Preventive and self-help measures include keeping fingernails short, and washing hands scrupulously before all meals. Sheets and nightwear should be changed frequently, washed at high temperature , and ironed. Whilst ointments may be used to relieve anal itching , a doctor's prescription for a drug such as mebendazole or piperazine is generally necessary in order to kill or paralyse the worms and cause them to pass out of the body in faeces.                                     

                   Bacteria ( constituting the kingdom of Monera ) are extremely widespread , and more than 16,000 species have been identified to date. They consist of single procaryotic cells with a protective wall. Some are aerobic - needing oxygen and therefore more likely to infect surface areas such as skin or respiratory track - others are anaerobic and multiply in oxygen-free surroundings such as the bowel or deep puncture wounds. Many types of (commensal) bacteria exist on the skin surface or in the bowel without causing ill-effects. Normally the immune system protects the body from infection so that harmful invading microbes are killed before they can multiply in sufficient numbers to produce symptoms of disease. Infectious diseases occur when the body is invaded by microbes against which its natural defences are ineffective. This may be because the body has little or no natural immunity to the infection in question , or because the number of invading microbes is too great for the immune system to overcome. Most bacterial (and viral) infections cause fever , and there may be inflammation and pus formation in the affected areas. Antibiotic or antibacterial drugs are effective either by killing bacteria through disintegrating their cell walls , or by inhibiting their capacity for growth and reproductive multiplication.

                      Mycoplasmas are the smallest organisms known capable of growth and reproduction outside of living host cells. They are typically 0.12 - 0.25micrometre diameter , small enough to pass through filters that will hold back bacteria. They completely lack a cell wall - and therefore the major components of a mycoplasma are the plasma membrane, cytoplasma (with inclusions) and chromosomal DNA. Commonly they are found in the human mouth and genital tract, as well as in arthritic joints. Primary atypical pneumonia which is common in many parts of the world as a cause of between 10 and 30% of all acute lower respiratory tract infections is mainly due to infection by pathogenic mycoplasma.

                       Rickettsiae are at the limit of visibility in ordinary light microscopes and belong to a borderland between bacteria and viruses. They resemble bacteria in containing both RNA & DNA , in having enzymes and demonstrable metabolic activities , in multiplying by binary fission , and in their sensitivities to antiseptics and antibiotics - but they resemble viruses in being unable to reproduce except inside host cells. Gram's method will weakly stain them. Humans become infected by the the bite of an infected tick, louse, flea or mite; and the systemic fever typhus can result in a subsequent fatality unless antibiotics such as tetracycline or chloramphenicol are used.

                       Chlamydiae , like the rickettsiae are obligate intracellular parasites with procaryotic cells; but their complex developmental cycle sets them apart from all other organisms. Chlamydiae have been identified as the agent of trachoma - the world's commonest cause of blindness, as well as of inclusion conjunctivitis. The causative organism has its primary habitat in the human genital tract where it is frequently associated with non-gonococcal or non-specific urethritis. 'Swimming bath conjunctivitis' is believed to be due to transmission of the organism from the genitalia of one bather to the conjunctivae of another via the water. Chlorination of the water to an adequate degree should be sufficient to prevent the disease from spreading.