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Human Biol: Prevention and Control of Infection

Year 12 Human Biology Assignment: Prevention and Control of Infection

1.B) Experiment A starts off with a slightly lower number of bacteria than experiment B, but has a steady inclining growth, ending with a higher number of bacteria. The growth pattern is exponential, but because it is on semi-log graph paper the graph becomes linear.

C) yes I think it is very likely that this strain of Staphylococcus could infect a person because over a short period of time  the bacteria has managed to grow rapidly starting with only 200 bacteria and growing rapidly to 9,000,000 over just 72 hours. If it continued to do this, after it had penetrated into the human body system, it would rapidly multiply within the body and infect cells.

D) Experiment B looks as if the drug Sulphonamide has been added at around the 48th hour when the results for the number of Bacteria stop increasing and begin to decline again. They continue to decrease after the 48th hour, indicating that the drug was working and killing off the bacteria and stemming the rapid increase of the number.

E) The number of bacteria decreases once the Sulphonamide is applied in the 48th hour. Compared to the experiment A, where the number of bacteria continues to increase, Experiment B is decreasing approximately 6.94 times slower than Experiment A is increasing between the 48th and 60th hour. Over this 12 hours this is quite a considerable difference, showing that the decrease is slower than the increase.

F) This drug would probably be ineffective against a viral infection because if it’s only aimed at a bacteria which has no nucleus and no organelles, unlike a virus which has a nucleus with DNA or RNA that infects the DNA of the human body that it is multiplying within.

2 A) A syndrome is described as ‘a group of symptoms that consistently occur together or a condition characterised by a set of associated symptoms’. This is why Acquired Immune Deficiency Syndrome is called a syndrome – because it is a condition characterised by a set of associated symptoms that consistently occur.  

2B) Most people have noticeable symptoms when initially infected with HIV (Human Immunodeficiency Virus) – fever, rashes, swollen lymph nodes, fatigue, and a variety of common symptoms that may develop in the first and last few weeks of the virus. The symptoms usually disappear, although the lymph nodes may stay enlarged, and a person can have the HIV (even with no symptoms) for years, or even decades before they will begin to display the symptoms of AIDS. Symptoms for AIDS can include swollen lymph nodes, weight loss, fatigue, recurring fever, diarrhoea, anaemia, and thrush. However, it is more likely that the person with AIDS will display more specific symptoms of the specific opportunistic infections and cancers that develop – the symptoms are primarily the result of infections that do not normally develop in individuals with healthy immune systems.

2C) Once in the body, HIV attaches to a number of different types of lymphocytes. HIV has its genetic material encoded in RNA. Once inside the cell, the virus uses an enzyme called reverse transcriptase to turn its RNA into DNA, which is then incorporated into the DNA of the infected lymphocyte. The lymphocyte then replicates the virus inside the cell, eventually destroying the cell.

One of the most important types of lymphocytes that the virus infects is the helper T lymphocyte, which activates and coordinates other cells of the immune system. Because the virus destroys this particular lymphocyte type, it weakens the body’s system for protecting itself against certain infections and cancers. This weakening of the body’s immune system is one of the reasons why it is not capable to rid itself of the HIV infection once it is underway.

The normal count of the helper T lymphocytes is roughly around 800 to 1,300 cells per microlitres of blood.  If the count falls below about 200 cells per microlitre of blood, then the immune system becomes less able to fight certain infections (eg pneumonia). These infection do not usually appear in people with healthy immune systems. A count of below about 50 cells per microlitre of blood is particularly dangerous, because additional opportunistic infections that can rapidly cause severe weight loss, blindness or death, commonly occur.

2D) Patients with AIDS commonly contract diseases such as influenza and pneumonia – diseases that don’t usually kill – and these can become fatal for the patient due to their poo immune system.  By the time the patient reaches the AIDS stage of the virus, their immune system is severely damaged and failing because the virus has killed many of the lymphocytes. Their helper T lymphocyte count is severely degraded from it’s usual number, and when it falls below 200 per microlitre of blood, that’s usually when the body begins to contract these opportunistic diseases and infections, because the immune system is weakened and unable to sufficiently fight them.

2E) At the moment the body cannot be vaccinated against HIV or AIDS because there is no known vaccination to date that has been trailed and proved to work. There are a few being trialled, however the process of the trialling is long and not strictly accurate, because it is given to people who are only at “high risk” of contracting the disease.

A vaccine ‘teaches’ the immune system how to defend itself against pathogens and is designed to prevent one specific disease or pathogen. This means that a vaccine matches with a certain disease. A preventative vaccine is meant for people who have not been infected with the pathogen that the vaccine is designed to protect against, but it not a treatment or cure for someone who is already infected with that specific pathogen.

This means that a HIV/AIDS vaccine will be harder to find because the virus kills off the helper T lymphocytes which co-ordinate and activate the other cells of the immune system. If these cells don’t work then they won’t be able to carry out what the vaccine has ‘taught’ them to do when infection occurs.

2F) AIDS itself is not contracted from an outside source, because it is the end stages of the Human Immunodeficiency Virus (HIV). However, the transmission of HIV requires contact with a body fluid that contains the virus or infected cells. HIV can appear in nearly any body fluid, but transmission is more likely to occur from blood, semen, vaginal secretions and breast milk. Although low concentrations of HIV are found in tears, urine, and saliva, transmission from these fluids is extremely rare. HIV is transmitted though:

·      Sexual contact with an infected person during which the mucous membrane lining of the mouth, rectum, vagina, or penis is exposed to infected body fluids (usually unprotected sex).

·      Injection or infusion of infected blood, as occurs during blood transfusions, sharing needles, or an accidental prick from a HIV infected needle. (This isn’t as much of a problem as it used to be, because since 1985 all donated blood for transfusions has been screened for HIV and where possible, blood products are treated with heat to eliminate the risk of HIV infection. There is also a big awareness and emphasis put on the necessity for clean needles to be used)

·      Transfer of the virus from an infected mother to a child before birth, during birth, or after birth through the mother’s milk (in around 25 to 30%* of pregnancies involving infected women, the virus is transmitted to the foetus through the placenta or, at birth during the passage through the birth canal)
*statistics from ‘The Merck Manual of Medical Information, Home Second Edition’ (2004) Pocket books: USA

Vulnerability to HIV infection increases when the skin or mucous membrane (which is very delicate) is torn or damaged (even minimally), as can happen during vigorous vaginal or anal sex or when either on or both of the partners has another Sexually Transmitted Disease (particularly herpes or syphilis) that produces breaks in the skin or irritation of the genitals.

Different groups of the population are more likely to contract HIV than others. HIV and AIDS used to be thought of as a “gay man’s disease”, and in the United States, Europe and Australia, HIV has mainly been transmitted through male homosexual contact and the sharing of needles among injecting drug users, but the transmission through heterosexual contact has been rapidly increasing. In 2000, America saw that 42% of the new HIV infections developed in homosexual men, 33% in heterosexual men and women, and 25% in injecting drug users. However, in Africa, the Caribbean and Asia, HIV infections occur principally through heterosexuals, and it occurs equally between men and women.
(statistics from ‘The Merck Manual of Medical Information, Home Second Edition’ (2004) Pocket books: USA)

2G) Certain precautions can be taken in the future to try and help prevent “the new plague” sweeping worldwide, such as by properly always using things such as protection (in particular condoms) during intercourse and always using a clean and new needle before injecting can help to minimise some of the numbers of infected people. Regular screenings for people who are sexually active could also be suggested seeing as HIV can often go unnoticed or unknown for a long time after contraction, which means the infected person, could unknowingly be transmitting it to others.

However this becomes a problem in some areas, because they don’t have enough money to do these sorts of things. An example of this is in Africa where there is a very high risk of contracting an STD including HIV. Because not many of the people in Africa can afford to use protection during intercourse, they don’t which leads to higher risks of transmission.

Drug users usually also have the same problems with money – they need all their money to feed their habit, so often resort to sharing needles or using unclean or old ones. There is also a certain risk factor involved in things such as getting tattoos (especially in most Asian parlours where it’s not mandatory to use clean and fresh needles each time).


December 5, 2008 Posted by | exams, homework, Human Biology, school, School Work | Leave a comment