Yesterday evening Deborah found her first deer tick of the season. She had been working out in the yard clearing leaves and downed sticks from the yard, and later found an adult deer tick attached to her leg. She removed the tick (directions for removal are provided at the end of this blog!) and put it into a jar of isopropyl alcohol, and, being a good biologist, brought it up to campus, took its picture through a dissecting microscope (photo on the left!), and added it to the Penn State New Kensington Invertebrate Collection.
Below is a composite of the two blogs I sent out last Spring and Fall in which I discussed deer ticks. For those of you who are interested in more information about Lyme Disease, one of my students is presenting a research poster about it at next week’s Research and Creative Exposition at Penn State New Kensington. The Exposition is Tuesday, April 8 from 1 pm to 3 pm in the Field House on the Penn State New Kensington Campus. Please come!
The “black-legged tick” (sometimes called the “deer tick” or the “bear tick”) is most precisely named Ixodes scapularis. It is a small, common tick found throughout the northeastern and north-central parts of the United States. It is also a transmission vector for a number of bacterial and viral pathogens including the bacterium that causes Lyme disease, Borrelia burgdorferi.
The life cycle of Ixodes scapularis stretches out over two or sometimes three years. Eggs laid in the fall in low, grassy or scrubby vegetation hatch the next summer into the very small, six-legged larva life forms. These tiny ticks typically seek out small hosts (like a white-footed mouse or a bird) but are able opportunistically to attach to larger mammals including humans. These larva, though, are not born with any of the pathogens associated with Ixodes scapularis and are, thus, unable to transmit any of its diseases. If these larvae feed on a host that is carrying one of I. scapularis‘ bacterial or viral pathogens, though, that tick will become infected with that disease causing agent and will carry it and be able to transmit it throughout the rest of its life cycle.
After the larva has taken its blood meal it molts into the larger, eight-legged nymph life form. This molt often is delayed until the following spring. These nymphs, then, seek a host for their blood meal. These hosts are usually mammals ranging in size from white-footed mice to deer to humans. Because of the timing of this nymph emergence the spring (May and June here in Western Pennsylvania) is a time of great risk for ticks bites (and disease transmission) for humans!
After the nymphs have taken their blood meals they molt into adults. These adults are especially abundant in the fall. These much larger life forms (like the tick in the picture above) typically attach to large mammals (like white-tailed deer or humans). The female adult ticks take a large blood meal from their hosts and then use the energy from this feeding to make eggs. The adult male ticks attach to the same hosts, but do not feed (and, therefore, do not transmit pathogens). They are there to find a female and to mate! The males die shortly after mating and the females die after dropping off of their hosts and laying their eggs in the grassy and scrubby vegetation. Those eggs then overwinter and hatch in the summer to start the life cycle all over again..
The number of Lyme Disease cases has greatly increased in recent years. The reason for this increase is attributed to increases in the most critical host in the black-legged tick’s life cycle: the white-footed mouse. Fragmentation of forest habitats and the optimal conditions of suburban ecosystems for these mice along with significant declines in their natural predators have led to great increases in their numbers. Black legged ticks, then, in their larval and nymphal life stages are very likely to find a white-footed mouse on which to feed. These mice are also significant reservoirs for the bacterium that causes Lyme disease, so the ticks have a very high probability of assimilating and then passing on these bacteria.
In 2011 Pennsylvania led the nation in the total number of cases of Lyme disease. Per capita numbers put the New England states ahead of Pennsylvania in disease occurrence, but it is a significant health problem throughout our state. The Center for Disease Control (CDC) has increased its estimate of the number of Lyme disease cases nationwide from 30,000 to 300,000 per year. Recommended therapies for Lyme disease have expanded from 10 days of antibiotic therapy to 30 or more days of treatment. There is also now a recognized Post Treatment Lyme Disease Syndrome in which debilitating symptoms of the disease can persist in patients for many years.
It is important to remember that the black-legged tick is not able to begin its blood feeding until after it has been attached to its host for at least 36 hours. Careful examination for ticks and their rapid removal is the best way to prevent contracting the Borrelia bacterium. Tick removal is best accomplished using a pair of forceps or a v-slotted, commercial “tick-remover.” Gently pull the tick from its spot of attachment making sure that you remove the feeding structures (the “head”) along with the body. Then dispose of the tick in whatever creative way you might wish! Ways to prevent tick attachment include wearing long pants and long-sleeved shirts when out in the woods or fields. Also, using DEET-based insect repellants on socks, pant legs, etc. reduces the chance of tick attachment. A thorough “tick check,” though, after being out in a potential tick habitat is a very effective way to reduce the chance of infection. There is a vaccine against the 36 known species of Borrelia in the works. This vaccine has passed early clinical trials and, hopefully, will be available soon to help prevent this potentially debilitating disease.
The black-legged tick is an unfortunate sign of both spring and fall. Let’s hope that soon we won’t have to worry about them when we go out hiking in our beautiful forests and fields.