Salmonella bacteria has been known to exist for over 100 years, associated with clinical disease in poultry, cattle, pigs, humans and other species. The organism survives well in the environment, but is readily inactivated by heat, sunlight and numerous disinfectants.
Transmission of the organism is usually by direct contact with contaminated food, water or surfaces. Sanitation of surfaces and hand washing are the most important procedures to reduce human exposure/infection.
Pigs are exposed/infected from their surroundings or pen mates via direct contact with surfaces, water and feed troughs contaminated by carrier animals. Many infected animals don't show signs, but are infected carriers or harbor organisms that can contaminate other pigs at slaughter.
During late 2008 and early 2009, a human outbreak of Salmonella typhimurium was traced to a peanut butter paste used in numerous food products. This salmonella is also frequently diagnosed as a cause of diarrhea in weaner/grower pigs. Salmonella cholerasuis is more frequently seen as a disease of grow/finish pigs.
Case Study No. 1
A producer retrofitted a farrow-to-feeder facility into a nursery. The facility had been thoroughly washed and disinfected before it received pigs. The “high-health” status pigs came from a breeding stock gilt multiplier at 14-17 days of age after being trucked for 10 hours. On arrival, pigs were quite chilled and dehydrated and were immediately given electrolytes.
By 4-7 days after arrival, the producer called to report that many pigs had diarrhea and many in the groups were losing weight. Several pigs were sacrificed and tissues were collected for diagnostics. Pure cultures of Salmonella typhimurium were recovered.
Treatment was instituted according to drug sensitivity, but clinical results were disappointing. There were 10-15% of the pigs that already had chronic damage and failed to perform, with more than 10% mortality.
In checking the source farm and other sites receiving the same pigs, it was found that no other locations had experienced a health challenge.
Further investigation revealed that the trucking firm had access to sawdust and shavings from a local sawmill that had been exposed to the outdoors. Some sections of the sawdust pile had large amounts of bird droppings, which probably contained the infectious salmonella bacteria.
To resolve the issue, the source farm selling the pigs established new requirements for bedding used to ship pigs. And the end producer made an extra effort to clean and disinfect the nursery facility so it wouldn't contaminate future deliveries.
Case Study No. 2
A producer was using an abandoned building site as an isolation facility for incoming gilts. In the warmer months, the animals were allowed onto an attached concrete floor for fresh air.
During June 2008, extreme amounts of rain caused a pond to form in the area surrounding the concrete floor and material oozed onto it. The gilts were happy to flop in the slop. Unfortunately, about 20% became severely ill within a week, and showed purple extremities and came down with a bad cough. Several died. Postmortem examinations revealed pneumonia, enlarged spleens and enlarged lymph nodes. Lab cultures identified Salmonella cholerasuis.
This farm did not have a history of salmonella.
Rather than take the risk of contaminating his entire operation, the producer decided to avoid using that group of gilts in his sow herd and instead purchased another group. The facility was thoroughly cleaned and disinfected and the material surrounding the concrete floor was removed and replaced with gravel. Intense rodent control was also instituted.
Salmonella is a ubiquitous organism and can contaminate a system in a number of ways. Minimizing stresses and other health issues reduces the risks of clinical disease and carrier animals.
It is now well known that time of transport and mixing of animals into large pens at slaughter plants can trigger shedding of salmonella in as little as four hours. These events create more risk of contamination of carcasses and final pork products.
Granted, the public's awareness about food safety is highly variable. However, public health officials are more intensely working to define risks from food-borne illness. Salmonella is becoming more recognized as a cause for food poisoning, and the entire food chain from producer to packer will be held more accountable.
Therefore, every producer should work closely with their veterinary advisor to develop a plan for the prevention and control of salmonella within their production system.