Order: Kinetoplastida

Family: Trypanosomatidae

• Family includes all hemoflagellates. Body is usually elongated and may be flattened, leaf-like in shape and having one nucleus.
• Consists of single flagellum attached to body by an undulating membrane. Flagellum arises from blepharoplast and passes anteriorly usually extending beyond the body.
• Posterior to blepharoplast, there is rod-shaped or spherical kinetoplast. It contains DNA and varies in structure under light microscopy. Kinetoplast and blepharoplast appear close together giving a fused appearance.
• Specific name is given for the developmental stage occurring in these parasites : ‘mastigote’ is derived from Greek word, which means whip (flagellum).

a. Trypomastigote:

• With complete undulating membrane and free flagellum.
• Body is leaf-like or blade-like.
• Most advanced stage
• Kinetoplast and kinetosome are near the posterior end and the flagellum forms border of an undulating membrane which extends along the side of body to anterior end.
• Nucleus is situated at middle of the body
• Commonly found in vertebrate host and also in arthropod vectors.

b. Epimastigote:

• Small flagellum and short undulating membrane
• Body is elongated
• Kinetoplast and kinetosome are just anterior to the nucleus.
• Found in arthropods and occurs as part of vertebrate development cycle
• Nucleus is at posterior end of body
• Develop into promastigote form inside the arthropod vector

c. Promastigote:

• Only short free flagellum is present
• Body is elongate or leaf-like
• Kinetoplast and kinetosome lie towards the anterior tip of body
• No undulating membrane
• Found in invertebrates
• Nucleus is situated at middle of body
• Develop into amastigote form inside the vertebrate host

d. Amastigote:

• Flagellum is absent or it has degenerated into a tiny fibril inside the body.
• Kinetoplast is present. It is rod-shaped and present infront of nucleus.
• Body is circular or oval.
• Nucleus is placed centrally or peripherally
• Found in vertebrate and invertebrate
• Develop into promastigote form inside the insect water.

Note: Only two genera: Trypanosoma and Leishmania  are of veterinary significance