Baylisascaris Infection in Bears

Disease Summary

Alternative Names (Synonyms)

• Ascarid infection
• Ascaridiasis

Disease Type

Infectious/Non-Infectious Agent associated with the Disease

• Baylisascaris transfuga (Toxascaris transfuga, Ascaris transfuga) (B10.48.w43, B16.9.w9, J4.155.w3, J27.24.w1, J157.58.w1)
• Baylisascaris multipapillata. (J4.155.w3, B10.48.w43, B16.9.w9)
• Ascarids are large white worms of the small intestine. The mouth lacks a buccal capsule but is surrounded by three lips. The eggs are thick shelled and infection is generally by ingestion of the egg containing an L2 larva. (B46)
• Baylisascaris larvae tend to invade the CNS of intermediate hosts, and can cause fatal disease in the intermediate host. (B504)
• Eggs 66.3-74.7 x 78.3-88.0 µm. (B16.9.w9)
• Length 15 cm plus. (B10.48.w43)
• Length: male 10 cm, females up to 25 cm. (P85.1.w3)

Baylisascaris (Toxascaris) transfuga:

• Male 76.5 - 129 mm long, 1.6 - 2.35 mm wide. Female 153.5 - 228.4 mm long, 3.1 - 4.0 mm wide. Eggs 0.083 x 0.075 mm. (J27.24.w1)
• Ova globular to sub-globular, 73-83 x 57-73 um, with a finely pitted surface. (P1.1979.w2)
• Adult males measure 108 - 110 mm, females 228-232 mm. The cervical alae may be reduced. There are rough areas peri-cloacally. There are no subdorsal post-cloacal papillae. (P1.1979.w2)
• Morphological characteristics include: presence of cervical alae, absence of an interlabium, absence of striation around the body at the site of the vulva. (J27.24.w1)
• The life cycle is direct, but also indirect using various rodents, birds or insects as intermediate hosts. (P1.1979.w2)
• 93% of shed eggs were found to be viable. (P85.1.w3)
• Coproculture at 25 °C and 95% humidity resulted in 10% of eggs being embryonated at day 15, 74% at day 30 and 82% at day 45. (P85.1.w3)
• Eggs may survive as long as 7-10 years in the environment. (P85.1.w3)
• Infection may be direct or via a paratenic host such as a rodent. (P85.1.w3)
• Eggs are highly resistant:
  • Survive at least two months at -20 °C. (P85.1.w3)
  • Develop to the infective stage when sunk in 10% formalin solution. (P85.1.w3)
  • Develop at low oxygen and in zinc sulphate solution. (P85.1.w3)

Toxascaris (Baylisascaris) melursus first described from a Melursus ursinus - Sloth bear in India. (J411.3.w1, J345.3.w2)

• Large, stout worms with a thick striated cuticle. Three well-defined semicircular lips surrounding the mouth. On the dorsal lip, two symmetrical papillae. On each of the ventro-lateral lips, two assymetric papillae, the lateral papilla small and the ventral papilla large. Well developed cervical alae, 1,5-4.5 mm long. Female 128-284 mm, maximum thickness 4 mm, head 0.6-0.8 mm diameter. Vulva 82 mm from the anterior end in a worm of 281 mm. (J411.3.w1)
• Male 115-208 mm, maximum thickness 2.5 mm, head 0.55-0.65 mm. Spicules short and stout, 0.85-1.02 mm long, covered with small granulations. (J411.3.w1)
• Eggs oval, 0.075-0.085 by 0.061-0.07 mm, with a thick transparent shell and outer yellowish irregular albuminous coat. Developing to larvae in five days at room temperature (65-80 °F). Larvae 0.3-0.35 mm long, 0.025 mm diameter. (J411.3.w1)

Infective "Taxa"

• Baylisascaris transfuga (Ascarididae - (Family))
• Baylisascaris multipapillata (Ascarididae - (Family))

Non-infective agents

Physical agents

References

Disease Author

Major References / Reviews

Code and Title List

Other References

Code and Title List

Detailed Clinical and Pathological Characteristics

• Heavy adult ascarid burdens cause moderate enteritis and, by interfering with digestion and nutrient absorption, reduced growth of the host. (B504)
• Baylisascaris transfuga in other species, such as rodents, can result in migration of larvae to the viscera, eyes and brain. (J11.90.w)
  • Baylisascaris transfuga larvae have been shown to have neurotropic affinities in laboratory mice. (J1.14.w10)

Clinical Characteristics

• Diarrhoea; (B16.9.w9, B64.26.w5)
• Coat dry and rough; (B16.9.w9, B64.26.w5)
• Anorexia; (B16.9.w9, B64.26.w5)
• Presence of ascarids in the faeces. (B16.9.w9, B64.26.w5)
• Severe infection may result in poor body condition. (B407.w18)
• Death may occur due to gut obstruction in overwhelming infections. (B16.9.w9, B64.26.w5)

Incubation

• --

Mortality / Morbidity

• Infection is common in bears in captivity, but mortality is rare. (B214.3.4.w16)
• In a survey of zoo-kept Tremarctos ornatus - Spectacled bears, ascarids were the commonest internal parasite reported. (P77.1.w19)
• Infection increases with age; a study of grizzly bears (Ursus arctos - Brown bear) in Montana and Wyoming found 40% of cubs to be infected with ascarids but 92% of six- to nine-year-old bears were infected. (J345.3.w3)
• These ascarids can obstruct the gut. (B10.48.w43, B407.w18)
• With overwhelming infection, obstruction of the gut may be fatal. (B16.9.w9)
• Death of a bear from parasitism with Baylisascaris transfuga has been recorded. (J1.14.w10)

Pathology

• Intestines: 
  • Ascarids in the small and/or large intestines. (J1.11.w11,J1.14.w9, J1.14.w10, J1.15.w10,  J1.16.w11, J2.33.w1, J11.90.w2, J210.7.w1, J345.3.w3, J413.7.w1, J423.69.w1)
  • Ascarids may be found completely filling parts of the small intestines. (J1.14.w9)

Human Health Considerations

Disease has been reported in either the wild or in captivity in:

• Found in bears in many areas of the world. (B24)
• Baylisascaris transfuga occurs throughout the black bear's range in Canada and the northern USA. (J1.11.w11)
• Infection rates in zoos may be 50-100%. (P1.1979.w2)
• Two or more Toxascaris multipapillata were found in the intestines of 17/55 Ursus americanus - American black bears from New York (Adirondacks, plus five from Allegany State Park), 1956-1959. One bear was host to 39 ascarids. (J413.7.w1)
• Toxascaris multipapillata were found in the intestines of two adult Ursus americanus - American black bears trapped in the Adirondacks, 1956-1958. (J413.7.w1)
• Toxascaris multipapillata were found in the small intestines of 5/17 Ursus americanus - American black bears from zoos in New York State, 1956-1958, with 17 worms found in one female bear. (J413.7.w1)
• Ursus arctos - Brown bear (various subspecies), Ursus americanus - American black bear, Melursus ursinus - Sloth bear, Ursus thibetanus - Asiatic black bear and Helarctos malayanus - Sun bear. (J157.58.w1)
• Toxascaris transfuga in the jejunum of Ursus arctos - Brown bear from the Zoological Garden of Prague, 1954-64 (J210.7.w1)
• Ascaris (Baylisascaris) transfuga in European brown bear Ursus arctos - Brown bear and grizzly bear Ursus arctos - Brown bear at Lincoln Park Zoological Gardens and Indian Boundary Zoo, Chicago. (J13.21.w2)
• Baylisascaris transfuga were found in 21% of Ursus americanus - American black bears during a study in Quebec, Canada, June 1971-November 1972. (J1.13.w11)
• Baylisascaris transfuga, one to four adult worms, was detected in five of seven intestinal tracts from Ursus americanus - American black bears of Minnesota examined during the summer; additionally, two adult worms were passed by one bear and two others were found in droppings found 6-16 October. (J1.11.w11)
• Baylisascaris transfuga was found in the small intestines of 53% of bears during a survey of Ursus americanus - American black bear from six states in the southeastern USA, July 1973-November 1976. This was the first report from the southeastern USA. There were no recorded associated pathogenic effects of the infections in these bears. (J1.14.w10)
• Baylisascaris were found in 25/29 (89%) intestinal tracts from hunter-killed Ursus americanus - American black bears in northern Wisconsin (1974-1975), with one to 132 worms per bear. In two bears parts of the duodenum were totally occluded by nematodes. Additionally, one Baylisascaris transfuga was taken from the anus of a female black bear captured July 1975. Eggs of Baylisascaris transfuga were detected in 59/92 faecal samples (64%) of bears live-trapped during summer 1974 and summer 1975. (J1.14.w9)
• Baylisascaris transfuga were found in the small and large intestines of 56/91 black bears (62%) during a study in northwestern Alberta, Canada, May 1976-September 1977. (J1.15.w10)J1.14.w9J1.14.w10, J1.15.w10, J345.3.w3
• Baylisascaris transfuga were found in 75.7% (53/70) of bears during a study of grizzly bears (Ursus arctos - Brown bear) from Montana and Wyoming. Average intensity of infection was 33.8 parasites per infected bear (range 1-480).[1976](J345.3.w3)
• Baylisascaris transfuga were found in the small intestines of 24/30 bears (80%) during a study of Ursus americanus - American black bears from Montana and Wyoming. Average intensity of infection was 22.7 worms/bear (range 1-177). [1976](J345.3.w3)
• Found in Ursus americanus - American black bear, Ursus arctos - Brown bear, Melursus ursinus - Sloth bear, Ursus maritimus - Polar bear and Ursus thibetanus - Asiatic black bear. (B16.9.w9)
• Baylisascaris transfuga has been reported from Ursus americanus - American black bear, Ursus arctos - Brown bear, Melursus ursinus - Sloth bear, Ursus maritimus - Polar bear, Helarctos malayanus - Sun bear and Ursus thibetanus - Asiatic black bear. It was noted that incidence of infection peaked June to August and was reduced over fall (autumn) and winter. (J4.155.w3)
• Baylisascaris multipapillata has been reported from Euarctos americanus (Ursus americanus - American black bear). (J4.155.w3)
• Collected from Melursus ursinus - Sloth bear, Yezo brown bears (Ursus arctos yesoensis) (Ursus arctos - Brown bear) and Ursus maritimus - Polar bear at Ueno Zoological Gardens, Japan. (J27.24.w1)
• Found at necropsy in the small intestines of Kodiak bear Ursus arctos - Brown bear in St Louis Zoological Park. (P1.1968.w4)
• Baylisascaris transfuga was found in 23% of small intestines during a survey of 22 Florida black bears Ursus americanus floridanus (Ursus americanus - American black bear) cubs (up to 12 months old) between 1998 and 2003. This parasite had not been reported previously in Ursus americanus in Florida. (J11.90.w2)
• Toxascaris (Baylisascaris) transfuga has been found in the following bears held at the Philadelphia Zoological Gardens: Ursus maritimus - Polar bear, Ursus syriacus (Ursus arctos - Brown bear), Ursus beringina (Ursus arctos - Brown bear) from Siberia, Ursus pruinosus (Thibetan bear; Ursus arctos - Brown bear) from Eastern Tibet and Ursus malayanus (Helarctos malayanus - Sun bear) from the Malay Peninsula, Sumatra, Borneo. (J157.11.w1)
• Baylisascaris sp. eggs were detected in 5% of 56 faecal samples from grizzly bears (Ursus arctos - Brown bear) collected from the central Canadian Arctic spring and summer 1995 and 1996. (J1.35.w7)
• In a 36-year-old wild-born captive Ursus maritimus - Polar bear, 250 Baylisascaris sp. nematodes were an incidental finding at necropsy. (J2.33.w1)
• Baylisascaris transfuga infection was confirmed based on measurements and morphology of eggs detected in faeces in a juvenile female Ursus americanus - American black bear, from Virginia; the bear also had gastrointestinal infections with coccidia, strongyloides and pinworms, as well as audycoptic mange. (P9.2004.w8)
• Baylisascaris transfuga were present in the small intestine of a wild 14-year-old female Ursus americanus - American black bear in northeastern Minnesota. (J1.16.w11)
• Two Toxascaris (Baylisascaris) transfuga were found at necropsy in the stomach of a 30-year-old Melursus ursinus - Sloth bear at Amsterdam Zoo. (J423.69.w1)
• Baylisascaris infection has been reported in a young adult Ursus maritimus - Polar bear. (J2.37.w2)
• In a survey of zoo-kept Tremarctos ornatus - Spectacled bears, ascarids were the commonest internal parasite reported. (P77.1.w19)

Further information on Host species has only been incorporated for species groups for which a full Wildpro "Health and Management" module has been completed (i.e. for which a comprehensive literature review has been undertaken). Host species with further information available are listed below:

Host Species List

• Bears (Ursidae - Bears (Family))
• Helarctos malayanus - Sun bear
• Melursus ursinus - Sloth bear
• Ursus americanus - American black bear
• Ursus arctos - Brown bear 
• Ursus maritimus - Polar bear
• Ursus thibetanus - Asiatic black bear

(List does not contain all other species groups affected by this disease)

Disease has been specifically reported in Free-ranging populations of:

• Baylisascaris transfuga occurs throughout the black bear's range in Canada and the northern USA. (J1.11.w11)
• Two or more Toxascaris multipapillata were found in the intestines of 17/55 Ursus americanus - American black bears from New York (Adirondacks, plus five from Allegany State Park), 1956-1959. One bear was host to 39 ascarids. (J413.7.w1)
• Toxascaris multipapillata were found in the intestines of two adult Ursus americanus - American black bears trapped in the Adirondacks, 1956-1958. (J413.7.w1)
• Baylisascaris transfuga were found in 21% of Ursus americanus - American black bears during a study in Quebec, Canada, June 1971-November 1972. (J1.13.w11)
• Baylisascaris transfuga, one to four adult worms, was detected in five of seven intestinal tracts from Ursus americanus - American black bears of Minnesota examined during the summer; additionally, two adult worms were passed by one bear and two others were found in droppings found 6-16 October. (J1.11.w11)
• Baylisascaris transfuga was found in the small intestines of 53% of bears during a survey of Ursus americanus - American black bear from six states in the southeastern USA, July 1973-November 1976. This was the first report from the southeastern USA. There were no recorded associated pathogenic effects of the infections in these bears. (J1.14.w10)
• Baylisascaris were found in 25/29 (89%) intestinal tracts from hunter-killed Ursus americanus - American black bears in northern Wisconsin (1974-1975), with one to 132 worms per bear. In two bears parts of the duodenum were totally occluded by nematodes. Additionally, one Baylisascaris transfuga was taken from the anus of a female black bear captured July 1975. Eggs of Baylisascaris transfuga were detected in 59/92 faecal samples (64%) of bears live-trapped during summer 1974 and summer 1975. (J1.14.w9)
• Baylisascaris transfuga were found in the small and large intestines of 56/91 black bears (62%) during a study in northwestern Alberta, Canada, May 1976-September 1977. (J1.15.w10)
• Baylisascaris transfuga were found in 75.7% (53/70) of bears during a study of grizzly bears (Ursus arctos - Brown bear) from Montana and Wyoming. Average intensity of infection was 33.8 parasites per infected bears (range 1-480).[1976](J345.3.w3)
• Baylisascaris transfuga were found in the small intestines of 24/30 bears (80%) during a study of Ursus americanus - American black bears from Montana and Wyoming. Average intensity of infection was 22.7 worms/bear (range 1-177). [1976](J345.3.w3)
• Baylisascaris multipapillata has been reported from Euarctos americanus (Ursus americanus - American black bear). (J4.155.w3)
• Baylisascaris transfuga was found in 23% of small intestines during a survey of 22 Florida black bears Ursus americanus floridanus (Ursus americanus - American black bear) cubs (up to 12 months old) between 1998 and 2003. This parasite had not been reported previously in Ursus americanus in Florida. (J11.90.w2)
• Baylisascaris sp. eggs were detected in 5% of 56 faecal samples from grizzly bears (Ursus arctos - Brown bear) collected from the central Canadian Arctic spring and summer 1995 and 1996. (J1.35.w7)
• Baylisascaris transfuga infection was confirmed based on measurements and morphology of eggs detected in faeces in a juvenile female Ursus americanus - American black bear, from Virginia; the bear also had gastrointestinal infections with coccidia, strongyloides and pinworms, as well as audycoptic mange. (P9.2004.w8)
• Baylisascaris transfuga were present in the small intestine of a wild 14-year-old female Ursus americanus - American black bear in northeastern Minnesota. (J1.16.w11)
• Baylisascaris transfuga and Baylisascaris multipapillata have been found in Ursus maritimus - Polar bears. (D315.3.w3)

Further information on Host species has only been incorporated for species groups for which a full Wildpro "Health and Management" module has been completed (i.e. for which a comprehensive literature review has been undertaken). Host species with further information available are listed below:

Host Species List

• Bears (Ursidae - Bears (Family))
• Ursus americanus - American black bear
• Ursus arctos - Brown bear 

(List does not contain all other species groups affected by this disease)

General Information on Environmental Factors/Events and Seasonality

• Incidence of infection peaked June to August and was reduced over fall (autumn) and winter. (J4.155.w3)
• An analysis of faecal samples from black bears in Quebec showed that the prevalence of eggs of Baylisascaris transfuga was low in autumn (October and November) prior to denning (found in 13% of samples) but higher (42%) in spring (May). This may indicate maturation of overwintering larvae. (J1.14.w11)

Regions / Countries where the Infectious Agent or Disease has been recorded

• In bears: North America, Europe, Japan(J1.11.w11,J1.14.w9, J1.14.w10, J1.15.w10,  J1.16.w11, J2.33.w1, J11.90.w2, J27.24.w1, J210.7.w1, J345.3.w3, J413.7.w1, J423.69.w1)

Regions / Countries where the Infectious Agent or Disease has been recorded in Free-ranging populations

• In bears: North America, (J1.11.w11, J1.13.w11, J1.14.w9, J1.14.w10, J1.15.w10, J1.16.w11, J1.35.w7, J11.90.w2, J345.3.w3, J413.7.w1, P9.2004.w8)

General Information on Investigation / Diagnosis

• Presence of worms in faeces. (B16.9.w9, B64.26.w5)
• Presence of worms in vomit. (B22.32.w15)
• Faecal flotation to detect ascarid ova: 66.3-74.7 x 78.3-88.0 µm. (B16.9.w9, B64.26.w5)
• Sugar flotation of faeces, with centrifugation. (J13.21.w2)
• Eggs of Transfuga papillata measured 78.3-88.0 x 66.3-74.7 um (average 83.4 x 69.6 um). (J4.155.w3)

• History & Documentation
• Physical Examination of Mammals
• Necropsy of Mammals
• Environmental Assessment
• Chapter 2 - B36 Field Manual of Wildlife Diseases - Specimen Collection and Preservation
• Chapter 3 - B36 Field Manual of Wildlife Diseases - Specimen shipment
• Appendix A - B36 Field Manual of Wildlife Diseases - Sample specimen history form

Similar Diseases (Differential Diagnosis)

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Specific Medical Treatment

• Piperazine adipate, 450 mg/4.5 kg body weight (estimated) in food once daily for three days was effective, reducing worm egg counts from 50/4 g faeces to zero. (J13.21.w2)
• Piperazine salts, 100 mg/kg orally, repeated monthly for chronic infection. (B10.48.w45)
• Piperazine salts, 100 mg/kg once orally. (B22.32.w15)
  • Piperazine citrate or piperazine adipate, 100-120 mg/kg were efficacious in control in bears at Ueno Zoological Gardens, Japan. (J27.24.w1)
• Dithiazine iodide was effective but 15 days of treatment resulted in severe diarrhoea and vomiting, so treatment was stopped. (J13.21.w2)
• Dichlorvos (19 mg/lb body weight) was effective, with worms being passed in the faeces following treatment, and faecal egg counts reduced to zero. Treated bears showed varying changes in faeces, which became soft to loose, and in some, depression and ataxia were noted. (J4.155.w3)
• Dichlorvos, 25 - 35 mg/kg orally, divided into two doses, with half the dose given on each of two consecutive days. (B10.48.w45); 15 mg/kg orally for two days. (B22.32.w15, P85.1.w3)
• Levamisole, 11 mg/kg orally or subcutaneously, repeated as required. (B10.48.w45); 10 mg/kg (P85.1.w3); 10 mg/kg once orally. (B22.32.w15) Note: This is toxic if a double dose is given. (B22.32.w15)
• Diethylcarbamazine, 10 - 60 mg/kg orally, repeated as necessary. (B10.48.w45)
• Mebendazole, 15 mg/kg daily for two days. N.B. this is not approved for use in carnivores. (B10.48.w45); 5 - 15 mg/kg daily orally for three days. (B22.32.w15); 15 mg/kg daily for two days, repeat after 2-3 weeks. (P85.1.w3).
  • Note: Re-infection occurred following treatment, despite housing in concrete with daily washing of cages. (J4.155.w3)
• Repeated treatment is required at intervals of four to eight weeks. (B22.32.w15)
• Pyrantel embonate, 25-60 mg/kg orally once. (B22.32.w15)
• Pyrantel pamoate 100 mg/kg orally. (P85.1.w3)
• Thiabendazole 12.5-25 mg/kg. (P85.1.w3)
• Fenbendazole, 50 mg/kg orally for three days or 20 mg/kg orally for five days. (B22.32.w15); 50 mg/kg orally for two days. (P85.1.w3)
  • 10 mg/kg daily for two consecutive days effectively reduced faecal egg counts to zero in Ursus arctos - Brown bear and egg counts were still negative 30 days post treatment. (P1.1980.w4)
• Ivermectin
  • Ivermectin at 0.2 mg/kg was "highly effective" in a group of polar bears in a circus, in which other anthelmintics had become progressively less effective. (P5.30.w1)
  • Ivermectin, 0.3 mg/kg once subcutaneously or orally, repeated every eight weeks. (B22.32.w15)
  • Ivermectin 0.3 mg/kg subcutaneously or orally. (P85.1.w3)
  • Treating repeatedly with ivermectin, orally every two weeks or parenterally every three weeks, may allow eventual elimination of this parasite from an enclosure. (P85.1.w2)
• Milbemycin oxime, 1.0 mg/kg (twice the normal canine dose rate of 0.5 mg/kg) given monthly for 18 months and then every other month. This regime decreased faecal egg counts of Baylisascaris transfuga from >200 epg (eggs per gram) to zero within six months. No side effects were noted and there were no problems with acceptance of the dose (8 - 10 x 23 mg tablets per bear, in food). (P9.1995.w10)
• Suggested treatments for Baylisascaris in Ursus maritimus - Polar bears are milbemicin oxime, 1 mg/kg orally, or mebendazole, 20 mg/kg daily for three days. (D315.3.w3)
• In a survey of zoo-kept Tremarctos ornatus - Spectacled bears, pyrantel pamoate, 6.6 mg/kg, piperazine adipate, 25 mg/kg, mebendazole, 22 mg/kg and levamisol hydrochloride, 10 mg/kg were reported as treatments for ascarid infections. (P77.1.w19)

• Treatment and Care
• Subcutaneous Injection of Mammals

General Nursing and Surgical Techniques

• Treatment and Care

Preventative Measures

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• Regular anthelmintic treatment can be used for control. (P1.1979.w2)

• Preventative Medicine for Mammals

Environmental and Population Control Measures

BEARS

• Ova can remain viable in the environment for years (e.g. five years); they are resistant to drying, freezing and exposure to sunlight. (B10.48.w43, B22.32.w15, P1.1979.w2)
• Ova are not destroyed by normal cleaning with water and disinfectants. Use of high-pressure water for cleaning assists in spreading ascarid ova around the enclosure. (B10.48.w43, B22.32.w15, P1.1979.w2)
• Ova can be destroyed by direct heat, i.e. use of a blowtorch, on surfaces which can resist this treatment (obviously not on either wooden or painted structures). (B10.48.w43, B407.w18, P1.1979.w2)
• Removal of faeces and spot application of a flamethrower to the site where the faeces were lying, prior to hosing down and disinfecting, should reduce the number of infective ova present. (P1.1979.w2)

• Environmental and Population Management
•