Arthropod Bite Pinnal Dermatitis
Arthropods commonly cause dermatitis of the pinnae either through direct damage from the bite of the parasite or as a result of hypersensitivity. Ticks can cause irritation at the site of attachment and may be found on the pinna or in the ear canal. The spinous ear tick (Otobius megnini), found in the southwestern USA, south and central Americas, southern Africa, and India, is a soft-shelled tick, the larval and nymphal forms of which parasitize the external ear canal of horses, cattle, sheep, goats, deer, rabbits, cats, and dogs. Clinical signs include head shaking, head rubbing, or drooped pinnae. Both the animal and the environment should be treated. Treatment involves mechanical removal of as many ticks as possible with a forceps and spraying or dipping the coat with pyrethrin/pyrethroid products or malathion. Treatment of secondary bacterial or yeast otitis externa is also important. Precautions to prevent reinfestations should be instituted.
Gotch ear is a condition described in cattle, and also in a goat, that results from infestation of the pinna with the Gulf Coast tick, Amblyomma maculatum. Adult ticks prefer feeding on animal ears, and when ticks are present in sufficient numbers the pinna becomes edematous, erythematous, and crusting at the tick-attachment sites. Curling of the tip of the ear and excoriations may also be seen. Spotted fever group rickettsiae, such as Rickettsia parkeri, have been suggested to cause the skin lesions, because ticks removed from the pinna of animals with gotch have been, in some cases, positive for Rickettsia spp by PCR. However, efforts to find the organisms in skin samples from affected areas have failed. Removal of ticks and treatment of any secondary infection are curative.