ALCES VOL. 47, 2010 Lankester and Foreyt - INFECTED WITH GIANT FLUKE

MOOSE EXPERIMENTALLY INFECTED WITH GIANT ( MAGNA)

Murray W. Lankester1 and William J. Foreyt2

1101-2001 Blue Jay Place, Courtenay, BC, Canada, V9N 4A8; 2Department of Veterinary Microbiology and Pathology, Washington State University, 413 Bustad Hall, Pullman, WA 99164-7040, USA

ABSTRACT: Moose (Alces alces) are abnormal, dead-end hosts of the giant liver fluke Fascioloides magna. The worms migrate extensively in moose causing considerable hepatic tissue damage before eventually dying. Few reach sexual maturity and eggs are seldom, if ever, passed in feces. Occurrence of the parasite in moose depends on the presence of a competent definitive host and suitable aquatic snail intermediate hosts of the genus Lymnaea. There is no clinical evidence that F. magna kills moose although the considerable tissue pathology seen in some heavily infected is suggestive that they do. In this study, 2 farm-reared moose calves (2 months old) and a yearling moose (15 months old) were given 50, 110, and 225 F. magna metacercariae, respectively, and observed for 12.5-16 months. No outward signs of disease were observed. The livers of the 2 infected as calves were swollen and contained bloody tracks, extensive fibrosis, and capsules; 1 and 11 immature flukes were recovered. The liver of the infected as a yearling had 3 large, thick-walled capsules but no flukes. Weight gain and behaviour of all were similar to those of uninfected farm-reared moose. Known aspects of the biology of this parasite and our experimental results suggest that F. magna is unlikely to have been a major factor in the recent moose decline in northwestern Minnesota.

ALCES VOL. 47: 9-15 (2011)

Key words: Alces alces, experimental infection, Fascioloides magna, liver flukes, moose, Odo- coileus.

The giant liver fluke (Fascioloides magna) The extensive and noticeable tissue dam- develops normally in white-tailed (Odo- age seen in some moose has led to speculation coileus virginianus), wapiti (Cervus elaphus that infection may cause death, particularly in canadensis), and caribou (Rangifer tarandus nutritionally stressed animals (Pybus 2001, caribou), but in moose (Alces alces) migrates Lankester and Samuel 2007). Based on counts extensively causing considerable damage to of flukes and liver cysts in dead moose, Murray liver tissue (Pybus 2001). Moose are an abnor- et al. (2006) concluded that the giant liver fluke mal dead-end host with few worms reaching was a significant mortality factor responsible maturity, and eggs are likely prevented from for a marked decline in the moose population leaving infected livers by the resulting fibrosis in northwestern Minnesota. However, no and thick-walled, closed capsules unconnected clinical evidence exists that links the presence to bile ducts (Lankester 1974). Infection in of flukes in livers with death of moose. To moose depends on continuous cohabitation better understand any such impact on moose, with normal cervid hosts and appropriate con- we administered metacercariae of the giant ditions for transmission, including persistent liver fluke to 3 captive, hand-reared moose, aquatic habitat for the required, intermediate observed their behaviour and weight gain fol- snail hosts of the genus Lymnaea. lowing infection, and performed subsequent necropsies.

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METHODS maturity. They were measured to the nearest Moose were acquired in 1977 and 1978 mm after formalin fixation. Protocols were as orphaned calves (0.5-2 months old) in approved by the Animal Care Committee of the vicinity of Thunder Bay, Ontario where Lakehead University. F. magna is unreported in deer. Two calves were infected shortly after capture; a third, RESULTS obtained the previous year, was infected when Both moose infected as calves showed 15 months old (Table 1). They were housed in a depressed appetite for 7-10 days after infec- compound without access to any infected water tion, but thereafter resumed normal feeding body from the date of capture. Initially they and behaviour until they were euthanized were bottle-fed a formulated milk diet (385 12.5-14 months later. A female yearling moose mL of Carnation milk with an equal volume raised from a calf, but not infected, died at 14 of whole milk and 2 egg yolks) supplemented months of age of accidental trauma and was with pelleted beet pulp, alfalfa hay, and com- considered a control; its liver weighed 3.3 kg mercial dairy ration (Nutrena Sweetflow-16; and was 3,050 cc in volume. Lankester et al. 1993). Animals were weaned at Calf #1 was given 50 metacercariae when 16-18 weeks of age and maintained thereafter 2 months old and euthanized 12.5 months later; on dairy ration and alfalfa hay supplemented its liver weighed 4.9 kg with volume of 4600 sporadically with fresh browse. cc and had a rounded marginal edge with a Metacercariae were obtained from Bald- single 3 cm long immature fluke (Table 1). win Enterprises (Monmouth, Oregon, USA) Seven capsules were present (4 were 3.5-4.5 and their viability on arrival was confirmed cm and 3 were 1.0-1.5 cm in diameter), most in a subsample by microscopic examination in the vicinity of the hilus, with one protrud- of flame cell movement. Both free and still- ing from the surface just beneath the serosa. encapsulated metacercariae were counted Capsules had thickened, fibrous walls with and immediately administered in water by incorporated black pigment. They were filled stomach tube to moose lightly anaesthetized with brown-black, pasty material and the larger with xylazine hydrochloride (Rompun, Haver- had a thin, stoney inner lining. Small, scattered Lockhart Laboratories, Mississauga, Ontario, patches (1-3 mm diameter) of black pigment Canada). were visible on the surface of the liver and in Moose were observed daily and any the omentum adjacent to the liver. clinical signs noted. They were eventually Calf #2 was given 35 and 75 metacercariae euthanized using T-61 (Hoechst Canada Inc., at 2 and 3 months old, and was euthanized 14 Montreal, Quebec, Canada), bled by cut- months after the first infection. Its liver ap- ting neck vessels, and hung to obtain whole peared somewhat enlarged (6.1 kg and 5,650 weights; visceral organs were removed and cc) with rounded marginal edge. Eleven inspected grossly. The liver was weighed, immature flukes (1.5-2.0 cm long) were re- its volume measured by water displacement, covered; 2 were in narrow (3-4 mm diameter) and sliced at thickness of 1-1.5 cm. Migrating blood-filled tracts while the precise location and encapsulated flukes were dislodged from of the others could not be determined. About liver tissue by gently agitating the slices in a 30-40% of the liver volume was comprised pail of warm physiological saline, and were of thick-walled capsules and diffuse fibrosis. recovered by pouring the saline through a 2 Ten capsules (3-4 cm in diameter) had thick, mm mesh screen. Flukes were pressed gently fibrous walls and 15 smaller capsules (1-1.5 between 2 glass microscope slides and exam- cm) had a grey-black inner lining (not stoney) ined for eggs in the uterus as an indication of and were filled with grey-black (clay-coloured)

10 ALCES VOL. 47, 2010 Lankester and Foreyt - MOOSE INFECTED WITH GIANT LIVER FLUKE

Table 1. Description of captive moose infected experimentally with metacercariae of the giant liver fluke (Fascioloides magna). All animals were captured as calves (0.5-2.0 months old; assumed born 15 May) in an area without F. magna and held in captivity without access to infected water until euthanasia. Calf Sex Age # of Infection Body weight Liver weight Liver # # (months) at metacercariae duration (kg) (kg) volume flukes capsules infection (months) (cc) 1 ♂ 2 50 12.5 291 4.9 4600 1 7 2 ♀ 2, 3 35, 75 14 218 6.1 5650 11 25 3 ♂ 15 225 16 334 3.8 3600 0 3 pasty material. Meandering tracts with fibrous repeated small doses or “trickle infections” walls (1-2 mm thick) were filled with dark over a period of time, as would more closely red blood. The antero-dorsal surface of the approximate what probably occurs in nature liver was covered with whitish fibrinous tags (Prestwood and Nettles 1977). The outcome and adhered firmly to the diaphragm. Diffuse of infection may also depend on host age at accumulations of black pigment were visible first exposure and whether the initial exposure on the surface of the liver, in omental fat, induces a degree of protection against further and in mesentery and lymph nodes around infection (i.e., concomitant immunity; Lank- the lower colon. ester 2002). The varying effects of dose on Moose #3 was given 225 metacercariae the outcome of F. magna infection are evident when 15 months old and euthanized 16 months from experimental infection of , a later. It exhibited vigorous rutting behaviour host not commonly infected in nature (But- and had developed average-sized antlers in terworth and Pybus 1993). Mule deer fawns the fall of its 3rd year. There was a whitish given 250-500 metacercariae all died within fibrinous coating over 25% of the diaphrag- 163 days of infection, whereas 3 of 4 fawns matic surface of the liver, but no areas of given 50 metacercariae survived; flukes ma- adhesions were seen nor was black pigment tured and eggs passed in their feces (Foreyt visible in the mesenteries. The liver (3.8 kg, 1992, 1996). 3600 cc) had a sharp marginal edge. Three In our experiment, F. magna was relatively whitish capsules (1.7-6.0 cm diameter) were efficient in reaching the liver of 2-month- visible as raised areas on the surface of the old moose given doses presumed moderate. liver. They had fibrous walls 4-6 mm thick and Considerable liver damage resulted but no were filled with pasty to hardened grey-black worms reached sexual maturity; the longest matter; no flukes were recovered. was 3 cm but mature flukes can be 8 cm long (Pybus 2001). The parasite had lower success DISCUSSION in reaching the liver of the moose infected at 15 Interpreting the results of parasitic in- months old and all flukes were dead 16 months fections reproduced experimentally is often after infection. Having to traverse the large difficult. In nature, the impact of infection functioning rumen of an adult moose may, on individuals commonly depends on dosage, in part, explain the lower recovery. Whether or numbers of infective forms acquired, and the diet provided to captive, experimental over what time period (Samuel et al. 1992, animals may have altered their response to Lankester 2002). These natural acquisition fluke infections cannot be judged. rates usually are unknown and experimenters , like moose, are dead-end hosts may be tempted to exaggerate doses to ensure of F. magna, yet commonly become infected infection. Seldom is it practical to administer in enzootic areas. Infections are generally

11 MOOSE INFECTED WITH GIANT LIVER FLUKE - Lankester and Foreyt ALCES VOL. 47, 2011 sub-clinical and go undetected until slaughter spp. (although non-pathogenic in moose) is (Wobeser et al. 1985, Pybus 2001). For ex- acquired similarly by moose ingesting meta- ample, 12 domestic calves given 1000 metacer- cercariae encysted on aquatic vegetation; cariae each and monitored for 26 weeks were moose <1.4 years old had fewer rumen flukes described as healthy but had conspicuous liver than older animals and calves <2.5 months damage. Relatively few flukes were recovered had none in a study in Sibley Provincial Park, (1-32) and weight gain of infected animals Ontario (Snider and Lankester 1986). was similar to that of controls (Conboy and Poor recruitment is a feature of moose Stromberg 1991). declines occurring in the past 15-20 years Weights of our infected calves were similar in areas west of Lake Superior (i.e., north- to those of calves raised at the facility in subse- western Ontario, southeastern Manitoba, and quent years (Lankester et al. 1993) and to those northwestern Minnesota; Lankester 2009). reviewed by Broadfoot et al. (1996) including However, our results indicate that moderate weights of their 11-month-old farm-reared doses of F. magna do not kill young moose animals (206 kg for females and 228 kg for and suggest that poor recruitment of young is males); mean liver weight for both sexes was unlikely explained by undetected calf mortality 4243 g (range = 3800-5500). Whole weights due to F. magna. An inference (Murray et al. of wild, 2.5-year-old moose in Manitoba were 2006) that liver flukes elicit high moose calf higher (288 and 332 kg; Crichton 1979) but mortality has been attributed to Karns (1972), calves reared in captivity often weigh less than but we could not confirm this interpretation. wild animals due to several factors including On the contrary, Karns (1972) reported that captive diets and digestive disorders (Addison the net productivity of moose was greater in et al. 1983, Welch et al. 1985). northwestern Minnesota where the prevalence In nature, calf and yearling moose are of F. magna was 87%, than in the northeast less likely to be found with giant liver fluke where only 17% of moose were infected; this infection than older animals (Karns 1972, difference in productivity would seem related Pybus 1990, 2001). Is this because they are to factors other than liver fluke. Recently, particularly susceptible to infection and die Maskey (2008, 2011) concluded that a low and unnoticed, or are they somewhat refractory, apparently declining prevalence of F. magna either physiologically or because their feeding (<20%) was probably not the cause of a moose habits reduce the likelihood of infection? Our decline in North Dakota occurring simultane- results suggest that calves are not unusually ously with a decline in adjacent northwestern vulnerable to hepatic disease, but their feed- Minnesota (Murray et al. 2006). ing habits probably reduce exposure. Moose It is noted that the number of flukes (in- encounter fluke metacercariae while feeding tensity of infection) in some moose in north- on aquatic plants, and Lepitzki (1998) found western Minnesota was high (Murray et al. that trematode metacercariae (presumably 2006). Moose classified as likely to have died F. magna) appeared on aquatic vegetation of fluke infection were defined as those with in greatest numbers during June and in mid- “signs of severe pathological damage to tissue August-early September in the marshes of and organs and no other overt cause of death” Vermilion Lakes, Alberta. Adult moose con- or those where “liver flukes were abundant.” sume submerged and floating aquatic plants Not surprisingly, this group had more flukes in greatest amount from mid-June to mid-July (48.1 ± 9.6, n = 23) than animals considered (Cobus 1972, Fraser et al. 1982), but calves dying of non-fluke related causes (14.2 ± 2.2, rarely forage in a similar manner at such a n = 69). However, the high prevalence of young age. The rumen flukeParamphistomum infection (89%, n = 100) was similar to that

12 ALCES VOL. 47, 2010 Lankester and Foreyt - MOOSE INFECTED WITH GIANT LIVER FLUKE

(87%, n = 128) found >30 years earlier when infections can be shown to cause the death the population was robust and moose hunt- of moose, the greatest impact of the disease ing was reinstated (albeit intensity data were would be expected in only a relatively small not reported, Karns 1972). Lankester (1972) portion of the population. examined a much smaller sample of moose from neighbouring southeastern Manitoba REFERENCES and found 64% of livers with signs of fluke Ad d i s o n , E. M., J. Ho e v e , D. G. Jo a c h i m , and D. infection; 1-5 immature flukes were recov- J. McLa c h l i n . 1988. Fascioloides magna ered from 3 of 7 animals with liver damage. () and Taenia hydatigena (Ces- Butterworth and Pybus (1993) found flukes toda) from white-tailed deer. Canadian (16.7 ± 7.3, range = 5-30) in 52% of moose Journal of Zoology 66: 1359-1364. (n = 22) in Banff National Park in Alberta, _____, R. F. McLa u g h l i n , and D. J. H. Fr a s e r . and 2.7 ± 0.3 flukes (range = 2-3) in 63% of 1983. Raising moose calves in Ontario. moose (n = 9) in Kootenay National Park in Alces 18: 246-270. British Columbia. Pybus (1990) found 4% Br o a d f o o t , J. D., D. G. Jo a c h i m , E. M. Ad d i - of adult moose (n = 191) with 3 ± 1 (range = s o n , and K. S. Ma c Do n a l d . 1996. Weights 2-5) flukes in the foothills region of Alberta, and measurements of selected body parts, and Shury (1995) found flukes (x = 8) in 40% organs and long bones of 11-month-old of moose >6 years old (n = 10) from Banff moose. Alces 32: 173-184. National Park. Bu t t e r w o r t h , E., and M. J. Py b u s . 1993. There are several other reasons why F. Impact of the giant liver fluke (Fasci- magna is unlikely a major factor in moose de- oloides magna) in and other ungulates clines. This parasite has a disjunct distribution in Banff and Kootenay National Parks. across North America and has never occurred Parks Canada, Banff National Park, Banff, in some areas where moose declines are known Alberta, Canada. (Lankester 2009). As well, the prevalence Co b u s , M. 1972. Moose as an aesthetic of giant liver fluke infection increases with resource and their summer feeding behav- age of the host and reaches a plateau in older iour. Proceeding of the North American animals (Lankester and Luttich 1988, Pybus Moose Conference and Workshop. 8: 2001). But the mean intensity of infection is 244-275. similar within infected age classes, suggest- Co n b o y , G. A., and B. E. St r o m b e r g . 1991. ing the development of an immunological Hematology and clinical pathology of resistance as infection accumulates (Pybus experimental Fascioloides magna infec- 2001). Results reported here, and the obser- tion in cattle and guinea . Veterinary vations of Pybus (1990) suggest that moose Parasitology 40: 241-255. react strongly to worms in the liver and liver Cr i c h t o n , V. F. J. 1979. An experimental hypertrophy accompanying infection may moose hunt on Hecla Island, Manitoba. eventually mitigate some of the hepatic tissue Proceedings of the North American Moose damage. Lastly, liver fluke infections have Conference and Workshop 15: 245-279. an aggregated distribution in definitive host Fo r e y t , W. J. 1992. Experimental Fasci- populations. Most individuals have relatively oloides magna infections of mule deer low-moderate numbers of worms while a few (Ococoileus hemionus hemionus). Journal heavily infected animals carry the majority of of Wildlife Diseases 28: 183-187. the parasite population (Addison et al. 1988, _____. 1996. Mule deer (Odocoileus hemio- Lankester and Luttich 1988, Mulvey and nus) and elk (Cervus elaphus) as experi- Aho 1993). Thus, even if the heaviest fluke mental definitive hosts for Fascioloides

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Rumen flukes (Paramphostomum spp.) Wo b e s e r , G., A. A. Ga j a d h a r , a n d H. M. in moose of northwestern Ontario. Alces Hu n t . 1985. Fascioloides magna: oc- 22: 323-344. currence in Saskatchewan and distribution We l c h , D. A., M. L. Dr e w , and W. M. Sa m u e l . in Canada. Canadian Veterinary Journal 1985. Techniques for rearing moose 26: 241-244. calves with resulting weight gains and survival. Alces 21: 475-491.

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