Trypanosomiasis

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Trypanosomiasis

• African trypanosomiasis
• (Sleeping sleepness)
• American trypanosomiasis
• (Chagas disease)

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African Trypanosomiasis

• Causative agents
• Trypanosoma brucei rhodesiense (East African form
• T. brucei gambiense (West-Central African form)
• Other name Sleeping sickness
• A systemic protozoal disease, organisms grow in
  blood, lymph, CSF, and intercellular spaces (in
  contrast to T. cruzi)

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African Trypanosomiasis History

• Recognized as far back as 14th century
• Only in 20th century has magnitude of problem
  been elucidated
• Progress towards elimination ensued over the
  first half of the century after recognition of
  agent, vector, and development of treatment
  regimes

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African Trypanosomiasis History
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Trypanosomes Classification

• Order Kinetoplastida
• kinetoplast disc shaped organelle containing
  DNA (kDNA) within a single large mitochondria
• Genera differ in host distribution, life cycles,
  and clinical relevance (veterinary and human)
• Family Trypanosomatidae
• Heteroxenous (most) require more than one
  living host to complete life cycle
• Hemoflagellates dependence on blood (host,
  invertebrate vector, culture)

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Trypanosomes Classification

• Section Salivaria
• Trypanosoma brucei T. vivax T. evansi, T.
  equinum T. congolense
• Anterior section develops in anterior portions
  of digestive tract
• Section Stercoraria
• T. cruzi T. rangeli T. lewisi
• Posterior section development in hindgut of
  insect

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Trypanosomes Classification

• Morphological stages - mastigote (from subphylum
  Mastigophora) mastix (Gr.) for whip
• Trypomastigote in the blood stream flagellum
  runs entire length from posterior
• includes metacyclic (infective) stage in tsetse
  fly
• Amastigote spheroid with very short flagella
  definitive for Leishmania
• Promastigote elongated with flagella extending
  forward

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Trypanosomes Classification

• Trypomastigotes in the blood stream

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Trypanosoma brucei spp. Microbiology

• Morphology
• pleomorphic in vertebrate host
• long slender/long flagella to stumpy/no flagella
• monomorphic forms
• after syringe passage from host to host, only
  slender forms like found in nature except no
  longer infective to fly and cannot be propogated
  in culture
• In vitro culture passage revert to form found
  in midgut
• differences in glucose and oxygen consumption
  owing to cytochrome oxidase systems present

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Trypanosoma brucei spp. Microbiology

• Life cycle
• Ingested trypomastigote in tsetse fly
• Multiply in posterior midgut, then migrate to
  foregut, esophagus, salivary glands
• transform into epimastigote in salivary glands
• attachment to host cell or remain free in lumen

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Trypanosoma brucei spp. Microbiology

• Life cycle
• after several asexual reproductions, transform
  into metacyclic trypomastigote (infective stage)
• In vertebrate host, trypomastigotes multiply in
  blood and lymph may invade CNS

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Trypanosoma brucei spp.
A-anterior flagellum C-nucleus E-kinetoplast
(mitochondrial genome)
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Trypanosoma brucei spp. Life cycle
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Trypanosoma brucei spp. Immunology

• Protective antibody response mounted by host
  leads to periods of remission
• Ab response not sufficient to completely
  eliminate organisms
• variant antigenic types (VAT)
• Mechanism for escaping host defense conducive to
  survival from host defense
• expression of new (unrecognized) surface
  glycoprotein
• without treatment, only limited by lifespan of
  host

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Trypanosoma brucei spp. Immunology

• variant-specific surface glycoprotein (VSG)
• released through flagella to coats entire
  organism
• only one gene (of 1,000) expressed at a time
• in chronic infection, VSG genes are
  heterogeneous, although a single VAT is
  predominant to which host mounts immune
  (antibody) response to

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Trypanosoma brucei spp. Immunology

• VSG surface coat lost when ingested by fly
• anamnestic expression re-expression of the VSG
  ingested by fly occurs within a few days after
  expression of VSG of metacyclic VAT
• during time promastigotes are without surface
  coat within fly, susceptible to antibodies taken
  with subsequent blood meals possible control
  mechanism

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Trypanosoma brucei spp. Immunology

• Trypanosomes show immunopositivity to monoclonal
  antibodies directed against the cytokine
  interferon-? (IFN-?)
• regions where the parasites are located are
  infiltrated with CD8 T-cells
• T. brucei induces production of IFN-? from CD8
  T-cells
• IFN-? binds to the trypanosomes and promotes
  their growth and proliferation

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African trypanosomiasis Epidemiology

• Occurrence tropical Africa, between 15º and 20º
  latitude
• Frequency incidence of up to 2, prevalence can
  reach 70 in epidemics
• WHO report (1995) of 26,000 cases reported,
  estimated there were probably 365,000

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African trypanosomiasis Epidemiology
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African trypanosomiasis Epidemiology
Distribution of gambiense and rhodesiense
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African trypanosomiasis Epidemiology
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African trypanosomiasis Epidemiology
Number of cases, 1940-1998
WHO Surveillance Report
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African trypanosomiasis Epidemiology

• Reservoir
• T.b.gambiense - primarily humans wild and
  domestic animals not established
• T.b.rhodesiense - wild animals, especially
  cervidae (bushbuck, antelope) cattle
• Trypanotolerant species
• Wild animals more than domestic livestock
• NDama (predominant breed of Bos taurus in
  Africa certain other breeds

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African trypanosomiasis Epidemiology

• Vector
• Glossina spp. - tsetse fly
• Name stems from sound made in flight means fly
  in Tswana
• Order Diptera (true flies)
• Hemataphagous - piercing/sucking fly (biting fly
  is really a misnomer)
• Holometabola complete metamorphosis
• egg larva (4) - pupa - adult
• Only found in sub-saharan Africa and isolated
  area of Arabian peninsula

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African trypanosomiasis Epidemiology

• Vector
• Glossina spp. - tsetse fly
• Glossina suptypes (Eastern)
• G. morsitans
• G. pallidipes
• Savannah type preference for savannah
  environment
• Completely dependent on wild animals for blood
  meal

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African trypanosomiasis Epidemiology

• Vector
• Glossina spp. - tsetse fly
• Palapalis subtypes (Western)
• G. palpalis
• Riverine types water edge vegetation in arid
  regions dense rain forest regions
• Principle hosts reptiles, particularly monitor
  lizards and crododiles will feed on
  wild/domestic ungulates

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African trypanosomiasis Epidemiology

• Vector tse-tse fly feeding on human

12 mm
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African trypanosomiasis Epidemiology

• Vector tse-tse fly

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African trypanosomiasis Epidemiology

• Natural habitat Gambia

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African trypanosomiasis Epidemiology

• Risk factors
• Geographic region
• Occupation
• Socioeconomic status
• Host susceptibility genetics?

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African trypanosomiasisClinical features

• Pathogenesis - general
• Typanosomes live in blood, lymph nodes, spleen
  therefore not intracellular
• Particularly abundant in intercellular spaces in
  brain
• Clinical course dependent on host susceptibility
• T.b.brucei - vertebrate hosts (equidae, dogs,
  some ruminants) exhibit acute disease with death
  in 2 weeks
• If survive, blindness common in dogs

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African trypanosomiasisClinical features

• Pathogenesis
• Humans
• Local reaction painful sore at site of bite,
  disappears after a couple of weeks
• Trypanosomes reproduce rapidly once enter blood
  and lymph sustem lymphadenopathy, genelarlized
  invasion of all organs
• Winterbottoms sign swollen nodes at base of
  skull sign of certain death according to slave
  traders
• binding of specific antibody to adsorbed
  trypanosome on host cell, coupled with
  complement, leads to lysis cause of anemia

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African trypanosomiasisClinical features

• Pathogenesis (mechanisms under investigation)
• Circadian rhythms - alterations in endogenous
  rhythms correlate with clinical symptoms
• Suprachiasmic nucleus (SCN) biological clock
  regulates hormonal, sleep, body thermostat
  activity
• Spontaneous rhythm of SCN is altered with
  trypanosome infection

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African trypanosomiasisClinical features

• Incubation period
• Rhodesiense days to weeks
• Gambiense much longer - months to years
• Clinical signs - early stages
• painful chancre at site of bite
• fever
• intense headache, insomnia
• lymphadenopathy, localized edema, rash
• anemia

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African trypanosomiasisClinical features

• Clinical signs - late stages
• severe wasting
• somnolence
• CNS signs increased apathy, dullness, tremors,
  convulsions, coma, death
• Gambiense more protracted course
• Rhodesiense more rapidly fatal
• both forms are always fatal without treatment

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African trypanosomiasisClinical features

• Late stages - severe wasting

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African trypanosomiasisClinical features

• Cattle, other livestock, horses
• Disease called nagana
• Primary agents T. congonense, T. vivax T.b.
  brucei

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African trypanosomiasisClinical features

• Economic impact on agriculture
• Major reduction in food production
• 3 million deaths per year
• 50 reduction in herd size
• 25 reduction in milk production
• 20 loss in calving

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African trypanosomiasis Diagnosis

• direct examination of aspirate or smear - wet
  mount for motile trypomastigotes
• concentration techniques usually required before
  microscopic examination (centrifugation of CSF,
  QBC for buffy coat)
• animal innoculation/isolation - for rhodesiense
• CATT (card agglutination trypanosome test) -
  useful for gambiense screeing and surveillance
• serology
• antibodies IFA, ELISA high levels of IgM
  common
• antigen PCR

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African trypanosomiasis Diagnosis

• T. b. rhodesiense (geimsa stain of blood smear)

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African trypanosomiasis Diagnosis
Direct geimsa stain of blood smear)
T. b. rhodesiense note dividing form on right
not seen with T. cruzi (Chagas disease)
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African trypanosomiasis Treatment

• Eflornithine difluoromethylornithine (DFMO)
• called the resurrection drug
• drug of choice, particularly with CNS involvement
• Due to limited availability in many areas, only
  saved for later stage disease
• Hemolymphatic disease stage (no CNS involvement)
• suramin (rhodesiense)
• pentamidine (gambiense)

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African trypanosomiasis Treatment

• if evidence in CNS - melarsoprol also recommended
  since crosses blood-brain barrier
• follow-up at 3, 6, 12, and 24 months after
  treatment to monitor for relapses

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African trypanosomiasis Control

• Education
• Surveillance backbone of control
• Of 60 million at risk, only 5-10 under
  surveillance
• Treatment programs for human infections
• Availability of effective drugs
• Economic barriers
• Accessibility issues

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African trypanosomiasis Control

• Vector control, especially tse-tse fly habitats
  reduction measures around villages
• Elimination of wild game reservoirs
• Agricultural use of cleared areas
• Grazing at night since flies are primarily day
  feeders
• Vaccine development unlikely
• Breeding trypanotolerant livestock

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African trypanosomiasis Control

• PAAT Programme Against African Trypanosomiasis
• Combined effort of FAO, WHO, IAEA, and OAU/IBAR
• Ultimate goal
• improve food security, sustainable agricultural,
  and rural development
• alleviation in tryp-affected areas