Esther van Praag, Ph.D.
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This parasite is cosmopolitan. It is generally referred to as the rabbit stomach worm. Two clearly defined subspecies have been identified and recognized to infest Lagomorphs:
• Obeliscoides cuniculi multistriatus infecting snowshoe hares (Lepus americanus),
• Obeliscoides cuniculi cuniculi infecting mainly the eastern cottontail rabbits (Sylvilagus floridanus).
Experimental crosses of males of O. c. c. and females O. c. m produced viable progeny with mixed systemic characters, but there is no evidence that this occurs in nature.
The type host of O. c. cuniculi is the pet rabbit, although the other subspecies is also occasionally found. The life cycle of Obeliscoides cuniculi is direct. Obeliscoides sp. does not represent a public health danger.
Obeliscoides cuniculi multistriatus
The eggs are about 96 * 46 mm in size and excreted with the feces. They generally have a thin shell. The larva develops inside the eggs and hatches after 30 - 36 h. The larvae reach the L3 stage on the 6th day, after which it becomes infective by penetrating the mucosa of the stomach. Within 24 h., the larva exsheates in the stomach and will develop into a mature adult.
The adult parasites are pink and have no buccal capsule. They are located in the mucus layer of the stomach. The males (10 - 15 mm long) have well developed lateral lobes on the bursa copula, supported by rays, and a pair of spicules. The females (15 - 18 mm) have a pointed tail and the vulva is in the caudal part of the body. Shedding of eggs starts 16 to 20 days after the infection and continues for 61 - 118 days.
Obeliscoides cuniculi cuniculi
The eggs are slightly smaller than the other subspecies: 83 * 47 mm. They are excreted with the feces at a 32 cells stage. The larva will develop from the L1 to the L3 stage on the 6th days. The larva resists temperatures of –4 to 2 °C but not desiccation.
After ingestion, the L3 larvae will exsheat within one hour and start invading the gastric mucosa. The final molt probably occurs as worms migrate from the mucosa, starting on days 5 after the ingestion, as worms can be observed on the surface of the gastric mucosa.
The presence of Obeliscoides cuniculi is usually asymptomatic in rabbits. Severe infestation can lead to hemorrhagic gastritis, accompanied by a failure to gain weight, anemia, anorexia and diarrhea in rabbits, during the first two weeks of infection only, after which the animals regain their normal condition. The presence of Obeliscoides cuniculi is diagnosed through fecal flotation, and identification of the eggs in the feces.
At necropsy, it was observed that adults worms adhere closely to the mucus coating of the stomach. Some worms were found in the gastric crypts. Pathological signs are limited to the stomach, with a thickened and granular (“cobblestone”) mucosa, due to the combination of larval parasites, glandular hyperplasia and infiltration of inflammatory cells.
J.E. Alicata (1932) Life History of the Rabbit Stomach Worm, Obeliscoides cuniculi. J. Agricultural Res. 44: 401-419.
D. Duwel, K. Brech (1981) Control of Oxyuriasis in Rabbits with Fenbendazole. Lab. Anim. 15: 101-105.
L.N. Measures, R.C Anderson (1983) Development of the Stomach Worm, Obeliscoides cuniculi (Graybill), in lagomorphs, woodchucks and small rodents. J. Wildl. Dis. 19: 225-233.
L.N. Measures, R.C. Anderson (1984) Hybridization of Obeliscoides cuniculi (Graybill, 1923) Graybill, 1924 and Obeliscoides cuniculi multistriatus Measures and Anderson, 1983. Proc. Helminthol. Soc. Washington 51: 179-186.
S.W. Russel, B.C. Ward, N.F. Baker (1970) Obeliscoides cuniculi: Comparison of Gastric Lesions in Rabbits with those of Bovine Osteratogiosis. Exp. Parasotol. 28:217-225.
T.R. Schoeb (1990) Internal Parasites of Rabbits, Dept. Comparative Medicine, University of Alabama, http://netvet.wustl.edu/species/rabbits/rabparas.txt
A.E. Sollod, T.J. Hayes, E.J.L. Soulsby (1968) Parasitic Development of Obeliscoides cuniculi in rabbits. J. Parasitol. 54: 129-132..