Entry, Exit and Transmission Flashcards
what is needed for attachment
receptor molecule
CD4 and CCR5 -HIV
C3d -EBV
entry for skin
pH 5.5
fatty acids
sebaceous gland secretions
compounds secreted by natural flora (Cutibacterium and Staphylococcus -> sebaceous areas (face and torso)
corynebacterium, staphylococcus and beta-proteobacteria are found in moist areas (armpits, elbow and knee creases)
entry for conjunctiva (eyes)
eyelashes tears -flushing action -lysozyme -cleaves NAM-NAG linkages IgA lactoferrin
damaged defenses (conjunctiva or eye lid damage) -> non -specialized microbes to cause infection
contaminated fingers, towels etc
ex loa-loa, pseudomonas aeruginosa and S. aureus
resp tract entry
inhaled dust, microbes etc. entrapped in mucus -carried up to throat via ciliary escalator and swallowed
some organisms can avoid cleansing
- attach via adhesins to specific cell-surface receptors on epithelial cells
- inhibit ciliary action e.g. Bordetella pertussis (whooping cough) -release toxin to make rigid
some avoid destruction by alveolar macrophages
- if microbe reaches alveoli typically removed by these cells
- Mycobacterium tuberculosis can survive in macrophages
oropharynx entry
defenses:
flushing action of saliva (1L/day)
chewing and other activities of tongue, lips and cheeks
secretory IgA and IgG
lysozyme
antimicrobial activities of leukocytes in saliva and at mucosal surfaces
Invasion:
invading and resident need to attach to mucosa or tooth surface
decreased resistance to infection
-gum infections (Vit C deficiency)
-Candida (yeast that causes “thrush”) if changes in microflora after antibiotics
Gastrointestinal tract entry
peristalsis -attachment -receptors -Vibrio cholera and rotavirus
counteract mucus, acids, enzymes and bile
Mucus
-barrier, block microial adhesion (microbe specific IgA)
-motile bacteria (E. coli, V. cholera) propel through mucus
V. cholera -mucinase (hydrolyzes mucin, main component of mucus)
how does H. pylori counteract mucus in gastrointestinal tract?
urease production degrades mucus and allows the gastric acid to degrade epithelial cells creating stomach ulcers
Urogenital tract entry
spread is one continuous tract
Vaginal defenses -no cleaning mechanism
-introduced of contaminated foreign object (penis)
lactobacilli colonization (reproductive years 10^8/ml
-glycogen-> lactic acid (pH 3.5-4.5)
invasion
- attachment
- minute local injuries
- impaired defense -estrogen imbalance
Urogenital tract bladder and urethral defences
mechanism of UT invasion
Bladder and urethral defences
flushing action of urine
mucosal layer of bladder -> IgA
Mechanisms of UT invasion via urethra -avoid flushing of urine attachment (gonococci, pili) -> parasite-directed endocytosis intestinal bacteria males urethra 20cm females 5cm longer path for males so less likely for infection foreskin and STIs
successful pathogen ->
transmission
shed from body surfaces or extracted via insects
factors affecting transmission
-numbers in shed -stimulation of coughing, sneezing or diarrhea
-stability in environment -resistance to desiccation and thermal inactivation (spores/cysts)
-efficiency of infection -e.g. shigella (10) and salmonella (1000000) want a lower number
types of transmission between humans
1) respiratory or saliva spread
2) faecal-oral spread
3) sexual spread
4) vectors (mosquitoes) ex malaria, sandfly fever and typhus
5) vertebrate reservoir ex brucellosis, rabies, q fever, lassa fever, Ebola virus, salmonellosis, MERS-CoV
6) vector-vertebrate reservoir ex plague, trypanosomiasis, yellow fever
7) ebola virus -> marburg virus
horizontal transmission
person to person
infected air, water, food, contact vectors etc.
e.g. polio, influenza, typhoid
vertical transmission
parent to offspring
ovum, sperm, placenta, milk contact
e.g. HTLV, HIV, CMV, rubella, Hep B
transmission from resp tract
sneezing facts
droplet?
more common when
other
nasal secretions and coughing
sneezing, 20,000 droplets outcome->size of droplets large droplets settle at 4m trapped in nasal mucosa 10uM suspended in air indefinitely, 1-4 uM can reach the LRT more common in winter other: tissues, hands and surfaces
transmission from gastrointestinal tract
recycling of fecal material back to mouth more common in resource-poor countries
after 19th century, adequate sewage disposal purified water
england -200 years earlier, no flush toilets and sewage disposal so most drinking water was contaminated -cholera and typhoid
same diseases in resource-rich countries but now spread by food and fingers vs water and flies
