Microbes, Disease and the Human Body

Infectious disease

Disease caused by infectious microbial agents (bacteria, viruses, fungi, protozoa, helminths)

Communicable disease

A disease that can spread from one host to another (e.g. AIDS)

Non-communicable disease

A disease that does not generally spread from one host to another (e.g. cancer)

Contagious disease

A disease that spreads very easily from one host to another (e.g. chicken pox)

Mutualism

A symbiotic relationship where both partners benefit (e.g. E. coli in the intestine)

Commensalism

A symbiotic relationship where one partner benefits and the other is neither harmed nor benefits (e.g. bacteria on the skin)

Parasitism

A symbiotic relationship where one partner benefits while the other is harmed; usually used for protozoa, worms and viruses, but strictly includes pathogenic bacteria

Primary pathogen

An organism that bypasses a healthy individual's immune system to cause disease

Opportunistic pathogen

An organism that usually causes disease only when the immune system is reduced or under some other special circumstance

Edward Jenner

Father of immunology; discovered vaccines in 1796 after observing that milkmaids exposed to cowpox did not contract smallpox

Benjamin Jesty

In 1774, 20 years before Jenner, gave his wife and two sons cowpox using a darning needle; the family survived smallpox

Louis Pasteur

Father of microbiology; contributed to biogenesis theory, pasteurisation and vaccines

Biogenesis theory

The theory that living things come from other living things

Pasteurisation

Heating food to destroy microbes

Attenuation

Weakening a virus so it does not harm the host; used by Pasteur in vaccine development

Ignaz Semmelweis

Suggested handwashing to midwives on hospital wards

Joseph Lister

Advocate and developer of antisepsis and sterilisation of surgical instruments

Robert Koch

Formally demonstrated microbes as disease agents (germ theory of disease) and developed Koch's postulates

Germ theory of disease

The theory that microbes cause disease

Koch's postulates

Four criteria designed to establish a causal relationship between a microbe and a disease

Koch's postulate 1 2 3 and 4

1. 1. The same pathogen is present in all diseased organisms but not in healthy organisms  

2. 2. the pathogen must be isolated from the diseased host and grown in pure culture

3. 3. the cultured microbe must recreate disease when introduced to a healthy host

4. 4. the pathogen must be re-isolated from inoculated, diseased experimental host           

    

Paul Ehrlich

Called antibiotics magic bullets; discovered Salvarsan in 1906, which specifically killed infectious microbes without ill effects on the patient and was used to treat syphilis

Salvarsan

Drug discovered by Paul Ehrlich in 1906 to treat syphilis

Alexander Fleming

Did not discover antibiotics; was the first to observe living organisms producing antibiotics

Howard Florey and Ernst Chain

Isolated penicillin from the fungus Penicillium notatum

Routes of infection

Eat it, drink it, breathe it, touch it, get splashed by it, or get bitten by something

Direct contact transmission

Spread of disease by direct contact (e.g. STDs)

Indirect contact transmission

Spread of disease by indirect contact (e.g. skin cells, hair, clothing)

Vehicle transmission

Spread of disease via a medium such as water, food or air

Vector transmission

Spread of disease by a living carrier (e.g. a mosquito bite)

Predisposing factors

Host factors that affect the chance of infection: age, sex, genetics, pre-existing disease and diet

Local infection

An infection isolated to one area of the body

Systemic infection

An infection that spreads through the whole body

Zoonosis

A disease that can spread from animals to humans

Ways disease spreads between hosts

From humans (at any stage of the disease, depending on the microbe), from animals (zoonosis), or from non-living sources (e.g. soil causing tetanus)

Emerging and re-emerging infectious diseases

Diseases showing an increase in incidence in the recent past, or with the potential to increase in the near future

Antibiotic resistance

A threat that could return us to the pre-antibiotic era