Tick-borne Diseases in Mississippi

JEROME GODDARD, PHD; LUCIUS M. LAMPTON, MD

Abstract

Ticks and tick-borne diseases continue to be a health issue for persons living in Mississippi, especially for those with environmental exposure from outdoor work or recreation. Mississippi has 18 species of ticks, 5 of which are considered significant medical or veterinary pests. This paper reviews tick-borne diseases occurring in Mississippi, including notes on their vectors and ecology, clinical and laboratory findings for each disease, and the various treatment options.

Tick Biology

There are three families of ticks recognized in the world today, 1) Ixodidae (hard ticks), 2) Argasidae (soft ticks), and 3) Nuttalliellidae (a small, curious, little-known group with some characteristics of both hard and soft ticks). The terms hard and soft refer to the presence of a dorsal scutum or “plate” on the back in the Ixodidae, which is absent in the Argasidae. Hard ticks display sexual dimorphism, whereby males and females look obviously different, and the blood-fed females are capable of enormous expansion. Their mouthparts are anteriorly attached and visible from dorsal view. Soft ticks are leathery and nonscutate, without sexual dimorphism. Their mouthparts are subterminally attached in adult and nymphal stages and not visible from dorsal view. Since soft ticks are almost never encountered in southern states, this paper will be limited to the hard ticks responsible for disease transmission in the state of Mississippi.

Hard ticks feed exclusively on blood and begin the process by cutting a small hole into the host epidermis with their chelicerae and inserting the hypostome into the cut, thereby attaching to the skin. Blood flow is maintained with the aid of anticoagulants and vasodilators secreted by the salivary glands. Some hard ticks secure attachment to the host by forming a cement cone around the mouthparts. Two phases are recognized in the feeding of nymphal and female hard ticks: a growth feeding stage characterized by slow continuous blood uptake and a rapid engorgement phase occurring during the last 24 hours or so of attachment.

Hard ticks generally occur in brushy, wooded, or weedy areas containing numerous deer, cattle, dogs, small mammals, or other hosts. Members of each stage (larvae, nymphs, and adults) (Figure 1) climb up on vegetation and attach to passing hosts after which they crawl around looking for a place to feed. Ticks may remain attached to a host for several days while blood-feeding (adults may remain attached 7-10 days).

The motile life stages of a hard tick, L-R, larva, nymph, and adult.

(Photo copyright 2014 by Jerome Goddard, PhD)

Erythema migrans lesion in a patient with Lyme disease.

(Centers for Disease Control photo)

Adult female Lone Star tick, Amblyomma americanum.

(Photo courtesy Dr. Blake Layton and the Mississippi State University Extension Service)

Erythema migrans-like lesion after tick bite in Mississippi – not Lyme disease.

(Photo courtesy Jerome Goddard, PhD)

Lyme Disease

Introduction: Lyme disease (LD), named after a town in Connecticut, is caused by the bacterium Borrelia burgdorferi and is a systemic tick-borne illness which may present with many clinical manifestations such as cardiac, neurologic, and joint problems. Initially, LD presents as a flu-like syndrome with headache, stiff neck, myalgias, arthralgias, malaise, and low-grade fever. Often, a more or less circular, painless, macular

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