Paragonimus westermani: Third Time's a Charm


In creating the taxonomy of Paragonimus westermani, a morphological approach is almost always taken. However, classification can be pretty tricky business, as the fluke is not only closely related to other Paragonimus spp., but there is also much variation within the P. westermani species itself. Nonetheless, size and shape of the organism are distinctions often made at the adult, metacercariae, and egg stages. In addition, the quality and presence or absence of features typical of a certain point in the life cycle (such as the size of the ventral sucker in the adult stage, the presence of an inner cyst wall at the metacercariae stage, etc.) are taken into consideration (Sugiyama 2013).
That being said, the taxonomic classification for the human lung fluke is as follows:

Domain: Eukarya
Kingdom: Animalia
Phylum: Platyhelminthes
Class: Trematoda
 Subclass: Digenea
Superorder: Epitheliocystidia
Family: Troglotrematidae
Genus: Paragonimus
Species: Paragonimus westermani

Domain: Eukarya
Paragonimus westermani fits into the Eukarya domain, first and foremost, because it possesses the membrane-bound organelles that are lacking in the other (Bacteria and Archaea) domains. Other characteristics that place the fluke here include lacking peptidoglycan in its cell walls, possessing introns in its genes, and lacking circular chromosomes (Campbell et al. 2008). All of your stereotypical, macroscopic organisms fall into this category, as do many microscopic critters (like the human lung fluke). Accordingly, all plants (ex. the Christmas cactus, Schlumbergera bridgesii), fungi (ex. the cow patty mushroom, Psilocybe cubensis), and animals are included here.

Kingdom: Animalia
The multicellular eukaryotes of the Eukarya domain are split into three kingdoms primarily by how they acquire nutrients. As the P. westermani first ingests and then digests its food, it belongs to the Animalia kingdom (Campbell et all. 2008). Organisms included in this kingdom are your everydayMonarch butterfly; Photo by Gene Wilburn, Retrieved from: animals, such as horses, cats, cows (Bos taurus), buffalo, etc. As everyone is most likely aware, though, animals within this taxonomic level can get pretty interesting, as they display a wide variety of characteristics. An example of this would be comparing the monarch butterfly (Danaus plexippus) to the manatee (Trichechus manatus).

Phylum: Platyhelminthes
As a member of the Platyhelminthes phylum, P. westermani is a dorso-ventrally flattened worm that’s bilaterally Aquatic flatworm; Photo by Richard Ling, Retrieved from: It lacks a body cavity and true anus, as well as skeletal, circulatory, and respiratory systems. Between the tegument, which serves as this organism’s body wall, and the internal organs exists parenchyma (various types of cells and the fluid between them).  However, as is characteristic of all Platyhelminthes, the lung fluke does possess a nervous system (Cheng 1964). The tiger flatworm (Maritigrella crozieri) is just one of the many cool-looking organisms within this phylum, but probably more familiar is the tapeworm. The term 'tapeworm,' however, is just a general term for a variety of species, including Taenia solium Dipylidium caninum, and T. saginata.


Class: Trematoda/ Subclass: Digenea
One of the three classes within the Platyhelminthes, Trematoda, contains all parasitic organisms. One of these is obviously P. westermani, and another is, ironically enough, the trematode fluke, or Echinostoma revolutum. Because it involves two or more hosts in its lifecycle as well as has two pronounced suckers on its body, the lung fluke then belongs to the Digenea subclass. This subclass is also where Paragonimus westermani obtains its trait of hermaphroditism (Chen 1964; Noble and Noble 1976).

Superorder: Epitheliocystidia/ Order: Plagiorchiida
The P. westermani fits into the Epitheliocystidia superorder because it possesses the characteristic, single flagellate tail during its cercaria stage. A thick-walled bladder is also a deciding feature in placing the fluke in this order (Noble and Noble 1976). One of the many organisms that share these traits and order with the human lung fluke is the lancet liver fluke (Dicrocoelium dendriticum).

Ruler highlighting metric units; Retrieved from:
Family: Troglotrematidae
Significant characteristics that place an organism within the Troglotrematidae family include extremely small size (less than 10 mm), an ovular shape, and a habitat within the organs of various birds and/or mammals. As P. westermani meets all of these criteria, it is decidedly in this family (Noble and Noble 1976).

Genus: Paragonimus
When it comes to determining which organisms fall within the Paragonimus genus, much molecular sequencing comes into play. Extensive, repeated analyses in both the nuclear and mitochondrial areas is performed. Displaying the mandated sequencing, P. westermani fits into this genus (Sugiyama et al. 2013).

Species: Paragonimus westermani
In English, Paragonimus comes from the roots "para" meaning "beside" and "gonimus" meaning "gonads." However, the name P. westermani specifically was derived from the name of zookeeper, C.F. Westerman because this species was first discovered in the necropsy of one of Westerman's Bengal tigers that died from the infection of this fluke. When it comes to identifying this species, once again size and shape of the adult organism are taken into consideration, as are the placement and appearance of its reproductive strucures and cuticular spines. Because earlier stages in development within these parasites vary so greatly, these stages are not often considered in the identification process (Procop 2009).

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P. westermani cladogram

Figure 1. A cladogram of P. westermani shows the relations that this parasite has at a rather distant level. Sources:,

Phylogenetic tree including species within the Paragonimus genus; Credited to:

Figure 2. Phylogenetic tree of Paragonimus spp. inhabiting the Asian continent created by comparing ribosomal DNA sequences of the infecting metacercariae stage of the fluke using the Neighbor Joining method (Prasad et al. 2009). The study leading up to and the ,creation of this tree is credited to: P. K. Prasad, V. Tandon, D.K. Biswal, L.M. Goswami, and A. Chatterjee of BMC Genomics.

Aside from the different lineages of Paragonimus westermani, this tree indicates that our lung fluke of interest is not more closely related to any one Paragonimus spp. than it is to another.


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