Nematodes: The Roundworms

Comprehensive flashcards covering General Characteristics, Aphasmid vs Phasmid classification, and detailed profiles of major medical nematodes including life cycles, diagnostic stages, and clinical symptoms.

What are the three layers that make up the supporting body wall of a nematode?

The body wall consists of: ($1$) an outer hyaline non-cellular cuticle, ($2$) subcuticular epithelium, and ($3$) a layer of muscle cells.

How is the sex of a nematode determined based on physical appearance?

Females are larger with a pointed posterior and no spicule, while males are small with a curved posterior and a spicule.

What is the difference between Oviparous, Oviviparous, and Viviparous nematodes?

Oviparous lay immature/unsegmented eggs (e.g., $Ascaris$ $lumbricoides$); Oviviparous lay embryonated/segmented eggs (e.g., $Enterobius$ $vermicularis$); Viviparous lay larvae instead of eggs (e.g., $Trichinella$ $spiralis$).

What are amphids and phasmids?

They are chemoreceptors located at the anterior end (amphids/cephalic) and posterior end (phasmids/caudal) of the worm.

Which three nematodes are classified as aphasmid (without caudal chemoreceptors)?

$Trichuris$, $Trichinella$, and $Capillaria$.

What is the common name and habitat of $Ascaris$ $lumbricoides$?

It is known as the Giant intestinal roundworm and its habitat is the small intestines.

What are the Diagnostic Stage (DS) and Infective Stage (IS) of $Ascaris$ $lumbricoides$?

The DS is the presence of fertilized or unfertilized ova in stool; the IS is the embryonated egg.

What are the three layers of an $Ascaris$ $lumbricoides$ fertilized eggshell?

($1$) Inner vitelline/lipoidal/lecithin layer, ($2$) middle glycogen layer, and ($3$) outermost mammillation/corticated layer.

What is the larval migration path for $Ascaris$ $lumbricoides$?

Intestinal wall $\rightarrow$ Blood vessel $\rightarrow$ Liver $\rightarrow$ Blood vessels $\rightarrow$ Lungs $\rightarrow$ Alveoli $\rightarrow$ bronchioles $\rightarrow$ pharynx $\rightarrow$ Small intestine.

What syndrome is associated with the larval migration of $Ascaris$ $lumbricoides$ involving eosinophilia?

Loeffler’s syndrome (also called Ascaris pneumonitis).

What are the common names for $Enterobius$ $vermicularis$?

Pinworm, Social worm, Society worm, and Seatworm.

Where does the gravid female of $Enterobius$ $vermicularis$ deposit her eggs?

She migrates to the perianal region to deposit eggs, which often causes pruritus ani (nocturnal itching).

What is the characteristic shape of an $Enterobius$ $vermicularis$ egg?

It is elongated, flattened on one side, and D-shaped.

What is the diagnostic method of choice for Enterobiasis?

The perianal swab using the Scotch tape swab (or Cellulose tape swab) technique.

What is the common name and diagnostic characteristic of the $Trichuris$ $trichiura$ egg?

Commonly known as Whipworm; the egg is barrel-shaped (football-shaped) with prominent hyaline bipolar mucus plugs, resembling a Japanese Lantern.

What is a severe clinical manifestation of heavy $Trichuris$ $trichiura$ infection in children?

Rectal prolapse.

What are the components of the 'Unholy Three' or Triad of infection?

[HAT]: Hookworm, $Ascaris$ $lumbricoides$, and $Trichuris$ $trichiura$.

What is the common name of $Capillaria$ $philippinensis$ and how is it transmitted?

Known as the Pudoc worm; it is transmitted by the ingestion of raw or undercooked freshwater/brackish water fish like the Ipon ($Hypseleotris$ $bipartita$).

What is 'borborygmi' in the context of $Capillaria$ $philippinensis$?

A peculiar abdominal gurgling sound caused by the infection.

Differentiate between the teeth structure of $Ancylostoma$ $duodenale$ and $Necator$ $americanus$.

$Ancylostoma$ $duodenale$ has $2$ pairs of teeth, while $Necator$ $americanus$ has a semilunar cutting plate.

What is the Infective Stage (IS) and Method of Transmission (MOT) for hookworms?

The IS is the $L3$/Filariform Larva (sheathed), and the MOT is skin penetration (direct penetration).

What condition is caused by chronic blood loss in hookworm infections?

Iron Deficiency Anemia, specifically Microcytic Hypochromic Anemia.

Why is $Strongyloides$ $stercoralis$ considered a facultative nematode?

It can exist as both a free-living organism in the soil and a parasitic organism in the small intestine.

What is the Diagnostic Stage (DS) for $Strongyloides$ $stercoralis$ in stool exams?

The Rhabditiform larva.

What is the 'Baermann Funnel Technique' used for?

It is a laboratory method where a fecal sample is suspended in warm water for up to $2$ hours to allow larvae to migrate for collection and microscopic examination.

In $Trichinella$ $spiralis$ infection, where are the larvae found in the human host?

They are encysted in striated muscle (skeletal muscle) within a 'nurse cell'.

How is $Trichinella$ $spiralis$ transmitted to humans?

Through the ingestion of undercooked or raw meat (usually pig or bear) containing encysted larvae.

Which filarial worm is associated with 'River Blindness' and what is its vector?

$Onchocerca$ $volvulus$, which is transmitted by the bite of the female black fly ($Simulium$ sp.).

How do the tails of $Wuchereria$ $bancrofti$ and $Brugia$ $malayi$ microfilaria differ?

$Wuchereria$ $bancrofti$ has no nuclei in the tail tip, while $Brugia$ $malayi$ has $2$ separate nuclei at the tip of the tail.

What is the periodicity of $Loa$ $loa$ microfilaria in the blood?

Diurnal (daytime).

What is the common name of $Dracunculus$ $medinensis$ and its intermediate host?

Commonly called the Guinea worm or Fiery serpent; its intermediate host is the aquatic crustacean ($copepod$) called $Cyclops$.

What is the traditional method for removing an adult $Dracunculus$ $medinensis$ worm?

Worms are attached to a stick and slowly retracted from the host by gradually turning the stick over time.

What is the 'Shepherd's Crook' referring to in parasitology?

The tail shape of the microfilaria $Mansonella$ $streptocerca$.