Unit 2: Protozoa
18
Lecture 8+9+10+11 – Subphylum
Mastigophora (Flagellates of blood
and tissues "Hemoflagellates")
The hemoflagellates of human include the genera
Trypanosoma and Leishmania.
1) All these organisms require 2 hosts in their life cycle.
Man or other mammals on the one hand and blood
sucking insect (intermediate host) on the other.
2) They live in the blood and tissue of man and other
vertebrate hosts, and in the gut of the insect vector.
3) Multiplication in both vertebrate and invertebrate hosts is
by binary fission.
4) They exist in two or more of the four developmental
forms or stages.
Hemoflagellates have 4 developmental forms:
1) Round intracellular stage called amastigote
(Leishmania)(Fig. 1). The amastigote is spherical or
subspherical, it lives and reproduces by longitudinal
binary fission in macrophage of skin, mucosa, lymph
node and RES.In preparation stained with Giemsa´s or
Wright's stain the cytoplasm is pale blue and the large
nucleus is red stain. In their cytoplasm in the median line
of the cell, there is a deep red rod like structure called
kinetoplast; a delicate filament called axoneme extends
from near the kinetoplast to the cell membrane.
Figure 1: Amastigote
2) Flagellated extracellular stage called promastigote
(leptomonas) .It is is the basic of the hemoflagelate.It is
pyriform without an undulating membrane with a
kinetoplast at the anterior end. A free flagellum near the
anterior end of the cell. There is no undulating membrane
(Figure 2).
Figure 2 Promastigote
3) Epimastigote (crithidia). Elongated extracellular stage
with kinetoplast placed more posteriorly close to and in
front of the nucleus. The flagellum runs alongside the
body as short undulating membrane before emerging from
the anterior end (Figure 3).
Figure 3: Epimastigote
4) Trypomastigote (trypanosoma) .The cell is elongated;
spindle shaped with a central nucleus and the kinetoplast
posterior to the nucleus situated at the posterior end of the
body .There is a long undulating membrane and a free
flagellum (Figure 4).
Figure 4: Trypomastigote
Unit 2: Protozoa
19
Leishmania
The genus Leishmania has been named after Sir William
Leishman, who discovered the species (Leishmania
donovani) that cause kala-azar.
Genus Leishmania are parasites of man, dog, gerbil, and
other rodents which represent the definitive hosts whereas
blood sucking sandfly of the genus Phlebotomus ( female
only) serve as intermediate hosts or vectors which
transmit the parasite from one mammalian host to another.
In man and reservoir host (dogs, rodent) , the organism in
the amastigote form is a parasites of macrophage cells
which multiply by binary fission and cause death of the
host cells.
Morphology:
The leishmania of man have been grouped into 3 species.
1) Leishmania tropica complex cause old world
cutaneous leishmaniasis.
2) Leishmania braziliensis complex and Leishmania
mexicana complex cause new world cutaneous and
mucocutaneous leishmaniasis.
3) Leishmania donovani complex cause visceral
leishmaniasis.
These species are morphologically similar but they
differ clinically, epidemiologically, immunologically
and biochemistry.
Life cycle (Figure 5)
2 stages in the life cycle are known:
1) Promastigote stage in sandfly and culture.
2) Amastigote in mammals and reservoir animal.
I. When a sandfly bite an infected person or reservoir host, it
sucks up parasitized macrophage or temporarily free
amastigote in the blood,
Midgut of the fly flagellated promastigote and after
rapid multiplication infective promastigote and
migrate forword. From the foregut they are regurgitated or
otherwise introduced into the skin of the next individual
when the sandfly takes another blood meal.
II. When a sand fly bites another healthy persons, the fly
inject the promastigote into the skin, the promastigote
rapidly changed to amastigote after phagocytosis by
macrophage, amastigote multiply filling the cytoplasm of
macrophage. The infected cells burst, the released
parasites are again phagocytosed and the process is
repeated. Cutaneous or visceral leishmaniasis depending
upon the species of the parasites and the host response.
Figure 5: life cycle of leishmania (Cutaneous and
Visceral)
Blepharoplast: A basal body in certain flagellated
protozoans that consists of a minute mass of chromatin
embedded in the cytoplasm at the base of the flagellum.
parabasal body, a cytoplasmic body of varying
appearance, structure, and function closely associated
with the nucleus, kinetoplast, and basal body in certain
parasitic flagellate protozoa- it is usually connected to the
basal body by a fibril or thread, which together are known
as the parabasal apparatus. More than one such structure
may be present in each organism. Some authorities
consider the parabasal body to be the Golgi complex of
these cells.
Unit 2: Protozoa
20
Leishmaniasis
A group of diseases caused by protozoa of the genus
Leishmania.
Leiahmaniasis classified into:
1) Cutaneous leishmaniasis.
2) Mucocutaneous leishmaniasis.
3) Visceral leishmaniasis.
1) Cutaneous leishmaniasis
Is classified into:
a) Old world cutaneous leishmaniasis (oriental sore, Delhi
boil)
b) New world cutaneous leishmaniasis.
The insect (vector) is a sandfly called phlebotomus
sandfly in old world cutaneous leishmaniasis and
lutzomyia for new world cutaneous leishmaniasis.
a) Old world cutaneous leishmaniasis.
1) Leishmania tropica minor (dry or urban cutaneous
leishmaniasis, oriental sore, Aleppo button, Jericho boil,
Delhi boil, Baghdad boil).It is anthroponotic disease
transmitted from human to human. L.tropica may
become viscerotropic.
2) Leishmania tropica major (rural or wet cutaneous
leishmaniasis).It is zoonotic disease.
3) Leishmania aethiopica (cutaneous and diffuse or
disseminated cutaneous leishmaniasis of Ethiopia, anergic
cutaneous leishmaniasis).
Incubation periods 2 weeks – 3 years
In Leishmania tropica and Leishmania aethiopica as log
as 3 years.
In Leishmania major 2 weeks.
Life cycle: As in figure 5.
Clinical features and pathogenesis(Leishmania tropica
and Leishmania major):
The lesion occur at the dermis at the site of the
inoculation of the promastigote.Mucous membrane are
rarely involved.
The lesion appears first as macule, then papule with
slightly raised center covered by a thin blister like layer of
epidermis.
The lesion then breaks down with discharge of a small
amount of clear or purulent exudate. At the ulcer crater
like base in the dermis, a granulation layer is formed and
the margin becomes indurated by infiltration of fibroblast.
In the dry type , the disease is chronic ,occurs in the
urban area , single lesion ,face is affected ,the ulceration is
slow and may not occur with little surrounding tissue
reaction ,the healing may take > 1 year, human is the only
reservoir.
In the wet type, the disease is acute, occurs in the rural
area, lower limb is affected, the ulceration is multiple and
prone to early ulceration with high degree of surrounding
tissue reaction and liable for secondary bacterial infection,
the healing may take 3-6 months, gerbils and other rodent
are the main reservoir.
Leishmania aethiopica
Cause cutaneous and diffuse or disseminated cutanous
leishmaniasis of aethiopia or called anergic cutaneous
leishmaniasis.
It occurs in the highlands of Ethiopia, in Kenya, and
possibly Yemen.
Morphologically it is indistinguishable from Leishmania
tropica.
The animal reservoirs are species of hyrax.
It cause disseminated leishmaniasis because of deficient
cell mediated immunity due to some characteristic of the
parasites itself.
The patient is not anergic to other infective agent, react
normally to, tuberculin skin test and have normal IgG
level but negative leishmanin skin test.
Clinically, three types have been described (lepromatoid,
intermediate and tuberculoid).
b) New world cutaneous leishmaniasis
(American cutaneous leishmaniasis).
They are caused by Leishmania mexicana complex and
Leishmania braziliensis complex. The American strains of
leishmania causing cutaneous leishmaniasis differ in their
tendency to involve the mucous membrane of the mouth
and nasopharynx by extension or metastasis.
Leishmania mexicana complex
1) Leishmania mexicana mexicana, found in Mexico,
Guatemala and Belize. It cause chiclero ulcer or bay sore
(name is derived from high occurance of the infection in
chicle collectrors) which affect the face, ears and does not
spread to the nasopharynx. The disease is mild and self-
limiting consisting of single papule, nodule or ulcer.
Unit 2: Protozoa
21
2) Leishmania mexicana amazonensis cause cutaneous
lesion with no nasopharyngeal involvement. It occurs in
Amazon basin.
3) Leishmania mexicana pifanoi cause disseminated
cutaneous disease in Venezuela.
Leishmania braziliensis complex:
1) Leishmania braziliensis guyanensis in Guiana,
Venezuela and Brazil.
2) Leishmania braziliensis panamensis in panama and
Colombia.
3) Leishmania braziliensis peruviana which cause uta
(resemble oriental sore) without nasopharyngeal
involvement.
2) Mucocutaneous leishmaniasis
It is caused primarily by Leishmania braziliensis which
cause Espundia start as papule at the site of bite and then
metastatic lesion forms, usually at the mucocutaneous
junction of the nose and mouth leading to disfiguring
granulomatous ulcerating lesion destroying the nasal
cartilage but not adjacent bone. Death occurs from
secondary bacterial infection.
Immunity to cutaneous leishmaniasis:
Host recovery in cutanous leishmaniasis depends on the
development of cell mediated immunity.
The usual cutaneous lesion heals spontaneously.
In certain instances, healing does not occur; these cases
may represent the 2 poles of the spectrum of response.
The first spectrum is the anergy as in leishmania
aethiopica.
The second spectrum represent the hypersensitivity
reaction in which the patient is capable for excellent Ab
and cellular responses but cannot completely eliminate the
parasites , so as the central lesion heals, active peripheral
ones continue to form . This stage is called leishmaniasis
recidiva or lupoid leishmaniasis (in Leishmamnia
tropica).
Diagnosis:
1) Specimens: Lymph node aspirate, scrapings and biopsies
from the margin of the lesion. The center of purulent
discharge is of no value.
2) Microscopic examination: The specimen smeared onto a
clean glass slide, the slide stained with Giemsa´s stain for
demonstration of amastigote within the macrophage or
spread out from ruptured cells.
3) Culture in NNN (Novy-MacNeal-Nicolle) medium or
inoculation in hamster.
4) Leishmanin skin test (The test done by i.d injection of a
suspension of killed promastigote) is positive in high % of
L.tropica and >95% of L.braziliensis.It is positive in
patient with active, healed or cured lesions and negative
in anergic persons (in diffuse leishmaniasis).False positive
seen in patient with tuberculosis, leprosy and mycosis.
Treatment:
1) Small lesion:
1. Freezing with liquid CO2 (cryotherapy).
2. Curettage
3. Infiltration with 1-2 ml of Na stibogluconate (pentostam) ®.
2) Drug therapy:
1. Na stibogluconate (pentostam) ®.
For multiple lesions or in disfiguring site.
The dose given i.m or i.v 20 mg /kg body weight for 20
days, repeated 10 days interval in resistant cases for
maximum 3 courses.
It acts by inhibition of the glycolytic enzyme and fatty
acid oxidation in leishmanial amastigote.
Na stibogluconate (pentostam) ® used for the treatment of
all form of cutaneous leishmaniasis except leishmania
aethiopica which respond to pentamidine.
2. Oral ketocanazole used daily for 4-8 weeks in treatment
of long standing cutaneous leishmaniasis.
3. Amphotericin B in cases not responding to pentostam.
4. Iraconazole in India to treat cutaneous leishmaniasis.
5. Clotrimazole 1% cream in Saudi Arabia.
6. Oral dapsone.
7. Intradermal injection of gamma interferon around the
lesion caused by L.tropica and L.guyanensis.This will
promote healing of ulcer.
8. Combined vaccine (heat killed L.amazonensis+viable
BCG) in treatment of American cutaneous leishmaniasis.
3)
Steroid
for treatment of leishmaniasis recidiva.
Epidemiology:
Cutaneous leishmaniasis is found around the
Mediterranean littoral, throughout Middle East and central
Asia as far as Pakistan and in Sub-Saharan West Africa
and Sudan.
Vaccination is practiced in certain areas by inoculating
serum from naturally acquired lesion into an
inconspicuous location on the body of a non-immune
person.
Unit 2: Protozoa
22
3) Visceral leishmaniasis
It is caused by at least three species belonging to the
Leishmania donovani complex with different geographical
distribution. The three species are (Leishmania donovani,
Leishmania infantum, Leishmania chagasi).
The causative agent is a parasites of the RES not confined
to the mucous membrane and subcutaneous tissue but
throughout the body.
a) Leishmania donovani.
occur in India, east Pakistan, Sumatra, Thailand, and the
central Africa, Chad, Ethiopia, Somali republic, Djibouti,
Kenya, Sudan , Gabon, Gambia and Niger .
It affects all age group.
Human is the only reservoir in India.
Various rodents in Sudan.
Dogs in china.
The vector is phlebotomus.
b) Leishmania infantum.
It is found along the whole Mediterranean littoral, near
east and Africa.
It occurs in children.
Human is an accidental host.
Dogs are the Reservoir.
The vector is phlebotomus.
c) Leishmania chagasi.
In central and South America.
Infect children.
Foxes, domestic dogs and cats are naturally infected.
The vector is lutzomyia.
Life cycle and pathogenesis:
Leishmania donovani has a predilection for the
reticulendothelial cells of the spleen, liver, bone marrow,
and visceral lymph node and as the promastigote stage of
the parasite introduced into the outer dermis by an
infected sandfly, the promastigote rapidly changed to
amastigote after phagocytosis by macrophage, amastigote
multiply filling the cytoplasm of macrophage. The
infected cells burst, after colonization in the dermis which
is in apparent, some of the organisms gain access to the
blood stream or lymphatics and are transported to the
viscera where lodge in fixed tissue macrophage and
rapidly multiply.
As the number of amastigote increase, those lead to
intense phagocytic activity and a remarkable increase in
the number of macrophage, increasing neutropenia, and
anemia.
The decrease in the bone marrow activity + cellular
destruction in the spleen , this lead to anemia, leukopenia
and thrombocytopenia leading to secondary bacterial
infection and bleeding tendency.
Spleen is enlarged due to a combination of proliferating
macrophage and sequestered blood cells.
Liver is enlarged.
Tonsils and lymph nodes are involved.
In fatal cases, the dermis contains large amounts of
amastigote inside the macrophage.
Note: In dogs, conspicuous lesions are on the skin,
cutaneous leishmaniasis due to infection with L.tpropica
and kala-azar caused by L.donovani are difficult to
distinguish.
Clinical features:
Incubation period = 10 days – many months.
The onset may be insidious (which is the usual) or acute.
In the insidious onset , the symptom begin with
intermittent fever (36.7-42C°) with 2 peaks daily ,
weakness , weight loss, massive enlargement of the spleen
, hyperpigmentation of the skins is seen in light skinned
patient ( kala-azar means black sickness) ,abdomen is
protuberant.
The course of the disease runs for months - years, initially
the patients feel well despite the fever. As the anemia,
leucopenia and thrombocytopenia increase, this lead to
weakness, infection, bleeding from the gums, lips, nares,
and the GIT. Untreated cases are fatal due to secondary
infection.
Complications:
1) Diarrhea or dysentery.
2) Bronchopneumonia.
3) Cancrum oris (gangrene of the oral cavity) less
frequently.
Unit 2: Protozoa
23
Dermal leishmaniasis:
Post kala-azar dermal leishmaniasis, present first as
hypopigmented or erythematous macules on any part of
the body or as nodular eruption especially on the face.
The organism may be present in the lesion. It is a delayed
hypersensitivity to parasite antigen and is interpreted as
an indication of inadequate treatment with residuance of
parasites that continue to propagate.
Diagnosis:
1) Nonspecific tests. Pancytopenia, reversed
Albumin/Globulin ratio.
2) Specimens. Bone marrow, spleen and lymph node
biopsies for detection of intracellular amasatigote (L-D
bodies).Splenic aspirates are the most sensitive method
for the diagnosis.
3) Culture in NNN (Novy-MacNeal-Nicolle) medium.
Note: The diagnosis is established by visualization of
amastigotes in smear, biopsies, or by growth of
promastigote in culture.
4) Serological tests: for detection of antigen or antibody.e.g.
I) indirect fluorescent Antibody test (IFAT).
II) Enzyme Linked Immunosorbant Assay (ELISA).
III) Direct agglutination test (DAT).
IV) Immunochromatographic K39 strip test
{Recombinant leishmanial antigens or synthetic
peptides (rK39)} (dipstick test).
The recombinant antigen is a 39 amino acid (rK39) cloned
from the C-terminus of the kinesin protein of Leishmania
species that cause visceral infecction. This test is used to
detect antibodies against K39 antigen in patient with
visceral leishmaniasis.
The sensitivity of the test is 100% and the specificity is
97%.
The test is simple, rapid (10 minutes), inexpensive,
requires no other reagents or instruments that can be
performed in the field by the paramedics.
These tests (serological) remain positive for several
months after cure has been achieved, so don’t predict
response to treatment or relapse.
5) Napier's Aldehyde test. One ml of the patient´s serum
mixed well with a drop of 40% formalin, shaken and kept
at room temperature.
A positive reaction is gellification and opacification of the
serum appearing in 2-20 minutes. This test is based on the
principle that a patient with visceral leishmaniasis has a
high concentration of IgG (hypergammaglobulinemia)
.This test is not diagnostic as other diseases cause also
hypergammaglobulinemia e.g. Multiple myloma, cirrhosis
of the liver and Schistosomiasis.
6) Leishmanin skin test is negative in the acute disease but
positive 2 months after recovery.
7) Polymerase chain reaction (PCR).
Treatment:
A. Pentavalent antimonial or pentavalent antimony
compounds (abbreviation: pentavalent Sb or Sbˇ), they
include:
1) Na stibogluconate (pentostam)® given by slow I.V infusion
2) Meglumine antimonite (Gliucantim) ® by I.M injection.
- Na stibogluconate for 28 days is the drug of choice.
B. B)Diamidines:Sudanese infections are generally
resistant to antimonials, and treatment, should be initiated
with pentamidine® at the rate of 2 to 4 mg /kg body
weight i.m for 10 – 15 days.
C. Amphotericin B can be used.
D. Allopurinol can be used in the treatment of visceral
leishmaniasis in patient with AIDS.
E. Antimony and Gamma interferon can be used
F. Miltefosine .It is antineoplastic and used as
antiprotozoal.It is used in the treatment of cutaneous and
visceral leishmaniasis in India, Colombia.
Immunity:
Lifelong immunity.
Massive polyclonal hypergammaglobulinemia with little
evidence of cell mediated immunity is the role in visceral
leishmaniasis. The elevated immunoglobulin level
diminishes rapidly when treatment begins.
Epidemiology:
Kala-azar is endemic in northern china, eastern india,
Afghanistan and Turkestan, Sudan, many foci around the
Mediterranean sea, Ethiopia, the east and west coasts of
Africa, Paraguay, Bolivia, northern Argentina, eastern
Brazil, and minor foci elsewhere in South and Central
America.
In most of these areas, the infection is endemic or
hyperendimic but on occasion it may become epidemic.
Control and prevention.
1) Destroying the stray dogs.
2) Using an insecticide.
3) Mosquitoes net.
4) Insect repellent cream.
5) Treatment of infective patient.
Unit 2: Protozoa
24
Trypanosoma
The hemoflagellates of the genus trypanosoma occur in
the blood of mammals as mature elongated
trypomastigote.
The trypomastigote is an Elongated bodies supporting a
longitudinal lateral undulating membrane and a flagellum
that borders the free edge of the membrane and emerge at
the anterior end as a whip like extension. The kinetoplast
is a darkly staining body lying in the posterior end of the
body immediately adjacent to tiny node (blepharoplast)
from which the flagellum arise, this form called
trypomastigote (Figure 1).
Figure 1: Trypomastigote
The forms that are seen in the vectors are called
epimastigote (crithidia)
Elongated extracellular stage with short undulating
membrane and a kinetoplast placed posteriorly in the
anterior end near the nucleus, this form called
epimastigote (Figure 2)
(Figure 2: Epimastigote)
Some species of trypanosomes apparently lives in their
natural vertebrate hosts without causing evident disease,
other cause variable degree of tissue pathology.
Three species of trypanosomes that commonly parasitize
man are all pathogenic and not infrequently cause death.
The three species are:
1) Trypanosoma brucei rhodesiense.
2) Trypanosoma brucei gambiense.
3) Trypanosoma cruzi.
Trypanosoma brucei brucie, Trypanosoma brucei
rhodesiense, Trypanosoma brucei gambiense and
Trypanosoma rangeli are called salivarian trypanosomes
because the forms of parasite that are infective for the
mammalian host develop in the saliva.
Trypanosoma cruzi differ in two aspects:
1) It is leishmania like in having dividing amastigote tissue
forms.
2) The infective stage develops in the hindgut of the vector
and emerges from the intestine (posterior station) in the
feces and this is called stercorian trypanosome.
Trypanosoma cruzi (Schizotrypanum)
Disease: chagas´ disease or American trypanosomiasis.
Life cycle (Figure 3):
Reservoirs are domestic cats, dogs and wild species such
as armadillo, raccoon, and rats.
Two main stages of Trypanosoma cruzi are found in
mammalian host, amastigote and trypomastigote, while
epimastigote (crithidial) and trypomastigote are found in
triatomine bug.
The reduviid bugs ingest trypomastigotes in the blood of
the reservoir hosts. In the insect gut, they multiply and
differentiate first into epimastigotes and then into
trypomastigote.
When the bug bites again, the site is contaminated with
feces containing metacyclic trypomastigotes, which enter
the blood of the host (or reservoir) through the bite wound
or intact mucous membrane (conjunctiva, mouth). The
parasites are engulfed by macrophages and become
amastigotes. After 4 or 5 days of multiplication by binary
fission, amastigotes again become trypomastigotes,
disrupt the cell, and enter the blood stream and other
tissues where the cycle continues as long as the host lives.
Many cells are affected, but myocardial, glial, and
reticuloendothelial cells are the most frequent sites.
To complete the cycles, amastigotes differentiate into
trypomastigotes, which enter the blood and are taken up
again by the reduviid bug.
In tissues the accumulation of multiplying parasites
produces pseudocysts; the amastigote are
Unit 2: Protozoa
25
indistinguishable from those of L.donovani but in
L.donovani, it invades only macrophages whereas in
T.cruzi, amastigote invades the cells of any tissue.
Other less frequent modes of human infection are by
blood transfusion and by congenital or transmammary
transmission, organ transplantation, rarely by eating food
contaminated with infective bug feces or by ingestion of
infected meat. Accidental laboratory infections have been
reported.
Infective stage = Metacyclic trypomastigote.
Pathogenesis:
The amastigote can kill cells and cause inflammation,
consisting mainly of mononuclear cells. Cardiac muscle is
the most frequently and severely affected tissue. Neuronal
damage leads to cardiac arrhythmias and loss of tone in
the colon (megacolon) and esophagus (megaesophagous).
During the acute phase, there are both trypomastigote in
the blood and amastigote intracellularly in the tissue .In
the chronic phase, the organism persist in the amastigote
form.
Clinical features:
Incubation period = 5-12 days
The disease is seen most commonly, and in its severe
form, in children younger than 5 years, in whom CNS
symptoms predominate, while in older children and
adults, the disease may be mild, subacute or chronic.
The first signs of acute Chagas´ disease develop at least 1
week after invasion by the parasites. When the organisms
enter through a break in the skin, an indurated area of
erythema and swelling (the chagoma), accompanied by
local lymphadenopathy, may appear.
Romana’s sign—the classic finding in acute Chagas´
disease, which consists of unilateral painless edema of the
palpebrae and periocular tissues—can result when the
conjunctiva is the portal of entry.
These initial local signs may be followed by malaise,
fever, anorexia, and edema of the face and lower
extremities. A morbilliform rash may also appear.
Generalized lymphadenopathy and hepatosplenomegaly
may develop. Severe myocarditis develops rarely; most
deaths in acute Chagas disease are due to heart failure.
Neurologic signs are not common, but
meningoencephalitis occurs occasionally. The acute
symptoms resolve spontaneously in virtually all patients,
who then enter the asymptomatic or indeterminate phase
of chronic T.cruzi infection
Symptomatic chronic Chagas´ disease becomes
apparent years or even decades after the initial infection.
The most commonly involved is the heart, also dilatation
of hollow viscera (megaesophagus, megacolon and
megaureter).
Death from chronic chagas´ disease is usually due to
cardiac arrhythmias and failure.
Laboratory diagnosis:
1) Acute disease
a. Wet blood preparation for motile organisms
b. Thick and thin blood film for demonstration of C-
shaped trypomastigote.
c. Culture in NNN medium
d. Muscle biopsy for amastigote
e. Polymerase chain reaction (PCR) when repeated
attempts to visualize the organisms are unsuccessful
2) Chronic Chagas´ disease
It is difficult because few trypomastigote in the blood
It is diagnosed by the detection of specific antibodies that
bind to T. cruzi antigens (serology) and by xenodiagnosis.
a) Serological test.
a) ELISA
b) Indirect fluorescent – antibody test
c) Indirect haemagglutination and
d) Complement fixation test.
b) Xenodiagnosis for chronics disease which consists of
allowing an uninfected, laboratory – raised reduviid bug
to feed on the patient and, after several weeks, examining
the intestinal contents of the bug for the organism.
Treatment:
The drug of choice for the acute form is nifurtimox, kills
the trypomastigote.
Benznidazole is an alternative drug.
No drug for chronic disease.
Unit 2: Protozoa
26
Trypanosoma gambiense and
Trypanosoma rhodesiense.
Disease:
They cause sleeping sickness (African trypanosomiasis).
Trypanosoma gambiense (Gambian or West African
sleeping sickness).
Trypanosoma rhodesiense (Rhodesian or East African
sleeping sickness).
Trypanosoma rhodesiense
(Rhodesian or East African sleeping sickness)
Life cycle (Figure 1)
The vector for both is the tsetse fly, but different species
of fly are involved.
Humans are the reservoir for Trypanosoma gambiense,
whereas Trypanosoma rhodesiense has reservoirs in
both domestic animals (especially cattle) and wild animals
(e.g., antelopes).
Tsetse fly ingests trypomastigote in blood meal from a
reservoir host.
They multiply in the insect gut and then migrate to the
salivary glands, where they transform into epimastigotes,
multiply further, and then form metacyclic
trypomastigotes, which are transmitted by the tsetse fly.
The development within the fly requires 3 weeks.
In man:
Metacyclic trypanosomes injected in the skin by tsetse fly,
multiply at the site of injection. Inside human,
multiplication in blood, lymph nodes, and spleen is by
binary fission as trypanosomal form.
Pathogenesis:
In the acute form, a cyclical fever spike occurs that is
related to antigenic variation of the surface
glycoprotein. The antigenic variation of surface
glycoprotein is explained by the fact that trypanosomes
may have 1000 or more variant surface glycoprotein
(VSG) genes and trypanosomes change their surface
antigen glycoprotein by turning off one gene coding for a
(VSG) and turning on another. As a result, one antigenic
type will coat the surface of the parasites for
approximately 10 days, followed by other types. These
antigenic variations allow the organism to evade the host
immune response (Figure 2).
Figure 2: antigenic variations in African trypanosome
VSG=Variant surface glycoprotein
A self-limited inflammatory lesion (trypanosomal
chancre) may appear a week or so after the bite of an
infected tsetse fly. The chancre subsides in a week or two
as the trypanosomes gain entry to the circulating blood.
Then they enter the lymph nodes, where a second focus of
inflammation occurs, with hyperplasia of the endothelial
lining of the blood sinuses and perivascular infiltration of
leukocytes. Thos process is rapid, fulminating, and often
causes death in a few months. Rarely the patient lives
long enough for the trypanosomes to invade the central
nervous system and produce the signs of the third stage of
the infection (Sleeping Sickness).
Clinical features:
Incubation periods= 1-2 weeks.
After the incubation period, the patient suffers from
headache, febrile paroxysms that recur frequently,
weakness, loss of weight. Lymph node enlargement is not
pronounced. Skin rash, odema and myocarditis may be
present. CNS signs are not common.
Death occurs within 1 year due to intercurrent infections.
Unit 2: Protozoa
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Trypanosoma gambiense
(Gambian or West African sleeping sickness
)
Life cycle: As for Trypanosoma rhodesiense (Figure 1)
Pathogenesis:
As for Trypanosoma rhodesiense, but the difference is
that T. gambiense enter the arachinoid spaces of the CNS
and the in brain substance. Thus following the initial
lesion in the skin, three progressive stages occur:
Parasitemia, Lymphadenitis, and CNS involvement.
Clinical features:
Incubation period = 6-14 days.
The initial lesion is an indurated painful skin ulcer
(trypanosomal chancre) at the site of bite. A Blood film
reveals trypanosomes. This period of symptom free last
for weeks or months, then the infection may be abortive
or the parasites invade lymphatic tissues leading to
intermittent weekly fever( febrile attack of about a week's
duration and then afebrile period) and lymphadenopathy
develop. Enlargement of the posterior cervical lymph
node (Winterbottom´s sign) is commonly seen. Axillary
and groin lymph nodes are also involved with
splenomegaly
After some months in the absence of treatment, the central
nervous system is invaded and is characterized initially by
headache, insomnia by night and sleepiness by day, mood
changes followed by muscle tremor, slurred speech and
apathy progress to somnolence, coma and death.
Diagnosis:
1) Thick or thin blood film, an aspirate of the chancre or
enlarged lymph node, bone marrow biopsy to reveals
the trypomastigote.
The likelihood of finding parasites in blood is higher in
stage I,II than in stage III disease and in patients infected
with T. b. rhodesiense rather than T. b. gambiense.
2) CSF in case of encephalitis reveals trypanosomes with
elevated protein level, pleocytosis, high IgM and CSF
pressure.
3) Culture in NNN medium.
4) Serological tests: card indirect agglutination test for
trypanosomiasis, and ELISA for IgM Ab.
Treatment:
Suramin is the most effective drugs but does not cross the
blood brain barrier.
Pentamidine is an alternative drug.
Melarsoprol in case of CNS involvement
Comparison of West African and East African
Trypanosomiases
Point of
Comparison
West African
East African
(Gambiense)
(Rhodesiense)
Organism
T. b.
gambiense
T. b. rhodesiense
Vectors
Tsetse flies
(palpalisgroup)
Tsetseflies
(morsitansgroup)
Primary reservoir
Humans
Antelope and
cattle
Human illness
Antelope and
cattle
Acute(early CNS
disease)
Duration of illness
Months to
years
<9 months
Lymphadenopathy Prominent
Minimal
Parasitemia
Low
High
Diagnosis by
rodent inoculation
No
Yes
Epidemiology
Rural
populations
Workers in wild
areas, rural
populations,
tourists in game
parks
Unit 2: Protozoa
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Unit 2: Protozoa
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