Week 5 Flashcards
Describe the structure of viruses
- 20 nm - 1 microm in size
- RNA or DNA
- No independent metabolism and no organelles
- Simple protein coat (& cell membrane from host cell)
- Has a H spike and N spike
- Has an envelope and capsid
What are koplik spots?
Little white spots on buccal mucosa - seen in early measles
What are the symptoms of Herpes Simplex Virus?
peri-oral (HSV-1) and genital (HSV-2) infections. Can also cause HSV encephalitis. May become latent in dorsal root ganglia –> recurrence
What is it called when HSV recurs in facial nerve?
Bell’s palsy
What are the symptoms of Varicella Zoster Virus?
fever and vesicles in a centripetal distribution. Can also cause VZV meningitis. Becomes latent in dorsal root ganglia –> recurrence
What is it called when VZV recurs in facial nerve?
Ramsey-Hunt syndrome (Herpes zoster oticus)
What are the clinical features of Epstein-Barr Virus?
Central: fatigue, malaise, loss of appetite, headache
Visual: Photophobia
Tonsils: Reddening, swelling, white patches
Lymph nodes: Swelling
Spleen: Enlargement, abdo pain
Gastric: Nausea
Systemic: Chills, fever, aches
Resp: Cough
Throat: Soreness, reddening
What is the treatment for Chronic HBV or HCV infection?
PEG-IFN-α for 48 weeks +/- other drugs
What does a change in neutrophils suggest?
bacterial infection
What happens to Hb in chronic infections?
Decreases
What does a change in lymphocytes suggest?
Viral infection
What happens to platelets in malaria and some viral infections?
Decreases
What happens to platelets in bacterial infections and some inflammatory disorders?
Increases
Give some examples of primary immunodeficiency
(intrinsic cause = usually genetic)
• Phagocyte deficiencies (innate cell-mediated immunity)
• Complement deficiencies (innate humoral immunity)
• Severe combined immuno-deficiencies (adaptive cell-mediated immunity)
• Predominantly antibody deficiencies (adaptive humoral immunity)
Give some examples of secondary immunodeficiency
(extrinsic cause = non-iatrogenic)
• Hyposplenism / Asplenism (eg. Have spleen removed)
• Haematological malignancies (cancer of blood cells)
• HIV / AIDS
Give some examples of immunosuppression
(extrinsic cause = iatrogenic)
• Steroids & other immunosuppressive drugs
• Cytotoxic chemotherapy (for malignancies)
• Total body irradiation (before bone marrow transplantation)
Describe Chronic Granulomatous Disease (CGD)
Aetiology :
multiple possible defects (most frequently X-linked) → phagocytes being unable to destroy ingested microbes
Pathology : lack of oxidative burst to produce free radicals → excessive granuloma formation occurs instead
Clinical Features : persistent & recurrent infections especially …
pneumonia
skin infections
abscesses (skin & internal)
septic arthritis & osteomyelitis
bacterial & fungal blood stream infections
Staph. aureus, Salmonella, Klebsiella, Burkholderia
Aspergillus, Candida
Investigations : nitroblue-tetrazolium (NBT) test uses microscopy (normal phagocytes reduce NBT to a dark pigment)
dihydrorhodamine (DHR) test uses flow cytometry (normal phagocytes reduce DHR to a fluorescent pigment) genetic analysis to identify exact genetic defect
Treatment : early diagnosis & treatment of any infections prophylactic antibiotics (co-trimoxazole & imidazoles) recombinant IFN-gamma (70% less infections) bone marrow / stem cell transplantation (curative)
Prognosis : without treatment most children die within 10 years with treatment if X-linked → 20% die within 10 years with treatment autosomal recessive → 50% die in 35 yrs
Describe Common Variable Immunodeficiency (CVID)
Aetiology : multiple possible defects (not X-linked) →
hypogammaglobulinaemia (IgG, usually IgA, possibly IgM)
Pathology : lack of antibodies to neutralise & opsonise pathogens → severe, persistent, unusual & recurrent infections & autoimmune, malignant, enteric & lymphoid disorders
Clinical Features : Streptococcus pneumoniae (LRTIs & septicaemia) Haemophilus influenzae (URTI/LRTIs & meningitis) Neisseria meningitidis (meningitis & septicaemia) Staphylococcus aureus (skin & soft tissue infections) Pseudomonas aeruginosa (ear infections & LRTIs) Giardia lamblia (intestinal infection) most common sites are ears & respiratory tract
Investigations : reduced immunoglobulins on simple blood test
↓ IgG always, ↓ IgA usually, ↓ IgM in ~50% normal B lymphocyte count, but immature types failure to produce antibodies in response to vaccines
Treatment : early diagnosis & treatment of any infections prophylactic immunoglobulin transfusions (IV every 3-4 weeks or SC every week)
immunoglobulin reactions can occur (“serum sickness”) “flu-like” symptoms (but no respiratory component) possible thrombotic events or anaphylaxis (very rare)
(less indication for bone marrow / stem cell transplantation)
Prognosis : good with regular immunoglobulin transfusions
How would you investigate hyposplenism/asplenism?
- Spleen function assessed by imaging (USS)
- Blood films show Howell-Jolly bodies in erythrocytes
What cells does HIV infect?
Th lymphocytes (aka T4 or CD4 cells)
What causes AIDS-defining diseases
CD4 < 200 cells/mm3
Give some examples of re-emerging infectious disease
TB, Multi-drug resistance TB, Flu, Dengue
What are some factors that contribute to emergence?
Agent:
- Evolution of pathogenic infectious agents (microbial adaptation & change)
- Development of resistance to drugs
- Resistance of vectors to pesticides
Host:
- Human demographic change (inhabiting new areas)
- Human behaviour (sexual and drug use)
- Human susceptibility to infection (immunosuppression)
- Poverty & social inequality
Environment:
- Climate & changing ecosystems
- Economic development & land use (urbanisation, deforestation)
- Deforestation forces animals into closer human contact - increased possibility for agents to breach species barrier between animals and humans
- Natural disasters & related outbreaks of infectious diseases (Malaria, Cholera, Plague)
- Global warming - spread of malaria, dengue, leishmaniasis, filariasis
- Technology & industry (food processing & handling)
Others:
- International travel and commerce
- Breakdown of public health systems (war, unrest, overcrowding)
- Deterioration in political systems and lack of political will
- Donor Agencies and Funding
Define incubation period
The time interval between initial contact with an infectious agent and the appearance of the first sign or symptom of the disease
