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C H A P T E R 2 0 8

Classification and Nomenclature of Parasites Lynne S. Garcia

Although common names frequently are used to describe morphologic forms according to age, , or nutrition, parasitic organisms, these names may represent different which often results in several names being given to the parasites in different parts of the world. To eliminate same organism. An additional problem involves alterna- these problems, a binomial system of nomenclature in tion of parasitic and free-living phases in the life cycle. which the scientific name consists of the and These organisms may be very different and difficult to is used.1-3,8,12,14,17 These names generally are of recognize as belonging to the same species. Despite these Greek or Latin origin. In certain publications, the scien- difficulties, newer, more sophisticated molecular methods tific name often is followed by the name of the individual of grouping organisms often have confirmed taxonomic who originally named the parasite. The date of naming conclusions reached hundreds of years earlier by experi- also may be provided. If the name of the individual is in enced taxonomists. parentheses, it means that the person used a generic name As investigations continue in parasitic genetics, immu- no longer considered to be correct. nology, and biochemistry, the species designation will be On the basis of life histories and morphologic charac- defined more clearly. Originally, these species -designa teristics, systems of classification have been developed to tions were determined primarily by morphologic dif­ indicate the relationship among the various parasite ferences, resulting in a phenotypic approach. With the species. Closely related species are placed in the same use of highly sophisticated molecular techniques, the genus, related genera in the same family, related families approach will continue to be more genotypic. Benefits of in the same , related orders in the same , and these studies also include the development of highly related classes in the same , one of the major specific and sensitive diagnostic tests and the ability to categories in the . As one moves up the diagnose parasitic on the basis of molecular classification schema, each category becomes more parameters rather than merely phenotypic characteristics. broad; however, each category still has characteristics in Although gaps in our knowledge concerning classifica- common. tion of all human parasites remain, the binomial system Parasites of are classified in a number of has allowed the classification of 1.5 million species of major divisions. They include the (amebae, organisms in the animal kingdom such that all published , , sporozoans, and ), the Fungi information can be retrieved, regardless of the language (microsporidia), the Platyhelminthes or (ces- spoken. The difficulty for the clinician arises when one todes, trematodes), the Acanthocephala or thorny- considers the rapid increase in information concerning headed , the Nematoda or roundworms, and the during the past few years and changing Arthropoda (, spiders, mites, ticks, and so on). considerations, such as the role of immunosuppression in Although these categories appear to be well defined, the host-parasite interaction and the modified definitions often considerable confusion occurs in attempting to of “normal flora” and “nonpathogenic” in this population classify parasitic organisms. One of the primary reasons of patients. is the lack of known specimens. Some organisms recov- The classification of parasites is presented in tabular ered from humans are very rare; thus, difficulty arises form. Although certain designations of species may be in determining morphologic and physiologic variation somewhat controversial, this classification scheme is among such groups. Type specimens must be deposited designed to provide some order and meaning to a widely for study before a legitimate species name can be given. divergent group of organisms. No attempt has been made Even when certain parasites are numerous, they may rep- to include every possible organism, and only those con- resent strains or races of the same species with slightly sidered clinically relevant in the context of human para- different characteristics. sitology are listed. The main groups that are presented In general, reproductive mechanisms are a valid include protozoa, fungi, (roundworms), ces- concept in determining definitions of species, but so todes (tapeworms), and trematodes (flukes). Some rele- many exceptions exist within parasite groups that taking vant information on is presented in Tables into consideration properties such as sexual reproduc- 208-1 and 208-2. The hope is that this information will tion, parthenogenesis, and asexual is diffi- provide some insight into the parasite groupings, thus cult. Another difficulty in recognition of species is the leading to a better understanding of parasitic infections ability and tendency of the organisms to alter their and the appropriate diagnostic and clinical approach. 2861 2862 SECTION XXII Parasitic Diseases

TABLE 208-1 Human -Borne Infections

Infection (Disease) Causative Agent Vector (Common Name) Protozoal spp. Mosquitoes spp. Sandflies cruzi Triatomid bugs East African rhodesiense Tsetse West Trypanosoma brucei gambiense Tsetse flies spp. Ticks

Helminthic Mosquitoes Filariasis malayi Mosquitoes Filariasis spp. Mosquitoes Filariasis perstans Biting midges Filariasis Biting midges Filariasis Biting midges volvulus Black flies Loiasis Deer flies tapeworm Dipylidium caninum Dog lice and fleas, human fleas Rat tapeworm infection diminuta Rat fleas, beetles, grain beetles Dwarf tapeworm Grain beetles (rare)

PROTOZOA moshkovskii Amebae—Intestinal Endolimax nana Iodamoeba bütschlii These organisms are characterized by having pseudopods hominis* (motility) and and stages in the life cycle and include some exceptions in which a cyst form has not Flagellates—Intestinal been identified. Amebae usually are acquired by humans through fecal-oral or mouth-to-mouth These organisms move by means of flagella and are contact (Entamoeba gingivalis). acquired by fecal-oral transmission. With the exception of (internal flagella) and those in the Current Name genera and Pentatrichomonas, they have the trophozoite and cyst stages in the life cycle. D. fragilis, * Trichomonas, and Pentatrichomonas species do not have a Entamoeba dispar* cyst stage. Entamoeba hartmanni† Entamoeba coli Current Name Entamoeba polecki lamblia† mesnili *Entamoeba histolytica is being used to designate the true , Dientamoeba fragilis whereas Entamoeba dispar now is being used to designate a nonpatho- Pentatrichomonas hominis gen. Unless containing ingested red cells (E. his- Trichomonas tenax tolytica) are seen during microscopic examination, the two organisms cannot be differentiated on the basis of morphologic features seen in permanent stained smears of fecal specimens and will be reported as E. histolytica/E. dispar. Fecal immunoassays for detection are *The taxonomic position of Blastocystis has always been somewhat con- available commercially for differentiation of E. histolytica from E. fusing, but it is now clear that this organism exists as a number of dispar and for detection of the E. histolytica/E. dispar group.7 Because serotypes or species. It has been recommended that all isolates from the differences in pathogenicity are genetic and not just phenotypic, and , including humans, be designated in the future the decision to treat is one that must be determined by the physician. as Blastocystis spp., serotypes ST1 to ST10 plus ST Unknown. This The finding of organisms in the E. histolytica/E. dispar group in organism has now been placed in the Stramenopila.21 patient specimens must continue to be reported to state and county †Although some individuals have changed the species designation for Departments of (follow your particular state reporting the genus Giardia to G. duodenalis or G. intestinalis, no consensus regulations). exists. Therefore, for this listing, the name Giardia lamblia is retained. †Entamoeba hartmanni is nonpathogenic and is totally different from E. However, molecular and epidemiologic evidence suggests that at least histolytica. “Small race E. histolytica” is incorrect and should not be two assemblages of Giardia infect humans, one of which is Giardia used at any time to designate E. hartmanni. duodenalis and the other, possibly a new species, Giardia enterica.16 208 Classification and Nomenclature of Human Parasites 2863

TABLE 208-2 Medically Important Arthropods Current Name

Local or Systemic Coccidia Problems Vector (Common Name) hominis reaction to bites Sucking lice Cryptosporidium spp. Bedbugs 18,19 Kissing bugs cayetanensis Biting midges () belli Sandflies hominis Black flies Sarcocystis suihominis Mosquitoes Sarcocystis bovihominis Deer flies Tsetse flies Soft ticks Fungi (Microsporidia*)—Intestinal Hard ticks Enterocytozoon bieneusi Painful bite Horseflies † Fire ants Encephalitozoon (Septata) intestinalis Centipedes Intense itching Human mites Amebae, Flagellates—Other Body Sites Chiggers Painful sting, potential Honeybees The amebae are pathogenic, free-living organisms that anaphylaxis Bumblebees may be associated with warm, freshwater areas. They Wasps, hornets, yellow have been found in the central nervous system, the eye, jackets and other sites. usually is acquired Fire ants by sexual transmission. This particular is found Scorpions in the genitourinary system. , ulcerations Fleas Nodular ulceration with Chigoe flea Current Name subsequent secondary infection Amebae Blistering of skin after Blister beetles fowleri contact with adult beetles spp. Bite, usually painless, Black widow spiders delayed systemic Hartmannella spp. reaction Initial blister followed by Brown recluse spiders diploidea extensive and South American brown Flagellates slow healing spider Trichomonas vaginalis

Apicomplexa, Sporozoa (Coccidia)— Other Body Sites Enteromonas hominis The coccidia are particularly important in the compro- intestinalis mised patient. They also may infect many individuals who have no apparent symptoms.6,7 On the basis of Ciliates—Intestinal molecular studies, the microsporidia are linked more closely to the fungi and have been reclassified with those These organisms, which move by means of cilia, are organisms. However, during this transition phase, the acquired by humans through fecal-oral transmission. listing will remain with the parasites. They have both the trophozoite and cyst forms in the life cycle. Current Name

Current Name Coccidia coli , Sporozoa *The microsporidia are now thought to be more closely related to fungi (Coccidia)—Intestinal than to protozoa; however, parasitologists have been reluctant to part with this group, whereas mycologists have been equally reluctant to These organisms are acquired by humans by of accept it. Consequently, the microsporidia will be retained within this various or through fecal-oral transmission through list for parasites, although they are classified within the Fungi.11,22,23 contaminated or water. †Formerly called Septata intestinalis.10,15 2864 SECTION XXII Parasitic Diseases

Fungi (Pneumocystis,* Microsporidia)— Babesiosis* Other Body Sites Babesia divergens Microsporidia Babesia duncani Nosema ocularum Babesia spp. Anncaliia (Brachiola) connori Flagellates (leishmaniasis, trypanosomiasis) Anncaliia (Brachiola) algerae Leishmaniasis Anncaliia (Brachiola) vesicularum complex (cutaneous Vittaforma corneae leishmaniasis) Pleistophora ronneafiei complex (cutaneous Trachipleistophora hominis leishmaniasis) Trachipleistophora anthropophthera complex (cutaneous Encephalitozoon hellem leishmaniasis) Encephalitozoon cuniculi complex (cutaneous Encephalitozoon (Septata) intestinalis† leishmaniasis) Enterocytozoon bieneusi ‡ complex (mucocutaneous Microsporidium africanum§ leishmaniasis) Microsporidium ceylonensis complex (visceral Tubulinosema acridophagus ¶ leishmaniasis) Leishmania infantum/Leishmania chagasi group () Sporozoa, Flagellates—Blood Trypanosomiasis and Tissues Trypanosoma brucei gambiense (West African trypanosomiasis) All of these organisms are borne. Diagnosis Trypanosoma brucei rhodesiense (East African may be somewhat more difficult to make than is that of trypanosomiasis) the intestinal protozoa, particularly if automated blood (American trypanosomiasis) differential systems are used. The Leishmania have under- Trypanosoma rangeli gone extensive revisions in classification. However, from a clinical perspective, recovery and identification of the organisms still are related to body site. Recovery of the NEMATODES organisms is limited to the site of the lesion in infections other than those caused by the Leishmania donovani Nematodes—Intestinal complex (visceral leishmaniasis). These organisms normally are acquired by ingestion of Current Name or penetration of the skin by larval forms from the . Apicomplexa, Sporozoa (malaria, babesiosis) Malaria Current Name lumbricoides Enterobius vermicularis () duodenale ** americanus stercoralis Strongyloides fuelleborni spp. trichiura (whipworm) *Pneumocystis carinii has been reclassified with the fungi and renamed philippinensis 5,20 Pneumocystis jiroveci. Consequently, it will be removed from future Oesophagostomum spp. (O. bifurcum most common in parasite listings. †Formerly called Septata intestinalis. humans—West ) ‡Enterocytozoon bieneusi has been recovered from sites other than the Ternidens diminutus (as high as 80% in ) intestinal tract. §This designation is now written as a true genus but remains a “catch- all” for those organisms that have not been (or may never be) identi- Nematodes— fied to the true genus or species levels. ¶New human pathogen, disseminated infection in a patient with mul- For the most part, these organisms rarely are seen within tiple myeloma (severely immunosuppressed, allogeneic stem cell the ; however, the first three are more transplant recipient).13 important. **Plasmodium knowlesi, a malaria parasite of macaque monkeys in South- east that is now established as a naturally transmitted parasite of humans in and other parts of , has been responsible for a number of .4 Thus, there are now five species *Molecular studies confirm that humans can also harbor a number of of malaria that infect humans. Babesia parasites that have not yet been identified.9 208 Classification and Nomenclature of Human Parasites 2865

Current Name transmitted through ingestion (life cycle in the human can bypass the intermediate beetle host). Humans spiralis can serve as both the intermediate and definitive hosts in Trichinella spp. H. nana and solium infections. or (visceral or ocular migrans) Current Name () (eosinophilic enteritis) latum (broad, tapeworm) procyonis (severe systemic visceral larva Dipylidium caninum (dog tapeworm) migrans, neural larva migrans) Hymenolepis (Rodentolepis) nana (dwarf tapeworm) medinensis (rat tapeworm) cantonensis ( tapeworm) Angiostrongylus costaricensis (beef tapeworm) spinigerum (Taiwanese variant of T. saginata) Gnathostoma spp. Anisakiasis (larvae from saltwater fish) Cestodes (Larval Forms)—Tissue spp. Phocanema spp. The ingestion of certain tapeworm eggs or accidental Contracaecum spp. contact with certain larval forms can lead to the diseases Pseudoterranova spp. shown in parentheses. Hysterothylacium spp. Porrocaecum spp. Current Name spp. Taenia solium () (hydatid disease) Echinococcus multilocularis (alveolar hydatid disease) Nematodes (Filarial Worms)—Blood, Echinococcus oligarthrus (polycystic hydatid disease) Other Body Fluids, Skin Multiceps multiceps (coenurosis) Diphyllobothrium spp. () These organisms also are arthropod borne. The adult mansonoides (sparganosis) worms tend to live in the tissues of lymphatics. Diagnosis is made on the basis of the recovery and identification of the larval worms (microfilariae) in the blood, other body TREMATODES fluids, or skin. Elephantiasis may be associated with some of the organisms listed. Trematodes—Intestinal

Current Name These organisms are uncommon within the United States, except for four species of Alaria, which are endemic Wuchereria bancrofti within North America. Current Name Loa loa buski (giant intestinal fluke) Mansonella ozzardi Echinostoma ilocanum Mansonella streptocerca Eurytrema pancreaticum heterophyes Dirofilaria immitis (“coin” lesion in the ) (dog yokogawai heartworm) Alaria spp. Dirofilaria spp. (may be found in subcutaneous nodules) Trematodes—, Lung CESTODES These organisms are not seen commonly within the United States; however, some Southeast Asian refugees Cestodes—Intestinal do harbor some of these parasites.

The adult form of these organisms is acquired by humans Current Name through ingestion of the larval forms contained in poorly cooked or raw meats or freshwater fish. In the case of Clonorchis () sinensis (Chinese ) Dipylidium caninum, infection is acquired by the acciden- tal ingestion of dog fleas. Both Hymenolepis nana and Hymenolepis diminuta are transmitted by ingestion of hepatica ( liver fluke) certain arthropods (fleas, beetles). Also, H. nana can be westermani (lung fluke) (lung fluke endemic in the United NEW REFERENCES SINCE THE SIXTH EDITION States) 3. Cox FEG. and classification of human parasitic protozoa Paragonimus spp. and helminths. In: Versalovic J, Carroll KC, Funke G, et al, editors. Metorchis conjunctus (North American liver fluke) Manual of clinical microbiology. Section VIII. . 10th ed. Washington, DC: ASM Press; 2011. p. 2041–6. 4. Cox-Singh J, Singh B. Knowlesi malaria. newly emergent and of Trematodes—Blood public health importance? Trends Parasitol 2008;24:406–10. 9. Gray JS, Weiss LM. Babesia microti. In: Khan NA, editor. Emerg- The schistosomes are acquired by penetration of the skin ing protozoan . New York: Taylor and Francis; 2008. by the cercarial forms that are released from freshwater p. 303–49. 11. Hirt RP, Logsdon JM, Healey B, et al. Microsporidia are related to . Although they are not endemic within the United fungi. evidence from the largest subunit of RNA polymerase II and States, occasionally patients are seen who may have these other proteins. Proc Natl Acad Sci U S A 1999;96:580–5. infections. 13. Meissner EG, Bennett JE, Qvarnstron Y, et al. Disseminated in an immunosuppressed patient. Emerg Infect Dis 2012;18:1155–8. Current Name 16. Monis PT, Caccio SM, Thompson RCA. Variation in Giardia. towards a taxonomic revision of the genus. Trends Parasitol 2009; mansoni 25:93–100. 21. Tan KS. New insights on classification, identification and clinical relevance of Blastocystis spp. Clin Microbiol Rev 2008;21:639–65. 22. Webster J, Weber RWS. Introduction to fungi. 3rd ed. Cambridge, UK: Cambridge University Press; 2007.

ARTHROPODS The full reference list for this chapter is available at See Tables 208-1 and 208-2. expertconsult.com. 208 Classification and Nomenclature of Human Parasites 2866.e1

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