Infectious Diseases

Disease

Any cause that impairs the function of an individual in some way; it harms the individual.

Infectious disease

Diseases caused by pathogens that can be passed from one organism to another, e.g., measles.

Non-infectious disease

Diseases that cannot be passed on and are not caused by pathogens, e.g., diabetes.

Causes of disease symptoms

Tissue destruction, blocked transport systems, starvation, production of toxic substances, inappropriate host defense responses.

Pathogens

Disease-causing agents.

Causes of non-infectious diseases

Genetics, poor nutrition/obesity, environmental factors (pollution, radiation, stress).

Chromosomal Disease

An example is Down syndrome or Sickle cell disease.

Primary pathogens

Pathogens that cause disease any time they are present.

Opportunistic pathogens

Pathogens that only cause disease when host defenses are weakened.

Major groups of Pathogens

Prions, viruses, bacteria, fungi, protists, and parasites.

Progress of disease

Stages include exposure, incubation period, infectious state, symptoms appear, recovery.

Prions

Smallest known pathogenic molecules that do not contain genetic material.

Causes of prion diseases

Genetics and infection.

Workings of Prions

They stimulate normal prion proteins to misfold, forming infectious prion forms and plaques in the brain.

Disease caused by prions

Creutzfeldt-Jakob disease (CJD).

Symptoms of CJD

Dementia and sudden muscle contractions leading to death.

Viruses

Tiny particles that must invade living cells to reproduce, damaging or destroying those cells.

Examples of viruses

Tobacco mosaic virus, Influenza, HIV, T4 bacteriophage.

Bacteriophages

Viruses that infect bacteria.

Reason for antibiotic ineffectiveness on viruses

Viruses are not alive.

Viruses are mutational

They modify their capacity for virulence.

Antigenic drift

Minor changes a virus makes to its surface antigens.

Antigenic shift

Changes in antigens when viruses exchange genetic material with other strains.

Bacteria

Single-celled organisms that lack a nucleus; prokaryotes.

Types of bacteria

Cocci, bacilli, spirilla.

Coccus

A spherical bacterium.

Bacillus

Rod-shaped bacteria.

Spirillum

Spiral-shaped bacterium.

Flagellae

Structures that provide motility for some bacterial species.

Anaerobic bacteria

Bacteria that do not require oxygen to survive.

Aerobic bacteria

Bacteria that require oxygen for survival.

Exotoxins

Highly toxic chemicals released by bacteria into their environment.

Endotoxins

Highly toxic chemicals produced inside bacterial cells, released when the bacteria ruptures.

Tetanus

A disease caused by the bacteria Clostridium tetani.

Typhoid Fever

A bacterial disease caused by Salmonella typhi, transmitted through contaminated food or drink.

Three groups of fungi causing disease in humans

Moulds, true yeasts, and fungi-like yeasts.

Examples of parasitic fungal diseases

Ringworm, athlete's foot.

Protists

Single-celled or simple multicellular eukaryotic organisms that do not fit in any other kingdom.

Pathogenic Protists

Plasmodium (malaria), Trypanosoma (sleeping sickness), Giardia (diarrhea), Sarcodines (amoebic dysentery).

Primary host

The host from which the adult parasite gets nourishment and reproduces.

Secondary host

An organism that harbors the immature parasite and helps it complete its life cycle.

Pathogenic Oomycetes

Cause diseases like Blight and Downy mildew.

Parasites

Organisms that live together where one benefits and the other is harmed.

Symbiont

The smaller participant in a symbiotic relationship, living in or on the host.

Host

An animal or plant that nourishes and supports a parasite.

Vector

An organism that transfers a parasite from one host to another.

Tapeworm

A parasitic flatworm.

Endoparasites

Parasites that live within the body of their host.

Ectoparasites

Parasites that feed on the external surface of the host.

Example of pathogenic nematodes

Trichinella spiralis.

Trichinosis

A disease caused by eating raw or undercooked meat infected with Trichinella larvae.

Wuchereria bancrofti

Causes elephantiasis.