One polysaccharide-producing bacteria of particular importance is Salmonella typhi. It is the bacterium that causes typhoid fever. A polysaccharide call the Vi polysaccharide is present on the surface of Salmonella typhi. In the United States about 400 cases occur each year, and 70% of these are acquired while traveling internationally. Typhoid fever is still common in the developing world, where it affects about 12.5 million persons each year.
People with typhoid fever usually have gradually increasing fever that can get as high as 103° (39°C) to 104° F (40° C). This fever can last for a week or more and can be life-threatening. In fact, many people believe that Alexander the Great died of this disease. Patients may also feel weak, have muscle pains, headache, and joint pain followed by stomach pains, blood in the stool, and loss of appetite. One to 5 percent of the people will become chronic carriers of the bacteria with no symptoms at all. They can release the Salmonella typhi bacteria in their stools and can give it to other people for as long as a year. The only way to know for sure if an illness is typhoid fever is to have samples of stool or blood tested for the presence of Salmonella typhi.
Previous studies have demonstrated that if a person makes antibodies to Vi polysaccharide they are usually protected from getting typhoid fever. There are currently two different vaccines used to prevent typhoid fever. Unfortunately, they don't work very well in children. The newest vaccine contains the Vi polysaccharide bound to a protein. This vaccine is very good at inducing antibody production to the Vi polysaccharide in children.
To see if this vaccine would protect children from getting typhoid fever researchers from the National Institutes of Health (United States) vaccinated over 11,091 Vietnamese children. The children were then followed for 27 months to see if they were protected from getting this disease. After this period of time it
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