Otobius megnini (Dugès, 1844) Banks, 1912
(Figures 5-02 through 5-04)
ETYMOLOGY:Oto = ear and bius = way of life; along with megnini for Dr. Megnin.
SYNONYMS:Argasmegnini Dugès, 1884; Rhyncopriumspinosum, Marx; Ornithodoros megnini (Dugès, 1844) Neumann, 1911.
HISTORY:Otobiusmegnini was originally described by Dugès in 1884 in Guanajuato, Mexico. This tick is an American species which has spread to such far-reaching areas as India and South Africa (Munaó Diniz, et al., 1987).
GEOGRAPHIC DISTRIBUTION:Otobiusmegnini is distributed throughout much of the western United States and is especially prevalent in the arid regions of the southwestern United States. Many of the reports of this parasite in northern, central and eastern states are probably the result of infested livestock shipments (Cooley and Kohls, 1944). In the United States, the eastern boundary for the naturall occurrence of Otobius. megnini is approximately the 97th meridian (Bishopp and Trembley, 1945). This soft tick has been reported in Central and South America (Argentina, Brazil and Chile), Australia, South Africa, and India (Cooley and Kohls, 1944). There have been only two reports of this soft tick in domestic cats (Brumpt, 1936, Cooley and Kohls, 1944).
LOCATION IN HOST: The larval and nymphal stages of members of the genus Otobius most often parasitize the ears of their hosts (Griffiths, 1978).
The unfed larva is 0.66 mm from the tip of the hypostome to the posterior extremity. Its body is oval. There are two pair of hemispherical, ocellus-like eyes. The integument is thin, striated with a few bristle-like hairs arranged symmetrically. The capitulum is visible in both dorsal and ventral views. The hypostome and palps are very long. The six legs are long. The engorged larva is much distended, broader in front. The capitulum is also distended as a conical anterior projection. The engorged larva is 4.00 by 2.5 mm (Cooley and Kohls, 1944).
The first nymphal stage is very much like the newly emerged second stage. However, it is smaller, has more slender legs (Figs. 5-02 to 5-03). It hypostome measures only 0.195 mm (Brumpt, 1936, Cooley and Kohls, 1944).
The second nymphal stage is the stage that is commonly found in the ears of the infested host (Cooley and Kohls, 1944) (Fig 5-04). The nymphs are widest at the middle. Their skin is mammillated and has numerous spine-like processes. The body is bluish grey, while the legs, mouthparts and spines are pale yellow. There are four pair of legs.
Adults, which are nonparasitic, have a constriction at the middle, giving the body a violin shape. The adults have a skin which is not spiny. This stage can be recovered from the environment of the host and is not collected from the host.
LIFE CYCLE: Eggs of Otobiusmegnini are laid on or near the ground for as long as 6 months. They hatch in 18 days or more. The larvae then crawl up vegetation, fence posts and feed bunks to await hosts. Unfed larvae may live off the host for more than 2 months. If they find host, they locate in the ears where they engorge for 5 to 10 days. The larvae molt to the nymphal stage in the ears. Here they engorge for about a month. However, the nymphs may remain in the ear for as long as 7 months. When ready to molt, they crawl out of the ears to the ground where they molt to adults. The females may lay eggs for as long as 6 months. While ixodid (hard) ticks are often referred to as one-, two-, or three-host ticks, argasids are often referred to as many-host or multi-host ticks. Otobiusmegnini is the exception to this rule. It is a single host tick (Hoskins and Cupp, 1988).
CLINICAL PRESENTATION AND PATHOGENESIS: Although clinical signs have not been reported in domestic cats, lions have been reported to develop pruritis (manifested by shaking of the head, ear scratching, and holding the head to one side) as a result of the larvae and nymphs moving and feeding within the external ear canal. The condition may advance such that the inflammatory response and secondary infection may penetrate the tympanic membrane causing otitis media and interna, and ultimately encephalitis. Usually infestation in lions is asymptomatic.
DIAGNOSIS: The otoscope may be used to visualize the ticks within the external ear canal. A cotton swab or blunt forceps may be used to remove the waxy exudate. This exudate must be examined for the presence of larvae and nymphs (Griffiths, 1978). Otobius can be distingished from Ornithodoros by the fact that the nymphal stage is beset with spines. The nymphs of Ornithodoros may be mammillated or tuberculated, but they lack spines as are present in Otobius. Otobiusmegnini nymphs may be distinguished from the nymphs of Otobiuslagophilus by the fact that in Otobiusmegnini the integument has numerous heavy spines anteriorly and thinner spines posteriorly while the spines on Otobius lagophilus are all of one size. Also, if the ventral surface of the hypostome of Otobiusmegnini is examined, it will be found that there are four teeth (denticles) on each side of the midline while there are only three on each side of the midline in Otobiuslagophilus. The adults differ in that the pits on the dorsal surface of Otobiusmegnini are separated by a distance that is twice or more the diameter of one pit, while the pits on the dorsal surface of Otobiuslagophilus are closer together than the diameter of a single pit.
TREATMENT: Any of the popular acaricides used for treating infestation of hard ticks on cats, should prove effective in treating Otobiusmegnini. When applying any medication to the ear, great care should be taken to avoid damaging the external ear canal.
EPIZOOTIOLOGY: This tick is usually diagnosed in cats who are allowed to roam freely and is seldom found in house cats. This tick is usually acquired from a pen, corral, or limited range area where larvae migrate onto the host animal. This tick may be found on hosts throughout the year, but its destructive effects are particularly recognizable during winter and spring, especially following long periods of drought when both range and livestock are poor (Bishopp and Trembley, 1945).
HAZARDS TO OTHER ANIMALS: The larvae and nymphs of Otobiusmegnini may occur on domestic animals such as cattle, sheep, horses and dogs and on a wide range of wild animals (Eads and Campos, 1984). These animals include mules, asses, goats, hogs, coyotes, deer, mountain sheep, cottontail rabbits, jackrabbit, ostrich (Cooley and Kohls, 1944), collared peccary and pronghorn (Eads and Campos, 1984). This tick is a suspected vector of Coxiellaburnetii, the etiologic agent of Q fever (Munaó Diniz, et al., 1987, Hoskins and Cupp, 1988).
HAZARDS TO HUMANS: Human parasitism by Otobiusmegnini is a potential health problem in the southwestern United States, especially in rural areas where people live in close contact with domesticated animals (Eads and Campos, 1984). As with domesticated and wild hosts, the ticks infesting the human cases had a predilection for the ear canal (Bishopp and Trembley, 1945, Eads and Campos, 1984).
CONTROL/PREVENTION: Accurate identification of soft ticks from the parasitized host or from the environment is a prerequisite to their control (Hoskins and Cupp, 1988). The cat's ability to roam freely to areas frequented by livestock (sheds, yards or kraals) should be restricted.
Bishopp FC, Trembley HL. 1945. Distribution and hosts of certain North American ticks. J Parasitol 31:1-53.
Brumpt E. 1936. Contribution a l'étude de l'évolution des Ornithodores. Biologie et longévité de l'Ornithodorusmegnini. Ann Parasitol 14:647-651.
Cooley RA, Kohls GM. 1944. The Argasidae of North America, Central America and Cuba, Monograph 1. Am Midl Nat. Notre Dame, IN, University of Notre Dame, 21-36.
Eads RB, Campos EG. 1984. Human parasitism by Otobiusmegnini (Acari: Argasidae) in New Mexico, US. J Med Entomol 21:244.
Hoskins JD and Cupp EW. 1988. Ticks of veterinary importance. Part II. The Argasidae family: Identification, behavior, and associated diseases. Comp Cont Ed Prac Vet 10:699-709.
Munaó Diniz LS, Belluomini HE, Travassos Filho LP, and da Rocha MB. 1987. Presence of the ear mite Otobius megnini in the external ear canal of lions (Panthera leo). J Zoo An Med 18:154-155.