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AS Biology > Infectious Diseases > Flashcards

Infectious Diseases Flashcards

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1
Q

What is a disease?

A

A disease IMPAIRS normal functioning of an organism, leading to poor health

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2
Q

What is an INFECTIOUS disease

A

A disease that is caused by pathogens and can be passed on between individuals

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3
Q

What is a non infectious disease

A

A disease that is not caused by pathogens and cannot be passed between people

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4
Q

What is an infectious disease key phrases

A

Transmissible
Passed on from infected organism to uninfected organism
Caused by pathogen (eg HIV causes AIDS, Mycobacterium tuberculosis causes TB)
Caused by virus, bacterium, fungus, protoctist

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5
Q

Examples of non infectious disease

A

Sickle cell anaemia
Coronary heart disease (CHD)
Emphysema

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6
Q

What type of pathogen causes Cholera

A

Bacterium

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7
Q

What bacterium causes Cholera

A

Vibrio Cholerae

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8
Q

How is cholera transmitted

A

FECAL-ORAL route
1. Enters body in contaminated food and water
2. Bacteria breeds in SMALL INTESTINE and secretes CHOLERAGEN (choleragen enters by endocytosis)
3. Choleragen reduces the ability of the epithelium of the intestine to absorb salts and water in the blood —> increased conc of salts in blood —> higher water potential gradient
4. These are lost in the faeces causing diarrhoea, if not treated loss of fluid can be fatal

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9
Q

Treatment of cholera

A

Oral rehydration therapy (ORT) - solution of salts and glucose to hydrate the body
Make sure FLUID INTAKE = FLUID LOSSES in the urine and faeces to maintain OSMOTIC balance of blood and tissue fluids
Take ANTIBIOTICS

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10
Q

Prevention and control of cholera

A

Transmission most likely to occur in CROWDED and IMPOVERISHED condition —> REFUGEE CAMPS
Improper access to proper sanitation, a clean water supply and uncontaminated food
Best controlled by treating sewage effectively, providing a clean water supply and maintaining good hygiene in food preparation
No fully effective vaccine against cholera —> intestinal cells ANTIGENIC CONCEALMENT, antibodies cannot reach intestines

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11
Q

Mode of action of cholera

A

Bacteria bypasses stomach and enters lumen of small intestine
Enters intestinal cells by endocystosis, choleragen released
Choleragen inhibits protein channels, salts/ions canot enter bloodstream
High conc of ions —> low water potential in intestine
Water enters by osmosis —> diarrhoea

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12
Q

Global distribution of cholera

A

West and East Africa, Afghanistan
Unknown in MEDC’s due to sewage treatment and cleaned piped water
Transmission cycle broken

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13
Q

Explain how it is possible to reduce the number of deaths during a cholera epidemic

A

Provide boiled water to kill bacteria
Provide ORT containing electrolytes and salts
Absorption of salts helps absorbs glucose
Absorption of salts increases water uptake by osmosis
Deaths usually caused by rapid dehydration
Rapid provision of medical supplies
For severe cases antibiotics should be taken
Safe sewage disposal

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14
Q

Explain why cholera is unlikely to be transmitted in developed countries

A

Transmission cycle broken
Sewage treatment plans, mains drainage
Human faeces does not come in contact with drinking water supply
Water treatment plants
Drinking water is piped to homes

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15
Q

Explain why cholera is likely to be transmitted in underdeveloped countries

A

Greater exposure to contaminated water and food supply
No safe drinking water sources
Lack of hygiene
Faeces and sewage mixed with drinking water
Insufficient access to oral cholera vaccines
Lack of education
Differences in effectiveness of surveillance and reporting
Refugee camps
Increase in antibiotic resistance
Lack of health services
Inadequate access to healthcare and medicine

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16
Q

Explain how cholera bacteria are transmitted from one person to another

A

Fecal oral route
Bacteria leaves infected person in faeces
Bacteria enters water supply
Bacteria ingested by uninfected person

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17
Q

Discuss the problems involved in preventing the spread of cholera

A

Poor sanitation, no treatment of faecal waste
Contaminated of drinking water supply
Poverty, poor living conditions
Poor hygiene
Lack of education about transmission and health
Refugee camps
Lack of water purification
No rehydration therapy available
No effective vaccine

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18
Q

What type of pathogen cause Malaria

A

Protoctist

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19
Q

What protoctist causes malaria

A

Plasmodium

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20
Q

What are the 4 species of plasmodium

A

Plasmodium FALCIPARUM
Plasmodium MALARIAE
Plasmodium OVALE
Plasmodium VIVAX

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21
Q

How is malaria transmitted

A

Mosquito acts as a VECTOR for malaria
Female anopheles mosquito containing plasmodium in salvia feeds on human blood
When a mosquito bites an infected person, plasmodium is taken up into the mosquitos body and eventually reaches its salivary glands

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22
Q

How can malaria be prevented?

A

Reducing the population of mosquitos: removing sources of water in which the can be, releasing large numbers of sterile males

Preventing mosquito bites: mosquito nets, dark clothing, long sleeved clothes, repellent

Prophylactic drugs- drugs that prevent pathogens from breeding (quinine and chloroquine, mefloquine, proguanil)

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23
Q

Where is malaria prevalent?

A

Topical and subtropical regions- where humidity is high

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24
Q

Reasons for worldwide concern over the spread of malaria

A

Increase in drug resistant forms of plasmodium
Difficulties in developing a vaccine
Change in climate and environmental changes that favour the spread of mosquitos
Migration of people

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25
Q

What is the relevance of anticoagulants in malaria?

A

Anticoagulant in saliva is passed when mosquito feeds/takes a blood meal
anticoagulant prevents blood clotting when the mosquito sucks blood

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26
Q

Discuss the factors that determine the distribution of malaria worldwide

A

Tropics, subtropic
Areas: Africa, Central America, South America, South Asia
Countries: India, Sri Lanka, china, Vietnam, Naya
Areas where both parasite and anopheles are present
Anopheles survive in hot humid areas
Parasite needs to reproduce within he mosquito
Poor health facilities
Mosquitoes resistant to repellent
Parasite resistant to prophylactic drugs
High population density —> lots of mosquitos
Human activity —> breeding sites for anopheles

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27
Q

Describe how malaria is passed from an infected person to an uninfected person

A

Female anopheles mosquito takes BLOOD MEAL from an infected person and feeds on uninfected person
Plasmodium transmitted in mosquitos saliva
Blood transfusion

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28
Q

Unlike malaria, TB is found across the whole world, explain the distribution pattern

A

Anopheles mosquito survives within the tropics
Plasmodium needs to reproduce within the mosquito
Eradicated in some countries outside the tropics
LEDCs do not have mosquito control programmes
Mosquitos resistant to insecticides or repellents
Plasmodium resistant to prophylactic drugs eg chloroquine
TB is airborne and is transmitted through water droplets
Does not require a vector

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29
Q

Describe one method of controlling the spread of malaria by targeting its vector and explain its effect

A

Elimination of free standing water
Removes mosquito breeding sites

Use insecticides
Kills adult mosquitos

30
Q

Explain why it has been difficult to develop an effective vaccine for malaria

A

Plasmodium has many antigens
Many different stages of life cycle
More than one plasmodium species
Different stages of life cycle
Mutation changes antigens due to antigenic shift/drift
Parasite only vulnerable at certain stages of life cycle
Antigenic concealment

31
Q

Type of pathogen that causes TB

A

Bacterium

32
Q

What is the bacterium that causes TB called?

A

Mycobacterium tuberculosis, mycobacterium bovis (rarely)

33
Q

How is TB transmitted?

A

M.tuberculosis can enter lungs in airborne droplets of liquid that are breathed in
M.bovis is the causative form of TB in cattle

34
Q

Prevention and control of TB

A

Chest x ray and sputum test
Increasing standards of living
BCG vaccine
Treatment of HIV by drug therapy reduces the risk that an HIV positive person will get TB
Drugs- isoniazid and rifampicin

35
Q

TB cannot always be cured with antibiotics because

A

Many strains of M.tuberculosis bacterium that have evolved resistance to most of the antibiotics that are used
The bacteria reproduce inside body cells, where it is difficult for drugs to reach them
Drugs need to be taken over a long period

36
Q

Describe the global distribution of TB

A

Both high income and low income countries
Poor housing in inner cities in the developed world and rising homelessness
Breakdown of TB control programs
Increased migration
Refugee camps

37
Q

Suggest why fatality ratios of TB are higher in some of countries than in others

A

Overcrowded housing
Not diagnosed early enough
DOTS- direct observation treatment short course
Lack of vaccination
Antibacterial drugs not available
Medical services not available
TB lined to HIV/AIDS
Not completing antibiotic treatment course
No facilities for isolating people

38
Q

Discuss the problem to be faced in the eradication of TB

A

Tb found worldwide
High incidence in developing countries (LEDCs)
Problem with vaccine (BCG) —> does not work well for all ethnic groups etc
Difficult to identify infected people
Difficulty with contact tracing
Difficult to diagnose

39
Q

Explain why the antibiotics used to treat TB are taken in combination over a long period of time

A

Bacteria likely to be resistant to at least one antibiotic
Less likely to be resistant to all
Antibiotics used is very small
Change/mutation in DNA
Bacteria are inside cells, protected from antibiotics
Mycobacteria divide slowly
Ensures all bacteria killed
Bacteria remains
Prevents development of antibiotic resistance

40
Q

What type of pathogen causes AIDS

A

Virus

41
Q

What is the name of the virus that causes AIDS

A

HIV- human immunodeficiency virus

42
Q

What is HIV, what is its structure?

A

Retrovirus, contains RNA
Protein core contains 2 RNA molecules
Retrovirus- uses RNA to produce a single strand of DNA inside the host cell, using reverse transcriptase

43
Q

How is HIV transmitted

A

Infected blood from one person entering another (sharing hypodermic needles)
Exchange of fluids from penis, vagina or anus —> sexual contact
Transmission across placenta from mother to foetus or in breast milk
Promiscuous sex

44
Q

Mode of action of HIV

A

HIV attaches to receptors on T-helper cells
Viral RNA fuses with T-helper cell
Viral RNA acts as a template to male a single strand of DNA (cDNA) by using reverse transcriptase
Viral DNA formed
Viral DNA inserts itself into chromosomal DNA of the host cell —> provirus
Viral DNA transcribed into mRNA
New viruses are made from the protein and RNA
Infected T cell bursts open to release new viruses, destroying it which infects other host cells

Role of T-helper cells is eventually reduced or not carried out
Macrophages and T killer cells are not activated
B cells not activated, fewer antibodies produced
Cytokines not released
Immune system weakened and compromised

45
Q

When is HIV considered AIDS

A

When CD4 cell count is below 200

46
Q

How can HIV be prevented and controlled?

A

Blood transfusions screened
Hypodermic needles should be sterile and only used once, disposed safely
Contact tracing, sexual contact traced
Contraception
Less promiscuous sex
Education programs

47
Q

Why is there no vaccine available for HIV/AIDS

A

Virus mutates rapidly- antigens on viral coat keep changing
Harder for immune system to recognise the virus

48
Q

What is the global distribution of HIV/AIDS

A

Global, increasing worldwide
Most prevalent in sub Saharan Africa (Gambia think Geo)

49
Q

Medicine available for HIV/AIDS

A

No treatments, virus mutates rapidly so antigens on viral coat keeps changing
Drugs available to help with symptoms and prolong life
Zidovudine, similar to nucleotide thymine —> binds to reverse transcriptase blocks it’s action

50
Q

Suggest how HIV infection may have led to an increase in malarial infections

A

HIV infects T cells
Both contracted through blood transfusion

51
Q

List two factors in the prevention and control of HIV/AIDS that would help improve average life expectancy in African countries

A

Education to prevent transmission
Anti HIV drug therapy
Access to contraception
Avoid promiscuity
HIV positive mothers avoid breast feeding
Screening before blood transfusion
Needle exchange schemes

52
Q

What type of pathogen causes small pox

A

Virus

53
Q

What virus causes small pox

A

Variola virus

54
Q

How is small pox transmitted

A

Airborne- inhalation of droplets of moisture containing the virus

55
Q

Prevention and control of small pox

A

Eradicated by vaccine programme coordinated by WHO

56
Q

What kind of pathogen causes measles

A

Virus

57
Q

What virus causes measles

A

Morbillivirus

58
Q

How is measles transmitted

A

Airborne- inhalation of droplets of moisture donating the virus

59
Q

How can measles be prevented and controlled?

A

Vaccination, two doses
If infected, prevent close contact —> isolation

60
Q

What is an antibiotic

A

Substance that kills bacteria without harming human cells

61
Q

What is the mode of action of penicillin

A

When new bacterial cells grow it secretes autolysins which create small holes in cell wall —> allows cell wall to stretch and create cross links
Penicillin inhibits glycoprotein peptidase enzymes by blocking or altering the shape of the active site
This prevents the synthesis of links between peptidoglycan molecules in bacterial cell walls, cross links cannot form
Bacteria takes up water by osmosis which causes cell lysis

62
Q

How do antibiotics work

A

By interfering with the growth or metabolism of the target bacterium
Eg. Synthesis of bacterial cell walls, activity of proteins in bacterial cell surface membranes, bacterial enzyme action, bacterial DNA synthesis

63
Q

Why do antibiotics not affect viruses?

A

No cell wall
When a virus replicates, it uses the host cell’s mechanisms for transcription and translation —> antibiotics cannot bind to host cell proteins

64
Q

Why are some antibiotics ineffective against bacteria

A

Thick cell wall rescues permeability
Some enzymes break down penicillin

65
Q

Development of resistance to penicillin

A

Natural selection
Use of penicillin produces SELECTIVE PRESSURE against bacteria causing mutations to occur
Causes bacteria to have GENETIC VARIATION —> new alleles of genes
Gene produced is resistant to penicillin and is found in plasmids of bacteria
Penicillin resistant gene codes for production of b lactamase, enzyme which breaks down penicillin
Survive and reproduce
Pass on their advantages allele to next generation
Higher proportion of bacteria is resistant

66
Q

How can antibiotic resistance be reduced?

A

Use antibiotics only when necessary, not for viral infections
Course needs to be complete
Change the type of antibiotic prescribed
Avoid wide spectrum antibiotics
Minimise use in agriculture

67
Q

What is vertical transmission

A

Bacteria reproduce asexually by binary fission
One bacterium contains mutant gene, proving antibiotic resistance to other generations

68
Q

Horizontal transmission

A

Plasmids contain antibiotic resistant genes
Plasmids transferred between bacteria
Conjugation occurs- thin tube forms between two bacteria to allow exchange of DNA

69
Q

Why does antibiotic resistance occur?

A

Overuse of antibiotics
Incorrect use of antibiotics
Eg- treatment for non serious infection

70
Q

What is a consequence of antibiotic resistance?

A

Reduced effectiveness of antibiotics
Increase in incidence of antibiotic resistance

71
Q

Suggest two ways streptomycin acts as ribosomes to inhibit protein synthesis

A

Binding of tRNA prevented
No anticodon, codon bringing
Peptide bond not formed
mRNA attachment prevented
Inhibition of enzymes involved in translation
Ribosome movement along mRNA hindered
Inhibits association of large and small subunits

72
Q

Suggest why streptomycin does not harm mammalian cells

A

Cell surface membrane impermeable
Degraded before entry into cell
Broken down m enzymes
Eukaryotic, 80S ribosomes- different ribosome structure

AS Biology (5 decks)

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