Ticks and Related Problems

Ticks are small arachnids in the order of Parasitiformes. Many species of ticks can transmit diseases from an infected host to an uninfected host. The most significant transmissions in PA are spirochetes which cause Lyme disease and rickettsia which causes Rocky Mountain spotted fever.

Two common PA ticks are in the Ixodidae family, the American dog tick (Dermacentor variabilis) and the blacklegged tick (or deer tick) (Ixodes scapularis). Both of these are known as ‘hard ticks’ because they have a scutum or hard shield. Ticks can be killed by crushing with a pebble against a rock or other hard surface, or by burning in a fireproof container.

Lyme disease was first recognized in Sweden in 1908, and first identified in the U.S. in 1975 after an outbreak of arthritis in Lyme, CT. Transmission of the spirochete Borrelia burgdorferi, the causative agent, occurs by bite of Ixodes ticks. Second growth forest in the northeastern U.S. has created wood ‘edge’ habitat which resulted in increased deer population. The perfect storm that caused high numbers of blacklegged ticks in the northeastern U.S. is where the heaviest concentration of human population exists; spirochete infection percentages of ticks are high; and the tick’s range is expanding. Two factors in tick population density are: a high number of host species (white tailed deer), and high enough humidity for the ticks to remain hydrated.

The blacklegged tick is a 3-host tick. In June and July tick eggs, which were deposited early in the spring, hatch on the soil. The larvae ‘quest’ (ambush) hosts in low vegetation and leaf litter. Larvae are about the size of a pinhead and prefer small rodents, primarily white-footed mice. After feeding for 3 to 5 days, engorged larvae drop to the ground where they overwinter. The following May they molt into nymphs, which feed on various small hosts.

The engorged nymphs detach, drop to the forest floor where they molt into adult stage, which become active in October. Adult ticks remain active throughout the winter on days when temperatures are above freezing. Adult female ticks feed from a host for 5 to 7 days. Adult ticks feed and mate on large mammals, primarily white-tailed deer. Beginning in May adult females lay between 1000 to 3000 eggs on the forest floor.

The blacklegged tick is an important vector (carrier) of the Lyme disease spirochete, Borrelia burgdorferi. Before and after larval tick feeding, the nymphs transmit Lyme spirochetes to hosts. Human exposure to blacklegged ticks is heaviest during summer when high nymphal activity and human outdoor activity coincide. Their small size, high numbers vs. the adult stage, and difficulty in recognizing their bites make nymphs the most important stage to consider for reducing disease risk.

The American dog tick is the primary vector for Rocky Mountain spotted fever, which was first discovered in the late 19th century in the Rocky Mountain region. RMSF is vectored by D. variabilis to dogs and humans following its contamination from rodents. Overwintering larvae can acquire RMSF from mother to egg, causing infected larvae. Larvae and nymphs rarely bite humans, so the adult tick is the primary life stage of concern to people. Transmission occurs when the tick is attached for 6 to 8 hours, and sometimes longer.

Controlling ticks by removing leaves, clearing brush and tall grass around homes and edges of gardens is a recommended practice. Also, avoiding tick infested areas in May to July is prudent. Wear light colored clothing so that adult ticks may be spotted easily. Tuck long pant legs into socks or boots and shirts into pants. Spray insect repellent containing DEET on clothes and exposed skin other than face, and treat clothing with permethrin which kills ticks on contact. Wear a hat and long sleeved shirt for added protection. After being outside, remove clothing and wash and dry at high temperatures; inspect your body carefully and remove attached ticks with tweezers. Grasp the tick as close to the skin surface as possible and slowly pull straight back avoiding crushing the tick’s body. Ticks should not be removed by handpicking because secretions can be transferred from a person’s hands to his eyes, mucous membranes, mouth, etc. It is important to remove the tick slowly because mouthparts are covered with sharp backward directed barbs.

University of Connecticut has determined that the invasive Japanese Barberry creates a perfect humid environment for ticks. UCT study determines ‘when measured, we find 120 infected ticks/acre where Barberry is not contained; 40 ticks/acre where Barberry is contained; and 10 infected ticks/acre where there is no Barberry’. An excellent reason for getting rid of this horrible invasive plant if you still have it. Birds eat the berries and drop seeds in the woods.

Nature provides a native mammal to help in destroying ticks. An article in the April/May issue of National Wildlife Federation magazine states that opossums ‘act like vacuum cleaners when it comes to ticks.’ In a field test, scientists applied 100 ticks to the necks of 3 rodent species, 2 ground nesting bird species and opossums. Only 3% of ticks on opossums survived to drop off. Opossums kill the ticks with their grooming, and examination of feces proved that the ticks were eaten. Based on this study results, they calculate a single opossum might kill 4,000/ticks/week during the high population fall period each year.

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