Causal Agent:Coenurosis is infection by the metacestode larval stage (coenurus) of Taenia multiceps and T. serialis.

Life Cycle:

The definitive hosts for Taenia multiceps and T. serialis are members of the family Canidae.  Many canids can serve as definitive hosts for T. multiceps, but only dogs and foxes can serve as hosts for T. serialis.  Eggs and gravid proglottids are shed in feces into the environment , where they are ingested by an intermediate host .  Many animals may serve as intermediate hosts, including rodents, rabbits, horses, cattle, sheep and goats.  Eggs hatch in the intestine, and oncospheres are released that circulate in blood until they lodge in suitable organs (including skeletal muscle, eyes, brain and subcutaneous tissue).  After about three months, oncospheres develop into coenuri.  The definitive host becomes infected by ingesting the tissue of an infected intermediate host containing a coenurus .  The adult cestodes reside in the small intestine of the definitive host , .  Humans become infected after the accidental ingestion of eggs on fomites or in food and water contaminated with dog feces .  Eggs hatch in the intestine, and oncospheres are released

that circulate in blood until they lodge in suitable organs and after about three months develop into coenuri .  Coenuri of T. multiceps are usually found in the eyes and brain; those of T. serialis are usually found in subcutaneous tissue.

Geographic Distribution:Widespread; most of the cases are from Africa, although cases also appear in sheep-raising areas of Europe, South America, the United States and Canada.

Clinical Features:Coenuri in the skin or subcutaneous tissue usually present as painless nodules.  The lesions are often fluctuant and tender.  Most subcutaneous nodules manifest on the trunk, sclera, subconjuctiva, neck, shoulders, head and limbs.  Coenuri in the neck may affect neck movement and swallowing.  Clinically, coenuri may mimic lymphomas, lipomas, pseudotumors, or neurofibromas.  Coenuri in the central nervous system may cause headache, fever and vomiting.  Localizing neurologic symptoms may also develop, including nerve palsies, jacksonian epilepsy, pachymeningitis, obstructive or communicating hydrocephalus, and intracranial arteritis with transient hemiparesis.  Coenuri in the eye cause both intraocular and orbital infections, and patients may present with varying degrees of visual impairment.  If not removed, coenuri in the eye may cause painful inflammation, glaucoma and eventually blindness.

Laboratory Diagnosis:Diagnosis is made by the observation of coenuri in biopsy or autopsy specimens.  Coenuri are usually readily distinguished from cysticerci by the presence of multiple protoscoleces.

Diagnostic findings

Microscopy

Treatment:Removal of the coenurus effectively treats intracranial coenurosis in most cases.  There have also been reports of successful removal of coenuri from patients' eyes, resulting in a recovery of sight.  Coenuri are susceptible to praziquantel, but caution should be used, especially in cases of intraocular coenurosis.  For more information on the general treatment of cestode infections, including infections of the larval stages, see the recommendations in The Medical Letter (Drugs for Parasitic Infections).

 Microscopy

Coenurosis is infection by the metacestode larval stage (coenurus) of Taenia multiceps and T. serialis.  Coenuri may be found in most tissue types, but those of T. multiceps have a predilection for the central nervous system and eye; those of T. serialis are usually found in subcutaneous tissue.  Coenuri are thin-walled, whitish or gray, and spherical to polycephalic in shape.  A coenurus contains multiple protoscoleces, which distinguishes it from a cysticercus, which contains a single protoscolex.  Also, the length of the large hooklets on the protoscoleces can be useful in separating cysticerci from coenuri:  the long hooklets of a metacestode of T. serialis and T. multiceps measure 110-175 µm long; those of T. solium measure 100-130 µm long.

A B

A: Large, polycephalic coenurus removed from the shoulder of a baboon (Papio sp.).B: Close-up of a coenurus of T. multiceps removed from the eye of a patient, broken open to show multiple protoscoleces.

C D

C: Coenurus removed from a subcutaneous nodule in the shoulder area of a patient, stained with hematoxylin and eosin (H&E).  Image taken at 50x magnification.  Although the species was not identified in this case, the pathology is consistent with T. serialis.D: Higher magnification (200x) of the coenurus in Figure C.

E F

E, F: Higher magnification (200x) of the same specimen shown in Figures C and D.  The black arrows point to hooklets in the protoscoleces.