Helminths Flashcards
(158 cards)
0
Q
Name three helminths.
A
Nematodes (roundworms), Trematodes (flatworms) and Cestodes (tapeworms).
1
Q
What are helminths?
A
Eukaryotic multi-cellular parasitic worms with a complex life cycle.
2
Q
What is the phylum for nematodes (roundworm)?
A
Nemata or Nematoda.
3
Q
Nematodes are only free living. True or False?
A
False. Some are free living and some are parasitic.
4
Q
Why is the structure of nematodes described as ‘a tube within a tube’?
A
Because it’s digestive system is like a tube with openings at both ends. They are large in size and are cylindrical with unsegmented bodies.
5
Q
What are the usual sites of infection?
A
Gut, tissue and blood.
6
Q
How are gut nematodes diagnosed?
A
By analysing eggs or larva in stool.
7
Q
Give four examples of gut nematodes.
A
Roundworm, Pinworm, Hookworms and Whipworm.
8
Q
How are blood and tissue nematodes transmitted?
A
Via insect bites.
9
Q
Give three examples of diseases caused by blood and tissue nematodes.
A
Filaria, river blindness and Calabar swellings.
10
Q
What is the name of the large intestinal roundworm?
A
Ascaris lumbricoides
11
Q
What disease does it cause?
A
Ascariasis.
12
Q
What is the common age of infection and why?
A
5-9 years due to contaminated soil, food and toys. Also contracted by the use of human faeces as fertiliser.
13
Q
Where is the incidence highest?
A
In warm climates with poor sanitation.
14
Q
Explain the life cycle.
A
Food contaminated with infective eggs are ingested. They hatch in the upper small intestine.
The larvae penetrates the intestinal wall and ethers the venules or lymphatics where they pass through the liver, heart, and lung to reach alveoli. In 1 to 7 days they grow up to 1.5 cm.
They then move to the small intestine where they mature in 2 to 3 months.
A female grows to 20-35cm and can live in the intestine for 12 to 18 months with the ability to produce 25 million eggs.
The eggs are excreted in faeces and infective larvae are formed within the egg.
The eggs are resistant to chemical disinfectant and survive for months in sewage but are killed by heat (40 degrees C for 15 hours).
15
Q
List some symptoms of the worm burden.
A
Vague abdominal pain, vomiting, fever and distension. In severe cases, weight loss and loose stool may occur.
16
Q
What are the means of asymptomatic carriers?
A
10-20 worms may go unnoticed except in a routine stool examination.
17
Q
Name the drug used for treatment of ascariasis.
A
Mebenazole.
18
Q
What are the three filariae and what do they cause?
A
Wuchereria bancrofti: Bancroftian Filariasis.
Brugia malayi: Brugian lymphatic filariasis of humans.
Brugia timori: a human filarial parasite from Indonesia.
19
Q
Many species of mosquitos including Anopheles are responsible for the transmission of lymphatic filariasis. True or False?
A
True.
20
Q
How many people are threatened by LF?
A
1.4 billion people.
21
Q
When is it usually contracted?
A
Before the age of 5.
22
Q
What signs are produced by LF?
A
Swelling of the limbs and breasts (lymphoedema) and genitals (hydrocele), or swollen limbs with dramatically thickened hard, rough and fissured skin (elephantiasis).
23
Q
What problem does this propose?
A
It prevents afflicted individuals from experiencing a normal working and social life, furthering the cycle of poverty.
24
What is the epidemiology?
Mostly in the tropical and subtropical regions, amongst the poorest countries such as central Africa and in many parts of Asia.
25
How is LF contracted?
Through poor sanitation and housing quality.
26
How do adult worms damage the lymphatic system and how long do they survive?
By causing fluid to collect and cause swelling, leaving patients permanently disabled and disfigured. They can persist for as long as 10 years.
27
When do symptoms appear in children?
During puberty because of the long latency period of the disease. Of all LF sufferers, children will benefit most from the elimination programme.
28
Explain the life cycle of Wuchereria bancrofti.
The female worms release large numbers of very small worm larvae which circulate the bloodstream. When a human is bitten by a mosquito, the mosquito ingests the larvae. The larvae develop in the mosquito into an infective stage and are then spread to other people via mosquito bites. After a bite, the larvae pass through the skin, travel to the lymphatic vessels and develop into adult worms.
29
What is the periodicity of microfilariae?
During the day they are present in the deep veins and during the night they migrate to the peripheral circulation.
30
How is the asymptomatic form of infection characterised?
By the presence of thousands or millions of larval parasites (microfilariae) in the blood and adult worms lodged in the lymphatic system (maintains the fluid balance between tissues and blood, essential for immune defence system).
31
Acute episodes of local inflammation involving skin, lymph nodes and lymphatic vessels often accompany the chronic lymphoedema or elephantiasis. True or False?
True.
32
How do some of these come about?
By the body's immune response to the parasite, but most are the result of bacterial infection of skin where normal defences have been partially lost due to underlying lymphatic damage.
33
How can the damage be slowed down or even reversed?
By careful cleansing which is helpful in healing the infected surface areas.
34
Chronic and acute manifestations of filariasis tend to develop more often and sooner in who?
Refugees or newcomers rather than in local populations who are continually exposed to the infection.
35
LF affects men more often than women with worse symptoms. True or False?
True. 10-50% of men suffer from hydrocele (fluid-filled balloon like enlargement of the sacs around the testes) and elephantiasis of the penis and scrotum.
36
Where can lymphoedema occur?
Arms, legs, breasts, scrotum and penis. Others who are infected show no signs of clinical disease, but have damaged lymphatic vessels and are at risk of developing lymphoedema.
37
Why does the skin become hard and thick?
Because patients suffer from many acute attacks of infection over time and the disease progresses from the early stages of lymphoedema to elephantiasis (thickening and hypertrophy of tissues infected with the worms may lead to the enlargement of tissues, especially the extremities).
38
What are the methods used for diagnosis?
Blood test during 10pm-2/4am to view parasites in peripheral blood during their 'nocturnal periodicity'. Urine specimens and Antigen detection kits called ICT can detect infection within minutes and can be carried out at any time of day.
39
The strategy for interrupting transmission is an annual single co-administration of two drugs for at least five years. Name these drugs.
Single doses of albendazole and mectizan or DEC.
40
What is DEC?
An inexpensive and effective anti-filarial drug which is used to treat LF in many countries. Available in tablet form for daily intake at meal times. Can not be used in most of Africa because severe side reactions can occur when other infections, such as river blindness are present.
41
How does A. lumbricoides affect the respiratory system?
After infection with many larvae, migration of worms to the lungs can produce pneumonitis resembling an asthmatic attack.
42
How are the eggs in stool identified?
Knobby-coated, bile stained, fertilised and unfertilised oval eggs with thick walled outer shell.
43
What causes inflammation seen for W. bancrofti infection?
Caused by the presence of molting adolescent worms and dead or dying adults within the lymphatic vessels.
44
How are the worms identified in terms of structure?
W. bancrofti, B. malayi and Loa loa demonstrate a sheath on their microfilariae. Further identification is based on study of head and tail structures. Exact species identification is not necessary because treatment is the same.
45
There are no animal reservoirs for W. bancrofti unlike B. malayi which sees infection in cats and monkeys. True or False?
True.
46
How is LF prevented?
Education regarding filarial infections, mosquito control, use of protective clothing and insect repellents.
47
What is the phylum for Trematodes?
Platyhelminthes
48
Describe their structure.
Flat, leaf-shaped worms. Hermaphroditic. 2 muscular suckers; oral (incomplete digestive system) and ventral (attachment).
49
How many hosts are required?
A definitive host and two intermediate hosts. Intermediate hosts (in which the larval asexual phase occurs): molluscs in all cases (snails and clams), some flukes need other intermediary hosts, vectors. Final host (in which the adult sexual phase occurs).
50
What disease does blood flukes such as schistosoma haematobium (urinary form), S. mansoni (intestinal) and S. japonicum (intestinal) cause?
Bilharzias.
51
What are the infective forms for schistosomes?
Skin penetrating cercariae released from snails.
52
What is the epidemiology?
Major parasitic infection of tropical areas.
53
How are people put at risk?
Lack of hygiene, play habits, agricultural domestic and recreational activities which expose them to infested water.
54
What is the distribution of S. mansoni? And is there any reservoirs?
Found in Africa, South America (Brazil, Suriname, Venezuela), the Caribbean (Puerto Rico, St. Lucia), parts of the Middle East. No.
55
What is the distribution of S. haematobium? And are there any reservoirs?
Found in large parts of Africa, Arabia, the Middle East, Mauritius. No.
56
What is the distribution of S. japonicum? And are there any reservoirs?
Found in Far East (china and Philippines) and few places in indonesia. Water buffalo is a reservoir.
57
Describe the schistosome life cycle.
Infection is initiated by ciliated, free-swimming cercaria in fresh water that penetrate intact skin, enter the circulation and develop in the intrahepatic portal circulation (S. mansoni and S. japonicum) or in the vesical, prostatic, uterine plexuses and veins (S. haematobium).
58
How do they escape the host immune system?
Adult worms coat themselves with self-antigens. Minimal host inflammatory response to adult worms. This leads to chronic infection.
59
Schistosomes' eggs elicit strong inflammatory response from the host. True or False?
True.
60
Production of enzymes by the larvae inside the eggs causes what?
Tissue destruction and allow the eggs to pass through the mucosa and into the lumen of the bowel and bladder, where they are passed to the external environment in the faeces and urine.
61
What does the 1) penetration of cercariae 2) onset of laying eggs 3) presence of eggs in tissues all lead to?
1) skin rash. 2) katayama syndrome. 3) chronic schistosomiasis, granulomas, fibrosis.
62
Asymptomatic allows for brown hematin pigment present in macrophages and neutrophils so what does symptomatic schistosomiasis, bilharziasis show?
The first sign is inflammation at the site of penetration of cercariae.
63
How does katayama fever from schistosoma mansoni (acute schistosomiasis) come about?
When female lays eggs; 5 weeks after infection. Symptoms include abdominal pain, fever, nausea, weight loss, headache, hepatosplenomegaly and leukocytosis with eosinophilia. Granuloma formation around eggs trapped in the liver and intestinal wall.
64
What is schistosoma mansoni?
Chronic schistosomiasis.
65
Describe what intestinal schistosomiasis involves.
Manifest several years after infection involving cellular, granulomatous inflammation around eggs trapped in the tissues, with subsequent fibrosis. Large intestine shows most severe lesions. Prevalence in Egypt.
66
What does hepatosplenic schistosomiasis involve?
Involves a cellular, granulomatous inflammation around eggs trapped in the liver, leading to fibrosis and hepatosplenic disease.
67
How long does symptoms take to appear for hepatosplenic schistomosias?
18 months and 20 years.
68
The fibrosis in the granuloma leads to portal vein fibrosis in the liver as the inflammatory response spreads to portal blood vessels due to trapped eggs and leading to cirrhosis of the liver. True or False?
True.
69
Why is blood flow through the liver inhibited?
Due to portal hypertension.
70
Accumulation of fluid in the abdominal cavity is common and liver damage is irreversible. True or False?
True.
71
What is associated with stunted growth in children?
Visceral schistosomiasis.
72
What effect does hepatosplenomegaly have?
Causes pyrexia (high temp), anaemia and haemorrhage from the GIT.
73
What does the granuloma that forms around eggs consist of?
T & B lymphocytes, macrophages, giant cells, epitheliod cells, mast cells, plasma cells, fibroblasts and eosinophils.
74
What is a epitheloid cell?
A modified macrophage that is adapted for secretion as opposed to phagocytosis. Hence, there is abundant Golgi bodies and endoplasmic reticulum within the cytoplasm. Epitheloid cells merge to form multinucleate giant cells. They are one of the defining elements of a granuloma.
75
What is the primary cause of pathology in a S. japonicum infection?
Granulomatous reaction to egg trapped in the liver.
76
Both acute and chronic infections are similar to that of S. mansoni infections. True or False?
True.
77
What is the difference between the acute and chronic stage of the disease?
The acute disease (katayama fever) is more common whereas the chronic stage of the disease may be more severe, due to the greater egg output and longevity of S. japonicum females compared to S. mansoni.
78
Describe what happens in a S. haematobium infection.
Adult parasites and egg deposition are found in small venules around the bladder and ureter. Eggs pass through the bladder wall, to leave the body in the urine. The disease is chronic in nature. Most frequently affected organ is urinary bladder, where calcification of eggs trapped in the tissues often occurs. The disease 'urinary schistomosias' is characterised by blood in the urine (haematuria).
Cancer of the bladder (squamous cell carcinoma) is an important complication of infection with S. haematobium.
Eggs may be deposited in the liver, leading to granuloma formation. This can also be seen in the lungs.
79
What are the methods used for diagnosis?
Recovery of eggs in stool, rectal biopsy, urine samples.
80
Name two drugs used for treatment.
Praziquantel or oxamniquine.
81
How else would you treat schistosome infection?
Chemotherapy may terminate disposition of eggs but does not affect lesions due to eggs. Antihistamines and corticosteroids for schistosomal dermatitis (a sensitisation reaction to repeated invasion of the skin by cercariae of schistosomes).
Control of molluscs using molluscacides.
82
What are the preventative measures?
Improved sanitation, clean drinking water, hygiene education would reduce infective water contact and the contamination of water sources. Vaccination strategies in progress.
83
Where can fasciola hepatica (sheep liver fluke) be found?
In snails, water plants, sheep, cattle, humans, buffalo.
84
What is fascioliasis caused by? And what are the two types of flukes?
Caused by liver flukes. Fasciola hepatica (sheep liver fluke) and fasciola gigantica (giant liver fluke).
85
Describe fasciola hepatica.
One of the most studied herbivore parasite with wide distribution. The disease has serious economic consequences for farmers that lose their cattle due to severe liver damage.
86
What is the epidemiology of fasciola hepatica?
Found in Latin America such as Bolivia. The most common infection is in sheep and cattle in comparison to humans.
87
Where is it localised?
In the bile ducts of its hosts.
88
What is the definitive and intermediate host?
Definitive host: sheep, cattle, goats, rabbits.
Intermediate host: lymnaeid snail.
Humans are mostly seen as accidental hosts to this parasite and the rate of infection of humans is significantly lower.
89
Describe the structure of the parasite.
Can be 3cm long and 1.5cm wide with an anterior cephalic cone, branched reproductive organs and oral suckers used to effectively anchor the parasite in the bile duct.
90
Describe it's life cycle.
Eggs have an incubation period of 14-17 days and hatch in water to release miracidium. The miracidium infects lymnaeid snail where larval multiplication occurs giving rise to cercariae. One miracidium can give rise to 600 cercariae. The cercariae then develops into a metacercariae which is enveloped in a cyst and attaches to aquatic vegetation. Once it is ingested by a definitive host the metacercariae excysts into the intestine.
The liver fluke burrow into the liver and travel into the bile ducts where the adult fluke develops. The eggs are passed in faeces contaminating the water and vegetation.
91
What are the symptoms and how do they arise?
Caused by biliary obstruction. In humans, high fever, diarrhoea, chills, bile inflammation, liver enlargement and jaundice are reported.
92
Inflammation of the bile duct is caused by?
Mechanical obstruction. Bacteria infection may also lead to more inflammation.
93
What happens to the snails infected by the parasite?
They become enlarged, supporting further parasitic growth.
94
What are the methods for diagnosis?
Eggs can be found in a stool sample or biliary aspirate. Ultrasonography to observe adult worms in the liver. ELISA can be a more accurate diagnostic test to check for antigens of Fasciola hepatica.
95
What drugs are used for treatment?
Bithionol: side effects - skin reaction, vomiting, diarrhoea, abdominal pain.
Praziquantel: effective in lowering the level of infection.
Triclabendazole: perfect cure rate with a single dose reported with minimal side effect. However, this drug has not been approved for human use in the US.
Poor response to praziquantel.
96
What are the preventative measures?
Avoid eating raw liver, limited consumption of aquatic vegetation, chemical treatment of water, use molluscicides.
97
Where is clonorchis sinensis (Chinese liver fluke) found?
In snails, freshwater fish, uncooked fish, dogs, cats, humans.
98
What is the epidemiology?
Endemic in china, Taiwan, Hong Kong and Korea.
99
What is the life cycle?
Eggs are passed with the bile into the faeces. In freshwater, eggs are ingested by aquatic snails. Human consumption of raw fish allows the parasites to reach the biliary tree of the liver. Cats, dogs, pigs, and several other fish eating mammals are also susceptible.
100
What are the symptoms?
Infection in humans is usually mild and asymptomatic. Severe infections lead to a loss of appetite, diarrhoea and fever.
101
What is the effect of a liver infection?
Obstruction of the bile duct and liver cirrhosis, chronic jaundice and eventually cholangiocarcinoma (cancerous growth in one of the ducts that carries bile from the liver to the small intestine).
102
What are the definitive hosts for opisthorchis?
Dogs, cats and other fish eating animals.
103
What is the epidemiology?
Eastern Europe and Southeast Asia, Thailand.
104
What are the similarities between opisthorchis and clonorchiasis?
Life cycle and symptoms are similar. Cholangiocarcinoma is more pronounced than in clonorchiasis.
105
Where can paragonimus westermani (lung fluke) be found?
In snails, freshwater crab, crayfish, uncooked crab, pigs, monkeys and humans.
106
What is the epidemiology?
Found in Africa, North and South America and Asia.
107
What are the symptoms?
Tuberculosis-like and include fever, chronic cough and thoracic pain.
108
What are the preventative measures?
Avoidance of raw and undercooked food (meat, fish, crabs etc).
109
Name two drugs used for treatment.
Praziquantel and or triclabendazole.
110
Describe the life cycle.
Eggs are shed by the definitive host via expectoration or in faeces. They develop to larvae and invade snails. Cercariae which finally abandon the snail and seek a crustacean (crab or crayfish) develop to an infectious stage for the definitive host. They then invade the lungs where they are coughed up in sputum or swallowed and passed in faeces. Humans becomes infected by eating infected raw crustacean.
111
What are the clinical syndromes?
The fluke provokes the development of a fibrous tissue capsule with bloody purulent material containing eggs. There is inflammatory infiltrate around the capsule. Worms may migrate to the brain where they lay eggs and cause a granulomatous abscess resulting in symptoms similar to epilepsy. They can also invade the spinal cord.
112
What are the symptoms?
Dry cough, followed by production of blood stained rusty brown sputum. Pulmonary pain and pleurisy (inflammation of the lining of the lungs and chest may develop).
113
How would you diagnose?
Look at history and symptoms. Eggs are found in rust coloured sputum, often being examined for tuberculosis. Eggs are large and ovoid with a thick, yellowish brown shell and distinct operculum.
114
How are schistosomes different from regular Trematodes?
They have a cylindrical body and separate bodies for male and female worms. They are not hermaphrodite. They do not have a operculum which is a lid that opens to allow larval worm to find a mollusc rather the eggshell splits to liberate the larva. They are not found in ducts, tissues or cavities.
114
What are the egg features for Chinese liver fluke?
Distinct operculum with prominent shoulders and a tiny knob at the posterior pole.
115
What are the features for S. mansoni eggs? And where can they be seen?
Oval with a sharp lateral spine. Eggs are primarily deposited in the intestine, spinal cord and brain.
116
What are the features of S. japonicum eggs?
Smaller than S. mansoni eggs and their spine is not clearly visible.
117
What are the features for S. haematobium eggs?
Similar in size to S. mansoni but have a terminal spine.
118
Define 'clay pipestream fibrosis'.
In fatal schistosomiasis, fibrous tissue reacting to the eggs in the liver, surrounds the portal vein in a thick, grossly visible layer.
119
What is cercarial dermatitis and what causes this?
Develops due to infection with S. haematobium. Usually called 'swimmers itch' where the nonhuman schistosomes have cercariae that penetrate human skin and produce severe dermatitis. These schistosomes cannot develop into adult worms in the human host and their natural hosts are birds. Immediate drying of the skin when people leave such waters offers some protection.
120
What is the phylum for Cestodes?
Platyhelminthes.
121
Describe the tapeworm structure.
Flat, ribbonlike, hermaphroditic.
Scolex - attachment organ.
Zone of proliferation - undifferentiated area behind the scolex (neck region).
Strobilia - chain of segments (proglottids)
Immature proglottids - developing reproductive organs
Mature proglottids - mature reproductive organs
Gravid proglottids - contain eggs in the uterus.
122
Name five tapeworms pathogenic to man.
Taenia solium (pork tapeworm)
T. saginata (beef tapeworm)
Echinococcus granulosus and E. multilocularis (hydatid)
Diphyllobothrium latum (fish or broad tapeworm)
Hymenolepsis nana (dwarf tapeworm)
123
How many hosts do tapeworms pass through to complete life cycle?
Two.
124
What's the name of the disease caused by Taenia solium and T. saginata?
Taeniasis and or cysticercosis.
125
What's the distribution of the disease?
Worldwide including china, Mexico, India, Africa. Incidence higher in developing countries and high incidence of pork tapeworm.
126
Describe the structure of T. saginata (longest tapeworm).
4-6 meters long.
A pear shaped head (scolex) with four suckers but no hooks or neck.
Long flat body with several hundred segments (proglottids).
Each segment with a branched uterus.
Egg is roundish and yellow-brown that contains an embryo with 3 hooklets.
127
Describe the structure of T. solium.
Smaller than T. saginata.
A globular scolex with four suckers and a circular row of hooks (rostellum) that gives it a solar appearance.
A neck and a long flat body.
Proglottids with a 7-12 branch uterus.
Eggs of T. solium and T. saginata are indistinguishable.
128
Explain the life cycle of T. saginata.
A tapeworm larval cyst (cysticercus) is ingested with poorly cooked infected meat.
Larva escapes the cyst and passes to the small intestine where it attaches to the mucosa by the scolex suckers.
The proglottids develop as the worm matures in 3-4 months. The adult may live in the small intestine as long as 25 years and pass gravid proglottids with the faeces.
Eggs extruded from the proglottid contaminate and persist on vegetation for several days and are consumed by cattle or pigs in which they hatch and form cysticerci.
129
Explain the life cycle of the pork tapeworm.
Eggs are ingested by the pig and the ingestion of infected pork, poorly cooked causes Taeniasis. Or it could be the ingestion of eggs by faecal contamination by humans (human cysticercosis).
130
Describe what happens after ingestion of the cysticerci.
After ingestion the eggs pass through the lumen of the intestine into the tissues and migrate preferentially to the brain and muscles (also lung, liver, eye). There they form cysts that can persist for years. In some cases the cysts will eventually cause an inflammatory reaction presenting as painful nodules in the muscles and seizures when the cysts are located in the brain.
131
What are the two distinct clinical syndromes?
Taeniasis (caused by the adult worm in the intestine): abdominal pain, diarrhoea, nausea.
And human cysticercosis (caused by ingestion of eggs of T. solium): extra neural cysticercosis or neurocysticercosis (headaches and acute onset seizures).
Cysticercosis symptoms are a result of inflammatory/immune responses against cyst.
132
What is the incidence of cysticercosis?
Neurological cases seen in Mexico and muscular involvement in India.
133
What methods are used for diagnosis?
Recovery of eggs and proglottids in stool.
Antibodies are produced in cysticercosis and are useful epidemiological diagnostic tool whereby their presence indicates cysticercosis.
134
Name two drugs used for treatment.
Niclosamide and praziquantel. And in some cases surgery is required.
135
Name the disease caused by diphyllobothrium latum (fish or broad tapeworm). (Largest tapeworm)
Diphyllobothriasis.
136
What is the epidemiology?
Distributed worldwide. In the subarctic and temperate regions. Associated with eating of raw or improperly cooked fresh water fish.
137
Describe the structure.
Scolex resembles two almond-shaped leaves. Proglottids are broader than they are long. Egg contains an embryo with 3 pairs of hooklets.
138
What is the life cycle?
Infected by eating uncooked fish that contains plerocelarvae, which attaches to the small intestinal wall and mature into adult worms in 3-5 weeks.
Eggs discharged from gravid proglottids in the small intestine are passed in the faeces. The egg hatches in fresh water to produce a ciliated coracidium which needs to be ingested by a water flea (cyclops) where it develops into a procercoid larva.
When infected cyclops are ingested by the freshwater fish, the procercoid larva penetrates the intestinal wall and develops into a plerocercoid larva, infectious to man.
139
What are the symptoms?
Abdominal discomfort, loss of weight, loss of appetite and some malnutrition. Anaemia and neurological problems associated with vitamin B12 deficiency(due to host and worm competition for B12.) are seen in heavily infected individuals.
140
What are the methods used for diagnosis?
Eggs (with a knob at the bottom of the shell) and empty proglottids in stool. History of raw fish consumption.
141
What is the treatment?
Praziquantel or niclosamide. Freezing for 24 hours, thorough cooking or pickling of fish kills the larvae.
142
Name the disease caused by Echinococcus granulosus and E. multilocularis. (Smallest tapeworms).
Hydatid disease.
143
Describe the life cycle.
Eggs are ingested by humans, a six-hooked larval stage called an oncosphere hatches, penetrates the intestinal wall and enters circulation to be carried to various sites primarily lungs,liver and CNS. This same cycle occurs in the viscera of herbivores. When the herbivore is killed by a canine predator, the ingestion of cysts produces adult tapeworms in intestine to initiate egg production.
144
What are the clinical syndromes?
Disease caused by hydatid cysts.
The symptoms comparable to those of a slowly growing tumour, depend upon the location of the cyst.
Large abdominal cysts produce increasing discomfort.
Liver cysts cause obstructive jaundice.
Peribronchial cysts may produce pulmonary abscesses.
Brain cysts produce intracranial pressure and Jacksonian epilepsy.
Kidney cysts cause renal dysfunction.
The contents of a cyst may produce anaphylactic responses.
Infection of man is accidental because it is a dog parasite.
145
What are the methods used for diagnosis?
Clinical symptoms of a slow-growing tumour accompanied by eosinophilia are suggestive.
Intradermal test with hydatid fluid.
Radiography to locate pulmonary cysts and calcified cysts.
Detection of antibodies against hydatid fluid antigens using ELISA.
146
What are the treatment and control measures?
Surgical removal of cyst.
High dose of mebendazole.
Avoid infected cats and dogs.
147
What is the mode of transmission for Hymenolepis nana?
Oral-faecal route.
148
What is the reservoir?
Rodents (intermediate host).
149
What disease is caused by it?
Infects children causing enteritis.
150
What makes this Cestode different?
It does not require an intermediate host to develop into its infective stage.
151
What is the life cycle?
Embryonated eggs in faeces is ingested by insect (or by humans from contaminated food, water, or hands) which is then eaten by a rodent. Worm develops into a adult in the small intestine and resides there for several weeks. Eggs can be released through the genital atrium of the gravid proglottids. Gravid proglottids can also disintegrate releasing eggs that are passed in stool.
152
Tapeworms have no digestive system, and food is absorbed from the host intestine through the soft body wall of the worm. True of False?
True.
153
What is a chain of proglottids called?
Strobila
154
How is T. solium and saginata differentiated?
Gravid proglottids of T. solium are smaller than those of T. saginata and contain only 7-13 lateral uterine branches versus 15-30 for the beef tapeworm. Cysticercosis produced by T. saginata does not occur in humans. And T. saginata lacks a crown of hooklets on the scolex.
155
How are D. latum eggs different from other tapeworm eggs?
They are operculated (provided with a lid).
156
What is the epidemiology of E. multilocularis?
Found in Canada, Alaska, Montana (basically the US).
