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.

Hosts

• 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.

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Read More:

1. Morphology of Trypanosoma gambiense | Diagram
2. Life Cycle of Ascaris lumbricoides | Diagram
3. Life Cycle of Leishmania donovani | Diagram

Reference:

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