n. a genus of tiny Gram-negative aerobic bacteria. B. pertussis causes *whooping cough, and all the other species are able to break down red blood cells and cause diseases resembling whooping cough.
Among the smallest and simplest microorganisms are the viruses. First described as ?lterable agents, and ranging in size from 20–30 nm to 300 nm, they may be directly visualised only by electron microscopy. They consist of a core of deoxyribonucleic or ribonucleic acid (DNA or RNA) within a protective protein coat, or capsid, whose subunits confer a geometric symmetry. Thus viruses are usually cubical (icosahedral) or helical; the larger viruses (pox-, herpes-, myxo-viruses) may also have an outer envelope. Their minimal structure dictates that viruses are all obligate parasites, relying on living cells to provide essential components for their replication. Apart from animal and plant cells, viruses may infect and replicate in bacteria (bacteriophages) or fungi (mycophages), which are damaged in the process.
Bacteria are larger (0·01–5,000 µm) and more complex. They have a subcellular organisation which generally includes DNA and RNA, a cell membrane, organelles such as ribosomes, and a complex and chemically variable cell envelope – but, unlike EUKARYOTES, no nucleus. Rickettsiae, chlamydia, and mycoplasmas, once thought of as viruses because of their small size and absence of a cell wall (mycoplasma) or major wall component (chlamydia), are now acknowledged as bacteria; rickettsiae and chlamydia are intracellular parasites of medical importance. Bacteria may also possess additional surface structures, such as capsules and organs of locomotion (?agella) and attachment (?mbriae and stalks). Individual bacterial cells may be spheres (cocci); straight (bacilli), curved (vibrio), or ?exuous (spirilla) rods; or oval cells (coccobacilli). On examination by light microscopy, bacteria may be visible in characteristic con?gurations (as pairs of cocci [diplococci], or chains [streptococci], or clusters); actinomycete bacteria grow as ?laments with externally produced spores. Bacteria grow essentially by increasing in cell size and dividing by ?ssion, a process which in ideal laboratory conditions some bacteria may achieve about once every 20 minutes. Under natural conditions, growth is usually much slower.
Eukaryotic micro-organisms comprise fungi, algae, and protozoa. These organisms are larger, and they have in common a well-developed internal compartmentation into subcellular organelles; they also have a nucleus. Algae additionally have chloroplasts, which contain photosynthetic pigments; fungi lack chloroplasts; and protozoa lack both a cell wall and chloroplasts but may have a contractile vacuole to regulate water uptake and, in some, structures for capturing and ingesting food. Fungi grow either as discrete cells (yeasts), multiplying by budding, ?ssion, or conjugation, or as thin ?laments (hyphae) which bear spores, although some may show both morphological forms during their life-cycle. Algae and protozoa generally grow as individual cells or colonies of individuals and multiply by ?ssion.
Micro-organisms of medical importance include representatives of the ?ve major microbial groups that obtain their essential nutrients at the expense of their hosts. Many bacteria and most fungi, however, are saprophytes (see SAPROPHYTE), being major contributors to the natural cycling of carbon in the environment and to biodeterioration; others are of ecological and economic importance because of the diseases they cause in agricultural or horticultural crops or because of their bene?cial relationships with higher organisms. Additionally, they may be of industrial or biotechnological importance. Fungal diseases of humans tend to be most important in tropical environments and in immuno-compromised subjects.
Pathogenic (that is, disease-causing) microorganisms have special characteristics, or virulence factors, that enable them to colonise their hosts and overcome or evade physical, biochemical, and immunological host defences. For example, the presence of capsules, as in the bacteria that cause anthrax (Bacillus anthracis), one form of pneumonia (Streptococcus pneumoniae), scarlet fever (S. pyogenes), bacterial meningitis (Neisseria meningitidis, Haemophilus in?uenzae) is directly related to the ability to cause disease because of their antiphagocytic properties. Fimbriae are related to virulence, enabling tissue attachment – for example, in gonorrhoea (N. gonorrhoeae) and cholera (Vibrio cholerae). Many bacteria excrete extracellular virulence factors; these include enzymes and other agents that impair the host’s physiological and immunological functions. Some bacteria produce powerful toxins (excreted exotoxins or endogenous endotoxins), which may cause local tissue destruction and allow colonisation by the pathogen or whose speci?c action may explain the disease mechanism. In Staphylococcus aureus, exfoliative toxin produces the staphylococcal scalded-skin syndrome, TSS toxin-1 toxic-shock syndrome, and enterotoxin food poisoning. The pertussis exotoxin of Bordetella pertussis, the cause of whooping cough, blocks immunological defences and mediates attachment to tracheal cells, and the exotoxin produced by Corynebacterium diphtheriae causes local damage resulting in a pronounced exudate in the trachea.
Viruses cause disease by cellular destruction arising from their intracellular parasitic existence. Attachment to particular cells is often mediated by speci?c viral surface proteins; mechanisms for evading immunological defences include latency, change in viral antigenic structure, or incapacitation of the immune system – for example, destruction of CD 4 lymphocytes by the human immunode?ciency virus.... microbiology
Healthy people are inoculated with vaccine as a protection against a particular disease; this produces ANTIBODIES which will confer immunity against a subsequent attack of the disease. (See IMMUNISATION for programme of immunisation during childhood.)
Vaccines may be divided into two classes: stock vaccines, prepared from micro-organisms known to cause a particular disease and kept in readiness for use against that disease; and autogenous vaccines, prepared from microorganisms which are already in the patient’s body and to which the disease is due. Vaccines intended to protect against the onset of disease are of the former variety.
Autogenous vaccines are prepared by cultivating bacteria found in SPUTUM, URINE and FAECES, and in areas of in?ammation such as BOILS (FURUNCULOSIS). This type of vaccine was introduced by Wright about 1903.
Anthrax vaccine was introduced in 1882 for the protection of sheep and cattle against this disease. A safe and e?ective vaccine for use in human beings has now been evolved. (See ANTHRAX.)
BCG vaccine is used to provide protection against TUBERCULOSIS. (See also separate entry on BCG VACCINE.)
Cholera vaccine was introduced in India about 1894. Two injections are given at an interval of at least a week; this gives a varying degree of immunity for six months. (See CHOLERA.)
Diphtheria vaccine is available in several forms. It is usually given along with tetanus and pertussis vaccine (see below) in what is known as TRIPLE VACCINE. This is given in three doses: the ?rst at the age of two months; the second at three months; and the third at four months, with a booster dose at the age of ?ve years. (See DIPHTHERIA.)
Hay fever vaccine is a vaccine prepared from the pollen of various grasses. It is used in gradually increasing doses for prevention of HAY FEVER in those susceptible to this condition.
In?uenza vaccine A vaccine is now available for protection against INFLUENZA due to the in?uenza viruses A and B. Its use in Britain is customarily based on advice from the health departments according to the type of in?uenza expected in a particular year.
Measles, mumps and rubella (MMR) vaccines are given in combination early in the second year of life. A booster dose may prove necessary, as there is some interference between this vaccine and the most recent form of pertussis vaccine (see below) o?ered to children. Uptake has declined a little because of media reports suggesting a link with AUTISM – for which no reliable medical evidence (and much to the contrary) has been found by investigating epidemiologists. (See also separate entry for each disease, and for MMR VACCINE.)
Pertussis (whooping-cough) vaccine is prepared from Bordetella pertussis, and is usually given along with diphtheria and tetanus in what is known as triple vaccine. (See also WHOOPING-COUGH.)
Plague vaccine was introduced by Ha?kine, and appears to give useful protection, but the duration of protection is relatively short: from two to 20 months. Two injections are given at an interval of four weeks. A reinforcing dose should be given annually to anyone exposed to PLAGUE.
Poliomyelitis vaccine gives a high degree of protection against the disease. This is given in the form of attenuated Sabin vaccine which is taken by mouth – a few drops on a lump of sugar. Reinforcing doses of polio vaccine are recommended on school entry, on leaving school, and on travel abroad to countries where POLIOMYELITIS is ENDEMIC.
Rabies vaccine was introduced by Pasteur in 1885 for administration, during the long incubation period, to people bitten by a mad dog, in order to prevent the disease from developing. (See RABIES.)
Rubella vaccine, usually given with mumps and measles vaccine in one dose – called MMR VACCINE, see also above – now provides protection against RUBELLA (German measles). It also provides immunity for adolescent girls who have not had the disease in childhood and so ensures that they will not acquire the disease during any subsequent pregnancy – thus reducing the number of congenitally abnormal children whose abnormality is the result of their being infected with rubella via their mothers before they were born.
Smallpox vaccine was the ?rst introduced. As a result of the World Health Organisation’s successful smallpox eradication campaign – it declared the disease eradicated in 1980 – there is now no medical justi?cation for smallpox vaccination. Recently, however, there has been increased interest in the subject because of the potential threat from bioterrorism. (See also VACCINATION.)
Tetanus vaccine is given in two forms: (1) In the so-called triple vaccine, combined with diphtheria and pertussis (whooping-cough) vaccine for the routine immunisation of children (see above). (2) By itself to adults who have not been immunised in childhood and who are particularly exposed to the risk of TETANUS, such as soldiers and agricultural workers.
Typhoid vaccine was introduced by Wright and Semple for the protection of troops in the South African War and in India. TAB vaccine, containing Salmonella typhi (the causative organism of typhoid fever – see ENTERIC FEVER) and Salmonella paratyphi A and B (the organisms of paratyphoid fever – see ENTERIC FEVER) has now been replaced by typhoid monovalent vaccine, containing only S. typhi. The change has been made because the monovalent vaccine is less likely to produce painful arms and general malaise, and there is no evidence that the TAB vaccine gave any protection against paratyphoid fever. Two doses are given at an interval of 4–6 weeks, and give protection for 1–3 years.... vaccine
Symptoms The ?rst, or catarrhal, stage is characterised by mild, but non-speci?c, symptoms of sneezing, conjunctivitis (see under EYE, DISORDERS OF), sore throat, mild fever and cough. Lasting 10–14 days, this stage is the most infectious; unfortunately it is almost impossible to make a de?nite clinical diagnosis, although analysis of a nasal swab may con?rm a suspected case. This is followed by the second, or paroxysmal, stage with irregular bouts of coughing, often prolonged, and typically more severe at night. Each paroxysm consists of a succession of short sharp coughs, increasing in speed and duration, and ending in a deep, crowing inspiration, often with a characteristic ‘whoop’. Vomiting is common after the last paroxysm of a series. Lasting 2–4 weeks, this stage is the most dangerous, with the greatest risk of complications. These may include PNEUMONIA and partial collapse of the lungs, and ?ts may be induced by cerebral ANOXIA. Less severe complications caused by the stress of coughing include minor bleeding around the eyes, ulceration under the tongue, HERNIA and PROLAPSE of the rectum. Mortality is greatest in the ?rst year of life, particularly among neonates – infants up to four weeks old. Nearly all patients with whooping-cough recover after a few weeks, with a lasting IMMUNITY. Very severe cases may leave structural changes in the lungs, such as EMPHYSEMA, with a permanent shortness of breath or liability to ASTHMA.
Treatment Antibiotics, such as ERYTHROMYCIN or TETRACYCLINES, may be helpful if given during the catarrhal stage – largely in preventing spread to brothers and sisters – but are of no use during the paroxysmal stage. Cough suppressants are not always helpful unless given in high (and therefore potentially narcotic) doses, and skilled nursing may be required to maintain nutrition, particularly if the disease is prolonged, with frequent vomiting.... whooping-cough
After an incubation period of 7–10 days, the illness starts with a mild cough, sneezing, nasal discharge, fever, and sore eyes. After a few days, the cough becomes more persistent and severe, especially at night. Whooping occurs in most cases. Sometimes the cough can
cause vomiting. In infants, there is a risk of temporary apnoea following a coughing spasm. The illness may last for a few weeks. The possible complications include nosebleeds, dehydration, pneumonia, pneumothorax, bronchiectasis (permanent widening of the airways), and convulsions. Untreated, pertussis may prove fatal.
Pertussis is usually diagnosed from the symptoms. In the early stages, erythromycin is often given to reduce the child’s infectivity. Treatment consists of keeping the child warm, giving small, frequent meals and plenty to drink, and protecting him or her from stimuli, such as smoke, that can provoke coughing. If the child becomes blue or persistently vomits after coughing, hospital admission is needed.
In developed countries, most infants are vaccinated against pertussis in the 1st year of life. It is usually given as part of the DPT vaccination at 2, 3, and 4 months of age. Possible complications include a mild fever and fretfulness. Very rarely, an infant may have a severe reaction, with high-pitched screaming or seizures.... pertussis
*Immunization against the infection was introduced in the UK in the 1950s and offers protection. An attack usually confers lifelong immunity. Despite good vaccine coverage resulting in the current low levels of disease, whooping cough is still a significant cause of illness and death in the very young. Medical name: pertussis.... whooping cough
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