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Y2 Clinical Pathology > Core microbiology > Flashcards

Core microbiology Flashcards

1
Q

What is a parasite

A

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

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2
Q

What is a host

A

An organism which harbours the parasite

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3
Q

What is symbiosis

A

Living together, close, long term interaction between two different species

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4
Q

What is mutualism

A

An association in which both species benefit from the interaction

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5
Q

What is 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 commensalism

A

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

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7
Q

What are the classes of host

A

Definitive host: harbours the adult stage parasite or where it utilises the sexual method of reproduction, in majority of parasitic infections, man is this

Reservoir host: An animal or species infected by a parasite which serves as a source of infection for humans or other species

Intermediate host: Harbours the larval or asexual stages of parasite, some parasites require two intermediate hosts in which to complete their lifecycle

Paratenic host: host where the parasite remains viable without further development

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8
Q

What are protozoa

A

Single celled organisms- can be free-living or parasitic in nature and multiply in humans

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9
Q

How are GI protozoa transmitted

A

Faecal - oral route

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10
Q

How are blood protozoa transmitted

A

By arthropod vector

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11
Q

What are the types if protozoa and examples

A

Flagellates:

  • giardiasis lamblia
  • trichomonas vaginalis

Amoeboids

  • entamoeba sp
  • acanthamoeba sp

Sporozoans

  • plasmodium sp
  • cryptosporidium sp
  • toxoplasma sp

Trypanosomes

  • trypanosome sp
  • leishmania sp
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12
Q

What are helminths

A

Large multicellular organisms
Adults generally visible by eye
Adults cannot multiply in humans

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13
Q

What are the types of helminths

A

Platyhelminths (flatworms):

  • custodes (tape worms)
    • taenia sp
    • echinococcus sp
  • Trematodes (flukes)
  • -schistosoma sp

Nematodes (round worms)

  • Intestinal nematodes
    • Ascaris sp
    • trichuris sp
  • Tissue nematodes
    • wuchereria sp
    • onchocerca sp
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14
Q

What is an ectoparasite

A

Broadly include blood sucking arthropods and those that burrow into the skin

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15
Q

What are the ectoparasites and examples

A 
Insects:
- aedes sp
- anopheles sp
- culcinae
Lice:
- pedicures humans capitus
- pthiris pubis
Mites:
-scabies sp
- chigger mite
Arachnids (ticks)
- ixodidae
- argasids
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16
Q

What are the things to focus on with 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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17
Q

What are the three types of lifecycle

A

Direct
Simple indirect
Complex indirect

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18
Q

What is an example of a direct life cycle

A

Infective embryonated eggs are eaten by a bird while feeding,
Bird sheds parasite eggs into environment in faeces,
Eggs mature in the environment and become infective

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19
Q

What is an example of an indirect cycle

A

Infected bird
Bird sheds parasite eggs into the environment in faeces
sowbug eats eggs of parasite
Eggs hatch in sowbug and infective larvae develop within sowbug
Bird eats sowbug and becomes infected

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20
Q

What is an example of complex indirect life cycle

A

Infected bird
Bird sheds parasite eggs into the environment in faeces
First intermediate host: eggs eaten by amphipod where first and second stage larvae develop
Second intermediate host: Amphipod is eaten by amphibian where infective stages of larvae develop
Paratenic host: Fish eats the amphibian and larvae encyst in body of fish. No further development of the parasite
Birds feed on fish and become infected and to complete life cycle

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21
Q

What is ascariasis

A

Caused by macro parasite: intestinal nematode, ascaris lumbricoides
Peak prevalence in 3 - 8 year olds
Areas of poor hygiene
1 adult worm can produce 200,000 eggs per day
Acquired by ingestion of eggs
More than 1 billion people affected worldwide

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22
Q

What are clinical implications of ascariasis

A

Lung migration:

  • Loefflers syndrome
    • dry cough
    • dyspnoea
    • wheeze
  • -haemoptysis
    • eosinophilic pneumonitis

Intestinal phase:

  • Malnutrition
  • Malabsorption
  • Migration into hepatobiliary tree and pancreas
  • Intestinal obstruction
  • Worm burden
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23
Q

What is the treatment and control of ascariasis

A

Treatment: albendazole (prevents glucose absorption by worm, worm starves - detaches - passes)

Control: 
WHO action against worms
Improve sanitation
Education
Community targeted deworming
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24
Q

What is schistosomiasis sp

A 
Macroparasite (helminth - platyhelminth - trematode/fluke)
200 million people effected worldwide
Caused by fluke, Schistosoma: 
S. haematobium
S. mansoni
S. intercallatum
S. japonica
S. mekongi
Causes chronic disease resulting in bladder cancer and liver cirrhosis
Snails as intermediated host
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25
Q

What are the clinical implications of schistosomiasis

A

Initial infection incubation period 14-84 days
Often asymptomatic
Symptomatic acute infection:
Katayama syndrome:
rash, fever, headache, myalgia and respiratory symptoms. Often with eosinophilia and hepatic and/or splenomegaly
Swimmers itch
Katayma fever
Chronic schistosomiasis
Effects of eggs in distant sites eg spine and lung

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26
Q

What are the public health risks of schistosomiasis

A

Undernutrition
Anaemia
Hepatic fibrosis and associated increased risk of oesophageal varies
Renal failure
Bladder tumours
Increased risk of transmission of HIV
Case reports of poor birth outcomes in maternal infection

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27
Q

How is schistosomiasis diagnosed

A

Urinary:

  • terminal stream microscopy
  • serology

Hepatic/intestinal:

  • stool microscopy
  • rectal snip microscopy
  • serology
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28
Q

What is the treatment of schistosomiasis

A

Praziquantel:
20mg/kg x2 doses 4-6 hours apart
Mechanism unknown - increased ionic permeability titanic contraction, detachment , death

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29
Q

What is the control of schistosomiasis

A

Chemical treatment to kill snail intermediate hosts
Chemoprophylaxis
Avoidance of snail infested waters
Community targeted treatment, education and improved sanitation

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30
Q

What is hydatid disease

A

Macroparasite
Platyhelminth - cestode - tapeworm
Human is accidental host]Usual hosts are sheep and dogs\FOund all over the world wherever sheep are farmed
Caused by echinococcus sp

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31
Q

What are the clinical implications of hydatid disease

A 
Cysts: 70% liver, 20% lungs
May remain asymptomatic for years
Mass effect
Secondary bacterial infection
Cyst rupture - hypersensitivity
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32
Q

How is hydatid disease diagnosed

A 
Serology
Histology (if cyst ruptures) - do not biopsy/aspirate as risk of spread
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33
Q

What is the treatment od hydatid disease

A

Albendazole and praziquantel for daughter cysts (E gransulosus)

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34
Q

What are the public health risk of strongyloidiasis

A

Strongyloidiasis hyper infection syndrome mortality rates up to 90%
25 cases in UK 60 years post world war II
602 prisoners of war in the Far East screened for tropical diseases and 15% infected 30 years after return from tropics
Sexual transmission in MSM in LA and NYC
24 heterosexual couples
Transmission from patient with hyper infection syndrome with larva isolated bronchial secretions to his wife

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35
Q

How are strongyloides diagnosed

A 
Serology
Stool culture (charcoal filtration method)
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36
Q

How is strongyloides hyper infection syndrome diagnosed

A

Can be difficult as serology often negative in hyper infection and direct microscopy often negative and stool culture/ concentration methods often required

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37
Q

How are strongyloides treated

A

Ivermectin 200ug/kg for 2 days
or Albendazole 400mg bd for 7 days
Treatment of hyper infection syndrome / disseminated strongyloidiasis
Stop or reduce immunosuppressive therapy

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38
Q

What is the control of strongyloides

A

Wear shoes when walking on soil
Avoid contact with faecal matter or sewage
Proper sewage disposal and faecal management

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39
Q

What is malaria

A

Microparasite
Protozoa- sporozoan
4 human species of plasmodium

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40
Q

What are fungi

A 
Kingdom of organisms
Eukaryotic microorganisms
Single celled to macroscopic
Growth forms mainly hyphal or yeast
Glucan-chitin cell wall
reproduce asexually and/or sexually, spore formation
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41
Q

What are the types of fungal disease

A

Superficial infection - affecting skin, hair, nails and mucocutaneous tissue

Subcutaneous infection - affecting subcutaneous tissue, usually following traumatic implantation

Systemic infection - affecting deep-seated organs

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42
Q

What is a dermatophyte

A

Group of slow growing moulds seen as causes of disease in skin, hair and nail

Originate in soil (geophilic), other animals (zoophilic) and humans (anthropophilic)

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43
Q

What is tinea pedis

A

Uni or bilateral
Itching, flaking, fissuring of skin
Plantar: soles of feet dry and scaly, if skin of whole foot affected “Moccasin foot”
Hyperhidrosis, secondary to infection may increase severity
Secondary bacterial infection (sweating)
May spread to infect toe nails
Typical cause is Trichophyton rubrum

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44
Q

What is tinea unguium (onychomycosis)

A

Thickening, discolouring, dystrophy
Four types:
-Lateral/distal subungual
-Superficial white - usually immunocompromised
- Proximal
-Total nail dystrophy
Typical causes are Trichophyton rubrum and T. interdigitale

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45
Q

What is Tinea cruris

A

Also known as jock itch
More prevalent in men than women
Itching, scaling, erythematous plaques with distinct edges
Satellite lesions sometimes present
May extend to buttocks, back and lower abdomen
Typical cause T. rubrum

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46
Q

What is Tinea capitis

A

Mainly seen in pre-pubescent children
Range from slight inflammation, scaly patches, with alopecia, black dots, grey patches to severe inflammation
Kerion celsi: boggy, inflamed lesions, usually from zoophilic dermatophytes
Favus: presence of cup shaped crusts or scatula

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47
Q

What is Tinea corporis

A

Circular, single or multiple erythematous plaques
May extend from scalp or groin
Invasion of follicle “Majocci’c granuloma”
Typical causes are wide range of dermatophytes, anthropophilic or zoophilic

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48
Q

How are dermatophyte infections investigated

A

Microscopy and culture

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49
Q

How are dermatophyte infections treated

A

Tropical anti fungal therapy: mild disease (self diagnosis and treatment)
- Terbinafine
- Clotrimazole
Systemic anti fungal therapy: severe disease
- Griseofulvin
- Terbinafine
- Itraconazole

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50
Q

How should Tinea capris be treated

A

Always with systemic anti fungals as topical therapy will not be curative

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51
Q

What is Malassezia

A

Genus of yeasts
EG M. sympodialis, M. restricts and M. globosa
Part of normal skin flora in all humans from shortly after birth
Most common on head and trunk
Causes of disease:
-pityriasis versicolor
- role in seborrhoea dermatitis and atopic eczema

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52
Q

What is pityriasis versicolor

A 
Hype or hypopigmented lesions
Upper trunk
Between puberty and middle age
More common in tropics
Relapsing
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53
Q

How is pityriasis versicolor diagnosed

A

Microscopy:

  • yeast cells and hyphal segments “sphagetti and meatballs”
  • culture difficult and not interpretable
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54
Q

How is pityriasis versicolor treated

A

Topical antifungals:
- clotrimazole
If fails then oral fluconazole or itraconazole

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55
Q

What is candida

A

Large genus of yeasts
Often colonises the mucosal surfaces and GI tract in healthy people
Cause of superficial mucosal (oral and vaginal) disease “thrush”, also occasionally skin disease and keratitis
Cause of systemic disease, once present in circulatory system, can infect almost any organ in the body

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56
Q

What range of Candida species cause candida disease

A 
Candida albicans
Candida glabrata
Candida parapsilosis
Candida parapsilosis
Candida krusei
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57
Q

What is the epidemiology of oral candidosis

A

HIV/AIDS- sometimes even with anti-retroviral therapy, T-cell immunity important to prevent mucosal candidosis
Antibiotic use- suppressed normal bacterial flora, less competition for yeasts
Head and Neck cancer - radiotherapy and chemotherapy affect salivary secretions
General debilitation in hospitalised patients- increases colonisation and risk of oral disease

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58
Q

What is candida vulvovaginitis

A

affects 70-80% all women at lease once during child baring years
Prutris, burning sensation, +/- discharge
Inflammation of vaginal epithelium, may extend to labia major
Often more florid infections during pregnancy
~10% of women will suffer from recurrent vulvovaginsl candidosis
Diagnosis by positive culture in symptomatic patients

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59
Q

How is superficial candidosis diagnosed

A

Clinical diagnosis and empiric therapy

Culture with identification and antifungal sensitivity testing where appropriate eg recurrent disease

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60
Q

How is superficial candidosis treated

A

Usually oral azaleas, fluconazole highly effective

Resistance in normally sensitive species or naturally resistant species can be a problem

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61
Q

When should oral fluconazole or other azaleas not be used and why and what to use instead

A

In pregnant women as increases risk of teratologies (eg heart defects)
Topical azoles eg clotrimazole

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62
Q

What is systemic candidosis

A

Infection of almost any organ in the body
Defined by site of infection
Usually acquired from colonised skin or mucosal sites or from GI tract
Usually seen in the compromised host
Disseminated disease may be identified from blood culture

63
Q

How is systemic candidosis treated

A

Depends on Candida sp. sensitivity, severity, need for oral agent
Echinocandins eg Anidulafungin (IV)
Azoles eg flucanazole (oral)
Liposomal amphotericin B (IV)

64
Q

How is systemic candidosis diagnosed

A

Culture (from sterile site)
-Blood
-Peritoneal fluid
Imaging results

65
Q

What is hepatosplenic candidosis

A

Disseminated form of Candidosis
In patients who have leukaemia and other haematological malignancy
Candidaemia (Candida in blood) during period of neutropenia (may or may not be detected)
During neutrophil recovery Yeats lodge in liver and spleen
Abcess formation (bulls eye sign), fever, liver function disturbance
Antifungal therapy may be ineffective as dead fungus continues to trigger inappropriate inflammatory response

66
Q

How does malaria present clinically

A

Parasites rupture red cells, block capillaries and cause inflammatory reaction

Fever and rigors (alternate days with falciparum malaria, every 48hrs or 72 hrs with benign malaria)

Cerebral malaria (confusion, headache, coma)

Renal failure (black water fever

Hypoglycaemia

Pulmonary oedema

Circulatory collapse

Anaemia, bleeding and DIC (Disseminated intravascular coagulation)

67
Q

How is malaria diagnosed

A

Thick and thin microscopy
Serology - detection of antigen in blood
PCR - detection of malarial DNA

68
Q

How is malaria treated

A

Antimalarials

Supportive therapy

69
Q

How is malaria controlled

A 
Insecticide
Larvicide spraying on breeding pools
Filling in of breeding pools
Larvivorous species introduced in to breeding `areas
Insecticide impregnated bed nets
Chemoprophylaxis
Vaccine
70
Q

What is the background for cryptosporidiosis

A

Cause: Cryptosporidium parvum and hominis (micro-parasite, sporozoan)
Diarrhoeal disease
Human to human spread with animal reservoir
Faecal-oral spread
World wide distribution
Sporadic cases can lead to outbreaks

71
Q

How does cryptosporidiosis present clinically

A 
Watery diarrhoea with mucus no blood
Bloating, cramps fever, nausea, vomiting
Last up to 2 weeks
Sever in: 
-very young/very old
-immuno-compromised
72
Q

How is cryptosporidiosis diagnosed

A

Faeces sample:

  • acid fast staining
  • antigen detection
73
Q

What is the treatment for cryptosporidiosis

A

In the symptomatic:

  • rehydration
  • nitazoxanide

For immunocompromised:

  • paromoycin (kills parasite)
  • nitazoxanide (effectiveness is unclear)
  • octreotide (reduce cramps)
  • HAART initiated in HIV patients

Severe cases:
Combination therapy, paromomycin, nitazoxanide and azithromycin

74
Q

How is cryptosporidiosis controlled

A

Human - human:
-hand hygiene
-filter or boil drinking water
Isolate symptomatic patients in healthcare setting
-ensure symptomatic children are kept away from school

Animal-human:
- pasteurise milk and dairy products
Boil or filter drinking water if camping

75
Q

What is the background for trichomoniasis

A

Caused by Trichomonas vaginalis
Flagellated protozoan
Sexually transmitted
Incubation 5-28 days

76
Q

What are the symptoms for trichomoniasis

A 
Men are asymptomatic
Women:
- smelly vaginal discharge
-dyspareunia
-dysuria
-lower abdominal discomfort
-punctuate haemorrhages on cervix (strawberry cervix)
77
Q

How is trichomoniasis transmitted

A

Sexual intercourse

78
Q

How is trichomoniasis diagnosed

A

Identification of organism in genital specimens on direct microscopy
PCR increasingly available

79
Q

How is trichomoniasis treated

A

Metronidazole single dose of 2g or 200mg ads/ 400mg bd for 5-7 days
Treat partner simultaneously

80
Q

How is trichomoniasis prevented

A

General advice about STI prevention

Barrier contraceptives

81
Q

What is giardiasis

A

Flagellated protozoan
Faecal oral transmission
Spectrum of disease: asymptomatic carriage to severe diarrhoea and malabsorption
Can cause chronic disease

82
Q

What are the symptoms of giardiasis

A 
Last 1-3 weeks
Diarrhoea
Abdominal pain
Bloating
Nausea and vomiting
83
Q

How is giardiasis diagnosed

A

Identification of cysts or trophozoites in faeces

84
Q

How is giardiasis treated

A

Metronidazole/tinidazole

85
Q

How is giardiasis prevented

A

No vaccine available
Hygiene measures
Boiling water

86
Q

What is aspergillus

A

Genus of moulds - filamentous fungi
Producing airborne spores
Exposure to aspergillus spores universal by inhalation
Airways may be colonised by aspergillus sp

87
Q

What are examples of aspergillus in medicine

A

Aspergillus fumigatus
Aspergillus niger
Aspergillus flavus
Aspergillus terreus

88
Q

What is aspergillosis

A

Reaction to inhaling aspergillus

89
Q

What is an aspergilloma and who do they affect

A

Solid balls of fungus
Patients with cavities from previous TB, sarcoid or surgery
May break up causing haemoptysis which is potentially fatal

90
Q

What is the allergic form of aspergillosis

A

Allergic bronchopulmonary aspergillosis
Wheezing, breathlessness, loss of lung function, bronchiectasis
Airways inflammation
IgE and IgG reaction to aspergillus
Responds to steroids and/or anti fungal therapy

91
Q

What is chronic pulmonary aspergillosis

A

COPD
Chronic respiratory symptoms, cough, wheezing breathlessness, chest pain
Consolidation cavitation on chest CT
Positive culture of Aspergillus from sputum and BAL
Positive for Aspergillus IgG

92
Q

What is invasive aspergillosis

A

Haematological malignancy
Low neutrophil counts
Angioinvasion of lung tissue
Dissemination in 25% of cases to extra pulmonary sites
Halo and air crescent signs on CT
Moderate to poor prognosis even with aggressive anti fungal therapy

93
Q

What is the treatment of aspergillosis

A

Aspergilloma- resection
Allergic aspergillosis- steroids +/- antifungals
CPA and invasive aspergillosis - antifungals, itraconazole and voriconazole, amphotercin B

94
Q

How is aspergillosis diagnosed

A

Culture
Serology
Imaging

95
Q

What are some factors which affect reference range

A 
Age
Gender
DIet
Pregnancy
Time of the month
Time of the day
Time of the year
Weight
Stimulus
96
Q

What is staphylococcus aureus

A 
Primary pathogen
30-50% carry in nose
Cause:
-skin/soft tissue infection
-Bacteraemia/septicaemia
-Osteomyelitis/ septic arthritis 
-Endocarditis
-Pneumonia
-UTI
-Meningitis
97
Q

What is staphylococcus epidermidis

A 
Opportunistic pathogen
Skin commensal
Most people carry it on their skin
Causes infection in association with foreign bodies eg:
-intravascular catheters
-prosthetic joints
-prosthetic cardia valves
Adheres to plastics/metals using glycocalyx (slime) forming biofilms
98
Q

What is streptococcus pyogenes

A 
Group A strep
Commonest cause of bacterial sore throat
Causes:
Scarlet fever
Necrotising fasciitis (flesh eating bug
Other SSTIs
Invasive infections such as pneumonia
Puerperal sepsis
Secondary immunological presentations such as glomerulonephritis
99
Q

What does streptococcus pneumonia cause

A 
Bacterial pneumonia (most common)
Bacterial meningitis (most common)
Other common childhood infections eg otitis media
100
Q

What is streptococcus agalactiae

A

Group B strep

Commonest cause of bacterial meningitis and sepsis in neonates

101
Q

What is a neonate

A

Baby under three months

102
Q

What is the streptococcus millers complex

A

Three closely related species of pus forming streptococci

Associated with abscesses: dental, lung, liver, brain and others

103
Q

What is virdans streptococci

A

Collective name for a number of species of a-haemolytic streptococci that inhabit the upper respiratory tract eg S orals, S mitis
Classic cause of subacute bacterial endocarditis

104
Q

What is streptococcus gallolyticus

A

Formerly known as streptococcus Boris
A typer of a-haemolytic streptococcus that forms part of bowel flora
Bacteraemia with this organism can be associated with colonic malignancies

105
Q

What is listeria monocytogenes

A

Gram positive bacillus
Rare but significant cause of sepsis and meningitis in pregnancy, neonates and immunosuppressed patients
Zoonosis, able to grow at low temperatures
Associated with consuming cheese made from unpasteurised milk and other foodstuffs

106
Q

What are corynebacterium species

A

Gram positive bacilli
Number of species are commensals of skin and the upper respiratory tract
Occasional opportunistic infections associated with devices and trauma
Classic cause of diphtheria (corynebacterium diptheriae)
Rarely seen in UK due to immunisation

107
Q

What is propionibacterium acnes

A

Gram positive bacillus
Referred to us cutibacterium acnes
Associated with acne
Can also cause divice-associated and post-procedural infections

108
Q

What are enterobacteriaceae (coliforms)

A

Collective term for a number of species of gram negative bacilli found in bowel flora
Common species include Escherichia coli, Klebsiella pneumoniae and enterobacter cloacae

109
Q

What is E. coli

A

Commonest cause of:
-Urinary tract infection
- Bacteraemia (sources include urinary, biliary and intra-abdominal
Cause of nosocomial infections eg line infections, pneumonia, wound infections
Toxigenic strains (eg 0157) are associated with severe diarrhoea and haemolytic uraemia syndrome (HUS)

110
Q

What is pseudomonas aeruginosa

A

Multi-resistant gram negative bacillus
Opportunistic pathogen
Can cause respiratory infections, UTIs, soft tissue and other infections in vulnerable patients
Often produces characteristic green pigment

111
Q

What is neisseria meningitidis

A

Gram negative diplococcus
Causes meningococcal sepsis and/or meningitis
Classic presentation is of a purpuric non-blanching rash (sepsis)
Reduction in cases since introduction of vaccination

112
Q

What is neisseria gonorrhoeae

A

Gram negative diplococcus
Cause of gonorrhoea
Opthalmia neonatorum
Can rarely cause invasive infections (eg septic arthritis) secondary to primary sexually transmitted infection

113
Q

What is haemophilia influenzae

A

Gram negative bacillus
Forms part of normal respiratory tract flora
Can cause respiratory tract infections (eg pneumonia, infective exacerbations of COPD)
Capsulated types (B) associated with meningitis and epiglottis
Only type b infections prevented by HIb vaccine

114
Q

What are anaerobes

A

Grow in the absence of oxygen
Part of polybacterial infections eg dental infections, lung abscesses, colonic abscesses, post-trauma skin/soft tissue infections

115
Q

What are examples of anaerobes

A

Clostridium species:

  • C difficile (antibiotic-associated diarrhoea/colitis)
  • C perfringens (classical cause of gas gangrene)
  • C tetani (cause of tetanus)
  • C botulinum (cause of botulism)

Bacteroides species
Fusobacterium species
Prevotella species

116
Q

What are mycobacterium species

A

Often referred to as Acid Fast Bacilli (AFBs)
Do not stain using conventional gram staining
Mycobacterium tuberculosis cause of TB
Others are sometimes referred to as Atypical mycobacteria and cause respiratory infections in those with chronic lung disease or opportunistic infections in immunocompromised patients

117
Q

What do spirochetes cause

A

Treponema pallidum causes syphilis

Other species cause infection such as leptospirosis and lyme disease

118
Q

What is a virus

A

Simple micro-organism
Not capable of independent existence
Need a host cell to survive
Steal energy, metabolic intermediates and enzymes from host cells to replicate

119
Q

What are the structures of a virus

A

Genome (RNA or DNA)
Capsid (protein coat)
Envelope (lipid bilayer)
Some viruses also carry their own enzymes

120
Q

What are some Human DNA viruses

A 
Parvovirus
Papovavirus
Adenovirus
Herpesvirus
Poxvirus
121
Q

What are some human RNA viruses

A 
Picomavirus
Reovirus
Togavirus
Coronavirus
Orthomyxovirus
Rhabdovirus
Parmyxovirus
122
Q

What is the life cycle of a virus

A

Adsorption: interaction between host receptor molecule and virus ligand (determines host-specificity of the virus)

Penetration; receptor-mediated endocytosis or in some enveloped viruses, membrane fusion

Uncoating: Nucleic acid is liberated from the phagosome and/or capsid, by complex enzymatic and/or receptor-mediated processes

Synthesis: Nucleic acid and protein synthesis are mediated by host and/or viral enzymes. These take place in nucleus or cytoplasm, depending on specific virus

Assembly: Assembly of virus components is mediated by host and/or viral enzymes

Release: Complete virus particles are released by budding of host cell membrane or disintegration of host cell

123
Q

How are viruses classified

A

Genetic material:

  • DNA vs RNA
  • Single vs Double stranded
  • If single, positive sense vs Double, negative sense

Presence or absence of an envelope

124
Q

What is the herpes virus

A

Double stranded enveloped DNA viruses
9 types known to infect humans
Characteristed by their ability to establish latency and reactivate

125
Q

What is the herpes simplex 1

A

HSV-1, cold sores
Exists worldwide
80% of UK population have it
Direct contact with vesicle fluid from lesions
Latency in sensory nerve ganglia causes periodic reactivations
Vesicles/ulcers to skin or mucous membranes - typically mouth
Encephalitis (brain inflammation) often severe or fatal HSV-1 commonest cause of viral encephalitis woldwide

126
Q

What is the herpes simplex 2 virus

A

HSV-2, genital herpes,
Exists worldwide
~10-20% population
Direct contact with vesicle fluid from lesions
Latency in sensory nerve ganglia results in periodic reactivations
Vesicles/ulcers to skin or mucous membranes, typically genitals/bum
Meningitis often follows an outbreak of genital lesions
Neonatal herpes from vertical transmission from mother’s genital tract at birth, severe disseminated viraemia (life-threatening)

127
Q

What is the herpes virus of varicella zoster virus

A

Primary infection: chicken pox
Reactivation: herpes zoster or shingles
95% of UK had chicken pox by 20
In tropic this decreases to 50%
Transmission:
-Respiratory droplet from person with chicken
-Direct contact with vesicle fluid from person with chicken pox or shingles
-Latency established in dorsal root ganglion of whole CNS
Chicken pox: febrile illness with widespread vesicular rash
Shingles/ herpes zoster: reactivation causing unilateral vesicles in a dermatomal distribution

128
Q

What is the herpes virus Epstein Barr Virus

A

Glandular fever, infectious mononucleosis
90-95% in the UK are infected by age 25, of these 50% before age of 5
Transmission: virus is shed in saliva and genital secretions ‘kissing disease’
Clinical presentation:
Infectious mononucleosis (primary):
- tonsilitis, fever, lymphadenopathy, hepatosplenomagy
- Atypical lymphocytes on blood film (look like monocytes ie mononucleosis)
Reactivation caused by latency in B cells:
-if unwell or immunosuppressed
-associated with malignant B cell lymphoproliferative disorders

129
Q

What is the herpes virus cytomegalovirus

A

CMV
Transmission:
-saliva or genital secretions
-donated blood, stem cells or solid organ
-latency in myeloid progenitors/monocytes/ dendritic cells
Clinical syndromes:
-infectious mononucleosis (primary infection)
-congenital CMV infection
– infants born to mothers who have infection during pregnancy
– retinitis, deafness, microcephaly, hepatosplenomegaly in the neonate
- Reactivation in immunosuppressed patients
–can cause retinitis, colitis and pneumonitis

130
Q

What is the most common cause of the common cold

A

Rhinovirus

131
Q

What is rhinovirus

A

Common cold
Transmission: aerosolised respiratory secretions and droplets from nose and eyes
Common cold: sneezing, nasal obstruction and discharge, sore throat, cough, headache and fever

132
Q

What is influenza

A

Infect humans and animals and can spread between species
Peaks in winter annually
3 distinct types (A,B, C):
-Influenza A mutates regularly so strains vary every year
-2 important surface proteins H and N have multiple variants (H1N1 (swine), H3N2(seasonal))
Aerosolised respiratory secretions
Clinical syndromes:
-Primary influenza illness (fever, myalgia (muscle aches), then headache, cough, sore throat, nasal discharge
-Post-influenza secondary bacterial lung infection (S. pneumonia, H. influenza, S. aureus

133
Q

What is respiratory syncytial virus

A

RSV
commonest in young children
Aerosolisation of respiratory secretion
Bronchiolitis affects children under 2 years (inflammation of smallest airways (bronchioles), causes cough, wheeze, hypoxia, apnoea)

134
Q

What is HIV

A

Virus is present in blood, genital secretions, breast milk
Transmitted vertically, sexually, needlestick
HIV targets helper T lymphocytes CD4 cells, part of the cell-mediated immune system
2-6 weeks after transmission, patients may develop an acute seroconversion illness (flu-like)
Asymptomatic chronic infection follows a steady state between virus and immune system that lasts 5-15 years

135
Q

What is AIDS

A

Rise in viral load and fall in CD4 count, patient becomes vulnerable to opportunistic infections

136
Q

What are some AIDS defining illnesses

A

Pneumocytis pnuemonia
Cryptococcal meningitis
Kaposi’s sarcoma

137
Q

What are the 5 primary hepatotoxic viruses and how are they transmitted

A

Hepatitis A faeco-oral
Hepatitis B blood borne
Hepatitis C blood borne
Hepatitis E faeco-oral spread

138
Q

What is Hepatitis A

A

Faeco-oral virus shed in the faeces of infected individual
Nausea, myalgia, fevers, jaundice, right upper quadrant pain - usually self limiting
Endemic in the developing world associated with contaminated water
Infection in children is usually asymptomatic, 50% infected adults are symptomatic
Associated with lower socioeconomic groups, returning tourists and MSM

139
Q

What is Hepatitis E

A

Faeco-oral virus shed in the faeces of an infected individual
Nausea, myalgia, fevers, jaundice, right upper quadrant pain - usually self limiting
In Western Europe and North America, clusters of cases are associated with pigs and undercooked pork
95% cases are aymptomatic
Fulminant hepatitis with high mortality in infected pregnant women

140
Q

What is Hepatitis B

A

Vertical, sexual, parental transmission
After transmission, acute clinical hepatitis may occur but 90% children and 50% young adults are asymptomatic
Then either clear or becomes chronic
Risk of chronicity os inversely related to age at infection
Chronic hepatitis -> cirrhosis -> hepatocellular carcinoma

141
Q

What is Hepatitis C

A

In UK 50% of people who inject drugs have evidence of hepatitis C
Transmission:
-sharing needles, needlestick injuries, transfusion of contaminated products
-vertical and sexual transmission is less common
After transmission, ~25% develop acute clinical hepatitis
15% then clear virus but 85% will become chronically infected
Chronic hepatitis -> cirrhosis -> hepatocellular carcinoma

142
Q

What is the norovirus

A

Norwalk named after town in Ohio where the virus was first discovered
90% adults been infected
Associated with point source outbreaks eg cruise ships, hospitals, military
Transmission:
-ingestion/inhalation of aerosolised vomit particles
Vomiting is dominant feature

143
Q

What is the rotavirus

A

Virus looks like a wheel on electron microscopy
Virus of childhood 80-100% infected by 3yo
Seasonal peaks in winter
Major cause of infant mortality in developing world
Transmission:
-faeco-oral, contaminated food, water and aerosolised faeces and vomit
Fever vomiting and watery diarrhoea

144
Q

What are the enteroviruses

A

> 70 serotypes exist
Most identified in stool samples during polio research
Includes poliovirus, echoviruses and COxsackie A and B
Peak in summer/autumn in UK
Faeco-oral transmission through contaminated food/water
Replicate in gut but do not cause GI symptoms
From gut -> lymph nodes -> blood
Fever-rushsyndromes in children
Meningitis
Severe disseminated disease in neonate

145
Q

What is Mumps

A

Endemic childhood infection worldwide
Transmission:
-virus shed in saliva and respiratory secretions
-respiratory droplet transmission
-very infectious
Clinical:
-Acute parotitis - unilateral or bilateral
-Orchitis - affects 20-30% males with mumps and typically develops 4-5 days after parotitis
-Meningitis - Occurs in up to 15% of mumps cases, can lead to meningoencephalitis and sensorineural deafness, prior to MMR vaccine mumps was one of most common causes of viral meningitis

146
Q

What is measles

A

Occurs in clusters of unvaccinated
Respiratory droplet transmission
Highly infectious
Clinical:
-Primary measles: fever, coryza, cough, conjunctivitis, Koplik’s spots on inside of cheek. Then maculopapular rash
-Acute post infectious measles encephalitis: occurs 7-10 days after acute infection, high mortality rate, immune mediated
-Subacute sclerosing pan-encephalitis SSPE: 7-10 years after natural measles infection, progressive, degenerative and fatal disease of the CNS

147
Q

What is Rubella

A

German measles
Rare in UK due to vaccine
Droplet transmission from respiratory route
Clinical:
Primary rubella:
-mild illness, fever and maculopapular rash
-Arthralia/arthritis occurs in 30% adults
Congenital rubella:
-Classic triad (bilateral cataracts, sensorineural deafness, microcephaly
-risk of foetal malformation is highest in first 12 weeks of pregnancy

148
Q

What is parovirus B19

A

Slapped cheek syndrome or fifth disease
Peaks in spring
Respiratory droplet transmission
Infects and kills erythrocyte progenitor cells, causing transient anaemia
Clinical:
-Erythema infectiosum: fever, coryza, fiery red rash to cheeks, lacy rash to body
- Transient aplastic crisis: affects those with high erythrocyte turnover eg sickle cell, thalassemia
-Infection in pregnancy: 7-10% petal loss if maternal parvovirus infection in first 20 weeks, 2-3% develop hydros foetalis: severe foetal anaemia-> heart failure -> oedema, ascites

149
Q

What is a prion

A

Small infectious particle containing protein and no nucleic acid
Prion proteins exist naturally in cells but:
-gene mutation leads to changes in folding pattern of proteins
-prion becomes resistant to protease enzyme
-prion accumulates abnormally in cell
-promotes other proteins to abnormally fold

150
Q

How are abnormal prions found

A

Inherited (genetic defects)

Transmitted via consumption or direct exposure

151
Q

What do the human prion diseases have in common

A

Manifest in CNS
Produce spongiform change in brain tissue
Have long incubation times of up to 30 years
Are progressive and fatal

152
Q

What is CJD

A 
Sporadic Creutzfeld-Jakob disease
Very rare
1 in million
Gene mutation
Progressive ataxia, depression, dementia then death
153
Q

What is new variant CJD

A

Directly linked to BSE (bovine spongiform encephalopathy)
Same structure prion and in CJD
Cases associated with consumption of infected beef

Y2 Clinical Pathology (11 decks)

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