Transmission of Disease (2.2.2)

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Name 3 things a pathogen must be able to do in order to cause disease.
Travel from one host to another in order to spread. Get into host tissues and obtain nutrients. Cause damage to host tissues.
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What are the most common forms of pathogen transmission?
A vector, physical contact, droplet infection.
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What is a vector?
Another organism that acts as a carrier to move the pathogen from host to host.
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What is droplet infection?
When a pathogen is passed on by droplets of moisture when we cough and sneeze.
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What organism is malaria caused by?
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Why is it difficult to develop a malaria vaccine?
There are 4 different types of Plasmodium.
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What is the vector that spreads malaria?
The female Anopheles mosquito. It carries Plasmodium in its mouthparts and passes it from person to person when taking a blood meal before laying eggs.
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Give three other ways the malarial parasite can be spread?
Across the placenta. Unscreened blood transfusions. Unhygienic medical practices.
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Describe the cycle of malaria transmission.
Plasmodium gametes in blood. Mosquito sucks blood then lays eggs. Plasmodium develops, migrates to mosquito's salivary glands. Uninfected person is bitten. Plasmodium migrates to liver. Multiplies in liver then released into blood. More gametes made.
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Why is it difficult for the immune system to defend the body against malaria?
The antigens on the pathogen's surface change frequently- this makes it hard for the immune system to recognise it. The pathogen is hidden inside cells a lot of the time. It is easy for reinfection to occur, because it uses a vector.
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Give 3 precautions to reduce the risk of malaria.
Mosquito nets over beds. Take prophylactic drugs before visiting countries where malaria occurs. Wear long sleeves and trousers.
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Why is it difficult to completely eradicate malaria?
There are 4 different types, and there are different stages to the life cycle.
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What would make you more at risk of TB?
Overcrowding. Poor ventilation. Poor health. Poor diet.
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How is TB spread?
By droplet infection.
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What does TB do?
Damages cells in the lungs.
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What two bacterium cause tuberculosis?
Mycobacterium tuberculosis, and Mycobacterium bovis (associated with cattle).
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What is a symptomless carrier?
People who are infected with TB but it's inactive or controlled by the immune system. But they can still pass it on to others.
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Give 3 symptoms of TB.
Weight loss, night sweats, coughing up blood-stained mucus.
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What could be 2 reasons for the increase in TB cases?
More people with HIV. More people travelling.
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How is TB treated?
Taking a combination of several antibiotics over a long time period. It's unlikely the bacteria will be resistant to all of the antibiotics given.
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What is a syndrome?
A collection of diseases linked to a common cause.
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Give 4 ways that HIV can enter the body.
Sharing needles. Across the placenta. Unprotected sex. Blood to blood contact.
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What does the HIV virus do?
Uses glycoprotein to attach to host cell. Inserts RNA and reverse transcriptase. Uses enzyme to convert RNA to DNA. Inserts this DNA into host cell DNA. DNA is replicated with human DNA for many years. It is suddenly activated- this is AIDS.
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What is it called when the virus is dormant?
The person is described as HIV positive but they don't yet have the symptoms of AIDS.
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What happens when the virus becomes active?
It attacks and destroys some of the cells in the human immune system. This leaves the body much more vulnerable to infections.
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Describe the life cycle of HIV.
Virus particles carried from body fluid of one person to another. Virus enters T lymphocyte. DNA copy is made of viral DNA. DNA copy inserted into chromosome. Lymphocyte divides normally. Years later viral DNA takes over cell. Cell dies- releases HIV
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Why is it difficult to develop a vaccine?
The virus mutates frequently, changing its surface proteins.
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What can contribute to the poor health of people in developing countries?
Poverty, lack of proper shelter, poor nutrition, poor hygiene, inadequate health services.
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Card 2


What are the most common forms of pathogen transmission?


A vector, physical contact, droplet infection.

Card 3


What is a vector?


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Card 4


What is droplet infection?


Preview of the front of card 4

Card 5


What organism is malaria caused by?


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