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Salmonella Infection: Symptoms, Causes, Diagnosis & Treatment

Salmonella bacteria is a pathogen that is found mostly in the intestinal tract of humans and animals [1] . Every year it affects thousands of livestock and millions of humans. It can commonly occur in the form of gastroenteritis. Most people contract fever, diarrhoea or abdominal cramps within twelve and seventy two hours of infection. This gets cured somewhere between a period of four to seven days, without serious treatment [2] .

However, it can even become severe causing systemic infection, which is also known as enteric fever [1] . The salmonella can rapidly increase from intestines to blood stream [2] . This stage requires immediate antibiotic or hospitalization. Old people, infants and people with low immunity are more prone to be affected by this bacteria.

Diseases Commonly Caused By Salmonella

There are three major clinical disease forms of salmonellosis, namely gastroenteritis, septicemia and enteric fever. In the septicemic stage, the patient is an intermediate zone, where he or she is not experiencing any abdominal symptoms, and the bacteria is still isolated in the faeces. The severity of the disease gets completely dependent on the immunity of the patient, or the strength of the bacterial isolate.

Salmonella gastroenteritis can incubate any time between six to forty eight hours, depending on the dosage of bacteria. As a result, nausea, stomach pain, vomiting and diarrhoea can take place. Headaches and myalgia are normal symptoms. Sometimes it can be accompanied by a fever of 38°C to 39°C.

A more dangerous systematic fever form of salmonellosis is an enteric fever. The bacteria can incubate any time after 10 to 14 days of infection. Typhoid is the most commonly caused enteric fever, by bacteria Salmonella typhi. Gastroenteritis usually occurs a few days before this fever; the major symptoms can be headaches, myalgia, fever, loss of weight and constipation. It can be fatal if not treated on time.

Symptoms Of Salmonella Infection

The common symptoms of salmonellosis include gastroenteritis, septicaemia, enteric fever, infections and asymptomatic carrier stage. Serovars like S. typhi, S. paratyphi-A usually showcase strong symptoms in the body. S. choleraesuis causes focal infections or septicaemia. S. typhimurium leads to gastroenteritis. However, a serovar can produce any symptom depending upon the situation.

Non-typhoid salmonella enters the body through unhygienic food and can spread from one person to another. The bacteria must have certain attributes to be called a virulent pathogen:

• It should be able to attack cells.

• A full lipopolysaccharide coat must be present.

• It should be able to multiply intracellularly.

• It can enhance the toxins within the body.

This bacteria once ingested, can make colonies inside ileum and colon. It attacks the epithelium in the intestinal layer and rapidly grows inside the follicles. Their ability to invade the system depends on the rearrangement of cytoskeleton cells; they undergo a process called ruffling once they attack.

Salmonella proliferates intracellularly and then gradually spread to lymph nodes and other body parts through blood circulation. Their spread and confinement are controlled by reticuloendothelial cells. However, depending on the host defence mechanism, the pathogens can cause infection in the liver, gallbladder, bones, spleen, meninges, etc. They get killed mostly when they try to spread beyond intestine .[4]

Our body can show symptoms of ulcers, which is an intense inflammatory response of the body, against salmonella. This enhances the effects of cytotoxins, which prevent protein synthesis. Once the mucosa layer in the epithelium is attacked, it produces inflammatory cytotoxins like IL-1, IL- 8, IL-6, TNF-2, etc. They cause a burning sensation and may even disrupt the intestinal functions. This can easily cause symptoms like fever, shocks, abdominal pain, diarrhoea and leucocytosis. The faeces may contain blood and stool.

Once salmonella invades the epithelium, it does not escape the phagosome and secrets fluid that causes diarrhoea. Hence, the intracellular spread does not escape beyond intestines; it stays confined and limited. Once the bacteria reach lamina propria, it causes enteric fever.

The factors that make an individual highly susceptible to salmonellosis are as follows:

• Gastric surgery

• Inflammatory intestine disease

• Frequent use of intestine

• Leukaemia

• Carcinoma


• Sickle cell anaemia

Causes Of Salmonella Infection

Non-typhoid Salmonella is mainly found in animals like chicken, pigs, turkey, cows, etc. and this bacteria can survive in any meat or animal product that is not thoroughly cooked. However, salmonella in typhoid can spread from contact, as it lacks enough presence in the animal reservoir. Human faeces contain this bacteria easily which can be passed on to the local water body. However, children rarely carry chronic typhoid organism. Indeed, frequent use of antibiotics in cattle and humans can decrease resistance to salmonella. [5]

Diagnosis Of Salmonella Infection

The identification of salmonella is done by bacterial isolation; this is carried out by biochemical testing. Specimens of blood, faeces and urine are taken for thorough analysis. The specimen is taken on agar media, and gets added to enrichment solution made of tetrathionate or selenite. Any growth in the solution is even reflected on the subcultured agars.

The colonies suspected to cause disease are then biochemically reacted with triple sugar iron, as well as lysine- sugar agar. The appropriate identification of salmonella type is done and carefully sent to the reference lab. Serologic testing is carried out to confirm the details.[6]

Treatment Of Salmonella Infection

The common treatment includes fluid retention using oral medium or through veins; medicines to control vomiting, abdominal pain. Typhoid, septic and enteric fevers may need heavy doses of antibiotics like ampicillin or chloramphenicol and would take a longer time to be cured. However, antibiotics are not recommended for normal gastroenteritis, as the bacteria will stick to the faeces for a longer time than required. The strains may also develop immunity and may not discard easily.


It is difficult to get completely rid of salmonella from the surrounding. Nevertheless, salmonella is mostly present in poultry farms and animal meat. Taking good care of their hygiene and medicines can significantly reduce human exposure to this bacteria. For example, all animals can be given medical check-up and treatment before distribution across farms. This can significantly reduce salmonella presence in them [1] .

The cross-slaughtering of animals can be avoided to prevent contamination through carcasses. These practices should be closely observed. All processed food should be securely packaged to avoid contamination. People should be carefully trained in slaughterhouses, restaurants and houses to maintain strict hygiene while cutting meat. The government should have effective surveillance programs to control the expansion of the disease.

Recently, the government of the United States approved the use of radiation to decrease the contamination in poultry animals. This pasteurization method has not been widely accepted so far, but it definitely reduces the seriousness of this worldwide problem.

Vaccines are easily available for typhoid salmonella, especially for children. However, there are no vaccines for non- typhoid species. The scientists are making greater research and coming up with more medicines to combat the threat of salmonellosis [1] .

View Article References
  1. [1] Giannella, R. A. (1996). Chapter 21: Salmonella. Medical Microbiology, 4.
  2. [2] Salmonella. Retrieved from
  3. [3] Boyle, E. C., Bishop, J. L., Grassl, G. A., & Finlay, B. B. (2006). Salmonella: from pathogenesis to therapeutics. Journal of bacteriology, 189(5), 1489-1495.
  4. [4] Pham, O. H., & McSorley, S. J. (2015). Protective host immune responses to Salmonella infection. Future microbiology, 10(1), 101-110.
  5. [5] Karkey, A., Thompson, C. N., Tran Vu Thieu, N., Dongol, S., Le Thi Phuong, T., Voong Vinh, P., Arjyal, A., Martin, L. B., Rondini, S., Farrar, J. J., Dolecek, C., Basnyat, B., … Baker, S. (2013). Differential epidemiology of Salmonella Typhi and Paratyphi A in Kathmandu, Nepal: a matched case control investigation in a highly endemic enteric fever setting. PLoS neglected tropical diseases, 7(8), e2391
  6. [6] Andrews, J. R., & Ryan, E. T. (2015). Diagnostics for invasive Salmonella infections: Current challenges and future directions. Vaccine, 33 Suppl 3(0 3), C8-15.
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