Infectious Lecture Flashcards
Infection
Colonization of the human host
Carriage
Establishment of a long term harmless relationship host and the bacteria
Disease
Infections that result in pathology
Pathogen
Biological agent (microbe) that can cause disease to its host
Virulence
Relative capacity of a pathogen to cause disease
- Number of infecting microbes
- Entry route into body
- Effects of host defense mechanisms
- Virulence factors –> components of pathogen that damage the host
Categories of infectious agents
Prions Viruses Bacteria Fungi Protozoa
Prions
Abnormal form of host protein (PrP) via mutation
Found in neurons
Conformational change that confers resistance to proteases
Protease resistant PrP promotes conversion of the normal PrP to the protease resistant form
Accumulation of abnormal PrP
Neuronal damage and spongiform changes
- Mad cow disease
Skin entry
Barrier
Low pH
Fatty acids inhibit growth of microorganisms
Break in skins, burns, insect or animal bites
GI tract entry
Contaminated food and drink
Defenses:
- acidic gastric secretion
- layer of mucus covering intestinal epithelium
- lytic pancreatic enzymes and bile detergents
- defensins
- normal flora disruptions by antibiotics
Respiratory Tract Entry
Mucociliary defenses (secreted by globlet cells; cilia brush the virus down)
Small particles phagocytosed by alveolar macrophages
Influenza virus
Influenza Virus
binding causes epithelial cells to be taken up into the cells
Virus multiples
Virus comes out and secretes neuraminidase so that the virus can spread (lowers the viscosity)
Urogenital Tract Entry
Defenses: regular flushing, Low pH (lactobacilli; unfavorable to microbes), and local breaks in mucosa (STD; breaks allow entry)
Spread and dissemination
APC picks up the infection
Takes it to the lymphatic (lymph and blood)
Can move into the blood stream and spread everywhere in the body
– Also can get spread via placental transfer or maternal milk
Transmission
Skin shedding, coughing/sneezing, sex, urine/feces, insect vector (bug bites), animal to human (zoonotic) or nosocomical (acquired in hospital)
How do microorganisms cause disease?
- Cause direct cell death
- Release toxins that kill cells at a distance or damage tissue (travels via blood)
- Induce host immune response- necessary to fight infection but may cause tissue damage (cannot turn off and on at the right time then it causes more damage than it is helping – inflammation)
Viruses
Obligate intracellular parasites (can only live within the cell bc they need it to replicate) Protein coat (capsid) Aggregate within cells to form inclusion bodies (used for diagnostics)
Diagnostic methods for viruses?
Inclusion bodies Serologic testing (antibodies) Molecular diagnostics (PCR; looks for certain DNA sequences)
Viruses enter and replicate?
Damage the host cell
- Tropism (ten to infect certain cells)
- – Bc of certain receptors or machinery
Once inside the host the viruses?
Direct cytopathic effects
Antiviral immune response – CD8 T cells go and kill the cell
Transformation of host cell into benign or malignant tumor
Hep B
Sits in the liver while the immune system continuously attacks
Immune evasion by microbes
When macrophage takes up the microbes, it destories them via phagosomes but the microbe can escape by changing their coat so they cannot be recognized, secreting a protein so that it will not be expressed on MHC, or developing a big capsule around it so they cannot be reached
INF-gamma
First defense
- Bind INF-gamma and take it up so that it cannot act on it and get rid of it
Acute Viral Infections
"transient" Elicits effective immune response- eliminates the agent - Measles - Mumps - Poliovirus - West Nile Virus
Measles
ssRNA of paramyxovirus family
- One serotype (only one antigen)
- CD46 (all nucleated cells) and SLAM (cells of the immune system)
- Measles rash first
- Can cause transient but severe immunosuppression
Mumps
Belongs to paramyxovirus family
- Enters via the upper respiratory tract
- Spreads via lymph nodes
- Replicates in T cells
- Spreads via blood to the salivary and other glands
Poliovirus
Infects only humans via CD155
- Invades the CNS and replicates in motor neurons of the spinal cord or brain stem
West Nile Virus
Flavivirus group
- Inoculated by a mosquito
- Replication in skin cells
- Migrate to lymph nodes where it again replicates
- Enters blood stream and cross BBB
Chronic Latent Infections
Acute phase followed by a latent stage where the viruses persist in a non replicating and non infectious form with periodic reactivation and shedding of infectious virus
Herpes Simplex Virus
Varicella-Zoster
Herpes Simplex Virus
Cold sores
- Spreads to sensory neurons at the site of infections and remains latent in neurons
- Can cause corneal blindess
Varicella-Zoster Virus
Acute- chickenpox
Reactivation- shingles
- Latent in dorsal root ganglia is reactivated and infects sensory nerves supplying the skin
Chronic Productive Infections
High mutation rate and escape control by immune system
Continued viral replication leads to persistent viremia
- Hep B
Hep B
Acute and chronic liver disease
- Cellular injury from the immune response to infected liver cells rather than due to cytopathic effects of the virus – cannot control the infections (chronic infection develops – cirrhosis)
Transforming infections
Viruses that cause cancer
Epstein-Barr Virus
Epstein-Barr Virus
Infectious mononucleosis- Lymphomas in immunocompromised patients
- Atypical activated T cells
Transmitted via salvia
Tonsils- infections B cells
Productive/latent
EBNA2 and LMP1- B cell activation and proliferation
Heterophile antibodies (via B cells)- agglutinate RBCs
Fungal infections
Fungi- eukaryotes with cell wall (chitin) and egosterol containing cell membranes
- Grow as multicellular filaments (molds)
- Grow as single cells/chains of cells (yeast)
- Asexual spores are “conidia”
- Diagnosed via histologic exam or culture
Types of fungal infections
Superficial and cutaneous
Subcutaneous
Endemic (systemic; into the blood stream)
Opportunistic (immunocompromised)
Candidasis
Thrush
Candida albicans
Benign commensals (one benefits another is not harmed)
Breach of skin or mucosal membranes
Shift between commensal and pathogen
Vaginitis Diaper rash
- Steroidal antibiotics = ^ susceptibility
Candidasis invasion
Adhesions- adhesion to host cell is main virulence determinant
Aspartyl proteinases, catalase - help invasiveness
Bacterias that cause different candidasis?
Candida esophagitis
Candida vaginitis
Cutaneous candidiasis
Invasive candidasis
Cryptococcosis
Cryptococcus neoformans
- Encapsulated yeast that causes meningocencephalitis
Glucuronoxylomannin
- principal capsular polysaccharide - major viruelence factor
Aspergillosis
Asperigillus fumigatus
- Responsible for allergies and sever infections
Aflatoxin (carcinogen)
- produced by aspergillus growing on peanuts - responsible for liver cancer
Zygomycosis
Bread mold fungi - Zygomycetes
- Airborne asexual spore
- Immunocompromised individuals
