Paragonimiasis is a zoonotic infection caused by a highly evolved parasite with a complex life cycle that includes at least three hosts. Two intermediate hosts, a snail and a crustacean, and a mammalian definitive host are necessary to complete the life cycle of this parasite. Human and animal infections result from the consumption of raw or undercooked crustaceans (i.e., the second intermediate host) or through consumption of raw or undercooked meat from a paratenic host. Paragonimus is the only human parasite where the adults reside in the human lung. The genus Paragonimus is highly successful and is endemic in Asia, Africa, and the Americas. Paragonimus kellicotti is the species endemic to North America. Physicians in countries without endemic disease may encounter patients with paragonimiasis who have immigrated with the disease or who contracted the disease while traveling or through ingestion of imported contaminated food. Many infections are subclinical and cause only mild disease. Sometimes, however, severe infections occur and may be fatal. Two of the five patients with P. kellicotti infections that have been reported over the past three decades were associated with relatively severe disease. These patients required surgery, with one requiring a second course of praziquantel. The most recently reported patient had a remote P. kellicotti infection, but the residual pleural effusion caused by the Paragonimus infection became infected by bacteria and directly contributed to his demise.
The diagnosis of paragonimiasis should be considered when the appropriate clinical signs and symptoms, radiologic findings, and food history are supportive. Cough and hemoptysis are the most common presenting symptoms in patients with paragonimiasis. Diagnosis may be achieved through the demonstration of the characteristic operculate eggs in respiratory secretions, stool, or tissue biopsy specimens. Immunodiagnostics are excellent tools for assisting with the diagnosis of imported paragonimiasis, particularly for patients who do not have demonstrable eggs in clinical specimens. The utility of immunodiagnostics for detecting infections caused by P. kellicotti remains to be determined. Praziquantel is an effective treatment, but surgery may be necessary for patients with complicated pleural disease or cerebral paragonimiasis. Control of paragonimiasis in animals is impractical because of wild animal reservoirs, but in humans infections may be averted through the avoidance of certain foods and by thorough cooking. Crayfish in North America may harbor P. kellicotti and therefore should be thoroughly cooked prior to consumption.