Controlling salmonella – Animal Health

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Published: June 27, 2002

Salmonella is a zoonotic organism, which means it can be passed from an

animal to a human.

According to a 1996 U.S. study, salmonella-tainted food costs between

$600 million and $3.5 billion US a year in human medical expenses and

productivity losses.

Salmonella typhimurium DT 104 is of particular concern. This strain is

resistant to at least five antibiotics.

Of all salmonella strains, this one causes the highest mortality rates

in people.

At least five outbreaks of DT104 have been reported in the United

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States. Three were linked to consumption of noncommercial or homemade

cheese that was contaminated with salmonella. One was traced to

exposure to infected dairy cattle. The other occurred in elementary

school children believed to have consumed contaminated milk or

contacted infected animals.

Though the most recognized source of salmonella DT104 is cattle, it has

also been isolated from sheep, goats, pigs, dogs, mice, cats, horses

and turtles.

It is thought to pass between animals via a fecal-oral route, which

means the bacterium is passed in the feces and consumed by the next

host. Overcrowded conditions and stress will promote the spread of

salmonella organisms.

Humans can be infected directly through contact with ill farm animals

or indirectly by consuming contaminated food. Occasionally, infected

pets can pass it to humans. Cats’ coats can become contaminated through

grooming because they shed large numbers of salmonella from their

mouths.

Salmonella is not a benign illness in people. More than 40 percent of

afflicted individuals need to be hospitalized and up to three percent

will die. The infection typically causes intestinal signs such as

vomiting and diarrhea, but in some people the bacteria can reach the

bloodstream, causing the blood infection septicemia.

The exact cost of salmonella to cattle producers is difficult to

determine because it includes treatment costs, deaths, increased cull

rates, reduced efficiency and decreased weight gain.

Infected cattle will suffer from fever, mental dullness, loss of

condition, decreased milk production, loss of appetite, dehydration and

diarrhea that can progress to dysentery. Because many other infections

can cause similar symptoms, the only way to diagnose salmonella is to

culture feces or blood.

Treating salmonella DT104 is difficult because it is resistant to

antibiotics commonly used in cattle.

It is unlikely salmonella will be eradicated from domestic animals in

the near future. The infection can, however, be controlled by a number

of management procedures:

  • Clean up fecal material and compost it away from cattle.
  • Use footbaths to prevent fecal transfer.
  • Work with calves first, and then adult cattle.
  • Keep feed and water off the ground.
  • Quarantine newly purchased livestock for a month.
  • Isolate sick animals. Minimize animal density.
  • Prevent access to feed storage areas by animals other than cattle.

Because of DT104’s resistance to antibiotics, concern has been raised

that antibiotic use in cattle could cause more resistance to develop.

In the United Kingdom, DT104 became harder and harder to kill with

fluoroquinolones, which was a new antibiotic at the time. The

resistance was blamed on the use of those antibiotics in cattle, but

the claim was not substantiated because fluoroquinolones weren’t

available for use in cattle until a year after the resistance pattern

emerged.

Jeff Grognet is a veterinarian and writer practising in Qualicum Beach,

B.C.

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