Baylisascaris columnaris (Leidy, 1856)

Sapp, Sarah G. H., Gupta, Pooja, Martin, Melissa K., Murray, Maureen H., Niedringhaus, Kevin D., Pfaff, Madeleine A. & Yabsley, Michael J., 2017, Beyond the raccoon roundworm: The natural history of non-raccoon Baylisascaris species in the New World, International Journal for Parasitology: Parasites and Wildlife 6 (2), pp. 85-99 : 88-90

2.1. Baylisascaris columnaris

Originally identified as Ascaris alienata by Leidy (1851), the species was renamed Ascaris columnaris in 1856, and then reassigned to Baylisascaris by Sprent in 1968 ( Leidy,1851; Sprent, 1968). Morphologically, B. columnaris is highly similar to B. procyonis , with only subtle distinguishing features, including the structure of cervical support in the cuticle (a wide arch in B. procyonis compared with a narrow A-shape in B. columnaris ), shape of denticles (equilateral triangles versus elongated triangles), male tail terminal shape (spike versus knob), and the number of preanal papillae (average of 40 versus 43, although there is considerable overlap in range) ( Franssen et al., 2013; Sprent, 1968). However, it is likely that enough natural variability occurs between the two species such that identification based only on morphological characteristics is inadequate and molecular identification is ideal ( Berry, 1985).

Skunks are the definitive host for B. columnaris . Infection has primarily been detected in the striped skunk ( Mephitis mephitis ), the most broadly-distributed and studied skunk species in North America, but infections have also been detected in Eastern spotted skunks ( Spilogale putorius ) ( Table 2). Sympatric Western spotted skunks ( Spilogale gracilis ) and hog-nosed skunks ( Conepatus sp. ) and may be potential hosts as well but testing has been limited. Ascarids identified as B. columnaris have been reported in American badgers ( Taxidea taxus ); however, it is likely that these are actually B. melis or B. devosi ( Table 2). Further surveys that utilize molecular parasite species identification tools will be useful in elucidating the full definitive host range of B. columnaris .

2.1.1. Distribution and ecology

Contemporary surveys on B. columnaris are generally lacking; more surveillance is needed to accurately characterize the distribution and eco-epidemiology of this parasite because most recent reports are from captive pet skunks ( d’ Ovidio et al., 2016). From published reports, B. columnaris appears to be well-established in the northeast, upper Midwest, and prairie regions of the United States and Canada, apparently uncommon in arid regions of the west and southwest ( Table 2). In southern Ontario, Canada, prevalence in M. mephitis was significantly lower in spring months compared to late summer or early fall ( Berry, 1985), similar to the general seasonal patterns observed for B. procyonis in northern climates ( Kidder et al., 1989). Similar seasonal variation in prevalence and intensity have been observed for other gastrointestinal helminths of skunks, such as Physaloptera maxillaris ( Cawthorn and Anderson, 1976) . It is likely that the resource-limiting nature of skunk torpor/overwinter fasting causes the loss or developmental arrest of helminths, potentially including B. columnaris , but more research is needed to investigate this phenomenon ( Dragoo, 2009).

2.1.2. Natural infections in de fi nitive hosts

Similarly to B. procyonis in raccoons, B. columnaris infection is generally not associated with morbidity or mortality in wild skunk definitive hosts. However, peritonitis or intestinal perforation associated with high worm burdens in captive skunks have been documented ( Goodey and Cameron, 1923; Nettles et al., 1978). Goodey and Cameron (1923) noted that skunks from a United Kingdom fur farm exhibited poor body condition, failure to thrive, and inferior coat quality possibly associated with high-intensity B. columnaris infection, and possibly resulting in economic losses. Few recent studies have investigated the occurrence of B. columnaris among farmed skunks or its economic impacts, although infection control should be straightforward with appropriate enclosure cleaning and regular administration of anthelminthics, most of which are highly efficacious against intestinal stages of the related parasite B. procyonis ( Bauer and Gey, 1995) . Given these data, it is possible that wild skunks with high worm burdens may develop disease.

In Europe, 15 of 60 (25%) pet striped skunks primarily from Germany and Italy were positive and additional infections have been reported from the Netherlands and Poland; all were genetically-confirmed as B. columnaris ( Franssen et al., 2013; d’ Ovidio et al., 2016; Janczak ́et al., 2016). Worm burdens were not determined, but in one study, eggs per gram of feces (EPG) ranged from 150 to 14,500 (mean of 4713 EPG) (d'Ovidio et al., 2016). This is relatively low compared to natural B. procyonis infections, which may average 26,000 EPG ( Kazacos, 2016). Importantly, many of these infected pet skunks were housed near or with other pet species (e.g. dogs, guinea pigs, parrots), and none of the skunks had ever received anthelminthic treatment ( d’ Ovidio et al., 2016). Although there are no published reports, B. columnaris infections have been diagnosed in pet skunks from the United States (Yabsley, unpublished data). Given the popularity of skunks as pets and the potential for larva migrans in various hosts, education of pet owners is needed to reduce the risk of transmission.

2.1.3. Experimental infections in de fi nitive hosts

Experimental infections of B. columnaris in skunks have provided data on the fate of larvae within the definitive host and the development of patency. Berry (1985) experimentally infected striped skunks by feeding them mouse carcasses containing unknown numbers of L 3 larvae. Two juvenile female skunks became patent ~48 days post-inoculation ( DPI) and one mature male skunk became patent at 93 DPI. Another route of exposure investigated was inoculation with larvated eggs; inoculation of an unspecified number of embryonated eggs resulted in intestinal infections in three juvenile skunks. The youngest individual (38 days old) was sacrificed at 10 DPI and one L 3 larva was recovered from skeletal muscle, suggesting that at least some larvae undergo early somatic migration in the definitive host following egg inoculation. This individual also had a small number of L3 and L 4 larvae within the lumen of intestine. Numerous L 3 and L 4 larvae were observed in the lumen of the small intestine in another juvenile “young of the year” skunk scarified at 19 DPI; additional larvae larvae were recovered via digestion of the walls of the anterior and posterior small intestine. The remaining juvenile animal was sacrificed at 139 DPI, and although immature adults were found in the intestine at necropsy, eggs were never detected in the feces. The limited number of experimental infection trials in skunks and the low sample sizes makes determining the average onset of patency difficult, and host age and route of infection may be important factors not fully investigated .

To investigate susceptibility of raccoons to B. columnaris , two juvenile raccoons were inoculated with unreported numbers of either L 3 larvae (in mouse tissue) or embryonated eggs ( Berry, 1985). The raccoon inoculated with larvae became infected as L 4 larvae were present in the small intestine of the raccoon upon necropsy; however, infection was not allowed to proceed so it is unknown if the raccoon would have become patent. Thus it is unknown if raccoons can serve as alternative definitive host for B. columnaris . The single raccoon inoculated with embryonated B. columnaris eggs did not develop an intestinal infection ( Berry, 1985).

2.1.4. Natural infections in non-de fi nitive hosts

There are no reports of naturally-acquired B. columnaris larva migrans in wild or captive paratenic hosts. There have been suspected cases in captive animals that were linked to co-housing with infected skunks. For example, an outbreak involving a whiteheaded marmoset ( Callithrix geoffroyi ) and two species of tamarins ( Saguinus nigricollis , Saguinus midas ) in a zoological park in Texas was likely due to a skunk (of unknown infection status) housed in the enclosure. These primates developed signs of NLM, were treated unsuccessfully with fenbendazole, and were subsequently euthanized ( Huntress and Spraker, 1985). Infection with B. columnaris in a captive emu ( Dromaius novaehollindiae ) in Indiana with fatal NLM was suspected based on the history of a skunk (also of unknown infection status)being previously held in the enclosure ( Kazacos et al., 1982). However, species identification was not confirmed in the emu case. Raccoons are also reportedly common in the area where the emu was housed and B. procyonis is highly prevalent in Indiana ( Kazacos et al., 1982).

The paratenic host range of B. columnaris is likely broad given its biological and phylogenetic similarity to B. procyonis and experimental host range. However, molecular techniques will be required in future case studies or surveys to investigate possible natural paratenic hosts. Additionally, B. columnaris could be a zoonotic parasite, given its similarities to B. procyonis and case reports in primates. It is possible that some presumed B. procyonis natural infections are actually B. columnaris , due to the extreme difficulty of species identification through adult/larval morphology, egg morphology (from environmental samples), or current serologic techniques which are cross-reactive among Baylisascaris spp. ( Dangoudoubiyam et al., 2010; Berry, 1985). No human cases have been reported, and even if zoonotic, it is unlikely to represent as significant a public health threat as B. procyonis , as skunks are generally in lower densities in urban areas compared to raccoons ( Gehrt, 2004). Therefore, potential human contact with skunks feces is limited. Nonetheless, individuals with frequent contact with skunks and skunk feces (pet owners, wildlife rehabilitators, fur farmers, trappers, etc.) should take precautions against potential exposure to B. columnaris . Recently, antibodies to Baylisascaris (presumed to be mostly due to B. procyonis exposure, but could be due to other species) were detected in wildlife rehabilitators ( Sapp et al., 2016a).

2.1.5. Experimental infections of non-de fi nitive hosts

B. columnaris produces disease due to larva migrans in a variety of experimentally-infected paratenic host species, particularly rodents and lagomorphs. Compared to B. procyonis , B. columnaris generally causes less mortality in experimentally-infected rodents due to slower and more limited NLM. Independent experiments by Sprent (1952b) and Tiner (1953a) demonstrated that neurological signs were generally noted between 17 and 25 days in laboratory mice inoculated with an unspecified number of eggs, compared to 7‾10 days for B. procyonis . However, dose is likely important in the rate of disease development as has been shown with B. procyonis ( Tiner, 1953a; Sheppard and Kazacos, 1997; Sapp et al., 2016b). Domestic rabbits ( Oryctolagus cuniculus ) inoculated with 100,000 eggs, considered a very high dose, rapidly developed severe neurologic disease involving seizures, epistaxis, ataxia, and dyspnea, with onset between 4 and 10 DPI ( Church et al., 1975).

This generally delayed onset of neurological disease compared to B. procyonis is most likely due to the relatively slower growth of L3s within paratenic hosts. In a 20 day trial of experimental infection of laboratory mice, B. columnaris larvae grew to approximately 1000 M m in length by the end of the trial, compared to B. procyonis that achieved this size by day 10 and reached an average maximal length of 1200 M m by day 20 ( Tiner, 1953b). Experimental trials in laboratory mice suggest that neurological disease does not become readily apparent until larvae within the brain have reached a length of ~1000 M m ( Tiner, 1953b) In laboratory mice, B. procyonis reaches an average length of ~1000 M m in ~8‾10 days post infection, after which survival of infected hosts fell dramatically, whereas B. columnaris took ~16 days to reach 1000 M m in length, after which time some mortality occurred ( Tiner, 1953b). In some cases, mice inoculated with B. columnaris eggs were able to recover from clinical disease or survived despite the presence of larvae in the brain ( Tiner, 1953b). Similarly, B. procyonis larvae have been detected in wild-caught, presumably normally-acting, Peromyscus leucopus further suggesting that some rodents can survive infections of the brain ( Page et al., 2001; Sapp and Yabsley unpublished data). The observed differences larval growth between B. columnaris and B. procyonis may also reflect differences in paratenic host species adaptation. In experimentally-infected meadow voles ( Microtus pennsylvanicus ), B. columnaris larvae achieved a greater average length (1570 M m) than B. procyonis (1060 M m) by 10 DPI ( Berry, 1985). The study was terminated at 10 DPI for larval morphological analysis, so other infection dynamics were not assessed. The impact of larval size on disease severity could also explain why cerebral infection with other smaller larval ascarids such as Toxocara canis (that achieves a maximal length of about 500 M m in rodent brains) produces overt disease much less frequently than B. columnaris or B. procyonis , although host factors, including brain size, likely play a role in the rate and severity of neurologic disease ( Tiner, 1953a; Sprent, 1955).

A large proportion of larvae in inoculated paratenic host species become encapsulated within the intestinal wall and mesentery within 1‾4 DPI ( Berry, 1985). Encapsulated larvae were also abundant in the lungs, heart, kidneys, and liver shortly after inoculation in laboratory mice and in a groundhog ( Marmota monax ), presumably due to liver-lung migration ( Sprent, 1952b; Berry, 1985). Numerous larvae migrated within skeletal muscle and became encapsulated after 10 DPI in inoculated Microtus pennsylvanicus ( Berry, 1985) . In inoculated experimentally-infected rabbits, extensive larval granulomas with eosinophilic infiltration were observed in the lungs, liver, brain, eyes, kidneys, heart, and gastrointestinal tissues ( Church et al., 1975).

Similar to other Baylisascaris species, B. columaris larvae within tissues are resistant to freezing. Encapsulated larvae in tissues remained viable and recovered substantial motility after a periods of freezing ranging from 8 to 18 weeks at –20 C, which was superior to freeze-susceptible B. transfuga and T. canis larvae in the same experiment ( Sprent, 1953a). However, experimental trials to confirm infectiousness of previously-frozen Baylisascaris larvae have not been conducted.