Chapter 17: sexually transmitted diseases

CHAPTER 16b: SEXUALLY TRANSMITTED DISEASES (STDs)

I. Viral Infections

A. Pathogens: Viruses, bacteria, and other organisms that cause disease. B. Viruses: Incapable of independent reproduction. They reproduce only inside a living host cell—obligate intracellular parasites. 1. Virus particles are generally very small, about ten times smaller than a bacterium. 2. Composed of an inner core of nucleic acid (DNA or RNA) and an outer capsid composed of protein subunits that surrounds and protects the genetic material. 3. Many viruses that infect animal cells also have an outer envelope derived from the host 4. Reproductive cycle of a typical DNA animal virus: a. Binding of the virus to the plasma membrane of the host cell. b. Penetration of the virus into the cell. c. Replication of the viral genetic material. f. Release of new viruses from the host cell. 5. Latency: A period of time during which some viruses can remain hidden in the cell a. Various factors such as exposure to UV light, stress, and lowered immune status can induce the virus to reproduce and be released from the cell.
II. Genital Warts

A. Caused by Human Papillomaviruses (HPVs). 1. In addition to genital warts, HPVs also cause warts of the hands and feet. 2. Over 6.2 million individuals become infected each year with a form of HPV that causes 3. Many carriers are asymptomatic or they have minimal symptoms. 4. When present, warts most commonly occur on the penis and near the vaginal opening. a. A newborn can become infected while passing through the birth canal. 5. Associated with cancer of the cervix and tumors of the vulva, vagina, anus, penis, and a. Believed to be involved in 90-95% of all cases of cancer of the cervix. b. Each year about 15,000 women in the United States learn that they have cervical cancer; an estimated 4,100 women will die of the disease this year. Worldwide, about 500,000 new cases of cervical cancer are diagnosed each year, resulting in 250,000 deaths. 6. Teenagers with multiple sex partners are particularly susceptible. 7. There is presently no cure for an HPV infection. 8. Current treatment consists of surgery, freezing, application of acid, or laser burning. 9. Even if warts are removed, they may recur and the virus can continue to be transmitted. 10. A vaccine is currently available against the most common HPV. III. Genital Herpes

A. Caused by Herpes Simplex Virus (HSV). B. HSV-1 causes cold sores and fever blisters. 1. Crossover infection can occur where HSV-1 causes a genital infection and HSV-2 2. Approximately 45 million individuals are now infected with herpes and a million more 3. Individuals infected with genital herpes can be asymptomatic carriers. 4. Symptoms may include a tingling or itching sensation before blisters appear on the a. Once blisters rupture, they leave painful ulcers that may take five days to three b. Blisters may be accompanied by fever, pain during urination, swollen lymph nodes in the groin, and in women, a heavy vaginal discharge. 5. After the ulcers heal, the disease is only latent. Blisters can recur, although usually at less frequent intervals and with milder symptoms. a. Fever, stress, sunlight, and menstruation are associated with a recurrence of 6. The herpes virus can cross the placenta and infect an infant before birth. An infant can also be born with a herpes infection if it comes in contact with a lesion in the birth canal. a. Herpes infections in an infant can cause neurological disorders, including brain damage. Blindness and even death may result. 7. Genital herpes lesions shed infective viruses. Virus can even be spread when there are no 8. Presently, there is no cure for genital herpes. 9. The drugs acyclovir and vidarabine are being used for treatment to disrupt viral 10. The ointment Zovirax relieves initial symptoms and Valtrex is the drug of choice to IV. Hepatitis
A. Hepatitis A is acquired from sewage-contaminated drinking water and food. It can also be sexually transmitted through oral/anal contact. 1. A Hepatitis A vaccine is available. B. Hepatitis C is most frequently caused by illegal injection of drugs. 1. Infection can lead to chronic hepatitis, liver cancer, and death. 1. Hepatitis B Virus (HBV) is a DNA virus that is transmitted in the same way as HIV, through sharing needles and through sexual contact. a. Hepatitis B is more infectious then HIV though. b. Very common for an AIDS patient to also have a Hepatitis B infection. c. Like HIV, Hepatitis B can be passed from mother to child by way of the d. Approximately 70% of infected persons have flu-like symptoms, including fatigue, fever, headache, nausea, vomiting, muscle aches, and dull pain in the upper right of the abdomen. Jaundice can also be present. e. Hepatitis B infections can be acute, lasting 3-4 weeks, or chronic, leading to liver i. Death from chronic liver disease occurs in 15-25% of infected persons. f. Currently, no treatment exists, but a vaccine is available.
V. Bacterial Infections

A. Bacteria: Microscopic organisms that occur in 3 shapes: B. Bacteria can be free-living or symbiotic- live in close association with another species. 1. Have an ability to pass from one host to the next. 2. Penetrate the host’s tissues. 3. Withstand the host’s defense mechanisms. 4. Induce illness in the host. D. Bacteria reproduce by binary fission -one cell simply splits into two. E. Antibiotics: Medications that kill bacteria by interfering with one of their metabolic F. There are currently no vaccines available for STDs caused by bacteria. VI. Chlamydia

A. Caused by the bacterium Chlamydia trachomatis. B. Considered an obligate parasite. Like a virus, chlamydia grows within body cells. 1. After the bacterium enters a cell by endocytosis, its life cycle occurs inside the endocytic vacuole, which eventually bursts and liberates many new infectious chlamydia. 2. Chlamydia is the leading STD in the U.S. a. As many as 18% of American women have vaginal chlamydial infections, and b. It is estimated that the infection rate could be high as 50% on college and c. For every reported case in men, more than 5 cases are detected in women. i. This is mainly due to increased detection of asymptomatic infections ii. The low rate in men suggests that many of the sex partners of women with chlamydia are not diagnosed or reported. 3. Chlamydial infections in women are usually mild or asymptomatic. a. About 8-21 days after an infection, they may experience a vaginal discharge b. If the chlamydial infection goes undetected or is treated improperly, Pelvic i. This is a painful condition in which the chlamydial infection spreads from ii. May result in blockage of the oviducts with the possibility of sterility or 4. About 8-21 days after infection, men may experience a mild burning sensation on 5. If a newborn comes in contact with chlamydia during delivery, pneumonia or a. Erythromycin eye drops at birth prevent this occurrence. 6. Chlamydial infections can be cured with the antibiotics tetracycline, doxycycline, and Gonorrhea
A. Caused by the bacterium Neisseria gonorrhoeae. B. Reported gonorrhea rates declined steadily until the late 1990s, and then they increased by a. Rates of infection remain high among adolescents, young adults, and African b. Women using birth control pills have a greater risk because hormonal contraceptives cause the genital tract to be more receptive to pathogens. C. Persons with gonorrhea often have chlamydia as a secondary infection. Infection with either gonorrhea or chlamydia increases the risk of an infection with HIV. D. Male diagnosis of gonorrhea is easy if symptoms are present. Typical symptoms include pain during urination and a milky urethral discharge. Approximately 20% of cases in men though are asymptomatic. E. In women, the bacteria may first settle within the vagina or near the cervix, from which it 1. Unfortunately, the majority of women are asymptomatic until they develop severe pains 2. Gonorrhea proctitis is an infection of the anus, with symptoms that include anal pain and 3. Oral/genital contact can cause infection of the mouth, throat, and the tonsils. 4. Gonorrhea can spread to internal parts of the body, causing heart damage or arthritis. 5. Eye infection leading to blindness can occur as a baby passes through the birth canal. a. Because of this, all newborns receive erythromycin eye drops as a protective 6. Women have a 50-60% risk of acquiring a gonorrheal infection from an infected partner, while men have a 20% risk of contracting the disease after even a single exposure to an infected partner. 7. Previously easily cured by the antibiotics penicillin or tetracycline, 30% of modern strains are antibiotic resistant. The antibiotic cephalosporin is now recommended. 8. It is standard medical practice to treat anyone who is known or suspected to have either gonorrhea or chlamydia as if they have both diseases and treat with antibiotics appropriate for both diseases.
VIII. Syphilis

A. Caused by the bacterium Treponema pallidum. 1. The number of new cases of syphilis in 2001 was the fewest in the U.S. since 1945. However, outbreaks of syphilis have recently been reported among gay and bisexual men. 2. The disease involves three stages which can be separated by latent periods during which a. Primary stage involves the appearance of a hard chancre-ulcerated sore at the site b. Secondary stage involves the appearance of a rash all over the body, including i. Indicates the bacteria have invaded and spread throughout the body. ii. Not all cases of secondary syphilis go on to the tertiary stage. Some spontaneously resolve the infection and some simply do not progress beyond the secondary stage. c. The tertiary stage lasts until the patient dies and involves neurological and i. The patient may become mentally impaired, blind, or show signs of ii. Weakened arterial walls (aneurysms) are seen, particularly in the aorta. iii. Large, destructive ulcers (gummas) may develop on the skin or within B. Syphilitic bacteria can cross the placenta, causing birth defects, blindness or stillbirth. C. Diagnosis of syphilis can be made by blood tests or by microscopic examination of fluids D. Tracing sexual partners is very important to controlling syphilis. E. The cure for all stages of syphilis is some form of penicillin. IX. Other Infections

A. Trichomoniasis is a sexually transmitted disease caused by the protozoan Trichomonas vaginalis. 1. This organism accounts for about ¼ of all cases of vaginitis. 2. Trichomoniasis is characterized by the presence of an abundant, frothy, white or yellow, foul-smelling vaginal discharge accompanied by itching that can be severe. 3. Most often acquired through sexual intercourse, and an asymptomatic partner is usually the reservoir of infection. To avoid passing the condition back and forth, both partners should be treated simultaneously. B. Candida albicans is a yeast that can cause diaper rash, thrush, and a form of vaginitis in women. 1. Candida albicans is a normally occurring organism in the vagina. Yeast infections can result from taking birth control pills or antibiotics that disrupt the normal balance of bacterial flora. 2. An estimated 13 million cases of candidal vaginitis occur annually. 3. A woman usually notices a white, clumpy discharge that looks something like cottage cheese. Associated symptoms include intense itching and soreness of the vaginal and vulval tissues, which typically become red and dry. 4. OTC intravaginal preparations are available. Treatment should continue well beyond the two days it takes for symptoms to disappear. C. Pubic lice or “crabs” is caused by the parasitic crab louse Phthirus pubis (an insect). 1. Crabs can be contracted by direct contact with an infested person or by contact with his 2. Pubic hair, underarm hair, and eyebrows can be infected. 3. Severe itching may result from infestation. 4. Treatment involves medication such as lindane which is applied to the infested area. a. All sexual partners need to be treated. b. Undergarments and sheets should also be washed in very hot water.

Source: http://www.elmhurst.edu/~bio/renee/BIO104/Chapter%2016b.pdf