The Salmonella genus includes over 2,500 strains of bacteria. Over 1,400 of these serotypes cause disease. The Salmonella genus divides into two different species: Salmonella enterica and Salmonella bongori. All pathogenic strains are in the Salmonella enterica species which divides into 6 different subgroups based on immunoreactivity of surface antigens and other distinctions. Between 95% and 99% of the genetic material of Salmonella bacteria are the same. Two types of pathogenic Salmonella, Salmonella enteritidis and Salmonella typhimurium (typhoid fever), are the most common in the United States and account for half of all human infections. The World Health Organization (WHO) divides Salmonella disease into three categories: typhoidal salmonella, nontyphoidal salmonella, and animal salmonella. The last category is rarely found in humans, but if spread to humans, may be life-threatening.
Refrigeration prevents the growth of Salmonella bacteria but does not kill them. Heat of 57-60 degrees Celsius or 134-140 degrees Fahrenheit will de-activate the bacteria. In 2006, the Center for Disease Control (CDC) reported that salmonella related infections cause an estimated 1.4 million cases of food borne illness and more than 500 deaths annually in the United States. As a potential biological agent, Salmonella bacteria would be most likely be weaponized as aerosol or contaminated food and water.
History of Salmonella
Salmonella bacteria were discovered by an American scientist Dr. Daniel E. Salmon, an American veterinary surgeon. Dr. Salmon assisted with the wiping out of pleuro-pneumonia among New York State cattle and studied livestock diseases, especially Texas Fever, in the South of the United States before being asked to organize a veterinary branch under the Bureau of Agriculture in 1883. In 1884-5, Dr. Salmon isolated the salmonella bacteria (Salmonella choleraesuis) in the intestine of a pig. Initially, he named the bacteria Hog-cholerabacillus. Some controversy surrounds the discovery. Some historians suggested that it was Dr. Salmon's research partner, microbiologist and pathologist Dr. Theobald Smith, who first isolated the bacteria and Dr. Salmon who took all the credit. Additionally, Dr. Salmon collaborated with Dr. Smith to study the use of heat-killed organizations in immunization.
During the 1980s, there was a widespread increase in salmonella diseases particularly in the northern United States. In 1984, 186 cases of salmonellosis (Salmonella enteritidis) were reported on 29 flights to the United States on a single international airline. An estimated 2,747 passengers were affected overall. No specific food item was implicated, but food ordered from the first class menu was strongly associated with disease.
In 1985, a salmonellosis outbreak involving 16,000 confirmed cases in 6 states was caused by low fat and whole milk from one Chicago dairy. This was the largest outbreak of food borne salmonellosis in the U.S. FDA inspectors discovered that the pasteurization equipment had been modified to facilitate the running off of raw milk, resulting in the pasteurized milk being contaminated with raw milk under certain conditions. The dairy has subsequently disconnected the cross-linking line.
In August and September, 1985, Salmonella enteritidis was isolated from employees and patrons of three restaurants of a chain in Maryland. The outbreak in one restaurant had at least 71 illnesses resulting in 17 hospitalizations. Scrambled eggs from a breakfast bar were epidemiologically implicated in this outbreak and in possibly one other of the three restaurants. The plasmid profiles of isolates from patients all three restaurants matched.
Since the 1980s, salmonella outbreaks have been reduced but continued to periodically erupt in developed countries as well as developing countries. Between 1985 and 1999, the US Center for Disease Control (CDC) received 841 reports of Salmonella enteritidis outbreaks affecting residents of 43 states, Washington DC and Puerto Rico. 62% of the outbreaks were food-related. In 2006-2007, over 290 victims across 39 states were infected by salmonella from jars of Peter Pan and Wal-Mart's Great Value brand peanut butter.
Salmonella as a Biological Weapons Agent
As an incapacitating agent, Salmonella bacteria are readily available and often difficult to separate from natural outbreaks of food-poisoning. France's biological weapons program during World War I and World War II, Japan's infamous Unit 731, and South Africa's Project Coast all studied the potential use of Salmonella bacteria as a biological weapons agent.
Terrorist groups have also found Salmonella bacteria to be an easily accessible biological agent. In September 1984, in an attempt to influence local elections in Antelope, Oregon, it was suspected that the Rajneesh cult contaminated local salad bars with Salmonella enterica. The group's aim was not to kill but to incapacitate. Hundreds were affected. There were 751 reported cases of illness, 45 were hospitalized, and no fatalities resulted.
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