Chapter 5 - Subphylum
Kinetoplasta
Trypanosomes and their kin
Taxonomy of Protozoans from
Chapter 5
Phylum Euglenozoa
Subphylum Kinetoplasta (formerly an Order)
Class Trypanosomatidea
Order Trypanosomatida
Family Trypanosomatidae
Genera: Trypanosoma, Leishmania
Subphylum Kinetoplasta
• Members of this groups
are characterized by the
presence of a kinetoplast
• The kinetoplast lies
beside the kinetosome
(sometimes called the
basal body or
centriole) at the base
of the flagellum
The KinetoplastMitochondrion
• Leishmania and other
trypanosomatids have a single
mitochondrion that contains a
large mass of mitochondrial DNA
known as kinetoplast DNA.
• The kDNA consists of a giant
network of catenated minicircles
and maxicircles. There are
approximately 10,000 minicircles
and 50 maxicircles per network.
• This is one of the most unusual
DNA structures in nature.
Family Trypanosomatidae
• Typically referred to as the hemoflagellates
• Single nucleus; elongate with a protruding
flagellum or more rounded with a
nonprotruding flagellum
• 8 body types (we will study 4 major ones)
– They vary in size, body shape, location of the flagellum,
location of the kinetoplast, and other structures
Types of Trypanosomatids
1. Promastigote - elongated form
with antenuclear kinetoplast;
flagellum arising near it and
emerging from the anterior end
of body; e.g. Leptomonas
2. Epimastigote - elongated
form with a juxtanuclear
kinetoplast; flagellum arising
near it and emerging from the
side of the body to run along
short undulating membrane; e.g.
Blastocrithidia and some
Trypanosoma
Types of Trypanosomatids con’t
3. Trypomastigote - the “true”
trypanosome type; postnuclear
kinetosplast; flagellum arising
near it to run along a long
undulating membrane
4. Amastigote - rounded or oval
forms devoid of external
flagellum; e.g. Leishmania
Genus Trypanosoma
• Life cycle usually includes both an invertebrate and a vertebrate host
(=heteroxenous life cycle)
• Usually found in the blood and tissue fluids of vertebrate hosts; but, some
of the more popular pathogenic forms (e.g. T. cruzi) occur intracellularly
• They typically occur in the digestive tracts of invertebrates, especially
arthropods
• Divided into 2 main groups or “sections”:
– Salivaria - develop in the anterior part of the digestive tract of insect vector
(=anterior station); infect new hosts as a consequence of insect biting
– Stercoraria - develop in the hindgut of insect vector (=posterior station);
leave insects with the feces and infect new hosts through the skin or mucous
membranes or by lesions made by vector bites
Section Salivaria, Type Example:
Trypanosoma brucei
• Widely distributed throughout Africa
especially between latitude 15oN and 25o S;
strongly dictated by the distribution of the
insect vectors (e.g. tsetse flies of the genus
Glossina)
• T. brucei brucei is primarily a parasite of
native ruminants such as antelopes; also occurs
in a variety of livestock (e.g. sheep, goats,
horses, mules, donkeys, and camels)
• It is extremely pathogenic to these animals and
causes the disease known as nagana; humans
are not susceptible
• The vectors for T. brucei are tsetse flies
Section Salivaria con’t
T. b. gambiense and T. b. rhodesiense cause African Sleeping
Sickness
• T. b. gambiense is endemic to west and central portions of Africa
• It causes a chronic form of sleeping sickness
• Vectors include: Glossina palpalis and G. tachinoides
• T. b. rhodesiense occurs in central and east central Africa
• It causes a more acute form of sleeping sickness
• Vectors are the same species of tsetse flies used by T. brucei:
G. morsitans, G. pallidipes and G. swynnertoni)
Generalized Life Cycle
• The life cycle of T. b.
brucei is highly
polymorphic in its
vertebrate host
Generalized Life Cycle
1. Infected tsetse fly takes a blood meal, injecting metacyclic trypomastigotes
into its host
2. Metacyclic trypomastigotes transform into slender trypomastigotes,
3. These forms
multiply and spread
rapidly within the
host, eventually
migrating to the
cerebralspinal fluid
Generalized Life Cycle cont.
4. and 5. Trypomastigotes are ingested by the tsetse flies when they take another
blood meal from an infected mammalian host
6. These transform into procyclic trypomastigotes in the insect’s midgut; here they
undergo asexual reproduction
7. Procyclic forms migrate forward to the foregut and transform into epimastigotes
8. Epimastigotes
undergo several
generations of
asexual reproduction
in the salivary glands
and eventually
transform into
metacyclic
trypomastigotes; the
infective stage in
vertebrates hosts
Pathogenesis
• T. brucei primarily invade the blood, lymph, and spinal fluid
• The course of T. brucei infections depend on the susceptibility of the
animals involved
• Horses, mules, and even dogs are acute sufferers and can die within 2
weeks of infection
• Symptoms of the infection include: anemia, edema and fever
• Cattle suffer the same kinds of symptoms but often live a few extra
months
• Pigs can recover from the infection
Pathogenesis cont.
• In humans, T. b. gambiense causes the Gambian or slow,
chronic form of sleeping sickness
• It primarily invades the blood, nervous, and lymphatic system;
may also be an invasion of the dermis with the production of
chancre soars
• 1-2 week incubation period followed by fever, chills, headache,
and loss of appetite
• Later invasion and enlargement of the spleen, liver, and lymph
nodes
• Invasion of nervous system and organs leads to weakness,
anemia, apathy, headache, disturbed vision, etc.
• Coma, emaciation and death complete the course of the disease,
which may last for several years
Pathogenesis cont.
• T. b. rhodesiense causes the Rhodesian or quick, acute form of
human sleeping sickness; usually results in death within a year
• Rhodesian trypanosomiasis rarely, if ever, causes the symptoms
normally associated with sleeping sickness
• Compared with Gambian sleeping sickness, there is less invasion
of the CNS, but the lymph nodes become swollen and congested
• The effects on the cardiac system are more severe
Immunology
• Infections are often highly variable for the life of the organism,
attributable to the ability of these parasites to change the
chemical composition of their surface coat (glycocalyx)
• They produce a parade of successive variant antigenic types
(VATs) in the vertebrate host
• There is a period of remission during which the host produces
antibodies that are capable of destroying the parasite
• However, the parasite counters this by producing a new
surface glycoprotein for which the host has not yet developed
antibodies
• Once this is accomplished the parasite can begin to multiply
rapidly
Immunology cont.
VAT Life
Cycle of T.
brucei
Immunology cont.
• The clinical course of the infection is characterized by an increase in trypanosome
numbers, followed by a crash or sudden decrease in the population which is repeated
over a number of cycles.
• Again, remission coincides with an increase in host protective antibody against
specific surface expressed antigens on the trypanosome, located in the surface coat or
glycocalyx. The cyclic nature appears to occur due to an almost endless change in
the Variant Antigen Type (VAT).
Diagnosis
• Diagnosis of African Sleeping Sickness
is a multi-step procedure:
– Step 1. Clinical assessment: telltale
neurological signs and/or mental
dullness accompanied by enlarged
and sensitive cervical lymph nodes
- Winterbottom’ sign
– Step 2. Examination of blood
smears, marrow, or cerebralspinal
fluid for trypomastigotes
– Step 3. Test for specific antibodies
in the blood
Winternbottom’s sign
Treatment
•
•
•
•
Trypan blue and trypan red
Suramin sodium
Melarsoprol
Difluoromethylornithine
Section Stercoraria, Type
Example: Trypanosoma cruzi
• T. cruzi is the causative agent of Chagas’
disease
• T. cruzi infections are prevalent
throughout South America and Latin
America, affecting an estimated 12-19
million people
Life Cycle
• Reduvid bug takes a blood meal and releases trypomastigotes in its feces
near the site of the bite wound. Trypomastigotes enter the host through the
wound or through intact mucosal membranes, such as the conjunctiva .
• Inside the host, the trypomastigotes invade cells, where they differentiate
into intracellular amastigotes
• Amastigotes undergo
asexual reproduction and
differentiate into
trypomastigotes, and then are
released into the circulation
as trypomastigotes
• Trypomastigotes infect
cells from a variety of tissues
and transform into
intracellular amastigotes in
new infection sites.
Life Cycle cont.
• The “kissing” bug becomes infected by feeding on human or animal blood that
contains circulating parasites .
• The ingested trypomastigotes transform into epimastigotes in the vector’s midgut
• The parasites multiply and differentiate in the midgut and differentiate into
infective metacyclic trypomastigotes in the hindgut .
Pathology
• Upon introduction into the human, the parasites
invade cells of the subcutaneous tissue at the site
of the infection, causing an acute inflammatory
reaction or swelling often called a chagoma
• When they enter through the conjunctiva of the
eye, they cause a unilateral edema of the eyelid
and conjunctivitis, a syndrome known as
Romana’s sign
Romana’s sign
• In acute cases, about 1-3 weeks after infection, fever, headache, malaise and
prostration may develop
• Chronic symptoms include: dysfunction of the peripheral and CNS,
myocardial damage, and gastrointestinal problems
Diagnosis
• Examination of fresh blood
within the first month or two
following infection may reveal
T. cruzi trypomastigotes
• Direct agglutination tests with the IgM
serum fraction
• Xenodiagnosis
Genus Leishmania: Life Cycle
• Upon biting a host, the
sand fly (G.
Phlebotomus) vector,
ingests amastigotes
from infected host
• These migrate to the
hindgut and transform
to promastigotes, which
undergo asexual
reproduction
Phlebotomus sp.
Genus Leishmania: Life Cycle cont.
• Promastigotes migrate
forward to the esophagus and
are inoculated into a new host
when vector bites another
victim
• Inoculated promastigotes are
ingested by macrophages and
then undergo transformation to
become amastigotes
• Following asexual
reproduction, infected host
cells rupture and a large
number of amastigotes are
released
• These are engulfed by other
phagocytic cells, spreading the
infection
Leishmania tropica and L. major
• L. tropica and L. major are responsible for what is called cutaneous
leishmaniasis, cutaneous ulcers commonly referred to as oriental sores
• Endemic to west-central Africa, the Middle East, and into India; also been
reported from countries in SA
• Found primarily in macrophages around cutaneous sores
• Sand flies must feed at these sites in order to acquire the infective
amastigotes
Pathogenesis
• In humans, the initial sign of the infection is the appearance of a vascularized
papulae or nodule on the skin at the feeding site of the insect
• The papulae become ulcerated after a few weeks, erupt, and spread forming
cutaneous lesions ,most commonly on the hands, feet, legs and face
• Two types of oriental sores are produced by these parasites
– L. tropica: urban type; dry lesions, chronic, numerous amastigotes
– L. major: rural type, acute, few amastigotes
Cutaneous leishmaniasis
Leishmania donovani
• L. donovani is the causative agent for visceral leishmaniasis,
also known as dum-dum fever or kala-azar, an often fatal
disease of humans
• In the mammalian host, amastigote-infected cells can be found
in many sites, e.g. spleen, liver, bone marrow, lymph glands, and
intestinal mucosa
Amastigote in bone marrow cells
Epidemiology
• Visceral leishmaniasis has a wide geographic distribution.
– North-Eastern China, India, Middle-East, Southern Europe
(Mediterranean bassin),
– Northern Africa, Central-East Africa and, in foci, Central and South
America
Pathogenesis
• The disease typically starts off slowly with
fever, chills, and general anemia
• Since leishmaniasis is primarily a disease of the
reticulo-endothelial system, replacement of
infected cells produces hyperplasia and
consequent enlargement of the visceral organs
associated with the system (e.g., spleen and
liver)
• A concomitant decrease in RBC and WBC
production results in anemia and leukopenia,
facilitating secondary bacterial infection
Symptoms of visceral leishmaniasis
• In areas of India, a post-kala-azar dermal
leishmanoid may develop in which numerous
parasite-laden nodules appear in the skin
Post-kala-azar dermal leishmaniasis