Session 11 ILOs - Streptococci, Pharyngitis & EBV

Question 1

Highlight a range of virulence factors found in Streptococcus pyogenes

Answer 1

Gram positive cocci, can be classified 2 methods:
1. By haemolysis nature (Lancefield classification)
2. By pus-forming nature (Sherman group)
Viridans steptococci - produces pus
Pyogenic steptococci - doesn’t produce pus

Virulence factors:

• Hyaluronic acid capsule - inhibits phagocytosis by neutrophils or macrophages
• M protein - resists phagocytosis by inhibiting activation of complement pathway
• Adhesins - helps with the first step in infection which is adhesion
• Streptolysins O and S - lysis of RBCs, neutrophils and platelets
• DNAses - degrades DNA

= causes host cellular damage, either directly or as a consequence of the host’s immune system

Question 2

Describe streptococcal pharyngitis including microbiological features, clinical presentation and complications

Answer 2

Streptococcal pharyngitis or ‘strep throat’:

• Peak incidence 5-15 years
• Spread by droplets (overcrowding)

Microbiological features:
- If swabbed, would find group A streptococcus

Clinical presentation:

• Abrupt onset of sore throat (hurt to swallow liquid)
• Malaise / fever / headache
• Lymphoid hyperplasia
• Pus on tonsils

Complications:

• Scarlet fever, due to infection with exotoxin strain with a local or haematogenous spread, leads to high fever, sepsis, arthritis or jaundice
  1. Pus-related complications i.e. accesses that could rupture and cause meningitis or brain abscess e.g. peritonsilar cellulitis/abscess
  2. Non-pus related complications
• If untreated, patients can develop M protein-specific antibodies
• Rheumatic fever

Question 3

Describe other clinical infections caused by Streptococci

Answer 3

Skin infections:

• Impetigo (childhood infection)
• Erysipelas (facial lesions)
• Cellulitis
• Necrotising fascitis (infection of deeper tissues and fascia with high mortality)
• Toxic shock syndrome from deep tissue infection with strep pyogenes

Question 4

Outline common causes of pharyngitis

Answer 4

Most likely caused by:

• Streptococcus pyogenes (bacterial)
• Epstein-Barr virus (viral)
• Candida albicans (fungal)

Question 5

Outline management strategies for pharyngitis

Answer 5

Need to discover the cause of the pharyngitis which will determine the management strategy

• Viral pharyngitis requires supportive treatments e.g. pain relief and fluids
• Bacterial pharyngitis is treated with broad spectrum antibiotics
• Fungal pharyngitis is treated with antifungal medications.

Question 6

Describe features of EBV

Answer 6

• Epstein-Barr virus is a member of the herpes virus family and is one of the most common human viruses, found all over the world.
• Most people get infected with EBV at some point in their lives.
• EBV spreads most commonly through bodily fluids, primarily saliva = the kissing disease

EBV infection causes several human diseases, including infectious mononucleosis, autoimmune disorders, and a number of malignancies

Question 7

Describe the microbe-host interaction for EBV

Answer 7

EBV can infect epithelial cells, B cells and T cells

• EBV initially enters the mouth and infects the epithelial cells of the pharynx, replicating in this and then find the B cells (main target) in the lymphoid tissue (tonsils)
• B cells then travel through the lymphatic tissues which allows the infection to spread to other lymphoid tissues
• Over time, infection is controlled by antibodies and cytotoxic T cells
• The whole process takes about 4-8 weeks, in most people the disease is asymptomatic

Question 8

Describe the main clinical features of EBV infection

Answer 8

Clinical features:

• Fatigue
• Fever
• Inflamed throat / pharyngitis (due to the epithelial cell infection)
• Swollen lymph nodes in the neck (due to immune response)
• Enlarged spleen
• Swollen liver
• Rash
• Atypical lymphocytosis (have a much bigger nucleus and lots of cytoplasm)

Many people become infected with EBV in childhood and do not because distinguishable symptoms from other childhood illnesses.

Diagnosing:

• Challenging because the symptoms are similar to other illnesses
• Confirmed with a blood test that detects antibodies, however 9/10 adults have antibodies that show that they have a current or past EBV infection

Prevention and treatment:

• No vaccine (can prevent by avoiding sharing with people)
• No specific treatment, only supportive