There are three current multistate outbreaks of Salmonella in the United States. Two–infections linked to Butterball Brand Ground Turkey and Precut melons–are outbreaks that began in 2019 and the third involving ground turkey was a 2018 outbreak of raw ground turkey products that remain open.

Taken together, the three have sickened 279 people resulting in 107 hospitalizations and one death. One or the other of these outbreaks has spread the Salmonella infections to nearly every one of the 50 states.

How were these outbreaks possibly made worse?

It can happen, according to Yaohui Sun and Alex Mogilner of New York University. Salmonella bacteria can “flip an electric switch” as they catch a ride inside immune cells, causing migration out of the gut to invade other parts of the body.

Sun, Mogilner and their NYU colleagues discovered how the switching mechanism works, sometimes upping the toxicity of Salmonella, a common food-borne pathogen that comes in hundreds of strains or stereotypes.
Their findings were reported in the open-access journal PLOS Biology on April 9.

Salmonella causes over 400,000 deaths each year, making it both the commonest and deadliest cause of food poisoning, according to the NYU study. Deaths result when the bacteria escape the gut inside immune cells called macrophages.

“Macrophages are drawn to bacteria in the gut by a variety of signals, most prominently chemicals released from the site of the infections,” according to Science Daily’s summary of the study. “Once there, they engulf the bacteria like a regular part of their infection-fighting job.”

But they might not remain there. They might enter the bloodstream “disseminating the bacteria and greatly increasing the gravity of the infection.”

The NYU researchers found tissues in the gut can generate electrical fields that can drive the migration of cells, including macrophages.

In the new study, PLOS reports the authors first showed that the lining of the mouse cecum (the equivalent of the human appendix) maintains a cross-membrane electrical field and that Salmonella infection altered this field and contributed to the attraction of macrophages.

Measurements of the polarity of the local charge indicated that the macrophages were attracted to the anode or positively charged pole within the field. Once they engulfed bacteria, however, they became attracted to the cathode and reversed their migratory direction, moving away from the gut lining, toward vessels of the circulatory system. This switch was driven by an in the composition of certain charged surface proteins on the macrophages; the mechanism by which bacterial engulfment triggers this change is still under investigation.

“Dissemination, rather than localized infection, is the greatest cause of mortality from Salmonella (and other food-borne bacteria), and so understanding more about this polarity switch is likely to help develop new treatments to reduce deaths from food-borne bacterial infections,” Mogilner told Science Daily.

As for those three active outbreaks, the one that’s been active for the longest time involves Salmonella Reading from raw turkey products mostly associated with Jennie-O Turkey produced in Minnesota and Wisconsin.  Jennie-O recalled ground turkey in both November and December of 2018.

The federal Centers for Disease Control and Prevention (CDC) in Atlanta last reported on the outbreak on Feb. 13, 2019, when 279 illnesses were confirmed in 41 states and the District of Columbia.  CDC has not declared the outbreak over.   It did report a common supplier for all the turkey products involved, including pet food, has not been identified.

Butterball Brand ground turkey was, however, immediately named as the source for the first Salmonella outbreak to get underway in 2019.   It is smaller than the 2018 outbreak, involving six confirmed cases in three states.   Only one ill person has required hospitalization and the Butterball outbreak hasn’t caused any deaths.

CDC’s reported on the first Salmonella outbreak on March 14, 2019.    The strain involved is Schwarzengrund.

And, on April 12, 2019, CDC disclosed the ongoing outbreak of Salmonella Carrau involving pre-cut melons.   In the initial announcement, the agency blamed 93 illnesses in nine states on the outbreak.  No deaths have resulted, but 23 people have required hospital treatment,

In concert with the outbreak announcement, Caito Foods in Indianapolis recalled a massive amount of pre-cut melon products.

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