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
2
Q
What is a host
A
An organism which harbours the parasite
3
Q
What is symbiosis
A
Living together, close, long term interaction between two different species
4
Q
What is mutualism
A
An association in which both species benefit from the interaction
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
6
Q
What is commensalism
A
An association in which the parasite only is deriving benefit without causing injury to the host
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
8
Q
What are protozoa
A
Single celled organisms- can be free-living or parasitic in nature and multiply in humans
9
Q
How are GI protozoa transmitted
A
Faecal - oral route
10
Q
How are blood protozoa transmitted
A
By arthropod vector
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
12
Q
What are helminths
A
Large multicellular organisms
Adults generally visible by eye
Adults cannot multiply in humans
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
14
Q
What is an ectoparasite
A
Broadly include blood sucking arthropods and those that burrow into the skin
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
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
17
Q
What are the three types of lifecycle
A
Direct
Simple indirect
Complex indirect
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
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
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
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
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
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
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
25
What are the clinical implications of schistosomiasis
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
26
What are the public health risks of schistosomiasis
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
27
How is schistosomiasis diagnosed
Urinary:
- terminal stream microscopy
- serology
Hepatic/intestinal:
- stool microscopy
- rectal snip microscopy
- serology
28
What is the treatment of schistosomiasis
Praziquantel:
20mg/kg x2 doses 4-6 hours apart
Mechanism unknown - increased ionic permeability titanic contraction, detachment , death
29
What is the control of schistosomiasis
Chemical treatment to kill snail intermediate hosts
Chemoprophylaxis
Avoidance of snail infested waters
Community targeted treatment, education and improved sanitation
30
What is hydatid disease
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
31
What are the clinical implications of hydatid disease
```
Cysts: 70% liver, 20% lungs
May remain asymptomatic for years
Mass effect
Secondary bacterial infection
Cyst rupture - hypersensitivity
```
32
How is hydatid disease diagnosed
```
Serology
Histology (if cyst ruptures) - do not biopsy/aspirate as risk of spread
```
33
What is the treatment od hydatid disease
Albendazole and praziquantel for daughter cysts (E gransulosus)
34
What are the public health risk of strongyloidiasis
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
35
How are strongyloides diagnosed
```
Serology
Stool culture (charcoal filtration method)
```
36
How is strongyloides hyper infection syndrome diagnosed
Can be difficult as serology often negative in hyper infection and direct microscopy often negative and stool culture/ concentration methods often required
37
How are strongyloides treated
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
38
What is the control of strongyloides
Wear shoes when walking on soil
Avoid contact with faecal matter or sewage
Proper sewage disposal and faecal management
39
What is malaria
Microparasite
Protozoa- sporozoan
4 human species of plasmodium
40
What are fungi
```
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
```
41
What are the types of fungal disease
Superficial infection - affecting skin, hair, nails and mucocutaneous tissue
Subcutaneous infection - affecting subcutaneous tissue, usually following traumatic implantation
Systemic infection - affecting deep-seated organs
42
What is a dermatophyte
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)
43
What is tinea pedis
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
44
What is tinea unguium (onychomycosis)
Thickening, discolouring, dystrophy
Four types:
-Lateral/distal subungual
-Superficial white - usually immunocompromised
- Proximal
-Total nail dystrophy
Typical causes are Trichophyton rubrum and T. interdigitale
45
What is Tinea cruris
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
46
What is Tinea capitis
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
47
What is Tinea corporis
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
48
How are dermatophyte infections investigated
Microscopy and culture
49
How are dermatophyte infections treated
Tropical anti fungal therapy: mild disease (self diagnosis and treatment)
- Terbinafine
- Clotrimazole
Systemic anti fungal therapy: severe disease
- Griseofulvin
- Terbinafine
- Itraconazole
50
How should Tinea capris be treated
Always with systemic anti fungals as topical therapy will not be curative
51
What is Malassezia
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
52
What is pityriasis versicolor
```
Hype or hypopigmented lesions
Upper trunk
Between puberty and middle age
More common in tropics
Relapsing
```
53
How is pityriasis versicolor diagnosed
Microscopy:
- yeast cells and hyphal segments "sphagetti and meatballs"
- culture difficult and not interpretable
54
How is pityriasis versicolor treated
Topical antifungals:
- clotrimazole
If fails then oral fluconazole or itraconazole
55
What is candida
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
56
What range of Candida species cause candida disease
```
Candida albicans
Candida glabrata
Candida parapsilosis
Candida parapsilosis
Candida krusei
```
57
What is the epidemiology of oral candidosis
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
58
What is candida vulvovaginitis
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
59
How is superficial candidosis diagnosed
Clinical diagnosis and empiric therapy
| Culture with identification and antifungal sensitivity testing where appropriate eg recurrent disease
60
How is superficial candidosis treated
Usually oral azaleas, fluconazole highly effective
| Resistance in normally sensitive species or naturally resistant species can be a problem
61
When should oral fluconazole or other azaleas not be used and why and what to use instead
In pregnant women as increases risk of teratologies (eg heart defects)
Topical azoles eg clotrimazole
62
What is systemic candidosis
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
How is systemic candidosis treated
Depends on Candida sp. sensitivity, severity, need for oral agent
Echinocandins eg Anidulafungin (IV)
Azoles eg flucanazole (oral)
Liposomal amphotericin B (IV)
64
How is systemic candidosis diagnosed
Culture (from sterile site)
-Blood
-Peritoneal fluid
Imaging results
65
What is hepatosplenic candidosis
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
How does malaria present clinically
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
How is malaria diagnosed
Thick and thin microscopy
Serology - detection of antigen in blood
PCR - detection of malarial DNA
68
How is malaria treated
Antimalarials
| Supportive therapy
69
How is malaria controlled
```
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
What is the background for cryptosporidiosis
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
How does cryptosporidiosis present clinically
```
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
How is cryptosporidiosis diagnosed
Faeces sample:
- acid fast staining
- antigen detection
73
What is the treatment for cryptosporidiosis
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
How is cryptosporidiosis controlled
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
What is the background for trichomoniasis
Caused by Trichomonas vaginalis
Flagellated protozoan
Sexually transmitted
Incubation 5-28 days
76
What are the symptoms for trichomoniasis
```
Men are asymptomatic
Women:
- smelly vaginal discharge
-dyspareunia
-dysuria
-lower abdominal discomfort
-punctuate haemorrhages on cervix (strawberry cervix)
```
77
How is trichomoniasis transmitted
Sexual intercourse
78
How is trichomoniasis diagnosed
Identification of organism in genital specimens on direct microscopy
PCR increasingly available
79
How is trichomoniasis treated
Metronidazole single dose of 2g or 200mg ads/ 400mg bd for 5-7 days
Treat partner simultaneously
80
How is trichomoniasis prevented
General advice about STI prevention
| Barrier contraceptives
81
What is giardiasis
Flagellated protozoan
Faecal oral transmission
Spectrum of disease: asymptomatic carriage to severe diarrhoea and malabsorption
Can cause chronic disease
82
What are the symptoms of giardiasis
```
Last 1-3 weeks
Diarrhoea
Abdominal pain
Bloating
Nausea and vomiting
```
83
How is giardiasis diagnosed
Identification of cysts or trophozoites in faeces
84
How is giardiasis treated
Metronidazole/tinidazole
85
How is giardiasis prevented
No vaccine available
Hygiene measures
Boiling water
86
What is aspergillus
Genus of moulds - filamentous fungi
Producing airborne spores
Exposure to aspergillus spores universal by inhalation
Airways may be colonised by aspergillus sp
87
What are examples of aspergillus in medicine
Aspergillus fumigatus
Aspergillus niger
Aspergillus flavus
Aspergillus terreus
88
What is aspergillosis
Reaction to inhaling aspergillus
89
What is an aspergilloma and who do they affect
Solid balls of fungus
Patients with cavities from previous TB, sarcoid or surgery
May break up causing haemoptysis which is potentially fatal
90
What is the allergic form of aspergillosis
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
What is chronic pulmonary aspergillosis
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
What is invasive aspergillosis
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
What is the treatment of aspergillosis
Aspergilloma- resection
Allergic aspergillosis- steroids +/- antifungals
CPA and invasive aspergillosis - antifungals, itraconazole and voriconazole, amphotercin B
94
How is aspergillosis diagnosed
Culture
Serology
Imaging
95
What are some factors which affect reference range
```
Age
Gender
DIet
Pregnancy
Time of the month
Time of the day
Time of the year
Weight
Stimulus
```
96
What is staphylococcus aureus
```
Primary pathogen
30-50% carry in nose
Cause:
-skin/soft tissue infection
-Bacteraemia/septicaemia
-Osteomyelitis/ septic arthritis
-Endocarditis
-Pneumonia
-UTI
-Meningitis
```
97
What is staphylococcus epidermidis
```
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
What is streptococcus pyogenes
```
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
What does streptococcus pneumonia cause
```
Bacterial pneumonia (most common)
Bacterial meningitis (most common)
Other common childhood infections eg otitis media
```
100
What is streptococcus agalactiae
Group B strep
| Commonest cause of bacterial meningitis and sepsis in neonates
101
What is a neonate
Baby under three months
102
What is the streptococcus millers complex
Three closely related species of pus forming streptococci
| Associated with abscesses: dental, lung, liver, brain and others
103
What is virdans streptococci
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
What is streptococcus gallolyticus
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
What is listeria monocytogenes
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
What are corynebacterium species
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
What is propionibacterium acnes
Gram positive bacillus
Referred to us cutibacterium acnes
Associated with acne
Can also cause divice-associated and post-procedural infections
108
What are enterobacteriaceae (coliforms)
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
What is E. coli
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
What is pseudomonas aeruginosa
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
What is neisseria meningitidis
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
What is neisseria gonorrhoeae
Gram negative diplococcus
Cause of gonorrhoea
Opthalmia neonatorum
Can rarely cause invasive infections (eg septic arthritis) secondary to primary sexually transmitted infection
113
What is haemophilia influenzae
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
What are anaerobes
Grow in the absence of oxygen
Part of polybacterial infections eg dental infections, lung abscesses, colonic abscesses, post-trauma skin/soft tissue infections
115
What are examples of anaerobes
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
What are mycobacterium species
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
What do spirochetes cause
Treponema pallidum causes syphilis
| Other species cause infection such as leptospirosis and lyme disease
118
What is a virus
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
What are the structures of a virus
Genome (RNA or DNA)
Capsid (protein coat)
Envelope (lipid bilayer)
Some viruses also carry their own enzymes
120
What are some Human DNA viruses
```
Parvovirus
Papovavirus
Adenovirus
Herpesvirus
Poxvirus
```
121
What are some human RNA viruses
```
Picomavirus
Reovirus
Togavirus
Coronavirus
Orthomyxovirus
Rhabdovirus
Parmyxovirus
```
122
What is the life cycle of a virus
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
How are viruses classified
Genetic material:
- DNA vs RNA
- Single vs Double stranded
- If single, positive sense vs Double, negative sense
Presence or absence of an envelope
124
What is the herpes virus
Double stranded enveloped DNA viruses
9 types known to infect humans
Characteristed by their ability to establish latency and reactivate
125
What is the herpes simplex 1
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
What is the herpes simplex 2 virus
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
What is the herpes virus of varicella zoster virus
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
What is the herpes virus Epstein Barr Virus
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
What is the herpes virus cytomegalovirus
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
What is the most common cause of the common cold
Rhinovirus
131
What is rhinovirus
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
What is influenza
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
What is respiratory syncytial virus
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
What is HIV
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
What is AIDS
Rise in viral load and fall in CD4 count, patient becomes vulnerable to opportunistic infections
136
What are some AIDS defining illnesses
Pneumocytis pnuemonia
Cryptococcal meningitis
Kaposi's sarcoma
137
What are the 5 primary hepatotoxic viruses and how are they transmitted
Hepatitis A faeco-oral
Hepatitis B blood borne
Hepatitis C blood borne
Hepatitis E faeco-oral spread
138
What is Hepatitis 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
What is Hepatitis E
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
What is Hepatitis B
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
What is Hepatitis C
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
What is the norovirus
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
What is the rotavirus
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
What are the enteroviruses
>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
What is Mumps
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
What is measles
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
What is Rubella
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
What is parovirus B19
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
What is a prion
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
How are abnormal prions found
Inherited (genetic defects)
| Transmitted via consumption or direct exposure
151
What do the human prion diseases have in common
Manifest in CNS
Produce spongiform change in brain tissue
Have long incubation times of up to 30 years
Are progressive and fatal
152
What is CJD
```
Sporadic Creutzfeld-Jakob disease
Very rare
1 in million
Gene mutation
Progressive ataxia, depression, dementia then death
```
153
What is new variant CJD
Directly linked to BSE (bovine spongiform encephalopathy)
Same structure prion and in CJD
Cases associated with consumption of infected beef
