African trypanosomiasis Flashcards
What species cause HAT?
Trypanosoma brucei - broad species
Sub species
West african - caused by T.b gambiense
East african - caused by T.b rhodesiense
What is the vector for african trypanosomiasis?
Tsteste fly - glossina mortisans
painful bite
Identified by hatchet cell
Trypanosomiasis only in sub saharan africa
How do east and west african trypanosomiasis differ?
caused by different species, rhodesiense vs gambiense
location, east vs west africa
reservoir, animals - wild game, cattle vs humans - domesticated pigs
progression - weeks to months vs months to years
Pathophysiology of trypanosomiasis
Tsetse fly bites its host, thereby injecting metacyclic trypomastigotes into the skin
Trypomastigotes then transform into bloodstream trypomastigotes, allowing them to travel throughout the body where they multiply by binary fission
What does antigenic shift cause?
Antigenic shift - near continuous modulation of variacble surface glycoproteins, which allows the parasite to rapidly switch expression of surface proteins to constantly evade host immune repsonses.
as a result there are typical waves of parasitemia that occur with each antigenic shift and then subside as immune system begins to develop a response.
What is stage 1 and the clinical presentation?
1-3 weeks after bite, trypanosome parasites spread through blood stream and lymph nodes - stage 1, early haemoplymphatic stage - trypmastigotes can be seen on blood smear
- slow progression - WA
- rapid progression - EA
- fevers
- headaches
- malaise - feeling unwell and tired
- Arthralgia - joint pain
- waves of fever
- chancre at bite site
other non specific symptoms
- pruritus
- rash
- weight loss
- facial swelling
What is the immune response?
Symptoms may subside as non-specific polyclonal B cell activation with large production of IgM and resultant enlargement of the spleen and lymph nodes
Diffuse lymphadenopathy, hepatomegaly and more commonly, splenomegaly are often present
What is the clinical presentation of stage 2 - late/encephalitic/CNS phase?
Trypomastigotes can easily pass into the CSF
Onset in weeks – EA
Months – WA
Diagnosed by WCC in CSF
CNS related symptoms
- Headaches, poor concentration
- Difficulty completing tasks
- Psychosis, personality change
- Tremor, ataxia
Hallmarks of late disease is alteration in the normal circadian rhythm, with reversal of the sleep-wake cycle, hence name sleeping sickness
Convulsions may occur as the disease progresses, especially in children, though meningismus and focal neurologic signs are often absent
Clinical deterioration until coma or stupor results
Stage II disease is universally fatal without treatment
What can you look for when diagnosing?
Non specific abnormalities
Anaemia, leukocytosis and throbocytopenia, likely due to splenic sequestration
Hypergammaglobulinemia with polyclonal IgM is characteristic
Other common findings include elevated ESR/CRP and hypoalbuminemia
How to diagnose HAT with microscopy?
Definitive diagnose requires detection of parasite in blood, CSF, or lymph node aspirate
Testing the buffy coat increases sensitivity
Giemsa stain
How to diagnose HAT with serology?
Antibody testing is available for T.b gambiense but is not sufficient for definitive diagnosis as you can get false positives or cross reactions with other types of trypanosomes. There is neither antigen or antibody testing for T.b rhodesiense
Most frequently used detection method is the card agglutination test for T.b gambiense (CATT), relies on the agglutination of trypanosomes and antibodies and has a sensitivity of 94-98%
What are morula cells?
Engorged plasma cells, rare to see but can be used to diagnose trypanosome.
Treatment of T.b gambiense and rhodesiense stage 1 and 2
Gambiense:
stage 1 - pentamidine, fexinidazole
stage 2- nifurtimox plus elfornithine (NECT)
rhodesiense:
stage 1: suramin
stage 2: melarosprol
Drugs for west african tryps
Pentamidine – hypotension, electrolyte disturbances
Nifurtimox – GI upset
Eflornithine – dizziness, headaches, nausea
Fexinidazole – neuropsychiatric, QT prolongation
drugs for east african try[s
Suramin – nephrotoxicity, myelosuppression and peripheral neuropathy have been reported
Melarsoprol – arsenic derivative, used for late CNS stage of EA tryps. Common side effects include irritation at the injection site, abdominal pain, vomiting, diarrhoea, myocarditis and peripheral neuropathy
