ENTAMOEBA HISTOLYTICA. The main risk with dysentery is dehydration.
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.
Bacillary dysentery is caused by bacteria of the genus Shigella and is spread by contact with a patient or carrier or through contaminated food or water. Epidemics are common in overcrowded, insanitary conditions. Symptoms develop 1–6 days after infection and persist for up to 2 weeks; they include diarrhoea, nausea, abdominal cramping, and fever. An attack may vary from mild diarrhoea to states of severe dehydration and gastrointestinal haemorrhage. In most cases, provided fluid losses are replaced, recovery occurs within 7–10 days; antibiotics may be given to eliminate the bacteria. Compare cholera.
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