Infectious Disease Report: Salmonella

In the early 1900s, New York state was a hotspot for outbreaks of typhoid fever. George Sober, a sanitary engineer, attributed these outbreaks to one woman, a cook by the name of Mary Mallon. Mallon was the first described case of a healthy carrier of Salmonella typhii, the bacteria that causes typhoid fever, and exhibited no symptoms but harbored the bacteria inside of her. Over the course of her career, it is believed that Mallon infected one hundred and twenty two people, and caused the deaths of at least five people. Her name was eventually associated with any person who willingly or not infected others with disease, dubbed as ‘Typhoid Marys’. Typhoid is only one of several diseases caused by the genus Salmonella, which will be outlined in this paper.

Salmonella, a genus that is part of the non-coliform group of Enterobacteriaceae, are bacillus-shaped bacteria that are 2-5 μm long and 0.7-1.5 μm in diameter, arranged as pairs or singles. They have peritrichous flagella, flagella covering the whole of their body, making them a motile species. Salmonella is gram-negative, staining red during a GRAM stain test. Salmonella species are facultative anaerobes, capable of generating ATP whether oxygen is present or not. Salmonella are chemotrophs, organisms that obtain their energy through the use of organic materials in oxidation and reduction reactions.

It appears that the first marked outbreak of Salmonella happened in Germany, where the ingested meat of a sick cow caused 50 persons to become infected, and for one man to die. Salmonella typhimurium was found in the deceased man’s blood and spleen tissue, matching the same bacterium isolated from the cow meat. Foodborne outbreaks would continue to be the main cause of disease in Europe during the 20th century, but in the United States most outbreaks involved bacterium that had a reservoir species.

It wasn’t until 1969 that these outbreaks restricted to reservoir species would become rare in the United States. It’s believed that a major change in sanitation is the reason for the decline. Sewage disposal techniques were refined, drinking water began to be treated, and the hygiene of farms were improved. The typical clinical illness at the time, typhoid fever, was replaced by gastroenteritis, and most outbreaks began to occur in hospitals.

Going into the 1970s, the mode of transmission of Salmonella changed once again. Rather than being largely isolated to hospitals, large outbreaks were attributed to infected foods, primarily foods with animal origins that came from animals that were otherwise healthy but were carriers of Salmonella. In the 1990s, internally contaminated eggs from hens with infected ovaries caused Salmonella outbreaks to rapidly increase.

Pathology

Salmonella bacteria cause a host of diseases, including gastroenteritis, enteric fever, septicemia, and typhoid fever. Most bacterium enter the body through ingestion of contaminated foods, where they then infiltrate the ileum, colon, and intestinal epithelium. After reaching the epithelium, the organisms multiply intracellularly and spread to lymph nodes, where they can then reach the rest of the body through systemic circulation (Giannella, 1996). Multiplication within the intestines causes an inflammatory response and the hypersecretion of fluids. Salmonella can survive within macrophage’s lysosomes. A few Salmonella strains can produce an intoxicating enterotoxin.

Salmonella causes acute inflammation in the intestine, and may also create ulcers. Damage to the intestine may be caused by the release of proinflammatory cytokines synthesized by the epithelial cells.

A condition called salmonellosis, or gastroenteritis, occurs in a large number of the Salmonella serotypes, causing inflammation in both the large and small intestines, as well as diarrhea, vomiting, abdominal cramps, headache, and fever. Symptoms usually last a few days to a week. Salmonellosis is contracted from the ingestion of contaminated food, the handling of eggs and raw poultry, or contact with reservoir animals.

The typhi serotype causes typhoid fever, a more severe disease characterized by high fevers, abdominal pain, body aches, lethargy, and skin rashes. Untreated infections of typhoid fever result in mortality in as much as 10% of cases. The Widal test is an inexpensive agglutination test that is used for the diagnosis of typhoid fever, however individuals who have been exposed to other forms of Salmonella may flag as false positives and those with immunodeficiencies may flag for false negatives. It can also be diagnosed with an ELISA test and DNA confirmation. Some people may carry typhi but do not present with symptoms; these people continuously shed the bacteria from their feces, infecting others.

Response and Treatment

Salmonellosis infections are not usually treated with antibiotics unless the case is severe. It is usually treated with oral rehydration therapy, which involves the consumption of water with added sugars and salts to treat dehydration caused by diarrhea. Immunocompromised patients who require antibiotics are typically given fluoroquinolones, third-generation cephalosporins, and ampicillin; however, antibiotic resistance is a concern.

For instance, the typhi serovar has seen numerous drug resistances throughout its history. Isolated cases of chloramphenicol (which was the drug of choice for treating typhoid fever prior to the 1970s) resistance began to appear in Mexico in 1972, followed by reports in India, Vietnam, and Bangladesh. To combat the resistance, treatment was switched to ampicillin and trimethoprim-sulfamethoxazole, but by 1975 a case of trimethoprim-sulfamethoxazole resistant typhi was reported in France. In present day, typhi has been defined as being multi-drug resistant to ampicillin, chloramphenicol, and trimethoprim-sulfamethoxazole.

Preventative healthcare of Salmonella involves thorough washing of the hands after handling raw eggs or contact with reservoir species. All surfaces where raw eggs or poultry were prepared should be cleaned thoroughly. Vaccines are available for the typhi strains, primarily for people traveling to areas where typhoid fever is common.

Programs throughout the world dedicated to identifying infected chicken populations have increased the likelihood of dealing with outbreaks in animals and animal products destined for human consumption (Gast, 2013). In Denmark, animal feeds are treated to kill Salmonella strains, reducing the spread of salmonellosis. Contamination can also be reduced by improving slaughtering methods to avoid cross-contamination, training employees who work with animals or food in hygienic care, and improving the storage and cleaning of animal products in plants, restaurants, and the home.

Epidemiology

Salmonellosis is a worldwide disease. Globally, there are an estimated 93 million annual cases, with 155,000 deaths, attributed to non-typhoidal Salmonella strains. In the US, cases have remained stable, with roughly 16 cases occurring for every 100,000 people. In the EU, the number is slightly higher at 20 cases occurring for every 100,000 people. Surveillance numbers are not available for developing countries.

Non-typhoid strains of Salmonella have a large animal reservoir covering numerous species such as chickens, turkeys, pigs, cows, and several wild species as well. Because of its large animal reservoir and its ability to survive freezing temperatures and animal products not thoroughly cooked, the most common mode of transmission is through infected foods.

Salmonella is frequently found in poultry and poultry products, such as eggs. Infected chickens and eggs are one of the main sources of Salmonella infections, due to the widespread consumption of the animal and its products throughout the world (Gast, 2013). In a study, Salmonella was found in 41% of California turkeys, 50% of Massachusetts chickens, and 21% of Washington frozen egg whites. Salmonella is also abundant in reptile populations, such as farmed alligators, snakes, lizards, and turtles. In 1996, it was estimated that reptile-specific infections accounted for 3-5% of the 2-5 million cases.

On the other hand, the typhi serovar of Salmonella does not have a stable animal reservoir, and instead is commonly transmitted from person-to-person. It is mainly spread through water that has been contaminated by feces, although transmission through the handling of contaminated foods is also possible. Approximately 3% of typhoid infected individuals go on to become chronic carriers, carrying typhi but remaining asymptomatic for weeks to years.

Socio-Politico-Economic Considerations

Salmonellosis lacks a nationwide program to control its spread. This, along with its significant animal reservoir and chronic human carriers, make it a major public health concern. Radiation treatment has been approved to reduce Salmonella contamination in poultry within the United States, but has not been widely accepted.

In order to control the spread of Salmonella, education should be made more available about the US radiation therapy to make it more acceptable, as this treatment would greatly reduce the number of contaminated chicken and chicken products. All establishments that handle animals and animal products should have strict guidelines on how to handle and treat possibly contaminated animals and food, and how to clean possibly contaminated surfaces. And lastly, areas where the typhi serovar is abundant should have vaccines readily available to the public.

Works Cited

1. Gast, R.K. 2013. Salmonella Infections. In Diseases of Poultry. 13th edition. D.E. Swayne, ed. Wiley-Blackwell Publishing, Ames, Iowa. p. 677.
2. Tauxe, Robert V. (1991) Salmonella: A Postmodern Pathogen. Journal of Food Protection: July 1991, Vol. 54, No. 7, pp. 563-568.
3. Mitchell, Mark A. & Shane, Simon M. Seminars in Avian and Exotic Pet Medicine, Vol 10, No 1 (January), 2001: pp 25-35.
4. Crump, J. A., Sjölund-Karlsson, M., Gordon, M. A., & Parry, C. M. (2015). American Society for Microbiology: Epidemiology, Clinical Presentation, Laboratory Diagnosis, Antimicrobial Resistance, and Antimicrobial Management of Invasive Salmonella Infection. DOI: 10.1128/CMR.00002-15.
5. Giannella, Ralph A. (1996). Medical Microbiology: Chapter 21 (4th ed.). Galveston (TX): University of Texas Medical Branch at Galveston.
6. OpenStax College. (2018). Microbiology. OpenStax College. Retrieved from https://openstax.org/details/books/microbiology.
7. Marineli, F., Tsoucalas, G., Karamanou, M., & Androutsos, G. (2013). Mary Mallon (1869-1938) and the history of typhoid fever. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3959940/.
8. Rovid-Spickler, Anna, Leedom-Larson, K. R. (2013). Salmonellosis. Retrieved from http://www.cfsph.iastate.edu/DiseaseInfo/factsheets.php