244 16 HIV/AIDS Infection and Cell Organelles A LTHOUGH MANY OF their characteristics are similar to those of cells, viruses are not cells. They contain genetic material and a few proteins, but they do not conduct cellular functions. For example, a virus can neither metabolize nutrients needed to grow and to develop essential structures, nor can it reproduce on its own. To reproduce, a virus must infect a living host cell. Viruses are specific to their hosts. Some infect one kind of animal, while others infect plants or even bacteria. Once it is inside the host cell, the virus takes over the cell’s structures, enzymes, and organelles that will enable it to reproduce. Challenge How does HIV take over a cell’s structures and organelles during infection and use them to reproduce? MATERIALS FOR EACH PAIR OF STUDENTS set of 13 Cell Structures and Organelles Cards colored pencils FOR EACH STUDENT Student Sheet 16.1, “Scientific Diagram of HIV Infection” Student Sheet 2.1, “Disease Information,” from Activity 2 sticky notes An electron microscope image of HIV virus budding from a human cell membrane
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244
16 HIV/AIDS Infection and Cell Organelles
ALTHOUGH MANY OF their characteristics are similar to those of cells, viruses
are not cells. They contain genetic material and a few proteins, but they
do not conduct cellular functions. For example, a virus can neither metabolize
nutrients needed to grow and to develop essential structures, nor can it reproduce
on its own. To reproduce, a virus must infect a living host cell. Viruses are specific
to their hosts. Some infect one kind of animal, while others infect plants or even
bacteria. Once it is inside the host cell, the virus takes over the cell’s structures,
enzymes, and organelles that will enable it to reproduce.
Challenge ! How does HIV take over a cell’s structures and organelles during infection and use them to reproduce?
MATERIALSFOR EACH PAIR OF STUDENTS
set of 13 Cell Structures and Organelles Cards
colored pencils
FOR EACH STUDENT
Student Sheet 16.1, “Scientific Diagram of HIV Infection”
Student Sheet 2.1, “Disease Information,” from Activity 2
sticky notes
An electron microscope image of HIV virus budding from a human cell membrane
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HIV/AIDS INFECTION AND CELL ORGANELLES • ACTIVITY 16
Procedure 1. With your partner, spread out the Cell Structures and Organelles cards on the
table. Sort out the cell structures and organelles that you think the HIV virus
would directly need in order to reproduce many copies of itself. Set the other
Cell Structures and Organelles cards aside.
2. Discuss with your partner the path that you think the HIV virus would take
within the cell as it takes over the cell. Lay out the cards in the order you
decide on.
3. Pick a colored pencil, and on your Student Sheet 16.1, “Scientific Diagram of
HIV Infection,” do the following:
a. Trace the path of the virus infection through the various structures or
organelles you decided on in Step 2.
b. Next to each structure or organelle in the path, write an explanation of why
you think that structure or organelle is involved.
4. Visit the Science and Global Issues page of the SEPUP website at sepuplhs.org/sgi.
With your partner, follow the simulation of the life cycle of the HIV virus.
5. Watch the narrated version of the simulation. As you watch and listen, with a
different colored pencil add to or change the path you traced, where appro-
priate, on Student Sheet 16.1, “Scientific Diagram of HIV Infection.”
6. For more detail, view the step-through version of the simulation and read the
descriptions of each stage of the process. At each step you can click “Play” to
watch the animation of only that stage.
7. Follow your teacher’s directions for reading the case study about rotavirus. As
you read, use the “Read, Think, and Take Note” strategy.
8. Complete the information for rotavirus on Student Sheet 2.1, “Disease Infor-
HIV/AIDS INFECTION AND CELL ORGANELLES • ACTIVITY 16
GLOBALLY, ONLY A few infectious diseases cause the majority of deaths for children younger than five years old. Rotavirus, with the severe diarrhea it causes, is one of them.
Rotavirus causes approximately 40% of all cases of severe diar-rhea in infants worldwide. More than 85% of rotavirus deaths occur in Asia and Africa.
SYMPTOMS AND DISEASE MECHANISM
The symptoms of rotavirus infection include severe
vomiting, fever, abdominal pain, and watery diarrhea over several days. These symptoms are usu-ally milder in adults, who nor-mally recover. Rotavirus is an RNA virus that infects cells that line the small intestine, the ones that absorb nutrients and water.
When the virus infects and kills these cells, unabsorbed nutrients and water leave the body rapidly in diarrhea and vomit, making the patient weak and dehy-drated. Rotavirus is transmitted
(Continued on next page)
CASE STUDY
Rotavirus
Burden of DiseaseTOTAL NUMBER WITH DISORDER
NUMBER OF DEATHS PER YEAR
Worldwide more than 100 million 450,000
United States 55,000–70,000 hospitalizations
20–60
Rotavirus deaths of children younger than 5, before widespread introduction of vaccine
SCIENCE & GLOBAL ISSUES/BIOLOGY • CELL BIOLOGY
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in contaminated water or food, airborne droplets, and contact with contaminated surfaces. Therefore, safe water, sanitation, and refrigeration of food are important for controlling rota-virus transmission.
ROTAVIRUS PREVENTION AND TREATMENT
Exclusive breastfeeding is a strategy for preventing diarrheal infections, including rotavirus, in infants up to six months old. Exclusive breastfeeding means the baby ingests no food or drink besides its mother’s breast milk. The baby is allowed vita-mins, minerals, or medicines, but no water. Breast milk con-tains nutrients, antibodies, and other elements that boost the immune system, and breast-feeding eliminates the need for infants to eat food or take in drink that may be contaminated.
In 2007, a vaccine became avail-able to prevent rotavirus infec-tion, and widespread distribution of the vaccine could be a major boost for prevention of the disease. The World Health Organi zation now recommends
rota virus vaccine be adminis-tered to infants as soon as pos-sible after six weeks of age. The maps on the following page show the first countries to introduce the vaccine and the approxi-mately 80 countries that had introduced the vaccine by the end of 2015. Studies of the impact of the vaccine show sig-nificant reductions in hospital-izations and deaths.
Currently, there is no drug treatment for rotavirus infec-tion. Only oral or intravenous rehydra tion with electrolytes is prescribed. This maintains homeostasis of water and salts in the blood.
CHALLENGES TO PREVENTION AND TREATMENT
For HIV-positive mothers, breastfeeding is not a good option for preventing rotavirus in their infants because breast milk can transmit HIV. In these cases it is safer to feed babies a breast milk replacement, such as infant formula. But with for-mula, the baby does not get the antibodies to protect against diseases that breast milk would carry from mother to child.
Currently there are two major roadblocks to global use of a rotavirus vaccine. First, more vaccine is going to countries where rotavirus is much less of
Distribution of Improved Sanitation (% of population)1
AFRICA THE AMERICAS EASTERN MEDITERRANEAN
EUROPE SOUTHEAST ASIA WESTERN PACIFIC
33 87 60 93 37 69
1. Data from WHO organization of world regions.
Model of a rotavirus
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HIV/AIDS INFECTION AND CELL ORGANELLES • ACTIVITY 16
a problem than to those with the greatest need for the vac-cine. This is partly a matter of the relatively high cost of the vaccine, which is about $20
or more per child. Second, the rotavirus vaccines, like many vaccines, must be kept refrigerated to prevent their spoiling—a difficult task in
remote tropical and subtrop-ical areas of the world that do not have a reliable supply of electricity. "
In routine immunization schedule in 2007 (11 countries)Immunization support approved (3 countries)
National immunization programs (76 countries)Regional immunization programs (3 countries)