Mode of transmission

It’s transmitted by a vector called Glossina (tsetse fly) between animals and from animals to human beings following bites

• Glossina palpalis-along rivers and responsible for Trypanosoma brucei gambiense transmission
• Glossina morsitans-responsible for Trypanosoma Rhodesiense transmission

Life cycle

The tsetse fly (genus Glossina) is a large, brown, biting fly that serves as both a host and vector for the trypanosome parasites.

While taking blood from a mammalian host, an infected tsetse fly injects metacyclic trypomastigotes into skin tissue. From the bite, parasites first enter the lymphatic system and then pass into the bloodstream. Inside the mammalian host, they transform into bloodstream trypomastigotes, and are carried to other sites throughout the body, reach other body fluids (e.g., lymph, spinal fluid), and continue to replicate by binary fission.

A tsetse fly becomes infected with bloodstream trypomastigotes when taking a blood meal on an infected mammalian host. In the fly’s midgut, the parasites transform into procyclic trypomastigotes, multiply by binary fission, leave the midgut, and transform into epimastigotes. The epimastigotes reach the fly’s salivary glands and continue multiplication by binary fission.

The entire life cycle of the fly takes about three weeks.

Horse-flies (Tabanidae) and stable flies (Muscidae) possibly play a role in transmission of nagana (the animal form of sleeping sickness) and the human disease form.

Mechanism

Tryptophol is a chemical compound that induces sleep in humans. It is produced by the trypanosomal parasite in sleeping sickness.

Clinical picture

It occurs in three phases for both species

a) Primary chancre stage

It’s more commonly seen in Trypanosoma brucei Rhodesiense. It’s characterized by;

• Appearance of a painful indurated nodule at site of fly bite lasting for 1-2 weeks then resolves
• Fever
• Headache
• Joint pains
• itching
• Localized swelling of lymphnodes
• Scar formation

b)     Systemic/blood stage

It occurs following dissemination of Trypanosomes to blood and lymph nodes. It’s characterized by;

• Fever for a few weeks
• Lymphadenopathy
• General malaise
• Anemia
• Severe headache
• Myalgia
• arthralgia

Other signs and symptoms

• pruritic rash for 6-8 weeks
• hepatosplenomegaly
• impotence and menstrual irregularities
• cardiac failure for Trypanosoma brucei Rhodesiense
• abortion and still births in pregnancy

c) cerebral stage

It occurs due to invasion of the brain by the Trypanosomes. It’s characterized by;

• progressive mental deterioration tremors
• over sleeping during day (sleeping sickness)
• restlessness at night
• hemiplegia
• facial palsy
• coma
• death if un treated