Paragonimus westermani

Paragonimus westermani, commonly known as the oriental lung fluke, is a parasitic flatworm belonging to the class Trematoda. It is a significant cause of paragonimiasis, a food-borne parasitic infection affecting the lungs and occasionally other organs. This article provides an overview of Paragonimus westermani, including its lifecycle, transmission, clinical manifestations, diagnosis, treatment, and prevention.

Lifecycle

The lifecycle of Paragonimus westermani involves multiple hosts. The adult flukes reside in the lungs of the definitive hosts, which are typically mammals including humans, dogs, and cats. Eggs are excreted in the sputum or feces of the infected host and hatch in freshwater, releasing miracidia. These miracidia infect a suitable snail intermediate host, transforming into sporocysts, rediae, and then cercariae. The cercariae are released from the snail and infect freshwater crustaceans, such as crabs and crayfish, becoming metacercariae. Humans and other definitive hosts become infected by consuming undercooked or raw crustaceans containing metacercariae.

Transmission

Transmission of Paragonimus westermani to humans primarily occurs through the ingestion of raw or undercooked freshwater crustaceans contaminated with metacercariae. In some cultures, eating raw crustaceans is a traditional practice, which increases the risk of paragonimiasis. Human-to-human transmission does not occur.

Clinical Manifestations

The clinical manifestations of paragonimiasis can vary. Early infection may be asymptomatic or present with nonspecific symptoms such as fever, cough, and abdominal pain. As the disease progresses, chronic cough, hemoptysis (coughing up blood), chest pain, and dyspnea (difficulty breathing) can occur. Extrathoracic manifestations, including neurological symptoms due to migration of the flukes to the brain, can also be seen in some cases.

Diagnosis

Diagnosis of paragonimiasis is based on clinical symptoms, dietary history, radiological findings, and laboratory tests. Serological tests can detect antibodies against Paragonimus species. Microscopic examination of sputum or feces may reveal the presence of Paragonimus eggs. Imaging techniques such as chest X-rays and CT scans are useful for detecting pulmonary abnormalities.

Treatment

Treatment for paragonimiasis involves the use of antiparasitic medications. Praziquantel is the drug of choice, effective in eliminating the adult flukes. In cases of extrapulmonary paragonimiasis, such as cerebral involvement, additional treatments including surgery may be necessary.

Prevention

Prevention of paragonimiasis focuses on avoiding the consumption of raw or undercooked freshwater crustaceans. Public health education and improved food safety practices are essential in endemic areas. Boiling, frying, or other thorough cooking methods can kill the metacercariae in contaminated crustaceans.

See Also

• Trematoda
• Paragonimiasis
• Praziquantel