Disease

Detecting and

responding

DISEASE AND THE

IMMUNE RESPONSE

DISEASE

• What is disease?

• What is a non-infectious disease?

• examples

• What is an infectious disease?

• Examples

• Transmission – methods? –

(see homework)

• Incubation period

Detecting

• Humans, Animals, plants need a way of

detecting when they are “invaded” by

foreign cells or tissue so they can defend

themselves effectively.

• Immune system’s job

Pathogens

• Pathology – study of disease

• Pathogen – disease causing organism or non-cellular agent

• Main groups:• Viruses

• Bacteria

• Fungi

• Protozoans

• Prions

• Multicellular eukaryotic parasites

VIRUSES

• Non cellular infectious agents

• Can only be seen with an e.m.

• Completely parasitic (obligate intracellular

parasites)

• Host relationship is very specific –

glycoproteins on virus interact with

receptors on host cell membrane – e.g.

influenza virus and RBC’s

Size and shape of viruses

How Big?

• http://www.cellsalive.com/howbig.htm

structure

Structure

Viral diseases

DNA viruses RNA viruses

Gastroenteritis Influenza

Respiratory tract infection Polio

Chicken pox Colds

Shingles Rubella

Warts AIDS

Measles

Mumps

diarrhoea

rabies

Transmission Electron Micrograph of an

Influenza A Virus

Transmission Electron Micrograph of HIV-1

Image provided by Dr. Edwin P. Ewing, Jr.Courtesy of the Centers for Disease Control and Prevention

Transmission Electron Micrograph of

Coronavirus

Image provided by Dr. Erskine Palmer.Courtesy of the Centers for Disease Control and PreventionNote the glycoproteins (arrows) on the viral envelope.

Transmission Electron Micrograph of

Poliomyelitis viruses

Image provided by J. J. Esposito and F. A. Murphy.

Courtesy of the Centers for Disease Control and Prevention.

Poliomyelitis viruses are naked viruses.

Polio - symptoms

Hosts

• Can infect all kinds of cells- human, plant,

animal, bacteria

• Many viruses spread by vectors – e.g.

mosquitos Ross River Virus

Reproduction

Treatment

• Antibiotics not effective

• Drugs which interfere with making of viral DNA or RNA might stop reproduction

• Vaccines most effective – inject or swallow inactivated virus into host – initiates the production of antibodies which help fight off the infection when it arrives.

• Rest – fast mutation of coat proteins on some viruses are a huge problem eg AIDS

PRIONS

• See p 137 AM

• PrPc proteins – normal and infectious

versions

• Discovered with Kuru in New Guinea

• E.g. CJD (Creutzfeld Jakob Disease)

• Bovine spongy encephalitis (Mad Cow

disease)

• No cure

Prions

Prions are implicated in BSE (Bovine Spongiform Encephalopathy or Mad Cow Disease) and its human counterpart nvCJD (new variant Creutzfeldt Jakob Disease). These and similar diseases are known as TSEs (Transmissible Spongiform Encephalopathies). TSEs afflict other species, most famously sheep (scrapie).

• Prions are pathogenic variants of proteins that are naturally produced in nerve cells and certain other

cells. The normal "healthy" prions are referred to as PrPc (Prion Protein cellular). The word "prion"

stands for "proteinaceous infectious particle" and so should properly only be applied to the

pathogenic variants. In this picture, the production of PrPc is illustrated from the nucleus at bottom

right. RNA that codes for PrPc is produced in the nucleus and exits via the nuclear pore. The RNA

then passes along ribosomes attached to the rER. PrPc is formed in the rER and then progresses up

through the Golgi. At the upper face of the Golgi, vesicles containing PrPc bud off and travel to the

cell surface. Here, they fuse with the cell membrane and so discharge their cargo at "PrPc". By this

means, the cellular proteins come to sit on the exterior of the cell.

• PrPc encounter rogue (purple) prions. These are termed PrPsc (sc stands for scrapie, the prion

disease of sheep). The rogue prions seem to force the normal proteins to change shape. Both types

of protein, the PrPc and their corresponding prions, are the same chemical - just different shapes. It

is this shape-flipping which is equivalent to the transmission of infection. Such a conformational shift

or flip could happen at the cell surface or in caveolae (one is shown as a small invagination in the cell

membrane). Residual PrPc might continue to be flipped by contact with the rogue conformations for

some time in these vesicles. Prions polymerise, finally appearing as purple fibrils in the picture at "P".

PrPsc is resistant to degradation by the enzymes contained in the lysosomes that are seen floating

nearby. Consequently, PrPsc accumulates in the cell. PrPsc vesicles may also travel to the Golgi and

intercept PrPc that is being processed there. In this way, PrPc particles could be switched to the

rogue form before they reach the surface of the cell. By such mechanisms, PrPc might be switched to

PrPsc at various points in and on the cell.

• Prions could enter the brain along the axons of neurons. This probably happens by a retrograde flow

of prion filled vesicles. These are shown in the picture as purple spheres ascending the axon like

elevators going up a shaft . Another route of entry could be the blood, probably in immune cells. A

lymphocyte is shown exiting the capillary at bottom left where it could then contact the astrocyte.

Astrocytes and other glial cells also support the production of prions.

BACTERIA

• Prokaryotic cells

•Features?

No nucleus – circular DNA

No membrane bound organelles

Very small

Mostly heterotrophic some autotrophic

Structure

Features

• Shaped – cocci, bacilli, spirilla

• Many are pathogenic, many not

• Cause disease by disrupting host cell’s;

producing powerful toxins; disrupting

host immune system

• Often defined by differential staining

• Gram positive (purple) and Gram

negative bacteria (pink/red)

Diseases

• Tetanus – Clostridium tetani

• Botulism - Clostridium botulinum

• Pneumonia - Pneumococcus

• Diphtheria

• Tuberculosis – Mycobacterium tuberculosis

• Food poisoning – Salmonella typhi, Staphylococcus aureus

• Throat infections - Streptococcus

• Typhoid fever

• Syphilis

• chlamydia

Reproduction

Binary fission

Treatment

• Antibiotics – natural eg penicillin or

synthetic

• Tetracycline

• Work by destroying bacterial structures

or cell membrane

Penicillium and bacterial inhibition

Fungal infections

• Cause many plant diseases e.g. Rust in

wheat

• In animals – ringworm, athletes foot, tinia,

thrush – usually not serious or life

threatening

• Mostly pathogenic in plants

• Transmitted via direct contact

Structure

Cell wall made of chitinNon motile usuallyFilamentous – have hyphaeProduce spores

Yeasts are a sub group –unicellular fungi - thrush

Yeast infection

Life-cycle

Protozoans

• Summarise Malaria parasite from text p

148

• Name pathogen, describe life cycle,

disease and treatment

Multicellular parasites - worms

• Flatworms – platyhelminthes

• Inhabits intestines of humans and other

animals

• May be up to 10m long

• Each segment in chain has

reproductive organs

• Round worms – nematodes

• Thread, pin, hook worms see p 162 text