Infectious Diseases

Question 1

What is a disease

Answer 1

An abnormal function of the body
- condition that impairs the normal functioning of an organism, leading to poor health
- each disease is associated with a set of symptoms
- infectious/non-infectious

Question 2

Infectious diseases

Answer 2

• transmissible / communicable / contagious / transferable

• passed from one (infected) person / host / organism, to another

• caused by a pathogen / microorganisms / (x2) virus / bacterium / fungus / protoctist / worm

Question 3

Modes of transmission of infectious diseases

Answer 3

• direct contact (if pathogen cannot survive outside the body)
• water
• food
• faeces
• animals e.g. insects
• indirectly from person to person
• symptomless carriers (spread pathogen even if don’t have disease)

Question 4

Pathogen def
Examples

Answer 4

Organism that causes disease
e.g. virus, bacterium, fungi, protoctists

Question 5

Examples of pathogens that cause diseases

Answer 5

• HIV —> virus that causes AIDS

• Mycobacterium tuberculosis —> bacterium that causes TB

Question 6

Parasite

Answer 6

Organism that live on/in another organism (host) and causes damage to that organism

Question 7

Some parasites can cause …

Answer 7

Disease
Therefore is a pathogen

Question 8

Example of pathogen that can cause disease

Answer 8

Plasmodium species —> single-called parasite that causes malaria

Question 9

Examples of infectious diseases

Answer 9

• cholera

• malaria

• HIV/AIDS

• tuberculosis (TB)

Question 10

Causes of malaria

Answer 10

• by a protoctist / Plasmodium

• several different species - cause different types of malaria

• Plasmodium infects RBC and breeds inside them

• toxins released when Plasmodium bursts out of cell - causes fever

Question 11

…

Question 12

Key phrases - Malaria causes

Answer 12

• Plasmodium / falciparum / malariae / ovale / vivacité

• (only) female feeds on blood

• female requires blood (protein) for (development of) eggs

• (only) female carries pathogen / disease-causing organism / Plasmodium / parasite

• (only) female transmits the disease

• (only) female is vector

Question 13

…

Question 14

Transmission of Malaria

Answer 14

1. Female Anopheles mosquito feeds on human blood to obtain the protein needed to develop they eggs
2. If the person they bite is infected with Plasmodium, they will take up some of the pathogen’s gametes with the blood meal
3. Gametes fuse and develop in mosquito’s gut to form the infective stages
4. Infective stages move to the mosquito’s salivary glands
5. When mosquito feeds again, it injects the anticoagulant that prevents blood meal from clotting so it flows out of host into the mosquito
6. The infective stages pass out into the blood
   together with the anticoagulant in the saliva
7. parasite enters the hepatocytes (liver cells) where they mature and multiply
8. burst out of the hépatite and enter the RBCs, where they multiply

Question 15

Prevention and control

Answer 15

• remove population of mosquitos

• prevent mosquitos biting people

• use Prophylactic drugs

Question 16

Methods to remove population of mosquitos

Answer 16

• remove sources of water

• layer of oil on water

• stock ponds, irrigation and drainage ditches and other forms fo water, with fish

• spray a bacterium

Question 17

Methods to prevent mosquitos biting people

Answer 17

• sleep under mosquito net soaked in insect repellent every 6 months

• wear long sleeves - especially at dusk

• insect repellent - some resistant to DDT and other insecticides

Question 18

Drugs used to prevent malaria

Answer 18

Prophylactic drugs - prevent infection and breeding in a person
- take drug before, during and after visiting an area with high cases of Malaria

• chloroquine - inhibits protein synthesis and prevents parasite spreading inside the body

• proguanil - inhibits sexual reproduction of Plasmodium inside the biting mosquito (stops gametes fusing in gut)

Question 19

Name and type of pathogen that causes cholera

Answer 19

Vibrio cholerae / V. Cholerae

Bacterium

Question 20

Name and type of pathogen that causes Malaria

Answer 20

Plasmodium - malariae, falciparum, ovale, vivax

Protoctist

Question 21

Name and type of pathogen that causes tuberculosis (TB)

Answer 21

Mycobacterium tuberculosis / Mycobacterium bovis

Bacterium

Question 22

Name of pathogen that causes HIV/AIDS

Answer 22

Human Immunodeficiency Virus (HIV)

Question 23

Transmission of cholera

Answer 23

Contaminated food and water
E.g. water/food in contact with untreated sewage

Question 24

Transmission of malaria

Answer 24

• Female anopheles mosquito
• Blood transfusion and re-use of unsterile needles
• Mother to child across placenta

Question 25

Transmission of TB

Answer 25

• airborne - infected people cough/sneeze —> Mycobacterium tuberculosis bacteria enter the air in tiny droplets of liquid —> uninflected people inhale —> spread faster in overcrowded conditions • Mycobacterium bovis occurs in cattle - spread to human through contaminated meat and unpasteurised milk

Question 26

Transmission of HIV/AIDS

Answer 26

• retrovirus • sexual contact • infected blood / contaminated needles - e.g. IV drug users using the same needle • mother to foetus in early stages of pregnancy, birth or breastfeeding • promiscuous sex —> mucus lining of rectum not as thick as vagina —> less natural lubrication —> damage occurs more easily during intercourse —> virus pass from semen to blood

Question 27

Retrovirus

Answer 27

Virus with the ability to make DNA from RNA because they have reverse transcriptase

Question 28

Infectious diseases are caused by

Answer 28

Pathogens

Question 29

Small pox pathogen

Answer 29

Variole virus

Question 30

Small pox transmission

Answer 30

Inhalation of droplets of moisture containing the virus

Question 31

Prevention and control of smallpox

Answer 31

Eradicated by a vaccination programme coordinated by WHO

Question 32

Mode of action of penicillin

Answer 32

• penicillin inhibits a group of enzymes (glycoprotein peptidases) by blocking or altering the shape of the active site • enzymes used by bacteria to form cross-links between the peptidoglycan molecules that make the cell walls —> so, penicillin causes the peptidoglycan chains to not link up and stops cross-links from forming • when a newly formed bacterial cell is growing, it secretes enzymes (antolysins), which make little holes in the cell wall —> alone wall to stretch so a new reptidoghycan chain can link • when penicillin present, cross-links can't form, cell wall not made, but autolysins Keep making new holes • bacteria takes up water by osmosis and the cell swells which then bursts due to the weakened cell wall which can't withstand the increased pressure as the turgar of cells not resisted by cell walls • penicillin doesn't harm viruses or human cells —> don't have cell walls and don't contain peptidoglycans —> don't have peptidase or cytoplasm