Cuterebrosis in a Florida Horse: First Equid Record for North America

Abstract

Larvae of Cuterebra spp. (Diptera: Oestridae) typically infest mice, rats, chipmunks, rabbits, hares, and certain other rodents or lagomorphs native to the Americas (Sabrosky 1986). However, non-native members of these orders, as well as mammals in other orders such as artiodactyls (e.g., deer and pigs), carnivores (raccoons, domes tic cats and dogs, etc.), and primates (humans), can be parasitized by these bot flies (Hall 1925; Sabrosky 1986; Baird et al. 1989; Glass et al. 1998; Harris et al. 2000; Suedmeyer et al. 2000; Safdar et al. 2003; Slansky & Huckabee 2006; Slansky 2007a). Infestation of these atypical or accidental hosts, an affliction termed cuterebrosis or cuterebriasis, occurs when they contact first in stars of Cuterebra spp. newly hatched from eggs oviposited in the habitats of the typical hosts (Catts 1982; Slansky & Kenyon 2003). Published cases of cuterebrosis in perissodac tyls (donkeys, horses, zebras, etc.) are few and mostly unsubstantiated. Knipling & Bruce (1937) reported that a second instar of Cuterebra buc cata (Fabricius), a lagomorph-infesting species, was removed from a mule in South Carolina (16 VII-1935), but they provided no justification for this species assignment. Second instar Cuterebra spp. are very difficult to identify visually to spe cies (even currently) and there were no descrip tions of second instars of other Cuterebra spp. for comparison at the time of Knipling & Bruee's (1937) report. Thus, I consider the assignment of C. buccata for their specimen as unsubstantiated. Dalmat (1942) indicated that asses (donkeys) were atypical hosts o? Cuterebra spp., but no de tails were given. Similarly, Sabrosky (1986) men tioned mules as atypical hosts of these bot flies, but supportive information was not provided. During curation of the immature insect collec tion in the Department of Entomology & Nema tology at the University of Florida, an isopro panol-preserved larva that appeared to belong to a Cuterebra species was encountered. This speci men had been collected from beneath the hide of a horse in Marion Co., Florida (ll-VII-1991). This specimen possesses characteristics typical of a third instar Cuterebra spp., including dark brown cuticular platelets covering its body (Fig. la), 2 pair of sensory tubercles and 2 sharply pointed mouth hooks on its head (Fig. lb) and on its anal segment (Fig. lc), 2 kidney-shaped spiracular plates, each containing 3 wedge-shaped sections with serpentine spiracular slits (Fig. lc inset). The larva is coated with a substantial amount of white material, which most likely is purulent matter from the host, as is often seen when these larvae infest atypical hosts (Slansky 2007b). The species o? Cuterebra that this specimen be longs to is unclear, as there are no taxonomic keys for species identification of larvae in this genus. However, the platelets covering its exterior either are ovoid, have blunt, single tips, or are multi pointed, indicating this is a larva of a rodent-in festing Cuterebra species rather than that of a lagomorph-infesting species, third instars of which lack flattened, multipoint platelets and have many single-pointed, spine-like platelets (Knipling & Brody 1940; Dalmat 1942; Bennett 1955; Haas & Dicke 1958; Baird & Graham 1973; Slansky 2007a). There are three rodent-infesting species of Cuterebra in Florida: C. americana (Fabricius) (its main typical hosts are Neotoma woodrats), C. fontinella (Clark) (Peromyscus mice) and C. emasculator Fitch (Sciurus squirrels) (Slansky 2006). Cuticular platelet patterns are available only for the latter two species (Bennett 1955; Slansky & Huckabee 2006), and of these, this specimen more closely resembles C. fonti nella (F.S., unpublished observations). However, determining the species of this specimen must await a morphological description of the third in star of C. americana, knowledge of intraspecific variation in morphological characteristics of these larvae (see Slansky & Huckabee, 2006), and/or molecular analyses (Otranto et al. 2003; Noel et al. 2004) of the candidate species. This appears to be the first record for Florida of cuterebrosis in a horse or other perissodactyl, and the first such record for a horse in North America. Based on the scarcity of published reports, infes tation of these animals by larvae o? Cuterebra ap pears to be a very rare phenomenon that should pose little concern to horse owners. This contrasts with the common occurrence of larvae oiGastero philus spp. bot flies, which use horses and other perissodactyls as typical hosts and can require treatment to avoid pathological effects (Wall & Shearer 1997; Catts & Mullen 2002). One might expect that these animals would be exposed to Cuterebra spp. larvae both while grazing, espe cially lagomorph-infesting species that likely ovi posit in grassy areas (e.g., Suedmeyer et al. 2000), and in their stalls, especially rodent-infesting species that may inhabit barns (F. S., unpublished observations). Thus, the rarity of published re ports of cuterebrosis in perissodactyls may indi cate that these atypical hosts exhibit resistance to