multilocularis

Echinococcus multilocularis, commonly called the fox tapeworm, is a small cestode in the family Taeniidae. It is the causative agent of alveolar echinococcosis (AE) in humans and other accidental hosts. The parasite is of medical importance in the northern hemisphere, where wildlife cycles sustain transmission.

Life cycle and hosts: The adult parasite resides in the small intestine of definitive hosts such as red foxes (Vulpes vulpes), dogs, and other canids. Eggs are shed in feces and contaminate the environment. Small wild rodents or other intermediate hosts ingest the eggs; the oncospheres hatch and develop into metacestodes that form infiltrative, multiloculated lesions in the liver and occasionally in other organs.

Pathology and clinical features: In humans, alveolar echinococcosis behaves like a malignant tumor. The liver is most commonly affected, with progressive, infiltrative growth that can mimic cancer and may metastasize to distant sites if untreated. Symptoms are often nonspecific and may include abdominal pain, hepatomegaly, weight loss, or jaundice in advanced cases. The disease tends to progress slowly over years or decades.

Diagnosis and treatment: Diagnosis relies on imaging techniques such as ultrasound, CT, or MRI to reveal infiltrative hepatic lesions, complemented by serology and molecular methods. Biopsy is generally avoided due to the risk of dissemination. Treatment combines surgery and antiparasitic therapy: radical surgical resection when feasible, liver transplantation in selected cases, and long-term antiparasitic therapy with albendazole (or sometimes other benzimidazoles) for inoperable disease or as adjuvant therapy. Prognosis depends on disease extent, timely diagnosis, and access to comprehensive treatment.

Epidemiology and prevention: AE is endemic in parts of Europe, Asia, and North America, particularly in rural areas with abundant wildlife and dog populations. Prevention focuses on reducing human exposure to eggs, regular deworming of dogs, proper hygiene, and avoidance of ingestion of contaminated food or water.