Paragonimiasis, also known as oriental lung fluke infection is one of the most important food-borne parasitic zoonoses caused by one or more of the trematode species of the genus Paragonimus. The disease is endemic in many parts of Asia, Africa and South America. Among 11 species known to cause infections in humans, P. westermani has been regarded as the most common and widely distributed human pathogen in Asia. In South and Southeast Asia, P. heterotremus has also been increasingly detected as an important cause of infection in humans.
The natural definitive hosts of the parasite comprise large varieties of wild mammals of the canidae and felidae families and humans. A wide range of fresh water snails serve as first intermediate hosts, and crabs as well as crayfish serve as second intermediate hosts. Humans acquire infection commonly by ingestion of uncooked or undercooked crustaceans containing metacercariae, the larval stage of the parasite. Rarely, infections are acquired through ingestion of infected uncooked or undercooked meat of pig and wild boar, which serve as paratenic hosts.
The incubation period may vary from 1 to 2 months or even longer. The parasites primarily infect lungs, but extra-pulmonary infections are not uncommon. Pulmonary paragonimiasis is the commonest clinical form of paragonimiasis. Major presenting symptoms comprised pain or tightness in the chest, difficult breathing, and coughing up rusty brown or blood-stained sputum (hemoptysis). Pulmonary paragonimiasis presenting with bloody sputum or recurrent hemoptysis was generally mistaken for sputum smear negative pulmonary tuberculosis or some other serious conditions with similar symptoms. Extra pulmonary paragonimiasis is due to aberrant migrations of juvenile worms, which deviate from the normal route of migration to the lungs through the intestine, abdominal cavity, diaphragm and pleural cavity. It is likely to occur more commonly in children and in heavy infections. Paragonimiasis is dignosed in the laboratory by microscopic demonstration of Paragonimus eggs in the sputum and other clinical specimens such as faeces and pleural fluid. Diagnosis can also be made by enzyme-linked immunoabsorbent assay (ELISA) assays specific to Paragonimus. Praziquantel is the drug of choice for both pulmonary and extra pulmonary paragonimiasis.
The control strategies for paragonimiasis should include the epidemiological surveys to determine the magnitude of the problem, training of public health care providers about the diagnosis and management of paragonimiasis, screening of all patients attending TB clinics, DOTS microscopy centers, hospitals and rural health centers for both tuberculosis and paragonimiasis. People should be educated not to consume fresh and improperly cooked crabs and crayfish, and to clean hands, utensils, cutlery boards, strainers, knives after processing fresh crabs and crayfish. Public health authority should also ensure the continuous supply of praziquantel in the hospitals and dispensaries.
References:
Chai JY. Paragonimiasis. Handb Clin Neurol. 2013;114:283-96.
Kalhan S, Sharma P, Sharma S, Kakria N, Dudani S, Gupta A. Paragonimus westermani infection in lung: A confounding diagnostic entity. Lung India. 2015;32(3):265-7.
Singh TS, Sugiyama H, Rangsiruji A. Paragonimus & paragonimiasis in India. Indian J Med Res. 2012;136(2):192-204.
