adj. being able to move spontaneously, without external aid: usually applied to a *microorganism or a cell (e.g. a sperm cell).
Shigellosis This form is usually caused by Shigella dysenteriae-1 (Shiga’s bacillus), Shigella ?exneri, Shigella boydii, and Shigella sonnei; the latter is the most benign and occurs in temperate climates also. It is transmitted by food and water contamination, by direct contact, and by ?ies; the organisms thrive in the presence of overcrowding and insanitary conditions. The incubation is between one and seven days, and the severity of the illness depends on the strain responsible. Duration of illness varies from a few days to two weeks and can be particularly severe in young, old, and malnourished individuals. Complications include perforation and haemorrhage from the colo-rectum, the haemolytic uraemic syndrome (which includes renal failure), and REITER’S SYNDROME. Diagnosis is dependent on demonstration of Shigella in (a) faecal sample(s) – before or usually after culture.
If dehydration is present, this should be treated accordingly, usually with an oral rehydration technique. Shigella is eradicated by antibiotics such as trimethoprimsulphamethoxazole, trimethoprim, ampicillin, and amoxycillin. Recently, a widespread resistance to many antibiotics has developed, especially in Asia and southern America, where the agent of choice is now a quinolone compound, for example, cipro?oxacin; nalidixic acid is also e?ective. Prevention depends on improved hygiene and sanitation, careful protection of food from ?ies, ?y destruction, and garbage disposal. A Shigella carrier must not be allowed to handle food.
Entamoeba histolytica infection Most cases occur in the tropics and subtropics. Dysentery may be accompanied by weight loss, anaemia, and occasionally DYSPNOEA. E. histolytica contaminates food (e.g. uncooked vegetables) or drinking water. After ingestion of the cyst-stage, and following the action of digestive enzymes, the motile trophozoite emerges in the colon causing local invasive disease (amoebic colitis). On entering the portal system, these organisms may gain access to the liver, causing invasive hepatic disease (amoebic liver ‘abscess’). Other sites of ‘abscess’ formation include the lungs (usually right) and brain. In the colo-rectum an amoeboma may be di?cult to di?erentiate from a carcinoma. Clinical symptoms usually occur within a week, but can be delayed for months, or even years; onset may be acute – as for Shigella spp. infection. Perforation, colo-rectal haemorrhage, and appendicitis are unusual complications. Diagnosis is by demonstration of E. histolytica trophozoites in a fresh faecal sample; other amoebae affecting humans do not invade tissues. Research techniques can be used to di?erentiate between pathogenic (E. dysenteriae) and non-pathogenic strains (E. dispar). Alternatively, several serological tests are of value in diagnosis, but only in the presence of invasive disease.
Treatment consists of one of the 5nitroimidazole compounds – metronidazole, tinidazole, and ornidazole; alcohol avoidance is important during their administration. A ?ve- to ten-day course should be followed by diloxanide furoate for ten days. Other compounds – emetine, chloroquine, iodoquinol, and paromomycin – are now rarely used. Invasive disease involving the liver or other organ(s) usually responds favourably to a similar regimen; aspiration of a liver ‘abscess’ is now rarely indicated, as controlled trials have indicated a similar resolution rate whether this technique is used or not, provided a 5-nitroimidazole compound is administered.... dysentery
Pseudomonas Aeruginosa
A pathogenic bacterium of the genus pseudomonas – rod-like, motile gram-negative bacteria (see GRAM’S STAIN) – that occurs in pus from wounds and is associated with urinary tract infections. The bacteria mostly live in soil and decomposing organic matter and help to recycle nitrogen in nature. Most of the bacteria in this genus are harmless to humans.... pseudohypertrophic muscular dystrophy
– all potentially fatal disesases.... haemophilus
infertility units. Safety concerns relate to a higher-than-expected rate of abnormalities in the SEX CHROMOSOMES after ICSI, and also the potential risk of transmitting paternal genetic defects in the Y chromosome to sons born after ICSI.... intracytoplasmic sperm injection
Granulocytes Also known as polymorphonuclear leucocytes (‘polys’), these normally constitute 70 per cent of the white blood cells. They are divided into three groups according to the staining reactions of these granules: neutrophils, which stain with neutral dyes and constitute 65–70 per cent of all the white blood cells; eosinophils, which stain with acid dyes (e.g. eosin) and constitute 3–4 per cent of the total white blood cells; and basophils, which stain with basic dyes (e.g. methylene blue) and constitute about 0·5 per cent of the total white blood cells.
Lymphocytes constitute 25–30 per cent of the white blood cells. They have a clear, non-granular cytoplasm and a relatively large nucleus which is only slightly indented. They are divided into two groups: small lymphocytes, which are slightly larger than erythrocytes (about 8 micrometres in diameter); and large lymphocytes, which are about 12 micrometres in diameter.
Monocytes Motile phagocytic cells that circulate in the blood and migrate into the tissues, where they develop into various forms of MACROPHAGE such as tissue macrophages and KUPFFER CELLS.
Site of origin The granulocytes are formed in the red BONE MARROW. The lymphocytes are formed predominantly in LYMPHOID TISSUE. There is some controversy as to the site of origin of monocytes: some say they arise from lymphocytes, whilst others contend that they are derived from histiocytes – i.e. the RETICULO-ENDOTHELIAL SYSTEM.
Function The leucocytes constitute one of the most important of the defence mechanisms against infection. This applies particularly to the neutrophil leucocytes (see LEUCOCYTOSIS). (See also ABSCESS; BLOOD – Composition; INFLAMMATION; PHAGOCYTOSIS; WOUNDS.)... leucocytes
Louse-borne relapsing fever is an EPIDEMIC disease, usually associated with wars and famines, which has occurred in practically every country in the world. For long confused with TYPHUS FEVER and typhoid fever (see ENTERIC FEVER), it was not until the 1870s that the causal organism was described by Obermeier. It is now known as the Borrelia recurrentis, a motile spiral organism 10–20 micrometres in length. The organism is transmitted from person to person by the louse, Pediculus humanus.
Symptoms The incubation period is up to 12 days (but usually seven). The onset is sudden, with high temperature, generalised aches and pains, and nose-bleeding. In about half of cases, a rash appears at an early stage, beginning in the neck and spreading down over the trunk and arms. JAUNDICE may occur; and both the LIVER and the SPLEEN are enlarged. The temperature subsides after ?ve or six days, to rise again in about a week. There may be up to four such relapses (see the introductory paragraph above).
Treatment Preventive measures are the same as those for typhus. Rest in bed is essential, as are good nursing and a light, nourishing diet. There is usually a quick response to PENICILLIN; the TETRACYCLINES and CHLORAMPHENICOL are also e?ective. Following such treatment the incidence of relapse is about 15 per cent. The mortality rate is low, except in a starved population.
Tick-borne relapsing fever is an ENDEMIC disease which occurs in most tropical and sub-tropical countries. The causative organism is Borrelia duttoni, which is transmitted by a tick, Ornithodorus moubata. David Livingstone suggested that it was a tick-borne disease, but it was not until 1905 that Dutton and Todd produced the de?nitive evidence.
Symptoms The main di?erences from the louse-borne disease are: (a) the incubation period is usually shorter, 3–6 days (but may be as short as two days or as long as 12); (b) the febrile period is usually shorter, and the afebrile periods are more variable in duration, sometimes only lasting for a day or two; (c) relapses are much more numerous.
Treatment Preventive measures are more di?cult to carry out than in the case of the louse-borne infection. Protective clothing should always be worn in ‘tick country’, and old, heavily infected houses should be destroyed. Curative treatment is the same as for the louse-borne infection.... relapsing fever
Bacteria are very widely distributed. Some live in soil, water, or air; others are parasites of humans, animals, and plants. Many parasitic bacteria do not harm their hosts; some cause diseases by producing poisons (see endotoxin; exotoxin).... bacteria
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