KINETOPLASTIDS. Kinetoplast. Nucleus

Size: px

Start display at page:

Download "KINETOPLASTIDS. Kinetoplast. Nucleus"

Melvyn Johnston
5 years ago
Views:

1 KINETOPLASTIDS Kinetoplast Nucleus widespread parasites animals (fish humans) insects plants monophyletic group related to euglenoids unifying feature = kinetoplast Giemsa staining structure

2 KINETOPLAST mitochondrial DNA located near base of flagellum initially believed to function in movement

3 Kinetoplastid DNA relatively abundant concatenated mass of mini-circles and maxi-circles maxi-circles = mitochondrial DNA few copies encode several MT genes mini-circles; unknown function many copies heterogeneous, rapidly evolving both encode guide RNA genes edit MT transcripts (mrna)

4 undulating membrane flagellum flagellar pocket kinetoplast nucleus mitochondrion subpellicular basal body microtubules

6 Disease Causing Kinetoplastids Trypanosoma brucei complex African trypanosomiasis Trypanosoma cruzi African trypanosomiasis Chagas disease 60 million at risk Leishmania species 25-45,000 reported cases leishmaniasis 3-500,000 estimated cases

7 Trypanosoma brucei complex T. b. brucei game animals/livestock (nagana) T. b. rhodesiense E. African trypanosomiasis T. b. gambiense W. and Central African sleeping sickness trypanosome lytic factor (TLF) found in human sera component of HDL fraction human parasites resistant to TLF resistance associated with decreased uptake of HDL

8 Species Distribution

9 tsetse = Glossina

10 Comparison of T. brucei Subspecies rhodesiense gambiense tse-tse vector G. morsitans G. palpalis ecology transmission cycle non-human reservoir epidemiology disease progression dry bush or woodland ungulate-fly-human wild animals sporadic, safaris rapid, often fatal rainforest, riverine, lakes animal-fly-human, human-fly-human domestic animals endemic, some epidemics parasiemia high low asymptomatic carriers rare common slow (~1 yr) acute chronic

12 Endemic T. gambiense transmission

13 T. rhodesiense transmission wild animal reservoir Zoonosis: infection naturally transferable between animals and humans bush buck

14 Metacyclic trypomasitgotes transferred with saliva during tse-tse feeding. 2. Trypomastigotes replicate in blood stream and tissues of mammal.

15 Blood Stage blood-stream forms long slender rapid replication binary fission preadaptation for tsetse morphological (short stumpy) metabolic (mitochondria) slower replication

16 Metacyclic trypomasitgotes transferred with saliva during tse-tse feeding. 2. Trypomastigotes replicate in blood stream and tissues of mammal Preadaptation for tse-tse Ingestion by tse-tse.

17 7. Maturation to metacyclic trypomastigotes. 7 long-slender 6. Migration to salivary glands and transformation to epimastigotes Procyclic trypomastigotes replicate in tse-tse midgut. loss of surface coat metabolic changes (mitochondria) 5 short-stumpy intermediate

18 maturation to metacyclic trypomastigotes in salivary glands

20 Infection tsetse are pool feeders metacyclic trypomastigotes in saliva and enter bite wound Tsetse Bite ± pain ± hypersensitivity

characterized by irregular fever and headache T.

21 Acute Symptoms and Blood Stage 1-2 week asymptomatic incubation period sometimes a local inflammation 'trypanosomal chancre' parasite replication at bite site invasion of blood characterized by irregular fever and headache T. rhodesiense can develop into fulminating infection T. gambiense can be selflimiting or slowly progressing to more serious disease

22 Lymphatic Stage disease progression often involves invasion of lymphatics Winterbottom s sign rash itching edema continued febrile attacks weight loss weakness cachexia

23 CNS Disease Course and Symptoms parasites crossing blood-brain barrier result in CNS involvement and nervous impairment described as meningoencephalitis increased apathy and fatigue confusion and somnolence motor changes including tics, slurred speech, incoordination convulsions, coma progression to CNS involvement is rapid (weeks) in Tr and slow (6-12 months) in Tg death results from disease (eg., convulsions, hyperpyrexia) or other infections

26 Ross, 1910 parasitemia fluctuates peak parasitemia usually associated with intermittent fever or other symptoms parasites from peaks are antigenically distinct, or variant antigenic types (VAT) VAT = different VSG

27 Variant Surface Glycoprotein VSG uniformly covers surface of parasite (10 7 copies) VSG forms nm electron dense surface coat

28 100 s of VSG genes conserved regions not accessible switch rate = per generation

29 Antigenic Switching gene conversion (duplicative transposition) transcriptional controls also contribute

30 VSG is immunogenic and host response clears parasites some trypanosomes will change VSG coat this population expands until host develops immunity against new VSG

31 Diagnosis Clinical Features travel or residence in endemic area history or scar of 'trypanosomal chancre' irregular fever and enlarged lymph nodes particularly posterior cervical behavioral changes/mental symptoms Laboratory Diagnosis serological tests IFA, ELISA, CATT limited use except epidemiological surveys demonstration of trypanosomes especially during fever definitive diagnosis

32 Detection of African Trypanosomes Blood examine on several days stained thin or thick smears fresh (characteristic movement) buffy coat (microhematocrit) mini-anion exchange chromatography technique (m-aect) inoculate rats or mice

33 Detection of African Trypanosomes Lymph Node Aspirates fresh or stained Cerebrospinal Fluid examine sediment cells and protein (presumptive)

34 Treatment Early Stage--no CNS involvement suramin pentamidine excellent prognosis Late Stage--CNS involvement melarsoprol tryparsamide eflornithine (resurrection drug) expensive 14 consecutive daily injections oral formulation in phase 3 trials

35 Prophylaxis and Control drugs contraindicated mask infections toxicity insect repellants protective clothing community activities surveillance and treatment traps, insecticides habitat alteration

Kinetoplastids Handout

Kinetoplastids Handout 1 Kinetoplastids widespread group of flagellated protozoa parasitize virtually all animal groups as well as plants and insects 3 distinct kinetoplastid species cause human disease