Infectious Disease 31 to 40
What is secondary tuberculosis?
Secondary TB is the pattern of disease that arises in a previously sensitised host. *
May follow shortly after primary infection, but commonly arises from reactivation of dormant primary lesions when host resistance is weakened, or from reinfection.
What are the main features of secondary pulmonary infection?
Characteristic feature is gross tissue necrosis, especially at apices- cavitation
secondary to cytokine/TNF and IL-1 etc
- Large lesions with caseous necrotic tissue = tuberculoma
- Cavity formation* – oxygen and CO2 present, bacilli replicate freely,
- erosion of blood vessels
- Infect other parts of lung local spread ….Bacilli in sputum
- Patient infectious
- Fibrosis and scarring with resolution
Pass: 3 required
How are influenza viruses classified?
Prompt: what is antigenic drift and shift?
A – humans, pigs, horses, birds, major cause of pandemics/epidemics. Subtypes determined by hemmaglutinin and neuraminidase in envelope. Shows antigenic drift (H & N mutations) – epidemics, antigenic shift (H&N replaced by recomb RNA from animal viruses) – pandemic
B & C no antigenic drift/shift – more in children – develop abs
Pass: require A, and some understanding of antigenic drift
How does the immune system specifically attack the influenza virus?
Abs to H & N if previous infection, cytotoxic T cells, anti-influenza protein in marcrophages (Mx1) induced by cytokines
What are the common causes of infective gastroenteritis?
Prompt: Give examples
1. Viral: Rotavirus (group A), Norwalk like virus, Enteric adenovirus
- Ingestion of preformed toxin: Stahpylococcus aureus, Vibrios & Clostridium perfringens.
- Toxigenic organism: proliferate within the lumen & form enterotoxin: E coli, Vibrio cholerae.
- Enteroinvasive organism: proliferate, invade & destroy mucosal epithelial cells: E coli, Shigella, Salmonella.
3. Parasites: Giardia Lamblia, Entamoeba histolytica.
Pass: Need viral and bacterial causes
Describe the Salmonella bacterium.
Salmonella are flagellated, gram-negative bacteria. S enteritidis, S typhimurium and others cause food borne and water borne gastroenteritis.
Pass: Need to describe the type of bacteria
How does Salmonella cause gastroenteritis?
Salmonella pass through intestinal epithelial cells via transcytosis with minimal epithelia damage in the terminal ileum and colon.
Salmonella enters into lamina propria that leads to 5-10% bacteraemia.
Pass: Need to say it’s an invasive infection and say location
What causes cholera?
1. Cholera is caused by Vibrio cholerae which is a gram-negative bacteria
2. Vibrio cholerae produces enterotoxins known as Cholera toxins
3. There is no epithelial cell invasion.
How does Vibrio Cholerae cause diarrhoea?
Cholera toxin binds with the G-protein in the epithelial cells which stimulates adenyl cyclase and increase intracellular cyclic AMP, resulting in the massive secretion of chloride, sodium and water. The massive watery diarrhoea overwhelms the reabsorptive function of the colon. This results in litres of dilute “ricewater” diarrhoea with few leukocytes produced. There is massive sodium, chloride and bicarbonate and fluid losses.
Pass: Need to say it’s due to Toxin, cause rice water diarrhoea
What is “Atypical Pneumonia”?
Prompt: Tell us about the pathological changes.
- Interstitial Pneumonitis
- Lack of exudate
- Different Clinical Picture
What organisms are usually involved?
- Mycoplasma, Q fever, Legionella, psittacosis (3 to pass)
- Viruses (name at least one)
What are the non-bacterial causes of meningitis
Pass: Viruses plus 2
What are the typical CSF findings in Viral Meningitis
- Normal Glucose
- Mildly elevated Protein
- No bacteria seen
Pass: 3 of 4
What are the common viral causes?
- Coxsackie (enteroviruses)
- Non paralytic Polio
Pass: 2 of 4
What are the 2 clinical conditions caused by Varicella Zoster virus?
- Chicken pox
Describe the pathogenesis and clinical course of infection with this virus.
PROMPT – Start with how the virus is transmitted.
- Starts with aerosol or direct contact spread
- -> Haematogenous dissemination
- -> Vesicular skin lesions
- -> Vesicles rupture, crust over then heal
- Some virus lies dormant in dorsal root ganglia and reactivated later with immunosuppression
- Reasonable sequence
What are the complications of chicken pox?
- Lung – interstitial pneumonia
- Nervous system – encephalitis, transverse myelitis
- Skin and mucous membranes – shingles, bacterial superinfection
- Gut – necrotising visceral lesions
- 3 to pass
What organism is responsible for measles infections and how is it transmitted?
- Virus, RNA, paramyxo
- Respiratory transmission
- Bold to pass
What type of immune response occurs in measles?
- T-cell mediated controls infection and causes rash
- Antibody mediated protects against reinfection
- Antibody mediated
What are the clinical features of measles?
- Koplik spots
- Lymph nodes
- 3 bold to pass
What are the complications of measles?
- Secondary bacterial infection
- Subacute sclerosing panencephalitis
- 2 as minimum
Describe the pathogenesis of glandular fever.
- EBV transmitted by close contact (saliva)
- Envelope g/protein binds to B cells
- Viral infection begins naso/oropharyngeal lymphoid tissues (especially tonsils)
- EBV accesses submucosal lymphoid tissues
- B cell infection
- Lysis infected cells and virion release (minority) or
- Latent infection (EBV genes expressed)
- Symptoms appear on initiation host immune response (cellular CD8+ cytotoxic T and NK cells)
- Atypical lymphocytes (characteristic)
- Reactive T cell proliferation lymphoid tissues – lymphadenopathy and splenomegaly
- IgM Ab (viral capsid Ag) and later IgG
- Healthy – cease viral shedding with few resting B cells but acquired defects may -> B lymphomas
- To pass:
- Lymphoid tissue
- Involves B (latent and lysis) and T cells
What are the clinical features of glandular fever?
- Classically – fever, sore throat, lymphadenitis, splenomegaly
- Atypical presentation common – fatigue, lymphadenopathy, hepatitis, rubella-like rash
- 4 clinical features to pass
What are the outcomes of glandular fever??
- 4-6 weeks most resolve – some fatigue longer
- Hepatic dysfunction – j, abn. LFTs, appetite
- Splenic rupture
- Other systems – nervous, renal, lungs, heart.
- Transformation – lymphomas
- 3 outcomes to pass
Turbid, low sugar, high protein, pleocytosis with neutrophil predominance, no bacteria.
A 10 yo boy presents with a headache and fever. These are his CSF results. What is the likely diagnosis and why?
- Acute bacterial meningitis
- Diagnosis + 2 reasons