What is it?
Typhoid fever is an infection caused by Salmonella bacteria. The affected usually have a high fever lasting for several days. Other common symptoms include weakness, headache, stomach pain, and constipation.
In 2013, there were 11 million new cases of typhoid fever reported worldwide, and 161 000 deaths resulting from it. The disease is most common in India.
What causes it?
The bacterium that causes typhoid fever, the Salmonella bacterium, spreads because of poor sanitation and also sometimes through flying insects that have been feeding on feces.
What happens during it?
Normally, bacteria don’t get far if they try to infect us through something we ingested. The contents of our stomach are very acidic, which kills most bacteria. The Salmonella bacteria can tolerate this. They enter the small intestine, and from there they gain access to the rest of the body.
We have white cells called macrophages whose job it is to basically engulf any invaders. They take the invader inside them in a vesicle and then make it fuse with another vesicle containing substances that will destroy it. The Salmonella bacteria are able to hide from the immune system and reproduce inside macrophages, because they are able to make this fusion not happen.
After the bacteria have multiplied inside the macrophages for a while, they quite literally make them kill themselves and leak to the bloodstream.Now the immune system is able to detect them and starts a violent response including fever. At some point the bacteria invade the gall bladder. The gall bladder contains substances that are released to the small intestine to help with digestion, and this is how the bacteria end back in the intestine. Some of the bacteria are shed with feces, while some of them continue the same cycle. This is why someone without symptoms might be a carrier of the Salmonella bacteria – they can be found in the feces sometimes decades after the original infection.
How can it be treated?
While typhoid fever is very treatable, it causes death in 10-30% of cases if it is left untreated. The diarrhea associated can cause dangerous dehydration, which is why oral rehydration is highly recommended. Antibiotics are also often useful.
Sources: https://en.wikipedia.org/wiki/Typhoid_fever, http://emedicine.medscape.com/article/231135-overview#a5, http://rnspeak.com/pathophysiology/typhoid-fever-pathophysiology-schematic-diagram/