Answer to Case 60
The arthropod was a nymphal hard tick (order Acarina, family Ixodidae), which are morphologically different from soft ticks such as Ornithodoros spp. from the family Argasidae).  This particular nymphal tick was probably a Lone star tick (Amblyoma americanum), though species identification of nymphal ticks is usually not absolute.  Figure A shows a tick still attached to the same person featured in this month's case studies.  Diagnostic features of hard ticks include the following, which are also labeled in Figure B:

• The mouth parts are visible from the dorsal view.  Mouth parts of soft ticks are subterminally attached and thus not visible from a dorsal view.
• The presence of a dorsal plate (scutum).  This feature is absent in soft ticks.
• Hard ticks display sexual dimorphism, meaning that there are visual differences between males and females (e.g., the scutum is larger in males than in females).

A	B

Ticks are important arthropod vectors of human disease, second only to mosquitoes.  Some of the diseases that can be transmitted by hard ticks are listed below:

• Babesiosis—vector is Ixodes scapularis (black legged tick).
• Lyme Disease—vectors are Ixodes scapularis and I. pacificus.
• Erlichiosis—vector is Amblyoma americanum (Lone star tick).
• Rocky Mountain Spotted Fever—vectors are Dermacentor variablis (American dog tick) and D. andersoni (Rocky Mountain wood tick).

Soft ticks are vectors of relapsing fever, a spirochetal disease.  In addition, it is important to be able to distinguish ticks from other arthropods, such as lice or fleas.