HSC biology module 7 IQ 1 (causes of infectious disease)

define pathogen

any organism which is capable of causing disease

what are the 6 types of pathogens?

1. bacteria

2. fungi

3. protists

4. viruses

5. prions

6. macroscopic parasites

what are bacteria?

prokaryotic, unicellular organisms, which dont have membrane bound organelles and are each made of one cell

Where are bacteria found?

everywhere including the air, soil, water and human body. Only a small portion are pathogenic, the majority actually benefit your health.

How do bacteria cause disease?

by releasing toxins or damaging host tissues.

give examples of bacteria causing disease

tuberculosis, tetanus and crown gall (plants)

outline the bacterial disease of tuberculosis

Caused by the bacterium mycobacterium tuberculosis which enters the lungs as a person inhales infectious droplets.

Once inside the lungs it is eaten by macrophage where it survives and replicates causing them to develop a hard layer of dead tissue leading to chest pain, chronic cough and weakness.

what are protists?

eukaryotic, unicellular microorganisms without a cell wall

what diseases do protists cause?

malaria, phytophthora dieback (plants)

outline the protist disease of malaria

Caused by plasmodium which floats freely in the blood of an infected person after bring transmitted by female mosquitos.

It feeds on the haemoglobin in the red blood cells causing them to pop.

Symptoms include fever, muscle pain, nausea, weakness and headaches.

what are fungi

Eukaryotic, non-photosynthetic organisms with a cell wall

How do fungi cause disease?

via the enzymes they produce. (fungi produce digestive enzymes and chemicals into their surroundings in order to break down organic matter. They then absorb simple nutrients meaning they digest their food before they eat it which is harmful when the thing being digested is still alive).

give examples of fungi causing disease

athletes food, chytridiomycosis (frogs), stem rust (plants)

what are viruses?

Non cellular entities, consisting of a single type of nucleic acid (DNA or RNA) encased in a protein coat (capsid)

How do viruses cause disease?

by attaching to a host cell, which it then penetrates and hijacks the hosts enzymes and nutrients to make its own viral proteins and nucleic acid. These viral materials assemble into new viruses which are released from the host cell and infect other cells.

give examples of viral diseases

influenza (humans), tobacco mosaic virus disease (plants)

outline the viral disease of influensa

Caused by the influenza virus which damages human lung tissue. Most symptoms are caused by the body's own immune response, caused by the release of cytokines from infected cells.

Symptoms include: fever, cough, nasal congestion

What are prions?

Non cellular infectious proteins, which are abnormally folded versions of a protein needed within an organism

How do prions cause disease?

in a variety of ways depending on the structure, function and location of the normal protein.

Prions usually affect brain and neural tissue, which leads to neurodegeneration.

give examples of disease caused by prions

kuru (humans), creutzfeldt-jakob disease (humans)

outline kuru disease

Caused by a prion found in contaminated human brain tissue. Spread by eating the brains of infected individuals. Most common in New Guinea where some populations of native people consumed the brains of the deceased as part of their funeral ritual (this ritual is now extremely rare).

what are macroscopic parasites?

Multicellular pathogens which can be seen by the naked eye

how do macroscopic parasites cause disease?

by either competing for nutrients from the host organism or by producing toxins/damaging host tissue.

give examples of macroscopic parasites

ticks, fleas, tapeworm, mosquitos

define endemic

a disease that is constantly present in a certain population or region, with relatively low spread

define epidemic

when there is a sudden increase in the cases of a disease spreading through a population.

define pandemic

when there is a sudden increase in the cases of a disease spreading through several countries, continents, or the whole world.

what are methods of transmission via direct contact

touching, sexual contact, kissing, biting

what are methods of transmission via indirect contact

airborne, touching contaminated surface, contaminated food/water, vector transmission

What did Louis Pasteur do?

proposed the germ theory of disease (rejecting spontaneous generation)

How did Pasteur's disprove spontaneous gneration

the swan neck flask experiment - proved that microbes could not generate spontaneously but had to be transferred

what is the swan neck flask experiment?

'swan necked flasks' hold boiled meat broth. As the broth cooled outside air entered the flask; any microorganisms present in the air were trapped in the thin curved neck. Thus no bacterial or fungal growth was observed.

Bacterial growth was only observed if the curve of the flask was broken off and thus its contents exposed to the air.

What are Koch's postulates?

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

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

3. The pathogen from the pure culture must cause the disease when it is inoculated into a healthy, susceptible laboratory animal.

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

What did Koch's postulates prove?

germ theory of disease

name some factors contributing to disease spread in agriculture

overuse of antibiotics and pesticides, loss of genetic diversity, overcrowding

name an animal disease

foot rot in sheep and cattle

what causes foot rot?

bacteria

what are the effects of foot rot?

inflammation and pus, lameness, weight loss

name a plant disease

Panama disease in banana trees

what causes panama disease?

fungi

what are the effects of panama disease?

yellow, wilting leaves, stem splitting, damage to tissue, nutrient deprivation

define infection

the way that pathogens break and enter our bodies without getting caught

how do pathogens establish infection?

1. entry

2. invasion

3. establishment

4. invading immune system or evading immune system

5. exit

6. transmission to next host

how do pathogens enter the body?

respiratory tract, gastrointestinal tract, genitourinary tract, skin

what happens during pathogenic invasion?

pathogens either infiltrate cells or travel through blood and tissue fluids

what are pathogens aided by during invasion

invasins

which can induce clotting and disrupt cell membranes

what happens during pathogen establishment

pathogens establish themselves in the host by adhering to the cell surface using adherence factors.

how do pathogens evade the immune system

formation of biofilms, covering themselves in native antigens, travelling to safe spaces (e.g intestines or within cells)

when do pathogens exit the body

once reproduction is established some will leave to infect new hosts

what is involved in the secondary line of defence?

inflammatory response, phagocytosis, cell death