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M2 | Microbiolgy > Intestinal infections by Nematodes > Flashcards

Intestinal infections by Nematodes Flashcards

1
Q

Adult morphology of Trichinella spiralis

A

Adult worm 🪱

• The adult T. spiralis, a small white worm

• The male measures about 1.5 mm by 0.04 mm and
- the female about 3 mm by 0.06 mm

  • The anterior half of the body is thin and pointed, to burrow into the mucosal epithelium
  • The females are viviparous
  • The posterior end of the male has a pair claspers, that are used to hold the female worm during mating
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2
Q

Larvae morphology of T.spiralis

A

The larva becomes encysted in the striated muscle

  • The larva in the cyst is coiled and hence, the name spiralis
  • Trichinella cysts are is formed by the tissue reaction around the larvae
  • Cysts develop preferentially in muscles which are constantly active such as diaphragm, biceps, muscles of jaw, extraocular muscles
  • Cysts lie longitudinally along the muscle fibers
  • The larva remains infective inside the cyst for years and eventually becomes calcified and dies
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3
Q

What is viviparous?

A

ova with a larvae inside ( giving birth to larvae no egg stage )

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4
Q

What is the disease caused by T.spiralis ?

A

Trichinellosis

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5
Q

Who is the host in T.spiralis?

A
  1. Human
  2. pigs
  3. some wild animal (bears)
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6
Q

Where does the adult worm in T.spiralis live ?

A

live deeply buried in the mucosa of small intestine of pig, bear, rat or human

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7
Q

Where is the encysted larvae found in T.spiralis ?

A

present in the striated muscles of these hosts

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8
Q

Mode of infection in T.spiralis

A

eating raw or undercooked pork meat containing the viable larvae

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9
Q

What is “ nurse cell “ ?

A

A muscle cell carrying larva of T. spiralis

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10
Q

What is the infective stage of T.spiralis ?

A

Encysted larva found in the muscles of pigs and other animals

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11
Q

How are cysts released in T.spiralis ?

A

By gastric juices

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12
Q

How man times does the larvae T.spiralis peneterate the mucosa to develop in adults ?

A

Moult 4 times

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13
Q

When does the male die in T.spiralis ?

A

after fertilizing the female

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14
Q

Which blood vessels does the female motile larvae enter into?

A

intestinal lymphatics or mesenteric venules and are transported in circulation to muscles

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15
Q

In which cells are the larvae encysted ?

A

Muscle cells

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16
Q

How is the passage of T.spiralis in oig to pig is facilitated?

A

feeding pigs with untreated garbage, which may contain bits of pork with infective cysts), rat to rat, and pig to rat

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17
Q

Who is considered the dead end host in T.spiralis ?

A

Humans

  • the cysts in human muscles are unlikely to be eaten by another host
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18
Q

Clinical featutures of T.soiralis in the “ Stage of intestinal invasion “?

A
  1. Malaise
  2. nausea
  3. vomiting
  4. diarrhea
  5. abdominal cramps

*Onset is within hours of ingestion of infective food

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19
Q

Clinical featutures of T.soiralis in the “ Stage of muscle invasion “

A

Fever, myalgia, periorbital edema, pain in affected muscle(s). The stage is seen few weeks after infection

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20
Q

Clinical featutures of T.soiralis in the “ Final stage”

A

The infective larvae become encysted in this stage and all symptoms subside

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21
Q

Direct methods of diagnosis in T.spiralis

A
  • Detection of spiral larvae in muscle tissue by muscle biopsy.
  • Detection of adult worms and larvae in the stool during the diarrheic stage.
  • Xenodiagnosis: For xenodiagnosis, biopsy bits are fed to laboratory rats. The larvae will be seen in the muscles of such infected rats
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22
Q

Indirect method diagnosis of T.spiralis

A
  • Serology :
    •There is hypergammaglobulinemia with elevated serum IgE.
  • T. spiralis antibodies can be detected by ELISA
  • Bachman intradermal test:
  • ID injection of dilution of the larval antigen. An erythematous wheal appears in positive cases within 15–20 minutes. The test remains positive for years after infection.
  • Radiological examination: Calcified cysts may be demonstrated on X-ray examination
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23
Q

Disease of Ascaris lumbricoides

A

Ascariasis

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24
Q

Adult morphology in A.lumbricoides

A

They are large cylindrical worms, with tapering ends

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25
Q

Male worm morphology in A.lumbricoides

A
  • The adult male worm is smaller than female. It measures 15–30 cm in length and 2–4 mm in thickness.
  • Its posterior end is curved ventrally and carries 2 copulatory spicules
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26
Q

Female wirm morphology in A.lumbricoides

A
  • The female is larger than male, measuring 20–40 cm in length and 3–6 mm in thickness.
  • Its posterior extremity is straight
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27
Q

Describe the 2 tyoe eggs in A.lumbricoids

A
  1. The fertilized eggs, laid by females after mating . They are embryonated and will develop to the infective eggs
  2. The unfertilized eggs are nonembryonated and cannot become infective
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28
Q

A.lumbricoid Egg development in soil

A

The fertilized eggs emberyo develops the infective rhabditiform larva coiled within the egg

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29
Q

Infective stage of A.lumbricoid

A

Eggs containing the infective rhabditiform larva

30
Q

How the egg is transmitted in A.lumbricoid ?

A

Ingestion of eggs containing the infective rhabditiform in food or water contaminated with human feces

31
Q

Explain how A.lumbricoid is developed in man

A
  • The rhabditiform larvae penetrate the intestinal mucosa, to lungs, where they grow and moult twice.
  • larvae pierce the lung capillaries to the alveoli, crawl the respiratory passages to the throat and are swallowed to reach intestine
32
Q

What is the symptoms due to the Migrating Larvae in A.lumbericoid

A

Loeffler’s syndrome ——-> Ascariasis pneumonia

33
Q

Symptoms due to the Adult Worm in A.lumbricoid

A
  1. Asymptomatic infection
  2. Nutritional effects: when the worm burden is heavy.
  3. Mechanical effects: Masses of worms causing luminal occlusion
34
Q

What are the Ectopic ascariasis (Wanderlust) symptoms ?

A

Acute biliary obstruction
Pancreatitis
Obstructive appendicitis

35
Q

Diagnosis of A.lumbericoid

A
  1. Parasote detection :
    * Adult Worm:
    can occasionally be detected in stool
  • Eggs:
    Main diagnosis of ascariasis is made by demonstration of eggs in feces
  1. Serological tests :
    * Serodiagnosis is helpful in extra intestinal ascariasis like Loeffler’s
    syndrome
36
Q

Ancylostoma duodenale & Necator americanus are which type of worm?

A

Hook worm

37
Q

Adult morphology of hookworm

A
  • They are cylindrical, pale pink or greyish white.
  • The body is curved with the dorsal aspect concave and the ventral aspect convex.
  • The posterior end of the male is expanded into a copulatory bursa with 2 long retractile copulatory spicules projecting from the bursa.
38
Q

Egg morphology of hook worm

A
  • Oval measuring 60 μm by 40 μm.
  • Surrounded by an outer thin transparent hyaline shell membrane.
  • When released by the worm in the intestine, the egg contains an un-segmented ovum and develops during its passage in feces to segmented ovum
  • There is a clear space between the segmented ovum and the inner egg shell
39
Q

How many blastomeres are found in the hook worm >

A

4 to 8 blastomeres

40
Q

What is the characteristic diagnose feature in hook worm ?

A

clear space between the segmented ovum and the inner egg shell

41
Q

Whi is the definite host in hookworm ?

A

Human only

42
Q

Mode of infection in Ancylostoma duodenale & Necator americanus

A

Penetration to the skin, when a person walks barefooted on soil containing the filariform larva

43
Q

What is the infective form in both Ancylostoma duodenale & Necator americanus?

A

Third stage filariform larva

44
Q

Pathogenesis of the larvae in soil of hook worm

A
  • The embryo (rhabditiform larva) develops inside the eggs.
  • Rhabditiform larva released and moults twice, to become

the third-stage infective filariform larva

45
Q

After skin penetration where is the larvae carried ?

A

along the venous circulation to the right side of the heart and to the lungs

46
Q

Explain the destination of larvae after being carried ?

A

*they escape from the pulmonary capillaries into the alveoli, migrate up the respiratory tract to the pharynx.

•They are swallowed, reaching their final destination small intestine

47
Q

Clinical features due to migrating larvae in hook worms

A
  1. Ground itch
  2. Creeping eruptions
  3. Respiratory manifestations
48
Q

Clinical features due to adult larvae in hook worms

A

Adult worms suck blood and the minute bleeding at their sites of attachment lead to :

microcytic hypochromic anaemia

Epigastric pain, vomiting and diarrhea

49
Q

Direct diagnosis of hookworm

A
  1. Direct wer microscopy :
    * oval segmented eggs in feces
    * by concentration methods is the best method of diagnosis
  2. Stool sample :
    * examined 24 hours or more after collection
    * the eggs may have hatched and rhabditiform larvae may be present
  3. Stool culture :
    * Harada Mori method” is carried out to demonstrate third stage filariform larvae
50
Q

Indirect diagnosis of hook worms

A

Blood examination:

  • reveals microcytic, hypochromic aneamia and eosinophilia
51
Q

Morphology of Strongyloides stercoralis adult female worm

A
  • The female worm is thin, transparent, about 2.5 mm long and
    0. 05 mm wide.
  • The worm is ovoviviparous.
52
Q

Morphology of Strongyloides stercoralis adult male worm

A
  • The male worm are shorter and broader than female measuring 0.6–1 mm in length and 40–50 μm in width.
  • The copulatory spicules, which penetrate the female during copulation, are located on each side of the gubernaculum.
53
Q

Disease of Strongyloides stercoralis

A

Strongyloidosis

54
Q

Describe the S.stercoralis egg structure

A
  • They are oval and measure 50–60 μm in length and 30–35 μm in breadth.
  • Eggs hatch out to rhabditiform larva.
  • The larva and not the egg, which is excreted in feces and detected on stool examination.
55
Q

Describe the S.stercoralis larva structure

A
  • Rhabditiform Larva (L1 first stage)

• In intestine and passes down in feces.

  • Filariform Larva (L3 third stage)
  • L1 larva moults twice to become the L3 larva.
  • It is the infective stage of the parasite to human
56
Q

Who is the natural host in s.stercoralis?

A

Human

57
Q

What is the infective form of S.stercoralis ?

A

Filariform larva

58
Q

Mode of infection in S.stercoralis

A
  1. Penetration of skin by the third stage filariform larva, when a person walks barefoot.
  2. Autoinfection: Explains the persistence of the infection in patients for years.
59
Q

What makes the S.stercoralis unique ?

A

it has a parasitic cycle and a free living soil cycle

60
Q

Direct development of rhabditiform larva in S.stercoralis

A
  • Walking barefoot, the infective larvae penetrate the skin
  • The larvae are carried to the right side of the heart, to the lungs, escape from the pulmonary capillaries into the alveoli, up to the pharynx, swallowed, reaching small intestine
  • In the intestine, they mature into adults
61
Q

Free-living /indirect development of rhabditiform larva in S.stercoralis

A
  • The rhabditiform larva passed in stools develop in soil into free-living males and females
  • They mate in soil
  • The female lays eggs, hatch to rhabditiform larvae
  • R€ epeat the free-living cycle or under unfavorable environment develop into the filariform larvae, infect humans and initiate the parasitic phase
62
Q

What are the types of auto infection?

A
  1. External

2. Internal

63
Q

External autoinfection in S.stercoralis

A
  • The rhabditiform larvae mature into the infective filariform larvae during their passage down the gut.
  • They cause reinfection by piercing the perianal and perineal skin during defecation causing a radiating “perianal creeping eruption” a form of“cutaneous larva migrans”.
  • They enter blood and are carried to the right heart and the lungs to complete the life cycle
64
Q

Internal auto infection in S.stercoralis

A
  • It is seen typically in immunodeficient hosts, the rhabditiform larvae mature into the infective filariform larvae in the bowel itself
  • Then penetrate to reach the mesenteric venules and are carried in circulation to complete the life cycle
65
Q

Hyper infection in S.stercoralis

A

Patients with immune defects, extensive internal autoinfection

66
Q

Clinical features of S.stercoralis

A

It is generally benign and asymptomatic.

Blood eosinophilia and larvae in stool being the only indications of infection

67
Q

Cutaneous manifestations of S.stercoralis

A
  • Pruritus and urticaria, around the perianal skin.
  • Larva currens ‘racing larvae’: rapidly progressing linear or serpigenous urticarial tracks caused by migrating filariform larvae.
  • These often follow autoinfection
68
Q

Pulmonary manifestations of S.stercoralis

A

When the larvae escape from the pulmonary capillaries into the alveoli.
It causes Bronchitis, bronchopeumnia and loffeler’s syndrome

69
Q

Intestinal manifestations of S.stercoralis

A

Mucus diarrhea often present

70
Q

Diagnosis of S.stercoralis

A
  • Stool examination:
  • Direct wet mount of stool: Demonstration of the rhabditiform larvae in freshly passed stools .
  • Concentration methods for stool examination

M2 | Microbiolgy (17 decks)

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