LIFE CYCLE OF TRYPANOSOMA GAMBIENSE

SYSTEMATIC POSITION

Phylum- Protozoa

Subphylum- Sacromastigophora

Superclass- Mastigophora

Class- Zoomastigophora

Order- Kinetoplastida

Genus- Trypanosoma

Species- gambiense

INTRODUCTION

• Trypanosoma is a haemoflagellate digenic  parasite found in the blood of amphibians, reptiles, birds and mammals.
• 3 species of Trypanosomes are found pathogenic and are present in human blood which causes a deadly disease known as African sleeping sickness.
• The three species are as follows:

1. Trypanosoma gambiense
2. Trypanosoma rodesiense
3. Trypanosoma cruzi

• Trypanosoma gambiense is an endoparasite. Being digenic, primary host  is Man and secondary host is Tse-tse  fly.

HABITAT

• It occurs in  the blood of man and later on enters the cerebrospinal fluid of the central nervous system. 
• It is generally confined to  man of central and western Africa and causes African sleeping sickness.

DIFFERENT STAGES

• Morphologically, Trypanosoma occurs in the following four different stages:

1. Leishmania stage
2. Leptomonad stage
3. Crithidial stage
4. Trypanosome stage

LIFE CYCLE

• Trypanosoma gambiense are  digenic parasites completing their life cycle in two hosts. 
• Primary  host is human and secondary host is tse-tse fly (Glossina palpalis).
• The mammal  like pigs, buffaloes etc. acts as reservior host that harbours the parasite.

The life cycle of Trypanosoma gambiense completes in two phases i.e.,  in man and in tse-tse fly.

1. Life cycle in man
2. Life cycle in tse-tse fly

LIFE CYCLE IN MAN

Life cycle of Trypanosoma gambiense, inside the body of man completes in three phases which are as follows:

• Infection
• Multiplication
• Metamorphosis

Infection

• An healthy person  get infected by the parasite (Trypanosoma gambiense),  if a tse-tse fly containing the infective stage of parasite (i.e., Metacyclic form) in its  salivary gland,  bite him to suck the blood.
• While sucking the blood Tse-tse fly injects some saliva into the blood stream of man. Its saliva contains an anticoagulant which checks the clotting of blood.
• Along with saliva large number of parasites present in it are also introduced into the blood stream of man.

Multiplication

• All the stages of parasites in man is extracellular, as they are present in the blood plasma and not inside the blood cells.
• In human blood plasma, the metacyclic form is transformed into a long slender form with flagella as locomotory organelle.
• These long slender form swims freely with its flagellum and divides actively by longitudinal binary fission. The multiplying Trypanosomes obtain energy by anaerobic glycolysis.

Metamorphosis

• When the absorption of glucose ceases due to antibodies in blood, glycolysis  is hampered and the Trypanosomes stops multiplying.
• Now, they shrinks to short stumpy form without free flagellum.
• During transformation from long slender form to  short stumpy form the intermediate form with somewhat short flagellum is also appeared.
• This stumpy form do not feed and ultimately die if they are not sucked up by the tse-tse fly along with the blood meal.

LIFE CYCLE IN TSE-TSE FLY (Glossina palpalis)

• When a tse-tse fly  suck the blood of an infected person, it also take in the short stumpy forms along with the sucked blood. It is the stumpy form which continue its development inside the tse-tse fly.

Inside the body of tse-tse fly the parasite develops under the following headings:

1. Development in mid  gut
2. Development in salivary gland

Development in mid gut

• Further development of the Tse-tse fly proceeds in the insect mid gut within the peritrophic membrane.
• Here. the parasites (short stumpy form) transform into long slender forms and multiply by longitudinal binary fission.
• The kinetoplast  moves father from the posterior end of the body.
• The energy yeilding process is related to mitochondrial oxidation of pyruvic acid.

Development in salivary gland

• Now, the long slender forms make their way into the salivary gland via the oesophagus and mouth parts of insect.
• Here, they metamorphose into the crithidial forms with shortened body, reduced free flagellum and kinetoplast in front of nucleus.
• The crithidial form divides in the lumen of salivary gland and transform into the slender metacyclic form.
• The metacyclic form established in the salivary gland of tse-tse fly.
• When the tse tse fly bites  an uninfected person, the parasites again get inoculated in the body of the person and the cycle repeats.

PATHOGENESIS AND PROPHYLAXIS

• Trypanosoma gambiense causes African sleeping sickness, when it enters into the cerebro-spinal fluid of brain. The bite of tse-tse fly causes itching and irritation near the wound and dark red leison develops. The parasite causes anaemia, loss of weight, weakness. It also invades the lymph gland and causes swelling of the gland followed by enlargement of spleen and liver.

The control measures taken should include:

1. Eradication of breeding ground of vector.
2. Protection from bites of fly.
3. One gram of Suramin should be injected to the person every two to three months