Emerging Diseases

Lecture 4: Important Types of Germs

4.1: Overview4.2: Characteristics of Germs

4.3: Summary

4.1: Overview

The germs that cause infectious diseases are of various types.

Some are alive and are made of cells but others are not alive = no cells.

Overview : Five Types of Germs and Examples of their Diseases

• Parasites-tapeworms, amoebas, protozoa• Fungi- athlete’s foot, yeast infections• Bacteria-anthrax, syphilis, Staph infections• Viruses- AIDS, cervical cancer (HPV), influenza• Sub-viral pathogens- Mad Cow, Hepatitis D

List goes from largest in size to smallest

4.2: Characteristics of Germs- Parasites

Includes single-celled protozoa as well as multicellular organisms

All “parasites” are EukaryotesMay live within body cavities or may burrow

deep into soft tissuesProtozoa are very diverse-Plasmodium, Giardia,

Pneumocystis, Cryptosporidium

4.2: Characteristics of Germs- Fungi

Eukaryotic cellsMay live in visible colonies or as individual cellsSpecialists at living on other organismsCell wall made of chitin

4.2: Characteristics of Germs- Bacteria

Single prokaryotic cellsLiving pathogensSimple life styleReady to take advantage of opportunityMost have rigid cell wall, primitive types do not

e.g. mycoplasmas

4.2: Characteristics of Germs-Viruses

Nonliving, noncellularVery small (electron microscope)Simplest ones consist of only a few genes (RNA

or DNA) protected by a protein coatRequire cells to reproduce

4.2: Characteristics of Germs-Subviral Pathogens

Nonliving, noncellularVery small (electron microscope)May be defective virus-like particles, or an

individual RNA or protein moleculeRequire cells to reproducePrions-a type of infectious protein-are the most

famous

4.3. Summary-Parasites

Include protozoa such as Giardia lamblia-causes Giardiasis or “beaver fever”

Protozoa are living, eukaryotic organisms that may be single-celled or sometimes two-celled and may have a cell wall.

Include multicellular parasitic worms such as Taenia

saginata the beef tapewormParasitic worms are eukaryotic, multicellular animals that

do not have a true cell wall but may have a tough outer coating, they usually penetrate or attach to soft body surfaces.

4.3: Summary-Fungi

Include organisms classified as yeasts and molds

Fungi are living, eukaryotic organisms that may be single-celled or sometimes live in colonies. They have a special cell wall made of chitin.

Include Candida albicans causes “thrush” and

various species that cause diseases such as athlete’s foot

4.3: Summary-Bacteria

Include organisms classified as true bacteria and as mycoplasmas.

Bacteria are living, prokaryotic organisms that may be single-celled or sometimes live in colonies. Mycoplasmas are the simplest known living organism. True bacteria have a cell wall but mycoplasmas do not.

Bacillus anthracis is a bacterium that causes anthrax.Mycoplasma pneumoniae is a mycoplasma that causes

pneumonia.

4.3: Summary-Viruses

Non-living and do not contain cells.Require cells for reproduction.Include agents that cause diseases such as AIDS

(HIV-1), infectious mononucleiosis (Epstein-Barr Virus) and smallpox (Variola Virus).

4.3: Summary-Subviral Pathogens

Non-living and do not contain cells.Require cells for reproduction.Include agents that cause diseases such as prions

(infectious proteins) that cause Mad Cow Disease and others.

Also includes agents such as the Hepatitis Delta agent that causes Hepatitis D.