Sparganosis: A Zoonotic Cestodiasis
Sparganosis is an infection of tissues by second stage larvae (spargana or plerocercoid) of pseudophyllidean tapeworms. Sparganosis due to pseudophyllidean cestodes such as Sparganum spp. (e.g. Sparganum proliferum) and Spirometra spp. (e.g. Spirometra mansonoides, Spirometra erinaceieuropaei) can occur in body cavities or in tissues of intermediate and paratenic hosts. Sparganum proliferum is phylogenetically identified as a new species in the order pseudophyllidea. The life cycle and the definitive host of Sparganum proliferum is unknown but believed to be similar to that of Spirometra spp. The definite hosts of Spirometra spp. are carnivores, and the eggs are shed in feces. The eggs embryonate in the environment, hatch in water and release coracidia. Coracidia are ingested by intermediate hosts, copepod crustaceans (Cyclops spp.), and develop into procercoids. Second intermediate hosts including fish, reptiles, and amphibians ingest infected copepods and acquire procercoid larvae. Procercoids develop into plerocercoids in the second intermediate hosts. Predators of the second intermediate hosts are infected by the plerocercoids. Plerocercoidosis/sparganosis develops after ingesting procercoids or plerocercoids with contaminated water or infected intermediate hosts. Humans and other mammals including apes, pigs, dogs, and cats can serve as paratenic or second intermediate hosts and develop sparganosis.
Sparganosis has a worldwide distribution. The majority of cases in humans have been reported from Japan, Korea, China and Southeast Asia, but a few cases have been reported from the southern United States in broad areas of Atlantic and Gulf states. Sparganosis in Asia and Americas are attributed to Spirometra erinaceieuropaei and Spirometra mansonoides, respectively. Human infection may occur through various ways including drinking untreated contaminated water containing larvae or first intermediate hosts, ingesting raw or inadequately cooked flesh of infected secondary intermediate hosts or paratenic hosts (frogs, snakes, and game such as feral swine) and applying flesh of an infected intermediate host as a poultice to a wound, which is most commonly practiced in the Orient. After ingestion, the larvae penetrate the intestine wall and disperse in the body. A direct infection of open wounds or mucous membranes with plerocercoids has been described in humans. Hunters and other individuals who use wild animals for private and commercial meat production, and veterinary professionals could be exposed to sparganosis.
Diagnosis, Treatment and Control
Grossly, sparganosis usually appears as slowly growing migratory subcutaneous nodules in the tissues of infected intermediate and paratenic hosts. The parasite can be found anywhere in the body including central nervous system. Due to lack of distinct morphologic features, spargana must be fed to a definitive host before the parasite can be definitively identified. Sparganosis is usually diagnosed following surgical removal of the worms from infected tissues. The infection may also be diagnosed by the presence of eosinophilia or identification of the parasite in tissue specimens from excisional biopsies. Microscopically, extensive pyogranulomatous and eosinophilic dermatitis, and panniculitis with abundant intralesional cestode larvae would be observed in biopsy specimens. In humans, if excisional biopsy is not feasible to remove and identify the parasite, an antisparganum ELISA test could be used for diagnosis. MRI imaging is the most valuable method of detection of human cerebral sparganosis.
Knowledge of the epidemiology of the disease and the cultural practices in a given area is important to determine appropriate control measures to avoid infection. In humans, history of exposure to infected animals, drinking contaminated water, and handling or consumption of flesh of infected secondary intermediate hosts or paratenic hosts with a clinical history of a painful, migratory, subcutaneous nodule would suggest possible sparganosis. As preventive measures dinking water should be properly boiled or filtered and animal flesh must be sufficiently cooked before consumption. The practice of applying a poultice made from infected tissues of intermediate hosts should be avoided. Currently there is no effective treatment of sparganosis. Complete removal of the granulomas together with the cestode larvae is the treatment of choice.