Abstract: Mink (Mustela vison Schreber, 1777) skulls (n = 630) from 18 geographic regions throughout central Ontario were examined for levels of sinus worm (Skrjabingylus nasicola (Leuckart, 1842)) infection by exposing and counting adult worms present in each sinus cavity. Site differences in both infection prevalence (range 55.6%-100%) and infection intensity (2.4 [+ or -] 0.3 to 16.1 [+ or -] 2.2 worms per infected animal; mean [+ or -] SE) were found, but neither latitudinal nor longitudinal trends were apparent. Temporal differences in infection prevalence were not observed among selected regions sampled over two and three consecutive trapping seasons; however, at two of the three sites monitored, infection intensities increased approximately twofold. Juvenile animals of either sex indicated elevated levels of infection prevalence relative to adult males, while juvenile males, but not females, indicated significantly higher infection intensities than those seen in the adult male cohort. No bias toward left or right sinus location was noted in either prevalence or intensity of infections. Comparison of age- and sex-adjusted body mass failed to provide evidence for reduced physical condition in infected animals.
Resume : Nous avons determine le niveau d'infection de visons (Mustela vison Schreber, 1777) par le nematode parasite des sinus (Skrjabingylus nasicola (Leuckart, 1842)) en exposant et denombrant les vers adultes dans chacune des cavites des sinus de cranes (n = 630) provenant de 18 regions geographiques de tout le centre de l'Ontario. Il y a des differences d'un site a l'autre dans la prevalence de l'infection (etendue 55,6%-100%) et dans son intensite (2,4 [+ ou -] 0,3 a 16,1 [+ ou -] 2,2 vers par animal infecte; moyenne [+ ou -] erreur type), mais il n'y a pas de gradient en fonction ni de la latitude ni de la longitude. Il n'y a pas de difference temporelle dans la prevalence de l'infection dans les regions choisies et echantillonnees durant deux ou trois saisons consecutives de piegeage; cependant, a deux des trois sites ayant fait l'objet de monitorage, l'intensite de l'infection a a peu pres double. Les jeunes animaux des deux sexes possedent des niveaux de prevalence de l'infection eleves par comparaison avec les adultes males; de plus, les jeunes males, mais non les femelles, ont des intensites d'infection significativement plus grandes que celles observees chez la cohorte des males adultes. Il n'y a pas de tendance preferentielle pour les sinus droits ou gauches ni dans la prevalence, ni dans l'intensite des infections. La comparaison des masses corporelles corrigees en fonction de l'age et du sexe n'indique pas de diminution de la condition physique chez les animaux infectes.
[Traduit par la Redaction]
Introduction
Sinus worms (genus Skrjabingylus Petrov, 1927) are stout crimson nematodes that inhabit the nasal sinus cavities of certain mustelids, including mink (Mustela vison Schreber, 1777), skunk, polecat, and weasel. The most widely distributed member of this genus, Skrjabingylus nasicola (Leuckart, 1842), has been the subject of considerable epidemiological study in the past.
Transmission of S. nasicola to its definitive host, the mink or weasel, can occur via ingestion of terrestrial gastropods harbouring the infective third-stage larvae or presumably more commonly through feeding on infected rodents, shrews, amphibians, or reptiles that serve as paratenic hosts (Hansson 1967; Gamble and Riewe 1982; Jennings et al. 1982). Following ingestion, the larvae undergo two additional molts and, by moving anteriorly through the spinal subarachnoid space to the olfactory nerves, migrate through the cribiform plate of the ethmoid bone to enter the nasal and frontal sinuses, arriving as early as 6 days post infection. Upon maturation in the sinuses, adult male worms range between 6 and 15 mm (mean of 11 mm), while females reach lengths of 10-32 mm (mean of 19 mm) (Lankester 1970; Lankester and Anderson 1971). Manifestations of infection are frequently marked by distinctive bone pathologies of the sinus region, commonly described as variants of discoloration, swelling or enlargement, and thinning or perforation of the external sinus wall (Santi 2001).
Previous studies assessing infections of Skrjabingylus spp. in mustelids have relied heavily upon examining museum specimens for sinus pathologies as an index of both the prevalence and the intensity of parasitism. Epidemiological studies based on observable sinus damage among weasel specimens (Mustela erminea L., 1758, Mustela frenata Lichtenstein, 1831, and Mustela nivalis L., 1766) indicate the widespread distribution of S. nasicola infection throughout North America, including regions as far north as the Northwest Territories (Dougherty and Hall 1955). Studies employing fresh specimens in which the sinuses were opened and the resident nematodes extracted confirm widespread distribution but have also provided evidence that prevalence and intensity values can vary substantially from site to site. In Ontario, the prevalence of S. nasicola infection among weasel and mink was found to be generally high yet variable (74%-100% at three sites examined--Chapleau, Lindsey, and Lake Huron districts; Lankester 1970). However, a survey of the prevalence and intensity of S. nasicola infections encompassing a broad geographical range within the Province has not been conducted to date.
Considerable variation also exists with respect to the patterns of infection occurrence and manifestation. Several studies report evidence that both prevalence and infection intensity tend to be higher in older animals (Dougherty and Hall 1955; Hansson 1969; Gamble and Riewe 1982; Fuller and Kuehn 1984), or alternatively in juveniles (Popov 1943 in Dougherty and Hall 1955; Hansson 1968), whereas other studies have reported no sex- or age-related differences (Debrot and Mermod 1980). Others have reported asymmetrical damage to the sinus …
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