stand emerging infectious diseases and to reduce the burden of disease and mitigate its expression.

Vector-borne diseases, including diseases transmitted by ticks, continue to be a public health concern in the United States and abroad. Ticks are arthropods that belong to two large groups: hard (ixodid) and soft (argasid) ticks. Soft ticks undergo no more than seven molts during their life cycle while hard ticks undergo three (see Figure 1-1). The life cycle duration varies

FIGURE 1-1 The life cycle of a three-host tick, such as Ixodes and Dermacentor sp., illustrating the common host for each stage. In this example, beginning prior to the first host, the eggs hatch to larvae and then feed on the first host. After the larval feeding is complete, the larvae drop from the host and molt to the nymph stage. At this stage, the nymph attaches and feeds again. It then drops off of the second host and molts to an adult. The adult tick attaches to a third host for a final meal. Following the final meal, the tick drops off and eggs laid by a female tick restart the process.

FIGURE 1-1 The life cycle of a three-host tick, such as Ixodes and Dermacentor sp., illustrating the common host for each stage. In this example, beginning prior to the first host, the eggs hatch to larvae and then feed on the first host. After the larval feeding is complete, the larvae drop from the host and molt to the nymph stage. At this stage, the nymph attaches and feeds again. It then drops off of the second host and molts to an adult. The adult tick attaches to a third host for a final meal. Following the final meal, the tick drops off and eggs laid by a female tick restart the process.

SOURCE: Reprinted with permission of Dr. Jeremy Gray.



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