Revision of Practical Parasitology

Comprehensive practice flashcards covering clinical stool examination, helminthology, protozoology, and medical entomology based on the practical parasitology revision notes.

What is the minimum number of stool samples that should be examined for a parasitology workup?

Minimum $3$ samples should be examined in a clean, water-tight container with a screw-cap lid.

What is the smallest acceptable amount of stool for a specimen?

$$2-5\,gm$$

What substance is responsible for the normal light to dark brown color of stools?

Stercobilinogen, which is a product of bilirubin metabolism.

In which condition might the fecal odor of stools become offensive?

Intestinal amoebiasis.

What are the common stool artifacts that can mislead a laboratory worker?

Leukocytes, air bubbles, oil droplets, Charcot-Leyden crystals, plant fiber, hair fiber, and plant cells.

Describe the morphology of an adult Fasciola worm.

Large trematode ($3-8\,cm$ in length), leaf-like with an anterior cone, possessing an oral sucker and a ventral sucker at the junction of the anterior cone with the body.

What are the diagnostic features of a Fasciola spp. egg?

Large sized, oval, operculated, yellowish-green (bile-stained), and contains a one-cell stage embryo surrounded by numerous yolk cells.

What is the length and shape of a Fasciola spp. cercaria?

About $1\,mm$ in length, with a heart-shaped body ($1/3\,mm$) and a simple leptocercous tail ($2/3\,mm$).

What is the size and suckers characteristic of a mature Heterophyes heterophyes worm?

Small sized ($1-3 \times 0.3-0.5\,mm$) and pear-shaped; it has an oral sucker, a ventral sucker near the middle, and a genital sucker.

Where is the encysted metacercaria of Heterophyes heterophyes found?

In fish muscles.

How can you distinguish a male adult Schistosoma from a female?

The male has a gynaecophoric groove and numerous testes behind the ventral sucker, while the female is cylindrical with a long uterus containing numerous eggs.

What is the primary diagnostic feature of a Schistosoma haematobium egg?

Spindle-shaped, large, thin-shelled, and translucent with a terminal spine.

How does a Schistosoma mansoni egg differ from a Schistosoma haematobium egg?

It is larger and has a sharp lateral spine.

Describe the scolex of Taenia saginata.

Globular in shape with $4$ cup-shaped suckers, but no rostellum and no hooks.

How many main uterine branches are found in the gravid segment of Taenia saginata compared to Taenia solium?

Taenia saginata has $15-30$ main uterine branches, while Taenia solium has $7-13$ on each side.

What are the characteristics of a Taenia spp. egg?

Spherical, small-sized, with a brownish, radially striated embryophore surrounding a hexacanth embryo (onchosphere).

What are the two types of Cysticercus (larval stage of Taenia spp.)?

Cysticercus cellulosae (associated with T. solium, has $4$ suckers and $2$ rows of hooks) and Cysticercus bovis (associated with T. saginata, has $4$ suckers and no hooks).

What are the layers of a Hydatid cyst (larval stage of Echinococcus granulosus)?

It is composed of an outer laminated non-nucleated layer and an inner germinal layer.

What is the length of adult Ascaris lumbricoides and how do you differentiate the sexes?

$15-25\,cm$ long; males are thinner with a ventrally coiled posterior end, while females have a straight posterior end.

What is the shape and content of an Enterobius vermicularis egg?

Plano-convex (one side flattened, other convex), colourless/translucent, and contains a fully developed larva.

Describe the appearance of a Trichuris trichiura egg.

Barrel-shaped, $50 \times 25\,\mu m$, thick-shelled with a mucoid plug at each pole, and golden brown in color.

What stage of embryo is found in a freshly deposited Ancylostoma duodenale egg?

Four-cell stage embryo.

What are the diagnostic features of Wuchereria bancrofti microfilaria in a blood film?

Measures $300 \times 8\,\mu m$, has a hyaline sheath, graceful curves, and an interrupted column of nuclei.

What are the components of Giemsa stain?

Eosin and methylene blue (azur).

Describe the ring stage of Plasmodium species.

The parasite fills about $1/3$ of the red blood cell and contains a vacuole that pushes the nucleus to one side, creating a ring shape.

What are 'Schuffner’s dots' and in which stage of Plasmodium are they seen?

A characteristic dotted appearance in an enlarged, infected red cell seen during the Trophozoite stage.

What are the morphological features of a Plasmodium falciparum gametocyte?

Slender, crescentic, or sausage-shaped, with a diameter about $1.5$ times the infected red cell.

Identify the three forms of Trypanosoma trypomastigotes.

1. Slender form (free flagellum), 2. Stumpy form (no free flagellum), 3. Intermediate form (short free flagellum).

Describe the morphology of Toxoplasma gondii trophozoites.

Banana-shaped or crescentic with one end pointed and the other rounded, and a vesicular nucleus.

What characterizes the trophozoite stage of Entamoeba histolytica?

Amoeboid shape with finger-like pseudopodia and a vesicular nucleus containing a centrally situated karyosome.

How many nuclei are present in a mature Entamoeba histolytica cyst?

Four nuclei.

Describe the appearance of a Giardia lamblia trophozoite.

Pear-shaped with a sucking disc, $4$ pairs of flagella, and $2$ vesicular nuclei that look like two eyes.

What are the distinct characteristics of the Balantidium coli trophozoite?

Oval body covered with cilia, a cytostome (mouth), a cytopyge (anus), and two nuclei: a large kidney-shaped macronucleus and a small rounded micronucleus.

Where is the siphon tube located on a mosquito larva?

On the $8^{th}$ segment of the abdomen.

What is the shape of the respiratory organs in a Culex pupa?

A pair of tubes called respiratory trumpets.

Describe the posterior spiracles of a Musca sp. third-stage larva.

Two D-shaped chitinised peritremes, each containing three sinuous spiracular openings and a button.

What are the general characters of Order Siphonaptera (e.g., Pulex irritans)?

Bilaterally compressed body, wingless, mouthparts adapted for piercing and sucking, and legs adapted for jumping.

Describe the morphology of Pediculus humanus capitis (head louse).

Dorso-ventrally flattened, head with $5$-segmented antennae, and legs ending in a single tarsal joint with a curved claw for fixing to hairs.

What distinguishes an adult male hard tick (Ixodidae) from an adult female?

The scutum covers the whole dorsal surface of the male body, while it only covers a small anterior part in the adult female.

How many pairs of legs do hard tick larvae have compared to adults?

Larvae have $3$ pairs of legs, while adults have $4$ pairs.

What is the cause of human itch and what does the adult mite look like?

Sarcoptes scabiei; a small globular mite ($0.2-0.5\,mm$) with a transversely striated cuticle and four pairs of short, stout legs.