Helminthic Pathogens Flashcards
1
Q
Helminths
A
parasitic worms that feed on a living host to gain nourishment and protection,
while causing poor nutrient absorption, weakness and disease in the host
2
Q
most common helminths recognized in the U.S.
A
primarily Intestinal Nematodes
3
Q
Intestinal Nematodes
A
live in the small bowel (intestine) and are referred to as intestinal parasites
4
Q
helminths classification
A
Nematodes or roundworms (large size an unsegmented body)
- Trematodes, which includes flukes or flatworms
- Cestodes or tapeworms
5
Q
_______ all share a similar _______ and are _______ organisms that are _____ to the naked
eye.
A
Helminths all share a similar morphology and are multicellular organisms that are visible to the naked
eye.
6
Q
How are Helminths caught?
A
The worms are usually caught through treading on contaminated soil, in warm, humid places
or countries that have poor sanitation and hygiene
7
Q
If an infected person or animal has defecated on soil, helminth eggs present in their feces contaminate
the soil
A
-eggs mature and hatch to produce larvae that grow into adult worms of up to 13
mm in length.
- adult worms can penetrate human skin, which can happen if a person walks on
contaminated soil.
-worms then enter the bloodstream and migrate towards the lungs and also the throat where they are swallowed and transported to the gut.
8
Q
Nematodes or roundworms
A
cylindrical, un-segmented and have lips, teeth and
dentary plates
-large size
-worms are either male or female
-live primarily as adult worm in the intestinal tract
-nematode infections are most commonly confirmed by detecting the characteristic eggs in feces.
9
Q
Trematodes or flatworms
A
flat, leaf-shaped and un-segmented
- hermaphroditic (both male and female reproductive organs)
10
Q
Cestodes or tapeworms are
A
segmented and hermaphroditic
-have a sucker
and a projecting, hooked rostellum (is a knob-like protrusion at the extreme anterior end of a tapeworm)
11
Q
What do you look at to confirm nematodes?
A
- size and shape
- Thickness of shell
- Presence or absence of specialized structure: e.g. polar plugs, knobs, spines, opercula.
- The presence and characteristics of larvae within the eggs
12
Q
Enterobius (Oxyuris) vermicularis (Human pinworm)
A
-Physiology & Structure: small (adult female: 8-13 mm) white worm found in perianal folds of an infected
child.
-Infection: it is initiated by ingestion of embryonated
eggs
-Eggs hatch in the small intestine and larva migrate to the large intestine, where they mature into adults
in 2 to 6 weeks
-Fertilization of the female by the male produces
the characteristic asymmetric eggs.
-eggs are laid in the perianal folds by the
migrating female (many as 20,000 eggs are
deposited)
-The eggs rapidly mature and are infectious within
hours
13
Q
Where is Enterobius most common?
A
temperate region, where person-to-person
spread is greatest in crowded conditions, such as in day-care centers, schools and mental
institutions
14
Q
How many cases of pinworm infection are reported worldwide?
A
500 million cases
-Most common helminthic infection in the U.S.
15
Q
How does pinworm infection occur?
A
When the eggs are ingested and the larval worm is free to develop in the intestinal mucosa
- eggs may be transmitted from hand-to-mouth by children scratching the perianal folds in response to the irritation caused by the migrating, egg-laying, female worms,
- eggs may find their way to clothing and play objects in day-care centers
16
Q
Eggs can also survive for _____ periods in the _____, and under ____ in the rooms inhabited by
infected people
A
long, dust, beds
17
Q
Autoinfection (Retroinfection)
A
eggs hatch in the perianal
folds and the larval worms migrate into the rectum and large intestine.
18
Q
True or False: An animal reservoir for Enterobius is known
A
False
19
Q
Enterobius symptoms
A
-Many children and adults show no symptoms and serve only as carriers
-Patients who reacts to the secretions of the migrating worms experience:
o severe nocturnal perianal pruritus
o loss of sleep
o fatigue
-pruritus may cause repeated scratching of the irritated area and lead to secondary bacterial infection
-Worms that migrate to the genital area may produce genitourinary problems and granulomas
20
Q
Diagnosis of Enterobius
A
suggested by the clinical manifestations and confirmed by detection of the characteristic eggs on the anal mucosa
-Occasionally, the adult worms are seen in stool sample
21
Q
What is the method of choice for diagnosing enterobius?
A
anal swab with a sticky surface that picks
up the eggs for microscopic examination
-Sample should be collected when the child arises and before bathing and defecation to pick
up eggs laid by migrating worms during the night
22
Q
How many swabbings may be required to detect eggs?
A
Three swabbing, one per day for 3 consecutive days, may be required to detect the diagnostic
eggs
-Eggs are rarely seen in fecal specimens
23
Q
Enterobius vermicularis eggs
A
thin-walled eggs are 50 to 60 x 20 to 30 μm
-ovoid
-flattened on one side (not because children sit on them), but this is an easy way to correlate
the egg morphology with the epidemiology of the disease.
24
Q
Enterobius vermicularis treatment and control
A
Albendazole or Mebendazole keeps the worm from absorbing sugar
(blocks glucose uptake), so that the worm loses energy and dies
-One dose initially (two times a day for 28 days: 1 cycle) and repeat treatment after 2 weeks for a total of three cycles
-Personal hygiene, clipping of fingernails, washing of bed cloths and prompt treatment of
infected individuals all contribute to control
25
How to avoid reintroduction of organism and reinfection in family environment?
common to treat the entire family simultaneously
| -Reinfections are common
26
Ascaris Lumbricoides (Roundworm)
large (20 to 35 cm in length) pink worms that have a complex
| life cycle
27
Roundworm infection
ingested infective egg releases a larval worm
that penetrates the duodenal wall, enters the
blood stream, is carried to the liver and heart, and
then enters the pulmonary circulation
-larvae break free in the alveoli of the lungs,
where they grow and molt
-In about 2-3 weeks, the larvae pass from the
respiratory system to be coughed up, swallowed,
and returned to the small intestine
28
Where do male and female worms mature?
small intestine (primarily jejunum)
-fertilization of
the female by the male initiates egg production
-Up to200,000 eggs/day for as long as a year.
-Female worms can also produce unfertilized eggs
in the absence of males
-Eggs are found in the feces 60 to 65 days after the
initial infection
-Fertilized eggs become infectious after approx. 2 weeks in the soil
29
Ascaris Lumbricoides (Roundworm) Epidemiology
prevalent in areas where sanitation is poor and where human feces are
used as fertilizer
-this parasite (more than
any other) affects the world’s population because food and water are contaminated
30
True or False: No animal reservoir is know for A. lumbricoides
True
-Although an almost identical species from
pigs (A. suum) can infect humans
31
______ eggs are quite hardy and can survive extreme ______ and persist for several _____ in _____ and _____
Ascaris, temperatures, months, feces, sewage
32
What is the most common helminth infection worldwide?
Ascariasis
| -estimated 1 billion people infected.
33
Ascaris Lumbricoides (Roundworm) clinical symptoms
infection caused by ingestion of only a few eggs may produce no symptoms
- single adult Ascaris worm may be dangerous since it can migrate into the bile duct and the liver and damage the tissue
- worm has a tough, flexible body occasionally allows it to perforate the intestine, creating peritonitis with secondary bacterial infection.
34
True or False: adult worms attach to the intestinal mucosa
False
-depend on constant motion to
maintain their position within the bowel lumen
35
After infection with many larvae, migration of worms to the lungs can produce
pneumonitis
36
In some cases, accumulation of worms in the intestine can cause
obstruction, perforation and
| occlusion of the appendix
37
Patients with many larvae may also experience
abdominal tenderness, fever, distention and
| vomiting.
38
Ascaris Lumbricoides (Roundworm) diagnosis
Examination of the sediment of concentrated stool reveals the knobby-coated, bile-stained, fertilized and unfertilized eggs
- Eggs are oval
- 55 to 75 μm long
- 50 μm wide
- Occasionally, adult worms pass with the feces, dramatic because of large size
39
decorticated egg
thick-walled outer shell can be partially
| removed
40
Ascaris Lumbricoides (Roundworm) treatment
Treatment of symptomatic infection is highly effective
-Albendazole or Mebendazole
-Pyrantel pamoate (depolarizing neuromuscular blocking agent, thereby causing sudden contraction, followed by paralysis, of the helminths) and piperazine are alternatives
-Patients with mixed parasitic infections should be treated for
ascariasis first to avoid provoking worm migration and possible intestinal
perforation
-Eggs can persist in contaminated soil for 3 years or more
41
Trichuris trichiura (Whipworm)
```
resembles the handle and lash of
a whip
-Ingested eggs hatch into a larval worm
in the small intestine and then migrate
to the cecum (the first section of the
large intestine), where they penetrate
the mucosa and mature to adults
-About 3 months after the initial
infection, the fertilized female worm
starts laying eggs and may produce
3,000 to 10,000 eggs/day
-Female worms can live for as long as 8
years
-Eggs passed into the soil mature and
become infectious in 3 weeks
```
42
Trichuris trichiura eggs
distinctive with dark bile staining, a barrel shape, and the presence of polar plugs in the egg shell
- measuring 50x24 μm
- thick wall
43
What is T. trichiura worldwide distribution, and prevalence directly correlated with?
poor sanitation and the use of human feces as fertilizer
44
True or False: There is a recognized animal reservoir for T. trichiura
False
45
Clinical Symptoms of T. trichiura
generally related to the intensity of the worm burden
-usually asymptomatic with small number
-secondary bacterial infection may occur because the heads of the worms penetrate deep into the intestinal mucosa
-Infections with many larvae may produce abdominal pain and distention, bloody diarrhea, weakness, and weight loss
-Appendicitis may occur as worms fill the lumen, and prolapse of the rectum is seen in
children because of the irritation and straining during defecation
-Anemia and Eosinophillia are also seen in severe infections
46
Trichuris trichiura diagnosis
Stool examination reveals the characteristic bile-stained eggs with polar plugs
-Light infestations may be difficult to detect because of the paucity of eggs in the stool specimens
47
Trichuris trichiura treatment and control
Albendazole or Mebendazol
-prevention depends on education, good personal hygiene, adequate sanitation, and
avoidance of the use of human feces as fertilizer
48
Protective Responses to Intestinal Helminths
Most intestinal Helminths induce both protective and pathological immune responses by CD4 T-cells
-TH2 responses tend to be protective, which induces B-cells to switch to the IgE phenotype creating an unfriendly
environment for the parasite, and leading to its expulsion and the generation of protective immunity
-TH1 response DOES NOT clear the pathogen and tends to produce an inflammatory reaction that
damages the mucosa
-TH1 response is generated when the activating dendritic cells express IL-12
49
goblet cells
glandular simple columnar epithelial cells whose sole function is to secrete mucin, which dissolves in
water to form mucus.
50
M2 macrophage
produce the enzyme Arginase, which increases the contractibility of intestinal smooth muscle and promotes tissue remodeling and repair.
51
Pathological Responses to Intestinal Helminths
```
If the CD4 T-cell response to a Helminth
parasite is polarized to produce
predominantly TH1 effector T-cells (for
example, by the production of IL-12 by
dendritic cells), it DOES NOT clear the
pathogen
-not balanced by a protective TH2
response, the TH1 response leads to
persistent infection and chronic intestinal
pathology.
```
52
Ancylostoma duodenale & Necator americanus (Hookworms)
two human hookworms
-Ancylostoma duodenale (Old World hookworm)
and Necator americanus (New World hookworm)
-differ in geographic distribution, structure of mouth parts, and relative size
-Both species have mouthparts designed for sucking blood from injured intestinal tissue
53
Ancylostoma duodenale & Necator americanus (Hookworms) life cycle
human phase of the hookworm life cycle
is initiated when a filariform (infective form)
larva penetrates intact skin
-larva then enters the circulation, is
carried to the lungs, coughed up, swallowed, and develops to adulthood in the small intestine
-adult N. americanus has a hooklike head,
which accounts for the name commonly
used
54
How many eggs do hookwors lay?
Adult worms lay as many as 10,000 to 20,000 eggs/day
-Egg laying is initiated 4 to 8 weeks
after the initial exposure and can persist for
as long as 5 years
-On contact with soil, the Rhabditiform
(noninfective) larvae are released from the
eggs and within 2 weeks develop into
filariform (infective) larvae
-This form can penetrate exposed skin
55
How does transmission of hookworms occur?
infections requires the deposition of egg-containing feces on shady, well-drained soil and is favored by warm, humid (tropical) conditions
-Hookworm infections are reported worldwide in places where direct contact with contaminated soil can lead to human disease
-occur primarily in warm subtropical
and tropical regions and in Southern parts of the U.S.
56
How many people are estimated to be infected with hookworm?
more than 900 million individuals worldwide, including 700,000 in the U.S
57
Ancylostoma duodenale & Necator americanus (Hookworms) symptom
larvae may produce an allergic reaction and rash at sites of entry, and larvae
migrating in the lungs can cause pneumonitis and eosinophilia
-Adult worms produce the gastrointestinal symptoms of nausea, vomiting and diarrhea
-blood is lost from feeding worms, a Microcytic Hypochromic Anemia (IDA) develops
-severe, chronic infections, emaciation and mental and physical retardation may occur
related to anemia from blood loss and nutritional deficiencies
-Intestinal sites may be secondarily infected by bacteria when the worms migrate along the intestinal mucosa
58
Ancylostoma duodenale & Necator americanus (Hookworms) diagnosis
Stool examination reveals the characteristic non-bile-stained segmented eggs
- Larvae are NOT found in stool specimens unless the specimen was left at RT for a day or more
- The eggs of A. duodenale and N. americanus can NOT be distinguished
- larvae must be examined to identify these hookworms specifically
59
Ancylostoma duodenale & Necator americanus (Hookworms) treatment
Albendazole (single 400mg dose) or Mebendazole; (100mg twice daily for 3
days) Pyrantel pamoate is an alternative in several 11mg/kg doses over 3 days
-iron therapy is indicated to increase Hb
level to normal. Blood transfusion may be necessary in severe cases of anemia
-Wearing shoes in endemic areas helps reduce the prevalence of infection.
60
Strongyloides Stercolaris
life cycle of Strongyloides stercolaris differs in 3 aspects compared to
hookworm:
1. Eggs hatch into larvae in the intestine and
before they are passed in feces,
2. Larvae can mature into filariforms in the
intestine and cause autoinfection
3. A free-living, nonparasitic cycle can be
established outside the human host
-skin-penetrating larva enters the circulation
and follows the pulmonary course
-coughed up, swallowed , and adults develop in the small intestine
-Adult females burrow into the mucosa of the duodenum and reproduce parthenogenetically.
-Each female produces about a dozen eggs each day, which hatch within the mucosa and release rhabditiform (noninfective) larvae into the lumen of the bowel
61
Strongyloides Stercolaris epidemiology
Similar to Hookworms in its requirements for warm temperatures and moisture
- demonstrates low prevalence but a somewhat broader geographic distribution, including parts of the northern U.S. and Canada
- Sexual transmission also occurs, rare but documented
62
True or False: Animal reservoirs such as domestic pets, are recognized
True
63
Strongyloides Stercolaris symptoms
commonly provokes pneumonitis from migrating larvae
-Heavy worms loads may involve the biliary and pancreatic ducts, the entire small bowel, and the colon, causing inflammation and ulceration leading to epigastric pain, vomiting, diarrhea,and malabsorption
-Autoinfection may lead to chronic Strongyloidiasis that can last for years, even in nonendemic areas.
-severe, chronic infections, are at risk of developing severe life threatening
hyperinfection syndrome, which is associated with a mortality rate of approimately 86%
64
Strongyloides Stercolaris diagnosis
difficult because of the intermittent passage of low numbers of first stage larvae in the stool
- Examination of concentrated stool sediment reveals the larval worms (Eggs are NOT seen).
- Collecting samples from 3 stools, one per day for 3 days is recommended (larvae may occur in waves)
65
Strongyloides stercoralis larvae:
180 to 380 μm long and 14 to 24
μm wide
-length of the buccal cavity and esophagus
and by the structure of the genital promirdium
66
Strongyloides Stercolaris treatment
Ivermectin with Albendazole
| -Education, proper sanitation, and prompt treatment of existing infections
67
Trichinella Spiralis
adult form of this organism lives in the duodenal and jejunal mucosa of flesheating
mammals worldwide
-infectious larval form is present in the striated muscles of carnivorous and omnivorous mammals
-swine are most frequently involved
68
Trichinella Spiralis life cycle
infection begins with meat the contains
encysted larvae is digested
-larva leave the meat in the small intestine
and within 2 days develop into an adult worm
-single fertilized female produces more than
1,500 larvae in 1 to 3 months
-larvae move from the intestinal mucosa into
the bloodstream and are carried in the
circulation to various muscle sites throughout, the body, where they coil in striated muscle fibers and become encysted.
-encysted larva remain viable for many years and are infectious if ingested by a new animal host
69
What muscles are most frequently invaded by Trichinella Spiralis?
extraocular muscles of the eye; the tongue, the deltoid, pectoral, and intercostal muscles, the diaphragm and the gastrocnemius muscle.
70
Trichinella Spiralis epidemiology
Occurs worldwide in humans, and its greatest prevalence is associated with the consumption of pork products
- one of the few parasitic diseases still seen in the US
- estimated that more than 1.5 million Americans carry live Trichinella cysts in their musculature and that 150,000 to 300,000 acquire new infection annually
71
Trichinella Spiralis symptoms
< 10 larvae are deposited/g of tissue are usually asymptomatic
-100 generally have significant disease
-1,000 to 5,000 have a very serious course
that occasionally ends in death
-mild infections, patients may experience
only an influenza-like syndrome with slight
fever and mild diarrh
-more extensive larval migrations,
persistent fever, gastrointestinal distress,
marked eosinophilia, muscle pain, and
periorbital edema
-heavy infections, severe neurologic
symptoms. Lethal trichinosis results when myocarditis, encephalitis, and pneumonitis combine.
-The patient dies 4 to 6 weeks after infections
-Respiratory arrest often follows heavy invasion and muscle destruction in the diaphragm
72
Trichinella Spiralis Laboratory Diagnosis
usually established with clinical observation, especially when an outbreak can be
traced to consumption of improperly cooked pork
-lab may confirm the diagnosis if the encysted larvae are detected in the implicated meat or in a muscle biopsy specimen from the patient
-Marked eosinophilia is characteristically present in patients with Trichinosis
-Serologic procedures (ELISA anti-trichinella Abs) for diagnostic confirmation
-Significant Ab titers are usually absent before the 3rd week of illness but then may persist for years
73
Trichinella Spiralis treatment
Treatment is primarily symptomatic because there are no good parasitic agents for tissue
larvae
-Treatment of the adult worms in the intestine with Mebendazole may halt the production of new larvae
-Education regarding disease transmission from pork is essential, especially the
recommendation that meat be cooked until the interior is gray
-Quick freezing of pork at -400C effectively destroys the organisms, as does low temperature storage at -200C for 20 days or more
-Microwave cooking do not kill all larvae.
74
Trematodes (Flukes)
generally flat, fleshy, leaf-shaped worms (flukes)
-they are equipped with 2 muscular suckers
-oral type, which is the beginning of an
incomplete digestive system.
-A ventral sucker, which is an organ for attachment
-digestive system consist of lateral tubes that do not join to form an excretory opening
-Most flukes are hermaphrodite
-
75
What flukes are the only exception for hermaphrodites?
Schistosomes
-they have cylindric bodies, and separate male and female worms
exists
76
All flukes require
intermediate hosts for the completion of their life cycles
77
the first intermediate host are
mollusks (snails and clams).
78
Fluke eggs
equipped with a “lid” at the top of the shell call operculum
| -lids open to allow the larval worm to find its appropriate snail host
79
Fasciolopsis Buski
Humans ingest the encysted larval stage (Metacercaria) when they peel the husk from aquatic vegetation (e.g. water chesnuts) with the teeth
-Metacercariae are scraped from the husk,
swallowed, and develop into immature flukes in the duodenum
-fluke attaches to the mucosa of the small intestine with 2 muscular suckers, develops into an adult form, and undergoes self-fertilization
-Egg production is initiated three months after the initial infection with the Metacercariae
-operculated eggs pass in feces to water, where the operculum at the top of the eggshell pops open, liberating a free-swimming larval stage (Miracidium)
-Glands in the Miracidium produce lytic substances that allow the penetration of the soft tissues of snails.
-In the snail tissue, the Miracidium develops through a series of stages by asexual germ cell propagation.
-The final stage Cercaria in the snail is a free-swimming form that after release from the snail, encysts on the aquatic vegetation, becoming the Metacercaria , or
infective stage
-egg, 130 to 150 μm long and 65 to 90 μm wide, with a thin operculum at one end
80
Fasciolopsis Buski epidemiology
depends on the distribution of its appropriate snail host, F. Buski is found in China, Vietnam, Thailand, parts of Indonesia, Malaysia and India.
-Pigs, dogs, and rabbits serve as reservoir host in these endemic areas
81
Fasciolopsis Buski symptoms
relates directly with the worm burden in the small intestine
- Attachment of the flukes in the small intestine can produce inflammation, ulceration and hemorrhage
- Severe infections produce abdominal discomfort similar to that of a duodenal ulcer, as well as diarrhea
- Stools may be profuse, a malabsorption syndrome is common, and intestinal obstruction can occur
- Mark Eosinophilia is also present.
82
Fasciolopsis Buski diagnosis
Stool examination revels the large, golden, bile-stained eggs with an operculum on the top
-The appearance of the eggs are similar to those of Fasciola hepatica
83
Fasciolopsis Buski treatment
Praziquantel (increases the permeability of the membranes of schistosome cells).
- Proper sanitation, education regarding the safe consumption of infective aquatic vegetation (water chesnuts)
84
Fasciola Hepatica
commonly called the sheep liver fluke, F. hepatica is a parasite of herbivores (particularly sheep and cattle) and humans
85
Fasciola Hepatica life cycle
Human infection results from the ingestion of watercress that harbors the encysted
Metacercariae
-larval flukes then migrate trough the
duodenal wall and across the peritoneal
cavity
-penetrate the liver capsule, pass through the liver parenchyma
-enter the bile ducts to become adult worms
-Approximately 3 to 4 months after the initial
infection, the adult flukes start producing
operculated eggs that are identical to those
of F. buski, seen in stool examination
86
Fasciola Hepatica epidemiology
Infections have been reported worldwide in sheep-raising areas
- appropriate snail as an intermediate host
- areas include former Soviet Union, Japan, Egypt and many Latin American countries
- Human infection is rare in the US but several well-documented cases have been reported in travelers from endemic areas
87
Fasciola Hepatica symptoms
Migration of the larval worm through the liver produces irritation of this tissue, tenderness, and hepatomegaly
- Pain in the right upper quadrant, chills, fever, and marked eosinophilia are commonly observed
- worms take up residence in the bile ducts, their mechanical irritation and toxic secretions produce hepatitis, hyperplasia of the epithelium, and biliary obstruction
- Some worms invade the liver inducing necrotic foci referred to as liver rot
- severe infection, secondary bacterial infection can occur, and portal cirrhosis is common
88
Fasciola Hepatica diagnosis
Stool examination revels the large, golden, bile-stained eggs with an operculum on the top
-Examination of a sample of the patient’s bile differentiate the species
89
Fasciola Hepatica treatment
Triclabendazole (inhibits microtubule formation; available through the CDC
Drug Service, under a special protocol, which requires both CDC and FDA to agree that the drug is indicated for treatment of a particular patient
90
Schistosome
“snail fever” is a major parasitic infection of tropical areas, with some 200 million infections worldwide.
-three schistosomes most frequently associated with human disease are:
o Schistosoma mansoni
o Schistosoma japonicum
o Schistosoma haematobium
-male and female
-eggs DO NOT have an operculum
-infective forms are skin-penetrating Cercariae liberated from snails.
91
Schistosomes life cycle
Infection is initiated by ciliated, free-swimming, freshwater Cercariae that penetrate intact skin
-Enter the circulation, and develop in the intrahepatic portal circulation (mansoni and japonicum) or in the vesical, prostatic, rectal, and uterine plexuses and veins
(haematobium).
-Adults pair up and migrates to mesenteric veins
-Eggs pass through the mucosa and into the lumen of the
bowel and bladder, where they are passed to the external environment in the feces and urine
-eggs hatch on reaching fresh water to release motile Miracidia, which invade the snail host
92
Schistosoma mansoni
resides in the small branches of the inferior mesenteric vein near the lower colon
- eggs of S. mansoni are oval, and possess a sharp lateral spine.
- 115 to 175 μm long and 45 to 70 μm wide
93
Schistosoma mansoni epidemiology
distribution depends on the availability of the snail host
-most widespread, it is endemic in Africa,
Saudi Arabia, and Madagascar. It has also become well established in Brazil, Suriname, Venezuela and Puerto Rico
94
Schistosoma mansoni symptoms
Cercarial penetration of intact skin may be seen as dermatitis with allergic reactions, pruritus and edema
-Migrating worms in the lungs may produce cough; as they reach the liver: hepatitis and also intestinal abnormalitis
-Eggs deposition in the bowel mucosa results in inflammation
and thickening of the bowel wall associated with abdominal pain, diarrhea and blood in the stool
-Chronic infection produces a dramatic hepatosplenomegaly with large accumulation of ascitic fluid in the peritoneal cavity
95
Schistosomiasis Diagnosis
established by the demonstration of characteristic eggs in feces
96
Schistosomiasis treatment
praziquantel (increases the permeability of the membranes of schistosome cells towards calcium ions) and the alternative is oxamniquine
97
cestodes (tapeworms)
bodies are flat and ribbon, and the heads are equipped with organs of
attachment
-head or scolex usually has 4 muscular cup-shaped suckers and a crown of hooklets
-individual segments of tapeworms are called proglottids and the chain of proglottids is called strobila
-no digestive system, food is absorbed from the host intestine through the wall of the worm
98
True or False: ALL tape worms are Hermaphrodites
True
99
Taenia solium
larval stage (Cysticercus) consist of a scolex, which is invaginated into a fluidfilled
bladder
-After a person ingest pork muscle containing a larval worm, attachment of the scolex with its four
muscular suckers and crown of hooklets initiates infection in the small intestine
-worm then produces proglottids until a
strobila of proglottids is developed, which may be several meters in length
-sexually mature proglottids contain eggs,
an as these proglottids leave the host in feces, they can contaminate water and vegetation ingested by swine
-gravid proglottids have a similar length and
width (1 cm x 1cm) and contain few (<12)
lateral uterine branches.
-eggs in swine become a six-hooked larval
form, called oncosphere, that penetrates the
pig’s intestinal wall, migrates in the circulation to the tissues, and becomes a cysticercus to
complete the cycle
100
Taenia solium epidemiology
Infection is directly correlated with eating insufficiently cooked pork
-prevalent in Africa, India, Southeast Asia, China, and some Latin American countries and Slavic countries. It is seen infrequently in the U.S
101
Taenia solium symptoms
in the intestine seldom causes appreciable symptoms
- intestine may be irritated at sites of attachment, and abdominal discomfort, chronic indigestion, and diarrhea may occur
- Most patients become aware of the infection only when they see proglottids or a strobila (the sum of all proglottids) in their feces
102
Taenia solium diagnosis
Stool examination may revel proglottids and eggs, and treatment may produce the entire worm for identification
-eggs are spheric, 30 to 40 μm in diameter, and possess a thick , radially striated shell containing a six-hooked hexacanth embryo
-eggs are identical to those of T. saginata (beef tapeworm), so
eggs alone are NOT sufficient for species identification.
103
Taenia solium treatment
Niclosamide (inhibits glucose uptake, oxidative phosphorylation, and anaerobic metabolism of the tapeworm)
-Prevention of infection requires that pork be either cooked until the interior of the meat is gray or frozen at -20 C for at least 12 hours
104
Taenia solium (pork) vs saginata (beef)
Gravid proglottids of T. solium are
smaller (7 to 12) lateral uterine branches than T. saginata (15 to 30)
-scolex of T. solium is globular and
armored with hooks in addition to four
suckers.
-T. saginata has NO hooks (unarmed scolex
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Cysticercosis
involves infection of people with the larval stage of T. solium (the Cysticercus), which
normally infects pigs
-Human ingestion of water or vegetation
contaminated with T. solium eggs from human feces initiates the infection.
-Autoinfection may occur when eggs from a person infected with the adult worm are transferred from the perianal area to the mouth on contaminated fingers
-Once ingested the eggs hatch in the stomach of the intermediate host, releasing the hexacanth embryo or oncosphere
-oncosphere penetrates the intestinal wall and migrates in the circulation to the tissues, where it develops into a cysticercus over 3 to 4 months
-
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cysticerci may develop in
muscle, connective tissue, brain, lungs and eyes
| -remain viable for as long as 5 years
107
True or False: People DO NOT get cysticercosis by eating undercooked
pork.
True
| -Eating undercooked pork can result in intestinal tapeworm if the pork contains larval cysts
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Cysticercosis epidemiolgy
found in areas where T. solium is prevalent and is directly correlated with human fecal
contamination
-In addition to fecal-oral transmission, autoinfection may occur when a proglottid containing eggs is
regurgitated from the small intestine into the stomach, allowing the eggs to hatch and release the infectious oncosphere
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Cysticercosis symptoms
Serious disease may follow as the cysticerci lodge in the brain and the eye
- n the brain: hydrocephalus, meningitis cranial nerve damage, seizures (neurocysticercosis) and visual defects.
- In the eye: lost of vision, or visual defects
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Cysticercosis diagnosis
Presence of cysticerci in the eye.
| -Central nervous system lesions may be detected by computed tomography
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Cysticercosis treatment
Praziquantel (increases the permeability of the membranes of schistosome
cells towards calcium ions).
-Concomitant steroid administration may be necessary to minimize the inflammatory response to dying larvae.
-Surgical removal of cerebral and ocular cysts may be necessary.
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Taenia saginata (beef tapeworm)
Infection results after a person ingest a cysticerci in insufficiently contaminated cooked beef
-After excystment, the larvae develop into adults in the small intestine and initiate egg production in mature proglottids
-adult worm may parasitize the jejunum and
small intestine of humans for as long as 25 years, attaining a length of 10 m
-adult T. saginata worm lacks a crown of
hooklets on the scolex and has a different
proglottid uterine branch structure
-Occurs worldwide and is one of the most frequent causes of cestode infections in the US
-symptoms similar to T. solium
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Taenia saginata (beef tapeworm) diagnosis
recovery of proglottids and eggs or
an entire worm whose scolex lacks hooklets.
-Study of the uterine branches
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Taenia saginata (beef tapeworm) treatment
praziquantel
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Echinococcus granulosus
example of accidental human infection, with humans serving as dead-end intermediate hosts in a life cycle that occurs naturally in other animals
-adult tape worms are found in nature in the intestines of dogs, coyotes, wolf, dingo
-larval cyst stage is present in the viscera of
hervivores (sheep, catle, swine, deer, moose
-Adult tape worms in the canine intestines produce infective eggs (identical to the Taenia species) that pass in feces
-eggs are ingested by humans , a six-hooked larval stage (oncosphere) hatches. It penetrates the human intestinal wall and enters the circulation to be carried to various tissue sites, e.g. liver and lungs but
also central nervous system and bone
-same cycle occurs in the viscera of herbivores
-humans the larvae form a unilocular hydatid cyst, which is a slow-growing tumor-like
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Echinococcus granulosus Epidemiology
Human infections is directly correlated with raising sheep in many countries in Europe, South America, Africa, Australia and New Zealand
- occurs in Canada and in the U.S. were cases reported in Alaska, Utah, New Mexico, Arizona, California, Alaska and Mississippi
- Human infection follows ingestion of contaminated water or vegetation as well as hand-to-mouth transmission of canine feces carrying the infective eggs
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Echinococcus granulosus symptoms
unilocular cyst grows slowly, 5 to 20 years may pass before symptoms appears
- majority of cases the cyst is located in the liver or lungs where it produces pressure
- Rupture of the cyst can occurs producing: fever, and occasionally anaphylactic shock and death
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Echinococcus granulosus diagnosis
difficult
- Clinical, radiographic, scanning, CT, and serologic findings.
- Central nervous system lesions may be detected by computed tomography
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Echinococcus granulosus treatment
Surgical resection of the cyst is the treatment of choice
- If the condition is inoperable because of the cyst location, therapy with high-dose Albendazole, Mebendazole or Praziquantel may be considered
- Dogs should not be allowed in the vicinity of animal slaughter and should never be fed the viscera of slain animals
