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Arthropod Bite Pinnal Dermatitis in Animals

By

Sandra Diaz

, DVM, MS, DACVD, The Ohio State University

Last full review/revision Aug 2021 | Content last modified Aug 2021

Arthropods commonly cause dermatitis of the pinnae either through direct damage from the bite of the parasite or as a result of hypersensitivity. Ticks Ticks Ticks are obligate ectoparasites of most types of terrestrial vertebrates virtually wherever these animals are found. Ticks are large mites and thus are arachnids, members of the subclass Acari... read more 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 Otobius spp Otobius megnini, which is exceedingly specialized biologically and structurally, infests the ear canals of pronghorn antelope, mountain sheep, and Virginia and mule deer in low rainfall biotopes... read more ), 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.

Treatment in large animals involves both the animal and the environment. As many ticks as possible should be mechanically removed with forceps, and the coat sprayed or dipped with acaricides. Acaricide choices include diazinon, pyrethroids, carbaryl, and avermectins (ivermectin, doramectin, eprinomectin). These products can be applied with a high-pressure sprayer or as pour-ons. Longterm use of acaricides may result in selection of resistant ticks and environmental pollution.

Vaccines are an environmentally friendly alternative to acaracides and although they have been shown to be relatively effective against tick infestations in Australia, Cuba, Mexico, and other Latin American countries, they are not able to completely control infestation or transmission of pathogens transmitted by ticks. These vaccines are not yet available in the USA.

Gotch ear, described in cattle, horses, mules, and a goat, results from infestation of the pinna with the Gulf Coast tick, Amblyomma maculatum Otobius spp Otobius megnini, which is exceedingly specialized biologically and structurally, infests the ear canals of pronghorn antelope, mountain sheep, and Virginia and mule deer in low rainfall biotopes... read more . 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 necrosis may occur.

Spotted fever Rocky Mountain Spotted Fever in Dogs Spotted fevers are diseases caused by a set of related bacteria in the Rickettsia genus, of which Rocky Mountain spotted fever is the most severe. After transmission of the pathogen through... read more 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. The two main differential diagnoses for gotch ear are a bite from another tick and trauma to the ear. Removal of ticks and treatment of any secondary infection are curative.

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