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IMS > Infection > Flashcards

Infection Flashcards

1
Q

Parasite

A

An organism which depends on another for its survival to the detriment of its host

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2
Q

Endoparasites

A

Live inside body e.g. Helminths and protozoa

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3
Q

Ectoparasites

A

Live outside the body e.g. Fleas, lice, bed bugs and ticks

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4
Q

Human endoparasite- Protoza- Amoebae

Examples and causes

A 
Example: Entamoeba histolytica
•	Invades large bowel lining
•	Causes dysentery (infections of intestine)
                       -Abdominal cramps
                       -Bloody diarrhoea
•	Excreted with faeces
•	Spread via contaminated food & water
•	Risks: poor hygiene/sanitation
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5
Q

Human endoparasite- Protoza sporozoa- example and causes

A
  • Example: Plasmodium falciparum (malaria)
  • Lifecycle in both humans and mosquitoes
  • Infects red blood cells and liver
  • Symptoms: fever, headache, joint pains
  • Complications include: kidney failure, coma, death
  • Risk: geographical
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6
Q

What are helminths? What types are there?

A

Helminths (worms):

  • Complex organisms
  • Some have complex life cycles with more than one host
  • Other species have their own helminths which can accidentally cause human disease

Types:
• Cestodes (tapeworms)- Segmented, flat
• Trematodes (flukes)- Unsegmented, flat
• Nematodes (round worms)- Cylindrical, have digestive tract with lips, teeth and anus

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7
Q

What are cestodes and examples

A

Cestodes – tapeworms:

Example: taenia saginata (beef tapeworm)
•	Intestinal parasite of human (obligatory host)
•	Largely asymptomatic
                     -abdominal pain
                      -malnutrition
•	Diagnosis
                       -patient-faeces
                       -stool microscopy for eggs
•	Cattle/pigs are intermediate hosts
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8
Q

How do cestodes enter humans?

A
  1. Eggs in faeces – passed into environment
  2. Cattle/pigs ingest contaminated eggs vegetation
  3. Eggs hatch and penetrate intestinal wall
  4. Humans affected ingesting raw/undercooked infected meat
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9
Q

What are trematodes and examples?

A

Trematodes – flukes

  • Example: Schistosoma haematobium (bilharzia)
  • Human host: infection of veins around bladder
  • Causes bladder inflammation, bleeding into urine (haematuria)
  • Intermediate host freshwater snail
  • Diagnosis: urine microscopy for eggs
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10
Q

How do trematodes enter a human?

A
  1. Eggs in urine/faeces – passed into environment
  2. Miracidium  hatches from egg – infects snail (first intermediate host)
  3. Cercarie  leave snail + penetrate skin human in water
  4. Immature worm enters blood stream  veins near intestine/bladder
  5. Worms reach sexual maturity in abdominal cavity – females produce eggs
  6. Eggs enter intestinal tract/bladder
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11
Q

Example of ectoparasite- bedbug

A

• Example: Cimex lectularius
• Wingless insect
• Worldwide infestation of human dwellings
• Hide in cracks in furniture & walls
• Emerge at night to feed – 5-10 minutes for a blood meal
• Itchy rash after bite
• Can transmit other infections
-protozoa in South America (trypanosomiasis)

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12
Q

What are the two forms of fungal infections?

A

2 main forms:
• Yeasts- Single cells which bud
• Moulds- Filamentous strands

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13
Q

What is a severe invasive fungal infection?

A

Example: cryptococcus neoformans (yeast)
Infects patients with low resistance due to failing immune system e.g. HIV.
Causes meningitis (inflammation of membranes lining brain).
Headache, neck stiffness, confusion, coma, death.

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14
Q

Structure of bacteria

A
  • Unicellular organisms (prokaryotes)
  • Cell membrane
  • Cell wall
  • No nucleus- genetic material in form of DNA
  • Reproduce asexually
  • Move using flagellae and pili
  • Too small to see without a microscope and special stains
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15
Q

Bacterial infection- Example: streptococcus pneumoniae aka pneumococcus

A
  • Gram-positive cocci in pairs (diplococci)
  • Colonise nose & throat (40-50% adults)
  • Invade other sites e.g. lungs causing pneumonia
  • Cough, dirty sputum, chest pain ,breathless, fever
  • Complications: blood stream infection, meningitis, death
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16
Q

Structure of a virus

A
  • Dependent on infection of host cell for metabolism & replication
  • Contain protein core surrounding genetic material (DNA or RNA)
  • Protein coat
  • +/- outer membrane
  • Very small: 1/100th size of bacteria
  • Can only be seen with powerful electron microscopes
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17
Q

Virus infect host cells for differing lengths of time

A
  • Acute infection: norovirus infects hosts for days, causing diarrhoea and vomiting (gastroenteritis)
  • Chronic infection: hepatitis C virus causes liver inflammation for years
  • Latent infection – herpesviruses can be dormant for decades before reactivating to cause disease
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18
Q

Viruses can cause a wide spectrum of disease

A
  • Some cause trivial infections e.g. rhinovirus – common cold
  • Some cause severe chronic disease eg HIV
  • Some cause acute life threatening disease e.g. Ebola – viral haemorrhagic fever
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19
Q

Some viruses can cause latent infection- example

A

• Example: varicella zoster virus
• Primary infection causes chickenpox
-Characteristic rash & fever
• Virus becomes dormant in sensory nerve roots
• Reactivates years later as shingles
-Same rash
-Confined to dermatome = area supplied by single sensory nerve

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20
Q

Some viral infections contribute to cancers

A

Epstein-Barr virus:
• Usually causes mild illness e.g. ‘glandular fever’
• Infects immune system cells (B cells) and epithelial cells of nose and mouth (nasopharynx)
• Causes latent lifelong infection
• Contributes to certain cancers with other factors
-Nasopharyngeal carcinoma
-Lymphoma in HIV infection

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21
Q

Prions- what are they?

A
  • Smallest infective agents known
  • Proteinaceous Infectious particles
  • Lack nucleic acid, i.e. not a living organism
  • Proteins are abnormal and accumulate, mainly in neural tissue
  • They are very difficult to destroy- Standard sterilisation techniques e.g. disinfectants and heating do not work
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22
Q

Prion diseases

A

• CJD = Creutzfeldt–Jakob disease
-rare fatal, degenerative neurological disease
-transmitted via human growth hormone, surgical instruments and corneal grafts
• Variant CJD - typically occurs in young adults
-Thought to be derived from bovine spongiform encephalopathy (BSE or mad cow disease)
• Kuru - similar to vCJD
-spread by cannibalism
-especially brains of deceased relatives

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23
Q

What is normal microbial flora?

A

Most mucocutaneous (a region of the body in which mucosa transitions to skin) surfaces of humans harbour multiple types of bacteria. These vary according to site.

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24
Q

What is cystitis?

A 
•Infection of lower urinary tract
-Lower abdominal pain
-Urgency 
-Dysuria (painful or difficult urination)
-Frequency
•Most commonly bacteria from gut flora
-E.g. Escherichia coli
-E.coli:  Gram-negative bacillus
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25
Q

Endogenous infection- migration

A

Bowel flora e.g. E.coli contaminates perineum (the area between the anus and the scrotum or vulva)
• Gains access to urethra -causes infection
• Spreads to bladder (cystitis) and beyond
• UTI = Urinary Tract Infection

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26
Q

Endogenous infection perforation

A

• Diseases of bowel especially colon e.g.
-Cancer
-Diverticular disease
• Perforation of bowel wall leads to contamination of abdominal cavity with faecal flora
• Severe life-threatening infection results
-Faecal peritonitis

27
Q

Endogenous infection-blood spread

A

Endocarditis:
• Dental work may allow mouth flora e.g. streptococci to enter blood stream
• Circulation of organisms allows them to reach distant sites e.g. heart valve
• Invasion can occur especially if valve tissue is abnormal e.g. congenital defect
• Causes inflammation ‘vegetation’ and structural damage

28
Q

Exogenous infection: direct contact

A

Impetigo:

  • superficial skin infection due to staphylococci and/or streptococci
  • spreads rapidly from person to person
29
Q

Exogenous infection: indirect contact

A

• Micro-organisms can be transmitted indirectly via hands, equipment, furniture etc
• Major route of health-care associated infections
• Examples
-methicillin-resistant staphylococcus aureus (MRSA)
-Clostridium difficile
-Norovirus gastroenteritis

30
Q

Injuries – dirty wound- infection example

A

Tetanus (Lockjaw)

  • Clostridium tetani
  • Bacterium present in soil
  • Contaminates wounds
  • Releases toxin causing muscle spasm
  • Prevented by vaccination
31
Q

Injuries- bites- infection example

A

Malaria:

  • Parasite infection
  • Life-cycle -Mosquitoes and humans
  • Causes severe febrile (having or showing the symptoms of a fever) illness affecting all body systems
32
Q

Airborne infection

A

Influenza virus

  • Coughing & sneezing
  • Droplets formed containing infectious viruses
  • Inhaled by others
33
Q

Oral route – foodborne or water-borne

A
  • Food prepared with poor hygiene - E.g. not washing hands after going to toilet
  • Contaminate food with harmful bacteria
  • Result: food poisoning
  • Vomiting, diarrhoea
34
Q

Blood-borne infection

A 
E.g. hepatitis B virus
•	Liver infection
•	Some viruses spill into blood (and other body fluids)
•	Transmission by blood exposure
-Transfusion
-Sharing of needles etc
-Tattoos & body piercing
35
Q

Sexual transmission

A 
E.g. Chlamydia – risks increased by:
•	unprotected sex
•	new partners
•	multiple partners
•	partners with high risk e.g. prostitutes
36
Q

Mother to baby transmission ‘vertical’

A
  • During pregnancy e.g. rubella
  • At time of birth e.g. herpes
  • Breast milk e.g. HIV
37
Q

Some infections may be transmitted in more than one way e.g. HIV

A 
•	Blood borne e.g. injection drug use
•	Vertical
-perinatal (time before birth)
-breast feeding
•	Sexual
38
Q

Some infections require more than one step

A

E.g. staphylococcus aureus soft tissue infection
Step 1: colonisation of skin – joins skin flora
Step 2: penetration of skin – spreads & damages

39
Q

Micro-organism/pathogen factors in infection

A 
•	Infectious dose
-Minimum number of organisms required to produce disease
•	Direct infection of cells/tissues
•	Virulence factors & toxins
-Invasion
-Disease
•	Resistance to antibiotics
40
Q

Virulence factors

A

Allow invasion of host tissues e.g. streptolysin O
• Lyses cells - ‘cytolysin’
• Produced by certain streptococci (Group A)

41
Q

Toxins- example

A 
Cholera
•	Severe watery diarrhoea -‘rice water’
•	Bacteria produce toxin
•	Binds to gut lining cells (mucosa)
•	Massive loss of fluid and electrolytes
•	Causes severe dehydration, kidney failure & death
42
Q

Cholera toxin mechanism

A
  • Cholera toxin enters cells of gut lumen
  • Activates adenyl cyclase increasing cAMP
  • Reduces Na+ absorption
  • Increases Cl- secretion, decreases Na+ absorption
  • Water and other electrolytes drawn into bowel lumen = diarrhoea
43
Q

Antibiotic resistance

A 
•	Micro-organisms readily mutate e.g.
-HIV, staphylococci
•	Frequently mutate to escape antibiotic use
•	More antibiotic use = more mutations
•	Failure of antibiotic treatment
44
Q

Host (patient) factors in infection

A
  • Environment
  • Barriers to infection
  • Genetics
  • Behaviour
45
Q

Host (patient) factors in infection- environment

A 
•	Geography
•	Climate
•	Poverty
-Availability of health care e.g. vaccination
•	Public Health infrastructure
-Sanitation	
•	Distribution of other infection hosts
-Insect or other vectors
46
Q

What is Dengue fever?

A
  • Virus infection
  • Transmitted by Aedes mosquito
  • Fever & rash & muscle pain
  • Severe form: bleeding, shock & multi organ failure
47
Q

Barriers to infection

A

• Skin & mucous membranes- cuts (wound infection) and abrasions (conjunctivitis-eyes are red and sore)
• Stomach acid
– Hydrochloric acid - pH 2
– Very few organisms survive this
– Commonly used drugs for stomach ulcer increase pH
– Patients taking these are more susceptible to food poisoning
– E.g. Campylobacter from poorly cooked chicken
• Native bacteria /normal flora:

Normal gut bacteria
– 1012/g faeces
– Prevent colonisation by pathogenic (disease-causing) bacteria
– Antibiotic treatment destroys the normal ‘friendly’ bacteria
– This allows the pathogens (‘bad’ bacteria) to reproduce & cause disease
– E.g. diarrhoea due to clostridium difficile

Immune system

Immune system problems:

Treatments for other diseases

  • Cancers
  • Chemotherapy damages the immune system
  • Diseases due to overactive immune systems ‘autoimmune’
  • Asthma, types of arthritis, bowel inflammation ’colitis’
  • Usually treated by drugs which make the immune system less active e.g. corticosteroids

Immune system infection
E.g. Human immunodeficiency virus
• Infects white cells which control immune system
• Makes most infections commoner & more severe
• Causes infections by micro-organisms which don’t usually cause harm-opportunistic infection

48
Q

Host (patient) factors in infection- genetics

A 
Genetics and infection
•	Inherited immunodeficiency
-Major problems rare
-Life threatening infections
-Unusual infections
-Minor differences common
-Hepatitis C virus
•	Genetic defects can protect against infection
-E.g. Sickle cell disease (abnormal red cells) heterozygotes are protected against malaria

• Behaviour

Behaviour and infection risk

  • Occupation
  • Travel
  • Recreation
  • Sex
  • Drugs
  • Contacts- friends and pets
49
Q

4 major groups of pathogenic organisms- bacteria, viruses, fungi and parasites

A 
Bacteria:
•	Staphylococcus aureus
•	Streptococci
•	Escherichia coli
•	Tuberculosis
Viruses:
•	Rhinovirus (common cold)
•	Influenza
•	Hepatitis B/C
•	HIV

Fungi:
• Candida
• Tinea

Parasites:
• Malaria
• Hookworm

50
Q

Diagnosing infections

A

History- what the patient tells you

Non-specific symptoms
• Fever
-Sweats, chills, shivers
-Rigors (cold and hot)
• Loss of appetite +/- weight
• Aching muscles (myalgia) or joints (arthralgia)
Specific symptoms
• According to source
-Pneumonia – cough, breathlessness, sputum
-Meningitis – headache, neck stiffness, photophobia

Conditions that make people more susceptible to infection
-Past medical history: diabetes, immunodeficiency e.g. HIV
-Drug history: steroids, chemotherapy
Lifestyle activities that bring people in to contact with infection
-Occupation: healthcare worker, vet, farmer, sex worker
-Travel: ask where, when and what did they get up to…?
-Recreation: hobbies (e.g. watersports), food (e.g. takeaways/BBQ), injecting drugs
-Contacts: people (including sexual partners), animals, insects

51
Q

Investigations: basic blood tests- WBC

Investigations: other basic tests

A

Neutrophil- bacterial infections- pneumonia
Lymphocyte- glandular fever
Eosinophil- schistosomiasis

  • C-reactive protein (CRP) – marker of inflammation
  • U&E – urea and electrolyte levels (kidney function)
  • LFT – liver function tests
52
Q

To identify the bugs themselves you need to send the right sample(s) to the lab

A

• Any body fluid/tissue can be sent to microbiology for testing
• Hospitalised patients with suspected infection should have blood +/- urine sent for culture
• Choose and send other samples related to the body system(s) affected, e.g.:
-Pneumonia – sputum (a mixture of saliva and mucus coughed up from the respiratory tract)
-Gastroenteritis – faeces
-Tonsillitis – throat swab

53
Q

Having identified the right samples here’s some basic rules about taking/sending them

A

• Taking samples
-Samples for culture should be sent before antibiotic treatment starts if at all possible
-Blood cultures – the skin is covered with bacteria. Use aseptic technique to avoid contaminating the blood with them.
• Sending samples
-Provide background clinical information to help the lab
-Inform the lab if important samples are on the way

54
Q

How do we detect organisms that we can’t grow in the laboratory?

A

• Identify part of the organism
-Proteins (often called antigens) -antigen testing
-DNA/RNA (by Polymerase Chain Reaction)
• Identify the body’s immune response to the infection
-Antibodies (proteins made to neutralise a specific infection)
-IgM
-IgG

55
Q

Antibody testing

Classes of antibody tested

A

-IgM
 Initial antibody response
 Appears within a week, usually disappears after a few months
-IgG
 Later antibody response
 Appears 10-14 days
 Test for rising level (titre) in consecutive samples
 Persists throughout life (part of immunological memory)
 Also useful to test whether you are immune to an infection

56
Q

Problems of antibody testing:

A
  1. False positives – cross-reactivity
  2. False negatives – sampled too early/late, immunocompromised patient
  3. Not usually helpful in acute setting
57
Q

Treating infections- therapy

A

 Supportive therapy
-Symptomatic – e.g. paracetamol for fever/aches
-Dehydration/low blood pressure ‘shock’– IV (intravenous) fluids
 Specific therapy
-Antimicrobials (= all drugs/chemicals that kill microorganisms)
-An antibiotic = “a chemical substance derived from a mould or bacterium that can kill microorganisms and cure bacterial infections”
-Note:
 For many viral infections there is no specific treatment
 Some infections are self-limiting – no treatment is required
 Antibiotics must be started immediately for serious infections, e.g. meningitis

58
Q

Antimicrobials

A

All drugs/chemicals that kill microorganisms

59
Q

Antibiotic

A

A chemical substance derived from a mould or bacterium that can kill microorganisms and cure bacterial infections

60
Q

What ideally do we want an antimicrobial to do?

A

 Selective toxicity (effective against microbe without harming host)
 Bacteriocidal (= kills the organism) rather than bacteriostatic (= inhibits its growth)
 No resistance
 Good pharmacokinetics (i.e. reach high level in body and stay there, allowing fewer doses/day)
 No side effects
 Not inactivated by enzymes secreted by microbes, or by the host

61
Q

Problems with antimicrobials

A

 Variable spectrum of activity
-Broad spectrum (kills lots of different organisms)
-Narrow spectrum (kills few organisms)
 Some cannot be given orally
 Many cause side effects which can be serious, e.g. anaphylaxis (severe allergy)
 Bacterial resistance
-some antibiotics are now effective against very few organisms, e.g. penicillin
-some organisms are now resistant to many antibiotics, e.g. MRSA

62
Q

Preventing infections

A

Prevention involves interrupting the chain of transmission at one or more of the 3 stages (i.e. source, method of transmission, host susceptibility).

Reducing pathogens in the environment:

	General:
-Clean drinking water
-Improving sanitation
-Hygienic food preparation
	In hospital:
-Cleaning wards, rooms and equipment
-Filtered air in operating theatres
-Using sterile instruments when operating, taking blood etc.
63
Q

Route of transmission

A

Food/ water bourne- sanitation, clean water supplies food preparation hygiene

Contact e.g. MRSA- hand washing, wearing gowns, masks

Airborne e.g. TB - Isolate infected patient in a negative pressure room

Vector borne e.g. malaria- avoid mosquito bites: insect repellent, bed nets, long sleeves

64
Q

Protecting the potential host

A

 Prophylactic treatments
-Antimalarials
-Antibiotics given to very immunosuppressed patients, e.g. bone marrow transplant recipients
 Immunisation
-Passive (injected with antibodies) - e.g. chickenpox immunoglobulin
-Active (by stimulating the immune system with something which mimics the infection) – e.g. hepatitis B virus surface antigen

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