Disease

Question 1

How is the body a host?

Answer 1

Many organisms live in or on the human body in a symbiotic or parasitic relationships. These may help to defend us against disease aka beneficial (commensal and mutualistic) or harmful and cause disease (pathogenic).

Question 2

Define pathogenic.

Answer 2

Denotes an organism that cause damage to a host.

Question 3

Define infectious

Answer 3

Relating to a disease that can be passed from one organism to another.

Question 4

Define carrier

Answer 4

An individual who has the microorganism that causes a disease and can pass it on, but has no symptoms of the disease itself

Question 5

What is a disease reservoir?

Answer 5

A long term host of a pathogen that cause an infectious disease

Question 6

Define endemic

Answer 6

When a disease is always found at low levels in a certain area

Question 7

Define epidemic

Answer 7

The rapid spread of an infectious disease to a large number of people in a population

Question 8

Define pandemic

Answer 8

An epidemic of infectious disease that has spread through populations on multiple continents.

Question 9

Define vaccine

Answer 9

A treatment that provides active, acquired immunity to a disease

Question 10

Define antibiotic

Answer 10

A substance produced by microorganisms that affects the growth of other microorganisms

Question 11

Define antibiotic resistance

Answer 11

When a microorganism which should be affected by an antibiotic, is no longer susceptible to it

Question 12

Define antigenic types

Answer 12

Organisms with the same or very similar antigens on their cell surface,
Usually sub groups or strains of a microbial species which can be used to trace infections. They are normally identified by using antibodies from serum.

Question 13

Define vector

Answer 13

A living organism that transmits a disease from one organism to another

Question 14

Define toxin

Answer 14

A poisonous substance produced by microorganisms that damages their host

Question 15

Describe mutualistic bacteria that can become harmful.

Answer 15

E. coli is good in the large intestine for synthesising vitamin K but in the small intestine it can cause disease
Mites in hair follicles on eyelashes eat dead cells but can cause inflammation if they build up
Entamoeba grazes on dead cells of our gums but when it builds up it causes gingivitis

Question 16

Describe characteristics and treatment of cholera.

Answer 16

Gram negative Vibrio Cholerae. Can only reproduce inside the human host.
Source: contaminated water and food, faecal/oral transmission - people become carriers and act as reservoirs for the disease
Tissues affected: a toxin it produces affects the chloride channel proteins in the small intestine causing watery diarrhoea, because water and ions aren’t absorbed, leading to severe dehydration and a fall in BP
Prevention and treatment: proper sanitation, vaccine, antibiotics and fluid and electrolytes.

Question 17

Describe characteristics and treatment of Tuberculosis.

Answer 17

bacterium Mycobacterium Tuberculosis
Source: airborne droplet transmission
Tissues affected: lungs and neck and lymph nodes - symptoms include coughing up blood and chest pain. People lose their appetite and develop a fever.
Treatment: BCG vaccination of children to prevent disease, antibiotics as treatment

Question 18

Describe characteristics and treatment of Smallpox, Variola Major

Answer 18

Source: droplet transmission and bodily fluids
Tissues affected: skin then multiple organs, causing a rash then blisters
Treatment: vaccination - it is now eradicated due to its low rate of anti genetic variation and mutation, and the highly immunogenic nature of its component antigens. It also lacked an animal reservoir.

Question 19

Describe characteristics and treatment of influenza.

Answer 19

There are three subgroups, A, B and C. It’s RNA has 8 single strands instead of one. The phospholipid envelope around the virion has two antigens - haemagglutinin (H - enters) and neuraminidase (N - leaving).
Transmission: droplet transmission, contaminated surfaces
Tissues affected: upper respiratory tract - sore throat, cough, fever
Treatment: quarantine and hygiene. Antiviral drugs and vaccination but due to the number of different emerging types of the virus the vaccination had a limited effect.

Question 20

What are the 2 origins of the antigenic types of influenza?

Answer 20

1. Antigenic drift - no RNA proofreading enzymes so following each round of replication on average every new virion has a new mutation. This produces a gradual change in surface proteins
2. Antigenic shift - influenza A has 16 types of H and 9 times of N. If one cell is infected by viruses with different H as N combinations they can recombine and make new virus types.

Question 21

Describe the characteristics and treatment of malaria.

Answer 21

Caused by plasmodium.
Source: female mosquitos carrying plasmodium
Tissues affected: invades liver cells and then multiplied in red blood cells which then burst, releasing more parasites and causing sever bouts of fever
Treatment: nets, clothing, insect repellent, killing aquatic mosquito larvae with fish, draining breeding sites or spraying oil on the surface insecticides, bacterial infections, sterilisation, drugs and vaccines have limited effectiveness.

Question 22

Describe the transmission of malaria.

Answer 22

When a mosquito takes blood from an infected person it takes in the sexually reproducing stage of plasmodium called gametocytes. They produce zygotes, which develop into an infective stage, called sporozoites. These migrate from the mosquitos gut to salivary glands. Then the sporozoites are injected into the human during a blood meal and travel to the liver and reproduce asexually into merozoites. These are released into the blood and infect red blood cells where they do more reproduction. The red blood cell bursts releasing more merozoites which infect more red blood cells. Some merozoites become gametocytes.

Question 23

What is the pathogenicity of virus’s?

Answer 23

The way in which they cause diseases and is related to the way viruses produce more virus particles using the cells own metabolic pathways.

Question 24

What are the diseases mentioned?

Answer 24

Bacterial infections - cholera and TB
Viral infections - influenza and smallpox
Protoctistan infection - malaria

Question 25

What is the lytic cycle?

Answer 25

Viruses either enter the lytic or lysogenic cycle. Viruses immediately reproduce using the hosts metabolism to copy their own nucleic acid and synthesise new coat protein. Their release may be by lysis of the host cell or budding where they acquire an envelope from the hosts cell membrane.

Question 26

What is cell lysis? How does it make the virus pathogenic?

Answer 26

When bacteria are infected w a bacteriophage the pressure of new virus particles inside cause the bacteria to burst. In contrast in virus infected animal cells, the inflammation by T lymphocytes or antibodies brings about lysis.

Question 27

How can toxins cause a virus to be pathogenic?

Answer 27

Many viral components and their by products are toxic. The mechanisms are not well understood but the following have been observed. Eg measles causes chromosome fusion and herpes causes cell fusion.

Question 28

How can cell transformation cause a virus to be pathogenic?

Answer 28

Viral DNA can integrate into the host chromosome. If the DNA inserts into a proto oncogene or tumour suppressor gene, it can result in the cell undergoing rapid, uncontrolled division ie being cancerous.

Question 29

How can immune suppression cause a cell to become pathogenic?

Answer 29

Suppression of the reactions that cause B and T lymphocytes to mature.
Reduction in antibody formation
Reduction of phagocytic cells engulfing microbes.

Question 30

What is the lysogenic cycle?

Answer 30

Where viruses integrate their nucleic acid into the host cell genome and may remain there for many generations w no clinical effect.