Protozoans Virology Short And Long Essay Question And Answers

Protozoans Important Notes

1. Entamoeba histolytica

  • Occurs in three forms
    • Trophozoites
    • Pre cystic stage
    • Cyst
      • It passes its life cycle only in man
      • Diseases caused by it
        • Intestinal amoebiasis
        • Extra intestinal amoebiasis
          • Other Entamoeba are
            • Entamoeba coli
            • Entamoeba gingivalis

2. Species of Plasmodium

  • Pvivax
  • P falciparum
  • P malariae
  • P ovale

3. Stages of the life cycle of Plasmodium

  • Pre erythrocytic schizogony
  • Erythrocytic schizogony
  • Gametogony
  • Exo erythrocytic schizogony

4. Malarial pigment

  • Yellowish brown – P. vivax
  • Dark brown – P.falciparum, P.malariae
  • Dark yellowish brown- P.ovale

5. Malaria

  • Clinical features
    • Febrile paroxysm
    • Anaemia
    • Splenomegaly
  • Complications
    • Pernicious malaria
    • Black water fever

Read And Learn More: Microbiology Question and Answers

6. Cestodes

  • Taenia saginata
  • Taenia solium

7. Nematodes

  • Ascaris lumbricoides or round worm
  • Hookworm
    • Ankylostoma duodenale
    • Wuchereria bancrofti

Protozoans Long Essays

Question 1. Describe the morphology, pathogenesis, and life cycle of Entamoeba histolytica. Write about laboratory diagnosis of intestinal amoebiasis.

Entamoeba histolytica causes intestinal amoebiasis and hepatic amoebiasis

Entamoeba histolytica Morphology:

The parasite exists in 3 forms

Protozoans Parasite exists in 3 forms

Entamoeba histolytica Life Cycle:

  • E. histolytica passes its life cycle in only one host, the man.
  • The mature quadranucleate cysts are infective forms.
  • These cysts enter in to men through ingestion of water and food containing it
  • These reach the caecum or lower part of the ileum called excystation
  • Each mature cyst liberates tetranuclear amoeba
  • Forms eight meta cystic Trophozoites by binary fission
  • It gets lodged in the submucous tissue of the large intestine
  • E.histolytica secretes a proteolytic enzyme
  • Causes destruction and necrosis of tissues
  • Results in the formation of flask-shaped ulcers
  • Next, these Trophozoites are
    • Excreted along with blood and mucous in feces
    • Results in amoebic dys­entery
    • Enter into deeper layers
    • Enter into the portal vein
    • Reaches liver
    • Forms amoebic hepatitis and amoebic liver abscess
  • Effect of the parasite on the host decreases
  • This increases host tolerance and healing starts
  • Encystation occurs which is the transformation of Trophozoites into cysts and cysts.

Protozoans Life cycle of Entamoeba histolytica

Entamoeba histolytica Pathogenesis:

E. Histolytica can cause two types of pathological lesions as follows

1. Primary (or) Intestinal Amoebiasis:

Protozoans Primary or Intestinal Amoebiasis

  • This condition is called as amoebic dysentery.
  • This ulcer maybe generalized (or) may be localized to the ileocaecal (or) sigmoidorectal region.
  • Occasionally ulcers may involve deeper tissues and may cause perforation (or) peritonitis.
  • Erosion of blood vessels may lead to hemorrhage.
  • The superficial lesions generally heal without scar¬ring.
  • Deep ulcers form scars leading to strictures, partial obstruction, and thickening of the gut wall

2. Extra-intestinal amoebiasis [or) secondary (or) metastatic lesions.

  • Amoebic liver abscess:

Protozoans Amoebic liver abscess

Laboratory Diagnosis of Intestinal Amoebiasis:

1. Stool examination:

  • The stool is collected directly into a wide-mouthed con¬tainer and examined without delay.
    • Macroscopic Examination
      • The stool is an offensive odor
      • Dark brown and semifluid
      • Acid in reaction
      • Mixed with blood and mucous
    • Microscopic Examination
      • The cellular exudates is scanty, and consist of nuclear masses of a few pus cells, macrophages, and epithelial cells
      • RBCs are seen in clumps
      • Charcot- Leyden crystals are also seen

2. Blood Examination

  • In early cases, it is always negative
  • The antibody can be detected in later stages of invasive intestinal amoebiasis
  • The test used is ELISA haemagglutination assay (HIA).

3. DNA Probes:

  • DNA probes have been used to detect E. histolytica in stool specimens.

Question 2. Describe the life cycle of malarial parasites in man. Give a brief description of pathological lesions produced in man.

Malaria is a disease caused by four plasmodium species which are as follows:

  • P. vivax
  • P. Falciparum
  • P. Malaria
  • P. Ovale.

Malarial Life Cycle:

The malarial parasites pass their life cycle in two. hosts.

  1. Man intermediate host [a sexual development]
  2. Female anopheles mosquito – definitive host [sexual development].

Human cycle or schizogony or a sexual cycle:

  • The sporozoite is the infective form of a malarial parasite.
  • Man gets infected by the bite of the infected female Anopheles mosquito
  • This mosquito contains sporozoites in the salivary gland which enter directly into the blood circulation of man
  • By this human cycle starts which comprises of following stages.

1. Pre-erythrocytic schizogony

  • It is a developmental phase of sporozoites inside the liver cells
  • The shape of sporozoites- Round
  • Size-Varies
  • They undergo nuclear division to develop schizont
  • Each schizont contains 20,000-50,000 merozoites
  • Duration of this stage
    • P. vivax           – 8 days
    • P. falciparum  – 6 days .
    • P. malariae     – 13-16 days
    • P. ovale          –  9 days
  • After this period, the liver cells rupture
  • As a result, merozoites are released into the bloodstream

2. Erythrocytic schizogony:

  • Release of merozoites into the blood
  • Penetration of it into RBCs
  • Rupture of RBCs which leaves behind a residue of hemoglobin pigment called hemozoin
  • Release of merozoites
  • These attack new RBCs
  • Thus the cycle continues

3. Gametogony:

  • Some merozoites develop sexual forms known as microgametocytes and macro gametocytes

Protozoans Microgametocytes And Macrogametocytes

4. Exo-erythrocytic schizogony:

  • Some sporozoites enter liver cells but don’t multi-ply
  • Enter in the resting phase and are known as Hypno- zoite
  • These hypnozoites get reactivated
  • Forms schizonts
  • Releases merozoites called phanerozoic
  • Attack RBCs
  • Causes relapse of malaria

Protozoans Life cycle of Malarial parasite

Malaria Clinical Features:

  • Intermittent fever which is named as malaria is caused by plasmodium
  • It consists of

1. Febrile paroxysm

  • It comprises of three stages

Protozoans Febrile paroxysm

2. Anaemia

  • Microcytic or normocytic hypochromic anemia develops

3. Spenomegaly.

  • The spleen becomes enlarged and palpable
  • Black water fever, and pernicious malaria are the most commonly seen complications in falciparum malaria.

Protozoans Short Essays

Question 1. Laboratory diagnosis of extraintestinal amoe¬biasis

Diagnostic methods for extraintestinal amoebiasis are as follows

Protozoans Diagnostic methods for extraintestinal amoebiasis

Question 2. Leishmania donovani

It causes visceral leishmaniasis or kala-azar

Leishmania donovani Morphology:

It occurs in two forms:

Protozoans Leishmania donoval Morphology

Protozoans Amastigote and promastigote forms of leishmania donovani

Leishmania donovani Life Cycle:

  • The parasite has two stages in its life cycle
    • Amastigote form
    • Promastigote form
  • Initially, multiplication of amastigote form occurs in the reticuloendothelial cells in the host
  • Enlargement of host cells occurs
  • These cells rupture to release parasites into circulation
  • Blood-sucking insect obtains it by sucking
  • Development of Promastigote form from Amastigote form

Protozoans Life Cycle Of Leishmania Donovani

Leishmania donovani Clinical Features:

  • Pyrexia
  • Splenomegaly
  • Hepatomegaly
  • Lymphadenopathy
  • Anaemia

Question 3. The life cycle of plasmodium in mosquito

  • The sexual development of plasmodium occurs in mosquito
  • It starts in the human host by the formation of Gametocytes
  • The cycle includes the following steps
  • Bite of female anopheles from the patient
  • Mature sexual forms develop in the mosquito
  • In the midgut
  • 1 microgametocytes- develops 4-8 microgametes
  • 1 macrogametocyte- Develops 1 macrogamete
  • Fertilization of macrogamete occurs
  • Formation of zygote
  • Lengthening and maturation of zygote to form ookinete
  • Formation of oocyst from ookinete
  • Maturation of oocyst
  • Increase in size and number of sporozoites
  • Rupture of oocyst to release sporozoites in the body of the mosquito
  • Distribution of sporozoites into various organs and tissues especially in salivary glands

Question 4. Laboratory diagnosis of malaria

The demonstration of the parasite in the blood is the most important method for the diagnosis of malaria.

1. Microscopic examination of blood film:

  • Thick and thin smears of blood are prepared on the same slide (or) two different slides.
  • Blood is collected prior to antimalarial therapy

Protozoans Microscopic examination of blood film

2. Fluorescent microscopy:

  • A blood smear is prepared on a slide and is stained with acridine orange
  • The slide is observed under a fluorescent microscope.
  • The nuclear DNA of the malarial parasite is stained green and cytoplasmic RNA is stained red.

3. Blood counts:

  • Blood shows moderate leukopenia and monocytosis.

4. Serological tests:

  • Serological tests used are
    • ELISA
    • Indirect haemagglutination assay
    • Indirect immunofluorescence test.

5. DNA probes:

  • These are sensitive and specific diagnostic methods for the diagnosis of malaria
  • It can detect even a low parasitemia i.e., <10 parasites/dl

6. Polymerase chain reaction (PCR):

  • It can also be used.

7. Rapid diagnostic tests:

  • These are based on the detection of antigens using immune chromatographic methods.
  • In these tests, a dipstick containing monoclonal antibodies is directed against the parasitic antigens.
  • This test takes about 15 minutes.
  • Several commercial kits are available.
  • Kits available detect histidine-rich protein (HRP – II) of P. falciparum.
  • The test is commercially available as the parasite ‘F’ test.

Question 5. Complications of plasmodium falciparum infection?

Complications of P.Falciparum are:

  1. Pernicious malaria
  2. Black water fever.

1. Pernicious malaria:

  • It is life-threatening condition

Pernicious malaria Cause:

  • It is due to heavy parasitization.

Pernicious Malaria Clinical Features:

  • It is grouped into the following:

Protozoans Pernicious malaria clinical features

2. Blackwater fever:

Occurs in persons who are previously infected and had inadequate doses of quinine

Black water fever Clinical Features:

  • Intravascular hemolysis,
  • Fever,
  • Haemoglobinuria
  • Vomiting and prostration with the passage of dark red (or) blackish urine hence called backwater fever.

Black water fever Mechanism:

  • An autoimmune mechanism may be involved in hemolysis
  • Parasitized erythrocytes during previous infection act as antigen
  • Antibodies are formed against it
  • Due to this antigen-antibody reaction, massive destruction of erythrocytes occurs
  • There is excessive deposition of haemosiderin pigment in the liver, spleen, and kidneys.
  • Sequel of black water fever include
    • Circulatory failure
    • Renal failure,
    • Liver failure,
    • Anaemia.

Protozoans Short Question And Answers

Question 1. Draw morphological forms of Entamoeba His¬tolytica

Protozoans Different morphological of Entamoeba histolytica

Question 2. Amoebic dysentery

  • Amoebic dysentery is also known as intestinal amoebiasis
  • It is a condition in which the infection is confined to the intestine and is characterized by the passage of blood and mucus in the stool

Amoebic dysentery Types:

1. Acute amoebic dysentery

  • Multiple ulcers occur
  • These ulcers are deep and extensive
  • Its complications are
    • Pericaecal and pericolic abscess
    • Amoebic appendicitis
    • Perforation
    • Generalized peritonitis
    • Gangrene of guts
    • Fistula

2. Chronic amoebic dyssentery

  • A single latent ulcer is present in the caecum while multiple small superficial ulcers are scattered throughout the large intestine
  • Stricture formation occurs
  • Amoeboma in the caecum and large intestine develops

Question 3. E.gingivalis / Morphology of E.gingivalis

E.gingivalis Morphology:

  • It is a small amoeba measuring 10 – 20 (m in diameter and is actively motile by multiple pseudopodia.
  • It has the only trophozoite stage and there is no cystic phase.
  • It contains
    • The cytoplasm which is divided into clear ectoplasm and granular endoplasm.
    • Cytoplasmic inclusions consisting of bacteria leucocytes but never RBCs
    • Nucleus is spherical
    • Central karyosome.
    • Nuclear membrane lined with closely packed chromatin granules.

E.gingivalis Pathogenesis:

  • E.gingivalis is a parasite of human mouth.
  • It occurs as a commensal in gingival tissue around the teeth particularly in the unhealthy tissues such as in pyorrhoea alveolaris.
  • It is also found in the crypts and histologic sections of diseased tonsils.
  • It is transmitted by close contact like kissing.
  • Laboratory diagnosis depends on the demonstration of tro¬phozoites of E. Gingivalis in the material removed from the gingival margin of the gum (or) from the denture.

Question 4. Erythrocytic schizogony

  • It is the second stage of the human cycle of the malaria parasite
  • During this phase, the parasite resides inside RBC and passes through stages of Trophozoites, schizonts, and merozoites.
  • Following changes occur during this phase
  • Release of merozoites into the blood

Protozoans Erythrocytic Schizogony

Question 6. Plasmodium falciparum

Plasmodium falciparum is one of the malarial parasites

Stages of Human Cycle in P. Falciparum:

Protozoans Stages of Cycle in P. Falciparum

Protozoans Gametocytes of plasmodium species

  • P. falciparum is the most pathogenic among the plasmodium species infecting man
  • No relapse occurs in P.falciparum infection
  • It invades erythrocytes of all ages
  • The incubation period of it is 10-14 days


  • Pernicious malaria
  • Black water fever

Question. Black water fever

Occurs in persons who are previously infected and had inadequate doses of quinine

Black water fever Clinical Features:

  • Intravascular hemolysis,
  • Fever,
  • Haemoglobinuria
  • Vomiting and prostration with the passage of dark red (or) blackish urine hence called backwater fever.

Question 9. Kala-azar

Leishmania denovani produces the disease Salazar (or) visceral leishmaniasis.

Kala-azar Clinical Features:

  • Pyrexia,
  • Splenomegaly,
  • Hepatomegaly,
  • Lymphadenopathy and
  • Anaemia.

Kala-azar Laboratory Diagnosis:

1. Direct evidence:

Protozoans Direct evidences

2. Indirect evidence:

Protozoans Indirect evidences

3. Rapid immune chromatographic strip test:

  • It detects antibodies against the K39 antigen of L. donovani
  • It indicates active kala-azar

Question 10. Benign tertian malaria

  • Benign tertian malaria is caused by Plasmodium vivax
  • Initially, there may be continuous or remittent fever
  • In later stages, typical intermittent periodic fever develops
  • Initially, two broods of parasites undergo schizogony on alternate days but then one brood drops out.

Question 11. Mention the parasites found in peripheral blood smear.

Protozoans Peripheral blood smear

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