HEMOFLAGELLATES (HAT)

Question 1

General characteristics of hemoflagellates

Answer 1

• A single nucleus, a kinetoplast, and a single flagellum.
• Nucleus is round or oval and is situated in the central part of the body.
• Kinetoplast consists of a deeply staining parabasal body and adjacent dot-like blepharoplast.
• The portion of flagellum which is inside the body of the parasite and extends from the blepharoplast to surface of the body is an axoneme.
• A free flagellum at the anterior end traverses on the surface of the parasite as a narrow undulating membrane.

Question 2

What makes up the kinetoplast?

Answer 2

Parabasal body and blepharoplast together constitute the kinetoplast

Question 3

What are the diagnostic forms for the two hemoflagellate genera?

Answer 3

=Leishmania=> amastigote =Trypanosoma=> trypomastigote.

• The exception is Trypanosoma cruzi in which amastigotes may also be found.

Question 4

Morphological forms of hemoflagellates

Answer 4

=amastigote
=promastigote
=epimastigote
=trypomastigote

Question 5

Amastigote general morphology

Answer 5

=Rounded or ovoid, without any external flagellum.
=The nucleus, kinetoplast and axial filaments can be seen.
=The axoneme extends up to the anterior end of the cell

**Leishmania and T. cruzi (intracellular in vertebrate host)

Question 6

Promastigote general morphology

Answer 6

=Lanceolate in shape.
=Kinetoplast is anterior to the nucleus (antinuclear kinetoplast) near the anterior end of the cell, from which flagellum emerges.
=There is no undulating membrane

**It is the infective stage of Leishmania, found in the insect vector as well as in cultures in vitro

Question 7

Epimastigote general morphology

Answer 7

=Elongated, with the kinetoplast placed more posteriorly, though close to and in front of the nucleus (juxtanuclear kinetoplast). =The flagellum runs alongside the
body as a short undulating membrane, before emerging from the anterior end

**It is the form in which T. bruce/ occur in salivary gland of the vector tsetse fly and T. cruzi in the midgut of the vector reduviid bug.

NOTE: This stage is lacking in
Leishmania

Question 8

Trypomastigote general morphology

Answer 8

=This stage is elongated, spindle·
shaped with a central nucleus.
=The kinetoplast is posterior to the nucleus (postnuclear kinetoplast) and situated at the posterior end of the body. The flagellum runs alongside the entire length of the cell to form a long undulating membrane before emerging as a free flagellum from the anterior end.

**This is the infective stage of
trypanosomes found in arthropod
vector and in the blood of infected vertebrate.

NOTE: This stage is lacking in
Leishmania

Question 9

Trypanosomes general morphology

Answer 9

• Members of this genus exist at sometime in their life cycle as
  trypomastigote stage.
• However some trypanosomes such as T. cruzi assume amastigote forms in vertebrate hosts.

Question 10

Salivaria in trypanosomes

Answer 10

• The trypanosomes migrate to mouth parts of the vectors, so that infection is transmitted by their bite.
• Examples are T. gambiense and T. rhodesiense causing African
  trypanosomiasis, which are transmitted by the bite of tsetse flies.

Question 11

Stercoraria in trypanosomes

Answer 11

• The trypanosomes migrate to the hindgut and are passed in feces e.g. T. cruzi causing Chagas’ disease acquired by rubbing the feces of the vector bug into the wound caused by its bite.

Question 12

T. brucei gambiense epidermiology

Answer 12

• Found in 24 countries in tropical areas of west & central Africa in
  shaded areas along stream banks where the tsetse fly vector breeds.
• Accounts for 97% of reported cases of sleeping sickness.
• The course of the illness is chronic & less aggressive than
  Trypanosoma Brucei Rhodesiense.

Question 13

Which tsetsefly vectors transmit T.B gambiense? (2)

Answer 13

=Glossina palpalis
=Glossina tachinoides.

Question 14

T.B gambiense habitat

Answer 14

• In man & other vertebrate host.
• Essentially a parasite of connective tissue where they
  multiply rapidly.
• They then invade regional lymph nodes, blood and finally may
  involve CNS.

Question 15

T. brucei gambiense morphology

Answer 15

• In humans/vertebrate host= trypomastigote form with high pleomorphism.
• In insects= epimastigote and metacyclic trypomastigote forms.

Question 16

Hosts and Infective form of T. brucei gambiense

Answer 16

• Definitive(Vertebrate)host
  =man, game animals, and other
  domestic animals.
• Intermediate(Invertebrate) host =Tsetse fly of glossina species
• The infective form to humans is the metacyclic trypomastigote.

Question 17

• Mode of transmission of T. brucei gambiense:

Answer 17

1. Through the bite of tsetse fly .
2. Congenital transmission (recorded).

Question 18

Briefly describe the life cycle of T. brucei gambiense

Answer 18

• Metacyclic trypomastigotes inoculated into man when an infected tsetse fly takes a blood meal.
• These transform into slender blood trypomastigotes that multiply asexually before entering the peripheral blood and lymphatic circulation.
• The slender forms become non dividing short stumpy forms and enter the blood stream , CNS invasion occur in chronic infection.
• Trypomastigotes (short plumpy form) are then ingested by tsetse fly(male or female) during blood meal.
• In the midgut of the fly, short stumpy trypomastigotes develop into long, slender forms and multiply.
• In salivary glands they develop into epimastigotes,multiply and
  eventually transform into the infective metacyclic trypomastigotes.
• Thereafter, the fly remains infective throughout its life of about 6 months.

Question 19

How do trypanosomes evade the immune system?

Answer 19

=periodic antigenic change of surface glycoproteins called variant surface glycoprotein (VSG).
=resistance to trypanolytic serum
proteins(Trypanosome Lytic Factors 1 & 2), immunosuppression,
shedding of enormous VSG in circulation leading to formation of
immune complexes with antibodies.

Question 20

Pathogenesis of T. brucei gambiense

Answer 20

• Period of parasitemia after which the parasite gets localized predominantly in the lymph nodes.
• A painless chancre appears at the site of tsetse fly bite followed by intermittent fever, chills, rash, anemia, weight loss, and headache.

Question 21

• Systemic trypanosomiasis without CNS involvement is referred to as stage I disease. Signs?

Answer 21

• Hepatosplenomegaly and lymphadenopathy, particularly in the posterior cervical region (Winterbottom’s sign).
• Myocarditis may develop although common in T. brucei rhodesiense infections.
• Anemia, moderate leukocytosis, and thrombocytopenia.

Question 22

• Stage II disease involves CNS invasion occurring several months marking the start of ‘sleeping sickness’. Signs?

Answer 22

• Headache, mental dullness, apathy and day time sleepiness begin at this stage.
• The patient falls into profound coma followed by death from asthenia
• Histopathology show chronic meningoencephalitis with heavy
  infiltration by lymphocytes, plasma cells, and morula cells(atypical plasma cells)
• Brain vessels show perivascular cuffing followed by infiltration of the brain and spinal cord, neuronal degeneration and microglial proliferation.
• Abnormalities in CSF include raised intracranial pressure, pleocytosis, and raised total protein concentrations.

Question 23

Trypanosoma Brucei Rhodesiense (East African Trypanosomiasis) Epidermiology

Answer 23

• T. brucei rhodesiense is found in 13 countries in eastern and southern Africa.
• Represents under 3% of reported cases and causes an acute infection.
• First signs and symptoms are observed a few weeks or months after infection.
• The disease develops rapidly and invades the central nervous system.
• According to WHO ,Zambia currently reports <100 new HAT cases:
• These are mainly from the old foci in the tsetse fly-infested Luangwa River Valley comprising Chama, Mpika, Chipata, Mambwe & Rufunsa districts.
• The disease is also re-emerging in Rufunsa.
• Other areas are the Kafue ecosystem comprising Kafue National Park(KNP) and its surrounding Game Management Areas (GMA).

Question 24

T. brucei rhodesiense vectors and morphology

Answer 24

• Vectors= G. morisitans , G. palpalis and G. Swynnertoni found in the open savannah countries.
• The disease is a zoonosis.
• The reservoir host are wild game animals like bush buck, antelope
  and domestic animals like cattle.
• Its morphology, habitat, and life cycle is similar to T. brucei gambiense

Question 25

T. brucei rhodesiense Pathogenesis and Clinical Feature

Answer 25

• Incubation period of 4 weeks.
• Pathological features are similar in both diseases although edema,
  myocarditis and weakness are more prominent in East African sickness.
• Somnolence and lymphadenitis is less prominent than in T.b. gambiense
• Febrile paroxysms are more frequent and severe with heavy parasitemia.
• CNS involvement happens early and death can occur without its
  involvement.

Question 26

Lab Diagnosis of African trypanosomiasis

Answer 26

1. Microscopy
   * Definitive diagnosis is established by demonstration of trypanosomes in peripheral blood, bone marrow, lymph node, CSF & chancre fluid
2. Serodiagnosis
   * Antigen detection- Antigens from serum and CSF can be detected by ELISA.
   * Antibody detection- Various serological methods are used to detect the high serum IgM levels and later, CSF IgM antibodies in patients with African trypanosomiasis e.g. IHA,CFT,ELISA etc.

• Anemia and monocytosis.
• ↑ ESR due to rise in gamma globulin levels.
• Reversal of albumin: globulin ratio.
• Increased CSF pressure, raised cell count and proteins.