Lecture 28 - What causes infection

Question 1

Causes of infection

Answer 1

helminths - tapeworm
insects - fleas
protozoa - malaria
fungi - candida
bacteria - staphylococci
viruses - influenza
prions - kuru

Question 2

What is a parasite

Answer 2

an organism which depends on another for its survival tot e detriment of its host

Question 3

all infections are

Answer 3

parasites

Question 4

traditionally which are considered medical parasites

Answer 4

helminths, insects and protozoa

Question 5

What are the 2 types of medical parasites

Answer 5

edoparasites - live inside the body - major cause of illness
- helminthes and protozoa
Ectoparasites
- live outside body - minor symptoms, transmit other infections
- fleas, lice, bed bugs, ticks

Question 6

Endoparasites

Answer 6

protozoa

• unicellular organisms
• have some complex lifecycles involving more than 1 host

helminths

Question 7

protozoa (amoebae)

Answer 7

example: entamoeba 
histolytica 
invades large bowel lining
causes dystentery
-abdominal cramps
-blood diarrhoea
-excreted with faeces
-spread with contaminated water
risks: poor hygiene/sanitation

Question 8

Protozoa - sporozoa

Answer 8

Eg. Plasmodium falciparum (malaria)

• lifescycle in both humans and mosquitoes
• infects RBC’s and liver
• symptoms: fever, headache, joint pains
• complications include: kidney failure, coma and death
• risk: geographical

Question 9

Life cycle of malaria

Answer 9

gametocyte - sporozite - liver stages - merozite - trophozite and schizont

Question 10

Helminths (worms)

Answer 10

complex organisms

• some have complex life cycles with more than one host
• other species have their own helminths which can accidentally cause human disease

Question 11

Examples of helminths -worms

Answer 11

cestodes - tapeworms
-segmented, flat
trematodes - flukes
-unsegmented, flat
nematodes - round worms 
-cylindrical, have digestive tract with lips, teeth and anus

Question 12

cestodes

Answer 12

eg. taenia sanginata - beef tapeworm
- intestinal parasite of human obligatory host
-largely asymptomatic
-abdominal pain and malnutrition
diagnosis
-patient
-stool microscopy for eggs
-cattle are intermediate hosts

Question 13

What is the lifecycle of a cestode

Answer 13

-eggs passed into faeces
cattle become infected by -ingesting vegetation
-oncospheres hatch penetrate intestinal wall and circulate to musculature
oncopheres develop into cysticerci in muscle
- humans infected by ingesting raw or undercooked infected meat
- scolex attaches to intestine
-adults in small intestine

Question 14

Trematodes - flukes

Answer 14

example: schistosoma haematobium
Human host: infection of veins around bladder
causes bladder inflammation, bleeding into urine
-intermediate host freshwater snail
diagnosis: urine microscopy for eggs

Question 15

Life cycle of schistosoma spp

Answer 15

eggs passed in urine of faeces into fresh water
miracadium hatches from egg, infects, first intermediate host (snail)
cercariae leave snail penetrate skin wall
immature worm enters the blood stream and eventually ends up in veins near the intestine or bladder
worms reach sexual maturity in veins of abdominal cavity.
females produce eggs, eggs enter intestinal tract or bladder

Question 16

Ectoparasite - bedbug

Answer 16

example: cimex lectularius
wingless insect
worldwide infestation of human dwellings
-hide in cracks in furniture and walls
- emerge at night to feed - 5-10 minutes for a blood meal
-ithcy rash after bite 
can transmit other infections 
-protozoa in south america

Question 17

forms of Fungal infections

Answer 17

2 main forms - yeasts - single cells which bud
moulds - filamentous strands
- some can switch between yeast and mould

Question 18

Superficial fungal infections

Answer 18

skin and related structures

• tinea pedis (athletes foot)
• tinea corpis (ringworm)
• usually due to 3 common species of mould

Question 19

Sever invasive fungal infections

Answer 19

example: cryptococcus neoformans (yeast)
-infectious patients with low resistance due to failing immune system - HIV
Causes meningitis -
headache, neck stiffness, confusion, coma and death

Question 20

features of Bacteria

Answer 20

unicellular (prokaryotes)
cell membrane and wall
no nucleus
genetic material in form of DNA
reproduce sexually
move using flagellae and pili

Question 21

grouping of bacteria

Answer 21

shape - round (coccus), rod (bacillus)

grouping - clusters, chains or pairs

Question 22

Medical classification of bacteria

Answer 22

gram stain

• cell walls vary in composition
• some retain crystal violet stain, others do no
• gram -+ve - purple
• -ve pink

Question 23

What is the clinical importance of classification by appearance on shape grouping and gram stain

Answer 23

allows you to predict which antibiotics will be effective quickly
-which ones to prescribe

Question 24

Bacterial infection - eg. streptococcus pneumococcus

Answer 24

Gram - positive cocci, (diplococci)

• colonise nose and throat
• invade other sites eg. lungs causing pneumonia
• cough, dirty sputum, chest pain breathless, fever
• complications: blood stream, infection, meningitis, death

Question 25

Viruses

Answer 25

depend on infection and host cell for metabolism and replication -contain protein core surrounding genetic material, protein coat outer membrane very small : 1/100th size of bacteria -can only be seen with powerful electron microscopes

Question 26

Lifecycle of a virus

Answer 26

HIV ( GP120) binds to cell through CD4 receptors | - reverse transcription occurs, integrase allows it to integrate with cell - protease leaves cell

Question 27

eg of Common viral infections

Answer 27

rhinovirus

Question 28

sever viral infections

Answer 28

HIV

Question 29

Acute life threatening viral disease

Answer 29

ebola - viral haemorrhagic disease

Question 30

Examples of short terms and long term viral infections

Answer 30

acute: norovirus - causing diarrhoea and vomitting (gastroenteritis) chronic: hep C virus causes liver inflammation for years Latent infection - herpes virus can be dormant for decades before reactivating to cause disease

Question 31

Viruses that cause latent infection

Answer 31

varicella zoster virus - primary infection causes chickenpox - characteristic rash and fever - virus becomes dormant in sensory nerve roots - reactivates years later as shingles - same rasg - confined to dermatome

Question 32

What happens in glandular fever and what is it caused by | what can it contribute to

Answer 32

Epstein-Barr virus - usually causes mild illness -infects immune system cells (B cells) and epithelial cells of nose and mouth (nasopharynx) - very common - 90% -causes latent lifelong infection contributes to certain cancers in southern china lymphoma in HIV infection

Question 33

Prions

Answer 33

``` smallest infective agents known proteinaceous infectious particles proteins are abnormal and lack nucleic acid, not a living organism accumulate main in neural tissue -difficult to destroy - standard sterilisation doesnt work ```

Question 34

CJD = Creutzfeldt–Jakob disease

Answer 34

prion diease rare fatal, degenerative neurological disease transmitted via human growth hormone, surgical instruments and corneal grafts

Question 35

Variant CJD

Answer 35

typically occurs in young adults | Thought to be derived form bovine spongiform encephalopathy (BSE or mad cow disease)

Question 36

Kuru

Answer 36

similar to vCJD occurred in Papua New Guinea in 1950s spread by cannibalism especially brains of deceased relatives