Chapter 4 Flashcards
What receptor molecules does HIV need for attachment?
CD4 and CCR5
What receptor molecule does EBV need for attachment?
C3d
How does the skin stop entry by pathogens?
pH 5.5 (too acidic)
Fatty acids, sebaceous gland secretions and compounds secreted by natural flora
Constant shedding
How can pathogens gain entry via the skin?
Wounds/burns or other openings in the skin
Growth exceeds the rate of shedding of keratinous product
How does the conjunctiva stop entry by pathogens?
Eyelashes
The flushing action, IgA, lactoferrin and lysozyme of tears.
How can pathogens gain entry via conjunctiva?
Damage to the conjunctiva or eyelid.
Contaminated fingers, towels, etc. (herpes)
What does lysozyme cleave?
NAM-NAG linkages
How does the respiratory tract stop entry by pathogens?
Entrapment in mucus, carried up throat via ciliary escalator and alveolar macrophages.
How can organisms avoid cleansing by the respiratory tract?
Attach via adhesins to specific cell-receptors on epithelial cells
Inhibit ciliary action via toxin (Bordetella pertussis-whopping cough)
How can organisms avoid destruction by alveolar macrophages?
Myobacterium tuberculosis can survive in macrophages.
How can the oropharynx stop entry by pathogens?
Flushing action, activities of tongue, lips and cheeks, IgA, lysozyme and antimicrobial activities of leukocytes in saliva and mucosal surfaces.
How can pathogens gain entry via the oropharynx?
Attachment to the mucosa and/or tooth surfaces.
When there is decreased resistance to infection (gum infection due to vitamin C deficiency, Candida-thrush due to change in microflora because of antibiotics)
Dehydration
How can the GI tract stop entry by pathogens?
Peristalsis, mucus, acids, enzymes, IgA and bile
How can pathogens gain entry via the GI tract?
Flagella or other method of movement to propel through mucous (E. coli, V. cholera)
V. cholera produces mucinase
E. coli pumps out bile salts
H. Pylori produces urease which produces ammonia to neutralize, degrades mucous layer and exposes host cells to acid.
How does the vagina stop entry by pathogens?
Lactobaciili that produces lactic acid from glycogen to lower pH (5.0)
How can pathogens gain entry via the vagina?
Introduction of contaminated foreign object (penis), attachment, minute local injuries, estrogen imbalance
How does the bladder and urethra stop entry by pathogens?
Flushing action of the urine and the IgA in the mucosal layer of bladder, sterile urine
How can pathogens gain entry via the bladder and urethra?
Avoid flushing by urine via attachment by gonocooci or pili (gnorrhea) and forces host cell to take it inside (parasite-directed endocytosis)
Which gender is more likely to get a UTI?
Females, due to their short urethra
How does foreskin affect infections?
If you have foreskin, you are more prone to STI’s and HIV due to the moist area where they can live longer.
What is transmission?
When a pathogen is successful in gaining entry into the body.
What are some factors affecting transmission?
Numbers shed (coughing, sneezing, diarrhea)
Stability in environment (can survive outside of body, avoid desiccation, thermal inactivation)
Efficiency of infection (takes 10 shigella to infect, 10000 to infect salmonella)
Route of infection (1 rhinovirus in nasal cavity causes cold, 200 in pharynx)
What are the types of transmission between humans?
Respiratory or salivary spread (not readily controllable)
Fecal-oral spread (controllable by public health meaures)
Venereal spread (sexual-difficult to control due to social factors)
Vector (biting arthopod-malaria, typhus)
Vertebrae reservoir (rabies)
Vector-vertebrae reservoir (vector bites vertebrae who passes it to human-plague, yellow fever)
How do receptor molecules determine?
Microbial tropism and the distinctive patterns of infection
Cell susceptibility
How do keratinocytes of the skin protect? From what?
They form certain peptides locally and protect against invasion by group A streptococci.
How are pathogens transmitted via the respiratory tract?
Nasal secretions, coughing, sneezing
Also via the secretions on tissues, hands and other surfaces
What microbes can traverse the unbroken skin by their own activity?
Leptospira and the larvae of Ancylostoma and Schistosoma
How do biting arthropods transmit disease?
The pathogen will appear in the saliva or feces and will be transmitted during a blood feed.
How is rickettsia rickettsii transmitted?
It is present in the feces of the human body louse, which defecates when it feeds.
When the host scratches the affected area, it is introduced.
What does the outcome of transmission via sneezing depend upon?
The size of droplets.
Large droplets will settle easily. Droplets >10 microm will get stuck in the nasal mucosa. Very small droplets will stay suspended in the air indefinitely (can reach the lower respiratory tract)
How are pathogens transmitted via the GI tract?
Fecal matter back to mouth (diarrhea)
Used to be due to inadequate sewage disposal, contaminated drinking water (cholera, typhoid)
Now spread by food and fingers.
How are pathogens transmitted via the urogenital tract?
Through mucosal contact
Discharge (gonococci, chlamydia)
Mucosal sores (herpes simplex virus, HPV)
Semen (HBV, HIV)
Perinatal (newborn child) from the birth canal (opthalmia neonatorum, pneumonia, bacterial meningitis)
Where did the first immunologic study occur?
In London, England during a cholera outbreak
How does the presentation of gonorrhea differ between genders?
Asymptomatic in females
Discharge in males
How are pathogens transmitted by the oropharynx?
By saliva through kissing and contamination of fingers and objects with saliva
Paramyxovirus, HSV, HHV-6
How are pathogens transmitted by the skin?
Direct contact and shedding of the skin (dermatophytes-ringworm)
How are pathogens transmitted through milk?
Human milk (rare) by breast feeding, HIV, CMV, HTLV-1 Animal milk
How are pathogens transmitted through blood?
Blood sucking arthropods (malaria, west nile)
Needles and transfusion (Hepatitis B and C, HIV)
What can be transmitted by tissue transplant?
West Nile virus
What are some ways that certain microoganisms have developed to resist drying outside of the body?
Clostridial spores, amoebic cysts
More stable when dehydrated
What is vertical transmission?
When transmission occurs directly from parents to offspring (sperm, ovum, placenta, milk, blood)
What is horizontal transmission?
Individuals infecting other individuals by contact, respiratory or fecal-oral spread. Same generation, harder to control.
How are pathogens transmitted by animals?
From arthropods/invertebrate vectors (blood sucking ticks, insects, mites)
Direct from vertebrates (zoonoses) from direct contact, bites, scratches, contaminated water/food
Eating/drinking infected animal products
What types of animals act as intermediate hosts in transmission?
Shellfish (food poisoning, acute gastroenteritis)
Snails (schistosomes-blood flukes)
What kind of infections can we get from contact with domestic pets?
Salmonella from reptile droppings
Viruses from exotic birds and mammals
Toxocariasis from dogs
Toxoplasmosis from cats (can cross placenta)
How can people get animal transmitted diseases from their occupation?
Butchers, who are in contact with raw meat can get toxoplasmosis, Q-fever, MRSA
Farmers, who are in contact with domestic livestock can get brucellosis, cutaneous anthrax
What is a surface infection?
Multiply in epithelial cells at the site of entry and don’t penetrate deeper tissues
Can spread to other areas due to fluid flow (coughing, sneezing, mucous flow)
Large area of body may be covered
Innate immune system is involved
What is a systemic infection?
Shed via the blood/lymph
Migrates from surface to the deeper tissue
The longer they are around, the bigger the immune response
Ex: Meningococci from nasal mucosa to meninges
How does site of budding affect the location of infection?
The influenza is liberated by budding from the external surface of the lung epithelial cells as opposed to the basal layer where it could spread deeper into the tissues
Which pathogens are temperature sensitive?
Rhinovirus stays in the upper respiratory tract (cooler) than lower respiratory tract (warmer) Myobacterium leprae (only found on nasal mucosa, skin, superficial nerves)
How does systemic spread affect the location of infection? Example?
Some organisms are obliged to spread systemically because they fail to spread and multiply at the site of primary infection. Measles infect in respiratory tract but replicate on skin.
Typhoid infects GI tract
Mumps, respiratory canal to salivary glands
What is the stepwise invasion during systemic infections?
Pathogens may or may not divide at the site of infection, then get access to the secondary site (bone marrow, muscle) through circulatory system for more replication and then move to the place where it presents itself.
How is the spread of an infection to the blood and lymph stopped?
Antimicrobial compounds (complement, antibody), local macrophages, phagocytes and physical barriers
What are transient bacteraemia?
Bacteria that are common in normal individuals (after defecation or tooth brushing) that are spread from the blood but are usually filtered out and destroyed in macrophages lining the the liver and spleen.
Can localize the less well defended areas though.
What is an example of a less well defended site in the human body?
Congenital abnormal heart valves can be infected by viridans streptococci to cause infective endocarditis
What happens if a pathogen is free in the blood?
It will encounter antibodies and phagocytes, unless it is associated with circulating cells in the bloodstream.
Ex: Listeria, EBV, Rubella hide in lymphocytes and monocytes
Why does each circulating microorganism invade a characteristic organism?
Specific tissue receptors for certain microbes
Only some organs are suitable for their replication
Areas with local inflammation become sticky with slower flow so it may trap microbes.
What viruses can spread from peripheral nerves to the CNS?
Rabies, HSV, VZV
How do viruses spread via the nerves?
Will travel in axons to the CNS to hide and then come back down peripheral nerves during recurrent outbreaks
Host defences cannot control
How do viruses spread in the cerebral spinal fluid?
Most immune cells cannot cross the blood brain barrier so when a virus manages to cross it there is nothing to stop it.
How do viruses spread in the pleural and peritoneal cavities?
Microbes can easily spread from one visceral organ to another this way
Injury or disease in an abdominal organ provides a source of infection for peritonitis.
Chest wounds or lung infections for pleurisy
What does narrow vs. broad host range of a pathogen mean?
A narrow host range pathogen will only infect humans or those closely related to humans (measles, HIV, meningitis)
A broad host range pathogen will infect many different species (anthrax, rabies)
What are some genetic determinants of susceptibility?
Heterozogyte sickle cell anemia (RBCs are sickle shaped) for malaria in humans
What is the equation for infection?
Infection=(# of organisms)(virulence)/host resistance
What is virulence?
How well the pathogen can get into the host
What is virulence determined by?
Adhesion, Cell penetration, Toxin production, Interaction with immune system and Attenuation
What is ID50?
The number of pathogens that when injected into experimental animals will cause infection in 50% of the injected
