Topic 5 - Infection Flashcards
Lectures 15-16
What are the organisms which cause infection?
Helminths, Insects, Protozoa, Fungi, Bacteria, Viruses and Prions
What is a parasite?
AN organism which depends on another for its survival to the detriment of its host (traditionally only helminths, insects and protozoa are considered medical parasites)
What is an endoparasite?
Lives inside the body, major cause of illness (helminths and protozoa)
What is an ectoparasite?
Lives outside the body, minor symptoms but can transmit other infections (insects)
What is a protozoa?
Unicellular organisms, some have complex lifecycles involving multiple hosts
What is Entamoeba histolytica?
Example of an Amoebae
- invades large bowel lining
- causes dysentery (abdomical cramps + bloody diarrhea)
- excreted with faeces
- spread vie contaminated food and water
- due to poor hygiene/sanitation
What is Plasmodium falciparum?
Example of Sporozoa, commonly known as Malaria
- lifecycle in human and mosquito hosts
- infects RBC and liver
- symptoms: fever, headaches, joint pains
- complications: kidney failure, coma, death
- risk is geographical
What is a Helminth?
Worms! Complex organisms, some of which have complex lifecycles involving multiple hosts. Other species have their own helminths hat can accidentally cause human disease
What are the 3 types of helminths?
- Cestodes (tapeworms, flat and segmented)
- Trematodes (flukes, unsegmented and flat)
- Nematodes (round worms, cylindrical, have difestive tract with lips, teeth and anus)
What is Taenia saginata?
Beef worm. A cestode.
- intestinal parasite of humans
- largely asymptomatic (abdominal pain and malnutrition)
- diagnosed through stool microscopy for eggs
- cattle are intermediate hosts
What is Schistosoma haematobium (bilharzia)?
A trematode.
- human host, infects the veins around the bladder
- causes bladder inflammation, bleeding into urine (haematuria)
- intermediate host is the freshwater snail
- diagnosed through urine microscopy for eggs
What is Cimex lectularius?
The bedbug - an ectoparasite.
- wingless insect
- worldwide infestation of human dwellings
- hides in cracks and furniture
- emerge at night - blood meal 5-10mins long
- itchy rash after bite
- can transmit other infections (protozoa in South America)
What are the two main forms of fungal infections?
- Yeasts (single cells which bud)
- Moulds (filamentous strands)
- Some are able to switch (diamorphic fungi)
What is the difference between Tinea Pedis and Tenia Corporsis?
Both superficial fungal infections.
Tenia Pedis is athletes foot.
Tinea Corporis is ‘ringworm’ (not a worm)
What is Cryptococcus neoformans?
A severe invasive fungal infection
- infects patients with low resistance due to failing immune system
- causes meningitis
- headaches, neck stiffness, confusion, coma, death
What is meningitis?
Inflammation of the membranes lining the brain.
What are bacteria?
- Unicellular organisms
- Cell membrane
- Cell wall
- No nucleus
- Reproduce asexually
- Move using flagellae and pili
What are the classifications of bacteria?
Round - coccus
Rod - Bacillus
They can come in clusters, chains or pairs.
What do Gram Stains mean?
Gram positive - Purple
Gram Negative - Pink
The stain allows you to predict which antibiotics would be effective
What is streptococcus pneumoniae?
Pneumonia.
- gram positive cocci in pairs
- colonise nose and throat
- invade other sites such as lungs, causing pneumonia
- cough, dirty sputum, chest pain, breathlessness, fever
- complications include blood stream infection, meningitis and death
What are viruses?
- dependent on infection of host cell for metabolism anf replication
- contain DNA or RNA, a protein coat and an outer membrane
- very small 1/100th size of bacteria
What is an acute viral infection?
Norovirus infects host for days, causing diarrhea and vomiting
What is a chronic viral infection?
Hepatitis C causes liver inflammation for years
What is a latent viral infection?
Herpesviruses can be dormant for decades before reactivating to cause disease
What is the varicella zoster virus?
Primary infection causes Chicken Pox (rash and fever)
- virus becomes dormant in sensory nerve roots
- reactivates years later as Shingles (same rash, confined to dermatome)
Which virus can contribute to cancers?
Epstein-Barr virus.
- usually causes mild illness
- infects immune B cells and epithelial cells of the nose and mouth
- 90% of us get it
- latent lifelong infection
- contributes to certain cancers with other factors (nasopharyngeal carcinoma esp in Southern China and lymphone in HIV infection)
What are prions?
- Smallest infective agents known
- Proteinaceous Infectious particles
- Lack nucleic acid - not living
- Proteins are abnormal and accumulate in neural tissue
- Difficult to destroy as standard sterilization techniques do not work
What are some Prion diseases?
- Creutzfeldt-Jakob disease (rare fatal degenerative neurological disease, transmitted via human growth hormone, surgical instruments and corneal grafts.)
- Variant CJD typically occurring in younger adults (thought to be derived from bovine spongiform encephalopathy, BSE or mad cow disease)
- Kuru (similar to vCJD, but occured in 50s in Papua Nwe Guinea through cannibalism)
What is endogenous infection?
When normal flora from the skin, gut, upper airways ot genital tract gets in the wrong place. Infection basically comes from ourselves.
(eg, UTI - cystitis)
What is Cystitis?
UTI.
- Causes: lower abdominal pain, urgency, dysuria and frequency.
- Most commonly caused by gut flora bacteria such as E.Coli
What is exogenous infection?
Caught from someone/something else: another person, animals/insects or the environment.
Routes of transmission for endogenous infections?
Migration
Perforation
Blood
Routes of transmission for exogenous infections?
Contact Injuries (trauma/bites) Airborne Oral (food/water) Bloodborne Sex Mother to baby (vertical)
How is Endocarditis spread?
Blood - an endogenous infection.
- dental work may allow mouth flora to enter blood stream
- invasion can occur in heart valves esp if valve tissue is abnormal
- causes inflammation ‘vegetation’ and structural damage
What is Impetigo?
Exogenous infection through direct skin contact.
- superficial skin infection due to streptococci or staphylococci
- spreads rapidly between people
What is Tetanus?
Lockjaw.
- Clostridium tetani
- bacteria present in soil
- contaminates wounds
- releases tozin causing paralysis
- prevented by vaccination
What is Hepatitis B?
Blood-borne infection.
- liver
- some viruses spill into blood
- transmission by blood exposure
How does vertical transmission occur?
- During pregnancy (rubella)
- At the time of birth (herpes)
- Breast milk (HIV)
What are the pathogen factors in infection?
- Infectious dose
- Direct infection of cells/tissues
- Virulence factors and toxins
- Resistance to antibiotics
What is the Infectious Dose?
Minimum number of organisms required to produce disease
What is Cholera?
- Causes severe watery diarrhea
- bacteria produce toxin
- binds to gut lining cells
- massive loss of fluid and electrolytes
- severe dehydration, kidney failure and death
What is the Cholera toxin mechanism?
- cholera toxin enters cells of gut lumen
- activates adenyl cyclase increasing cAMP
- reduces Na+ absorption
- increases Cl- secretion
- water and electrolytes drawn into bown lumen resulting in diarrhea
What are the natural barriers to infection?
- Skin and mucous membranes
- Stomach acid
- Native bacteria
- Immune system
- Genetics
- Behaviour
What is Dengue fever?
- Viral infection
- transmitted by Aedes Mosquito
- Fever and rash and muscle pain
- Severe form causes bleeding, shock and multi-organ failure
What are the four MAJOR pathogenic organism groups?
Bacteria
Fungi
Viruses
Parasites
What History may patients tell you?
- Non-specific symptoms (sweat, chills, loss of appetite, muscle aches)
- Specific symptoms (eg, Pneumonia - cough, breathlessness, dirty sputum)
What History is important to ask?
- Conditions that may make the patient more susceptible to infection (past medical history & drug history)
- Lifestyle activities that may bring them in contact with infection (occupation, travel, recreation and contacts)
If WBC Neutrophil is elevated?
Bacterial infection
If WBC Lymphocyte is elevated?
Viral infection
If WBC Eosinophil is elevated?
Parasitic infection
What are some basic tests for infection?
C-Reactive Protein (CRP) - marker of inflammation.
U&E (Urea and Electrolyte levels - kidney function.
LFT - Liver Function Tests.
How do we detect organisms that can’t be grown in lab?
- Identify part of the organism (antigens or DNA/RNA)
- Identify bodys immune response to the infection (antibodies eg IgM or IgG)
What is the LgM antibody?
- Initial antibody responce
- Appears within a week, disappears after a few months
What is the IgG antibody?
- Later antibody responce
- Appears 10-14 days
- Test for rising levels in consecutive samples
- Persists throughout life
- Useful in testing immunity to infection
What is an antibiotic?
A chemical substance derived from a mold or bacterium that can kill microorganisms and cure bacterial infections. Form = of specific therapy.
Where does Penicillin come from?
Derived from a mould.
Where does Mupirocin come from?
Produced by Pseudomonas florescens (bacterium)
What does an ideal antimicrobial do?
- Has selective toxicity
- Bacteriocidal rather than bacteriostatic
- No resistance
- Good Pharmacokinetics (reaches high levels in body and stays that way, allowing lower doses/day)
- No side effects
- Not inactivated by microbes secretory enzymes
What are some issues of antimicrobials?
- Broad spectrum of activity
- Some cannot be given orally
- Many cause side effects eg. anaphylaxis
- Bacterial resistance
How do we prevent infection spread in hospitals?
- Cleaning wards, rooms and equipment
- WASHING HANDS
- Filtered air in operating theatres
- Using sterile equipment when operating, taking blood etc.
What are prophylactic treatments?
- Antimalarials
- Antibiotics given to immunosuppressed patients
