Microbial diseases

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Microbial diseases by Mind Map: Microbial diseases

1. Epidemiology

1.1. Study of the transmission, incidence, and frequency of disease.

1.1.1. How microorganisms enter a host? Portals of entry Mucous membrane Skin The parenteral route Numbers of invading microbes LD50 (lethal dose for 50% of the inoculated hosts) ID50 (infectious dose for 50% of the inoculated hosts) Adherence Adhesins or ligands Biofilms

1.1.2. How bacterial pathogens penetrate host defences? Capsules Resists the host’a defences by impairing phagocytosis. Cell wall components Contain chemical substances that contribute to virulence. Eg : Streptococcus pyogenes produced a heat-resistant and acid-resistant protein called M protein.. Antigenic variation Some pathogens can alter their surface antigens, thus avoiding the host‘a antibodies. Enzymes Coagulases — bacterial enzymes that coagulate the fibrinogen in blood and converted into fibrin. Kinases — bacterial enzymes that break down fibrin and thus dissolve clots formed by the body to isolate the infection. Hyaluronidase — enzymes secreted by certain bacteria to hydrolyse hyaluronic acid, a type of polysaccharide that holds together certain cells of the body. Collagenase — breaks down the protein collagen, which forms the connective tissue of muscles and other body organs and tissues. IgA proteases — destroy IgA antibodies produced by the host as a defence against adherence of pathogens to mucosal surfaces. Penetration into the host

1.1.3. How bacterial pathogens damage host cells? Using the host’s nutrients Direct damage The production of toxins Membrane-disrupting toxins / type II toxins Superantigens / type I toxins Endotoxins Plasmids, lysogeny, pathogenicity Lysogenic conversion

2. Transmission of disease

2.1. Contact transmission

2.1.1. Indirect contact transmission

2.1.2. Direct contact transmission

2.1.3. Droplet transmission

2.2. Vehicle transmission

2.2.1. Waterborne

2.2.2. Airborne

2.2.3. Foodborne

2.3. Vectors

2.3.1. Mechanical transmission

2.3.2. Biological transmission

3. Spread of infection

3.1. Reservoirs

3.1.1. Human reservoirs People without exhibiting any signs of illness but can harbour pathogens and transmit them to others — carriers Eg : AIDS, diphtheria, typhoid fever, hepatitis, gonorrhea

3.1.2. Animal reservoirs Zoonoses - wild & domestic animals that transmitted diseases to humans Eg : Rabies found in bats, skunks, foxes, dogs, cats. Lyme disease found in field mice.

3.1.3. Nonliving reservoirs Soil Eg : fungi which cause mycoses including ringworm and systemic infections, Clostridium botulinum which causes bumotulism Water Eg: Vibrio cholerae which causes cholera, Salmonella typhi which causes typhoid fever Improperly prepared or stored food

4. Development of disease

4.1. Incubation period

4.2. Prodromal period

4.3. Period of illness

4.4. Period of decline

4.5. Period of convalescence

5. Human microbiome

5.1. Normal microbiota

5.1.1. Benefits the host by preventing the overgrowth of harmful microorganisms — microbial antagonism Relationship between the normal microbiota & host — symbiosis Commensalism Mutualism Parasitism

5.2. Transient microbiota

6. Koch’s postulates

6.1. Provide framework for the study of the etiology of any infectious disease.

6.2. Limitations : some organisms cannot be grown in laboratory medium, infected individuals do not always have clear-cut symptoms, some diseases are polymicrobial, suitable hosts not always available for testing.

6.3. Criteria : same pathogen must be present in every case of the disease, pathogen must be isolated from the diseased host and grown in pure culture, same disease must be produce when pure culture is introduced into susceptible laboratory animal, pathogens must be recovered from experimentally infected hosts.

7. Classifying infectious disease

7.1. Identification

7.1.1. Symptoms

7.1.2. Signs

7.1.3. Syndrome

7.2. Disease behaviour

7.2.1. Communicable disease

7.2.2. Non-communicable disease

7.3. Occurrence of a disease

7.3.1. Reported by Incidence of a disease Prevalence of a disease

7.3.2. Frequency of occurrence Sporadic Endemic Epidemic Pandemic

7.4. Severity of a disease

7.4.1. Acute disease

7.4.2. Chronic disease

7.4.3. Subacute disease

7.4.4. Latent disease

7.5. Extent of host involvement

7.5.1. Local infection

7.5.2. Systemic infection

7.5.3. Primary infection

7.5.4. Secondary infection Caused by opportunistic pathogen