Category Archives: Practical Veterinarian


Endoparasites are those parasites that live within the body of the host. There are four major groups of endoparasites — nematodes, acanthocephalans, platyhelminths (trematodes and cestodes), and protozoans. Table Characteristics of the Major Helminth Groups provides distinguishing characteristics of the helminthic parasites. Table Characteristics of the Major Helminth Groups Characteristic Phylum Nemathelminthes Acanthocephala Platyhelminthes Cestodes… Read More »


Appearance and Morphology • Variable length, 1 mm to several meters. • Body covered with cuticle, may form specialized structures (e.g., alae). • Usually sexually dimorphic with males smaller than females. Classification Nematodes are divided among two classes: the Secernentea and the Adenophorea. The Adenophorea contains the whipworms, capillarids, and Trichinella spiralis, while the Secernentea… Read More »


Appearance and Morphology • Body divided into scolex, neck, strobila. • Scolex may contain holdfast organs in the form of suckers or slits and/or rostellum armed with hooks. • Neck is the germinal region from which the strobila arises. • Strobila is the rest of the body; composed of proglottids each of which contains one… Read More »


There are two types of trematodes — digenes and mono-genes. Monogenetic trematodes have direct life cycles and are primarily ectoparasites of aquatic vertebrates. Digenetic trematodes have indirect life cycles and are endoparasites of a wide variety of vertebrates. Unless the veterinarian is involved in fish farming or treating aquarium fish, monogenetic trematodes are not encountered… Read More »

Parasites of the Skin, Subcutaneous and Connective Tissue

Nematodes ACANTHOCHEILONEMA RECONDITUM • Distributed in areas of Europe, Africa, and North America in canids; low significance except for need to differentiate from microfilariae of D. immitis. Life Cycle • Indirect. • Intermediate host: fleas (Ctenocephalids felis, C. canis, Pulex irritans); also, ticks (Rhipicephalus sanguineus) and lice (Heterodoxus spiniger). • Adults produce microfilariae (mff) that… Read More »

Parasites of the Musculoskeletal System

Nematodes TRICHINELLA SPIRAUS • Worldwide distribution in a variety of mammals including pigs and humans; moderate significance to veterinary medicine but may be highly significant to public health. Life Cycle • Direct. • Unique in that the adult and infective larvae occur within the same host with no intervening free-living stage. • Adults live in… Read More »

Parasites of the Liver

Trematodes FASCIOLA HEPATICA • Worldwide distribution in ruminants, pigs, and horses; occasionally in humans; distribution in North America centers on the Gulf Coast/southeastern states, Pacific Northwest (including Montana), and eastern Canada; highly significant to veterinary medicine; low significance to public health. • Common name: liver fluke. Life Cycle • Indirect. • Intermediate host: lymnaeid snails;… Read More »

Parasites of the Urogenital System

Nematodes STEPHANURUS DENTATUS • Distributed in domestic and wild pigs in tropical and subtropical regions; locally significant in pigs raised in outdoor situations. • Common name: kidney worm. Life Cycle • Direct; indirect with paratenic host. • Eggs passed in urine; L1 develops and hatches; infective L3 develops in approximately 4 days; paratenic host becomes… Read More »


Ectoparasites, most of which are arthropods, are those parasites that live on the body of the host. Some spend their entire life on the host, others spend only parts of their life on the host, while still others only occasionally visit the host. The ectoparasites most veterinarians deal with direcdy are those that live all… Read More »

Myiasis-Producing Flies

(Insecta) The larvae of certain dipterans are capable of developing in the tissues of many domestic animals. This results in a condition called myiasis. There are two types of myiases: (1) facultative myiasis — larvae are free-living, but can become parasitic under certain conditions; and (2) obligatory myiasis — larvae are always parasitic, i.e., without… Read More »