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Chapter: Biology of Disease: Infectious Diseases and Treatments

Infections of the Urogenital System

Infections of the Urogenital System
The urinary system and the genital systems are subject to infections by specific respective pathogens.

INFECTIONS OF THE UROGENITAL SYSTEM

The urinary system and the genital systems are subject to infections by specific respective pathogens (Figure 3.16). Urinary tract infections (UTIs) are frequent in the developed world, with many millions of cases occurring each year. A number of factors, including diabetes mellitus , scarring, kidney stones, use of catheters or anatomical peculiarities of the urinary tract all predispose individuals to UTIs. These originate in the perianal area and move up the urethra into the bladder causing a short-lived, acute infection


called cystitis. Escherichia coliis the most common agent causing up to 80% of the relatively uncomplicated UTIs, like cystitis. Women are more prone than males to cystitis because of their relatively short urethra and the hormonal changes associated with the menstrual cycle . Cystitis is readily treated by increasing the uptake of fluids, particularly of acid drinks like cranberry juice, which causes increased flushing of the bladder, and by the use of antibiotics. Unfortunately, reinfections are frequent.

Pseudomonas aeruginosa has been known to cause UTIs followinghospitalization. Similarly, infections by Enterococcus faecalis and Klebsiellapneumoniae have followed organ transplants .Unfortunately,these organisms often show multidrug resistance against antibiotics. Thrush in the bladder, caused by the yeast Candida albicans can also occur following antibiotic treatment.

There has been a large increase in the incidence of sexually transmitted diseases (STDs) in the UK in recent years. Sexually transmitted diseases can affect the urinary system and the genital tract and are caused by a wide range of different pathogens. Human papilloma virus (HPV) can cause anogenital warts (condyloma acuminata). Strains 16 and 18 of HPV cause lesions in the cervix that are involved in the development of cervical carcinoma. Infection with Herpes simplex virus (HHV-2) can lead to genital herpes with painful ulcers and vesicular lesions of the genital mucous membrane. Infection with human immunodeficiency virus leads to acquired immunodeficiency syndrome (AIDS).

Some types of Chlamydia trachomatis are among the commonest causes of STDs producing local inflammations of the urethra and cervix. In contrast, other types are highly invasive and infiltrate the lymphatic system leading to necrosis (lymphogranuloma venereum).


The most widely known STDs are probably gonorrhea and syphilis caused by the bacteria Neisseria gonorrhoeae, a Gram-negative diplococcus, and Treponema pallidum a spirochete (Figure 3.20 (A) and (B)) respectively.Gonorrhea, a common STD, is a pelvic inflammatory disease whose major symptoms include a purulent inflammation of the uterine cervix and urethritis. In some women, however, the infection may be relatively asymptomatic and may go unnoticed. Syphilis was thought to have originated in the Americas and been brought to Europe by sailors on the Columbian expeditions. More recent evidence suggests that it was present in the Old World long before this. Treponema spirochetes can enter through mucous membranes or minute abrasions in the skin during sexual acts. The infection shows three stages of pathogenesis. Initially, an ulcer called a chancre develops at the site of infection. The infection then spreads to nearby lymph nodes causing them to swell and harden. Secondary syphilis develops after one to three months. It is characterized by the presence of highly infectious lesions on various parts of the body. The disease may lie dormant for many years but, if not treated with antibiotics, will develop into tertiary syphilis causing inflammations of the aorta and CNS. Dementia, heart attacks and death can all result. Patients with tertiary syphilis cannot infect others with the disease. Some patients may develop benign late syphilis, which is usually rapid in onset but does respond well to treatment. It usually begins three to 10 years after infection and is characterized by the development of gummas. These are tumor-like growths of a rubbery consistency that are most likely to affect the skin or long bones but can also develop in the eyes, mucous membranes, throat, liver and stomach lining. However, since the use of antibiotic treatments for syphilis they are increasingly uncommon.

The protozoan Trichomonas vaginalis (Figure 3.21) is a frequent colonizer of the mucosal membrane of the urogenital system. It is generally asymptomatic but an inflammatory reaction, trichomoniasis vaginitis, may result in a frothy cream-colored discharge.



A number of arthropods may be sexually transmitted. These include crab lice and the scabies mite (Figure 2.14(A)).


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