Macracanthorhynchus spp.

Synopsis

CAPC Recommends

• Reduce the risk of infection of acanthocephalans by limiting ingestion of insects, primarily beetles or millipedes.
• Macracanthorhynchus ingens and M. hirudinaceus are potentially zoonotic, and young children in particular should be monitored and kept from ingesting insects.
• Diagnosis is made through fecal examination or identification of the adult worm passed in feces or vomitus.

Species

Canine

Macracanthorhynchus ingens

Macracanthorhynchus hirudinaceus

Macracanthorhynchus ingens Adult

Macracanthorhynchus ingens egg (88 x 60um; 400x)

Introduction

• Macracanthorhynchus ingens is an acanthocephalan parasite that is primarily found in the intestines of raccoons.
• Macracanthorhynchus hirudinaceus is an intestinal, acanthocephalan parasite also known as the “Giant Thorny-Headed Worm of Swine,” as its primary definitive host is swine.
• M. hirudinaceus and M. ingens have occasionally been found in dogs, humans and various wildlife hosts.

Overview of Life Cycle

• Macracanthorhynchus hirudinaceus has an indirect life cycle that requires scarabaeoid or hydrophilid beetle larvae as intermediate hosts.
• Dogs infected with M. hirudinaceus shed eggs in their feces, which contain the larval (acanthor) stage. These eggs are then consumed primarily by larvae of various beetle species, and develop over 6-12 weeks within this host until reaching the infective stage (cystacanth) and encysting in the body cavity of the insect.
• Macracanthorhynchus ingens also develops in the larvae and mature forms of beetles or millipedes (reported in Narceus annularis and N. americanus) but may also be found in reservoir hosts such as frogs and snakes. Its life cycle is otherwise similar to M. hirudinaceus.
• Dogs become infected when they ingest the intermediate host, either as larvae or adult insects.

Stages

• Embryonated eggs contain larva (acanthor) with rostellar hooks, and are passed in the feces of an infected dog. They are wide and ovoid, with a thick, dark brown textured shell. Eggs are multi-layerd, large and dense.
• Adult M. hirudinaceus are large, flattened with transverse grooves, and vary from milky-white to pink to red. Females are generally longer and wider than males, reaching lengths of 480-500mm long and 8-9mm wide. Their proboscis has 5-6 rows of recurved hooks on the anterior end.
• The proboscis of the adult M. ingens has six spiral rows of 6 hooks. Males are 130-150mm long and 4-5mm wide, females are 183-300mm long and 5-88mm wide.
• Acanthocephalans are often mistaken for nematodes or cestodes.

Disease

• Infections with M. hirudinaceus have not yet been associated with clinical disease in dogs. However, treatment is still warranted due to the possibility of zoonotic disease associated with this helminth.
• For M. hirudinaceus, in swine definitive hosts, granulomatous lesions are found at the site of attachment in the intestinal wall. Mild infections are asymptomatic and severe infections cause slow growth and possibly emaciation. Rarely, the worm may perforate the gut and peritonitis may result.
• In a report by Fahnestoc, 1985, infection with M. ingens caused bloody and loose stools in two 4-month old dogs. Growth was unaffected.
• Lesions associated with M. ingens are circular mucosal ulcerations with edema, abcessation, and eosinophilic inflammation (but without small intestinal perforation).

Prevalence

• Macracanthorhynchus hirudinaceus has been reported in a broad range of locations, including North America, Asia, and the Middle East.
• Infections of M. ingens has been reported in North American dogs exposed to intermediate hosts.

Host Associations and Transmission Between Hosts

• Swine, domestic and wild canines, and foxes can harbor M. hirudinaceus in their intestinal tracts.
• Intermediate hosts for M. hirudinaceus are primarily the larvae and adults of scarabaeoid or hydrophilid beetles. The most important intermediate hosts in the United States are the June Beetle (Cotinis nitida), New World scarab beetles (genus Phyllophaga), and other beetles that feed primarily on dung.
• Raccoons, foxes, bears, mink, skunks, wolves, ring tailed cats, badgers, and moles have been found to be definitive hosts for M. ingens. Intermediate hosts are primariy beetles and millipedes in North America. Frogs (Rana pipiens), snakes, and rodents have been experimentally shown to be potential transport hosts as well.

Prepatent Period and Environmental Factors

• The prepatent period in experimentally infected canine hosts for M. ingens was 5-7 weeks, with a mean life span for adult worms of 23 days. Afterwards, infection was spontaneously eliminated. A prepatent period has not been established for M. hirudinaceus in canine hosts.
• In North America, the intermediate hosts (and parasites) are primarily active during the warm summer and early autumn, ceasing during the winter when soil temperatures fall to 40°F or less.

Site of Infection and Pathogenesis

• Small intestine.
• Granulomatous lesions are often found at the site of attachment for M. hirudinaceus, which then resolve after removal of the parasite.

Diagnosis

• Observation of eggs on fecal flotation, or more commonly fecal sedimentation.
• Adult worms found in feces of the definitive host.

Treatment

• There is no approved treatment of M. hirudinaceus in dogs, although ivermectin and lefluronomide have been used in the treatment of swine. At a concentration of 100ug/kg per day in medicated feed, efficacy of ivermectin was 100% in swine.
• Macracanthorhynchus ingens was spontaneously eliminated in experimentally and naturally infected dogs. In one reported case, empirical treatment with ivermectin at 500ug/kg once daily for 5 days, and then repeated once 3 weeks later, may have resulted in resolution of clinical signs(Pearce et. al, 2001).

Control and Prevention

• Prevent ingestion of the beetle or millipede intermediate hosts, especially in areas populated by wild or domestic swine and other wildlife vectors.

Public Health Considerations

• Human infection by M. hirudinaceus and M. ingens have been reported in cases where accidental or intentional consumption of the intermediate host (insect) occurred.

Selected References

• Dalimi, A., Sattari, A., Motamedi, Gh. A study on intestinal helminthes of dogs, foxes, and jackals in the western part of Iran. Vet Parasit. (2006) 142(1-2): 129-133.
• Fahnestock, GR. Macracanthorhynchiasis in dogs (part 1). Mod Vet Pract. (1985) 66:31-34.
• Fahnestock, GR. Macracanthorhynchiasis in dogs (part 2). Mod Vet Pract. (1985) 66:81-83.
• Pearce, JR, Hendrix, CM, et al. Macracanthorhynchus ingens infection in a dog. J Am Vet Med Assoc (2001) 219(2): 194-196.
• Petrochenko, V. I. 1971. Acanthocephala of domestic and wild animals. Lavoott R, translator; Epstein E, editor. Jerusalem: Wiener Bindery Ltd. p. 299-320.
• Sarkari, B., Mansouri, M., Najjari, M. et al. Macracanthorhynchus hirudinaceus: the most common helminthic infection of wild boards in southwestern Iran. J Parasit Dis (2016) 40: 1563.