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Biology > Chapter 10: Infectious Diseases > Flashcards

Chapter 10: Infectious Diseases Flashcards

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1
Q

What are infectious diseases?

A

They are transmissible diseases caused by pathogens as they are passed from the infected to the uninfected, reducing effectiveness of functions.

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2
Q

What is a disease?

A

A disease is an illness or disorder of the body or mind that leads to poor health. Each disease is associated with a set of signs and symptoms.

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3
Q

What organisms cause infectious diseases?

A

pathogens

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4
Q

What are non-infectious diseases?

A

They are diseases that are not caused by pathogens. They can be cardiovascular eg lung cancer, or inherited/genetic eg sickle cell anemia, or deficiency diseases caused by malnutrition and mental diseases.

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5
Q

What is a transmission cycle?

A

it is the way in which a pathogen passes from one host to another.

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6
Q

What can help to break transmission cycles?

A

Control methods such as vaccination can help attempt to break transmission cycles by removing the conditions that favour the spread of the pathogen.

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7
Q

What is the meaning of the word ‘endemic’?

A

Diseases that are always in populations are described as endemic.

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8
Q

What is the meaning of the word ‘epidemic’?

A

An epidemic occurs when there is a sudden increase in the number of people with a disease.

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9
Q

What is the meaning of the word ‘incidence’?

A

The incidence of a disease is the number of people who are diagnosed over a certain period of time.

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10
Q

What is the meaning of the word ‘prevalence’?

A

The prevalence of a disease is the number of people who have that disease at any one time.

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11
Q

What is the meaning of the word ‘pandemic’?

A

A pandemic occurs when there is an increase in the number of cases throughout a continent or across the world.

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12
Q

What is the meaning of the word ‘mortality’?

A

The death rate from different diseases is referred to as mortality.

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13
Q

What is the name of the pathogen that causes cholera?

A

Vibrio cholerae

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14
Q

What is the type of the pathogen that causes cholera?

A

Bacterium

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15
Q

What are the methods of transmission of cholera?

A

Food and water

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16
Q

How does cholera affect the body?

A

If the bacteria reach the small intestine which is the site of action and pass through the acidic contents of the stomach, they multiply and secrete a toxin choleragen, which disrupts the epithelial lining of the intestine. Thsi causes the salts and water to leave the blood resulting in severe diarrhoea.

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17
Q

How can cholera be treated?

A

Cholera patients can be given oral rehydration therapy or a solution of salts and glucose given intravenously to help regulate the osmotic levels.

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18
Q

What are some causes that lead to the spread of cholera?

A
  1. Developing countries do not have sewage treatment systems or clean water.
  2. Countries that have huge debts to pay, do not have the financial resources to provide drainage and clean water systems.
  3. People do not have access to proper sanitation and uncontaminated food.
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19
Q

How can cholera be prevented?

A

By sewage treatment and the provision of clean piped water which is chlorinated to kill bacteria.

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20
Q

What type of organism causes malaria?

A

Malaria is caused by one of four species of a protoctist.

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21
Q

What is the name of the organism that causes malaria?

A

Plasmodium

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22
Q

What are the methods of transmission of malaria?

A
  1. Anopheles mosquito (vector)
  2. Can be transmitted during blood transfusion and when unsterile needles are used.
  3. It can also pass across the placenta from mother to fetus.
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23
Q

Give a brief overview of the life cycle of plasmodium and how it is transmitted by the vector?

A

Female anopheles mosquitoes feed on human blood to obtain the protein they need to develop their eggs. If the person they bite is infected with plasmodium, they will take up some of the pathogen’s gametes with the meal. These gametes multiply in the mosquito and move to the vector’s salivary glands. When the mosquito feeds, she injects an anticoagulant from her salivary glands to prevent the meal from clotting and hence transmits the plasmodium into the blood. The parasite then enters the RBCs and multiply.

24
Q

What is a vector?

A

A vector is an organism which carries the disease from one person to another or from an animal to a human

25
Q

How can malaria be treated?

A

Through the use of anti-malarial drugs to treat the infected or prevent an infection from occurring if bitten by inhibiting protein synthesis and sexual reproduction of plasmodium in the mosquito.

26
Q

How can malaria be prevented?

A
  1. Reduce the number of mosquitoes: This is done by killing the insect vector and breaking the transmission cycle. Oil can be spread over the surface of water to prevent the mosquito larvae from breathing.
    Marshes can also be drained and vegetation cleared.
  2. Two biological control measures can be used: Stocking ponds, irrigation and drainage ditches and other permanent bodies of water with fish which feed on mosquitos larvae. Spraying a preparation mixture containing the bacterium which kills mosquito larvae but is not toxic to other forms of life.
  3. Avoid being bitten: People are advised to sleep under mosquito nets and use insect repellents. Soaking mosquito nets in insecticide every six months can help in prevention. People should not expose skin at mosquito peak hours.
27
Q

How can malaria be controlled?

A
  1. Increase public knowledge about malaria.
  2. Increase accessibility of healthcare in rural areas.
  3. Work with people in rural areas in order to tackle the situation more sensitively.
  4. Diagnose infected people so treatments can be started earlier.
  5. Use of simple dip stick tests to diagnose malaria quickly without need for laboratories.
  6. Use of modern techniques in gene sequencing and drug design.
  7. Development of vaccines targeted against different stages of the parasite’s life cycle (due to antigenic shift and different antigens per stage)
  8. A renewed international will to remove the burden of disease from developing countries, allied to generous donations from wealthy individuals and foundations.
28
Q

What are some factors of malaria that affect worldwide distribution?

A
  1. An increase in drug-resistant forms of plasmodium.
  2. An increase in the proportion of cases caused by one of the species that causes sever, often fatal malaria.
  3. Difficulties in developing vaccines against malaria
  4. An increase in the number of epidemics, because of climatic and environmental changes that favour the spread of mosquitoes.
  5. The migration of people from areas where malaria is endemic.
  6. An increase in the number of mosquitoes that have become resistant to insecticides.
29
Q

What are the full forms of HIV and AIDS?

A

Human immunodeficiency virus

Acquired immune deficiency syndrome

30
Q

What is the genetic material of HIV?

A

It is a retrovirus, which means that its genetic material is RNA, not DNA.

31
Q

How does HIV cause a variety of opportunistic infections? ref. AIDS

A

Once inside a host cell, the viral RNA is converted to DNA to be incorporated into human chromosomes. The virus infects and destroys the cell of the immune system known as Helper T cells. When the numbers of these cells are low, the body is unable to defend itself against infection, so allowing a range of pathogens to cause a variety of opportunistic infections. AIDS is not a disease. It is a collection of these opportunistic diseases associated with the immunodeficiency caused by HIV infection.

32
Q

How is HIV transmitted?

A

It is transmitted through sexual intercourse, intravenous needle sharing, exchange of bodily fluids, blood transfusions, pass through the placenta and breast milk from mother to fetus.

33
Q

How can HIV be treated?

A

There’s no cure, however, drug therapy prevents replication of the virus, prolonging life. It binds to the viral enzyme reverse transcriptase and blocks its action. This stops the replication of the viral genetic material and leads to an increase in some of the body’s lymphocytes. The pattern and timing of medication through the day must be strictly followed.

34
Q

How can HIV spread be controlled?

A
  1. Contract tracing can be used to identify and isolate sources of infection by testing for HIV antibodies. This can be used to isolate and treat more people, and prevents further spread of infection.
  2. Stop sharing needles or use sterile ones.
  3. Blood collected from donors should be HIV screened and heat treated to kill any viruses.
  4. If tested HIV+, be given medical drugs and psychological support.
  5. Mother to child transmission can be reduced by treating HIV positive women and their babies with drugs. However, HIV+ women in high income countries are advised not to breastfeed their babies, because of the risk of transmission even if they have a secure supply of drugs during this period. In contrast, women in low and middle income countries are advised to breastfeed, especially if they have a secure supply of drugs, as the protection this gives against other diseases and the lack of clean water to make up formula milk may outweigh the risks of transmitting HIV.
35
Q

How can HIV be prevented?

A
  1. The virus changes its surface proteins and therefore has an antigenic shift, which makes it harder for the body’s immune system to recognise it. This makes it harder to develop a vaccine.
  2. Education about spread of infection.
  3. Use of condoms and femidoms as they form barrier between body fluids.
36
Q

What are some factors affecting worldwide distribution of HIV/AIDS?

A

People with multiple partners at risk of spreading/ contracting infection
Most people living with HIV or at risk for HIV do not have access to prevention, care, and treatment, and there is still no cure.
Major proportion of people living with HIV in low and middle income nations.
In developing nations, widespread testing is not feasible and not all donated blood is tested.

37
Q

What are the type of organisms that causes TB?

A

Bacteria

38
Q

What are the names of the organisms that cause TB?

A

Mycobacterium bovis and mycobacterium tuberculosis

39
Q

How is TB transmitted?

A

It is transmitted through airborne droplets(M. tuberculosis) or via unpasteurised milk and undercooked meat (M. bovis). The airborne droplets are released into the air when someone coughs or sneezes, and an uninfected person inhales these droplets.

40
Q

How is TB treated?

A

Samples of sputum (mucus and pus) from their lungs are collected and TB bacteria is identified by microscopy. Infected patients are isolated and treated by drugs. Patients should take their full course of drugs otherwise they’ll harbour drug-resistant bacteria. The treatment takes a long time to kill the bacteria, which are slow growing and not very sensitive to the drugs used. DOTS(direct observation treatment short course) involves health workers or responsible family members making sure that patients are taking their medicine regularly helping to ensure that no drug resistant bacterium develops.

41
Q

What are some factors affecting the worldwide distribution of TB?

A

Prevalent in HIV+ positive areas.
Areas where access to healthcare is low, or drugs are expensive can cause MDR and XDR strains to form.
Increase in incidence due to some strains of TB bacteria becoming resistant to drugs as well as due to poor housing and homelessness.

42
Q

How is TB prevented?

A

Contact tracing and screening for symptoms of TB.
TB can be transmitted between cattle and humans. Thus, cattle should be routinely tested for TB and any found to be infected are destroyed. TB bacteria are killed when milk is pasteurized.
BCG vaccine which protects up to 70-80% of people who receive it, can be used to prevent TB.

43
Q

What type of organism causes measles?

A

A virus

44
Q

What is the name of the organism that causes measles?

A

Morbillivirus

45
Q

What is an antibiotic?

A

It is a drug that kills or stops the growth of bacteria, without harming the cells of the infected organism.

46
Q

In what ways do antibiotics interfere with bacteria?

A

o Synthesis of bacterial cell walls
o Activity of proteins in the cell surface membrane
o Enzyme action
o DNA and protein synthesis

47
Q

How does penicillin work?

A

Prevents synthesis of crosslinks between peptidoglycan polymers in bacterial cell walls by inhibiting enzymes that build these crosslinks.
o When a newly formed bacterial cell is growing, it secretes enzymes called autolysins, which make little holes in its cell wall.
o These little holes allow the wall to stretch so that new peptidoglycan chains can link together.
o Penicillin prevents the peptidoglycan chains from linking up, but the autolysins keep making new holes.
o The cell wall therefore becomes progressively weaker and it bursts due to osmotic pressure. The cell walls cannot stand the pressure potential exerted by the cell contents and the cells burst.

48
Q

Why does penicillin not affect human cells or viruses?

A

Penicillin does not affect human cells due to human cells not having cell walls. This also explains why penicillin and other antibiotics do not affect viruses as they do not have a cellular structure or metabolism.

49
Q

What is the name of the enzyme that can break down penicillin in bacteria?

A

B-lactamase which is a penicillinase

50
Q

Why doesn’t penicillin have an effect on M. tuberculosis and some other bacteria?

A

o Bacterium has thick impermeable cell wall;
o Has a gene that codes for an enzyme (β-lactamase/penicillinase) which breaks down penicillin;
o Proteins in the membranes of other species of bacteria can inactivate antibiotics so they have no effect;
o Bacterial membranes have proteins that pump out antibiotics if they enter cytoplasm;
o Sometimes, antibiotic simply can’t bind to intended site of action.

51
Q

What is DNA mutation with reference to antibiotic resistance?

A

It is when an existing gene within the bacterial genome changes spontaneously to give rise to a nucleotide sequence that codes for a slightly different protein that is not affected by the antibiotic, giving rise to antibiotic resistant bacteria.

52
Q

How do bacteria reproduce?

A

They reproduce asexually by binary fission. the DNA in the bacterial chromosome is replicated and the cell divides into two.

53
Q

What is vertical transmission and how does it work?

A

o Bacteria reproduce asexually by binary fission.
o DNA in bacterial chromosome is replicated;
o Cell divides into two;
o Each daughter cell receives a copy of the chromosome containing the antibiotic resistant gene.
o This method spreads the antibiotic resistance to create a population of antibiotic resistant bacteria.

54
Q

What is horizontal transmission and how does it work? What is a plasmid?

A

o Plasmid: small loops of double stranded DNA often containing resistant gene.
o Conjugation:
▪ Conjugation tube is formed between two bacteria to allow for the movement of DNA.
▪ One strand of plasmid is transferred from donor to recipient bacterium.
▪ Donor and recipient synthesise complementary strand to restore plasmid.

55
Q

What is multiple resistance?

A

It is when there are multiple resistant genes in plasmid.

56
Q

What factors affect selection pressure in terms of antibiotics?

A

o Increasing misuse of antibiotics increases selection pressure exerted on bacteria to evolve resistance to them. (If no external disturbing factor, no selective pressure, so no need to evolve resistance)
o Areas with widespread use of antibiotics (farms, hospitals), increases spread of resistance between bacteria.
o Resistance may first appear in non-pathogenic bacterium, then to pathogenic.

57
Q

How can antibiotic resistance be reduced?

A

o Using antibiotics only when appropriate and necessary; not prescribing them for viral infections
o Making sure that patients complete their course of medication
o Medicines should only be given if prescribed
o Narrow spectrum drugs should be used rather than wide spectrum drugs
o Reduce the use of antibiotics in drugs in agriculture
o Use of many antibiotics to destroy the pathogen to make sure it doesn’t mutate.

Biology (19 decks)

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