Trypanosoma brucei complex - Introduction, History, Habitat, Morphology, Culture

Introduction of Trypanosoma brucei complex

The Trypanosoma brucei complex consists of three species of parasites - Trypanosoma brucei brucei, Trypanosoma brucei gambiense, and Trypanosoma brucei rhodesiense. They are morphologically indistinguishable.

Trypanosoma brucei brucei causes a disease called nagana which occurs in antelopes as well as other African ruminants. These parasites do not cause disease in humans.

Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense, which are different in biology, growth rate and pathogenesis, is the causative agent of the parasitic disease called African sleeping sickness or African trypanosomiasis.

Trypanosoma brucei gambiense causes a chronic form of the disease called West African trypanosomiasis while Trypanosoma brucei rhodesiense causes East African trypanosomiasis which is a wasting disease resulting in death if left untreated.

History of Trypanosoma brucei complex

The Trypanosoma brucei complex was first demonstrated in 1895 by Bruce in horses and cattle suffering from nagana. Forde in 1902 was the first to demonstrate the motile Trypanosoma in the blood of a man suffering from the parasite infestation.

Dutton 1902 coined the name Trypanosoma brucei complex while its development insect vector – tsetse fly – was demonstrated in 1909 by Kleine.

Habitat of Trypanosoma brucei complex

Trypanosoma brucei complex is found to be infecting men and other vertebrates. These parasites are present in infected individuals’ connective tissue, lymph nodes, cerebrospinal fluid, and blood.

Morphology of Trypanosoma brucei complex

Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense occur in different morphological forms and depend on the host where the parasite is infesting.

Vertebrate forms

• In vertebrate hosts, Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense

  occur in two morphological forms

  Dividing long and slender trypomastigotes

  Non-multiplying short, thick and stumpy trypomastigotes

• trypomastigotes are pleomorphic as they are known to vary massively in their shape and size

Dividing long and slender trypomastigotes

• Dividing long and slender trypomastigotes are found in the blood during ascending parasitaemia

• homotype variable antigen type (VAT) is a particular parasite antigenic type in this form

• the trypomastigotes are slender and fusiform with a pointed anterior end and blunt posterior end

• measures 10μm – 35 μm in length and 1.5 μm to 3.5 μm in breadth

• the presence of a single central large oval nucleus

• one small kinetoplast contains blepharoplast and the parabasal body is located at the posterior end

• a flagellum at the anterior end, which originates from the kinetosome and transverses on the surface of the trypomastigote as a narrow undulating membrane which helps in motility

• the cytoplasm contains volutin granules

• if stained with Giemsa or Leishman stain, the flagella are reddish blue or red while the undulating membrane is stained blue

Non-multiplying short, thick and stumpy trypomastigotes

• Non-multiplying short, thick and stumpy trypomastigotes are found in the blood during the descending phase of parasitaemia

• lacks motility due to the absence of flagella

Insect/Invertebrate form

• Insect/Invertebrate forms are found in the salivary glands of the tsetse fly

• occurs in two distinct morphological forms:

  Epimastigotes

  Metacyclic trypomastigotes

Epimastigotes

• Epimastigotes have a surface coat and pre-nuclear kinetoplast

• the division takes place by attaching itself to the lumen of the salivary glands of its insect vector

Metacyclic trypomastigotes

• Metacyclic trypomastigotes lack motility due to the absence of flagella

• these trypomastigotes are small, stumpy

• the only stage of the Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense that are infective to humans

Culture of Trypanosoma brucei complex

The culture of the Trypanosoma brucei complex can be done in media as well as laboratory animals.

In media

• Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense can be cultured in-vitro in the NNN media and the Tabies’ biphasic media

• can also be grown in primary murine bone marrow culture (feeder layer) in RPMI 1640, Eagle’s minimum essential medium (MEM) which has been supplemented with 20% foetal calf serum (FCS) and salts

• in such cultures, the monomorphic forms of the parasite can be isolated inside the feeder layer while pleomorphic forms are found in the liquid medium

Laboratory Animals

• laboratory animals such as mice, rats, and guinea pigs can be used for the culture of Trypanosoma brucei rhodesiense

• the lab animals are more resistant to Trypanosoma brucei gambiense infections