Flagellates Chapter Notes | Microbiology - NEET PG PDF Download

Giardia Lamblia (Intestinal Flagellates)

Habitat

• Resides in the mucosa of the duodenum and upper ileum in humans.

Morphology

• Exists in two forms: Trophozoites and Cysts.
• Trophozoites:
  • Front view: Tear-drop, racket, or piriform shaped.
  • Lateral view: Sickle or spoon shaped.
  • Exhibits falling leaf-like motility.
  • Size: 15–20 µm.
  • Contains 2 nuclei, 4 pairs of flagella, 2 axostyles, 2 parabasal bodies, and 2 ventral sucking disks.
• Cysts:
  • Mature cyst is oval, size: 10–14 µm.
  • Contains 4 nuclei and an axostyle.
  • Passed in feces.

Life Cycle

• Infective stage: Cyst.
• Infective dose: As few as 10 to 25 cysts can cause infection.
• Route of infection: Feco-oral route.
• Cysts transform into trophozoites in the duodenum, where they multiply.
• Trophozoites attach to gastrointestinal tract mucosa using adhesive disks.
• Trophozoites shed into the lumen, transform back into cysts, and are passed in feces.
• Cysts are the diagnostic form of the parasite.
• Susceptible populations: Children, HIV-positive individuals, and those with achlorhydria or hypochlorhydria.

Pathogenesis

• Causes abnormalities in villous structure, leading to malabsorption of lipids and lipid-soluble vitamins.
• Types of malabsorption:
  • Fat malabsorption (steatorrhea): Results in foul-smelling, profuse, frothy diarrhea.
  • Disaccharidase deficiencies (lactate, xylose): Causes lactose intolerance.
• 
  • Malabsorption of vitamin B₁₂ and folic acid.
  • Protein-losing enteropathy.
• Antigenic variation in variant surface protein: Leads to chronic and persistent infection.

Laboratory Diagnosis

• Samples: Stool and duodenal contents.
• Microscopy: Detects trophozoites (indicating active infection) or cysts (indicating carrier state).
• String test/Entero test: Collects bile-stained mucus to examine for trophozoites.
• Antigen detection in stool (coproantigen): Performed using ELISA or immunochromatographic test (ICT), indicates active infection.
• Serum antibody detection: Performed using ELISA or indirect fluorescent antibody (IFA) test, indicates past infection.

Treatment: Metronidazole, Tinidazole, Nitazoxanide, or Furazolidone.

Trichomonas Vaginalis (Genital Flagellates)

Overview

• Most common parasitic cause of sexually transmitted diseases (STD) and nongonococcal urethritis (NGU).
• Habitat: Urethra, vagina, and prostate.

Morphology

• Only form: Trophozoite (no cystic stage).
• Trophozoite characteristics:
  • Exhibits twitching or jerky motility.
  • Pear-shaped.
  • Contains 5 flagella (4 anterior + 1 recurrent flagellum) supported by an undulating membrane and a fibrillary structure called costa.

Life Cycle

• Mode of transmission: Sexual route.
• Reservoir of infection: Women.
• Infective and diagnostic stage: Trophozoites.
• Trophozoites divide by longitudinal binary fission.

Clinical Disease

• Incubation period: 4–28 days.
• In men: Can be asymptomatic or cause urethritis, prostatitis, or cystitis.
• In women: Can be asymptomatic or cause vulvo-vaginitis, characterized by:
  • Profuse vaginal discharge with an offensive smell, high pH (>4.5).
  • Smell accentuated by adding 10% KOH (whiff test).
  • Strawberry appearance of vaginal mucosa (Colpitis macularis), seen in 2% of cases.

Laboratory Diagnosis

• Samples: Vaginal and urethral discharges, prostatic secretions, or urine sediment.
• Microscopy: Detects actively motile (jerky motility) trophozoites in vaginal or urethral discharges.
• Staining: Giemsa, Papanicolaou, or direct fluorescent antibody (DAF) test.
• Culture: Most sensitive, considered the gold standard, using media like Lash’s cysteine hydrolysate serum media.
• Antigen detection in vaginal smear: Performed using ICT or ELISA, more sensitive than microscopy, indicates recent infection.
• Serology by ELISA: Detects antibodies, indicating past infection.
• PCR: Used for detection.

Treatment

• Drug of choice: Metronidazole or Tinidazole (2 grams, single dose) for both sexual partners.
• Resistance: Rare but reported.

Hemoflagellates (Leishmania and Trypanosoma)

Exist in four morphological forms: Promastigote, Amastigote, Trypomastigote, and Epimastigote.

Various morphological forms of hemoflagellates

Leishmania

• Infective form: Promastigote.
• Mode of transmission: Bite of female sandfly during late evening or night.
• Infective dose: 10–1000 promastigotes per bite required to initiate infection.
• Promastigotes enter skin macrophages, transform into amastigotes, and are carried to organs like liver, spleen, and bone marrow.
• Diagnostic form in humans: Amastigote inside macrophages, known as LD body.

• VL: Stands for Visceral Leishmaniasis, a severe form of leishmaniasis that affects internal organs.
• CL: Refers to Cutaneous Leishmaniasis, which causes skin sores and lesions.
• LR: This denotes Leishmaniasis Recidivans, a type where the disease reappears after treatment.
• MCL: Represents Mucocutaneous Leishmaniasis, which affects the mucous membranes and can lead to significant tissue damage.
• DCL: Stands for Diffuse Cutaneous Leishmaniasis, characterized by widespread skin lesions that may not have the usual ulcers.
• PKDL: Refers to Post Kala-azar Dermal Leishmaniasis, a skin condition that can develop after successful treatment of visceral leishmaniasis.

Kala-Azar (Visceral Leishmaniasis)

• Bone marrow involvement causes:
  • Anemia, leucopenia, thrombocytopenia.
  • Hypergammaglobulinemia.
• Enlarged spleen and liver.
• Symptoms: Fever, hyperpigmentation (common in Indian cases).
• Lymphadenopathy: Common in African cases, not in Indian cases.
• Kala-azar with HIV:
  • Absence of hepatosplenomegaly.
  • Gastrointestinal and respiratory symptoms.
  • Reported in Southern Europe (France, Italy, Spain, Portugal) and in India (Bihar, sub-Himalayan region, other North Indian states).
  • Diagnosis: Amastigotes detected in bronchoalveolar lavage (BAL) and buffy coat region of blood; antibodies are negative.

Post Kala-azar Dermal Leishmaniasis (PKDL)

• Occurs 2–10 years after VL treatment (within 6 months in Sudan).
• Incidence: 50% in Sudan, 2–20% in India.
• Features: Nonulcerative hypopigmented macular lesions, later becoming nodular.
• Duration: Persists for 20 years (few months in Sudan).
• Treatment: Longer courses of antimonials, resolves slowly.

Virulence Factors

• Glycoprotein (gp-63), Lipophosphoglycan (LPG), Glycosylphosphatidylinositol.

Host Immune Response

• T helper 1 (Th1) Response:
  • Protective response.
  • Leishmanin skin test positive.
• T helper 2 (Th2) Response:
  • Indicates disease progression.
  • Leishmanin skin test negative.

Laboratory Diagnosis

• Samples:
  • Spleen aspirate (most sensitive).
  • Bone marrow aspirate (commonly preferred).
  • Lymph node aspirate (not useful in Indian cases).
  • Blood: Buffy coat region and BAL (for HIV-infected).
• Microscopy: Stained peripheral blood smear shows LD bodies (amastigotes).
• Culture: NNN medium (McNeal, Novy, and Nicolle) and Schneider’s Liquid medium (amastigotes transform to promastigotes).
• Serological tests:
  • Hypergammaglobulinemia: Detected by Napier’s aldehyde and Chopra’s antimony test.
  • Complement fixation test (CFT): Uses tubercle bacilli antigen like WKK antigen.
  • Immunochromatographic test (ICT): Detects antibodies to rK39 antigen.
  • Direct agglutination test (DAT), ELISA, IFA.
• Leishmanin (Montenegro) skin test:
  • Indicates delayed hypersensitivity reaction.
  • Positive in patients with good cell-mediated immunity (CL, LR, recovered VL).
  • Negative in patients with low cell-mediated immunity (active VL, DCL).
• PCR: Detects kinetoplast DNA.
• Animal inoculation: Chinese and golden hamsters.

Treatment

• Pentavalent antimonials: Drug of choice in most endemic regions except Bihar.
  • Sodium stibogluconate.
  • Meglumine antimoniate.
• Amphotericin B: Drug of choice in Bihar.
• Paromomycin: Used for diffuse CL caused by L. aethiopica.
• Miltefosine.
• Pentamidine: Drug of choice for CL caused by L. guyanensis.
• Prevention: Insect control, sleeping on top floors.

Trypanosoma Cruzi

Life Cycle

• Mode of transmission: Rubbing of reduviid bugs (Triatomine).
• Infective form: Metacyclic trypomastigotes.
• Invades macrophages, transforms into amastigotes, which multiply to form pseudocysts.
• Amastigotes transform back into trypomastigotes:
  • Slender, highly motile forms: Invade various organs.
  • Broader, less motile forms: Infective to reduviid bugs.

Acute Chagas’ Disease

• Chagoma: Subcutaneous nodule.
• Romana’s sign: Periorbital edema.
• Lymphadenopathy and hepatosplenomegaly.

Chronic Chagas’ Disease

• Caused by autoimmune hypothesis due to molecular mimicry.
• Parasite multiplication in muscles (skeletal, cardiac, GIT) and CNS leads to:
  • Cardiac form: Myocarditis, dilated cardiomyopathy.
  • Gastrointestinal form: Megaesophagus, megacolon.
  • Meningoencephalitis: Increased in HIV-infected individuals.

Diagnosis and Treatment

• Diagnostic form: C-shaped trypomastigotes in blood smear (may be confused with non-pathogenic T. rangeli).
• Culture: Blood inoculated in NNN media.
• Radioimmune precipitation assay (Chagas’ RIPA): Highly sensitive and specific.
• PCR: Detects kinetoplast DNA, useful in chronic disease.
• Xenodiagnosis.
• Animal inoculation in mice.

Treatment: Benznidazole (drug of choice), Nifurtimox.

Trypanosoma Brucei

Life Cycle

• Infective form: Metacyclic trypomastigotes.
• Mode of transmission: Bite of tsetse fly.
• Transforms into long slender trypomastigotes, then short stumpy forms (infective to tsetse fly).
• Undergoes periodic antigenic variation of surface glycoprotein (VSG).

Clinical Features

• Trypanosomal chancre.
• Stage I disease: Systemic febrile illness, lymphadenopathy.
• Stage II disease: African sleeping sickness, characterized by progressive daytime somnolence, restlessness, and insomnia at night.

Diagnosis

• Diagnostic form: Trypomastigotes seen in blood smear.
• CSF examination: Shows Mott cells (abnormal plasma cells containing IgM).
• Antigen detection: From serum and CSF using ELISA, useful for clinical staging and monitoring.
• Antibody detection: Card agglutination test for trypanosomes (CATT), ELISA, IFA.