Pathology and Epidemiology of Ceruminous Gland Tumors among Endangered Santa Catalina Island Foxes (Urocyon littoralis catalinae) in the Channel Islands, USA

Abstract

In this study, we examined the prevalence, pathology, and epidemiology of tumors in free-ranging island foxes occurring on three islands in the California Channel Islands, USA. We found a remarkably high prevalence of ceruminous gland tumors in endangered foxes (Urocyon littoralis catalinae) occurring on Santa Catalina Island (SCA)—48.9% of the dead foxes examined from 2001–2008 had tumors in their ears, and tumors were found in 52.2% of randomly-selected mature (≥ 4 years) foxes captured in 2007–2008, representing one of the highest prevalences of tumors ever documented in a wildlife population. In contrast, no tumors were detected in foxes from San Nicolas Island or San Clemente Island, although ear mites (Otodectes cynotis), a predisposing factor for ceruminous gland tumors in dogs and cats, were highly prevalent on all three islands. On SCA, otitis externa secondary to ear mite infection was highly correlated with ceruminous gland hyperplasia (CGH), and tumors were significantly associated with the severity of CGH, ceruminous gland dysplasia, and age group (older foxes). We propose a conceptual model for the formation of ceruminous gland tumors in foxes on SCA that is based on persistent, ubiquitous infection with ear mites, and an innate, over exuberant inflammatory and hyperplastic response of SCA foxes to these mites. Foxes on SCA are now opportunistically treated with acaricides in an attempt to reduce mite infections and the morbidity and mortality associated with this highly prevalent tumor.

Cancer Prevalence and Etiology in Wild and Captive Animals

“…In humans increased cancer prevalence has shown to be associated with reduced genetic diversity (Assié et al, 2008;Rudan et al, 2003). It is therefore interesting to note that some of the highest cancer prevalence's observed in wild mammals (>50%) have been recorded in species/populations with low genetic diversity, such as the Santa Catalina Island foxes (Urocyon littoralis catalinae; Funk et al, 2016;Vickers et al, 2015) and the South African Cape mountain zebra (Equus zebra zebra; Marais and Page, 2011;Marais et al, 2007;Sasidharan et al, 2011). Vickers et al (2015) suggested that the high prevalence of ceruminous gland tumors (carcinomas and adenomas) observed in the Santa Catalina Island foxes may have a genetic basis.…”

“…It is therefore interesting to note that some of the highest cancer prevalence's observed in wild mammals (>50%) have been recorded in species/populations with low genetic diversity, such as the Santa Catalina Island foxes (Urocyon littoralis catalinae; Funk et al, 2016;Vickers et al, 2015) and the South African Cape mountain zebra (Equus zebra zebra; Marais and Page, 2011;Marais et al, 2007;Sasidharan et al, 2011). Vickers et al (2015) suggested that the high prevalence of ceruminous gland tumors (carcinomas and adenomas) observed in the Santa Catalina Island foxes may have a genetic basis. Similarly, the high cancer prevalence observed in one of the South African Cape mountain zebra populations has also been suggested to be associated with concomitant low genetic diversity (Marais et al, 2007;Sasidharan et al, 2011).…”

Evidence‐based veterinary dermatology: a review of published studies of treatments forOtodectes cynotis(ear mite) infestation in cats

“…Otodectes cynotis can also infest hosts including dogs, foxes, ferrets and occasionally humans . Chronic otitis and ceruminous gland hyperplasia secondary to ear mite infestation can be predisposing factors for the development of ceruminous gland tumours in dogs, cats and foxes, and the underlying pathogenesis in foxes has been elucidated …”

“…[5][6][7] Chronic otitis and ceruminous gland hyperplasia secondary to ear mite infestation can be predisposing factors for the development of ceruminous gland tumours in dogs, cats and foxes, and the underlying pathogenesis in foxes has been elucidated. 8,9 The life cycle of O. cynotis lasts 3 weeks which occurs entirely in the ear canals of animals. Occasionally the mite can be found on other parts of the body such as the neck and tail.…”

A framework for how environment contributes to cancer risk

“…50%, and this elevated level could be explained by some combination of mite infections often associated with these cancers, and the accumulation of deleterious mutations in this highly inbred, low genetic diversity population (Vickers et al . ; Robinson et al . ).…”