Lecture notes Year 1 MBChB: Introduction to Medical Sciences (IMS)
Lecture notes Year 1 MBChB: Introduction to Medical Sciences (IMS)
Lecture notes Year 1 MBChB: Introduction to Medical Sciences (IMS)
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University of Leeds (UoL)
University of Leeds
Year 1 MBChB: IMS
All documents for this subject (12)
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INFECTION
INTRODUCTION TO INFECTION
Causes of infection Size Parasites in Medicine
Helminths - Tapeworm Parasite: organisms that depends on another for its survival to the
Insects - Fleas detriment to the host
Protozoa – Malaria All infections are parasites
Fungi - Candida Medical parasite: helminths, insects and protozoa
Bacteria - Staphylococci Endoparasites: live inside body; major cause of illness
Viruses - Influenza Ectoparasites: live outside body; minor symptoms but can transmit other
Prions - Kuru infections e.g. fleas, lice, bed bugs, ticks
Human endoparasites
Protozoa Helminths
Unicellular organisms Complex organisms
Some have complex lifecycles involving more than Some have complex lifecycles involving more than one
one host host
Other species have their own Helminths which can
accidently cause human disease
Protozoa
Amoebae Example: Entamoeba histolytica
Invades large bowel lining Worms – Helminths
Causes dysentery Cestodes (tapeworms) –
o Abdominal cramps segmented, flat
o Bloody diarrhoea Trematodes (flukes) –
Excreted with faeces unsegmented, flat
Spread via contaminated food & water Nematodes (round worms) –
Risks: poor hygiene/sanitation cylindrical, have digestive tract with lips,
teeth and anus
Sporozoa Example: Plasmodium falciparum (malaria)
Lifecycle in both humans and mosquitoes
Ringworm – colloquial term
Infects red blood cells and liver
Symptoms: fever, headache, joint pains
Cestodes
Trematodes
– tapeworms
- flukes
Complications: kidney failure, coma, death
Example:
Example: taeniaSchistosoma
saginata (beef
haematobium
tapeworm)(bilharzia)
Risk: geographical
Intestinal
Human parasite
host: infection
of humanof(obligatory
veins around
host)
bladder
Largely
Causes asymptomatic
bladder inflammation, bleeding into urine
o(haematuria)
abdominal pain
oIntermediate host freshwater snail
malnutrition
Diagnosis: urine microscopy for eggs
Diagnosis
o patient
o stool microscopy for eggs
Cattle are intermediate hosts
Ectoparasite – bedbug
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)
Fungal infections
Yeasts – single cells which bud
Moulds – filaments strands
Some can switch between yeast & mould (dimorphic fungi)
, Severe invasive fungal infections
Superficial fungal infections Example: cryptococcus neoformans (yeast)
Tinea pedis – athletes foot Infects patients with low resistance due to failing immune
Tinea corporis – ringworm system e.g. HIV
Usually due to 3 common species of mould Causes meningitis (inflammation of membranes lining brain)
Headache, neck stiffness, confusion, coma, death
Medical importance of bacteria
Bacteria - prokaryotes Responsible for:
Unicellular organisms o Pneumonia
Cell membrane, cell wall o Urinary tract infection
No nucleus – non-linear DNA o Cellulitis - skin
Reproduce asexually o Meningitis
Move using flagellae and pili o Cholecystitis
o Diverticulitis
o Appendicitis
Gram stain
Some retain crystal violet stain, others do not
Gram-positive (purple)
Gram-negative (pink)
Allows you to predict which antibiotics will be effective quickly
Tells you what antibiotic to prescribe
Viruses
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
Virus life cycle – HIV
Turns RNA into cDNA integrates it into our own cell, protease
packages it and send it out of the host cell
Viruses cause a wide spectrum of disease
Some cause trivial infections e.g. rhinovirus – common cold
Some cause severe chronic disease e.g. HIV
Some cause acute life threatening disease e.g. Ebola – viral
haemorrhagic fever
Viruses infect host cells for differing
lengths of time
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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