Pentastomids

(Armillifer spp., Porocephalus spp.)

Armillifer spp. are parasitic crustaceans belonging to the group Pentastomida, whose immature forms are incidentally discovered within the abdominal cavity and viscera of dogs and cats. They are mostly non-pathogenic.

Parasite species: Armillifer armillatus, Armillifer moniliformis, Armillifer grandis, Armillifer agkistrodontis, Porocephalus crotali
Common name: Visceral pentastomids
Hosts: Snakes and other reptiles are definitive hosts, small mammals (rodents) are intermediate hosts. Dogs, cats and humans are accidental hosts for larval and nymphal stages
Pre-patent period: N/A
Location in the host: Usually abdominal cavity within viscera
Distribution: Tropics and subtropics
Transmission route: Ingestion of parasite eggs shed by reptiles, ingestion of undercooked reptile meat/rodents
Zoonotic: Yes (snakes are primary reservoirs)

Distribution

Visceral pentastomiasis has been reported in humans throughout the tropics and subtropics and is considered an emerging zoonosis in West Africa. Armillifer armillatus is present in West and Central Africa, A. moniliformis in Southeast Asia, A. grandis in Africa, A. agkistrodontis in China, and Porocephalus crotali is worldwide distributed.

Clinical signs

Visceral pentastomiasis is usually asymptomatic. Rarely, large parasite loads may result in abdominal or thoracic involvement due to organ dysfunction.

Diagnosis

Nymphs may be incidentally discovered within the liver, mesenteries, spleen, and lungs during surgery (Fig. 1) or coiled opacities of calcified dead parasites may be observed on abdominal or chest radiographs.

Figure 1 Nymph of A. moniliformis (anterior end damaged) incidentally found withiin the omentum of a cat during surgery (Image credit: Dr. S. Teoh)

Treatment

Visceral pentastomiasis is usually asymptomatic and surgical removal of the nymphs should be considered only for symptomatic animals with high parasite loads.

Prevention and Control

Owners should be advised to prevent their animals from hunting and roaming freely.

Public health considerations

Dog (and cats) do not pose a direct risk to humans