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Y2 Clinical Pathology > Introduction to Parasites > Flashcards

Introduction to Parasites Flashcards

1
Q

What is the definition of a parasite?

A

an organism which lives in or on another organism (its host) and benefits by deriving nutrients at the other’s expense

A parasite does not necessarily cause disease

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2
Q

What is the definition of a host?

A

an organism which harbours the parasite

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3
Q

What is meant by symbiosis?

What are the 3 types?

A

living together and a close long term interaction between two different species

this can be mutualism, parasitism or commensalism

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4
Q

What is meant by mutualism?

A

an association in which both species benefit from the interaction

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5
Q

What is meant by parasitism?

A

an association in which the parasite derives benefit and the host gets nothing in return, but always suffers some injury

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6
Q

What is meant by commensalism?

A

an association in which the parasite is deriving benefit without causing injury to the host

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7
Q

What are the 4 classes of host?

A
  1. definitive host
  2. reservoir host
  3. intermediate host
  4. paratenic host
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8
Q

What is a definitive host?

A

either harbours the adult stage of the parasite or where the parasite utilises the sexual method of reproduction

in the majority of human parasitic infections, man is the definitive host

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9
Q

What is meant by a reservoir host?

A

an animal or species infected by a parasite which serves as a source of infection for humans or other species

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10
Q

What is meant by an intermediate host?

A

harbours the larval or asexual stages of the parasite

some parasites require 2 intermediate hosts in which to complete their life cycle

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11
Q

What is meant by a paratenic host?

A

host where the parasite remains viable without further development

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12
Q

What are the 3 categories of parasites?

A
  1. protozoa
  2. platyhelminths and nemathelminths
  3. arthropoda
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13
Q

What are examples of protozoa?

A
  1. flagellates
  2. ameoboids
  3. sporozoans
  4. trypanosomes
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14
Q

What are examples of helminths?

A
  1. flat worms - flukes and tapeworms
  2. roundworms (nematodes)
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15
Q

What are examples of arthropoda?

A
  1. ectoparasites (lice and mites)
  2. blood sucking arthropods (mosquitoes)
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16
Q

What are the characteristics of protozoa?

A

they are single-celled organisms

they can be free-living or parasitic in nature and multiply in humans

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17
Q

How do GI and blood parasites in the protozoa phylum tend to be transmitted?

A

GI parasites are transmitted via the faecal-oral route

Blood parasites are transmitted via arthropod vector

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18
Q

What are examples of flagellates?

A
  1. giardia lamblia
  2. trichomonas vaginalis
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19
Q

What are examples of amoeboids?

A
  1. entamoeba sp.
  2. acanthamoeba sp.
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20
Q

What are examples of sporozoans?

A
  1. plasmodium sp.
  2. cryptosporidium sp.
  3. toxoplasma sp.
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21
Q

What are examples of trypanosomes?

A
  1. trypanosoma sp.
  2. leishmania sp.
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22
Q

What are helminths?

How do they multiply within humans?

A

they are large multicellular organisms

adults are generally visible by eye

adults cannot multiply in humans

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23
Q

What are the 2 types of platyhelminths (flatworms)?

A

Cestodes (tapeworms):

  • Taenia sp.
  • Echinococcus sp.

Trematodes (flukes):

  • Schistosoma sp.
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24
Q

What are the different types of nematodes (roundworms)?

A

Intestinal nematodes:

  • Ascaris sp.
  • trichuris sp.

Tissue nematodes:

  • wuchereria sp.
  • onchocerca sp.
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25
Q

What are the two types of ectoparasites?

A

blood sucking arthropods and those that burrow into the skin

arhtropods are important transmitters of infection

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26
Q

What are the 4 main categories of ectoparasites?

A
  1. insects
  2. lice
  3. mites
  4. arachnids (ticks)
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27
Q

What are the 6 stages in how to approach parasites?

A

distribution:

  • where we find them

life cycles:

  • how they survive and breed

clinical manifestations:

  • how they affect the host

diagnosis:

  • how we identify them

treatment:

  • how we get rid of them

control:

  • how we prevent others from getting infected
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28
Q

What are the 3 different types of life cycle?

A
  1. direct
  2. simple indirect
  3. complex indirect
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29
Q

What are the stages in this direct lifecycle?

A
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30
Q

What are the stages in the indirect lifecycle?

A
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31
Q

What are the stages in this complex indirect lifecycle?

A
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32
Q

What type of parasite is ascarisasis?

A

macroparasite

intestinal nematode

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33
Q

In which group is the peak prevalence of ascariasis seen?

How is it acquired?

A

peak prevalence in 3-8 year olds

seen in areas of poor hygiene

acquired by ingestion of eggs

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34
Q

What happens when there is lung migration of ascariasis?

A

Loefflers syndrome

  1. dry cough
  2. dyspnoea
  3. wheeze
  4. haemoptysis
  5. eosinophilic pneumonitis
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35
Q
A
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36
Q

What are the consequences of the intestinal phase of ascariasis?

A
  1. malnutrition
  2. malabsorption
  3. migration into hepatobiliary tree and pancreas
  4. intestinal obstruction
  5. worm burden
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37
Q

What is the treatment for ascariasis?

How does it work?

A

albendazole

this prevents glucose absorption by the worm

the worm starves and detaches itself

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38
Q

What type of parasite is schistosomiasis sp.?

A

macroparasite

(helminth, platyhelminth, trematode/fluke)

it is also known as Bilharzia

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39
Q

What does Schistosomiasis sp. cause?

What is the intermediate host?

A

it causes chronic disease resulting in bladder cancer and liver cirrhosis

snails are the intermediate host

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40
Q

What are the stages in the life cycle of schistosomiasis?

A
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41
Q

What is the initial infection incubation period in schistosomiasis?

A

14 - 84 days incubation period

42
Q

What are the symptoms of schistosomiasis infection?

A

it is often asymptomatic

Katayama syndrome is a symptomatic acute infection:

  1. rash and fever
  2. headache and myalgia
  3. respiratory symptoms
  4. often with eosinophilia and hepato- and/or splenomegaly
43
Q

What are the other clinical features of schistosomiasis?

A
  1. swimmers itch
  2. katayama fever
  3. chronic schistosomiasis can persist for years
  4. effect of eggs on distant sites - e.g. lungs, spine
44
Q

What organisms can cause hepatic/intestinal schistosomiasis?

A

S. mansoni

S. intercallatum

S. japonicum

S. mekongi

45
Q

What organism causes urinary schistosomiasis?

What can this lead to?

A

S. haematobium

  1. haematuria
  2. bladder fibrosis and dysfunction
  3. squamous cell cancer
46
Q

What can hepatic/intestinal schistosomiasis lead to?

A
  1. portal hypertension
  2. liver cirrhosis
  3. abdominal pain
  4. hepatosplenomegaly
47
Q

What are the main public health risks associated with schistosomiasis?

A
  1. undernutrition due to the suppression of appetite and inflammation-mediated cachexia
  2. anaemia
  3. renal failure
  4. bladder tumours
  5. hepatic fibrosis and associated increased risk of oesophageal varices
48
Q

How does schistosomiasis affect sexually transmitted diseases and pregnancy?

A
  1. increased risk of transmission of HIV
  2. poor birth outcomes in maternal infection and association with decreased birth weight
49
Q

How is schistosomiasis diagnosed?

A

urinary:

  • terminal stream microscopy
  • serology

hepatic/intestinal:

  • stool microscopy
  • rectal snip microscopy
  • serology
50
Q

What is the main treatment for schistosomiasis?

A

Praziquantel

20 mg/kg x 2 doses 4-6 hours apart

(3 doses in S japonicum)

51
Q

What are the characteristics of Praziquantel?

How does it work?

A

it is well absorbed with an extensive 1st pass metabolism

inactive metabolites are excreted in urine

the mechanism of action is unknown

52
Q

What steps are taken in the control of schistosomiasis?

A
  1. chemical treatment to kill snail intermediate hosts
  2. chemoprophylaxis
  3. avoidance of snail infested waters
  4. community targeted treatment, education and improved sanitation
53
Q

What is hydatid disease?

What is it caused by?

A

macroparasite (platyhelminth - cestode - tapeworm)

the usual hosts are sheep and dogs (humans are an accidental host)

it is caused by Echinococcus sp.

54
Q

What are the clinical effects of hydatid disease?

A
  1. cysts - 70% in liver and 20% in lungs
  2. may remain asymptomatic for years
  3. mass effect - cysts remain asymptomatic until a certain size is reached
  4. secondary bacterial infection
  5. cyst rupture - hypersensitivity
55
Q

How is hydatid disease diagnosed?

A
  1. serology
  2. histology (if cyst ruptures)

no not biopsy or aspirate, as rupturing the cyst increases the risk of spread

56
Q

What is the treatment for hydatid disease?

A

Albendazole

Prazigantel is used for daughter cysts

57
Q

What is the appearance of a hydatid cyst like?

A

a ruptured hydatid has a classic waterlily appearance

58
Q

What are the missing stages in hydatid control?

A
59
Q

What are the 5 species of malaria?

What type of parasite is it?

A

microparasite (protozoa - sporozoan)

4 human species:

  1. P. falciparum
  2. P. vivax
  3. P. ovale
  4. P. malariae

1 monkey species:

  1. P. knowlesi
60
Q

What are most cases of malaria caused by?

A

2000 cases a year in the UK due to travel

70% of these are due to P. falciparum

61
Q

What is the vector involved in malaria?

A

Anopheles mosquito

62
Q

What is the clincal background behind the symptoms of malaria?

A

parasites rupture red blood cells, block capillaries and cause an inflammatory reaction

63
Q

What are the symptoms of malaria?

A
  1. fever and rigors
  2. cerebral malaria - confusion, headaches, coma
  3. renal failure in black water fever
  4. hypoglycaemia
  5. pulmonary oedema
  6. circulatory collapse
  7. anaemia, bleeding and DIC
64
Q

How do the patterns of fever and rigors vary in malaria?

A

they are alternative days in falciparum malaria

they are every 48hrs or 72hrs with benign malaria

65
Q

What are the differences in time frames of the erythrocytic cycle in different types of malaria?

A

P knowlesi - 24 hrs

P falciparum, P. vivax, P ovale - 48 hrs

P. malariae - 72 hrs

66
Q

What is an important clinical thing to remember about malaria when seeing patients?

A

returning traveller + fever = malaria

until proven otherwise

(also think about viral haemorrhagic fever)

67
Q

How is malaria diagnosed?

A

thick and thin microscopy

serology is used for detection of the antigen in the blood

PCR is used for detection of malarial DNA

68
Q

When are antimalarials used to treat malaria?

What are the different types?

A

used in Falciparum malaria

co-artem:

  • artemether/lumefantrine
  • atovaquone - proguanil

complicated:

  • IV artesunate
  • must complete a full oral course when able to stop IV
69
Q

What is the problem with IV artesunate treatment and how should it be monitored?

A

haemolysis occurs in 10-15% of patients following IV artesunate treatment

haemoglobin concentrations should be checked 14 days after treatment

70
Q

What is the purpose of supportive therapies in malaria treatment?

A
  1. management of seizures, pulmonary oedema, acute renal failure and lactic acidosis
  2. exchange transfusion is used in hyperparasitaemia
71
Q

What is the firstline treatment for non-falciparum malaria?

A

oral chloroquine

25mg base/kg over 3 days

the usual dose in adults is 10 tablets in total

72
Q

What is the treatment in non-falciparum malaria if the patient cannot tolerate oral chloroquine?

A

if the patient is vomiting and unable to tolerate oral chloroquine then IV quinine is given

when the patient can swallow, the FULL COURSE of chloroquine is completed

73
Q

When is primaquine used in malaria treatment?

A

Vivax and Ovale need primaquine 14 days to treat liver

this prevents recurrence (check G6PD status)

74
Q

What steps are involved in control of malaria?

A
  1. insecticide spraying in homes
  2. larvicidal spraying on breeding pools
  3. filling in of breeding pools
  4. larvivorous species introduced into mosquito breeding areas
  5. insecticide impregnanted bed nets
  6. chemoprophylaxis before travelling
75
Q

What is the distribution of strongyloidiasis like?

A

transmission occurs mainly in tropical and subtropical regions but also in temperate climates

76
Q
A
77
Q

What is significant about the lifecycle of strongyloidiasis?

A

autoinfection

the larvae in the large intestine penetrate intestinal mucosa or perianal skin and migrate randomly to other organs

this causes the infection to be ongoing

78
Q

What is the public health risk associated with strongyloidiasis?

A

strongyloidiasis hyperinfection syndrome has mortality rates up to 90%

Strongyloides spp. can be sexually transmitted in the MSM community

79
Q

How is strongyloides diagnosed?

A
  1. serology
  2. stool culture through charcoal filtration method
80
Q

How is strongyloides hyperinfection syndrome diagnosed?

A

it can be difficult as serology and direct microscopy are often negative

stool culture/concentration methods are required

81
Q

What is the treatment for strongyloides?

A

Ivermectin ug/kg for 2 days

OR

albendazole 400mg for 7 days

82
Q

What is the treatment of hyperinfection syndrome/disseminated strongyloidiasis?

A

if possible, stop or reduce immunosuppressive therapy

Ivermectin

200 ug/kg per day orally until stool and/or sputum is negative for 2 weeks

83
Q

What are the steps involved in strongyloides control?

A
  1. wear shoes when walking on soil
  2. avoid contact with faecal matter or sewage
  3. proper sewage disposal and faecal management
84
Q

What is cryptosporidiosis caused by?

How is it spread?

A

microparasite (sporozoan)

Caused by Cryptosporidium parvum and hominis

causes diarrhoeal disease and is transmited through faecal-oral spread

can also have human to human spread with animal reservoir

85
Q

Where is cryptosporidiosis most common?

A

worldwide distribution but is more common in temperate and tropical countries

86
Q

What is the incubation period for cryptosporidiosis?

what are the associated symptoms?

A

incubation period is normally 7 days (can be 2-10 days)

  1. watery diarrhoea with mucus (no blood)
  2. bloating and cramps
  3. nausea and vomiting
87
Q

In which groups can cryptosporidiosis be severe?

A

it is usually self-limiting and lasts up to 2 weeks

it can be very severe in:

  1. very old and very young
  2. immunocompromised
88
Q

Who is at risk of cryptosporidiosis by human-human spread?

A
  1. regular users of swimming pools
  2. child care workers and parents
  3. nursing home residents/carers
  4. healthcare workers
  5. travellers
89
Q

who is at risk of cryptosporidiosis through animal-human spread?

A
  1. backpackers, campers, hikers
  2. farm workers
  3. visitors to farms/petting zoos
  4. consumers of infected dairy products
90
Q

How is cryptosporidiosis diagnosed?

A
  1. acid fast staining in faeces sample
  2. antigen detection by EIA
91
Q

What is the treatment in symptomatic cryptosporidiosis?

A
  1. rehydration and drinking more fluid
  2. nitazoxanide
92
Q

What are the treatments for cryptosporidiosis in immunocompromised individuals?

A
  1. paromycin to kill parasite
  2. nitazoxanide
  3. octreotide to reduce cramps and frequency
  4. HAART should be quickly initiated in HIV patients

in severe cases, a combination of paromycin, nitazoxanide and azithromycin is used

93
Q

What is trichomoniasis caused by?

How is it transmitted?

A

Trichomonas vaginalis

it is a sexually transmitted flagellated protozoan

incubation period is 5-28 days

94
Q

What are the symptoms of trichominiasis?

A

men are asymptomatic

women:

  1. smelly vaginal discharge
  2. dyspareunia (painful sex)
  3. dysuria
  4. lower abdominal discomfort
  5. punctuate haemorrhages on cervix (“strawberry cervix”)
95
Q

How is trichomoniasis diagnosed?

A

identification of organism in genital specimens on direct microscopy

PCR

96
Q

What is the treatment of trichomoniasis?

A

Metronidazole

single dose of 2g for 5-7 days

treat partner simultaneously

97
Q

What is the prevention methods for trichomoniasis?

A
  1. general advice about prevention of STIs
  2. use of barrier contraceptive methods if sexually active
98
Q

What is giardiasis and how is it transmitted?

A

flagellated protozoan transmitted through faecal-oral transmission

99
Q

What are the symptoms of giardiasis?

How long do they last?

A

it can range from asymptomatic carriage to severe diarrhoea and malabsorption

symptoms usually lasdt 1-3 weeks

  1. diarrhoea
  2. abdominal pain
  3. bloating
  4. nausea and vomiting
100
Q

How is giardiasis diagnosed and treated?

A

Diagnosis:

  • identification of cysts or trophozoites in faeces

Treatment:

  • metronidazole
  • tinidazole
101
Q

What is involved in the prevention of giardiasis?

A
  1. no vaccine is available
  2. hygiene measures

.3 boiling water

102
Q
A

Y2 Clinical Pathology (76 decks)

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