Salmonellosis is one of the most common and widely distributed foodborne diseases, with tens of millions of human cases occurring worldwide every year.
– World Health Organization
Salmonella is the name for a genus of bacteria that can cause illnesses such as salmonellosis (often called “food poisoning”) and typhoid and paratyphoid fever in humans. Salmonellosis is among the most ubiquitous causes of foodborne illness in the world.
There are thousands of different types of salmonella bacteria; the species Salmonella enterica (S. enterica) has more than 2,500 strains, called “serotypes” or “serovars.” S. enterica is found in warm-blooded animals, including human beings, and in the environment. Another species, Salmonella bongori, is found in cold-blooded animals like reptiles.
This post focuses on the history and continued development of our understanding of the salmonella bacteria and the infections it causes. Among the topics discussed are medical discoveries, historical outbreaks, and the effects of salmonella today.
Discovery of Salmonella
The German pathologist Karl Joseph Eberth located salmonella in the abdominal lymph nodes and the spleen of typhoid patients in 1879. Eberth would eventually publish his findings in 1880 and 1881, and they were later observed and confirmed by German and English bacteriologists.
- enterica was discovered by Dr. Theobald Smith—an epidemiologist, bacteriologist, and pathologist—in 1885. Smith was working as an epidemiologist for the newly-created Bureau of Animal Industry (BAI), a subdivision of the Department of Agriculture, at the time of the discovery. The discovery was a result of Smith’s extensive research into the causes of hog cholera, a primary concern for farmers and agriculturalists at the time. The cause was later pinpointed as a viral infection, with S. enterica as a secondary invader.
The credit for the bacteria’s discovery was eventually given to Dr. Daniel Salmon, for whom the bacteria are named. He supervised the department in which Smith worked. Some believe Salmon was able to convince his colleagues due to his stature and tenure as an experienced scientist—something that Smith hadn’t yet achieved. Other sources say that Smith voluntarily credited Salmon for the discovery.
Despite the fact that Dr. Salmon was credited with the bacteria’s discovery, Salmon and Smith worked together to conduct important research. In 1886, the duo found that the bacteria could be used to induce immunity in animals—a groundbreaking discovery that would lead to the development of immunizations for cholera and typhoid.
History of Infections Caused by Salmonella
Salmonella infections have occurred in the United States since the earliest days of European colonization. Historians who study the early Jamestown settlement in colonial Virginia found that typhoid fever (caused by Salmonella typhi) claimed the lives of over 6,000 English settlers between 1607 and 1624. More than 250 years later, numerous combatants in the American Civil War contracted typhoid fever and died.
Many historians and scientists have studied devastating outbreaks in ancient times, theorizing that many have been the result of the spread of typhoid fever. In 430 B.C. in Athens, Greece, for instance, an outbreak of the disease claimed the lives of over one-third of the population—one of the most devastating outbreaks in history.
Medical advances, particularly in the area of immunizations, have drastically reduced the presence of typhoid fever. The first typhoid vaccinations were developed and subsequently available for public use in 1896. Almroth Edward Wright, a British bacteriologist and immunologist, is credited for the research and discovery of the world’s first effective thyroid vaccination.
Eventually, typhoid fever would become nearly eliminated in developed countries. The last deadly typhoid outbreak in the United States was in 1924-1925, when oysters grown in polluted waters sickened 1,500 people. At least 150 people died.
Salmonella and Outbreaks Today
Today, salmonellosis is one of the leading causes of foodborne illness. As with nearly every type of foodborne illness, salmonella can contaminate food along any point of the supply chain—a fact that makes the salmonella, along with other bacteria, difficult to contain.
Over the last two decades, the S. enterica serotype Enteritidis has become one of the most common causes of food poisoning in the US, according to experts.
In 2009, a multistate outbreak of salmonellosis caused by the strain S. typhimurium infected at least 714 individuals across 46 states. The source of this outbreak was traced back to peanut butter and paste products containing the bacteria. Nine people lost their lives.
The primary sources of salmonella are contaminated foods, particularly those of animal origin, like raw meat, poultry, eggs, and seafood. Food may also become contaminated during preparation if cooks and servers do not wash their hands properly after using the toilet. Frogs, lizards, snakes, and turtles, along with other amphibians and reptiles, can also carry salmonella bacteria.
Although most people who contract salmonellosis will eventually recover without medical intervention, complications can arise in people who suffer from autoimmune deficiencies. Elderly and very young individuals are also at risk of complications arising from salmonella poisoning.
The most common symptoms of salmonellosis are abdominal cramps, diarrhea, fever, and vomiting. The duration of illness is approximately four to seven days.