TOPIC 6 - infections Flashcards
What are helminths?
Complex organisms - worms
What is a cestode?
Tapeworm - segmented and flat
What is a trematode?
Fluke - unsegmented and flat
What is a nematode?
Round worms - cylindrical and have a digestive tract with lips , teeth and anus
Taenia Saginata
Beef tapeworm:
- intestinal parasite of human
- largely asymptomatic
- abdominal pain and malnutrition
- cattle are intermediate hosts- we eat cattle = eggs hatch in us
- diagnosis - stool microscopy for eggs or patient sees worm in stool
Bilharzia
- infects veins around the bladder
- bladder inflammation and haematuria (blood in urine)
- freshwater snails are intermediate hosts
- diagnosis - urine microscopy for eggs
- if fluke live in bladder for long time = chronic bladder inflammation = cancer
Endoparasites
Live INSIDE the body
- helminths
- protozoa
major cause of illness
Ectoparasites
Live OUTSIDE the body - fleas - lice - bed bugs - ticks minor cause of illness but can transmit
What is a parasite?
An organism which depends on another for its survival to the detriment of its host
What is protozoa?
Unicellular organisms, some have complex lifecycles involving more than one host
Entamoeba histolytica
Amoeba
- invades large bowel lining
- dysentery - abdominal cramps and bloody diarrhoea
- excreted with faeces
- spread via contaminated food and water (poor hygiene and sanitation
Plasmodium falciparum
Sporozoa (malaria)
- lifecycle in both humans and mosquitos
- infects red blood cells and liver
- fever, headache and joint pains
- eventually cause kidney failure, coma and death
- spread via mosquitos
What are the 2 main forms of fungi?
Yeast - single cells which bud
Mould - filamentous strands
Diamorphic fungi can switch between the two
Tinea pedis
Athlete’s foot
- usually starts between the toes
- itchy, scaly rash on feet
- usually occurs when sweaty feet are in tight, confined shoes (accumulation of moisture between the toes)
Tinea corporis
Ringworm
- superficial fungal infection of skin
- most common on arms and legs (glabrous skin)
- spread by skin to skin contact
Cryptococcus neoformans
Yeast
- infects patients with failing immune system (ie HIV)
- causes meningitis
- inflammation of membranes lining the brain
- headache, neck stiffness, confusion, coma, death
Bacteria
- prokaryotes
- peptidoglycan cell wall
- no nucleus
- reproduce asexually
- move using flagellae and pili
Common bacterial infections
Pneumonia UTI Cellulitis Meningitis Cholecystitis Diverticulitis Appendicitis
Round bacteria
Coccus
Rod bacteria
Bacillus
Stain used in gram staining
Crystal Violet- some bacterial walls retain crystal violet stain, other don’t
Colour of stain in gram positive
Purple
Colour of stain in gram negative
Pink
Clinical importance of classifying bacteria
- quickest way to identify them
- Allows you to predict which antibiotics will be effective quickly and so which prescribe
Streptococcus pneumoniae
Pneumococcus
- gram positive cocci in pairs
- colonise nose and throat
- invade other sights (lungs causing pneumonia)
- cough, dirty sputum, chest pain, fever
- blood stream infection, meningitis, death
What does diplococci mean
Cocci in pairs
Viruses
- depend on infection of host cell for metabolism and replication
- protein core surrounding genetic material, protein coat and outer membrane
- very small (need powerful electron microscope)
Acute infection
Norovirus infects hosts for days, causing diarrhoea and vomiting
Chronic infection
Hepatitis C causes liver inflammation for years
Latent infection
Herpesviruses can be dormant for decades before reactivating to cause disease
Varicella zoster virus
Chickenpox (latent infection)
- rash and fever
- virus becomes dormant in sensory nerve roots
- reactivates years later as shingles (same rash, confined to dermatome) due to stress, lowered immunity ect
Dermatome
Area supplied by single sensory nerve
Epstein-Barr virus
- usually causes mild illness (glandular fever)
- infects immune system cells, B cells, and epithelial cells of nose and mouth
- causes latent lifelong infection
- contributes to certain cancers with other factors
Prions
PROteinaceous INfectious particles
- lack nucleic acid - not a living organism
- proteins are abnormal and accumulate (mainly in neural tissue)
- very difficult to destroy- standard sterilisation doesn’t work
CJD
Prion - Creutzfeldt-Jakob disease
- rare fatal, degenerative neurological disease
- transmitted via human growth hormone, surgical instruments and corneal grafts
Kuru
Prion
- occurred in Papua New Guinea in 1950’s
- spread by cannibalism (in the one tribe they would eat the bodies of dead relatives - spread from the brain
Reservoir
Habitat in which the agent normally lives, grows and multiplies
Endogenous infection
When normal microbial flora (found on skin, gut, upper airways and genital tract) gets into the wrong place- eg.UTI
Cystitis
- infection of lower urinary tract
- lower abdominal pain, urgency, dysuria, frequency
- most commonly bacteria from gut flora
Dysuria
Painful urination
Exogenous infection
Communicable
- person-to-person
- non-human sources
- environment
Endogenous route of transmission
- migration
- perforation
- blood
Exogenous infection
- contact
- injuries
- airborne
- oral
- blood-borne
- sex
- Mother-to-baby (vertical)
Migration- endogenous infection
- bowel flora contaminates perineum
- gains access to urethra
- causes local infection
- spreads to bladder, cystitis, and beyond to reach kidneys = UTI
Perforation -endogenous infection
- diseases of bowel, especially colon-eg. cancer, diverticular disease
- perforation of bowel wall leads to contamination of abdominal cavity with faecal flora
- severe life-threatening infection
Blood spread- endogenous infection
- endocarditis (infection of the heart)
- dental work may allow mouth flora to enter blood stream
- circulation of organisms allows them to reach distant sites
- invasion can occur especially if heart valve tissue is abnormal
- causes inflammation, ‘vegetation’ and structural damage of heart valves
Impetigo
Direct contact
- superficial skin infection due to staphylococci or streptococci
- spreads rapidly from person to person so need cover up
Indirect contact
- micro-organisms can be transmitted via hands, equipment, furniture etc
- major route of health-care associated infections
- eg MRSA, clostridium difficile, norovirus gastroenteritis
Tetanus
- bacteria (clostridium tetani) present in soil
- contaminates wounds
- releases toxin causing muscle spasm
- prevented by vaccine
Influenza virus
Airborne infection
- coughing and sneezing
- droplets formed containing infectious viruses
- inhaled by others
Food-borne/ oral
- food prepared with poor hygiene
- contaminate food with harmful bacteria
- food poisoning
- vomiting and diarrhoea
Blood-borne infection
Hepatitis B
- liver infection
- some viruses spill into blood
- transmission by exposure to blood (transfusion, sharing dirty needles)
Sexual transmission
Chlamydia
- unprotected sex
- new partners
- multiple partners
- high risk (sex workers)
Mother to baby (vertical)
- during pregnancy (rubella)
- at time of birth (herpes)
- breast milk (HIV)
HIV, hep B and hep C transmission
- blood-borne
- vertical- placental or breast feeding
- sexual
Infections requiring more than one step
Staphylococcus aureus
- colonisation of skin
- penetration of skin
Factors that contribute to how serious an infection is
- infectious dose
- direct infection of cells/tissues
- virulence factors and toxins
- resistance to antibiotics
Ebola
Direct infection and damage/destruction of cells
- tissue damage
- destroys blood vessels
- decreased blood clotting ability- coagulation defects
- impairment of immune system- no antibodies produced
Cholera
- severe watery diarrhoea (‘rice water’)
- bacteria produce toxin
- binds to gut lining cells- mucosa
- massive loss of fluid and electrolytes
- causes sever dehydration, kidney failure and death
How does cholera cause illness
- cholera toxin enters cells of gut lumen
- activates adenyl cyclase increasing cAMP
- reduces Na+ absorption
- increases Cl- secretion
- water and other electrolytes drawn into bowel lumen = diarrhoea
Antibiotic resistance
- micro-organisms readily mutate
- frequently mutate to escape antibiotic use
- more antibiotic use = more mutations
- failure of antibiotic treatment
- rate of new development of antibiotics is slower than the rate of mutation
What is a superbug?
A super resistant bacteria that cannot be treated by antibiotics
Environment factors in infection
- geography
- climate
- poverty
- public health infrastructure
- distribution of other infection hosts- insects or other vectors
Dengue fever
Virus infection
- transmitted by Aedes mosquito
- fever, rash and muscle pain
- sever - bleeding, shock and multi organ failure
Barriers to infection
- skin and mucous membranes
- stomach acid
- native bacteria
- immune system
- genetics
- behaviour
Skin and mucous membranes can be compromised by …
Cuts - wound infection
Abrasions - conjuctivitis
Stomach acid can be compromised by …
- HCl - pH 2 (very few organisms can survive this)
- commonly used drugs for stomach ulcer increase pH
- patients more susceptible to food poisoning
Native bacteria can be compromised by …
- prevent colonisation by pathogenic bacteria as space taken up by our normal friendly bacteria
- antibiotic treatment destroys the normal ‘friendly’ bacteria
- pathogens can reproduce and cause disease as there now space for them
Immune system can be compromised by …
- treatment for other diseases - chemotherapy damages immune system
- drugs to make immune system less active (corticosteroids)
Immune system infection
HIV
- infects white cells
- makes most infections more common and more severe
- causes infections by micro-organisms which don’t usually cause harm
- opportunistic infection
Genetics and infection
Inherited immunodeficiency
Genetics can protect against infection - sickle cell disease trait are protected against malaria
Behaviours to increase infection risk
- occupation
- travel
- recreation
- sex
- drugs
- contacts
stages of malaria in blood
1- human bitten by anapholys mosquito 2- injects sporozoite in blood stream 3- these travel to liver 4- then released into blood as merozite 4- then turns into trophozoite and after into schizont 5- and finally bak into merozite so the cycle repeated
what is rhinovirus?
common cold
trivial infection
what are microbial flora ?
normal ‘friendly’ bacteria
everyone has living on them
bacteria vary according to site
diseases due to overactive immune systems / autoimmune?
asthma
types arthritis
bowel inflammation
what are the 4 major pathogenic groups?
- bacteria
- viruses
- fungi
- parasites
what are examples of non specific symptoms?
- sweat, chills, shivers
- fever
- rigors- episodes of uncontrolled shivering
- loss weight/appetite
- aching muscles/joints
what are specific symptoms?
idea as to where infection coming from
according to source
- pneumonia : cough breathlessness
- meningitis: headache, neck stiffness
why is the medical history of patient importnant
may have (past)conditions making the more susceptible to infection may be suppressed by (past)drugs
where do we examine a patient in infections?
whole patient - infections can effect whole body
- some produce signs that give away diagnosis - eg. chicken pox
what basic tests can we carry out for infections
- CRP- C reactive protein : marker of inflammation - protein increased in inflammation
- U&E- urea and electrolyte levels (kidney function)
- LFT: liver function tests (hep)
what test would you take for tonsilitis?
throat swab
patients in hospital with infection have what tests sent to lab?
blood and urine
sent for culture
what would you test for pneumonia?
sputum- phlegm
what would you test for gastroenteritis?
faeces
do you take a sample before or after anitibiotic?
before
what a lumbar puncture?
examination of cerebrospinal fluid for signs of meningitis
needle between 2 lumbar vertebra into spinal fluid
What tests do Microbiologists do with the samples you send?
- Antibody tests
- Microscopy
- Antigen detection
- Culture
- Antibiotic sensitivity testing
- PCR
what stain do we use to detect fungi?
calcofluor
what stain do we use to detect TB
Ziehl Nelson
whats an antibiotic sensitivity test?
Measurement of susceptibility of bacteria to antibiotics
Cover whole surface of agar plate with bacteria
Discs with certain antibiotics
Zone of inhibition around disc shows which antibiotic works on that bacteria
How do we detect organisms that we can’t grow in the laboratory?
•Identify part of the organism:
- Proteins (often called antigens)
- Detect DNA/RNA (by Polymerase Chain Reaction)
- Identify the body’s immune response to the infection
- Antibodies (proteins made to neutralise a specific infection)
- IgM- acute infection
- IgG- past infection/immunity
what is antigen protein testing?
- detection of protein fragments
- rapid and cheap
- detect acute infection
what is the PCR and why do we use it
- Polymerase Chain reaction
- DNA/RNA identification by multiplying DNA/RNA
- identifies unique genetic code sequence for specific infection
- used for acute infection
give examples of acute infections
• Meningitis • HIV • Hepatitis B and C • Respiratory viruses (e.g. influenza) SARS-CoV-2 (COVID-19)
what is antibody testing
Looks at antibodies produced in response to infection
what classes of antibodies are tested?
•IgM
Initial antibody response
Appears within a week, usually disappears after a few months
•IgG
Later antibody response
Appears 10-14 days
how do we get a false negative test?
test taken too late/early
takes time for antibodies to form
what is Supportive therapy
treat symptoms:
eg. paracetamol or IV fluids
what is Specific therapy
•Antimicrobials (= all drugs/chemicals that kill microorganisms)
•An antibiotic
for viral infections no specific treatment
What ideally do we want an antimicrobial to do?
- Selective toxicity (effective against microbe without harming host)
- Bacteriocidal (= kills the organism) rather than bacteriostatic (= inhibits its growth)
- No resistance – should be able to kill micororagnism
- 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
what are broad spectrum antimicrobials?
kills lots of different organisms
what are narrow spectrum antimicrobials?
kills few organisms
Problems with antimicrobials
- Variable spectrum of activity
- 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
how do we reduce transmission of food/water borne infections
sanitation
clean water supplies
food prep hygiene
how do we reduce transmission of contact infections- eg.MRSA
hand washing
gloves
gowns
masks
how do we reduce transmission of airborne infections eg. TB
isolate patient in negative pressure room- filters out-going air
how do we Protect the potential host
•Prophylactic treatments treat before infection- antimalarials
•Antimalarials
•Antibiotics given to very immunosuppressed patients
- immunisations
How do you make a diagnosis of an infection?
History - symptoms, travel, medical history, occupation, recreation, vaccination
Examination - infections can effect every body system
Investigation - e.g. LFT, urea and electrolyte levels, C-reactive protein
Testing
How is microbiology used in diagnosing an infection?
Antibody detection - IgM (marker of acute infection) or IgG (past infection or immunity) Culture Microscopy PCR Antigen detection Antibiotic sensitivity testing
How are infections treated?
Supportive therapy - e.g. to treat symptoms
Specific therapy - antimicrobials and antibiotics
Name some examples of antibiotics.
- Penicillin - derived from mould
- Mupirocin - produced by bacteria pseudomonas fluorescens (treats MRSA)
What makes a good antimicrobial drug?
Selective toxicity Bacteriocidal No resistance Good pharmacokinetics No side effects Not inactivated by enzymes secreted by microbe or host
What are some problems with antimicrobials?
Variable spectrum of activity
Some can’t be given orally
Many cause serious side effects
Bacterial resistance
Name some ways that antibacterials work?
Block cell wall synthesis Block DNA replication Block DNA-dependent RNA polymerase Inhibit protein synthesis Cell membrane inhibitors
How can infection be prevented?
Reduce pathogens in the environment - clean drinking water, hygienic food preparation
Prevent transmission - sanitation, hand washing, isolation of infected individuals
Protect the potential host - antimalarials, immunisation etc
Which infections currently do not have a vaccine?
Meningococcus group B
Hep C
HIV
Malaria
Lumbar puncture
Sample of spinal fluid
Suspected bacterial meningitis should be confirmed by lumbar puncture
Faeces culture
Investigation of suspected gastroenteritis
Brown top universal with spoon
Fluid culture
Fluid (like material obtained from sterile sites or from drains) should be collected in a sterile universal container with a white top
MC&S Culture Swabs
Cultures of swabs of material from wounds and other superficial parts of the body are used to identify the bacterial causative agent
Respiratory culture
Investigation of lower respiratory tract bacterial infections including pneumonia
Throat swab
Used for performing PCR and culture
MRSA culture
MRSA screening is aimed to prevent transmission of MRSA by identifying patients who are colonised or infected
