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Biology A-Level > HIV/AIDS and TB (Chapter 10) > Flashcards

HIV/AIDS and TB (Chapter 10) Flashcards

1
Q

What does AIDS stand for?

A

Acquired Immune Deficiency Syndrome

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2
Q

What is the pathogen of AIDS?

A

HIV (Human Immunodeficiency Virus)

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3
Q

What are the three methods of transmission of HIV?

A

1) sexual intercourse through semen and vaginal fluids
2) transmission of infected blood (e.g. through blood donation and the sharing of needles used by intravenous drug users)
3) mother to foetus across the placenta and through mixing of blood during birth

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4
Q

What are the sites of action of HIV?

A

T helper lymphocytes, macrophages, brain cells

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5
Q

What are the symptoms of HIV and AIDS?

A

HIV - flu-like symptoms then symptomless

AIDS - opportunistic infections (e.g. TB, Karposi’s sarcoma, pneumonia, malaria) and weight loss, diarrhoea

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6
Q

What kind of virus is HIV?

A

A retrovirus - it has RNA not DNA

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7
Q

What happens when HIV infects?

A

1) once inside a host cell, the viral RNA is converted to DNA to be incorporated into human chromosomes
2) the virus infects and destroys cells of the body’s immune system (helper T cells) so that their numbers gradually decrease
3) when the numbers of cells are low, the body is unable to defend itself against infection, ∴ allowing a rang of pathogens to cause a variety of opportunistic infections

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8
Q

What is AIDS?

A

A collection of opportunistic disease associated with immunodeficiency cause by a HIV infection

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9
Q

What is the only way that transmission of HIV is possible?

A

Through direct exchange of bodily fluids

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10
Q

How can HIV spread more easily?

A

Having multiple sex partners

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11
Q

Why may someone not have any symptoms of HIV until years later?

A

HIV is a slow virus

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12
Q

When is a person HIV+?

A

When they appear not to develop any initial symptoms except flu-like symptoms for several weeks after becoming infected

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13
Q

What is the difference between AIDS in developed and developing countries?

A

Most likely causes of death of people with AIDS:
Developed countries - cancers of internal organs, dementia
Developing countries: malnutrition, malaria and TB

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14
Q

Why does AIDS have an adverse effect on the economic development of countries?

A

1) it affects sexually active people in their 20s and 30s who are the most economically productive
2) the purchase of expensive drugs drains government funds

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15
Q

How is HIV/AIDS treated?

A
  • There is no cure for AIDS and no vaccine for HIV
  • Drug therapy can slow down the onset of AIDS significantly e.g. zidovudine which binds to the viral enzyme reverse transcriptase and blocks its action - but drugs are expensive and have side effects
  • Combination drug therapy
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16
Q

Why is the spread of HIV/AIDS difficult to control?

A

1) the virus has a long latent stage ∴ it can be transmitted by people who are HIV+ but show no symptoms of AIDS and do not know that they are infected
2) the virus changes its surface proteins, making it difficult for the body’s immune system to recognise it and to make a vaccine

17
Q

How do public health measures steps the spread of HIV/AIDS?

A

1) people can be educated about the spread of infection and encouraged to change behaviour to protect themselves and others
2) condoms, femidoms and dental dams reduce risk of infection during intercourse, forming a barrier between body and fluids, reducing chance of transmission

18
Q

What is contact tracing?

A
  • If a person who is diagnosed as HIV+ and identifies the people who they have put at risk of infection by sexual intercourse or needle sharing, then these people will be offered a HIV test
  • This test identifies the presence of antibodies to HIV
19
Q

How can the spread of HIV be prevented?

A

1) injecting drug users are advised to give up on their habit, stop sharing needles, or take their drug another way - needle exchange schemes also exist to exchange used needles for sterile ones
2) blood collected from blood donors is screened for HIV and heat-treated to kill any viruses and people who think they might have been infected are encouraged not to donate
3) HIV-testing is promoted most strongly to high-risk groups e.g. male homosexuals, prostitutes and injecting drug users
4) mother to child transmission is reduced by treating HIV+ women and their babies with drugs mothers are encouraged not to breastfeed their babies

20
Q

What are the two pathogens of TB?

A

Myobacterium tuberculosis and Myobacterium bovis

21
Q

What is are the methods of transmission of TB?

A

M. tuberculosis: airborne droplets

M. bovis: undercooked meat and unpasteurised milk

22
Q

What are the symptoms of TB?

A

Racking cough, coughing blood, chest pain, fever

23
Q

What is special about TB?

A
  • Some people become infected with and develop TB quite quickly, while in others the bacteria can remain inactive for many years
  • People with the inactive infection do not spread the disease
24
Q

What is the relationship between TB and HIV?

A
  • TB is often the first opportunistic infection to strike HIV+ people
  • HIV infection may reactivate dormant infection of M. tuberculosis or make then susceptible to infection
25
Q

When are TB bacteria most likely to become active?

A

When people are weakened by other diseases e.g. malnutrition or infected with HIV

26
Q

How is TB spread?

A

1) infected people with the active form of the illness caught or sneeze and TB is carried in the air in tiny droplets of liquid
2) uninfected people then inhale the liquid

27
Q

How is TB spread most rapidly?

A

Among people living or sleeping in overcrowded conditions - ∴ mainly attacks those in poor housing or the homeless

28
Q

Why did TB incidence decrease steeply?

A

1) improvements in housing conditions and diet
2) antibiotic streptomycin introduced in 1940s
3) vaccine introduced in 1950

29
Q

Why is TB on the increase?

A

1) some strains of TB bacteria being resistant to drugs
2) HIV/AIDS pandemic
3) poor inner city housing and homelessness
4) breakdown of TB control programmes - partial treatment for TB increase the chance of drug resistance
5) migration

30
Q

How is TB diagnosed and controlled?

A

1) samples of sputum (mucus + pus) from their lungs are collected for analysis
2) identification of TB bacteria is done very quickly by microscopy
3) if TB is confirmed, patients should be isolated while in most infectious state (at 2-4 weeks), particularly if infected with a drug resistant strain

31
Q

How is TB treated?

A
  • Treatment involves using several drugs to ensure that all bacteria are killed
  • Treatment is long (6-9 months or more) because it takes a long time to kill the bacteria as they are slow growing and not very sensitive to the drugs used
32
Q

How can drug-resistant TB arise?

A
  • If all the bacteria are not killed, drug-resistant forms remain to continue the infection
  • Many people do not complete their course of drugs because they feel better, but they may be harbouring drug-resistant bacteria which can spread if they become active
33
Q

Why does not treating TB or stopping treatment before all bacteria are completely eliminated increase the chance of antibiotic resistance arising?

A

Bacteria spread throughout the body, increasing the likelihood of mutation, as the bacteria survive for a long time and multiply

34
Q

How does the WHO try and prevent drug resistant TB?

A

They promote a scheme called DOTS (direct observation treatment, short course) to ensure that patients complete their course of drugs - this involves health workers or family members making sure that patients take their medication regularly for 6-8 weeks

35
Q

How is TB prevented?

A

Contact tracing and subsequent testing

36
Q

Describe the TB (BCG) vaccine?

A
  • Derived from M. bovis
  • Protects up to 70-80% of people who receive it
  • Not in immunisation programmes of UK or USA
  • Only used in high-risk countries or for high-risk people
37
Q

How is M. bovis transmission prevented?

A
  • Cattle are routinely tested for TB and any found to be infected are killed
  • TB bacteria are killed when milk is pasteurised

Biology A-Level (44 decks)

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