Infectious diseases

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Infectious Diseases By Andoh Wilson

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Infectious Disease Terms

Epidemiology

Epidemic

Endemic

Pandemic

Pathogen

Opportunist

Nosocomial

virulence

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Normal Micro flora & its importance

Prevent the growth of pathogens

Stimulate the immune system to produce antibodies that cross-react with invading pathogens

Aid in digestion of cellulose in ruminants.

Produce essential nutrients

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Koch’s Postulates

The same pathogen must be present in every case of the disease;

The pathogen must be isolated from the diseased host and grown in pure culture;

The pathogen from the pure culture must cause the disease when it is introduced into a healthy but susceptible organism.

The pathogen must be isolated from the inoculated animal and be shown to be the original organism.

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Modifications to Koch’s Postulates

Some infectious agents cannot be cultured e.g. prions

Some pathogens have non-virulent strains whose presence does not link them to a disease. E.g. non encapsulated Diplococcus pneumoniae

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Types of Pathogens

Bacteria

Gram positive

Gram negative

Acid-Fast e.g. Mycobacteria

Spherical described as cocci

Rod shaped described as bacilli

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Gram Positives

Unique Features

Thick peptidoglycan wall

No periplasmic space

No outer membrane (capsule)

E.g. Streptococcus pyogenes, Staphylococcus aureus, Bacillus anthracis, Clostridium tetani

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Gram Positive wall

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Gram Negatives

Unique features

Thin peptidoglycan wall

Has periplasmic space containing different degradative enzymes such as deoxyribonucleases, -lactamases and proteases

Outer membrane containing lipid A, an endotoxin

E.g. Neisseria, Salmonella typhi, E. coli, Yersinia pestis, Vibrio cholerae

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Gram Negative wall

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Types of pathogens