Infectious Disease: Airborne Pathogens

Question 1

Which of the following sites would be colonised in a normal healthy person?

• Blood
• Intestinal tract
• Lymph
• Nervous system
• oral cavity
• respiratory tract
• urogenital tract

Answer 1

• intestinal tract
• oral cavity
• respiratory tract
• urogenital tract

Question 2

What are the two main locations of bacterial infection?

Answer 2

1. Mucosal infections : colonisation of mucosal surfaces, requires adhesions, respiratory tract/gut
2. Invasion: requires colonisation, mucosal barrier breached, access to sub mucosal tissue and blood stream

Question 3

Explain airborne transmission.

- wtr to the kind of bacteria that participant in this

Answer 3

• many respiratory pathogens: often gram + bacteria, resistant to drying, also viruses, human often sole reservoir

Question 4

What are the virulence factors.

Answer 4

• factors that allow the organism to cause disease
  1. colonisation of the niche
  2. avoidance of the immune response
  3. acquisition of nutrients
  4. damage to the host
  5. dispersal

Question 5

Lets talk about Streptococcus pneumoniae.

Answer 5

• gram + diplocococcus
• found in nasopharynx of 20-40% of children
• most common causes of:
• bacterial meningitis
• problem in young and old
• community acquired pneumonia
• bacteraemia
• otitis media (ear infection )

Question 6

Streptococcus pneumoniae:

- capsule and toxins?

Answer 6

• capsule : resist phagocytosis
• toxins: pneumolysin and autolysin A
  L> pore forming toxins

Question 7

Meningitis - describe it.

Answer 7

• inflammation of the meninges, protective membranes of the CNS
• may resolve on its own(viral meningitis)
• may be life threatening: increased pressure on brain stem, neurological damage, apnoea (stop breathing) and death

Question 8

What are the symptoms of Meningitis ?

Answer 8

• 87% start with a headache
• the classic triad of diagnostic signs ( stiff neck, fever, altered menta status)
• other signs:
• sensitivity to light/sound
• irritability and delirium
• seizures
• rash in meningococcal meningitis

Question 9

NHS bacteria associated with meningitis???????

Answer 9

• Neisseria meningitidis (meningococcus)
  L> children and young adults
  L> always penicillin sensitive
• Haemophilis influenzae
  L> young children
  L> often B lactamase positive (resistant to penicillin)
  -Streptococcus pneumoniae (young and old, sometimes penicillin resistant, person to person spread is RARE)

Question 10

Meningitis:

- Neisseria meningitidis?

Answer 10

• usually airborne
• attaches to cells of the nasopharynx
• invasive: accesses the blood stream (bacteriemia, respiratory tract infection, meningitis)

Question 11

Meningitis:

- Neisseria meningitidis virulence factors.

Answer 11

• polysaccharid capsule
  (protects against phagocytosis, serum resistance)
• Lipopolysaccharide (endotoxin)
  L> serum resistance (innate immune system)
  L> release of LPS causes toxic shock
  -Adhesins: pili and opa proteins, attachment to nasopharynx

Question 12

Explain the treatment plan of meningitis.

Answer 12

• treat first, diagnose later
  L> give dose of benzylpenicillin immediately if meningooccal infection suspected
• a broad spectrum cephalosporin is usually given as empirical treatment of bacterial meningitis until the pathogen has been isolated and sensitivities are known
  L> then rationalised to as cheap and narrow spectrum an agent as possible
• chemoprophylaxis given to kissing contacts of meningococcal infection

Question 13

Give the stats of tuberculosis and what causes it.

Answer 13

• in 2007 approx 13.7 million chronic active cases, 9.3 million new cases and 1.8 million death
• 1/2 million new cases of multidrug resistant TB
• infection usually of the lungs
  L> can affect other organs
  L> caused by Mycobacterium tuberculosis
• most infections asymptomatic or latent
  L> approx 10% lead to active disease

Question 14

Actinobacteria: Mycobacterium :

- describe their characteristics

Answer 14

• rod shaped organisms, can be somewhat pleomorphic
• obligate aerobe
• facultative intracellular parasite (can live within macrophages)
• complex cell wall
• Mycobacterium tuberculosis
  L> causes TB
  L> some species grow very slowly (gen time of 15-20h)

Question 15

Describe the mycobacterial cell wall.

Answer 15

• plasma membrane
• peptidoglycan
• arabinogalactan
• Mycolic acids
• gram positive (although it doesnt stain as one)

Question 16

Describe the pathology of TB.

Answer 16

• usually infects the lungs
• cough with haemoptysis, plus quartet of fever, malaise, night sweats, weight loss
• if untreated it is often fatal

Question 17

Describe the disease course of TB.

Answer 17

• primary infection
• asymptomatic or non-specific symptoms:
  L> fever, malaise, weight loss, night sweats
• inhalation of droplets contaiing M.tb
  L> leading to lung infection
  L> delayed hypersensitivity rxn
  L> formation of tubercles (aggregates of macrophage)
  L> M. tuberculosis can grow in macrophage
• can progress to acute infection
  L> extensive destruction of lung tissue
• infection can reactivate : immune suppression (HIV)

Question 18

What are the virulence factors of Mycobacterium tuberculosis?

Answer 18

• thick complex lipid-rich cell walls (acid-fast bacilli, grows very slowly, causes chronic infections)
• intra-cellular pathogen (thrives inside macrphages, forming granulomas, antibodies have no effect, cell-mediated immune response needed for protection, controls vesicular trafficking in mammalian cells)

Question 19

Describe the treatment of TB.

Answer 19

• multi-drug regimens used (prevent the emergence of resistance during therapy and more effective)
• drugs specific to TB: ethambutol, isoniazid, pyrazinamide, rifampicin, streptomycin
• drug regime: initial phase- three drugs for two months. Continuation phase - 2 drugs for 4 months

Question 20

Explain viruses wrt respiratory tract infections.

Answer 20

• very common cause of respiratory infection
• usually acute self limiting infections
• cold
  L> short duration, mild symptoms
• influenza: outbreaks occur annually, epidemics and pandemics occur periodically
• common childhood infections: measles, mumps, rubella and chickenpox

Question 21

Explain symptoms, complications and acute resolving infections for Measles.

Answer 21

• acute, resolving infections: highly infections, can cause epidemics, paramyxovirus (encode a haemagglutinin), negative strand RNA virus
• symptoms: nasal, discharge, redness of eyes, cough, fever, cough and fever intensify and rash appears
• complications: inner ear infection, pneumonia, measles encephalomyelitis

Question 22

Describe the measles virus.
L> envelope
L>importance in virulence

Answer 22

• glycoproteins in envelope: haemagglutinin (H) and fusion (F) proteins
• important in virulence: bind to host cell receptors, allow fusion with host cell and viral uptake, vary between measles strains

Question 23

Infection process. Where are microorganisms most commonly found?

Answer 23

• mucous membranes

L> coated with a protective layer of viscous soluble glycoproteins called mucus