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PARASITOLOGY > TREMATODES > Flashcards

TREMATODES Flashcards

1
Q

Give a brief classification of the members of Phylum Platyhelminthes.

A
  • Platyhelminthes are flatworms categorized into 2:
  • Cestoda - cestodes e.g tapeworms.
  • Trematoda - trematodes e.g flukes.
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2
Q

Outline some of the developmental stages of Trematodes.

A
  • Miracidium - 1st larval stage from egg in water. Infects the snails.
  • Sporocyst - 2nd larval stage in the snail ( intermediate host).
  • Cercariae - final Larval stage. Is infective . Escapes from the snails in fresh water and may infect humans.
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3
Q

State one adaption of miracidia to their survival.

A

Miracidia are ciliated to allow them to swim easily in water and infect the snails which are the intermediate hosts.

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4
Q

Distinguish between Cercariae and metacercariae.

A
  • Cercariae may encyst to form the metacercariae.
  • The metacercariae are therefore encysted cercariae without a tail.
  • The metacercariae also have a hard outer cyst wall and can survive for prolonged periods in wet environments, compared to cercariae.
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5
Q

Give examples of the different categories of Trematodes.

A
  • Blood flukes E.g Schistosoma
  • Liver flukes E.g Clonorchis sinensis
  • Lung flukes E.g Paragonimus westermani
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6
Q

All trematodes are hermaphroditic except ?

A

Schistosomes. They are dioecious - they have separate male and female sexes.

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7
Q

Disease cause by Schistosomes?

A

Schistosomiasis/ Bilharzia.

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8
Q

State some of the distinguishing factors between an adult male and female Schistosoma worm .

A
  • Males are slightly smaller in size compared to females.
  • The male has a deep ventral groove called the gynecophoric canal , in which the female lies during copulation.
  • The gut of the female worm appears darker because it is filled with deposits of haematin , a breakdown product of Haemoglobin.

NB : Both the male and the female have 2 suckers , an anterior and a ventral sucker.

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9
Q

State the various effects of the different Schistosoma species .

A
  • Schistosoma mansoni affects the Gastrointestinal tract, causing Intestinal schistosomiasis.
  • Schistosoma japonicum , also causes intestinal schistosomiasis, but mainly in Asia.
  • Schistosoma haematobium affects the bladder and urinary tract, causing urinary schistosomiasis.
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10
Q

State the definitive and intermediate hosts of Schistosoma parasites.

A
  • Definitive hosts - humans .
  • Intermediate hosts - snails.
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11
Q

State the locations of the different species of Schistosomes in the human hosts.

A
  • Schistosoma japonicum - Superior Mesenteric Veins draining the small intestines.
  • Schistosoma mansoni - Superior Mesenteric Veins draining the large intestines.
  • Schistosoma haematobium - venous plexus draining the urinary bladder and also in the rectal venules.
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12
Q

Briefly describe the life cycle of the Schistosoma parasites.

A
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13
Q

Symptoms of Schistosomiasis are caused by ?

A

The body’s reaction to the presence of the eggs . The symptoms are not caused by the worms themselves.

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14
Q

Symptoms that may occur in children who have been repeatedly infected ?

A
  • Anaemia.
  • Malnutrition.
  • Learning difficulties.
  • Damage to the liver, bladder, intestines, spleen and lungs.
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15
Q

Some of the early clinical manifestations of Schistosomiasis include?

A
  • Rash / itchy skin.
  • Fever and chills.
  • Coughs.
  • Muscle aches.
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16
Q

Outline some of the major health complications that may arise due to Intestinal Schistosomiasis.

A
  • Abdominal pain.
  • Malena - blood in stool.
  • Haematochezia - fresh blood in stool.
  • Constipation.
  • Hematemesis - vomiting of blood.
  • Hemorrhoids - swollen / congested/ distended hemorrhoid veins around the anal openings.
  • Portal hypertension.
  • Splenomegaly.
  • Presence of the eggs in the liver may induce granulomas which lead to fibrosis, hepatomegaly and Portal hypertension. Granulomas are formed in response to the antigens secreted by the eggs.
  • Occasional embolic egg granulomas found in the brain or spinal cord. These may cause seizures, paralysis or even spinal cord inflammation.
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17
Q

Briefly discuss the mechanism through which Schistosoma parasites evade the host’s immune responses.

A

The surface of the Schistosoma parasites is coated with the host’s antigens , thereby limiting the ability of the immune system to recognize them as foreign .

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18
Q

State the microscopic distinguishing features of the 3 species of Schistosomes.

A
  • Schistosoma mansoni - eggs have a prominent lateral spine.
  • Schistosoma japonicum - eggs have a very small lateral spine.
  • Schistosoma haematobium - eggs have a large terminal spine.
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19
Q

State the major site of damage caused by invasion by Schistosoma japonicum and mansoni .

A
  • Schistosoma mansoni - damage the wall of the distal colon ( inferior mesenteric venules) .
  • Schistosoma japonicum - damage the walls of both the small and large intestines ( superior and inferior mesenteric venules) .
  • The damage is mainly due to :
    – Digestion of the tissues by proteolytic enzymes produced by the eggs.
    – Host’s inflammatory response to the presence of the eggs . This is what causes formation of granulomas in the venules.
20
Q

State two drugs that are effective in treatment of Schistosomiasis.

A
  • Praziquantel - taken orally. Single dose.
  • Oxamniquine.
21
Q

Methods of diagnosing Schistosomiasis?

A
  • Stool examinations - parasite eggs of Schistosoma mansoni and Schistosoma japonicum maybe seen microscopically.
  • Urine examination - for the eggs of Schistosoma haematobium.
  • Rectal snip examination - the lateral spine of Schistosoma mansoni can be seen
22
Q

State the major preventive measures taken against the spread of Schistosomiasis.

A
  • Eradication of the fresh water snails using molluscicides such as Niclosamide and CuSO4.
  • Avoid swimming or wading in fresh water , in areas that are endemic.
  • Wearing protective gear e.g while working in fresh water such as rice farms to prevent the cercariae from penetrating your skin.
  • Treatment of affected individuals to prevent transmission.
  • Improved sanitation - construction of toilets and latrines - proper disposal of feces and urine.
  • Mass treatment of communities and targeted treatment of school going children.
  • Drinking safe treated or boiled water as the parasite may cause infection if it comes into contact with the mouth or lips.
  • Boiling bathing water .
  • Vigorous towel drying if exposed to fresh water to prevent the parasite from penetrating the skin.
23
Q

State the various fresh water snail species that serve as intermediate hosts for Schistosoma parasites.

A
  • Biomphalaria - S. mansoni
  • Bulinus - S. haematobium
  • Oncomelania - S. japonicum
    Nb – Schistosoma japonicum is the only species with domestic animals as reservoir hosts.
24
Q

Outline some of the fresh water snail species that are suitable intermediate hosts for Fasciola hepatica parasites.

A
  • Galba
  • Fossaria
  • Pseudosuccinea
25
Q

What is the primary cause of the pathologies related to Fasciola hepatica infections ?

A

Pathologies are causes due to presence of the adult worms in the biliary tracts.

26
Q

State the symptoms associated with the early/ acute stages of infections with Fasciola hepatica.

A
  • These symptoms occur as a result of the migration of the parasite from the intestines to and through the liver.
  • GIT problems e.g Nausea , vomiting, abdominal pain& tenderness.
  • Fever, rash and difficulty in breathing.
  • Hepatomegaly.
  • Right upper quadrant pain.
  • Most infections are asymptomatic and the infected persons may not pass eggs through the feces at this stage.
27
Q

Briefly describe the life cycle of Fasciola hepatica parasites.

A
  • Humans are infected by ingesting Watercress or other aquatic plants contaminated with the infective metacercariae of Fasciola hepatica.
  • The metacercariae excyst in the duodenum, penetrate the gut wall and migrate through the intestinal wall, peritoneal cavity and liver parenchyma. They eventually reach the liver and the biliary ducts where they mature into adults.
  • The hermaphroditic adults in the Bile ducts produce immature and unembryonated eggs which are passed in stool.
  • The eggs become embryonated in fresh water, and they release miracidia which invade a suitable fresh water snail host.
  • In the snail , sporogeny occurs , and the miracidia differentiate into sporocysts , then rediae then to Cercariae which are ciliated.
  • The Cercariae are released from the snail , they swim and encyst on aquatic vegetation as metacercariae after they have shed off their tails.
  • The vegetation may be ingested by humans completing the cycle.
  • Adult flukes may be ingested by eating raw / undercooked sheep liver .
28
Q

State the symptoms associated with the chronic phase of Fasciola hepatica infections.

A
  • This phase occurs after the parasite settles in the bile ducts.
  • Inflammation and blockage of the bile ducts, liver, gall bladder and pancreas.
  • Obstructive jaundice.
  • Halzoun Pain - Painful pharyngitis caused by the presence of adult flukes on the posterior pharyngeal wall.
29
Q

How are adult flukes of Fasciola hepatica acquired by humans ?

A

By eating raw or undercooked sheep liver . The sheep may have grazes on aquatic plants such as Watercress on which the cercariae may have encysted.

30
Q

Diagnosis of Fasciola hepatica infections is based on ?

A
  • Stool examinations. Examining the Fasciola eggs found in the stool under a microscope .
  • Examining bile or duodenal contents may also yield some Fasciola eggs.
  • Blood tests to detect antibodies produces due to immune responses against the parasite .
31
Q

What are the effective treatment options against Fasciola hepatica?

A
  • Treatment with Triclabendazole.
  • Surgical removal of adult flukes in the pharynx and larynx.
32
Q

State one disadvantage of depending on Stool examinations to diagnose Fasciola hepatica infections.

A
  • Infected people don’t start passing eggs until they have been infected for several months. Even during the chronic phase of infection, it can be difficult to find the eggs in stool specimens in people with light infections.
  • The infection therefore, has to be diagnosed in other ways other than stool examinations.
33
Q

State the geographical distribution of Fasciola hepatica infections.

A

Endemic in Latin America, Africa, Europe and China.

34
Q

List down some of the measures effective in prevention of Fasciola hepatica infections.

A
  • Strict control of the growth and sale of watercress and other edible aquatic plants.
  • Avoid eating raw watercress and other edible aquatic plants, especially from endemic areas.
  • Travellers to areas with poor sanitation should avoid food or water , as it may be contaminated.
  • Vegetables grown in fields that may have been irrigated with polluted water should be thoroughly cooked.
  • Meat from potentially infected animals should be properly cooked e.g sheep liver.
35
Q

How do humans acquire infections caused by Fasciolopsis buski ?

A

Humans acquire the infection by ingesting aquatic vegetation , upon which the infective metacercariae of Fasciolopsis buski had encysted.

36
Q

Briefly discuss the life cycle of Fasciolopsis buski.

A
  • Humans are infected by ingesting Watercress or other aquatic plants contaminated with the infective metacercariae of Fasciola hepatica.
  • The metacercariae excyst in the duodenum, penetrate the gut wall and attach to the intestinal wall where they develop into adults.
  • The hermaphroditic adults in the intestines produce immature and unembryonated eggs which are passed in stool.
  • The eggs become embryonated in fresh water, and they release miracidia which invade a suitable fresh water snail host.
  • In the snail , sporogeny occurs , and the miracidia differentiate into sporocysts , then rediae then to Cercariae which are ciliated.
  • The Cercariae are released from the snail , they swim and encyst on aquatic vegetation as metacercariae after they have shed off their tails.
  • The vegetation may be ingested by humans completing the cycle.
37
Q

State the diagnostic methods and treatment options of Fasciolopsis buski infections .

A
  • Microscopic identification of eggs or adult flukes in the stool or vomitus of the patient.
  • Treatment with Praziquantel.
38
Q

State the symptoms that are likely to occur in cases of heavy Fasciolopsis buski infections.

A
  • Most infections are light and asymptomatic but the heavy infection are associated with damage inflicted on the intestinal mucosa by the adult flukes.
  • Diarrhea & vomiting.
  • Abdominal pain .
  • Fever.
  • Ascites- fluid collection in spaces within the abdomen.
  • Anasarca - swelling of body parts due to fluid accumulation.
  • Intestinal obstruction.
  • Ulcerations.
  • Abscess formation.
  • Haemorrhage.
  • Allergic reactions to the parasite which may present with skin rashes.
39
Q

What are some of the preventive measures effective in the prevention of Fasciolopsis buski infections?

A
  • Health education.
  • Proper disposal of human and animal waste.
  • Cooking food properly before consumption, whether they are plant based or animal based .
40
Q

Chinese liver fluke?

A

Clonorchis sinensis

41
Q

State the major intermediate hosts of Chlornochis sinensis.

A
  • Snails. ( Miracidium — Sporocyst — Rediae — Cercariae)
  • Fish - genus Cyprinidae e.g carp and goldfish.( Metacercariae)
42
Q

Localization of Chlornochis sinensis worms in the human hosts.

A

Bile duct , gall bladder, Pancreas.

43
Q

State some of the clinical manifestations of infections with Chlornochis sinensis.

A
  • Cholecystitis -inflammation of the gall bladder.
  • Cholelithiasis - gall stones .
  • Hepatic colic - painful contractions of the biliary tracts .
  • Liver cirrhosis which may result in death.
  • Also associated with profound weight loss and diarrhea.
44
Q

Diagnostic feature and treatment of Chlornochis sinensis infections ?

A
  • The eggs appear operculated when viewed microscopically.
  • Treatment with Praziquantel.
45
Q

Briefly describe the life cycle of Chlornochis sinensis parasites.

A
  • Humans are infected by ingesting Watercress or other aquatic plants contaminated with the infective metacercariae of Fasciola hepatica.
  • The metacercariae excyst in the duodenum, penetrate the gut wall and migrate through the intestinal wall, peritoneal cavity and liver parenchyma. They eventually reach the liver and the biliary ducts where they mature into adults.
  • The hermaphroditic adults in the Bile ducts produce immature and unembryonated eggs which are passed in stool.
  • The eggs become embryonated in fresh water, and they release miracidia which invade a suitable fresh water snail host.
  • In the snail , sporogeny occurs , and the miracidia differentiate into sporocysts , then rediae then to Cercariae which are ciliated.
  • The Cercariae are released from the snail , they swim and encyst on the skin or flesh of fresh water fish ,as metacercariae after they have shed off their tails.
  • The infected skin or flesh of the fresh water fish may be ingested by humans completing the cycle.

PARASITOLOGY (11 decks)

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