14 Entry, exit and transmission Flashcards
Pathogens have specific molecules that help bind to receptor molecules on host cells. Certain cells have certain receptors, which means that they are only susceptible to certain infections
CD4 molecule T cells - HIV
C3d receptor - EBV
Alpha-dystroglycan - M leprae
How does skin protect from infection?
Physical barrier
Dead layer
Fatty acids - pH 5.5
How do conjunctiva prevent infection?
What infections affect eye?
Lacrimal secretion - lysosyme
Blinking
Chlamydia - trachoma
Gonococci
HSV
Respiratory tract inhales 10 000 microbes per day, so needs good defenses.
What are the defenses?
How to microbes evade defenses?
Mucus + ciliary action
Cough
Macrophages
Attach firmly to surface of cell
Inhibit ciliary activity - Pertussis cytotoxin, pollution/ smoke
Ciliary destruction by virus - influenza, measles
Avoid phagocytosis - TB
How do following microbes attach to respiratory tract?
Microbial adhesion molecule/ receptor name
- Influenza A
- Rhinovirus
- Influenza A - haemagluttinin - sialyloigosaccharides
- Rhinovirus - capsid protein - ICAM-1
How do following microbes attach to respiratory tract?
Microbial adhesion molecule/ receptor name
- coxsackie A (common cold/ oropharyngeal vesicles)
- parainfluenza type 1
- RSV
- coxsackie A - capsid protein - ICAM-1 or integrin
- parainfluenza type 1 - envelope protein - sialoglycolipids
- RSV - envelope protein - sialoglycolipids
How do following microbes attach to respiratory tract?
Microbial adhesion molecule/ receptor name
- mycoplasma pneumoniae
- measles virus
- mycoplasma pneumoniae - fuses with cell - neuraminic acid
- measles virus - haemagluttinin - CD46
How do following microbes attach to respiratory tract?
Microbial adhesion molecule/ receptor name
- Haemophilus influenzae, strep pneumoniae, klebsiella pneumoniae
- surface molecule - carbohydrate sequence in glycolipid
Intestinal transit time means that any ingested bacteria, are excreted in faeces. Infecting bacteria must attach to epithelium to prevent this. Some have specific attachments for small or large bowel - which is shown by symptoms they cause
Where and how do these microbes attach to GI tract
- Poliovirus
- Rota virus
- Poliovirus - intestinal epithelium. Binds to Pvr (polio virus receptor)
- Rota virus - intestinal epithelium. Viral capsid VP4 attach to host cell glycans
Where and how do these microbes attach to GI tract
- Vibrio cholera
- Escherichia coli (EPEC and EHEC)
- Vibrio cholera - intestinal epithelium. Multivalent adhesion molecule 7 (MAM7)
- Escherichia coli - intestinal epithelium. Bacteria inject Tir an effector into host membrane, acting as receptor for bacterial surface protein intimin
Where and how do these microbes attach to GI tract
- Salmonella typhi (enteric fever)
- Shigella (dysentery)
- Salmonella typhi (enteric fever). Ileal epithelium. Binds using bacterial adhesins
- Shieglla (dysentery). Colonic epithelium. Surface protein IscA acts as adhesin and interacts with host cells after activating type III secretion system trigerring its uptake into epithelial cells
Where and how do these microbes attach to GI tract
- Giardia lamblia
- Entamoeba histolytica
- Ancylostoma duodenale (hookworm)
- Giardia lamblia. Duodenal/ jejunal epithelium. Binds to mannose-6-phosphate on host cell, in addition to mechanical succker called ventral disc help bind to microvilli
- Entamoeba histolytica. Colonic epihtelium. Lectin on surface of amoeba binds to host cell
- Ancylostoma duodenale. Intestinal epithelium. Binds using large mouth (buccal capsule)
Some GI pathogens do not just attach, but attach and penetrate
Can you name examples?
Trichinella
Trichuris
Echinococcus
Bacteria motility can help them travel through protective mucus, and reach susceptible epithelium
Which bacteria have motility properties?
Vibrio cholerae
E. coli
Mucinase is an enzyme which helps break down mucus barrier.
Which bacteria produce this?
V cholerae
Bacteria generally prefer alkaline environment. But need to evade gastric acid.
Which microbes are resistant to acid?
H Pylori
Mycobacterium tuberculosis - intestinal TB
Enteroviruses - poliovirus, coxsachieviruses, echoviruses
HAV - infects liver, then shed in biliary tract into faeces
What are examples of organisms which can resist bile?
Salmonella Shigella Enteroviruses Enterococcus faecalis E. coli Proteus Pseudomonas
Pathogens which are primarily anaerobic can thrive in GI tract.
What are examples of this?
Bacteroides fragilis
H pylori has special proteins to attach to gastric epithelium. It releases large amounts of urease, which creates a small surrounding area of ammonia in which they can survive. So treatment is antibiotics, as opposed to antacids
What are consequences of H pylori infection?
Gastritis
Gastric ulcers
MALT lymphoma
What lymphoid material is present in GI tract?
Peyer’s patches are localised collections of lymphoid tissues (MALT), lying just below epithelium surface. Contain “M cells” which take up foreign proteins and deliver them to underlying immune cells
Urogenital tract is continuum, so once infected, organism can quickly spread.
What defences does vagina have?
- Has glycogen on epithelium due to oestrogen. Lactobacilli colonise vagina, and metabolise glycogen to lactic acid - making pH about 5.0. Inhibits other bacterial growth except streptococci and diptherioids
- for STI to infect they need to enter via injury to epithelium (genital wars, syphilis) or impaired defences (tampons, oestogren imbalance)
Urinary tract has regular flushing as method of protection.
Exterior infection via urethra is almost always cause of infection.
Why are females at higher risk of UTIs?
14x more common in females
Shorter urethra 5cm (20cm men)
Urethra closer to anus
Sexual intercourse increases risk. Uncircumcised penis harbors bacteria
What are natural defences of oropharnyx
Flushing action of saliva - 1L per day
IgA antibodies
Lysosyme
Normal flora
What factors influence whether pathogen transmission will be successful?
Number of pathogens shed
Pathogens stability in environment - ability to resist drying, temperature etc. Some organisms produce spores (clostridium), or cysts (amoeba)
Number of pathogens required to infect fresh host - efficiency of infection
Ability to aid transmission - e.g causing coughing/ sneezing/ diarrhoea
Once in external environemtn, organisms become dried. Those which are more stable on drying, are able to survive longer, and spread
What are examples of organisms which are more stable on drying?
Spread in air via dust/ dry droplets -
- Tubercle bacilli
- Staphylococci
Spread from soil -
- Clostridial spores
- Anthrax spores
- Histoplasma spores
Spores can survive for years in soil
What are routes human-human transmission of pathogens
Respiratory/ salivary - large droplets/ pathogens can travel 4m. Smaller diameter pathogens can float in air indefinitely, and travel far. Crowded areas such as schools/ nursing homes spread respiratory infections, and meningitis in military recruits.
Faecal-oral
Sexual
Blood
Vertical
Milk
Why are respiratory pathogens more common in winter?
Colder temperature favours certain microbes growth
More close contact between humans
Heating - dry air impairs mucociliary clearance. More humid air favours growth of bacteria such as
STIs require mucosal contact.
What are ways in which microbes make this possible?
Gonocci/ chlamydia - discharge
Treponema pallidum/ HSV - ulcers
Which viruses have been detected in semen, and thought to be responsible for transmission?
HIV
HBV
CMV
Ebola
Apart form organisms which commonly cause UTIs, what microbes are transmitted in urine?
Humans -
Schistosomes
Typhoid - bacteria in bladder scarred by schistosomiasis
Polyomaviruses -
- JC virus PML
- Merkel cell virus - Merkel cell cancer
CMV
Zoonoses -
Leptospirosis - infected rats and dogs excrete
Lassa fever - infected rodent excretes
What are methods of transmission of zoonoses?
Virtually no human-human transmission, except for pneumonic plague and VHF.
Control aimed at controlling vectors/ animal infection
Arthropods - malaria, typhus
Vertebrae reservoir - brucellosis, rabies, Q fever, lassa fever, salmonellosis, ebola, MERS-CoV
Vector-vertebrate reservoir - plague, trypanosomiasis, yelllow fever
What are common organisms transmitted via saliva?
HSV
CMV
EBV
Rabies
Pasteurella - in cats/ dogs, transmit via bites/ scratches
Streptobacillus moniliformis - rat saliva, cause rat bite fever
What bacteria are commonly transmitted via the skin?
Staphylococci - impetigo, boils, neonatal sepsis
Streptococcus pyogenes - impetigo
Treponema pallidum - syphilis
Treponema pertenue - yaws
Dermatophytes are transmitted via skin, and cause ringworm/ fungal infection
What parasites are transmitted by skin?
Which protozoa is transmitted by skin?
Scabies - eggs from burrow transmitted by hand
Leishmania tropica - cutaenous leishmaniasis, skin sores are infectious
Milk is produced by a skin glad.
Which organisms are transmitted in human milk?
CMV
HIV
HTLV
Which organisms are transmitted by animal milk?
Mostly cow milk
All organisms are destroyed by pasteurisation
Brucella (cow/ goat/ sheep)
Mycobacterium bovis
Coxiella burnetii Q fever
Campylobacter jejuni
Salmonella Listeria Staphylococci Streptococcus pyogenes Yersinia enterocolitica
What is pasteurisation?
Process to sterilise milk
Heat treatment process - heating milk to high temperature to denature pathogens, then cooling
UHT (ultra high temperature) milk is treated at higher temperature, and immediately stored in packaging. Can last for months
Which human infections are transmitted via placenta?
T - toxoplasma - stillbirth/ CNS disease
O - other - syphilis, listeria, VZV, parvovirus B19
R- rubella
C - CMV - abortion/ malformation
(H - HSV - not transplacentally, but during delivery)
HIV
HBV - via placenta, but usually from breast milk
What does vertical transmission occur?
Via placenta, milk, or contact at birth
Which perinatal infections occur in neonates, transmitted perinatally during skin contact?
HSV
Gonococcal
Chlamydia
Many diseases are transmitted by arthropods. Once infection established, only ebola and plague are transmitted human- human
What are examples diseases causes by these classes of viruses?
Flaviviruses
Bunyaviruses
Flaviviruses
- yellow fever
- dengue
- zika
- west nile
- japanese encephalitis
Bunyaviruses
- haemorrhagic fevers
Many diseases are transmitted by arthropods.
What are examples diseases causes by these classes of bacteria?
Yersinia
Rickettsias
Spirochaetes
Yersinia
- plague
- tularaemia
Rickettsias
- Q fever
- spotted fevers
- typhus
- rickettsial pox
Spirochaetes
- relapsing fever
- lyme disease
Many diseases are transmitted by arthropods.
What are examples diseases causes by these classes of protozoa?
Trypanosomes
Leishmania
Trypanosomes
- sleeping sickness
- chagas disease
Leishmania
- leishmaniasis
Many diseases are transmitted by arthropods.
What are examples diseases causes by these classes of helminths?
Plasmodium
Nematodes
Plasmodium
- malaria
Nematodes
- lymphatic filariasis
- loiasis
- onchocerciasis
Domesticated animals such as cats and dogs can transmit multiple zooneses.
How can they transmit infection?
Bites/ scratches
Vectors carrying pathogen - ticks/ flies
Direct contact
Faeces
Domesticated animals such as cats and dogs can transmit multiple zooneses.
What are examples of diseases which can be transmitted?
Bites/ scratches
- rabies
- pasteurella
- Bartonella
Vectors carrying pathogen - ticks/ flies
- ticks RMSF
- sandflies leishmaniasis
Direct contact
- dermatophyte fungi
Faeces
- toxocariasis
- toxoplasma
- hydatid
- hookworm
