Life Cycle of Trypanosoma gambiense | Diagram

Trypanosoma gambiense is a species of parasite that causes African trypanosomiasis, also known as sleeping sickness. The life cycle of Trypanosoma gambiense involves two distinct developmental stages: one is found in the bloodstream of man and the another stage is found inside the blood-sucking tsetse fly. In this article, we will learn the life cycle of Trypanosoma gambiense.


Life Cycle of Trypanosoma gambiense
Fig: Life Cycle of Trypanosoma gambiense

  • Trypanosoma gambiense is a digenetic parasite which means it completes its life cycle in two hosts.
  • Man is the primary or principal or definitive host because, in the bloodstream of man, the parasite attains its sexual maturity.
  • The tsetse fly(Glossina palpalis) is the intermediate host or vector of the parasite because the fly transmits the parasite from one individual of the principal host to another.
  • Some mammals like antelopes, pigs, buffaloes, etc. often act as reservoir hosts because the parasite often utilizes them as a temporary refuge until the appropriate principal host is found.

Life Cycle in Man

1. Infection

      • The infection to man by the parasite is always initiated by the tsetse fly.
      • The infective metacyclic forms of the parasite Trypanosoma gambiense reside inside the lumen of the salivary glands of the tsetse flies.
      • When the fly bites a man to suck blood, it releases infective trypanosomes into his bloodstream.
      • To suck blood, the fly first punctures the skin surface of a man. Then the fly uses its saliva to prevent blood clotting. Thus the infective trypanosomes enter the bloodstream of man.

2. Multiplication

      • The parasites are extracellular as they are present in the blood plasma, not inside the cells.
      • The metacyclic forms of the trypanosomes are devoid of flagella. After the infection, they transformed into long slender forms with flagella.
      • With the beating of the free flagellum, trypanosomes swim freely in the blood.
      • In this stage, they multiply actively by longitudinal binary fission.
      • The multiplying trypanosomes obtain energy by anaerobic glycolysis.

3. Metamorphosis

      • When glycolysis is hampered due to the antibodies, the trypanosomes stop multiplying.
      • Then they shrink to short stumpy forms having no free flagellum.
      • During the transformation from long slender forms to short stumpy forms, the intermediated forms also appear.
      • These intermediate forms and short stumpy forms depend on their energy supply upon the aerobic oxidation of pyruvic acid.
      • The short stumpy forms do not feed and ultimately die, if they are not sucked up by the tsetse flies.

4. Relapse of Infection

      • Some of the long and slender trypanosomes do not undergo transformation, but change the antigens of blood to which the host has produced antibodies.
      • These slender forms survive and continue to multiply in the blood leading to future relapses of the infection.

Life Cycle in The Tsetse Fly

1. Transfer to Tsetse Fly

      • The tsetse flies suck the blood of an infected person and take the short stumpy forms of the trypanosomes.
      • The trypanosomes continue development inside the fly.

2. Development in Mid-gut

      • Further development occurs inside the mid-gut of the tsetse fly.
      • Here the trypanosomes transform into long and slender forms.
      • Then they multiply by means of longitudinal binary fission.

3. Development in Salivary Glands

      • The long and slender forms of the trypanosomes come to the salivary glands through oesophagus and mouthparts.
      • Here they metamorphose into crithidial forms.
      • The crithidial forms have shortened body, reduced free flagellum, and the kinetoplast in front of the nucleus.
      • The mitochondrion develops an extensive network of cristae.
      • The crithidial forms multiply in the lumen of the salivary glands.
      • Then the crithidial forms transform into slender metacyclic forms.
      • This metacyclic form enters into the blood stream of man when the tsetse fly bites a healthy man.

Frequently Asked Questions

Ques 1: Where Trypanosoma gambiense lives in human body?

Ans 1: It lives in the blood plasma of human.


Ques 2: What is the host of Trypanosoma gambiense?

Ans 2: Man is the primary host and Tsetse fly is intermediate host.


Ques 3: What is the infective stage of Trypanosoma gambiense?

Ans 3: The infective metacyclic forms of the Trypanosoma gambiense is the infective stage.


Ques 4: What type of pathogen is Trypanosoma gambiense?

Ans 4: It is a parasitic protozoan.

Ques 5: Is Trypanosoma gambiense unicellular or multicellular?

Ans 5: It is a unicellular parasitic protozoan.

————-THE END———-

Read More:

  1. Morphology of Trypanosoma gambiense | Diagram
  2. African Sleeping Sickness or Trypanosomiasis: Symptoms, Diagnosis, Treatment, and Prevention
  3. General Characters of All Phylum of The Invertebrates.


  1. “Modern Textbook of Zoology Invertebrates” written by R. L. Kotpal.

Leave a Reply

Your email address will not be published. Required fields are marked *