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Lecture

Chapter 4

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Department
Biomedical Physio & Kines
Course
BPK 140
Professor
Michael Walsh
Semester
Fall

Description
1 KIN 140 Section 4 Dr Mike Walsh I. Sexually Transmitted Diseases (STDs) Aka Sexually Transmitted Infections (STIs) STDs include acquired immunodeficiency syndrome (AIDS), chlamydia, gonorrhea, pelvic inflammatory disease (PID), genital warts, genital herpes, hepatitis B, syphilis, and others. Unfortunately you can have more than 1 STD at a time and the same one can reoccur many times. Little immunity is imparted to the host and therefore you can get the disease more than once. Having an STD can also lead to other diseases, so there is not a lot of upside. Another problem is that STDs can be asymptomatic for long periods while the host remains infectious. This leads to “6 degrees of copulation”. It takes between 3 and 7 sexual contacts to be linked to the sexual partners of everyone else. The spread of an STD is magnified when some individuals have a large number of sexual contacts. In the case of AIDS, a Canadian flight attendant was responsible for 40 of the first 248 cases identified in 8 different cities in the world. II. HIV (human immunodeficiency virus)/AIDS Overview HIV mutated from the monkey simian immunodeficiency virus (SIV). It turns out people eat monkey meat and can cut themselves while butchering the monkey, thus creating a portal of entry for bodily fluid (blood) exchange. When did the simian virus first become HIV is a bit of controversy. Some experts believe it came about via the proliferation of towns in Africa with an increase in sexual contacts and red light districts. Others believe it was the massive reuse of cheap needles in the 1950s that were used to control/eradicate diseases such as polio, smallpox and malaria. There are actually 2 forms of the HIV virus (HIV-1 and HIV-2). There are DNAand RNA viruses, both single and double stranded. HIV is a retrovirus. It has two single strands of RNAand is retro because it also has the enzyme, reverse transcriptase, which enables the virus to make DNAcopies of its RNA. The RNAmolecule has 9 or 10 genes that in turn encode 19 proteins. It is surrounded by a protein coat and then again by a lipid membrane which has surface glycoproteins for recognition of specific cells in which to bind. It is about 60x smaller than a red blood cell. 2 Alot of controversy surrounds HIV identification and the cause ofAIDS. Below is the mass-combined version. A. HIVAttack HIV is a very effective pathogen because it attacks the immune system that defends the body. The retrovirus attacks the T4 helper cells (specifically CD4 helpers). Thus it attacks the body’s ability to kill the virus and depresses our amplification mechanisms as well. With the immune system depressed, the infected person is also vulnerable to many other diseases. The virus attaches to a helper T cell and injects its 2 single stranded RNAmolecules. With the enzyme reverse transcriptase, a single viral RNAmolecule will be converted to a double-stranded DNA molecule that is inserted into the host’s DNA. This ‘viral’DNA may lie dormant for a long time. It can get active when the T cell gets activated. That is, when the T cell is stimulated to defend the body, the viral DNAstarts making proteins that make new viruses and in turn kill the immune cell that was going to protect the body. The HIV reproduction rate can be up to 10^10 virons per day. Coupled with a high mutation rate, the infected person can have many new HIV variants every day. Of course, this adds to the difficulty of creating a vaccine against the virus. Once infected it may take as long as 3 months, while the virus is replicating, before there are detectable levels of antibodies (made by the body) to HIV to make a positive confirmation of the infection. At this time the virus can be transmitted the easiest. It may take from 1-20 years before the infected person shows symptoms.At this time the person can still transmit the virus. In the symptomatic period the normal count of T helper cells (aka T4 or CD4 cells) falls from 800-1000 per microlitre to below 200 per microlitre and the patient is now considered to haveAIDS. Once the patient becomes symptomatic, this phase can last 6 months to 10+ years. This duration is quite drug effectiveness dependent. AIDS kills only a fraction of the people that cars, tobacco, heart disease etc kills. So why are we so concerned? We have no vaccine and no cure. It is the most infectious disease since the Black Plague. AIDS is mostly a disease of the young and 58 million people worldwide are infected. 3 B. HIV Transmission At any stage of HIV infection, the carrier is infectious. The virus is transmitted through some of the body’s fluids: vaginal fluid seminal fluid preseminal fluid blood breast milk HIV is not transmitted through saliva (as long as the oral lining is intact), sweat, or tears. Lets take a closer look at saliva. If for example a person recently flosses their teeth, they may create portals of entry. Performing unprotected oral sex while these temporary portals are available can create a successful transmission. Blood to blood and semen to blood are the most effective ways to transmit the virus. It is easier to get HIV via unprotected anal or vaginal intercourse rather than the oral route. The chance of infection increases if tissue linings are irritated (e.g., enemas, spermaticides, or flossing). For heterosexual activity, HIV is 12x more readily transmitted from male to female than the reverse because HIV is more concentrated in semen than it is in vaginal fluids. Outside of the body, HIV is easily destroyed with hot soapy water or dilute bleach. It also cannot survive on a toilet seat. C. AIDS Treatment There is no cure
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