Sparganosis is a rare parasitic infection caused by the larval stage of certain Spirometra tapeworm species, including S. mansoni and S. erinacei. Humans are accidental hosts in the parasite’s life cycle. This condition is not contagious from person to person. It is considered uncommon, with few human cases documented.
How People Get Infected
Humans can acquire sparganosis through three primary routes. The parasite’s adult form resides in definitive hosts like dogs and cats, which shed eggs into freshwater. These eggs hatch into larvae ingested by copepods, tiny freshwater crustaceans that act as first intermediate hosts.
One common way humans get infected is by drinking unfiltered water containing these infected copepods. The larvae then penetrate the intestinal wall and migrate to various body tissues. Another route involves consuming raw or undercooked flesh from a second intermediate host, such as frogs, snakes, or certain birds and mammals, which have ingested infected copepods.
The third mode of transmission involves direct contact with infected animal tissue, particularly through traditional medicinal practices. Applying raw flesh from an infected animal, like a frog or snake, as a poultice to an open wound or the eyes, allows the larvae to enter the human body.
Signs and Symptoms of Sparganosis
The clinical presentation of sparganosis varies significantly depending on where the larva migrates within the body.
Subcutaneous Sparganosis
This is the most frequently observed form, where larvae settle in the connective tissues beneath the skin. This results in slow-growing, rubbery nodules, 0.5 to 5 centimeters in size. These nodules can be painful or migratory, moving under the skin, and may appear on the chest wall, lower extremities, or face.
Ocular Sparganosis
When the larva invades the eye area, it leads to ocular sparganosis. Symptoms include painful swelling around the eye, excessive tearing, redness, and impaired vision.
Cerebral Sparganosis
This occurs when the parasite infects the brain, a severe yet less common manifestation. This form can lead to neurological symptoms like recurrent seizures, persistent headaches, and focal neurological deficits such as weakness, numbness, or abnormal skin sensations. Brain involvement may also cause increased intracranial pressure, memory problems, or loss of consciousness.
Medical Diagnosis and Treatment
Diagnosis often begins with imaging studies like MRI or CT scans, which can reveal suspicious lesions or masses. While these scans suggest infection, a definitive diagnosis is confirmed after the sparganum larva is surgically removed and identified. Blood tests, such as the antisparganum ELISA test, can offer supportive evidence, especially when surgery is not immediately feasible.
The main treatment for sparganosis is the complete surgical excision of the larva. This procedure is performed for symptomatic lesions or those causing a mass effect. Antiparasitic medications, such as praziquantel, have been explored, but their effectiveness against sparganosis has been variable and limited. Therefore, surgical removal remains the standard of care.
Prevention and Geographic Risk
Preventing sparganosis involves several practical measures to avoid contact with the parasite.
Prevention
Individuals should avoid drinking unfiltered or untreated water from natural sources like ponds or lakes that may contain infected copepods. Boiling or properly filtering water can eliminate these crustaceans.
Thoroughly cooking all meat, especially from potential intermediate hosts like frogs, snakes, or wild game, is another important preventive step. This ensures any present larvae are killed. Additionally, it is advised against using raw animal flesh, such as frog or snake meat, as a poultice or for traditional medicinal applications, as this can directly introduce larvae into open wounds or mucous membranes.
Geographic Risk
Sparganosis cases have been reported globally, but the infection is more common in specific geographic regions. Southeast Asia has a higher prevalence, with occurrences in countries such as China, Japan, Korea, and Thailand. Sporadic cases can also appear worldwide, often in travelers returning from endemic areas.