Salmonella control on farm – Why bother?

This article is based on a presentation prepared for an Schering-Plough Animal Health roadshow about salmonella, sources of contamination, laboratory testing, the diseases and control.

Why Bother?

  1. Salmonella can cause food poisoning
  2. It will put you out of business

Forget the legislation. I believe that we are all in the business of producing safe good quality affordable food for the British public. Unfortunately whilst politicians may think that they have provided a reasonable solution to dealing with a positive flock what egg pasteurising plant is going to want to take eggs from a known positive flock with all the extra machinery cleaning that will require. As well as checks to ensure that the cleaning has worked.


Salmonellae can be divided into different groups on the basis of their reaction to specific antibodies. In other words on the basis of their serological reactions. Hence serovars – serologoical variants.

The old and young are particularly susceptible as well as immunosuppressed patients.

Salmonellae can be excreted in large numbers in the faeces – millions per gramme. Regrettably chickens are like breweries for most salmonllae. One salmonella eaten and millions excreted.

  • Causes food poisoning
    • More than 2500 different serovars (strains)
  • Anyone can get salmonella
  • Symptoms
    • Watery diarrhoea
    • Stomach cramps
    • Vomiting
    • Fever
  • Transmission
    • Faecel contamination from an infected person or animal.
    • Eating faecally contaminated food mainly of animal origin.

Salmonella isolates reported to HPA by Year

Graph showing the number of salmonellae isolated year on year by the HPA.
Number of salmonellae isolated year on year by the HPA.

This graph shows the number of salmonellae isolated year on year by the HPA. It is a reflection of the total number of food poisoning cases because not every individual presents themselves to the doctor nor is ever patient sampled. However, the effects of vaccination, use of competitive exclusion products, improvements in hygiene are associated with a significant reduction in the number of isolations.

Gut damage in a dog dying from Salmonella enteritis

Gut damage in a dog dying from Salmonella enteritis. Left picture is a healthy gut and the right is infected with Samonella.
Gut damage in a dog dying from Salmonella enteritis. Left picture is a healthy gut and the right is infected with Samonella.

These 2 pictures show the severe damage that occurs to the villi in the intestine following infection with salmonella.

How did this occur?

Firstly, the salmonella must adhere to the intestinal cells (could be a dormant phase). Subsequent invasion of cells requires an actively developing salmonella.

At least 3 types of toxin are produced by salmonella. One is released from killed bacterial cells and will cause a fever, another is associated with increase water secretion by epithelial cells, whilst another causes intestinal cell damage.

Invasion of the cells is necessary for maximum disease.

The picture above shows:

  • The outer absorptive layer of cells is completely lost.
  • The villi shrivel with complete loss of internal structure.
  • The loss of the outer integrity of the villus will allow a blood borne infection, fever and in this case death.
  • The loss of absorptive surface area and integrity of the villi means inability to absorb food.
  • The irritation due to the inflammation causes hyper-motility of the gut and pain.

Not something to have your products associated with.

About David Parsons 19 Articles
David Parsons began his veterinary career in mixed practice which triggered his 39-year passion for poultry. Following positions as a veterinary research officer in the Poultry Department at the government’s Central Veterinary Laboratory and then as a poultry company veterinarian, he set up his own poultry veterinary practice in the southwest of England in 1985. He obtained his MSc in Applied Immunology in 1981, Certificate in Poultry Medicine and Production in 1989 and a Nuffield Farming Scholarship Trust to study the“Status of diseases specific to poultry and their control in Europe” in 1991.

He has been an Honorary External Lecturer at the University of Bristol Veterinary School on poultry medicine and production since 1999,a lecturer on the Institute of Animal Health’s poultry disease course since 2000 and is a regular monthly contributor of veterinary articles for backyard poultry keepers in the Practical Poultry magazine.