Endemic Paragonimus kellicotti infections in animals and humans in USA and Canada: Review and personal perspective

Authors: Dubey, Jitender

Submitted to: Food and Waterborne Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2022
Publication Date: 12/9/2022
Citation: Dubey, J.P. 2022. Endemic Paragonimus kellicotti infections in animals and humans in USA and Canada: Review and personal perspective. Food and Waterborne Parasitology. https://doi.org/10.1016/j.fawpar.2022.e00184.
DOI: https://doi.org/10.1016/j.fawpar.2022.e00184

Interpretive Summary: Food safety is a worldwide concern, especially infections transmitted from animals to humans (zoonosis). Among the zoonotic parasites, worms such as the pork worm (Trichinella) is transmitted to humans by eating undercooked infected pork. Paragonimus (called the lung fluke) is transmitted to humans by eating uncooked crustaceans and this parasite can cause serious consequences to humans. Paragonimus kellicotti is a fluke parasite of domestic and wild animals endemic in the united States. It can cause respiratory distress and even death. Although the parasite has been known for more than a century, recently there has been an upsurge of human infections in the US. This infection is acquired by humans, dogs, cats, and wildlife by eating uncooked crayfish infected with P. kellicotti encysted microscopic stage (called metacercaria). To better understand the disease paragonimiasis in humans, the author reviews the literature, especially experimental studies including development of new therapies in parasite free cats and dogs performed in 1975-1979, before the author joined ARS. This paper will be useful to veterinarians, physicians, parasitologists, and environmentalists.

Technical Abstract: Infections with the lung fluke, Paragonimus kellicotti, have been diagnosed in a variety of domestic and wild animals and humans in USA and Canada. Although there are several species of Paragonimus in other parts of the world; P. kellicotti is the only species definitively diagnosed in USA and Canada. Fresh water snails (several species) and crayfish (mainly Orconectes spp.) are its intermediate hosts. Humans and animals become infected with P. kellicotti by ingesting metacercaria encysted in the heart of crayfish. After ingestion, the fluke penetrates intestinal wall, enters peritoneal cavity, and reaches pleural cavity by direct penetration of diaphragm, 2-3 weeks post inoculation (p.i.). Young flukes penetrate lungs and become encysted in pulmonary nodules, often in pairs. Time to maturity is around 4-7 weeks p.i. Eggs are coughed up, swallowed, and are excreted in feces. Although the parasite has been known for more than a century, there has been an upsurge of human infections in the USA. Here, I review P. kellicotti infections in naturally infected hosts. Pathogenesis, diagnosis, and treatment in parasite-free cats and dogs experimentally infected P. kellicotti are reviewed to shed light on the pathogenesis of human paragonimiasis. Problems and challenges facing diagnosis of paragonimiasis, especially non-pulmonary infections, are discussed. Fluke stages are deposited in Smithsonian Museum.