Tick-born Lyme disease is becoming more of an issue with each season. Maryland has documented an increase in statewide-diagnosed cases from 1,248 in 2006 to 2,576 in 2007. Virginia doesn’t have 2007 figures yet, but it experienced an increase from 67 in 1997 to 357 in 2006. Both figures represent records for the States.
Lyme disease is a bacterium transmitted by the black-legged, or deer tick (Ixodes scapularis (dammini). With nearly 900 species of ticks worldwide, and four commonly found in our mid-Atlantic region, only the deer tick is known to transmit Lyme disease.
The four most common ticks in Virginia that are encountered by humans are the lone star tick, the American dog tick, the brown tick, and the deer tick. The lone star tick is found predominately east of the Blue Ridge Mountains. The American dog tick is found predominately west of the Blue Ridge Mountains. The brown dog tick can be found throughout Virginia but tends to be uncommon. The deer tick is uncommon also and is found primarily in the northern and eastern sections of Virginia.
Ticks, along with mites, make up the order Acarina, which, along with the orders of scorpions, daddy long-legs and spiders, make up the Arachnid Class of Arthropods. The Phylum Arthropods (joint-legged animals) include such diverse Classes as crustaceans (crayfish and sow bugs), insects, millipedes, centipedes, and the extinct trilobites.
Deer ticks, as all of our native ticks, require at least two years to complete their life cycle. In June and July, eggs deposited earlier in the spring hatch into tiny six-legged larvae. Peak larval activity occurs in August, when larvae attach and feed on a wide variety of mammals and birds, primarily on white-footed mice. After feeding for three to five days, engorged larvae drop from the host to the ground where they over winter. In May, larvae molt into nymphs, which feed on a variety of hosts for three to four days. In a similar manner, engorged nymphs detach and drop to the forest floor where they molt into the adult stage, which becomes active in October. Adult ticks remain active through the winter on days when the ground and ambient temperatures are above freezing. Adult female ticks feed for five to seven days while the male tick feeds only sparingly, if at all.
Adult ticks feed on large mammals, primarily upon white-tailed deer. Beginning in May, engorged adult females typically lay between 1000 to 3000 eggs on the forest floor at the site where they detached from their hosts.
Human exposure to blacklegged ticks is greatest during the summer months when high nymphal deer tick activity and human outdoor activity coincide. However, Lyme disease cases are diagnosed every month of the year. Their small size, their vastly greater abundance over the adult stages and the difficulty in recognizing their bites tends to make nymphs the most important stage to consider for reducing disease risk.
First recognized among cluster of children believed to have juvenile rheumatoid arthritis in Lyme, CT, 1975, the symptoms of Lyme disease includes fever, fatigue, headache and muscle and joint aches (after a 4 – 7 day incubation period). In about 75% of the cases, a red lesion forms at the site of the tick bite, and slowly gets bigger, usually with a clearing in the center, known as a bull’s eye. In some cases, these first symptoms don't occur. If this happens, or if the early disease is not treated, weeks to months after the tick bite other problems may develop such as nervous disorders, heart problems, or joint swelling and pain. After several months, 60% of untreated patients may develop severe joint pain and swelling, particularly in the knees.
The Shenandoah National Park’s Natural and Cultural Resources staff conducted a study during the 2007 season to test the effectiveness of various tick-resistant clothing and sprays (deet and Permanone, or permethrin). Believe it or not, the 21 employees documented 804 embedded ticks from May through September. Two employees got no bites, while two were treated for symptoms of Lyme disease.
While the use of Rhino Skin, Bug Skinz and Heat Gear did provide general protection (ticks were limited in distribution to neck, waist and ankles), the additional heat of the layers made them somewhat impractical in our seasonal heat and humidity.
Assessment of deet and permethrin was difficult, since application rates varied among employees. It appeared that permethrin was more effective in controlling first instar nymphs than was deet (permethrin is sprayed on clothing, not skin, like deet).
It was found that treatment of clothing on return to home was very important. The most success was obtained by putting all the clothing immediately into a permethrin-sprayed bag. This prevented ticks from leaving the clothing and dispersing within the home.
More details from this study can be found at: