Nematodes, Cestodes and Trematodes Flashcards
1
Q
- Name 5 species of clinically significant Cestodes
A
- Taenia saginata - beef tapeworm
- Taenia solium - pork tapeworm
- Diphyllobothrium latum - broad/fish tapeworm
- Hymenolepsis nana - dwarf tapeworm
- Echinococcus spp. - hydatid
2
Q
What are Helminths?
A
- ‘parasitic worms’
- 2 phyla
- Platyhelminthes - flatworms
- Cestodes - tapeworms
- Cyclophylidea ‘Land’
- Taenidae: T**aenia, Echinococcus
- Hymenolepidae: Hymenolepsis
- Pseudophyllidea ‘Water’
- Diphyllobothridae: Diphylobothrium
- Cyclophylidea ‘Land’
- Trematotodes - flukes
- Cestodes - tapeworms
- Nematodes - roundworms
- Platyhelminthes - flatworms
3
Q
What is the Generalised Tapeworm Lifecycle?
A
- Adults ⇒ definitive hosts
- Eggs ⇒ external environment
- Juveniles ⇒ Intermediate host
- Hymenolepsis nana ⇒ humans
- Taenia saginata ⇒ cattle
- Taenia solium ⇒ pigs
- Diphylobothrum latum ⇒ copepods, fish
- Hymenolepsis nana ⇒ larvae of cereal meal worms or fleas (rodent reservoir)
- Hymenolepsis diminula ⇒ fleas or flour beatles
- Diphylobothrum caninum ⇒ dog or human flea (Ctenocephalides canis or C. felis)
4
Q
Name 4 species of clinically significant Trematodes.
Etymology
A
- Fasciola hepatica - the liver fluke
- Paragonimus westermani - the lung fluke
- Opisthorchis sinensis - Chinese liver fluke (aka Clonorchis sinensis
- Schistosoma mansoni, S. japonicum, S. haematobium - schistosome or bilharzia flukes
- Etymology: old English word for Flounder
5
Q
5 species of Clin. significant Nematodes.
What is the etymology?
A
- Strongyloides stercoralis - threadworm
- Necator americanus & Ancylostoma duodenale - the Hookworms
- Ascaris lumbricoides - the Large Roundworm of Man
- Tricuris trichuria - the Whipworm
- Enterobius vermicularis - the pinworm
- Toxocara canis & toxocara cati - Visceral and ocular larva migrans
- From Greek “nema” or thread
6
Q
What is this?
Life cycle?
Symptoms?
A
- Ascaris
- largest of intestinal soil-transmitted helminths
- adults live in intestine, eggs passed in feces and contaminate environment, water and food
- Ascariasis caused by ingeting eggs on soiled hands or consuming fruit or veg that have not been washed or peeled
- eggs hatch into larva in small intesting, penetrate intestinal wall and migrate through blood and lungs where they may cause symptoms
- if coughed up and swallowed they return to gut to mature and reproduce
7
Q
What are these?
A
- left to right
- Necator americanus or Cyclostoma duodenalis (hookworm) egg
- tricuriasis (whipworm) egg
- fertile ascaris egg
8
Q
What is this?
Describe it.
A
- fertile Ascaris egg
- oval shape, about 60µm long
- brownish colour
- thick shell covered by a rough coat stained brown by bile in gut
9
Q
What is this?
Describe it?
Describe it and what triggers it to dev
A
- infective Ascaris egg
- oval, thick wall, contains visible larvum
- as the fertile egg leaves host, reduction in temperature, oxygen and moisture levels trigger ovum to develop into this infective stage
- takes 20-40 days to do so
- if ingested in contaminated food, will hatch in intestine and person will become infected
10
Q
What is this?
Describe.
A
- infertile Ascaris egg
- less common in feces than fertile eggs
- egg is longer an narrower than fertile ege, as large as 75-90µm long
- usually very dark in colour with flattened ends
11
Q
What is this?
Where is it found?
Life cycle?
A
- adult pinworm (Enterobius)
- worldwide distribution, commonly affects children
- female deposits eggs on perianal skin during night, and within a few hours of being laid they contain infected larvae (embryonated eggs)
- child scratches and autoinoculates self, eggs travel to intestin and hatch
- sometimes larvae hatch on perinal skin and migrate back to the intestine and mature
12
Q
What is this?
Describe.
Life Cycle
How diagnosed?
A
- Enterobius eggs
- oval in shape, colourless, with clear shell
- about 55 µm long
- eggs laid on perianal skin, eggs become infective within few hours, itching causes host to scratch and then reinfects self by swallowing fertile egss, which hatch in the intestine
- best collected from perianal skin at night “sellotape method” or “Graham swab”, eggs visible under microscope
13
Q
What is this?
Life Cycle?
Clinical disease?
Complications?
A
- trichuris (whipworm)
- round worm of humans found in warm moist climate and poor sanitation
- may occur in cecum, ileum, appendix and colon of humans
- ingestion of infective eggs in contaminated food/fingers
- light infections may cause few symptoms
- young children severe infections may cause chronic diarrhea, ulceration with blood and mucous passed in stool
- fe deficiency, wt loss
- prolapse rectum
14
Q
What is this?
What other symptoms may occur?
A
- prolapsed rectum in child
- caused by whipworm (Trichuris)
- fe def anemia, wt loss
15
Q
What is this?
Describe it.
Life Cycle.
How long does egg take to become infective.
A
- trichuris egg (whipworm)
- egg barrel-shaped, 50 µm long with clear mucoid plug at either end
- when passed in feces egg contains undeveloped ovum
- after about 3 weeks in soil becomes embryonated (infective)
- infective egg ingested from contaminated food or fingers, larvae hatch and develop in small intestine
- adult worms bore into wall of the large intestine and embed in anterior part of mucosa
- secretes digestive fluid into tissues of intestinal wall, liquefying surface, which is then taken up by the worm
16
Q
What is this?
Describe it?
Size, distinctive characteristics.
A
Trichuris (whipworm) egg.
egg barrel-shaped, 50 µm long with clear mucoid plug at either end
17
Q
What is this?
A
- hookworm (Ancylostoma duodenale or Necator americanus)
- adult parasites live in small intestine, sucking and ingesting blood through intestinal wall
- male worms 8-9 mm, females 11-12 mm, heads of both males and females are bent dorsally giving “fishing hook appearance”
18
Q
What is this?
Geographic distribution?
Life Cycle?
Disease?
A
- Ancylostoma duodenale
- hookworm
- worldwide in areas with moist warm climate
- this species predominant in Middle East, Africa, Southern Europe
- transdermal entry via hair follicles, also ingested orally ⇒ Wakana syndrome
- preferred site upper small intestine, but in very heavy infections may extend as far as lower ileum
- hookworm mouthparts of adult penetrate blood vessels, nourish by sucking blood
- cause chronic anemia, blood loss
- differentiate from N. americanus by teeth in buccal cavity. N. americanus has flat cutting plate
19
Q
What is this?
Geographical distribution?
How distinguished from similar parasite?
A
- Necator americanus
- hookworm
- this species predominates in America and Australia
- distinguished by flat cutting plates in N. americanus vs teeth in A. duodenale
20
Q
What is this?
FOBT?
A
- adult hookworm, either Necator americanus or Ancylostoma duodenale
- teeth embedded in small intestine wall
- FOBT usually positive
21
Q
What is this?
Life Cycle
A
- Hookwoorm eggs
- Ancylostoma duodenale and Necator americanus are indistinguishable
- Size: 57-76 µm, oval or ellipsoidal shape
- thin shell
- eggs passed into stool, hatch into rhabditiform larvae, which take about a week to develop into infective stage
- larvae penetrate skin usually of foot, travel through venous circulation through lungs up to trachea then swallowed, travel to small intestine, attach and mature into adults after feeding on blood
- female hookworms produce up to 30,000 eggs per day
22
Q
What is this?
Characteristic features?
A
- hookworm larvae
- long buccal cavity at anterior end, which differentiates them from Strongyloides larvae
- no notch at the tail end
23
Q
What is this?
sex?
Morphology? Identification
Life Cycle?
A
- Adults of Strongyloides stercoralis may be found in human host or soil
- in human host no parasitic males
- parasitic females are long and slender, measuring 2-3 mm
- in human host, female lays eggs in intestinal mucosa, larvae hatch almost immediately to only larvae are found in feces
- larvae similar to first stage Hookworm larve but have shorter mouth cavity and are found in freshly passed feces (hookworm larvae are found in stale faeces)
24
Q
What is this?
What do the arrows indicate.
A
- female Strongyloides sterocralis larva passed in fresh species
- Red arrow indicates short (compared to hookworm larva) cavity and rhabditiform esophagus
- also differentiated by notch at tail end (not shown here)
25
Q
What are the specific clinical features/syndromes associated with ascariasis?
Larval migration?
Adult gastrointestinal parasitism?
General features?
A
- larval migration⇒verminous pneumonia
- adult GI parasitism⇒
- lactose intolerance
- vitamin A malabsorption
- intestinal obstruction
- hepatopancreatic ascariasis
- General
- impaired growth
- impaired physical fitness
- impaired cognition
- reductions in school attendance and performance
26
Q
What are the specific clinical features/syndromes associated with trichuriasis?
Common name?
Larval migration?
Adult gastrointestinal parasitism?
General features?
A
- whipworm
- lm: none
- adult GI parasitism:
- colitis
- trichuris dysentery syndrome
- rectal prolapse
27
Q
What are the specific clinical features/syndromes associated with hookworm
parasite name?
Larval migration?
Adult gastrointestinal parasitism?
General features?
A
- Ancylostoma duodenalis
- Necator americanis
- lm:
- ground itch
- cough
- Wakana disease: when A. duodenale transmitted orally, characterized by nausea, vomiting, pharyngeal irritation, cough, hoarseness, dyspnea
- adult gi parasitism
- intestinal blood loss
- fe def anemia
- protein malnutrition
28
Q
Describe the lifecycle of Ascariasi lumbricoides.
A
- infection via fecal-oral transmission
- embryonated eggs swallowed, first stage larvae (L1) hatch, moult into L2 then penetrate intestinal mucosa and migrate to pulmonary circulation
- L3 migrate across alveolar wall, ascend tracheobronchial tree to larynx, then to small intestine
- Adult female A. lumbricoides produce thousands of eggs daily that pass into stool
- Egg production occurs 2-3 months after infection and worms can live for several years
- Eggs remain viable in warm moist soil for years
29
Q
Describe Trichuris trichuria lifecycle.
A
- embryonated eggs ingested via food or hands, hatch into larvae that moult in small intestine
- larvae develop into adult worms in cecum and ascending colon
- female worms lay thousands of eggs daily for several years
- eggs pass into stool, embryonate over 2-4 weeks in warm, moist soil
- survive for months
30
Q
Describe hookworm lifecycle.
Which species?
A
- Ancyclostoma duodenal and Necator americanus larvae free living in soil
- infect people by penetrating skin, usually feet
- larvae migrate to pulmonary capillaries, penetrate alveolare wall, migrate to larynx and are swallowed
- larvae moult and develop into mature worms in small intestine over 1-2 months
- can survive for months (A. duodenalis) or years (N. americanus)
- female worm releases thousands of eggs daily into stool
- after 5-10 days hatch in warm, moist, sandy soil or feces
- Rhabditiform larvae (L1) become infective after moulting to L2 & L3 larvae that survive for several weeks
- A. duodenalis can also be ingested orally and can cause Wakana syndrome (nausea, vomiting, pharyngeal irritation, cough, hoarseness, dyspnea)
- Zoonotic ancylostoma species can also infect people, causing cutaneous larva migrans (as well as possibly causing pathology similar to a. duodenalis or necator americanus in some people)
31
Q
What is Wakana syndrome and how does it occur.
A
- hookworm Ancyclostoma duodenalis can also be ingested orally instead of penetrating skin resulting in Wakana syndrome (nausea, vomiting, pharyngeal irritation, cough, hoarseness, dyspnea)
32
Q
What causes cutaneous larva migrans?
A
- infection by zoonotic ancyclostoma species
- eg dog or cat hookworm
33
Q
Strongyloides stercoralis lifecycle.
A
- complex lifecycle, may take multiple routes including complete lifecycle outside human host
- filariform larvae inject human host orally or percutaneously
- skin, esp feet ⇒ pulmonary capillaries to alveoli, then larynx to small intestine
- oral ingestion same route after penetrating intestinal mucosa to lungs etc.
- female adults penetrate gut wall, lodging in duodenal & jejunal lamina propria, laying up to 50 eggs daily
- eggs hatch within gut wall, rhabditiform larvae migrate to lumen and are passed with stol
- larvae might penetrate colonic wall or perianal skin to enter a newy cycle or disseminate to other organs
- autoinfection may last decades without repeated external exposure
34
Q
Describe possible clinical presentations with S. stercoralis.
A
- commonly assymptomatic in otherwise healthy
-
pulmonary migration of larvae ⇒ eosinophilic pneumonia with cough, dyspnea, wheezing, hemoptysis
- in hyperinfection pneumonia may be severe, fatal
- chronic strongyloidiasis: asthenia, anorexia, nause, abd pain, diarrhea, abdominal tenderness
-
larva currens common in chronic infection, serpiginous urticaria, typically over abdomen, torso, buttocks, groin
- lesions last a few days
- rarely reactive arthritis
- in immunosupressed strongyloides hyperinfection syndrome leading to pulmonary or intestinal failure
- disseminated strongyloidiasis to any organ in immune suppressed
35
Q
How many eggs will a femal ascaris worm produce per day?
A
- 200,000 sticky resistant eggs/day
36
Q
Ascaris: how many infections per year?
how many deaths?
A
1 billion infections
20,000 deaths
37
Q
What kinds of disease can ascaris larvae produce?
A
- A: pneumonitis
- seasonal fever, cough, hemoptysis, bronchospasm
- Dx: Eosinophilia, larvae in sputum, lobular consolidation
- B: ectopic e.g. brain
- C: allergy
38
Q
What are possible effects of ascaris adult worms?
A
- GI
- intestinal obstruction, also volvulus, intussusception, gangrene, perforation, rectal prolapse
- malnutrition, stunting, developmental
- lactose intolerance
- vit A deficiency
- bile duct migration: biliary coli, stones, liver abscess (20 bacterial), pancreatic duct, ascending cholangitis
- migration to mouth, nose or anus during fever
39
Q
Eosinophilia means …?
A
Worms
- predominantly nematodes (roundworms) and trematodes (flukes).
- non-invasive tapeworms (cestodes) dont usually cause it
- except Hymenolepsis nana
- Invasive tapeworms do. i.e. hydatid disease, but often not until rupture
40
Q
Ascaris treatment?
What about intestinal obstruction?
A
- mebendazole 100 mg bid x 3 days or
- albendazole 400 mg one dose
- deal with the obstruction first, hydratin, ng suction acutely, then deworm
- may require laparotomy
41
Q
What aspects of worm population dynamics limit success of mass deworming programs?
A
- heavy infections concentrated in few individuals
- worm “crowding” reduces egg output
- treatment rarely removes all worms
- surviving worm population compensates by producing mor eggs/worm
- worm prevalence in human population may diminish acutely but rises rapidly to baseline within a year
42
Q
Summary of worm treatments:
First and alternative for
Ascaris
trichuris
hookworm
strongyloides
A
- For Ascaris and hookworm, first line treatments are
- albendazole 400 mg single dose or
- mebendazole 500 mg single dose or
- mebendazole 100 mg bid for 3 days
- Trichuris needs longer courses:
- albendazole 400 mg od x 3 days or
- mebendazole 500 mg od x 3 days or
- mebendazole 100 mg bid for 3 days
- ivermectin 200 µgm/kg daily x 3 d
- Strongyloides needs Ivermectin 200µgm/kg daily x 2 d
- with long high doses of albendazole as alternatives
- Of the four, only hookworm cannot be treated with ivermectin
- This poses a problem for mass deworming campaigns that would then have to include both albendazole and ivermectin in order to target all 4 STH
43
Q
What are the early clinical features of hookworm disease?
A
- ground itch: unusual
- itch, edema, erythema, papulo-vesicular eruptions lasting 1-2 wks
- pulmonary sx: unusual
- cough (“foxhole cough” 1st WW), mucoid sputum, wheezing
- Initial intestinal sx
- abd pain, diarrhea, steatorrhea
- Initial eosinophilia
44
Q
What is this and what is it caused by?
A
- cutaneous larva migrans
- cat or dog hookworm larvae
45
Q
What are the chronic clinical effects of hookworm?
A
- chronic gi nutritional defects
- protein loss
- anemia esp if child has borderline iron intake/stores
46
Q
What distinguishes hookworm from trichuriasis and ascariasis in terms of worm burden distribution and age.
A
- hookworm burden increases with age, in contrast with ascaris lumbricoides and trichuris trichiuria, whic are most intense in childhood.
47
Q
How does skin pallor associated with hookworm respond to deworming.
A
- skin pallor associated with hookworm disease due to fe deficiency, which recovers quickly after deworming
- Pallor due to hypoproteinemia is slower to recover
48
Q
Treatment of hookworm anemia
A
- oral iron eg Ferrous sulfate 200 mg tid x 3 months after hgb normal
- folic acid 5 mg daily at least 1 month
- vit c if not present in diet
- deworm with albendazole or mebendazole
- nb NOT ivermectin
49
Q
What is this?
Outline diagnosis and treatment
A
- barrel shaped eggs in faeces
- proctoscopy shows worms in heavy infections
- treat with mebendazole or albendazole (or thiabendazole) - only moderately effective so REPEAT
- oral iron, hydration
50
Q
What are these and how are the species distinguished?
How many suckers?
A
- Taenia saginatum (left) - beef tapeworm
-
Taenia soleum (right) - pork tapeworm
- 13-30 primary lateral uterine branches on T. saginatum; 7-13 on T. soleum
- scolex on both have 4 suckers, but T. soleum has hooks, T. saginatum does not
- Eggs from both are identical
51
Q
What are these and how are they distinguished from other species?
A
-
Taenia species ova
- T. saginatum and T. soleum eggs indistinguishable
- eggs round, 33 -43 µm with thick radially striated dark brown wall
- inside each shell an embryonated oncosphere with 3 pairs of hooks
- egg in figure C still has primary membrane (yolk sac) that surrounds eggs in uterine branches
- distinguish T. saginatum and T. soleum by presence of hooks on scolex of latter
52
Q
What are these?
Distinguishing features?
A
- Diphyllobothrium latum ova
- egg pale yellow-brown and oval shape
- 65-70 µm
- operculum at one end can be hard to see
- egg contains mass of granulated yolk cells surrounding undeveloped ovum
- eggs mature and hatch in freshwater and after 1-2 wks hatch to release ciliated coracidium stage
53
Q
What are these?
How is the diagnosis made?
How long are the eggs infective in the environment?
What are the intermediate hosts?
What are the definitive hosts?
A
- Eggs of H. nana in an unstained wet mount. Note the presence of hooks in the central oncosphere and polar filaments within the space between the oncosphere and outer shell.
Diagnosis is by identifying the distinctive eggs in faeces: eggs of Hymenolepis nana are immediately infective when passed with the stool and cannot survive more than 10 days in the external environment.
When eggs are ingested by an arthropod intermediate host (beetles and fleas may serve as intermediate hosts) they develop into cysticercoids, which can infect humans or rodents upon ingestion and develop into adults in the small intestine
54
Q
What is this?
A
Hydatid Sand
55
Q
What is this?
A
Hydatid Cyst Cross Section
56
Q
Name the four main clinically significant species of tissue flukes and their 2nd intermediate hosts.
A
57
Q
Praziquantel dosing (fix this card)
A
tabs 600 mg, can be broken in 1/4 or have
child dose is 15 mg/kg
use height scale
58
Q
Describe the lifecycle of Necator americanus.
What are the clinical features of acute infection and the consequences of that infection.
A
- eggs are passed in the soil and embryonate there, hatching into larvae
- larvae “quest” on grass or pass through skin from ground, migrate through heart and lungs, coming out through trachea then descending into GI tract
- In some areas, oral ingestion of cysts is very common⇒Wakana syndrome
- larvae mature into adults after passing down GI tract to duodenum, anchor there and small intestine consuming blood
- Syndromes:
- ground itch
- cough
- Wakana disease: when larvae are transmitted orrally, they produce nausea, vomiting, pharyngel irritation, cough, hoarseness, dyspnea
- Adult GI parasitism in small intestine leads to
- intestinal blood loss
- fe def anemia
- protein malnutrition
59
Q
- What is the best initial treatment of a patient with high Loa loa microfilaraemia?
A
- Albendazole
- Treatment of individuals with high Loa loa microfilaraemia is associated with a risk of encephalopahty if ivermectin or DEC is used. Albendazole administration for 3 weeks initially reduces the microfilarial load and the risk of encephalopathy. Doxycycline is used in other filarial worms that carry Wolbachia, but this does not apply to Loa loa. Praziquantel is used in other parasitic infections, eg schistosomiasis, taeniasis.
60
Q
- How can the differentiation of adult Taenia species in humans most accurately be achieved?
A
- By examining the scolex
- The eggs of Taenia solium and T. saginata are identical in morphology and can’t be distinguished. Both may appear in faeces. Microscopy of mature proglottids can indicate species, as T. saginata proglottids have more uterine branches than those of T. solium (12-30 vs. 7-13), but since this is variable it is not very accurate. The scolices (heads) of T. saginata and T. solium are different: T. solium has hooks and suckers, whereas T. saginata has only suckers.
66
Q
- What is the intermediate host for schistosomes?
- What is the definitive host?
- Describe the life cycle.
- For which species of Schistosome do monkeys provide an animal reservoir?
A
- Snails are the intermediate host
- humans (and monkeys, which provide a reservoir) for S. hematobium and S. mansoni are the definitive hosts
- pair of adults inhabit parts of the venous system of the human host including the terminal venules of the bowel wall in the case of S. mansoni and japonicum; and of the bladder in the case of S. hematobium.
- the eggs migrate to the lumen of the bowel or bladder and are released into the environment
- in water they hatch to release a miracidium larva, which penetrates the snail intermediate host and multiply to produce mother, then daughter sporocysts that break out of the snail
- as cercariae and penetrate human skin, which migrate into the venules, where male and female forms unite and copulate and release eggs and so on …
69
Q
Which snails act as intermediate hosts for which species of schistosome?
A
- S. mansoni intermediate host Biomphalaria snails.
- S. hematobium, intermediate host snail Bulinus.
- S. japonicum east Asia, eradicated from Japan. Intermediate host snail Oncomelania.
- (Lymnea plays a role in transmission of Liver fluke)
70
Q
What are these and for what are they intermediate hosts?
A
- Bulinus - S. hematobium
- Biomphalaria - S. mansoni
- Oncomelania - S. japonicum
- Lymnea - Fasciola hepaticum (liver fluke)
71
Q
What is this?
A
- S. mansoni egg, note lateral spine
- size 150 x 60µm
73
Q
What is this?
A
- S. japonicum egg (S. mekongi similar)
- 85x60µm
74
Q
What is this?
A
- S. hematobium egg - note terminal spine
- 155x55µm
75
Q
- What is this?
A
- Biomphalaria glabrata, major intermediate snail host for S. mansoni
76
Q
What is this?
How long does it live in water after release from snail?
What is the name of the form that infects the snail?
A
- cercaria (of S. mansoni)
- about 8 hrs before utilizing glycogen stores (Parasitic Diseases). Beeching says cercariae survive for about 2 days in fresh water.
- miracidium
- Cercariae are highly motile, fork-tailed, non-ciliated organisms barely visible to the human eye (200–500 µm long).
- Cercariae (L-2 or stage-2 larvae) are released each day from infected snails in accordance with a circadian rhythm. Their release is triggered by light and temperature, which act as external cues (zeitgebers).
- They are especially attracted to shadows, to any water disturbance and, significantly, to the chemicals on human skin.
- Top part breaks off once penetrates skin, leaving tail behind and becomes schistosomulum.
77
Q
What is this?
A
- occurs primarily in heavy acute infections with S. mansoni and S. japonicum (Sj>Sm>Sh due to # of eggs and immunogenicity)
- The symptoms are often dramatic and appear approximately 2-10 weeks after initial exposure, when adult worm pairs begin releasing their eggs in the tissues.
- Some investigators believe that Katayama fever resembles some of the manifestations of serum sickness: passive production of IgG to first round of egg production
- There is also a clinical resemblance to typhoid fever.
- Patients experience hepatosplenomegaly and lymphadenopathy as well as an impressive eosinophilia. The affected individual is frequently febrile and has flu-like symptoms, including cough and headache. At this stage of the illness, schistosome eggs may not yet have appeared in the feces.
- serology might be positive now, but may need to repeat
- diff diagnosis:
- strongyloides stercoralis, trichuris trichuria, capillaris phillipensis - examine stool for eggs of these parasites, though schistosoma eggs my not be seen this early
- typhoid fever
- malaria
82
Q
What is this?
A
- calcified bladder pathognomonic of S. hematobium infection
83
Q
What is this?
differential diagnosis?
A
- edema around schistosoma eggs in left hemisphere
- pml, toxo, tb, lymphoma, glioma
84
Q
What is a schistosomulum?
A
- A ‘schistosomulum’ is the name given to a cercaria once it has penetrated the skin and lost its tail. It is technically a third stage larva (L-3). After remaining in the skin for several days in search of a post-capillary venule, schistosomula pass to the lungs. S. mansonischistosomula are regarded as slower migrants than others, e.g. S. japonicum. Schistosomula do not multiply in the body.
88
Q
What are the principles of treating neurocysticercosis?
A
- Before therapy is planned, proper characterisation of the specific type and brain involvement of neurocysticercosis is important.42 Therapeutic approaches might include symptomatic therapy, antiparasitic treatment, or surgery (lesion resection or shunt placement), and often more than one of these options are needed)
- Generally consider whether cysts still viable or calcified - no point in treating dead cysts
- location: parencymal vs meningeal or intraventricular
- size of lesion: intraventricular racemose i.e. growing like cluster of a florette, need more aggressive aproach
- treat with AED’s, pretreat with steroids
- for multiple active lesions, esp with edema treat with albendazole or praziquentel for 2 weeks.
- solitary lesions may do as well with short course - 3 days of albendazole or 1 day of praziquantel
- 1 paper suggesting combined P & A x 10 days for few lesions
89
Q
What is the differential diagnosis for neurocystecercosis on CT?
A
92
Q
What is this?
What is the lifecycle?
A
- Echinococcus granulosus or dog tapeworm causes 90% of Hydatid Disease in humans, the remainder being caused by Echinococcus multilocularis.
- It is 5.5 mm long
- The zoonotic cycle for E. granulosus involves dogs as the definitive host, sheep or other ungulates as intermediate hosts. Humans are accidental intermediate hosts through accidental ingestion of eggs in dog feces through direct contact with domestic dogs, or through ingestion of contaminated groundberries such as cloudberries (Asia, Arctic).
- The ingested eggs hatch as oncospheres in the small intestine and penetrate the mucosa and enter the blood stream, most travelling via the portal circulation to the liver, where the oncospheres develop into encysted larvae. Unless the human gets eaten be a dog or wolf it is a dead end cycle for the tapeworm.
- Indigenous peoples of the Canadian Arctic, especially the Inuit, are infected with a north- ern variant, E. granulosus var. canadensis, acquired in a sylvatic cycle involving moose and caribou (cervids), wolves, and sled dogs.
- Alveolar Hydatid Disease is caused by E. multilocularis, in which humans become infected by swallowing eggs passed by foxes and other Canidae**, mainly by eating contaminated wild ground fruits such as bilberries, lingonberries and cloudberries, widely eaten in Northern Europe, Canada and highland China.
93
Q
What is this?
A
Dog tapeworm oocyst
Dipylidium caninum
94
Q
What is this?
A
- Hydatid cyst characteristic calcified rim of mother cyst
98
Q
What is the geographic distribution of Echinococcus?
A
99
Q
What is this?
A
- Embryonated Echinococcus eggs (Iodine stain)
100
Q
What is this?
A
- The water-lily sign is seen in hydatid infections when there is detachment of the endocyst membrane which results in floating membranes within the pericyst that mimic the appearance of a water lily.
It is classically described on plain radiographs (mainly chest X-ray) when the collapsed membranes are calcified but may be seen on ultrasound, CT or MRI.
104
Q
What is this?
Distinguishing features?
Adult morphology?
Lifecycle?
A
- Operculated egg, with knob, yellow-brown ~70 μm
- 2–10mlongadult
Bothria – sucking grooves
Segments ‘wider than long’
- Definitive Host: Human swallows plerocercoid larva, which attach to small intestine and grow, producing proglottids, shed proglottids and eggs in stool
- (Reservoir Host: Bears)
- In water, eggs hatch into coracidium (aquatic larvum) that is ingested by
- 1st Intermediate host: copepod
- procercoid larvum develops here and is taken up by
- 2nd intermediate host
- fish, where plerocercoid larvum develops, which is eaten by
- 1st Intermediate host: copepod
- Definitive or reservoir host and so on …
- Disease: Fish Tapeworm
105
Q
How do you tell T. soleum from T. saginatum?
A
- mainly by scolex
- both have 4 suckers, but only T. soleum has hooks
- can also tell by examining proglottid microscopically but less reliable. T. saginatum proglottid has approximately twice as many uterine branches
- 15-32 vs 7-13
107
Q
Describe the lifecycle of the fish tapeworm.
A
- Definitive Host: Human swallows plerocercoid larva, which attach to small intestine and grows, producing proglottids, shed proglottids and eggs in stool
- (Reservoir Host: Bears)
- In water, eggs hatch into coracidium (aquatic larvum) that is ingested by
- 1st Intermediate host: copepod
- procercoid larvum develops here and is taken up by
- 2nd intermediate host
- 1st Intermediate host: copepod
fish, where plerocercoid larvum develops, which is eaten by
- Definitive or reservoir host and so on …
108
Q
What might this be?
A
- Echinococcus adult and egg
109
Q
What is this?
How would you distinguish from other clinically relevant cestodes?
A
- Scolex.
Rostellum: a knob-like protrusion at the extreme anterior end of a tapeworm, as an extension of the tegument. It is globular, spiny structure when it protrudes, and a circular hollow pit when retracted. It is structurally composed of a number of concentric rows of hooks.
4 suckers + hooks - by size of proglottids: smaller overall and each segment much wider than long
- scolex: taenia also have 4 suckers, t. soleum has hooks, but only h. nana has rostellum
110
Q
Identify these eggs
A
111
Q
Identify these eggs
A
113
Q
What is the lifecycle of trichinella?
A
- one definitive host is man, others in domestic cycle are pigs and rodents: in sylvatic cycle bears, rodents, wild boars act as definitive host
- there are no intermediate hosts
- the disease was widespread in 40’s but has been controlled through improved animal husbandry of pigs; still foci of disease in China, Thailand and other parts of Asia where pork is still eaten raw.
- the worm is not shed via eggs in stool, but passed from one host to another through eating raw or undercooked meat containing nurse cells containing larvae. Capsule is digested by pepsin in stomach, releasing larvae, which mature in intestine, copulate and release a fresh round of larvae which penetrate intestinal mucosa and disseminate via blood stream throughout body causing acute febrile illness 2-8 weeks after ingestion of affected meat associated with fever, diarrhea, abd pain, headache, periorbital edema, occasionally fatal causing death.
- recovery and development of immunity prevents further reproduction of larvae and expulsion of adults. Larvae which have made it to skeletal muscle penetrate it and take over cellular metabolism to develop protective coat, angiogenesis about larvum to create host-parasite nurse cell that may last decades. Unless the body is consumed raw by another carnivore this is a dead end for the parasite.
117
Q
What is this?
What kind of host for what kind of parasite?
A
- Bulimus snail
- intermediate host for S. mansoni
118
Q
What are the 3 main species of Schistosome causing human disease?
Which snails?
What kind of disease do they cause?
Where are they found?
What is/are the other 3 related minor species causing human disease and where are they found?
A
-
Schistosoma haematobium
- causes urogenital schistosomiasis
- throughout Africa, parts of Arabia, Near East, Madagascar & Mauritius
- snail Bulinus
-
S. mansoni
- bowel and liver primarily
- Africa, Madagascar
- exported by slave trade to parts of South America, Caribbean and Arabia where permissive snail intermediate hosts found
- snail Biomphalaria
-
S. japonicum
- bowel and liver primarily
- China, Phillippines and Sulawesi (now eliminated from Japan)
- small focus on Mekong river caused by related S. mekongi
- snail Oncomelania
-
S. intercalatum and sister species S. guineensis minor species confined to West africa.
- inhabits veins of lower bowel and produc terminal-spined eggs
119
Q
What is this?
What causes it?
Serology?
A
- cercarial dermatitis
- cercarial penetration of skin and entering capillaries
- acutely in human schistosomal infection, also dead end manifestation of infection by avian schistosome’s (swimmers’ itch).
- serology will be negative
121
Q
What is this?
What are features of this disease on bowel?
On liver?
A
- polyposis
- inflammation bowel wall
- strictures
- bleeding, overt or occult
- may screen with FOB, Calprotectin tests
- periportal fibrosis with relative preservation of liver fx until late, portal hypertension
- S. japonicum has sl different pattern of fibrosis with normal parenchyma surrounded by “building blocks” of fibrosis, prob related to diff pattern of egg deposition
- should not usually have ascites or evidence of liver failure, so if you see this, consider comorbidities, eg. alcohol, chronic hepatitis
- once portal hypertension develops, can get egg deposition in lungs due to egg deposits through portosystemic collaterals ⇒ pulmonary hypertension
- 17% of children under 10 in Lake Albert Uganda had some degree of liver fibrosis
- nb can also get spillover of S. eggs into systemic circulation with S. hematobium
124
Q
Outline an approach to returning traveller with possible eposure to schistosomiasis.
A
125
Q
Can you draw a family tree for Parasitic Worms?
A
126
Q
What are the 4 main groups of food borne trematode diseases?
What are the infectious agents for each disease?
Through consumption of what food?
What is the natural final host for each infection?
A
- for all, larval stages are ingested as meta-cercariae/cysts
- adult worms in liver, lungs or gut
- eggs released harmlessly into lumen of gi tract (unlike schistosomiasis in which eggs are the main component causing harm)
127
Q
What is this? (30µm x 16µm)
Outline the lifecycle.
A
- Opisthorchis viverrini egg, but it could just as well be Clonorchis sinensis egg as the two are almost identical (also Opisthorcois felineus)
- Natural definitive hosts include dogs & cats and lifecycles are much the same
- In this case man is the definitive host
- embryonated eggs pass from feces into water
- eggs are ingested by snail
- free-swimming cercariae penetrate and encyst in skin or flesh of fresh water fish
- metacercariae in fish are ingested by human host (or other fish eating mammal)
- excyst in duodenum & ascend the biliary tract, where they mature to become
- egg producing adults
128
Q
What are the 3 human liver flukes and where are they endemic?
A
129
Q
What is this?
What disease might it transmit?
Where?
A
- Fresh-water crabs like this one were implicated in a Paragonimus outbreak in January of 2007. Specialty dishes in which shellfish are consumed raw or prepared only in vinegar, brine, or wine without cooking play a key role in the transmission of paragonimiasis. Raw crabs or crayfish are also used in traditional medicine practices in Korea, Japan, and some parts of Africa.
- Several species of Paragonimus cause most infections;
- the most important is P. westermani, which occurs primarily in Asia including China, the Philippines, Japan, Vietnam, South Korea, Taiwan, and Thailand.
- P. africanus causes infection in Africa, and
- P. mexicanus in Central and South America.
- Although rare, human paragonimiasis from P. kellicotti has been acquired in the United States, with multiple cases from the Midwest. Several cases have been associated with ingestion of uncooked crawfish during river raft float trips in Missouri
130
Q
What is this?
(It measures 110µm x 60µm)
What disease does it cause?
Describe lifecycle
A
- Paragonimiasis
1. The eggs are excreted unembryonated in the sputum, or alternately they are swallowed and passed with stool .
2. In the external environment, the eggs become embryonated , and
3. miracidia hatch and seek the first intermediate host, a snail, and penetrate its soft tissues .
4. Miracidia go through several developmental stages inside the snail : sporocysts , rediae , with the latter giving rise to many cercariae , which emerge from the snail.
5. The cercariae invade the second intermediate host, a crustacean such as a crab or crayfish, where they encyst and become metacercariae. This is the infective stage for the mammalian host .
6. Human infection with P. westermani occurs by eating inadequately cooked or pickled crab or crayfish that harbor metacercariae of the parasite .
7. The metacercariae excyst in the duodenum , penetrate through the intestinal wall into the peritoneal cavity, then through the abdominal wall and diaphragm into the lungs, where they become encapsulated and develop into adults (7.5 to 12 mm by 4 to 6 mm). The worms can also reach other organs and tissues, such as the brain and striated muscles, respectively. However, when this takes place completion of the life cycles is not achieved, because the eggs laid cannot exit these sites. Time from infection to oviposition is 65 to 90 days.
Infections may persist for 20 years in humans. Animals such as pigs, dogs, and a variety of feline species can also harbor P. westermani.
133
Q
What is this?
(size 140µm x 75µm)
What disease?
What is the lifecycle?
A
- Fasciola hepatica egg
- Definitive host human (or sheep or cow)
- Snail is the intermediate host
- immature Fasciola eggs are discharged in biliary ducts and in stool
- Eggs become embryonated in water and
- Invade suitable snail intermediate host, including genera Galba, Fossaria, and Pseudosuccinea.
- Undergoes several developmental stages in snail (sporocysts, rediae and cercariae)
- Cercaria released from snail
- encyst as metacercariae on aquatic plants, esp watercress, where they are ingested by humans, cattle or sheep (or possibly by drinking unfiltered water)
- After ingestion the metacercariae excyst in duodenum and
- migrate through the intestinal wall, the peritoneal cavity and the liver parenchyma into the biliary ducts where they develop into adult flukes.
- In humans maturation from metacercariae into adult flukes takes 3-4 months. Adult flukes reside in biliary ducts of mammalian host.
135
Q
Outline the generic lifecycle of a FBT
A
136
Q
Outline the general clinical facts about trematodes
A
