North American paragonimiasis (Caused by Paragonimus kellicotti) in the context of global paragonimiasis

Abstract

Paragonimus species are highly evolved parasites with a complex life cycle that involves at least three different hosts, i.e., snails, crustaceans, and mammals. The adult forms of Paragonimus species reside and mate in the lungs of a variety of permissive mammalian hosts, including humans. Although human paragonimiasis is uncommonly encountered in North America, both autochthonous and imported disease may be encountered. Paragonimus kellicotti, the species endemic to North America, is a well-known pathogen in wild and domestic animals. Five patients with North American paragonimiasis have been reported in the recent medical literature. The biologic, clinical, radiologic, and laboratory features of paragonimiasis are reviewed, with emphasis on North American paragonimiasis whenever possible.

FIG. 1.

Life cycle of Paragonimus. The paired adult flukes (not shown) that are present in the definitive mammalian host (e.g., the dog and cat) sexually reproduce and produce eggs (12 o'clock). Proceeding clockwise, the operculate egg, which is released into the respiratory tract, is eventually passed into the environment. A ciliated miracidium is released from each egg in freshwater. The miracidium infects a permissive snail species. After asexual reproduction within the snail, infective cercariae are released. These infect a crustacean host, such as the crab or crayfish represented here. The crustacean may also become infected if it eats an infected snail. The ingestion of the infected crab or crayfish by a permissive definitive host culminates in egg production from sexually competent adults, thereby completing the cycle. (Reprinted with the permission of The Cleveland Clinic Center for Medical Art & Photography © 2008. All rights reserved.)

FIG. 2.

Several eggs the brain of a patient with cerebral paragonimiasis caused by P. mexicanus. Eggs in histologic sections are often distorted by the granulomatous response, as demonstrated here. Hematoxylin and eosin staining was used. Magnification, ×400.

FIG. 3.

Chest roentgenogram of a patient with North American paragonimiasis. The roentgenogram demonstrates bilateral pleural effusions and an infiltrate in the lower lobe of the left lung (arrow). (Reprinted from reference with permission of the publisher.)

FIG. 4.

CT scan of a patient with North American paragonimiasis. This patient with North American paragonimiasis has bilateral pleural effusions and thickening of the left pleura with possible cystic change (arrow). (Reprinted from reference with permission of the publisher.)

FIG. 5.

Plain skull film of a patient with chronic cerebral paragonimiasis. A type IV lesion, which is thought to resemble “soap bubbles,” is demonstrated (arrow). (Reprinted from reference with kind permission of Springer Science and Business Media.)

FIG. 6.

Clustered parasitic cysts/elements (arrow) are well-delineated in this CT scan of a patient with cerebral paragonimiasis. (Reprinted from reference with kind permission of Springer Science and Business Media.)

FIG. 7.

The excised pleura from a patient with North American paragonimiasis demonstrates mesothelial hyperplasia (arrowhead), an acute and chronic inflammatory cell infiltrate with eosinophils, and eggs of P. kellicotti that are entrapped in nonnecrotizing granulomas that are beginning to be surrounded by concentric fibrosis (arrows). Hematoxylin and eosin staining was used. Magnification, ×40.

FIG. 8.

A distorted, fractured egg of Paragonimus kellicotti, which has been phagocytosed by a giant cell, was one among many seen in the fibrotic, inflamed pleural tissue (also see Fig. 7). Hematoxylin and eosin staining was used. Magnification, ×400.

FIG. 9.

The eggs of Paragonimus are birefringent when exposed to plane-polarized light. This is the same microscopic field as shown in Fig. 8. Hematoxylin and eosin staining and plane-polarized light exposure were used. Magnification, ×400.

FIG. 10.

The operculate egg of P. kellicotti may be discovered only in the cytologic preparation, as was the case with this patient. Note the excellent preservation of the egg morphology. Egg size, 83 by 58 μm. Papanicolaou staining and oil immersion were used. Magnification, ×500.

FIG. 11.

An egg of Paragonimus westermani in a fecal specimen. This egg is broadest nearer to the opercular end of the egg (upper right aspect of image) and has an abopercular thickening of the eggshell, which are features not prominent in P. kellicotti. Iodine preparation was used. Magnification, ×400. (Courtesy of Lynne Garcia, reproduced with permission.)

FIG. 12.

An eosinophilic abscess (arrows), granulomatous inflammation, and fibrosis replace the pulmonary parenchyma in this patient with North American paragonimiasis. Hematoxylin and eosin staining was used. Magnification, ×40.

FIG. 13.

Calcification and fibrosis are common histologic finding in patients with chronic cerebral paragonimiasis. This infection was caused by P. mexicanus. Hematoxylin and eosin staining was used. Magnification, ×40.