Typhoid fever is an illness that is a sometimes life-threatening, caused by the Salmonella typhi bacteria. The Salmonella typhi bacteria is usually found in human waste (urine or fecal matter).You obtain typhoid when you ingest infected water, milk or food. Once this disease reaches the intestines, it spreads to the bloodstream. Salmonella typhi is only contracted in the human species and does not infect any other animals.
Typhoid does not have a vector, but there are certain people, called carriers, who continue to carry the Salmonella typhi bacteria in their intestines and bloodstream even when healthy again. Carriers continue to spread the virus through their feces, even though they are not aware that they still carry this virus.
Salmonella typhi is a gram negative bacteria. Gram negative means that when gram stained, the bacteria turns a pinkish or red color. Gram positive bacterium turn a purple color. Gram negative bacterium often cause ingestion or respiratory based illnesses, while gram positive are often plagues; transmitted through the bite of an infected animal or insect.
Some of the physical features of Salmonella typhi include a rode-shaped, flagellated form. Flagella are a slender thread-like fins that allow the bacteria to move or "swim". This bacteria has two membranes that set it apart from other bacterium. Membranes are layers in a bacteria. Salmonella typhi has both an outer membrane and an inner membrane.
Here is Salmonella typhi showing the shape and physical features such as the rod-shape, flagella and membranes.