Infectious Diseases Flashcards
Tapeworm is an example of what kind of organism?
Helminths
Fleas are an example of what kind of organism?
Insects
Malaria is an example of what kind of organism?
Protozoa
Candida is an example of what kind of organism?
Fungi
Staphylococci is an example of what kind of organism?
Bacteria
Influenza is an example of what kind of organism?
Virus
Kuru is an example of what kind of organism?
Prion
In terms of infectious diseases, helminths, insects and protozoa are all collectively considered what?
Medical parasites
What is the definition of a parasite?
An organism which depends on another for its survival to the detriment of its host
What are the 2 types of medical parasite and how can you distinguish between the 2?
1) Endoparasites: live inside the body, major cause of illness, helminths and protozoa
2) Ectoparasites: live outside the body, minor symptoms but can transmit other infections, fleas, lice, ticks
Entamoeba histolytica is a type of protozoa-amobae what part of the body does it invade, what symptoms does it causse, what is its life cycle and how is it spread?
BODY: invades the large bowel lining
SYMPTOMS: Dysentery, abdominal cramps, bloody diarrhoea
LIFECYCLE: organisms replicate in the bowel and are excreted in the faeces thus can contaminate water, they phagocytose RBC’s, travel around tissues engulphing red blood cells
SPREAD: via contaminated food and water so poor hygeine and sanitation is a big risk factor
Plasmodium falciparum (malaria) is a type of protozoa-sporozoa, what part of the body does it infect, what is its lifecyle, what are the complications of infection?
BODY: has a lifecycle in humans and mosquitos, infects the RBCs and liver
COMPLICATIONS: renal failure, coma, death (if left untreated)
LIFECYCLE: female mosquito (male mosquitos dont carry malaria) bites to feed on human blood whilst injecting malarial parasites from the salivary glands, parasites travel in the blood and replicate in the liver, come back into the blood stream where they infect RBCs, another mosquito will feed on the individuals infected blood and a lifecyle then occurs within the mosquito
Cestodes, trematodes and nematodes are all types of helminths, what is the difference between the 3?
1) Cestodes (tapeworms) - segmented, flat
2) Trematodes (flukes) - unsegmented, flat
3) Nematodes (round worms) - cylindrical, have digestive tract with lips teeth and anus
Taenia saginata (beef tapeworm) is a type of cestode, what part of the body is infected, what are the symptoms of infection, what tests are needed for diagnosis, what is its lifecyle?
BODY: intestine
SYMPTOMS: largely asymptomatic, abdominal pain, malnutrition
TESTS: stool microscopy for eggs
LIFECYCLE: Cattle are intermediate hosts, worm has a head with an attachment surface, attaches to intestine wall, grows in segments, segments contain eggs, segments break off and are passed out into the environment in human faeces, cattle or pigs become infected by ingesting vegetation contaminated with eggs, eggs hatch and penetrate the intestinal wall of animals, circulate to the musculature and develop in the muscle, humans can then be infected by ingesting raw or undercooked infected meat
Schistosoma haematobium (bilharzia) is a type of trematode, what part of the body does it infect, what are the symptoms, what tests are needed for diagnosis and what is the lifecylce?
BODY: infects the veins around the bladder
SYMPTOMS: bladder inflammation and bleeding in the urine (haematuria)
DIAGNOSIS: urine microscopy for eggs
LIFECYLCE: Freshwater snail is the intermediate host
Hatches from egg and infects snail, immature worm leaves the snail and enters the blood stream of a human, eventually ends up in blood vessels around the bladder or near the intestine, worms reach sexual maturity in the abdominal cavity, females produce eggs, eggs enter intestinal tract or bladder and are passed in the urine or faeces into fresh water
Cimex lectularius is a bedbug, as type of ectoparasite, what is the course of infection, what are the symptoms, although the infection is not major what is the added risk?
INFECTION: wingless insect, worldwide infection of human dwellings, hides in cracks in furniture and walls, emerges at night to feed for 5-10 minutes for a blood meal
SYMTPOMS: itchy rash after bite
MAIN PROBLEM: can transmit other infections, eg. protozoa in south america (tropanosomiasis)
What are the 2 main types of fungi which cause infection?
1) YEASTs: single cells, round cells
2) MOULDS: tend to grow in strands (filamentous strands)
Tinea pedis (athletes foot) and tinea corporis (ringworm) only infect the skin and related structures, what kind of fungal infection do they cause?
Superficial fungal infections
Cryptococcus neoformans (yeast) is a severe fungal infection, what does it cause?
Infects patients with low resistance due to a failing immune system
Causes meningitis (inflammation of membranes lining brain, difficult to treat if not detected in time, can be fatal)
symptoms: headache. neck stiffness, confusion, coma, death
Streptococcus pneumonia is what kind of infection, what is its course of infection the symptoms and complications?
Bacterial infection
INFECTION COURSE: gram positive diplococci, colonise in the nose and throat, can be invasive and virulent and invade other sites, eg. organs causing pneumonia
SYMPTOMS: cough, dirty sputum, chest pain, breathlessness, fever
COMPLICATIONS: bloodstream infection, meningitis, death
What is the rough structure of a virus and what characteristic makes them a virus?
Viruses are dependent on their host for metabollism and excretion
Contain a protein core surrounding genetic material (DNA or RNA) protein coat, with or without an outer membrane
HIV is a type of virus what part of the body does it infect and what is its course of infection?
Binds to receptors on CD4 white blood cells and injects its viral rna into the cell
The viral rna is copied into the host dna by reverse transcriptase and transcribed by the host cell to produce viral proteins and other viruses which are released into the bloodstream and go on to infect other CD4 cells
The host cell has a shorter life span and can no longer carry out its function - get depleted CD4 cells, hence immune deficiency in HIV
Rhinovirus is otherwise known as what?
Common cold
Norovirus is an example of what kind of infection (acute/chronic/latent) and causes what symptoms?
Acute infection
Causes diarrhoea and vomiting
Is hepatitis C is an example of what kind of infection (acute/chronic/latent) and causes what symptoms?
Chronic infection
liver inflammation for years
Herpes virus is an example of what kind of infection (acute/chronic/latent)?
Latent infection, can be dormant for years before reactivating and causing disease
Varicella zoster virus is an example of what kind of infection (acute/chronic/latent) and causes what primary infection and reactivates later to cause what possible second infection?
Latent infection
primary infection = chicken pox, characteristic rash and fever
Virus becomes dormant in sensory nerve roots
Reactivates years later as shingles
-get same rash but confined to dermatode where the virus was dormant
What viral infection can contribute to nasopharyngeal carcinoma and lymphoma in HIV infection? And what disease can it also cause?
Epstein barr virus
Usually causes glandular fever
Infects immune system (B cells) and epithelial cells of nose and mouth (nasopharynx)
Causes latent lifelong infection and contributes to these 2 cancer
What are prions?
smallest infective agents known
proteinaceous infectious particles
Lack nucleic acid (not a living organism)
How do prions cause infection?
Proteins are abnormal and accumulate mainly in neural tissue, they are very difficult to destroy: standard sterilisation techniques dont work
What kind of infection is CJD and how is it transmitted?
Prion disease
Rare, fatal, degenerative neurological disease
Transmitted via human growth hormone, surgical instruments and corneal grafts
Variant CJD is what kind of infection and is thought to be derived from what?
Prion disease
Typically occurs in young adults, thought to be derived from BSE (mad cow disease)
What kind of disease is Kuru, how is it spread?
Prion disease, similar to CJD, occurred in Papua New Guinea and spread by cannibalism, especially through the consumption of the brains of dead relatives
Candida and tinea are what kind of pathogen?
Fungi
Rhinovirus, influenza, Hepatitis B and HIV are what kind of pathogen?
Virus
Malaria and Hookworm are what kind of pathogen?
Parasite
Staphylococcus aureas, streptococci, escherichia coli, tuberculosis are what kind of infection?
Bacteria
What are the 4 sources of infection?
1) Endogenous flora
2) The environment
3) Other people
4) Animals/insects
Coughing, breathlessness and sputum production are likely to be symptoms of what bacterial infection?
Pneumonia
Headache, neck stiffness, photophobia are likely to be symptoms of what disease?
Meningitis
Neutrophils are generally raised in what kind of infection?
Bacterial infection
Lymphocytes are generally raised in what kind of infection?
Viral infection
Eosinophils are generally raised in what kind of infection?
Parasitic infection
In terms of infectious diseases what is C reactive protein?
CRP: made by the liver and is a marker of inflammation, mild infection = lower levels detected than in a serious infection
In suspected infection why would you do U&Es or LFTs?
test of kidney function and liver function, some toxins or infections may affect the liver or kidneys
Other than blood tests, what else could you send for testing and in pneumonia, gastroenteritis and tonsillitis which would be most useful?
1) Urine
2) faeces: gastroenteritis
3) sputum: pneumonia
4) throat swab: tonsillitis
in what suspected infection would a lumbar puncture be needed?
Need to a lumbar puncture to collect cerebrospinal fluid to be sent for culturing in suspected meningitis
What is antibiotic sensitivity testing?
Spread the bacteria across a culture medium
Place on discs containing antibiotic, antibiotics diffuse into culture plate
If antibiotic is effective there will be a bacteria free ring around the disc
What body fluid would need to be tested in Legionnaires disease (a type of pneumonia)?
Urine test
protein made by the bacteria migrates out of the lung, gets into the circulation and is excreted in the urine
What kind of test is needed to test for Hep B?
Blood test
How is PCR used in detecting infection?
Amplify a specific sequence and identify a unique genetic code sequence for specific information eg. meningitis, HIV, Hep B and C, Respiratory viruses
What are the 2 classes of antibody tested for in infection and at what stage are they raised?
IgM: initial body response, appears within a week, disappears after a few months
IgG: later Ab response, appears ~2 weeks after infection, persists throughout life, can be raised from previous infection, good marker of immunity
What are the 3 problems with Ab testing in infectious disease?
1) False positives - cross reactivity (from other infections)
2) False negatives - sampled too late/early, immunocomprimised patient
3) Not usually helpful in an cute setting
What does supportive therapy refer to in treatment of infectious diseases?
1) symptomatic - eg paracetemol for fever and aches
2) dehydration/low BP - IV fluids
What is an antimicrobial?
All drugs/chemicals which kill microorganisms
What is an antibiotic?
Chemical derived from a mould or bacterium that can kill microorganisms and cure bacterial infections ie. an antibiotic is a biologically derived substance
What are the 6 ideal antimicrobial properties?
1) selective toxicity
2) bacteriocidal
3) no resistance
4) good pharmacokinetics
5) no side effects
6) not inactivated by enzymes secreted by microbes or by the host
Vancomycin and penicillin interfere with what cell process?
Cell wall synthesis
Nalidixic acid and quinolones interfere with what cell process?
DNA synthesis
Trimethoprim interferes with what cell process?
folic acid metabollism
Polymyxins interfere with what part of the cell?
cell membrane
Tetracylcine and spectinomycin interfere with what cell process?
Protein synthesis
What is the difference between a broad spectrum and a narrow spectrum antimicrobial?
Broad spectrum: kills lots of different organisms
Narrow spectrum: kills few organisms
Give 2 examples of prophylactic treatment in infectious disease?
1) Antimalarials
2) Antibiotics given to immunosuppressed patients
What is the difference between passive and active immunisation?
Passive: given Ab eg. chicken pox immunoglobulin
Active: body stimulated to produce its own Ab eg. Hep B surface antigen
What does legislation regarding notification of communicable diseases require doctors to do if they come across certain infections?
They must notify the authorities
From bacillus anthracis (anthrax) to yersinia pestis (plague)
Used to identify and prevent outbreaks
What is the definition of healthcare associated infections?
Infections that occur as a result of contact with the healthcare system - tend to use a ball park figure of 48 hours after contact
Why do canulars, catheters and antibiotic treatment potentially make people more susceptible to infections?
Canulars - breaking of the skin
Catheters - breaking down of urinary tract defences
Disturbance of the host flora - by antibiotic treatment
What is the aseptic technique?
No touching, sterile equipment and clothing
What are the advantages of broad vs. narrow antibiotics in terms of C diff etc?
Narrow: dont carry risk of c diff but can only be used for specific infections when you know the diagnosis from tests
Broad: good if uncertain about the type until the culture gets back, but knock out gut flora and make you more vulnerable to c diff
What are the 3 ways MRSA can present?
1) COLONISATION: in nose, no symptoms
2) SKIN INFECTION: cellulitis, can enter skin by eczema, wound, canular
3) BLOODSTREAM INFECTION: severe, life threatening, all patients screened with a nose swab on admission
What is normal microbial flora?
Most mucous surfaces harbour natural bacteria, type and amount vary according to site eg. more in GI tract than in upper airways
What occurs in an endogenous infection?
Normal flora gets into wrong place, eg. flora from the gut such as gram -ve e coli can cause UTIs such as cystitis
What are the symptoms of cystitis?
Lower abdominal pain, urgency, dysuria (painful or difficult urination), frequency
By which 3 ways can endogenous bacteria cause infection in other places?
1) Migration
2) Blood
3) Perforation
What is vertical transmission of exogenous infection?
From mother to baby
Bowel flora (e.coli) can cause UTI how?
By migration
Bacteria in faeces contaminate faeces outlet, gains access to the urethra and travels up, causes local infection and spreads to the bladder
How can bacterial flora cause faecal peritonitis?
In diseases of the bowel, especially the colon
Perforation of the bowel wall leads to contamination of the abdominal cavity with faecal flora
Severe life threatening infection results (which is likely to spread into the blood stream)
How does mouth flora (streptococci) cause endocarditis?
Blood spread
dental work may allow mouth flora to enter blood stream
Circulation of the organism allows them to reach distant sites eg. heart valve
Invasion can occur especially if valve tissue is abnormal eg. congenital defect
Causes inflammation and structural damage and the valve cant function
By what route is impetigo transmitted and what bacteria is it caused by?
Superficial skin infection due to staphylococci/streptococci
Spreads rapidly from person to person by DIRECT CONTACT
What is the major route by which healthcare associated infections are transmitted?
Exogenous infection - indirect contact
transmitted via hand, equipment, furniture etc.
By what route is tetanus transmitted and what organism is it caused by?
Transmitted via injuries
Caused by clostridium tetani
Bacterium present in soil, contaminates wounds
Releases a toxin causing muscle spasm (hence lock jaw)
Prevented by vaccination
What commonly known infection is an exogenous infection transmitted by bites?
Malaria
What commonly known exogenous infection is airborne?
Influenza virus, coughing and sneezing, droplets formed containing infectious viruses are inhaled by others
What is the route of transmission of the Hep B virus and what does it cause?
Exogenous - blood borne
Chronic liver infection, causing various degrees of liver damage as it replicates in the liver some viruses spill into blood (and other bodily fluids)
Transmission by blood exposure (transfusion, sharing of needles, tattoos and body piercing)
What is the route of transmission of chlamydia?
Exogenous - sexual transmission
At what point can the vertically transmitted diseases rubella, herpes and HIV be transmitted?
Rubella - during pregnancy
At time of birth - herpes
Breast milk - HIV
What is meant by perinatal vertical transmission?
Through placenta
What are the 2 steps in staphylococcus soft tissue infection?
1) Colonisation of skin - joins skin flora
2) Penetration of skin - spreads and damages
What is an infectious dose?
Minimum number of organisms required to produce a disease, differs between pathogens eg. salmonella has a low infectious dose
Which cells does the ebola virus infect?
Macrophages and dendritic cells
What are virulence factors?
Virulence factors allow invasion of host tissues, streptolysin O lyses cells ‘cytolysin’
produced by certain streptococci (group A)
How does the cholera toxin work?
Cholera toxin enters gut lumen
Activates adenylate cyclase increasing cAMP
Reduces Na+ absorption, increases Cl- secretion
Water and other electrolytes drawn into the bowel = diarrhoea
How is dengue fever transmitted and what are the symptoms?
Virus transmitted by the Aedes mosquito
Get fever, rash and muscle pain, severe form: bleeding, shock and multi organ failure
Aedes mosquito only found in certain areas (south america and parts of Africa)
What are the barriers to infection?
1) Skin and mucous membranes
2) Stomach acid
3) Native bacteria
4) Immune system
How can genetics affect the chances of infection?
Inherited immunodeficiency
But genetic defects can protect against infection eg. heterozygotes in sickle cells disease are protected against malaria
What organism transmits dengue fever?
Aedes mosquito
What do you catch campylobactor from?
Poorly cooked chicken
