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Unformatted text preview: om infection. By knocking out the immune
system, it leaves the body vulnerable to invasion by
microbes that would not normally infect a healthy
person. 2. (a) The virus rapidly increases in numbers within the
first year of infection, followed by a large drop off
in numbers in the second year. Over the next 3-10
years, the HIV population gradually increases
(b) The helper T cell numbers respond to the initial
infection by increasing in numbers. After about a
year, their numbers steadily decrease as they are
attacked and destroyed by the HIV. 3. Transmission of HIV, (a)-(c), any three of: Blood or
blood products, vaginal secretions, breast milk, across
the placenta, shared needles among intravenous
drug users (contaminated with blood from other
drug users), sexual intercourse: both homosexual
(especially between males) and heterosexual
(between men and women). 4. HIV positive: Blood tests have detected the presence
of HIV in blood samples from a person (even though
they may not have exhibited any symptoms). 5. Blood donated by the public and used to obtain a
blood clotting factor (Factor VIII) for hemophiliacs was
contaminated with HIV from donors already infected
with the virus. This is particularly the case in countries
where people are paid to donate blood. 6. As a provirus, the viral DNA may remain latent
(unexpressed) and replicate along with the host’s
DNA for some time before becoming active and
transcribing its genes. This has implications for the
host too, who may be unaware of infection and remain
symptomless (the HIV provirus may lie dormant within Biozone International 2009 Photocopying Prohibited 25 Stem Cell Technology (page 149) Animal to human organ transplants (xenotransplants).
Issues can be categorized into those associated with
animal welfare and those associated with risks to
humans (individuals or the wider community).
• Transplants from animals would relieve some of the pressure on the human organ waiting list.
• Xenotransplants are not very compatible with human tissues; rejection rates are still
unacceptably high, even from GE animals
• Xenotransplants involve genetic engineering of animals to produce human proteins that are more
acceptable to the recipient. GE c...
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- Winter '13