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Mechanisms of Microbial Diseases > Upper Respiratory Tract Infections > Flashcards

Upper Respiratory Tract Infections Flashcards

1
Q

What are the two most common causes of death related to respiratory diseases in Canada?

A

Chronic lower respiratory diseases (TB, cystic fibrosis, COPD, etc.)
Influenza and pneumonia

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2
Q

Why are respiratory tract infections so common?

A

They are easily spread (the respiratory tract is open)

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3
Q

What makes up the upper respiratory tract?

A

Epiglottis
Larynx
Nasal cavity
Pharynx

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4
Q

What makes up the lower respiratory tract?

A

Trachea
Bronchi
Bronchioles

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5
Q

What are two types of respiratory tract infections?

A

Those that are restricted to the surface (common cold, influenza, etc)
Those that spread through the body (measles, mumps and rubella)

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6
Q

What are different types of respiratory invaders?

A 
Professional invaders (infect healthy respiratory tract)
Secondary invaders (infect when host defences are impaired)
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7
Q

What are the requirements of professional invaders to cause infection?

A

Adhesion to normal mucosa (in spite of mucocilliary system)
Ability to interfere with cilia
Ability to resist destruction in alveolar macrophage (e.g., TB)
Ability to damage local (mucosal, submucosal) tissues

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8
Q

What are the requirements of secondary invaders to cause infection?

A

Initial infection and damage by respiratory virus (e.g., influenza virus)
Local defences impaired (e.g., cystic fibrosis)
Chronic bronchitis, local foreign body or tumour
Depressed immune responses (e.g., AIDS, neoplastic disease)
Depressed resistance (e.g., elderly alcoholism, renal or hepatic disease)

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9
Q

What is rhinitis?

A

Also known as the common cold
It is caused by different types of viruses
Over 50% of cases are due to rhinovirus and coronaviruses
It induces a flow of virus-rich fluid (rhinorrhea)
It is usually self-limiting
There is no vaccine (there is lots of genetic diversity)

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10
Q

How is rhinitis transmitted?

A

Aerosol

Virus contaminated hands

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11
Q

Describe the pathogenesis or rhinitis

A

Viruses infect the nasal epithelium and replicates.
There is clear fluid outpouring from the lamina propr.
Cell damage allows the infection to spread (viral shedding)
Once the host defences are activating there is recovery

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12
Q

What viruses cause pharyngitis and tonsillitis (70% of the times)

A

Adenovirus
CMV
EBV

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13
Q

What bacteria causes pharyngitis and tonsillitis?

A

Streptococcus pyogenes

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14
Q

What is cytomegalovirus (CMV)?

A

Largest human herpes virus (multinucleated cell formation and/or intranuclear inclusions give cells distinct appearance)
Humans are their natural host

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15
Q

How is cytomegalovirus transmitted?

A

Saliva, urine, blood semen and cervical secretions

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16
Q

Describe cytomegalovirus pathogenesis

A

Initial infection is asymptomatic and the it spreads locally to lymphoid tissue and then systemically to lymph nodes and spleen (via circulation lymphocytes and monocytes)
Virus localizes in epithelial cells in salivary glands (saliva), kidney (urine), cervix (secretions), and testes (semen) - shedding for months

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17
Q

Do specific antibody and cell-mediated immunity clear the CMV?

A

Although they are activated, they do not entirely clear the virus. Infection is eventually controlled by CMI mechanisms however infected cells remain in the body for life and can be a source of reactivation if CMI become impaired

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18
Q

Why is CMV a successful pathogen?

A

It evades the host immune system because it a poor target for cytotoxic T cells; it interferes with the transport of MHC-1 molecules to the cell surface and induces the expression of Fc receptors on cell surface

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19
Q

Describe the illness caused by CMV

A

In infants and children, there is usually no symptoms
In adults it generally only causes mild illness
There is spectrum of symptoms however; in adolescents, it can cause a glandular fever-type illness, causing fever, lethargy, abnormal lymphocytes and mononucleosis

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20
Q

What can happen if there is a primary infection of CMV during pregnancy?

A

It can spread through the placenta to the fetus. There can also be reactivation during pregnancy
CMV is the second most common cause for mental retardation in babies

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21
Q

What is Epstein-Barr Virus (EBV)? What does it cause?

A

It is very similar to herpesvirus
Natural host is humans (species specific) - 95% of adults aged 35-40 are infected (but most of the time we don’t see the disease)
It causes mononucleosis (“kissing disease”)

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22
Q

How is EBV transmitted?

A

Through the exchange of saliva

23
Q

When does infection occur (peak age)?

A

There are two peaks: 1-6 years old and 14-20 years old

24
Q

What are the clinical features of EBV?

A

It is immunologically mediated
Virus replicates in the epithelial cells and B-lymphocytes (attaches to a specific C3d receptor, CD21).
The virus is shed from saliva from infected epithelial cells and spreads to B-lymphocytes in local lymphoid tissues (lymph nodes and spleen)
T-lymphocytes respond to infected B cells, which are now recognized as foreign (civil war in the body)

25
Q

What are the symptoms of EBV infection in infants?

A

We often don’t see clinical disease in infants

26
Q

What are the symptoms of EBV infection in young adults?

A

Infectious mononucleosis/glandular fever in 4-7 weeks after initial infection
Fever, soar throat, petechiae on hard palate (large spots), lymphadenopathy and splenomegaly
Anorexia, lethargy
Hepatitis may occur

27
Q

What causes the symptoms in EBV?

A

Cytokine release
Infected B cells cause polyclonal activation and production of potential autoantibodies (e.g., IgM to erythrocytes, which can lead to anemia)

28
Q

How do patients with EBV recover?

A

Recovery tends to be spontaneous (relax at home for a while)

We don’t prescribe antivirals for immunocompetent patients

29
Q

What is Burkitt’s lymphoma?

A

Restricted to parts of Africa and Papua New Guinea
EBV in the presence of malaria, which acts as a co-carcinogen, weakens T-cell control of EBV infection and possibly causes polyclonal activation of B cells (turns them into cancer cells)

30
Q

What is nasopharyngeal carcinoma?

A

Seen in China and South-East Asia
EBV DNA is detected in tumour cells
It requires a co-carcinogen: nitrosamines (found in preserved fish)

31
Q

What organism is the most common cause of bacterial pharyngitis/tonsillitis?

A

Steptococcus pyogenes

32
Q

What organisms tend to cause pharyngitis/tonsillitis; gram positive or negative? Why?

A

Gram positive because they have peptidoglycan so they don’t clump together as much. Gram negative organisms tend to clump together which makes them easier to get cleansed out

33
Q

What are the symptoms of bacterial pharyngitis causes by Strep. pyogenes?

A 
Sore, red throat
Difficulty swallowing
Sudden fever
Malaise
Loss of appetite
34
Q

Why is it important to treat bacterial pharyngitis causes by Strep. pyogenes with penicillin?

A

Because complications include quincy, scarlet fever and rheumatic fever, rheumatic heart disease, and acute glomerunephritis

35
Q

What is scarlet fever?

A

Characterized by a sandpapery rash
The rash spread to all over the body
The tongue is strawberry red
Headache chills and muscle aches

36
Q

What is rheumatic fever?

A

Fever, joint pain (knees, ankles, elbows, wrists)
Joint swelling
Possible cardiac problems (chest pain, shortness of breath)

37
Q

What is acute glomerunephritis?

A

Antibodies against Strep. pyogens bind with antigens and form immune complexes that circulate and depose in the glomeruli. This causes the activation of complement and coagulation systems (inflammation and blood in urine)
Hypersensitivity type III reaction

38
Q

What is parotitis?

A

Inflammation of the parotid glands (largest of the salivary glands)

39
Q

What causes parotitis?

A

Mumps virus, which is spread through airborne droplets

Close contact is necessary

40
Q

How is mumps treated?

A

There is no real treatment but it is prevented by an attenuated live virus vaccine (MMR vaccine)

41
Q

What are the complications due to mumps?

A

Meningitis
Encephalitis
Pancreatitis
Hearing loss

42
Q

What is otitis media? What causes it?

A

Infection of the middle ear
50% of the time it’s viral
Can be causes by S. pneumoniae and H. influenzae. Also can be caused by S. pyogenes, M. catarrhalis and/or S. aureus

43
Q

In whom do we see otitis media most often?

A

Preschool age patients

44
Q

Describe the clinical manifestations of otitis media

A

Early signs are non localized (fever and irritability)

Ear pain, changes in hearing, purulent discharge (late infection)

45
Q

What are complications due to otitis media?

A

Damage to the tympanic membrane (hearing loss)

46
Q

How is otitis media treated?

A

Empirical therapy

However, because 50% of infections are viral, physicians are advised to not give antibiotics for at least a week

47
Q

Describe the pathogenesis of otitis media

A

The organism causes infection by avoiding the cleansing function of the ciliated epithelial cells

48
Q

What is otitis externa? What causes it? How is it treated?

A

Outer ear infection
Caused by the commensal organisms of our skin (S. aureus, Candida albicans, Pseudomonas aeruginosa)
Treated with antibiotic ear drops

49
Q

What is acute sinusitis? What causes it?

A

Inflammation of the sinuses

The aetiology is similar to otitis media

50
Q

What are the symptoms of sinusitis?

A

Facial pain, local tenderness (pain is often confused with jaw pain)
Purulent nasal discharge (thick fluid)
Fever (50% of patients)
Headache

51
Q

What patients are more likely to develop sinusitis?

A

Patients who have experienced prolonged upper respiratory tract infection

52
Q

What are complications due to sinusitis?

A

Orbital cellulitis
Osteomyelitis
Meningitis
Brain abscess

53
Q

What is epiglottitis?

A

Inflammation of the epiglottis
Considered a true medical emergency because the swelling of the epiglottis can result in total blockage of the airway (patient can die)
Most often caused by H. influenzae (but we don’t know why)

Mechanisms of Microbial Diseases (13 decks)

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