Life Cycle
Further evaluation reveals moderate malnutrition and oral thrush. (a) What is the likely underlying diagnosis (1 mark)? (b) Which WHO stage can he be classified in and why (1 mark)? (c) Describe the life cycle of the aetiological agent (8 marks).
Life cycle
- Infective stage = the cyst (quadrinucleate, 10-15 micrometres), swallowed in faecally contaminated food or water (also sexual and oral-anal contact).
- The cyst survives gastric acid; in the small intestine it excysts into eight small trophozoites .
- Trophozoites live and multiply in the large intestine lumen (commensal, feeding on bacteria).
- As the stool dries they round up into cysts (the diagnostic and transmitting stage in formed stool).
- In some patients trophozoites invade the colonic wall , cause ulcers and may enter the portal blood to reach the liver .
Read this in Amoebiasis: Entamoeba histolytica and the free-living amoebae
Life Cycle
- Adults bite and feed on vertebrates inhabiting arthropod-rich areas
- Female lays 1-5 spherical eggs in moist but well-drained soil (e.g., riverbank)
- Only larvae are parasitic
- Attach to small mammals so they will have hosts on which to feed
- Rodents are important local hosts
Read this in Medical Entomology: Vectors and Vector-Borne Diseases — Notes
Life Cycle:
- Eggs passed in stool hatch in water to release miracidium.
- Miracidium infects Lymnaea snail.
- Inside snail: sporocyst → redia → cercaria.
- Cercariae exit snail and encyst on aquatic vegetation to become metacercaria.
- Humans ingest metacercaria on water plants.
Read this in Life Cycles of Medically Important Trematodes (Flukes) — Notes
Life Cycle:
- Eggs in urine (S. haematobium) or stool (S. mansoni/japonicum).
- Eggs hatch in freshwater, releasing miracidia.
- Miracidium infects snail (intermediate host).
- Inside snail: sporocysts produce cercariae.
- Cercariae emerge from snail and penetrate human skin.
Read this in Life Cycles of Medically Important Trematodes (Flukes) — Notes
What our notes say
- Further evaluation reveals moderate malnutrition and oral thrush. (a) What is the likely underlying diagnosis (1 mark)? (b) Which WHO stage can he be classified in and why (1 mark)? (c) Describe the life cycle of the aetiological agent (8 marks). (Paediatrics end of fourth year main exam: 1 July 2019, Paper One, 99 of 100 MCQs)
- INFECTIOUS DISEASE • 5\n\n Life cycle\nFlagellar promastigotes (10–20 µm) are introduced by the feeding\nfemale sandfly (Phlebotomus in the eastern hemisphere, Lutzomyia\nand Psychodopygus in the western hemisphere). (Davidson's Essentials of Medicine - 2nd)
- Antiretroviral (ARV) drugs are broadly classified by the phase of the retrovirus life-cycle that the drug inhibits. (HUMAN IMMUNODEFICIENCY VIRUS)
- ill effects and are not noticed until a worm is either vomited but their life cycles are identical (Fig. (Devendra K. Gupta, Krishna M. Goel - Hutchison’s Paediatrics. chdhe-Jaypee Broth)
- (c) Life cycle of HIV (a retrovirus that infects CD4 cells) (Paediatrics end of fourth year main exam: 1 July 2019, Paper One, 99 of 100 MCQs)
- Parasites have diverse life cycles and mechanisms of pathogenesis. (Common fungal and parasitic infections)
Study material on Life Cycle
- Life Cycles of Medically Important Trematodes (Flukes) — Notes
- Entamoeba histolytica and Amoebiasis: Life Cycle and Pathogenesis — Notes
- Davidson's Essentials of Medicine - 2nd
- Department Of Medical Microbiology & Parasit MCQs
- Cestodes (Tapeworms) — Notes
- Devendra K. Gupta, Krishna M. Goel - Hutchison’s Paediatrics. chdhe-Jaypee Brothers (2012)
- Medical Entomology: Vector Control and Review Questions — Notes
- Medical Entomology: Vectors and Vector-Borne Diseases — Notes
- Medical Entomology Past Paper MCQs
- Amebae: Medical Parasitology Overview — Notes
- Weekly Year 2: Parasitology Exam - May 29, 2026 (Sections B & C) — Essay Questions
- MICROBIOLOGY AND PARASITOLOGY MCQs
- Weekly Year 2: Parasitology Exam - May 15, 2026 (Sections B & C) — Essay Questions
- Enterobius vermicularis and Ascaris lumbricoides — Essay Questions
- Parasitology, Entomology and Bacteriology Question & Answers MCQs
Practice questions on Life Cycle
An organism without a known sexual stage in its life cycle would be classified in which of the following fungal groups?
- Zygomycetes
- Fungi Imperfecti
- Ascomycetes
- Basidiomycetes
Answer: B. Fungi with no known teleomorph (sexual stage) are historically classified as Fungi Imperfecti, also known as Deuteromycetes or Mitosporic fungi. The other options represent fungal phyla with known sexual reproduction.
Which one of the following vectors utilizes one host in its life cycle and pathogen transmission?
- Ornithodoros
- Amblyomma
- Mostly unchanged in early disease
- Hyalomma
- Boophilus
Answer: E. Boophilus ticks are one-host ticks that complete their entire life cycle (larva, nymph, adult) on a single host animal. The other genera are either two-host or three-host ticks that drop off between life stages to molt before finding new hosts.
Mosquito life cycle has larval instars.
- One
- Two
- Four
- Three
- Five
Answer: C. Mosquitoes undergo complete metamorphosis with four larval instars (developmental stages between molts): L1, L2, L3, and L4. After the fourth instar, the larva molts into a pupa, which then emerges as an adult mosquito. Each larval instar is progressively larger, with the fourth instar being the largest before pupation.
During what stage of the viral life cycle is the nucleic acid packed inside the capsid? ---
- At the time of uncoating
- Assembly
- Late protein synthesis (capsid)
- Early protein synthesis
- Penetration
Answer: B. The selected answer is the best-supported choice for this microbiology question.
A phage that exhibits both lytic and lysogenic life cycles is called ---
- Provirus
- Virulent
- Temperate
- Plaque
- Prophage
Answer: C. The selected answer is the best-supported choice for this microbiology question.
In which type of virus is the production of double-stranded DNA from RNA a necessary intermediate in the life cycle? ---
- Herpes virus
- T-even phage
- Retrovirus
- Influenza virus
- Polio virus
Answer: C. The selected answer is the best-supported choice for this microbiology question.