Baylisascaris (Kazacos, 2016)

Hoberg, Eric P., Burek-Huntington, Kathleen, Beckmen, Kimberlee, Camp, Lauren E. & Nadler, Steven A., 2018, Transuterine infection by Baylisascaris transfuga: Neurological migration and fatal debilitation in sibling moose calves (Alces alces gigas) from Alaska, International Journal for Parasitology: Parasites and Wildlife 7 (3), pp. 280-288 : 287

4.5. Broader implications for Baylisascaris

Assuming the cryptic nature of infections, the significance of this pattern of larval development in the life cycle of B. transfuga and potential transmission among moose (and other artiodactyls) and bears would remain to be established. The complete life cycle for B. transfuga in free-ranging wild hosts has not been elucidated and could involve direct transmission through ingestion of larvated eggs, or dissemination through infected mammalian paratenic hosts ( Bauer, 2013; Sapp et al., 2017). The latter pathway would be consistent with life history patterns currently known among congeners (e.g., Sprent, 1954, 1968; Anderson, 2000). Among black bears the diet is dominated by vegetation and vegetable resources, and among these omnivores, consumption of animals usually involves carrion or is opportunistic ( Pelton, 2003). In contrast, brown bears are considerably more carnivorous, and predation on ungulates may be seasonally important especially for populations in the continental interior of North America ( Schwartz et al., 2003). Such was reflected in observations (EPH) of a large brown bear stalking and hunting moose calves along the Igloo Creek Canyon in Denali Park, Alaska in June 2016. Rodents, especially the prolific and abundant Arctic ground squirrels [ Urocitellus parryii (Richardson) ] are also important sources of food at high latitudes for brown bears.

Life history and involvement of paratenic hosts across a broader assemblage of mammals, from rodents to ungulates, in the transmission of B. transfuga remains undefined (e.g., Tiner, 1953; Sprent, 1954; Testini et al., 2011; Bauer, 2013; Sapp et al., 2017). Further, the nature of abortion or neonatal mortality in moose, involving larval B. transfuga , also remains to be revealed and although logistically challenging to demonstrate, should be considered in diagnosis. Migration by developing larvae and L3 late in gestation may result in infections of the central nervous system as demonstrated in our study. In contrast, migration early in gestation could be a contributing factor in spontaneous abortion in some cases, although, again, evidence is lacking. Infections of neonatal ungulates, however, could be a factor in completion of transmission to carnivore definitive hosts, in this case either brown bear or black bear, which are common and widespread in Alaska and south into the temperate zone of North America.

Discovery of fatal neurological infections by B. transfuga in naturally infected mammalian hosts serves to demonstrate the potential for zoonotic infection, as widely established for B. procyonis in other regions and where raccoon definitive hosts are abundant ( Kazacos, 1997, 2001; 2016; Papini et al., 1996; Bauer, 2013; Testini et al., 2011; Sapp et al., 2017). More importantly in zones of sympatry for multi-species assemblages of Baylisascaris across the Holarctic region presumptive identification of B. procyonis in cases of neurological larval migrans must be considered with caution. Where possible presumptive identification of B. procyonis or other species of Baylisascaris should be confirmed and accompanied by molecular sequence comparisons established in a phylogenetic context (e.g., Camp et al., submitted).

Northward expansion, associated with habitat and environmental change linked to climate warming could lead to changing distribution for raccoons and skunks and therefore, as a consequence, increasingly broader distributions for B. procyonis and B. columnaris (e.g., Hoberg et al., 2008; Hoberg, 2010; Jenkins et al., 2013). Patterns of geographic colonization by these assemblages would also be predicted to directly influence helminth diversity. Potential lag times for invasion by parasites including B. procyonis may coincide with shifting abundance of definitive hosts on the periphery of expanding geographic ranges ( Hoberg and McGee, 1982; Hoberg et al., 2017). The expectation or anticipation of range shifts (either increasing or decreasing) for potential zoonotic pathogens and an array of hosts establishes a priority for definitive documentation of diversity and species. Baselines for identification and biodiversity can lead to surveillance and targeted monitoring to explore and anticipate the outcomes of environmental perturbation over time ( Brooks et al., 2014).