of Medicine found prophylactic treatment with 200 mg of doxycycline to be 87% effective in preventing Erythema migrans in adults if administered within 72 hours after the discovery of an attached tick. The transmission times for other species of ticks and other disease causing organisms are going to vary (longer and shorter)."
***All photos courtesy of Sean Healy
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published May 28, 2004