Recently, several inquiries about the spinose ear tick have been received by our Parasitology section. Most have centered on horses and alpacas, and the most common question asked is how to get rid of these minute, annoying pests.
Otobius megnini is the only soft tick that commonly parasitizes domestic mammals in North America. Traditionally considered to be pests of livestock, particularly in the arid regions of the Western US, this parasite routinely pops up in other parts of the country in a wide variety of hosts including, on occasion, humans. Fortunately, unlike other ticks, O. megnini is not the primary vector of any pathogenic organism. However, they can cause considerable irritation and pain, secondary bacterial infections, destruction of the ear canal and tympanic membrane, and otitis interna. Death of cattle and severe muscle spasms in horses also have been reported, although these appear to be unusual manifestations of infestation.
The life cycle of O. megnini also is relatively unique among ticks. In general, soft ticks tend to be multiple-host ticks with all stages feeding on a different host. Adult females may produce multiple batches of eggs, ingesting a bloodmeal prior to the deposition of each clutch. In contrast, O. megnini is a one-host tick in which only the larvae and nymphs are parasitic. Larval ticks, which are about 0.5mm in size, hatch in three to eight weeks and climb anything vertical to await the passing of a potential host. They can survive in the environment for up to two months without feeding. When larvae encounter a suitable host they crawl to the ear and attach below the hair line. After feeding for about a week and growing to around 4mm, they molt to the first nymphal stage. There are two nymphal stages, each with a spiny cuticle from which the common name is derived. Second-stage nymphs reattach and feed for several weeks to months, growing to around 8mm. Engorged nymphs then leave the ear and drop to the ground where they hide in cracks, crevices, beneath rocks or under the bark of trees where they undergo the final molt to adults. Mating occurs in the environment. Adults do not feed, but adult females can survive for two years, depositing up to 1500 eggs in several clutches.
Control can be somewhat difficult and tends to focus on direct treatment of the infested animal. Acaricide treatment of pastures is generally impractical. In stables, kennels, and other housing situations, however, environmental treatment may be helpful. Eradication of protected sites also will go a long way towards helping to decrease tick populations. Animal ears should be regularly inspected and any ticks that are present should be manually removed. Manual removal is as for any other tick--grasp the tick as close to the skin as possible with fine forceps and extract using slow, steady pressure. Be cautious, though, as many animals resist manipulation of the ear particularly if it is sore as a result of the infestation. In these cases, as well as an adjunct to manual removal, a topical insecticide can be used. For cattle, insecticide-impregnated ear tags can help control infestations. For other animals, avermectins have been used but the introduction of phenylpyrazoles has essentially replaced the use of avermectin compounds.
Parasite identification--Submit parasite. External or Internal--Fee=$10; External Exotic or Internal Exotic—Fee=$15.