Medic_Summaries (IMS) Topic 8
Infection
Parasites in medicine:
- A parasite is an organism that depends on another for survival, to the detriment of the host
- Strictly all infections are parasites
- Traditionally, only HELMINTHS, INSECTS and PROTOZOA considered medical parasites
- Endoparasites:
- Live inside body
- Major cause of illness
- Helminths (worms), Protozoa
- Ectoparasites:
- Live outside body
- Minor symptoms, but can transmit other infections
- Fleas, lice, bed bugs, ticks
Human endoparasites:
- Protozoa:
- Unicellular organisms (too small to see by eye)
- Some have complex lifecycles involving more than one host
Amoebae: eg. Entamoeba histolytica
- Invades large bowel lining
- Causes dysentery (abdominal cramps, bloody diarrhoea)
- Excreted with faeces
- Spread via contaminated food/water
- Risks: poor hygiene/sanitation
Sporozoa: eg. Plasmodium falciparum (malaria)
- Lifecycle in both humans and mosquitoes
- Infects red blood cells and liver
- Symptoms: fever, headache, joint pains
- Complications: kidney failure, coma, death
- Risk: geographical
- Helminths (worms):
- Complex organisms
- Some have complex lifecycles with more than one host
- Other species have own helminths that can accidentally cause human disease
Cestodes: eg. Taenia saginata (beef tapeworm)
- Segmented, flat
- Intestinal parasite of human (obligatory host)
- Largely asymptomatic (abdominal pain, malnutrition)
- Diagnosis: stool microscopy for eggs
- Cattle are intermediate hosts
Trematodes: eg. Schistosoma haematobium (bilharzia) (flukes)
- Unsegmented, flat
- Human host (infection of veins around bladder)
- Causes bladder inflammation, bleeding into urine (haematuria)
- Intermediate host (freshwater snails)
- Diagnosis: urine microscopy for eggs
Nematodes: eg. round worms
- Cylindrical
- Have digestive tract, lips, teeth and anus
1 Adapted from Lectures at the University of Leeds Medical School
, Medic_Summaries (IMS) Topic 8
Human ectoparasites:
- Bedbugs:
Bedbug: eg. Cimex lactularius
- Wingless insect
- Worldwide infestation of human dwellings
- Hide in cracks in furniture and walls
- Emerge at night to feed (five to ten minutes for a blood meal)
- Itchy rash after bite
- Can transmit other infections
Fungal infections:
- Two main forms:
- Yeasts: single cell that buds
- Moulds: filamentous strands
- Some can switch between the two (diamorphic fungi)
Superficial fungal infections:
- Skin/related structures:
- Tinea pedis (athlete’s foot)
- Tinea corporis (ringworm)
- Usually due to three common species of mould
Severe invasive fungal infections: eg. Cryptococcus neoformans (yeast)
- Infects patients with low resistance due to failing immune system (HIV)
- Causes meningitis (inflammation of membranes lining brain)
- Also causes headaches, neck stiffness, confusions, coma, death
Bacteria:
- Unicellular organisms (prokaryotes)
- Cell membrane
- Cell wall
- No nucleus (genetic material in form of DNA)
- Reproduce asexually
- Move using flagellae and pili
Medical importance of bacteria:
- Responsible for commonest severe infections in developed countries:
- Pneumonia
- UTIs
- Meningitis
- Cellulitis
- Cholecystitis
- Diverticulitis
- Appendicitis
Basic medical classification of bacteria:
- Shape: round (coccus); rod (bacillus)
- Grouping: clusters, chains, pairs
- Gram stain:
- Bacterial cell walls vary in composition
- Some resin crystal violet stain, others do not
- Gram-positive: PURPLE
- Gram-negative: PINK
Clinical importance of classification of bacteria by appearance:
- Allows you to predict which antibiotics will be effective quickly
- Tells you what antibiotics to prescribe
2 Adapted from Lectures at the University of Leeds Medical School
Infection
Parasites in medicine:
- A parasite is an organism that depends on another for survival, to the detriment of the host
- Strictly all infections are parasites
- Traditionally, only HELMINTHS, INSECTS and PROTOZOA considered medical parasites
- Endoparasites:
- Live inside body
- Major cause of illness
- Helminths (worms), Protozoa
- Ectoparasites:
- Live outside body
- Minor symptoms, but can transmit other infections
- Fleas, lice, bed bugs, ticks
Human endoparasites:
- Protozoa:
- Unicellular organisms (too small to see by eye)
- Some have complex lifecycles involving more than one host
Amoebae: eg. Entamoeba histolytica
- Invades large bowel lining
- Causes dysentery (abdominal cramps, bloody diarrhoea)
- Excreted with faeces
- Spread via contaminated food/water
- Risks: poor hygiene/sanitation
Sporozoa: eg. Plasmodium falciparum (malaria)
- Lifecycle in both humans and mosquitoes
- Infects red blood cells and liver
- Symptoms: fever, headache, joint pains
- Complications: kidney failure, coma, death
- Risk: geographical
- Helminths (worms):
- Complex organisms
- Some have complex lifecycles with more than one host
- Other species have own helminths that can accidentally cause human disease
Cestodes: eg. Taenia saginata (beef tapeworm)
- Segmented, flat
- Intestinal parasite of human (obligatory host)
- Largely asymptomatic (abdominal pain, malnutrition)
- Diagnosis: stool microscopy for eggs
- Cattle are intermediate hosts
Trematodes: eg. Schistosoma haematobium (bilharzia) (flukes)
- Unsegmented, flat
- Human host (infection of veins around bladder)
- Causes bladder inflammation, bleeding into urine (haematuria)
- Intermediate host (freshwater snails)
- Diagnosis: urine microscopy for eggs
Nematodes: eg. round worms
- Cylindrical
- Have digestive tract, lips, teeth and anus
1 Adapted from Lectures at the University of Leeds Medical School
, Medic_Summaries (IMS) Topic 8
Human ectoparasites:
- Bedbugs:
Bedbug: eg. Cimex lactularius
- Wingless insect
- Worldwide infestation of human dwellings
- Hide in cracks in furniture and walls
- Emerge at night to feed (five to ten minutes for a blood meal)
- Itchy rash after bite
- Can transmit other infections
Fungal infections:
- Two main forms:
- Yeasts: single cell that buds
- Moulds: filamentous strands
- Some can switch between the two (diamorphic fungi)
Superficial fungal infections:
- Skin/related structures:
- Tinea pedis (athlete’s foot)
- Tinea corporis (ringworm)
- Usually due to three common species of mould
Severe invasive fungal infections: eg. Cryptococcus neoformans (yeast)
- Infects patients with low resistance due to failing immune system (HIV)
- Causes meningitis (inflammation of membranes lining brain)
- Also causes headaches, neck stiffness, confusions, coma, death
Bacteria:
- Unicellular organisms (prokaryotes)
- Cell membrane
- Cell wall
- No nucleus (genetic material in form of DNA)
- Reproduce asexually
- Move using flagellae and pili
Medical importance of bacteria:
- Responsible for commonest severe infections in developed countries:
- Pneumonia
- UTIs
- Meningitis
- Cellulitis
- Cholecystitis
- Diverticulitis
- Appendicitis
Basic medical classification of bacteria:
- Shape: round (coccus); rod (bacillus)
- Grouping: clusters, chains, pairs
- Gram stain:
- Bacterial cell walls vary in composition
- Some resin crystal violet stain, others do not
- Gram-positive: PURPLE
- Gram-negative: PINK
Clinical importance of classification of bacteria by appearance:
- Allows you to predict which antibiotics will be effective quickly
- Tells you what antibiotics to prescribe
2 Adapted from Lectures at the University of Leeds Medical School
