Page 140 - parasitology for medical and clinical laboratoryprofessionals

120 CHAPTER 5

INTRODUCTION The term helminths refers to worm-shaped organ-
isms and are commonly referred to in lay terms as worms
This chapter is intended to lay the groundwork for when one thinks of parasitic infections particularly of
specific presentations of species of each of these the gastrointestinal tract. There is a significant social im-
three morphological types of “worms.” The materials pact placed on entire countries and regions of the world
presented here basically discuss the history of major where these parasites are found. Ecological and environ-
helminths and measures intended to eradicate them. mental conditions that contribute to the increase of and
Some of these parasites that inhabit various body organs prevalence of the “worms” are discussed in general in
have been well-known for centuries if not longer, and this chapter. Some of these organisms have complex life
evidence of some of them exist in anthropological cycles that utilize a reservoir and a host in order to com-
findings. When the student becomes acquainted in a plete a life cycle and to infest other organisms. Some are
general fashion regarding these types of parasites, it even self-infective, where a human may serve in a man-
is easier to distinguish them as to general types during ner as dual roles of both reservoir and host. Helminths
further studies in subsequent chapters. Some specific consist of three basic groups: round worm (nematodes),
species are introduced in this chapter, but will be flat worm (cestode), and fluke (trematode) (Table 5-1).
covered in depth later for information related to signs These three groups are characterized by distinctive ana-
and symptoms, recovery of the organisms, and the tomic differences and will be discussed in general in this
identification of the various species. section.

TABLE 5-1 Classification of Helminths

PHYLUM CLASS ATTRIBUTES EXAMPLES OF SPECIES
Aschelminthes Nematoda Intestinal involvement of host Enterobius vermicularis
Ascaris lumbricoides
Trichuris trichiura (trichiura)
Ancylostoma duodenale
Necator americanus
Strongyloides stercoralis
Blood and tissues Trichinella spiralis
Wuchereria bancrofti
Dracunculus medinensis
Brugia sp.
Loa loa
Oncocerca volvulus
Mansonella sp.
Platyhelminthes Trematoda Fasciolopsis buski
Heterophyes heterophyes
Metagonimus yokogawai
Fasciola hepatica
Clonorchis sinensis
Paragonimus westermani
Schistosoma sp.
Cestoda Diphyllobothrium latum
Taenia sp.
Hymenolepsis sp.
Dipylidium caninum
Echinococcus sp.