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parasites test 2 > test > Flashcards

test Flashcards

1
Q

what is the disease?

A

schistosomiasis

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2
Q

what are 2 other names for this disease?

A

bilharzia

snail fever

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3
Q

what is the causative agent of schistosomiasis?

A

parasites belonging to the genus Schistosoma

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4
Q

what are the 3 species responsible for most human cases?

A

s. mansoni
s. haematobium
s. japonicum

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5
Q

other human infections are also caused by which 2 species?

A

s. intercalatum

s. mekongi

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6
Q

schistosomes are blood flukes which are also known as

A

trematodes

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7
Q

adult worms are less than __cm long and live for ___ years

A

2

3-5

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8
Q

Why are Schistosomes unique among trematodes?

A

dioecious

with distinct sexual dimorphism

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9
Q

which sex are larger?

A

females

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10
Q

what defines the male?

A

they have longitudinal groove in which the female worm resides

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11
Q

where do the parasites live in the body?

A

in the veins around the bladder - s.haematobium

in the mesenteric (GI) blood vessels - s.mansoni, s.japonicum

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12
Q

thousands of eggs are released into the bloodstream, how many per species?

A

s. mansoni and s.haematobium = 20-300 per day

s. japonicum = 500-3500 per day

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13
Q

eggs reach ___ or ___ depending on species and are excreted in ___ or ___

A

bladder
intestine
urine
faeces

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14
Q

the individual in this case is infected with which species? how do you know?

A

s.mansoni

based on the structure of the large ovoid eggs

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15
Q

why does this parasite reduce haemaglobin levels?

A

parasite feeds on erythrocyes which can lead to anaemia - 9g dl usually 14-18gdl

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16
Q

what are eosinophilia?

A

white blood cells and one of the immune system components responsible for combating multicellular parasites

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17
Q

eosinophilia are also responsible for controlling mechanisms with __ and __

A

allergy and asthma

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18
Q

as well as the erythrocytes decreasing the parasite causes another thing to increasE?

A

eosinophilia to 1.1 x 10^9

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19
Q

the disease also causes oesophageal varices, what are these?

A

extremely dilated sub-mucosal veins in the lower third of the oesophagus

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20
Q

what are oesophageal varices a consequence of?

A

portal hypertension commonly due to cirrhosis

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21
Q

symptom of this disease is an abnormal liver with extensive granulomatous change and fibrosis caused by?

A

inflammation caused by macrophages leading damage/destruction of hepatocytes and laying down of connective tissue at these sites

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22
Q

the patient history points to this disease how?

A

lived in africa as a child played in nearby lake

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23
Q

what is the definitive diagnosis for this disease?

A

provided by the presence of Schistosoma eggs in stool sample

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24
Q

what did the endoscopy reveal about the patient?

A

extensive granulomas and schistosoma eggs in part of the colon closest to the rectum and anus

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25
Q

what is hepatomegaly?

A

enlargement of the liver

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26
Q

what is splenomegaly?

A

enlargement of the spleen

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27
Q

define endoscopic?

A

instrument used to examine the interior of a hollow organ or cavity of the body

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28
Q

define oesophageal varices

A

extremely dilated sub-mucosal veins in the lower third of the oesophagus

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29
Q

define cirrhosis

A

advanced liver disease. it is characterised by replacement of liver tissue by scar tissue

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30
Q

define granulomatous

A

organised collection of macrophages, inflammation response, attempt by body to localise an infection

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31
Q

define fibrosis

A

formation of excess fibrous connective tissue in an organ or tissue in a reparative or reactive process

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32
Q

define sigmoidoscopy

A

endoscopic examination of the sigmoid, the part of the colon closest to the rectum and anus

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33
Q

is this a water borne infection?

A

yes

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34
Q

which countries is the disease present in?

A 
tropical countries
africa
caribbean
eastern south america
south east asia
middle east
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35
Q

how many countries were statistically identified epidemics of Schistosomiasis?

A

74

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36
Q

how many people does schistosomiasis affect?

A

238 million

85% of whom live in Africa

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37
Q

how many people have severe consequences from the disease?

A

20 million

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38
Q

how many people die each year?

A

200,000

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39
Q

how many people are at risk of this disease?

A

600-700 million

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40
Q

in many areas schistosomiasis infects a large proportion of children under ____ years, why?

A

14

spend time swimming or bathing in contaminated waters

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41
Q

is schistosomiasis a NTD?

A

yes

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42
Q

what are reservoir hosts for the disease?

A

dogs, cats, rodents, pigs, horses, goats

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43
Q

where is s.mansoni found?

A

africa - southern and sub saharan
eastern south america - brazil, suriname, venezuela
caribbean (risk is low)

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44
Q

where is s.haematobium found?

A

africa - southern and sub saharan

middle east

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45
Q

where is s.japonicum found?

A

indonesia

south east asia

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46
Q

where is s.mekongi found?

A

cambodia and laos

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47
Q

where is s.intercalatum found?

A

central and west africa

48
Q

the pathology associated with infection can be divided into two main types, what are they?

A

acute and chronic

49
Q

most cases of schistosomiasis are which type?

A

chronic

50
Q

what happens when you are first infected?

A

generally no symptoms when first infected (may develop a rash or itchy skin within days of becoming infected - swimmers itch)

51
Q

when adult worms are present the eggs that are produced usually travel to the xxx,xxx,xx,xxx

A

liver spleen bladder intestine

52
Q

what are the 7 symptoms of chronic schistosomiasis?

A 
abdominal pain 
hepatosplenomegaly
diarrhoea / problems passing urine
eosinophilia
fever
fatigue
blood in stool / urine
53
Q

many infections are sub clinically symptomatic, what does this mean?

A

mild anaemia and malnutrition common in endemic areas

54
Q

what happens to schistosomiasis without treatment?

A

it can persist for years

55
Q

when children are repeatedly infected they can develop (3)

A

anaemia
malnutrition
learning difficulties

56
Q

continuing infection may cause ______ in the affected organs which results in manifestations of many types (see other cards).

A

granulomatous reactions and fibrosis

57
Q

there are 5 manifestations that can occur with continuing infection

A

colonic polyposis with bloody diarrhoea

portal hypertension with haematemesis

cystitis and ureteritis with haematuria which can progress to bladder cancer

pulmonary hypertension

glomerulonephritis

58
Q

what is colonic polyposis?

A

abnormal growth of tissue projecting from a mucous membrane

59
Q

what is portal hypertension?

A

high blood pressure in the portal vein system

60
Q

what is haematemesis?

A

vomiting of blood

61
Q

what is pulmonary hypertension?

A

increase of blood pressure in circulatory system of lings

62
Q

what is glomerulonephritis

A

inflammation either of the glomeruli or small blood vessels in the kidneys

63
Q

rarely seizures, paralysis or spinal cord inflammation occurs, what is this caused by?

A

eggs becoming lodged in the brain or spinal cord

64
Q

what is acute schistosomiasis also known as?

A

katayamas syndrome

65
Q

in some s.mansoni and s.japonicum infections rapid onset of non specific symptoms occurs ___ weeks after the initial infection which leads to acute schistosomiasis

A

2-12 weeks

66
Q

how do you diagnose acute schistosomiasis?

A

the lungs show as a patchy shadowing on a chest xray - accompanied by a dry cough

67
Q

what happens to non human infecting schistosome in humans?

A

they penetrate skin and then die

68
Q

non human infecting schistosomes can give rise to an allergic condition called ____ caused by?

A

swimmers itch / cercarial dermatitis

reaction caused by release of antigens by the dying parasites in the skin

69
Q

what are some reported cases of swimmers itch? the species (4)

A

s. bovis
s. mattheei
s. margrebowiei
s. rodhaini
s. spindale

70
Q

THE SYMPTOMS OF SCHISTOSOMIASIS ARE CAUSED BY THE BODYS IMMUNE REACTION TO WHAT?

A

THE EGGS PRODUCED FROM THE WORMS

NOT FROM THE WORMS THEMSELVES

71
Q

What is schistosomulae?

A

immature worm

72
Q

immunity correlates with levels of what?

A

IgE directed against schistosomulae

73
Q

host responses may provide degree of protective immunity to re-infection……

A

adults who have had a greater lifetime of exposure to parasite are less likely to be re infected than children

74
Q

what are the 5 immune responses against schistosomulae?

A

key antigens: glutathione S transferase and glyceraldehyde 3 phosphate dehydrogenase

level of antibody rise with age

schistosomulae are more susceptible to immune attack than adult worms

IgE mediates killing by opsonization to eosinophils

eosinophils degranulate to release toxic molecules

75
Q

what are the 3 immune responses against adult worms?

A

once adults mature there seems to be a ceiling on parasite load present in vasculature

may be because of physical space available in vasculature

not really subject to immune mediated killing - adult worms become coated with host proteins that may provide a form of host mimicry

76
Q

what explains why little if any inflammation is observed around adult worms?

A

host mimicry

77
Q

how does the causative agent enter the body and how is it spread? (life cycle)

A

eggs are eliminated with faeces or urine

under contact with freshwater the eggs hatch and release miracidia

miracidia swim using cilia located over their surface and infect freshwater snails by penetrating the snails foot

specific snail species are infected with different species of schistosoma

stages in the snail include 2 generations of sporocysts

sporocysts migrate to the snails hepatopancreas and begin to divide, producing thousands of cercariae

ercariae emerge dail ambient temperature a
The adult worms pair,
y e p
from the snail host in a circadian rhythm, d nd light.
pendent on
•
Young cercariae are hi and sinking to maintai
ghly mobile, alternating between vigorous u n their position in the water.
n
s n
s
e g
ward movement
•
Cercarial activity is pa chemicals found on hu
rticularly stimulated by water turbulence, by man skin.
shadows and by
• Upon release from the
snail, the infective cercariae swim, penetrate the skin of the
human host  , and sh • Via the circulatory sys
ed their forked tail, becoming schistosomula tem, the schistosomulae migrates via the lun
.
s to the liver
,.
• In the liver the schisto
omulae eventually resides in the liver sinuso
ids.
•
Juvenile S. mansoni an the liver, and it is duri
d S. japonicum worms develop an oral sucke g this period that the parasite begins to feed
r after arriving at on red blood cells.
•
channel of the shorter
with the longer female worm residing in the male.
gynaecophoric
Worm pairs of S. man
oni and S. japonicum relocate to the mesenteric or rectal veins.
S. haematobium migra
•
• The females deposit e
g
d a
gallbladder and the ab
(bladder) systems.
te from the liver to the perivesical venous ple gs in the small venules of the portal (spleen,
ominal portion of the gastrointestinal tract
)
xus of the bladder. pancreas,
nd perivesical
20-300 per day
S. mansoni and S. haematobium ay for S. japonicum
500-3500 per d
• Eggs are moved progre
ssively toward the lumen of the intestine (S. mansoni and S.


78
Q

in endemic regions what is critical for determining whether infection is likely / which species may be causing infection?

A

review of symptoms and residence history

79
Q

what is the primary methods of diagnosis in endemic regions?

A

examination of stool / urine for eggs - Kato-Katz technique

80
Q

In endemic regions the choice of sample to diagnose depends on what?

A

the species of parasite likely causing the infection

81
Q

the adult stages of s.mansoni and s.japonicum reside where?

A

in the mesentric venous plexus of infected hosts and eggs - shed in faeces

82
Q

adult stages of s.haematobium adult worms are found in the venous plexus of where?

A

lower uriniary tracts and eggs are shed in urine

83
Q

s.mansoni eggs characteristics

A 
large
114-180um long
45-70um wide
ovoid shape
lateral spine near the posterior end
84
Q

s.japonicum eggs characteristics

A 
small
70-100um long
55-64um wide
rounder
spine less conspicuous
85
Q

s.haematobium eggs characteristics

A

large
110-170um long
40-70um wide
conspicuous terminal spine

86
Q

why can testing of stool / urine be of limited use?

A

because will not detect lighter burden infections

87
Q

how can you increase the sensitivity of stool and urine examinations?

A

3 samples should be collected on different days - eggs are shed intermittently and in low amounts in light intensity infections

88
Q

in non-endemic areas, endemic methods of diagnosis are also used but also other methods can be used: (4)

A

endoscopy of bowel / bladdeer
biopses of bowel / bladder
ultrasonography - detect changes in organs
serologic testing

89
Q

why is the presence of antibody of schistosomiasis not a good diagnostic tool?

A

because it is indicative only of schistosome infection at some time and cannot be correlated with clinical status, worm burden, egg production, or prognosis because specific antibody can persist despite cure

90
Q

what is the front line treatment used?

A

praziquantel

91
Q

what does praziquantel kill?

A

cercariae and adult worms, it is less effective against juveniles

92
Q

how is praziquantel taken and in what doeses?

A

orally

20mg/kg every 4-6 hours for 1 day per year

93
Q

what is the cure rate off praziquantel?

A

60-90%

94
Q

what is the cost of praziquantel?

A

$0.15 - child

$0.30 - adult

95
Q

what are the WHO guidelins for community treatment based on disease impact on children in endemic villages?

A

50% children have blood in urine - everyone receives treatment

20-50% children have blood in urine - only school aged children are treated

<20% children have symptoms - mass treatment not implemented

96
Q

Where is praziquantel not licensed for use in humans?

A

UK

named patient basis

97
Q

within 6 months of treatment by Praziquantel ……..

A

90% of the damage done to internal organs can be reversed

98
Q

which part of the body is praziquantel well absorbed?

A

GI tract 80%

99
Q

what is the half life in adults?

A

0.8 to 1.5 in adults

100
Q

where is the drug metabolised?

A

through the cytochrome P450 pathway via CYP3A4

101
Q

what is the half life of metabolites?

A

4 to 5 hours

102
Q

praziquantel and its metabolites are mainly excreted ___

A

renally - within 24 hrs after a single oral dose 80% is found in urine

103
Q

what reduced the bioavailability of praziquantel?

A

chloroquine

104
Q

what is the mode of action of praziquantel?

A

not known but suggestions:

  1. may interfere with adenosine uptake in cultured worms - schistosomes unable to synthesise purines such as adenosine de novo
  2. may increase permeability of hte membranes of shcistosome cells towards calcium by targetting beta subunits of voltage gated calcium channels
  3. drug induces contraction of the parsit resulting in paralysis in the contracted state- dying parasite dislodged from site of action by host - destroyed by host immune reaction
105
Q

there are side effects of praziquantel due to the release of parasite material as they are killed stimulating host immune reaction

A

central nervous system - dizziness, headache, malaise.

GI tract - abdominal pain / cramps, vomitting, diarrhoea

106
Q

what diseases are referred to as NTDs?

A 
17 infections
trypanosomatid 
helminth
soil transmitted helminth
bacterial 
viral
107
Q

NTD control estimated to require how many $ in the next 5-7 years?

A

2-3 billion

108
Q

what is an NTD?

A

neglected tropical disease

109
Q

define NTD

A

group of infections causing substantial illness for more than one billion people globally

110
Q

where are NTD especially prevalent?

A

in low income populations in developing regions of the world

111
Q

how many countries are affected by NTD?

A

149

112
Q

NTDs kill an estimated ____ people every year

A

534 000

113
Q

How do NTD affect people?

A

they impair physical and cognitive development, contribute to mother and child illness and death, make it difficult to farm or earn a living and limit productivity in the workplace

114
Q

Some NTDs have known preventative measures or acute medical treatments which are available in the developed world but not used in the developing world. It is estimated that most NTD mass drug administration programs would cost how much?

A

less than 50cents

115
Q

The control measures being used against schistosomiasis are (2)

A

Reducing the number of infections in people - mass drug treatment of entire communities and targeted treatment of school age children

Eliminating the snails that are required for the parasites life cycle - predators - pestacides

116
Q

what are 4 problems with the control of schistosomiasis?

A

chemicals used to eliminate snails in freshwater sources may harm other species of animals in the water and if treatment is not sustained the snails may return to those sites afterwards

where water resource development projects have been implemented has provided more habitats for snail populations to flourish

resistance of snails to pesticides

runoff from pastures of waterbuffalo can contaminate fresh water sources as they are also hosts

117
Q

what are 4 preventative steps a traveller can take?

A

avoid swimming in freshwater

drink safe water - boil

water for bathing boil

water held in storage tank for 1-2 days

vigorous towel drying

parasites test 2 (2 decks)

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