BLOOD AND TISSUES – TRYPANOSOMA BRUCEI

**TRYPANOSOMA BRUCEI **

definition – a flagellated protozoan parasite causing African trypanosomiasis (sleeping sickness)

cause – bite of infected tsetse fly (Glossina species) that inoculates metacyclic trypomastigotes

types – Trypanosoma brucei rhodesiense (East‑African, acute), Trypanosoma brucei gambiense (West‑African, chronic), Trypanosoma brucei brucei (animal only)

morphology – spindle‑shaped, 15–30 µm long, single flagellum arising from flagellar pocket, undulating membrane, nucleus + kinetoplast, long slender form in blood, short stumpy form in tsetse

life‑cycle (step‑wise)

1. infected tsetse fly bites human → metacyclic trypomastigotes injected into skin
2. parasites enter lymphatics → reach bloodstream (slender proliferative form)
3. multiply → disseminate to skin, spleen, liver, bone‑marrow
4. differentiate into short stumpy forms → taken up by feeding tsetse
5. in tsetse mid‑gut → procyclic forms multiply, migrate to salivary glands
6. become epimastigotes → transform to metacyclic trypomastigotes → ready to infect next host

pathogenesis (step‑wise)

1. inoculation → parasites evade innate immunity by rapid motility
2. antigenic variation of VSG coat → escape antibody‑mediated clearance
3. proliferate in blood → cause haemolysis, anaemia, cytokine‑mediated fever
4. invade lymph nodes → lymphadenopathy, chancre at bite site
5. cross blood‑brain barrier (via infected macrophages) → enter CNS
6. CNS inflammation → sleep cycle disturbance, neuro‑psychiatric signs

clinical features – early (haemolymphatic) stage

• intermittent fever, chills, headache, myalgia
• malaise, weight loss, anaemia, thrombocytopenia
• lymphadenopathy (especially posterior cervical “Winterbottom’s nodes”)
• chancre at bite site (more common in rhodesiense)

late (neurological) stage

• sleep disturbance (day‑time somnolence, night‑time insomnia) → “sleeping sickness”
• personality change, irritability, confusion
• tremors, seizures, ataxia, cranial nerve palsies
• severe cases → coma, respiratory failure, death

complications

• severe anaemia, cardiac involvement, renal dysfunction
• secondary bacterial infections due to immunosuppression
• irreversible CNS damage if untreated

lab diagnosis – direct detection

• wet mount or thick blood smear (slender forms) → immediate visualization
• micro‑hematocrit centrifugation technique (MHT) for higher sensitivity
• lymph node aspirate or CSF examination (late stage) → stumpy forms in CSF

serology / immunology

• CATT (card agglutination test for trypanosomiasis) – screening for gambiense
• IFAT, ELISA for anti‑VSG antibodies
• PCR (species‑specific) for confirmation, especially in low‑parasitaemia cases

CSF analysis (late stage)

• presence of trypanosomes or elevated white cell count (>5 cells/µL) and protein → indication for CNS‑penetrating therapy

management (drug of choice by stage)
early stage (haemolymphatic) – pentamidine (gambiense) or suramin (rhodesiense)
late stage (CNS) – melarsoprol (arsenical, high toxicity) or eflornithine (gambiense) or nifurtimox‑eflornithine combination (NECT) for safer regimen
supportive care – antipyretics, blood transfusion if severe anaemia, treat secondary infections

memory trick for life‑cycle (rhyming)
“Bite‑Blood‑Grow‑Stump‑Fly‑Saliva‑Ready‑Go”

• Bite = tsetse bite, Blood = bloodstream slender, Grow = multiply in tissues, Stump = stumpy taken up, Fly = tsetse mid‑gut, Saliva = salivary gland maturation, Ready = metacyclic ready, Go = infect next host.