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
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
3
Q
What is viviparous?
A
ova with a larvae inside ( giving birth to larvae no egg stage )
4
Q
What is the disease caused by T.spiralis ?
A
Trichinellosis
5
Q
Who is the host in T.spiralis?
A
- Human
- pigs
- some wild animal (bears)
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
7
Q
Where is the encysted larvae found in T.spiralis ?
A
present in the striated muscles of these hosts
8
Q
Mode of infection in T.spiralis
A
eating raw or undercooked pork meat containing the viable larvae
9
Q
What is “ nurse cell “ ?
A
A muscle cell carrying larva of T. spiralis
10
Q
What is the infective stage of T.spiralis ?
A
Encysted larva found in the muscles of pigs and other animals
11
Q
How are cysts released in T.spiralis ?
A
By gastric juices
12
Q
How man times does the larvae T.spiralis peneterate the mucosa to develop in adults ?
A
Moult 4 times
13
Q
When does the male die in T.spiralis ?
A
after fertilizing the female
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
15
Q
In which cells are the larvae encysted ?
A
Muscle cells
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
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
18
Q
Clinical featutures of T.soiralis in the “ Stage of intestinal invasion “?
A
- Malaise
- nausea
- vomiting
- diarrhea
- abdominal cramps
*Onset is within hours of ingestion of infective food
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
20
Q
Clinical featutures of T.soiralis in the “ Final stage”
A
The infective larvae become encysted in this stage and all symptoms subside
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
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
23
Q
Disease of Ascaris lumbricoides
A
Ascariasis
24
Q
Adult morphology in A.lumbricoides
A
They are large cylindrical worms, with tapering ends
25
Male worm morphology in A.lumbricoides
* 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
26
Female wirm morphology in A.lumbricoides
* The female is larger than male, measuring 20–40 cm in length and 3–6 mm in thickness.
* Its posterior extremity is straight
27
Describe the 2 tyoe eggs in A.lumbricoids
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
28
A.lumbricoid Egg development in soil
The fertilized eggs emberyo develops the infective rhabditiform larva coiled within the egg
29
Infective stage of A.lumbricoid
Eggs containing the infective rhabditiform larva
30
How the egg is transmitted in A.lumbricoid ?
Ingestion of eggs containing the infective rhabditiform in food or water contaminated with human feces
31
Explain how A.lumbricoid is developed in man
* 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
What is the symptoms due to the Migrating Larvae in A.lumbericoid
Loeffler’s syndrome ——-> Ascariasis pneumonia
33
Symptoms due to the Adult Worm in A.lumbricoid
1. Asymptomatic infection
2. Nutritional effects: when the worm burden is heavy.
3. Mechanical effects: Masses of worms causing luminal occlusion
34
What are the Ectopic ascariasis (Wanderlust) symptoms ?
Acute biliary obstruction
Pancreatitis
Obstructive appendicitis
35
Diagnosis of A.lumbericoid
1. Parasote detection :
* Adult Worm:
can occasionally be detected in stool
* Eggs:
Main diagnosis of ascariasis is made by demonstration of eggs in feces
2. Serological tests :
* Serodiagnosis is helpful in extra intestinal ascariasis like Loeffler’s
syndrome
36
Ancylostoma duodenale & Necator americanus are which type of worm?
Hook worm
37
Adult morphology of hookworm
* 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
Egg morphology of hook worm
* 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
How many blastomeres are found in the hook worm >
4 to 8 blastomeres
40
What is the characteristic diagnose feature in hook worm ?
clear space between the segmented ovum and the inner egg shell
41
Whi is the definite host in hookworm ?
Human only
42
Mode of infection in Ancylostoma duodenale & Necator americanus
Penetration to the skin, when a person walks barefooted on soil containing the filariform larva
43
What is the infective form in both Ancylostoma duodenale & Necator americanus?
Third stage filariform larva
44
Pathogenesis of the larvae in soil of hook worm
* The embryo (rhabditiform larva) develops inside the eggs.
* Rhabditiform larva released and moults twice, to become
the third-stage infective filariform larva
45
After skin penetration where is the larvae carried ?
along the venous circulation to the right side of the heart and to the lungs
46
Explain the destination of larvae after being carried ?
*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
Clinical features due to migrating larvae in hook worms
1. Ground itch
2. Creeping eruptions
3. Respiratory manifestations
48
Clinical features due to adult larvae in hook worms
Adult worms suck blood and the minute bleeding at their sites of attachment lead to :
microcytic hypochromic anaemia
Epigastric pain, vomiting and diarrhea
49
Direct diagnosis of hookworm
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
Indirect diagnosis of hook worms
Blood examination:
* reveals microcytic, hypochromic aneamia and eosinophilia
51
Morphology of Strongyloides stercoralis adult female worm
* The female worm is thin, transparent, about 2.5 mm long and
0. 05 mm wide.
* The worm is ovoviviparous.
52
Morphology of Strongyloides stercoralis adult male worm
* 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
Disease of Strongyloides stercoralis
Strongyloidosis
54
Describe the S.stercoralis egg structure
* 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
Describe the S.stercoralis larva structure
* 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
Who is the natural host in s.stercoralis?
Human
57
What is the infective form of S.stercoralis ?
Filariform larva
58
Mode of infection in S.stercoralis
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
What makes the S.stercoralis unique ?
it has a parasitic cycle and a free living soil cycle
60
Direct development of rhabditiform larva in S.stercoralis
* 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
Free-living /indirect development of rhabditiform larva in S.stercoralis
* 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
What are the types of auto infection?
1. External
| 2. Internal
63
External autoinfection in S.stercoralis
* 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
Internal auto infection in S.stercoralis
* 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
Hyper infection in S.stercoralis
Patients with immune defects, extensive internal autoinfection
66
Clinical features of S.stercoralis
It is generally benign and asymptomatic.
Blood eosinophilia and larvae in stool being the only indications of infection
67
Cutaneous manifestations of S.stercoralis
* 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
Pulmonary manifestations of S.stercoralis
When the larvae escape from the pulmonary capillaries into the alveoli.
It causes Bronchitis, bronchopeumnia and loffeler’s syndrome
69
Intestinal manifestations of S.stercoralis
Mucus diarrhea often present
70
Diagnosis of S.stercoralis
* Stool examination:
* Direct wet mount of stool: Demonstration of the rhabditiform larvae in freshly passed stools .
* Concentration methods for stool examination
