Protozoan pathogens
Kinetoplastids
Leishmania and Trypanosoma
Learning outcomes
After this lecture, you should be able to:
• Discuss the lifecycle of Leishmania and
the associated disease conditions
• Explain the lifecycle of Trypanosoma and
the associated disease conditions
Leishmania
• Several different species
– L.donovani
– L. tropica
– L. braziliensis
– L. mexicana
• Cause different diseases
• Approx 20 different Leishmania species capable
of infecting humans
• Life cycles differ slightly in tissues affected and
clinical symptoms
Global distribution
Global distribution of reported cases of leishmaniasis and
Leishmania/HIV co-infection, 1990-1998 taken from the WHO web site
Lifecycle of Leishmania
Different stages
• The parasite has a number of different stages
• Presence of surface LPG molecule protects parasite
(lipophosphoglycan)
• Promasitgote
– Long, slender, free flagellum
– Found in the gut of infected sandflies
– Transferred during biting (female sandfly)
– Initial infective stage
• Amastigote
– Promastigote loses flagella to become amastigote
– Infect endothelial cells and reproduce cause cells to rupture,
induces tissue damage
– Diagnostic stage for the disease
– Convert back to promastigotes in sandfly gut
L. donovani
• Normally associated with viseral leishmaniasis
• Approx 500,000 cases each year mainly in India,
Bangladesh, Brazil
• Some rodents able to act as a reservoir
• Subvariants chagasi and infantum are found in
South America and China/Mediterranean
respectively
• Animal reservoirs include dogs, foxes and
porcupines
• donovani and infantum transmitted by
Phlebotomus sandfly, chagasi by the Lutzomyia
sandfly
Visceral leishmaniasis
• Fairly long incubation period
• Fever, diarrhoea, anaemia Taken from the WHO website
• Initial symptoms may resemble malaria
• Enlarged liver, spleen, weight loss
• Pigmented areas of skin develop
• If untreated can lead to death in a matter of
weeks
• Diagnosed by tissue biopsy to check for
amastigote parasites
• Can also be diagnosed serologically
Treatments
• Pentavalent antimonials i.e. stibogluconate
• Highly toxic
• Not very successful
• Recent develops include miltefosine (95%
effective)
• Need to control host reservoirs
• Protection from sandflies also important i.e.
repellents, screens
• Vaccines currently researching.
L. tropica
Taken from Wikipedia. This work is in the public domain in the United
States because it is a work of the United States Federal Government
under the terms of Title 17, Chapter 1, Section 105 of the US Code.
• Causes cutaneous disease
• Same lifecycle transmitted by Phlebotomus sandfly
• Found in Africa, Asia, Mediterranean Europe
• Reservoir in dogs, foxes
• mexicana is highly related and occurs in Central America
transmitted by the Lutzomyia sandfly
• Incubation period varies 2 weeks to 2 months from bite
• Lesion appears at site of bite
• Lesions often self heal without treatment but usually scar
• Raised area around outside contains replicating
parasites
Cutaneous leishmaniasis in Sri
Lanka
In 2011, 940 cases of CL were reported in Sri
Lanka, caused by L. donovani
Diagnosis and treatment
• Identify amastigotes from ulcers
• Can also be diagnosed serologically
• Treated using stibogluconate (antimonial)
• Fluconazole and miltefosine are effective
• Protection from sandflies through
screening and repellents
• Controlling reservoirs of insects
• Hope of developing vaccines??
L. Braziliensis
• Same lifecycle as others, transmitted by Taken from the WHO website
Lutzomyia sandfly
• Found in Central and South America
• Causes mucocutaneous Leishmaniasis
• Causes ulcers and also causes the destruction
of mucous membranes particularly the nose and
throat
• Often associated with oedema and other
infection which can cause severe facial
disfigurement
Treatment and diagnosis
• Diagnoses serologically or through
identification of the parasite
• Treated with stibogluconate or
amphotericin B
• Protective screens and repellents
• Work to develop a vaccine is underway
Trypanosoma
Trypanosoma
• Causes two different
forms of disease
• Trypanosoma brucei
– vector tsetse fly
– African
trypanosomiasis/
sleeping sickness
• Trypanosoma cruzi
– Transmitted by
triatomids
– American
trypanosomiasis/
Chagas disease Taken from the CDC web site
T. brucei lifecycle (Sleeping sickness)
T. brucei
A: Trypanosoma brucei sp. in a thin blood smear stained with Giemsa.
The trypomastigote is beginning to divide; dividing forms are seen in
African trypanosomes, but not in American trypanosomes.
T. brucei
• Two subspecies cause distinct disease patterns
– T. b. gambiense (West African sleeping sickness)
• No known reservoir
– T. b. rhodesiense (East African sleeping sickness)
• A number of animal reservoirs
• more severe disease is caused by rhodesiense
• Major pathogen of livestock both wild and
domestics animals causes Nagana
• Rare transmission can occur by the following
– Mother to child infection
• the trypanosome can cross the placenta and infect the
foetus, causing prenatal death.
– Organ transplantation
– Blood transfusion
Symptoms of disease
• haemolymphatic stage
– fever
– enlarged lymph nodes
– itching.
• meningoencephalitic stage
– lethargy
– tremors
• invasion of the CNS
– headaches
– sleepiness
– abnormal behaviour
– loss of consciousness
– coma
Diagnosis and treatment
• microscopic examination tissue samples to identify
parasites
– lymph node aspirates, blood, bone marrow, or, in the late stages
of infection, cerebrospinal fluid, blood smears
– Identify motile trypanosomes, or fix and stain with Giemsa.
• Antibodies can be used but not commercially available
– seroconversion occurs with T. b. rhodesiense so limits use of
AB’s
• acute infections
– Suramin (rhodes) or pentamidine (gambiense, less toxic drug)
both these drugs unable to cross blood brain barrier
• Chronic i.e. CNS
– Melarsoprol (arsenic based, highly toxic)
• As rhodesiense has a shorter incubation treatment often
required more quickly as disease progresses more
quickly and is more severe
• Controlling vector with insecticides etc protection from
vector
T. cruzi lifecycle (Chagas disease)
T. cruzi
C D
C, D: T. cruzi trypomastigotes in thin blood smears stained with Giemsa.
Note the typical C-shape of the trypomastigote that characterises
T. cruzi in fixed blood smears.
T. cruzi infection
• Bug bites takes meal then defecates
• Parasites in faeces, enter wound
• Eyes are a common point of entry
• Can also be transmitted congenitally and via blood
transfusion/transplants
• Parasites migrate to cardiac muscle, liver brain invade
cells to replicate which results in cell destruction
• A number of animal reservoirs
• Affect South and Central America, some cases in North
America
• Associated with poverty and found primarily in rural
areas
• Major cause of heart disease in Latin America
Symptoms
• Infections can be
– Asymptomatic
– Acute
– Chronic
• Initial symptoms, development of lesion at site of bite,
development of rash and swelling
• acute infection
– fever
– chills
– myalgia
– fatigue
• Chronic infection
– parasites replicate in liver heart brain etc causing massive tissue
damage
• Reactivation if immunocompromised can result in high
mortality rate e.g. AIDS, chemotherapy etc
Diagnosis and treatment
• Serological tests available (IgG antibodies used to diagnose
chronic infection)
• Microscopic examination of blood, blood smears stained
with Giemsa, for visualization of parasites during acute
infection.
• Limited number of available drugs
• drugs often have a large number of side effects usually
effective when given during the acute phase of infection but
may be helpful for chronic phase as well.
• Nifurtimox only useful against acute phase
• Allopurinol and benzimidazole useful against tissue
parasites
• Controlling animal reservoirs and vector essential
• Possible vaccine??
Revision questions
• Explain the differences in the lifecycles of
T. brucei and T. cruzi.
• Discuss the different infections caused by
Leishmania parasites.
Directed learning
• What is the current status of these
diseases in Sri Lanka? Please do some
research and spend some time making
notes to supplement your lecture slides.
Suggested reading materials
• Leishmania
– http://onlinelibrary.wiley.com/doi/10.1038/npg.els.000
3824/full
– http://onlinelibrary.wiley.com/doi/10.1038/npg.els.000
4265/full
• Trypanosomiasis
– http://onlinelibrary.wiley.com/doi/10.1038/npg.els.000
4287/full
