Chapter 8- Infectious Diseases Flashcards
In developed countries, infectious diseases are an important cause of death among which populations?
Elderly
Chronic disease
Immunosuppressed
What types of infections are caused by commensal organisms?
Opportunistic
What are the different routes of entry of infectious organisms?
Breaching of epithelial surfaces
Inhalation
Ingestion
Sexual transmission
Vertical transmission
What organisms are more likely to breach respiratory, GI and GU tract epithelium?
Virulent organisms which can damage/penetrate the mucosa
What types of organisms are more likely to cause skin infections?
Less virulent organisms that enter through injury
What are the three modes of vertical transmission?
- Placental-fetal
- At birth
- Postnatal (milk)
What are examples of host defences and how they provide resistance to infectious organisms?
Skin- thick, low pH, fatty acids
Respiratory system- macs, mucocilliary clearance, IgA
GI system- acidic pH, mucous, enzymes, bile, IgA, normal flora, defensins
UG tract- flushing, acidic pH
What are defensins?
Innate protection
Bind microbes membrane and form pores that cause their death
How do microbes evade the immune system?
Antigenic variation (hard to recognize)
Resistance to antimicrobial peptides
Resistance to killing by phagocytes
Evasion of apoptosis
Manipulation of host metabolism
Resistance to cytokines, chemokines, complement-mediate defences
Evasion of recognition (CD4 and 8)
Latent infection
How do microbes cause host damage?
Direct cell death
Release of toxins
Release of enzymes (tissue and vessel breakdown)
Induction of immune response (pyogens)
What are the possible mechanisms of bacterial injury?
Mobile genetic elements- bacteriophages and plasmids
Adhesion to host cells- adhesins and pili
Host cell entry- proteins and opsonization
Toxins/super Ags
What are bacteriophages?
Viruses against bacteria that can transfer genes that increase virulence
What are plasmids?
DNA rings that can transfer Ab resistance
How does opsonization help bacteria enter host cells?
Complement activation leads to engulfment, cells are able to replicate within the immune system
What toxins do gram positive and negative bacteria produce?
Gram neg- endotoxins (cell wall)
Gram pos- exotoxins (secreted)
What are super antigens?
Toxins stimulated by s large T cell response
What are the mechanisms of viral injury?
Tropism- infection of specific cell types
Direct cytopathic effects
Anti-viral immune response- infected cells are destroyed
Transformation of infected cells- processes are hijacked
What do viruses produce when they take over cellular production?
Degradative enzymes
Toxic proteins
Trigger apoptosis
Misfolded proteins
What are some common viruses and their characteristics?
Viral hemorrhagic fever- animal/insect vector, Ebola, hanta
Varicella-Zoster- latency in ganglia
CMV- affects immunocompromised, transplant patients and neonates, owl eye inclusions
HIV
Transforming viruses- EBV to Burkitt lymphoma and nasopharyngeal carcinoma, HPV to cervical cancer, HTLV-1
What are the characteristics of Staph aureus?
Gram pos clusters
Skin infections
Food poisoning
TSS
MRSA
What are the characteristics of Strep?
Infects skin, lung, heart valves and the oropharynx
Gram pos chains
Necrotizing faciitis
Rheumatic fever
Pneumonia
Scarlet fever
VRE
What are the characteristics of Neisseria meningitidis?
Gram neg diplococci
Acid fast (waxy cell wall)
Meningitis
What are the characteristics of Mycobacterium tuberculosis?
Gram pos rods
Acid fast
Delayed hypersensitivity
Necrotizing granulomas (caseating)
How does tuberculosis progress?
Primary complex or latent lesions become progressive secondary Tb which disseminates (miliary Tb)
Localized caseating, destructive lesions (often pulmonary)
What is Ghon complex?
Combination of parenchymal lung lesion and nodal involvement
What are the characteristics of Clostridium?
Anaerobic gram pos bacilli
Cellulitis
Gas gangrene
C. diff- colectomy with pseudomembranes, often with long term Ab use
What are the characteristics of Coccidiodmycosis?
Soil dwelling fungus
Inhalation
What are the characteristics of Cryptococcus?
Yeast causing disease in immunocompromised
Inhalation
Wild bird droppings
What are prions and their characteristics?
Misfolded proteins (beta pleated sheet) that resist degradation
Encourage the misfolding of other proteins
Cause CJD- transmissible spongiform encephalopathies
What form of CJD is most common?
Sporadic
What is required for the diagnosis of infectious disease?
Culture
Serologic ID
Molecular tests
Special stains
What are the different kinds of special stains and what are they used for?
Gram- all
Acid fast/ZN- mycobacteria and nocardiae
Silver- fungi, legionella, pneumocystis
PAS- fungi, amebae
Mucicarmine- cryptococci
Giemsa- H. pylori, Campy, malaria, leishmaniae
