Protozoans Pt 2

ANS 389C

phylum Euglenozoa

• flagella

  • may have 1 or more

• reproduces by binary fission

• cyst formation may occur in some species

  • dormant, tough outer wall to protect self in harsh conditions

Family Trypanosomatidae

• blood and tissue dwelling parasites

• all have arthropod vectors

  • tsetse fly

    • most African species transmission

Trypanosomiasis

• “sleeping sickness”

• globally significant disease in humans and animals

Family Giardiidae

• affects wild and domestic animals including humans

  • zoonotic

• common cause of chronic diarrhea in humans

structure of Giardia

• bilaterally symmetrical organism

• flagella

  • 8 flagella

  • 6 are free and extend from different parts of body

• large adhesive disc on ventral surface of body

Giardia Trophozoite morphology

• shape: pyriform to ellipsoid, bilaterally symmetrical

• dorsal side is convex

Giardia Trophozoite internal structures

• 2 median bodies

  • dark-staining, curved like hammer claws

  • also called Parabasal body

giardia when in cyst form

• ovoid

• 4 nuclei

• about same size as Trophozoite

giardia life cycle

• direct life cycle

• deposits cysts into environment in feces

• consists of 2 main stages

  • cyst stage

  • trophozoite stage

Giardia life cycle contd.

• cysts are deposited via feces into environment

• following ingestion of cyst by animal, the cyst ruptures in intestines to release trophozoite

• trophozoite adheres to intestine mucosal surface

trophozoites may replicate in 2 ways:

• binary fission - divides into more trophozoites

• encyst - trophozoite will encyst until release trophozoite at later time

family Trichomonadidae

• called “Trichomonads”

• found in cecum and colon of:

  • mammals, birds, reptiles, amphibians, fish, invertebrates

• reproductive disease in bulls called “Trichomoniasis”

  • Tritrichomonas foetus

family Babesiddae

• called “Piroplasms”

• found primarily in erythrocytes

• heteroxenous — tick vectors

disease caused by family Babesiidae

• cause disease called Babesiosis

  • spread by ticks

• severe in naive animals

• major constraint on livestock development

family Babesiidae life cycle

• infective sporozoites present in tick is injected into host via saliva of tick

• multiplication in host erythrocyte

major families of importance in order Eucoccidiorida

• Family Eimeria

• Family Isospora

order Eucoccidiorida life cycle (can be divided into 3 phases)

• sporulation

• infection and merogony (Schizogony)

• gametogony and oocyst formation

sporulation

the process by which certain protozoan parasites, develop from a non-infective oocyst (unsporulated oocyst), into an infective form (sporulated oocyst) containing sporozoites

process of sporulation

• unsporulated oocysts are passed in feces

  • they are NOT infective

  • contain a nucleated mass of protoplasm inside a resistant wall

• unsporulated oocyst will undergo a process of division and development called sporulation

• results in an infective sporulated oocyst

  • after 2-4 days

  • this is the final, ineffective stage

  • capable of causing infection

infection and merogony (asexual reproduction)

• upon ingestion by the host, the sporozoites are released from the sporulated oocyst

• in most species, each sporozoite then penetrates an epithelial cell, rounds up and is then known as a Trophozoite

• within the cell of the tissue, the Trophoblast continues to develop into a round structure called a Meront (Schizont)

  • inside each Meront are a large number of elongated nucleated organisms known as Merozoites

• when division is complete and the Meront is mature, the host cell and the Meront rupture and the Merozoites escape to invade neighboring cells in the host

• Merogony may be repeated, the number of meront generations depends on the species

Gametogeny and oocyst formation (sexual reproduction)

• merogony terminates when the Merozoites give rise to male and female gametocytes

• male gametocytes penetrate female gametocytes to result in an oocyst

• no further development usually takes place until this newly formed unsporulated oocyst is liberated from the body in the feces

Family Eimeriidae

• most important genera: Eimeria and Isospora

• infections commonly referred to as Coccidiosis

• genera are classified by:

  • number of sporocysts per oocyst

  • number of sporozoites per sporocyst

Eimeriidae life cycle and host specificity

• parasites are intracellular, often in intestinal cells

• undergo merogony in host tissue

• life cycle is mostly homoxenous (in one host)

• highly host-specific across most species

genera of veterinary interest in family Sarcocystidae

• Sarcocystis

• Neospora

• Toxoplasma

Sarcocystidae life cycle

life cycle similar to Eimeria and Isospora EXCEPT:

• the asexual stages occur in intermediate hosts

• the sexual stages occur in final hosts

family Sarcocystidae infectivity

normally non-pathogenic to final hosts but are pathogenic to intermediate hosts during the cystic tissue stages