Typhoid fever is caused due to infection with the virulent bacteria salmonella typhi. The bacteria after ingestion, passes down to the bowel. It penetrates the intestinal mucosa (lining) and enters the underlying tissue. If the immune system is able to stop the infection (prevent multiplication of the germ) here, the patient does not develop the disease but if the bacteria is able to multiply and then spread to the bloodstream, the person develops typhoid fever. The initial symptoms of the infection include fever, weakness, fatigue and exhaustion, pain in abdomen, headache, and sore throat.
From the bloodstream, the bacteria penetrate into the bone marrow, liver and bile ducts, and continue to be released into the bowel and bowel contents. In the second phase of the disease, the bacteria enter the immune tissue of the small intestine, and then the small-bowel symptoms such as severe pain i in the abdomen and change in stool consistency (diarrhoea or constipation) start.
Human beings are the only carriers of salmonella typhi. The bacteria are present in the bloodstream and intestinal tract of the patient with typhoid fever. In approximately 3 to 5 percent of people, the bacteria continue to be present in their body even after the symptoms go away with proper treatment.
Typhoid fever is transmitted by food and water contaminated by salmonella typhi. Food and water can get contaminated on being handled by a person who is shedding the bacteria (typhoid carrier), or if sewage contaminated with the bacteria gets into drinking water or food (faecal-oral route). Hence it is more common in areas where hygiene is not good.
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