test Flashcards
what is the disease?
schistosomiasis
what are 2 other names for this disease?
bilharzia
snail fever
what is the causative agent of schistosomiasis?
parasites belonging to the genus Schistosoma
what are the 3 species responsible for most human cases?
s. mansoni
s. haematobium
s. japonicum
other human infections are also caused by which 2 species?
s. intercalatum
s. mekongi
schistosomes are blood flukes which are also known as
trematodes
adult worms are less than __cm long and live for ___ years
2
3-5
Why are Schistosomes unique among trematodes?
dioecious
with distinct sexual dimorphism
which sex are larger?
females
what defines the male?
they have longitudinal groove in which the female worm resides
where do the parasites live in the body?
in the veins around the bladder - s.haematobium
in the mesenteric (GI) blood vessels - s.mansoni, s.japonicum
thousands of eggs are released into the bloodstream, how many per species?
s. mansoni and s.haematobium = 20-300 per day
s. japonicum = 500-3500 per day
eggs reach ___ or ___ depending on species and are excreted in ___ or ___
bladder
intestine
urine
faeces
the individual in this case is infected with which species? how do you know?
s.mansoni
based on the structure of the large ovoid eggs
why does this parasite reduce haemaglobin levels?
parasite feeds on erythrocyes which can lead to anaemia - 9g dl usually 14-18gdl
what are eosinophilia?
white blood cells and one of the immune system components responsible for combating multicellular parasites
eosinophilia are also responsible for controlling mechanisms with __ and __
allergy and asthma
as well as the erythrocytes decreasing the parasite causes another thing to increasE?
eosinophilia to 1.1 x 10^9
the disease also causes oesophageal varices, what are these?
extremely dilated sub-mucosal veins in the lower third of the oesophagus
what are oesophageal varices a consequence of?
portal hypertension commonly due to cirrhosis
symptom of this disease is an abnormal liver with extensive granulomatous change and fibrosis caused by?
inflammation caused by macrophages leading damage/destruction of hepatocytes and laying down of connective tissue at these sites
the patient history points to this disease how?
lived in africa as a child played in nearby lake
what is the definitive diagnosis for this disease?
provided by the presence of Schistosoma eggs in stool sample
what did the endoscopy reveal about the patient?
extensive granulomas and schistosoma eggs in part of the colon closest to the rectum and anus
what is hepatomegaly?
enlargement of the liver
what is splenomegaly?
enlargement of the spleen
define endoscopic?
instrument used to examine the interior of a hollow organ or cavity of the body
define oesophageal varices
extremely dilated sub-mucosal veins in the lower third of the oesophagus
define cirrhosis
advanced liver disease. it is characterised by replacement of liver tissue by scar tissue
define granulomatous
organised collection of macrophages, inflammation response, attempt by body to localise an infection
define fibrosis
formation of excess fibrous connective tissue in an organ or tissue in a reparative or reactive process
define sigmoidoscopy
endoscopic examination of the sigmoid, the part of the colon closest to the rectum and anus
is this a water borne infection?
yes
which countries is the disease present in?
tropical countries africa caribbean eastern south america south east asia middle east
how many countries were statistically identified epidemics of Schistosomiasis?
74
how many people does schistosomiasis affect?
238 million
85% of whom live in Africa
how many people have severe consequences from the disease?
20 million
how many people die each year?
200,000
how many people are at risk of this disease?
600-700 million
in many areas schistosomiasis infects a large proportion of children under ____ years, why?
14
spend time swimming or bathing in contaminated waters
is schistosomiasis a NTD?
yes
what are reservoir hosts for the disease?
dogs, cats, rodents, pigs, horses, goats
where is s.mansoni found?
africa - southern and sub saharan
eastern south america - brazil, suriname, venezuela
caribbean (risk is low)
where is s.haematobium found?
africa - southern and sub saharan
middle east
where is s.japonicum found?
indonesia
south east asia
where is s.mekongi found?
cambodia and laos
where is s.intercalatum found?
central and west africa
the pathology associated with infection can be divided into two main types, what are they?
acute and chronic
most cases of schistosomiasis are which type?
chronic
what happens when you are first infected?
generally no symptoms when first infected (may develop a rash or itchy skin within days of becoming infected - swimmers itch)
when adult worms are present the eggs that are produced usually travel to the xxx,xxx,xx,xxx
liver spleen bladder intestine
what are the 7 symptoms of chronic schistosomiasis?
abdominal pain hepatosplenomegaly diarrhoea / problems passing urine eosinophilia fever fatigue blood in stool / urine
many infections are sub clinically symptomatic, what does this mean?
mild anaemia and malnutrition common in endemic areas
what happens to schistosomiasis without treatment?
it can persist for years
when children are repeatedly infected they can develop (3)
anaemia
malnutrition
learning difficulties
continuing infection may cause ______ in the affected organs which results in manifestations of many types (see other cards).
granulomatous reactions and fibrosis
there are 5 manifestations that can occur with continuing infection
colonic polyposis with bloody diarrhoea
portal hypertension with haematemesis
cystitis and ureteritis with haematuria which can progress to bladder cancer
pulmonary hypertension
glomerulonephritis
what is colonic polyposis?
abnormal growth of tissue projecting from a mucous membrane
what is portal hypertension?
high blood pressure in the portal vein system
what is haematemesis?
vomiting of blood
what is pulmonary hypertension?
increase of blood pressure in circulatory system of lings
what is glomerulonephritis
inflammation either of the glomeruli or small blood vessels in the kidneys
rarely seizures, paralysis or spinal cord inflammation occurs, what is this caused by?
eggs becoming lodged in the brain or spinal cord
what is acute schistosomiasis also known as?
katayamas syndrome
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
2-12 weeks
how do you diagnose acute schistosomiasis?
the lungs show as a patchy shadowing on a chest xray - accompanied by a dry cough
what happens to non human infecting schistosome in humans?
they penetrate skin and then die
non human infecting schistosomes can give rise to an allergic condition called ____ caused by?
swimmers itch / cercarial dermatitis
reaction caused by release of antigens by the dying parasites in the skin
what are some reported cases of swimmers itch? the species (4)
s. bovis
s. mattheei
s. margrebowiei
s. rodhaini
s. spindale
THE SYMPTOMS OF SCHISTOSOMIASIS ARE CAUSED BY THE BODYS IMMUNE REACTION TO WHAT?
THE EGGS PRODUCED FROM THE WORMS
NOT FROM THE WORMS THEMSELVES
What is schistosomulae?
immature worm
immunity correlates with levels of what?
IgE directed against schistosomulae
host responses may provide degree of protective immunity to re-infection……
adults who have had a greater lifetime of exposure to parasite are less likely to be re infected than children
what are the 5 immune responses against schistosomulae?
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
what are the 3 immune responses against adult worms?
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
what explains why little if any inflammation is observed around adult worms?
host mimicry
how does the causative agent enter the body and how is it spread? (life cycle)
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.

in endemic regions what is critical for determining whether infection is likely / which species may be causing infection?
review of symptoms and residence history
what is the primary methods of diagnosis in endemic regions?
examination of stool / urine for eggs - Kato-Katz technique
In endemic regions the choice of sample to diagnose depends on what?
the species of parasite likely causing the infection
the adult stages of s.mansoni and s.japonicum reside where?
in the mesentric venous plexus of infected hosts and eggs - shed in faeces
adult stages of s.haematobium adult worms are found in the venous plexus of where?
lower uriniary tracts and eggs are shed in urine
s.mansoni eggs characteristics
large 114-180um long 45-70um wide ovoid shape lateral spine near the posterior end
s.japonicum eggs characteristics
small 70-100um long 55-64um wide rounder spine less conspicuous
s.haematobium eggs characteristics
large
110-170um long
40-70um wide
conspicuous terminal spine
why can testing of stool / urine be of limited use?
because will not detect lighter burden infections
how can you increase the sensitivity of stool and urine examinations?
3 samples should be collected on different days - eggs are shed intermittently and in low amounts in light intensity infections
in non-endemic areas, endemic methods of diagnosis are also used but also other methods can be used: (4)
endoscopy of bowel / bladdeer
biopses of bowel / bladder
ultrasonography - detect changes in organs
serologic testing
why is the presence of antibody of schistosomiasis not a good diagnostic tool?
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
what is the front line treatment used?
praziquantel
what does praziquantel kill?
cercariae and adult worms, it is less effective against juveniles
how is praziquantel taken and in what doeses?
orally
20mg/kg every 4-6 hours for 1 day per year
what is the cure rate off praziquantel?
60-90%
what is the cost of praziquantel?
$0.15 - child
$0.30 - adult
what are the WHO guidelins for community treatment based on disease impact on children in endemic villages?
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
Where is praziquantel not licensed for use in humans?
UK
named patient basis
within 6 months of treatment by Praziquantel ……..
90% of the damage done to internal organs can be reversed
which part of the body is praziquantel well absorbed?
GI tract 80%
what is the half life in adults?
0.8 to 1.5 in adults
where is the drug metabolised?
through the cytochrome P450 pathway via CYP3A4
what is the half life of metabolites?
4 to 5 hours
praziquantel and its metabolites are mainly excreted ___
renally - within 24 hrs after a single oral dose 80% is found in urine
what reduced the bioavailability of praziquantel?
chloroquine
what is the mode of action of praziquantel?
not known but suggestions:
- may interfere with adenosine uptake in cultured worms - schistosomes unable to synthesise purines such as adenosine de novo
- may increase permeability of hte membranes of shcistosome cells towards calcium by targetting beta subunits of voltage gated calcium channels
- 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
there are side effects of praziquantel due to the release of parasite material as they are killed stimulating host immune reaction
central nervous system - dizziness, headache, malaise.
GI tract - abdominal pain / cramps, vomitting, diarrhoea
what diseases are referred to as NTDs?
17 infections trypanosomatid helminth soil transmitted helminth bacterial viral
NTD control estimated to require how many $ in the next 5-7 years?
2-3 billion
what is an NTD?
neglected tropical disease
define NTD
group of infections causing substantial illness for more than one billion people globally
where are NTD especially prevalent?
in low income populations in developing regions of the world
how many countries are affected by NTD?
149
NTDs kill an estimated ____ people every year
534 000
How do NTD affect people?
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
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?
less than 50cents
The control measures being used against schistosomiasis are (2)
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
what are 4 problems with the control of schistosomiasis?
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
what are 4 preventative steps a traveller can take?
avoid swimming in freshwater
drink safe water - boil
water for bathing boil
water held in storage tank for 1-2 days
vigorous towel drying
