The Causes Of Typhoid Explained – How The Disease Spreads

One of the main causes of typhoid fever is the feco-oral transmission of typhoid bacteria. Unsafe sanitary practices lead to the contamination of water and food by the typhoid bacteria, in turn encouraging the spread of the disease.

causes of typhoid

Insects like the housefly are indirect causes of typhoid as they help in transmitting the disease through food and water.

The Causes Of Typhoid – How The Disease Spreads

The Infective Agent

The bacteria Salmonella typhi and Salmonella paratyphi are the main causes of typhoid fever. They are know to infect only humans.

The Spread Of Typhoid

The typhoid infection usually spreads through food and water that has been contaminated with the salmonella bacteria. This bacteria is transmitted to insects (e.g. the house fly) that feed on stools. When a person consumes water or food that has been contaminated by these insects, the Salmonella typhi bacteria enter the person’s body, causing the typhoid infection.

The Infectious Dose

The infectious dose is a term that refers to the number of bacteria that need to enter the body to cause the infection and the characteristic typhoid fever symptoms. This number can vary from 1 thousand to 1 million bacteria. The possible reason for such a large variation in number could be that the Salmonella bacteria have varying abilities to resist the highly acidic environment of the stomach.

Causes Of Typhoid – The Journey Of The Typhoid Bacteria

  • The body has a protective mechanism in the form of a highly acidic environment in the stomach to counter various bacteria. As a result, the ability of bacteria to escape unaffected from this environment decides their fate in the body.
  • Once the Salmonella typhi escapes from the strong acid barrier in the stomach, it travels to the small intestine, where it has to fight against other defense mechanisms of the body, such as Lysozymes (chemicals that destroy infective organisms) and small intestinal secretions that contain some cationic antimicrobial substances.
  • After passing through all the hurdles the body presents, the bacteria invade the intestinal membranes and stay inside Payer’s patches. Payer’s patches are collections of lymphoid cells (that protect against infections) in the intestinal walls.
  • After crossing the intestinal membranes, the bacteria enter the circulatory system and spread to various parts of the body like the liver, bone marrow, and the lymph nodes.
  • The bacteria then start forming colonies at these sites. During this phase, the patient may remain asymptomatic. The symptoms begin to manifest when an adequate number of bacteria have been produced after replication.

Individuals Susceptible To Typhoid

People who have a weak acidic barrier in the stomach are prone to the typhoid infection. Some of the factors that weaken the acidic barrier include:

  • Repeated Use Of Antacids: Drugs that decrease acidity, when consumed frequently, create an environment suitable for the typhoid bacteria.
  • Age: Children less than 1 year of age are susceptible to the typhoid infection
  • Diseases of the stomach associated with reduced acid production also weaken the acidic barrier of the stomach.
  • Intestinal diseases: These damage the intestines and favour the presence of the typhoid bacteria
  • Surgery: A history of surgery on the stomach or the intestines is also an important factor.
  • Excessive use of antibiotics: Antibiotics are used to cure various infections. But when used inappropriately, they may damage some helpful bacteria that live in the intestines and prevent the growth harmful organisms.

Are You A Carrier Of The Typhoid Bacteria?

The Carrier State

Though typhoid symptoms completely disappear after the treatment of the infection, there is a chance that the patient will keep shedding the bacteria through his stools or urine for more than a year. This bacteria often gets transmitted to food and water, contaminating both in the process.

About 1 to 5% of people with typhoid fever may end up becoming carriers of the Salmonella bacteria. The following people run the risk of turning into typhoid carriers:

  • People with stones in the gall bladder
  • Patients with cholecystitis i.e. inflammation of the gall bladder
  • People with cancers of the intestine, gall bladder, or the stomach
  • Those with structural defects in the gall bladder, which favor the prolonged stay of the bacteria inside the gall bladder

Who Is At Risk Of Being A Carrier?

Some people have a higher possibility of carrying the Salmonella bacteria and transmitting them, as they are given to interacting with a large number of people on a daily basis. Some of these people are:

  • Hotel cooks
  • Healthcare or hospital workers

People with previous episodes of typhoid are also prone to be carriers.

Measures To Prevent The Spread Of Typhoid

The following measures can go a long way in countering the spread of typhoid.

  • Washing hands properly after using the toilet, so as to avoid contaminating the food with unclean hands
  • Maintaining high standards of sanitation and hygiene, especially in public places
  • Staying away from food and water that could possibly be contaminated, such as street food

As the main causes of typhoid are usually unsanitary conditions and the consumption of contaminated food and water, it is best to take immediate precautions to counter these factors. The infection can be easily diagnosed by taking a typhoid test during the initial stages of the disease, when the symptoms start showing.


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