Prevention Diagnosis And Treatment Of Sexually Transmitted Infections Biology Essay

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Over 700,000 new sexually transmitted infections cases are diagnosed annually, with someone being diagnosed with an STI every 15 seconds. The World Health Organisation (WHO) defines STIs as "infections that are spread primarily through person-to-person sexual contact". Forty years ago, only two curable STIs were common. This figure has now increased to as many as 25 STIs, with several being incurable, including human papilloma virus (HPV), human immunodeficiency virus (HIV) and genital herpes.

Many STIs can cause adverse pregnancy outcomes including miscarriages, stillbirths, intrauterine growth restriction and perinatal infections. Some STIs can cause infertility or lead to ectopic pregnancy among women and the human papillomavirus can cause cervical and anogenital cancer (National Institute of Allergy and Infectious Diseases 2001).

The most reliable way to avoid transmission of STIs is to abstain from sexual contact or to be in a long-term monogamous relationship with an uninfected partner (MMWR 2006). Screening for common STIs before sexual contact with a partner might reduce the future risk of asymptommatic STI transmission (MMWR 2006).

Some STIs can be prevented by a pre-exposure vaccination. All unvaccinated individuals being evaluated for an STI are recommended to receive a hepatitis B vaccination (MMWR 2006). In addition, a hepatitis A vaccine is recommended for men who have sex with men (MSM) and illegal-drug users. Vaccines are under development or are undergoing clinical trials for other STDs, including HIV (MMWR 2006).

A vaccine that has become very controversial in the UK is the quadrivalent vaccine against human papillomavirus (HPV types 6, 11, 16, 18). The vaccine is thought to prevent cervical cancer, and is available for women under the age of 18 (Saslow, et al. 2007).

Male Condoms

Most male condoms are made from natural rubber latex. When used consistently and correctly and without slippage or breakage, male condoms cover the penis and will prevent the transmission of STIs (National Institute of Allergy and Infectious Diseases 2001). They may also reduce the risk of women developing pelvic inflammatory disease (PID) (Ness, et al. 2004).

Condoms that are lubricated with spermicides are not more effective in protecting against other STIs than normal condoms, and have been associated with urinary tract infections in young women (MMWR 2006).

Female Condoms

A female condom is a thin, loose-fitting and flexible plastic tube worn inside the vagina. A soft ring at the closed end of the tube covers the cervix during intercourse and holds it inside the vagina. Another ring at the open end of the tube stays outside the vagina and partly covers the lip area. Studies have shown that the female condom, if used consistently and correctly, is impermeable to sperm, sexually transmitted disease pathogens, and HIV ( (Leeper and Conrardy 1989). Female condoms are costly compared with male condoms (MMWR 2006). Most of the women in a study conducted by Farr et al. indicated that they liked using the device, would recommend it to others, and would select it above other barrier methods in the future (Farr, et al. 1994).

Diagnosis

The first step in STI diagnosis is to gather the patient's history. A physical examination will then be performed. During the physical examination the clinician will check for fever and document other vital signs. In women, the focus of the physical examination will be on the mouth, abdomen and pelvis. The oropharynx will be inspected for discharge and lesions and the abdomen for bowel sounds, distension, rebound, guarding, masses, and suprapubic or costovertebral angle tenderness. A pelvic examination will be performed for abnormal discharge or bleeding, pelvic masses or adnexal enlargement and for uterine, adnexal, or cervical motion tenderness. The anus will also be inspected for discharge and lesions. In men, the focus of the physical examination will be on the mouth, genitals, and anus/rectum. The oropharynx will be inspected for discharge and lesions, the urethra for discharge, the external genitalia for other lesions, and the anus for discharge and lesions.

Gonorrhoea and Chlamydia

A gram stain is sensitive and specific for gonorrhoea in men with urethral discharge. A negative gram stain is not sufficient to rule out infection in asymptomatic men. This test is much less accurate for infections of the cervix, pharynx, and rectum and is not recommended for diagnosis at these sites.

A laboratory culture test involves placing a sample of the discharge onto a culture plate and incubating it for up to 2 days to allow the bacteria to grow. The sensitivity of this test depends on the site from which the sample is taken. Cultures of cervical samples detect infection approximately 90 percent of the time. Culture also allows testing for drug-resistant bacteria and to detect gonorrhoea in the throat.

A number of commercial products using nucleic acid amplification technology are now available. These tests amplify the target nucleic acid, DNA or RNA or the probe after it has annealed to target nucleic acid (Ostergaard 1999). Such tests are generally more sensitive than liquid or solid phase hybridization tests which do not embody an amplification process and are considerably more sensitive than culture or antigen detection methods (Ostergaard 1999). In women, PCR and other amplification based tests can be usefully combined with routine cervical smear tests for cervical cancer (Bianchi, et al. 2002). They also permit the use of non invasive clinical samples such as urine (Ostergaard 1999). These tests are more expensive than cultures but typically yield more rapid results.

Many laboratories use antigen detection immunoassays because of their lower cost and ease of use. A new generation IDEIA®, called the IDEIA PCE® incorporates a polymer conjugate consisting of multiple copies of antibody and enzyme molecules to provide signal amplification (Okadome, et al. 2000). In high prevalence populations, such tests might be acceptable for screening purposes. Nevertheless, despite low cost, an analysis of diagnostic methods for Chlamydia screening to prevent PID in Maryland, USA, concluded that nucleic acid amplification-based methods were ultimately the most cost effective (Howell, et al. 1998).

Many clinicians prefer to use more than one test to increase the chance of an accurate diagnosis. Testing for Neisseria gonorrhoea and Chlamydia trachomatis is generally done simultaneously as the two organisms have similar clinical signs and symptoms.

Syphilis

Dark-field microscopy (DFM) can be useful when an active chancre or moist rashes are present. This test is used mainly to diagnose syphilis in primary, secondary, or early congenital syphilis.

Serology tests are the diagnostic identification of antibodies in serum. Syphilis serology tests can be treponemal or non-treponemal. Treponemal tests identify a direct antigen from the Treponema pallidum or an antibody to it (Mabey, et al. 2004). Antibodies can remain in the circulation for many years following exposure to syphilis which can result in a positive result that does not indicate active syphilis infection. Non-treponemal tests look for a marker, usually a cardiolipin, which is released when the bacteria damages cells during an infection. A positive non-treponemal test indicates an active infection, but a confirmatory test with a treponemal test is required to verify that it is a syphilis infection (Mabey, et al. 2004).

Rapid treponema-specific tests have become commercially available in the last few years. Most of these tests are available in lateral flow formats and are designed to detect all antibody isotypes (IgG, IgM, and IgA) against syphilis. The main disadvantage of rapid tests for syphilis is that, like all other treponemal tests, they will be reactive with virtually every patient who has ever had syphilis, even individuals who no longer have active infection (SDI 2003).

Genital Herpes

Below is a summary of the diagnostic tests for the Herpes Simplex Virus.

Test Type

Details

Specimen Source

Advantages

Disadvantages

Viral Culture

Similar to bacterial culture, as described above.

Swab of lesion

Highly Specific

Widely Available

Virus must be kept alive during transport to the lab

ELVIS Culture

(enzyme-linked virus-inducible system)

Uses cells created to contain the genetic code for an enzyme unrelated to herpes. When HSV from a patient's swab infects the ELVIS cells, this enzyme is activated and causes the cells to turn blue.

Swab of lesion

Highly specific

Rapid; 1-2 days

Can be falsely negative

Expensive

Antigen Detection

HSV Fluorescent Antibody Test

Swab of lesion

Inexpensive

Rapid; <1 day

Lower sensitivity than culture

PCR

Amplification of viral DNA

Swab of lesion

Very sensitive

Not widely available

Expensive

Serology (gG based)

Blood test based on detecting antibodies to gG-1 (for HSV-1 infection) or gG-2 (for HSV-2 infection

Blood

Highly accurate

Can be performed in absence of lesions

Tests that are not gG-based have inadequate accuracy

Table 1: adapted from 'diagnostic testing for genital and oral herpes' www.herpes.org

Treatment

Gonorrhoea

The recommended regimes for the treatment of gonorrhoea are Ceftriaxone (125mg IM in a single dose) or Cefiximin (400mg orally in a single dose) (MMWR 2006). The following treatments are not recommended for infections in MSM or infections acquired in areas with increased Quinolone resistant N. Gonorrhoea - Ciproflaxin (500mg orally in a single dose), Ofloxacin (400mg orally in a single dose) and Levofloxacin (250mg orally in a single dose).

N. gonorrhoea has become resistant to many antibiotics, including quinolones such as ciprofloxacin (CDC 2004). Ciprofloxacin will eventually not be advisable for the treatment of gonorrhoea. The level of tetracycline resistance in Neisseria gonorrhae is now so high as to make it completely ineffective in most parts of the world.

Treatment should include medication that will treat Chlamydia, because these STIs frequently exist together in the same person. Women suffering from PID require more aggressive treatment which is often administered intravenously.

Chlamydia

The recommended regimes for treating Chlamydia trachomatis is Azithromycin (1g orally in a single dose) or Doxycycline (100mg orally twice a day for 7 days). Alternative regimes include Erythromycin base, Erythromycin ethylsuccinate, Ofloxacin and Levofloxacin (MMWR 2006). Treatment prevents transmission to sex partners, and treatment of pregnant women usually prevents transmission to infants during birth.

A recent meta-analysis of Azithromycin versus Doxycycline for the treatment of Chlamydial infection showed that the treatments were equally effective (Lau and Qureshi 2002). These antibiotics may interact with the combined contraceptive pill and the contraceptive patch. To minimise transmission patients are instructed to abstain from sexual intercourse a further seven days after completing the recommended regimes. It is also beneficial for patients to be retested for C. trachomatis 3 months after treatment.

Syphilis

All stages of syphilis can be treated by parenterally administered Penicillin G. There are many preparations of Penicillin G such as benzathine, aqueous procaine, or aqueous crystalline. However benzathine and procaine should not be used in combination (CDC 2005). The length of treatment, dosage and preparation used depends on the stage of the STI. This therapy is also effective during pregnancy.

A possible adverse reaction called the Jarisch-Herxheimer reaction can occur within the first 24 hours after any syphilis therapy, but most commonly with early stage syphilis treatment (MMWR 2006). It is an acute febrile reaction that is accompanied by headaches and myaliga and may induce early labour or cause foetal distress in pregnant women.

Genital Herpes

Patients with a first clinical episode of genital herpes should receive antiviral therapy. This can be in the form of acyclovir, valacyclovir or famiciclovir. Valacyclovir has enhanced absorption after oral administration compared to acyclovir. Topical antiviral drugs have minimal benefits and its use is discouraged (MMWR 2006).

An established HSV-2 infection will cause reoccurrence of genital lesions. This can be treated with episodes of antiviral therapy to shorten the duration of lesions or with suppressive therapy to reduce the frequency of recurrence (MMWR 2006). The suppressive therapy also reduces the risk of HSV-2 transmission to partners.

Conclusion

Four of the most common STIs have been reviewed in terms of their prevention, diagnosis and treatment. The most reliable way to avoid transmission of STIs is to abstain from sex or to be in a long-term, mutually monogamous relationship with an uninfected partner. Person at risk should be regularly screened for STIs. Diagnosis varies between STIs, but the most common method is by bacterial or viral culture. Treatments also vary between STIs but as most are bacterial infections; these can be treated with antibiotics.

Word Count - 1991

This assessment is my own work and aspects where collaboration has been involved are acknowledged and, the sources are cited

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