Salmonellas and the Poultry Industry – Part II
By Martine Boulianne DVM PhD Dip ACPV
Part 2: Prevention and Control
By Martine Boulianne DVM PhD Dip ACPV
Prevention and Control
Unfortunately, salmonellas are closely associated with the poultry industry. They are transmitted horizontally and vertically (see part I, April issue) and for that reason, great grandparent and grandparent breeder flocks have to maintain a salmonella-free status.
However, breeder flocks (multipliers) should also pay more attention to Salmonella Enteritidis and Salmonella Typhimurium because of their impact on public health.
In this second part, I will describe detection programs at the primary breeder level, and will explain how the bacteria survives in the environment, as well as different detection methods and the various methods available to fight it.
Brief reminder of the transmission
Salmonellas can be transmitted vertically and horizontally. Transmission is vertical when it occurs from the mother to the chick. An infected hen can have bacteria present in her ovary and lay infected eggs, or a freshly laid egg can become infected by being put in contact with its mother’s contaminated droppings.
During horizontal transmission, birds directly contaminate one another by means of droppings, nasal secretions, or indirectly through mechanical vectors such as food, water, environmental dust, air, etc., or biological vectors such as rodents and other animals that can contaminate the bird. Mechanical vectors of salmonella are numerous. For example, environment, buildings, equipment, trucks, employees and guest boots and clothing, etc., are also a potential source of contamination whenever they are soiled with dusts, droppings or any organic matter capable of harbouring bacterium.
Knowing too well the risks of vertical transmission, primary breeder companies adhere to strict disease surveillance and detection programs that include salmonellas.
These programs vary slightly from one company to another, but comply with the NPIP directives (National Poultry Improvement Plan) from the United States Department of Agriculture (USDA). Created in 1935, the NPIP aimed initially at the detection and eradication of two expensive and devastating diseases; fowl typhoid and pullorum disease (see Part I).
Today, the NPIP also includes the detection of other salmonellas presenting a risk to human health i.e., Salmonella Enteritidis (SE) and Salmonella Typhimurium (ST). Furthermore, the objective of several primary breeding companies is to market breeders exempt from all salmonellas serotypes.
This NPIP program supplies details on sample collection, the type of sample, the frequency of tests, as well as the laboratory methods for isolation and identification of the bacteria.
As an example, here is the program of one main primary broiler breeder company: every grandparent flock is tested every three weeks, from three weeks of age to the end of its production period. Six drag swabs and four composite dust samples are taken. Once a week, the meconium or the delivery box bottom of chicks originating from those flocks are sampled. Samples negative at bacteriology are put in enriched growth environments and are retested to ensure their status. Finally, samples of any new litter, ingredients of the feed, environmental samples of the hatchery, trucks, feedmill and equipment, are regularly tested to verify for the absence of
Prevention of salmonella contamination
The prevention of contamination by salmonellas, as with most diseases, begins with the application of good biosecurity measures. These measures aim to stop the introduction of unwanted bacteria and viruses into the buildings. Because the bearers of bacteria and viruses are numerous, one has to watch all the potential points of entry.
This begins with the staff first. Every employee, as well as company managers, should have a pair of boots and a clean overall for each poultry house. Ideally, a building should be assigned to every employee. In the case where the employees has to work in several buildings, they should follow a daily visit order from the youngest to the oldest birds, or according to their known sanitary status, from non-contaminated to contaminated birds.
The use of boots specific to each poultry house is a far superior system then footbaths. Studies have demonstrated that footbaths do not represent a reliable control method because the contact time between a contaminated boot and the disinfectant is insufficient. Furthermore, the presence of organic matter in the footbaths adversely affects the efficiency of the disinfecting product.
Ideally, one could set up a system that allows the change of boots and overalls before entry to pens. This system can be as simple as a painted line (brightly coloured) on the ground with, on each side, boots and clothes for inside and those for outside. So, the employee sees the demarcation between the outside environment potentially contaminated and the clean environment of the poultry house, and should change before accessing the pens.
Guests pose an important risk to your flock. They can be direct or indirect disease vectors that could have fatal consequences for your operation (see box).
It is suggested to minimize the number of guests allowed onto your farm and apply strict biosecurity measures. Each high risk visitor should sign an entry registry and indicate if he visited other flocks in the last few days.
Any equipment (balance, vaccine equipment, fences used in bird catching, etc.) should first have been disinfected before entering your farm. Disposable boots and clean overalls should be worn before crossing the biosecurity line of every chicken barn. A garbage container should be available near the exit to facilitate discarding of soiled plastic boots.
For high-risk guests, a sequence of movements between buildings (from the youngest to the oldest or non-contaminated to the contaminated) should be respected during the visit.
Naturally, any equipment being transited between barns or from the henhouse to the hatchery, such as eggs flats, should first be washed and disinfected.
No animal should have access to the poultry house. Cats are very poor vermin exterminators and one should leave rodent control to professionals.
Dead rodents are an important reservoir for the dispersal and transmission of pathogenic microorganisms such as Salmonella Enteritidis. According to various studies, rodents play a very important role in horizontal transmission of salmonellas.
Naturally infected mice can excrete SE for a period of up to 18 months. Excretion is occasional and the reactivation of the infection, as for hens, happens during periods of stress. SE prevalence in individual feces is usually weak (< 10 per pellet), but some pellets can contain up to one million bacteria and a mouse defecates on average 100 pellets a day.
Rodents are an inevitable part of the environment in agricultural buildings, and it is extremely important to control them well and to leave this control in the care of professionals.
Contaminated feed can also be a salmonella vector. That is why commercial feedmills set up control and detection programs. So, any suspicious ingredient or feed originating from previously salmonella positive sources is systematically tested. The fact that feed is also subjected to heat at the end of pelleting and sprayed with organic acids also further prevents contamination.
Control measures with salmonella positive flocks
Experience has shown that an infected farm has a 50 per cent chance of contaminating the following flock. Implemented control measures must be rigorously followed; wash/disinfection/ fumigation must be carried out religiously and the environment tested and retested repeatedly in many locations to make sure that the salmonella was eliminated. This is often a very difficult task.
Salmonellas do not multiply or do so very little outside their host, but they are relatively resistant in the environment. For example, salmonellas were found still alive after more than a year in dust, in a frozen carcass after 13 months, in droppings after 28 months, and in dawn feathers after five years!
Fortunately, salmonellas have little resistance to heat. Heating for six minutes at 550C kills 90 per cent of bacteria in homogenized eggs. Heating for five minutes at 650C is enough to destroy 3 X 108 Salmonella Typhimurium per gram of poultry meat, and they cannot survive at 700C. This is why an adequate cooking kills all salmonellas.
In the case of a salmonella positive farm, it is vital, in order to avoid recontamination of the site, to trap rodents instead of using rodenticides. Trapping rodents will clear the environment of a potential bacteria multiplier. Again, in the case of a positive farm, it is strongly advised to regularly send trapped rodents to laboratories to know their salmonella status and the risk they represent for your birds.
Spreading salmonella contaminated dropping on your fields can contaminate the harvests, allow the rodents to contaminate themselves and re-introduce the bacterium into your poultry barn. A study on the storage of liquid manure in pits reveals that the older it is, the less contaminated it is. Salmonella counts decreased by 90 per cent after a month of storage if no new liquid manure was added to the pit.1 A study completed in Quebec with pig manure determined that the spreading of contaminated fertilizer must be done during the summer to allow UV rays from the sun to decrease the quantity of salmonellas.
Spreading done in summer soon after harvest will see an important decrease of the number of bacteria in the month following deposit on the ground. The warmer the ground, the more pathogenic bacteria are going to disappear completely.
By extrapolating these data to the poultry litter, one could recommend that it be stored in a heap for a period of several weeks, to allow it to warm up and inactivate salmonella, followed by a summer spreading.
All material being used to harvest dead carcasses (such as buckets) or that has been in contact with the location where carcasses are discarded, should be considered as contaminated material and should never reenter the buildings.
A freezer located near the road and in a different entrance for the renderer is an optimal solution to dispose of contaminated carcasses in a secure way. Composting, when mastered by the producer and done properly, also allows for the disposal of carcasses in a secure way. To kill salmonellas, a temperature higher than 70ºC must be reached inside the heap of compost, whatever the season.
When a lot has been diagnosed as salmonella positive, it is crucial to proceed with cleaning and disinfection when the building is empty in order to eliminate salmonellas before the introduction of a new lot. Verification of the efficiency of the cleaning is compulsory to break the contagion cycles between lots.
It is very important to remember that a disinfectant is effective only when organic material has been removed. All the equipment should be brought outside the poultry house. Once the building is empty, it is necessary to scrap, blow and remove the largest possible amount of organic material, to soak parts and surfaces in hot water and use a degreasing detergent to dislodge any remaining organic material (for approximately 30 minutes).
Before disinfecting, it is important to wash surfaces with a detergent. Studies have demonstrated that by adding washing with a detergent to the disinfection process, the number of bacteria is drastically lowered.
For instance, the number of bacterium by cm2 in a hog house after the exit of the pigs was 50 million. Washing with warm water dropped this to 20 million, and this was reduced to one hundred thousand when washed with warm water and a detergent. When disinfection was employed after washing with warm water and detergent, the number of salmonella was less than one thousand.2
Cleaning and disinfection protocols:
• Wash with water (warm under pressure).
• Let surface dry.
• Apply disinfectant according to manufacturer’s recommendations. However, if the barn is in an old building or has damaged surfaces, it may be necessary to increase the disinfectant concentration to eliminate salmonellas.
• Dry surfaces completely (ventilate and heat), minimum 12 hours, before reassembling the equipment.
• Downtime (a period when the building remains empty after cleaning and disinfection), of two weeks.
To set up the disinfection protocol, a disinfectant is necessary and the choice depends on the type of surface to be disinfected, present diseases on the farm, and type of water.
Various disinfectants can be used, according to the type of building and installations to be disinfected. Your veterinarian will be able to advise you on the adequate choice of the disinfectant to use for your installations. A study demonstrated the efficiency on salmonella of products containing gluteraldehyde, formaldehyde or Virkon®.
To verify the efficiency of the cleaning and disinfection process, samples can be taken to search for salmonellas when surfaces are dry.
I hope these few suggestions will be useful to you. They will certainly make you think about your actual biosecurity measures and hopefully help you with improving them. I end this article with the reminder that the most difficult part is not the implementation of new biosecurity measures, but the effects they will have in the short, medium and long terms.
Biosecurity is constant work and the dividends are not always visible … it is only during an unfortunate episode of disease that one notices their importance.
1 Dr. C. Côté, IRDA, personal communication
2 Gadd, J. The Pig Pen, Sept. 1999