Principles of Parasitology​-71

What is the global impact of malaria?

• fects >500 million people

• Causes 2.5 million deaths

What are the types of symbiotic relationships between organisms?

• Symbiosis (Ecto~ or Endo~)

• Commensalism

• Mutualism (Symbiosis sensu stricto)

• Parasitism – relationship where the parasite benefits at the expense of the host

What is a Final or Definitive Host?

Harbors the sexually mature parasite (= adult worm or sexual stage of protozoa)

What is an Intermediate Host?

Harbors the immature or asexual stage

What is a Reservoir Host?

An animal that harbors the same species of parasite as humans and thus is a potential source of the parasitic infection for humans (e.g., zoonotic infections)

What is a Vector in parasitology?

Usually, an arthropod that carries the parasite to its host

What is a Mechanical Vector?

A vector with no development of the parasite; also called a paratenic or transport host

What is a Biological Vector?

A vector in which some life cycle stages of the parasite occur

What are the three major types of parasitic organisms?

• Protozoa

• Helminths

• Arthropods

What type of organisms are protozoa?

Eukaryotes, unicellular (2–100 μm)

What type of organisms are helminths?

Multicellular (Metazoa; μm to m)

What type of organisms are arthropods?

Multicellular (Metazoa) with jointed feet

What are the major classes of protozoa?

• Amebae

• Ciliates (Ciliophora)

• Metamonada (Flagellates)

• Apicomplexa

What are the major classes of helminths?

• Nematodes (roundworms)

• Cestodes (tapeworms)

• Trematodes (flukes)

What are the life cycle forms of parasites?

• Infectious – e.g., cysts in protozoan infections, larvae or eggs in helminth infections

• Diagnostic – e.g., trophozoites in protozoan infections, eggs or worms in helminth infections

How do protozoa assimilate nutrients, and what is notable about their physiology?

• Nutrient uptake by:

  • Pinocytosis → digestive vacuoles

  • Phagocytosis → digestive vacuoles

  • Peristome and cytostome (in flagellates/ciliates)

  • Simple diffusion

• Many parasitic protozoa are facultative anaerobes

How do protozoa replicate and survive?

• Trophozoite: feeding stage of a protozoan parasite

• Cysts: used for survival and transmission

• No cysts → direct transmission or vector required

• Asexual reproduction:

  • Binary fission (merogony)

  • Multiple fission (schizogony)

• Sexual reproduction:

  • Gametogony and sporogony

• Immune evasion mechanisms for protection from the host

What are key features of helminth physiology and replication?

• Nutrient uptake by active ingestion or passive absorption

• Muscular motility requires considerable energy

• Metabolize carbohydrates, store glycogen

• Most helminths are oviparous (some viviparous)

• Often show high reproductive output (e.g., 200,000 eggs/day)

• Larvae differ morphologically from adults; undergo several developmental stages (molts)

• Protection from host via:

  • Cuticle or tegument

  • Secreted enzymes

  • Immune evasion mechanisms

What are the key features of nematodes?

• Multicellular; round, smooth, spindle-shaped

• Tubular alimentary tract; may have teeth or plates for attachment

• Separate sexes

• No single organelle; active muscular motility

• Adults usually anaerobic; larvae possibly aerobic

• Feed by ingestion or absorption of body fluids, tissue, or digestive contents

What are the key features of trematodes?

• Multicellular; leaf-shaped with oral and ventral suckers

• Blind alimentary tract

• Hermaphroditic (except Schistosoma group with separate sexes)

• No single organelle; muscle-directed motility

• Adults usually anaerobic

• Feed by ingestion or absorption of body fluids, tissue, or digestive contents

What are the key features of cestodes?

• Multicellular; head with segmented body (proglottids)

• Lack an alimentary tract

• Head equipped with hooks and/or suckers for attachment

• Hermaphroditic

• No single organelle; usually attach to mucosa; possible muscular motility in proglottids

• Adults usually anaerobic

• Absorb nutrients from the intestine

What are key physiological and reproductive features of arthropods?

• Among the largest groups in kingdom Animalia

• Segmented bodies, paired jointed appendages

• Well-developed digestive and nervous systems

• Separate sexes

• Possess a chitin exoskeleton