Updated: July 26, 2024
By Ashlyn Snyder , and Dr. Shawna Weimer
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FS-1137  |  July 2020

Understanding Salmonella; Its Presence and Control in Live Poultry

Salmonella is a common foodborne pathogen that can contaminate a variety of foods, including meat and vegetables. It is a significant cause of foodborne illness and death on a global scale (Knodler and Elfenbein, 2020). In the United States, there are an estimated 1.35 million infections and 420 deaths per year from Salmonella (CDC, 2020a).

In 2011, Salmonella caused one of the largest meat recalls in the U.S., totaling 36 million pounds of ground turkey (Bearson et al., 2017). Many foodborne illnesses and meat recalls are linked to Salmonella-contaminated eggs or chicken meat (Humphrey, 2006). Salmonella infections can also come from direct contact with live poultry. In fact, backyard poultry flocks are an increasingly important cause of Salmonella infections in people in the United States (CDC, 2018). Figure 1 shows the general trend that Salmonella outbreaks have been increasing since 2011.

A bar graph showing reported human cases and hospitalizations of selected salmonella outbreak investigations.
Figure 1. Reported human cases and hospitalizations of selected Salmonella outbreak investigations from 2011-2019 due to infection via live poultry. Source: Adapted from CDC, 2020b

As commensal, or non-harmful, resident bacteria in the gastrointestinal tract of poultry, Salmonella is difficult to eliminate among poultry flocks (White et al., 1997). Poultry growers can take many types of precautionary measures to prevent Salmonella spread and improve food safety. All the measures revolve around maintaining strong biosecurity practices and sanitation routines. Salmonella may cause intestinal infection which can lead to decreased bird welfare and performance. Bird management is important because stressors, such as heat, overcrowding, and lack of feed can increase flock susceptibility to Salmonella. As a result, poultry growers have a responsibility to manage the presence of Salmonella in their flocks and to prevent its spread from the farm to the table.

This Extension bulletin provides an understanding of what Salmonella is, how it is carried and transmitted by poultry, and what control strategies you can implement to reduce its survival and transmission in poultry flocks.

Salmonella is Zoonotic

Salmonella species are zoonotic, causing infections in both humans and animals. The species belong to the Enterobacteriaceae family (White et al., 1997) and thrive in the intestinal tract of the host. Over 2,300 Salmonella serotypes are known to exist, and nearly 100 can survive on food or in humans and animals (White et al., 1997). Of these, the serotypes Salmonella enteritidis and Salmonella typhimurium are the most prevalent in the United States, responsible for about half of all human food-related infections (USDA-FSIS, 2013).

Salmonella remains a common foodborne pathogen because it can spread via the oral-fecal route. An infected animal will spread the bacteria in its droppings, which contaminate the surrounding environment. In humans, consumption of foods contaminated with Salmonella will cause Salmonellosis (Salmonella infection) (CDC, 2020a). Contact with live, infected animals can also cause Salmonellosis (CDC, 2020a). Human infection typically results in gastroenteritis, with symptoms such as diarrhea, cramping, and fever. Infection can lead to more serious complications among individuals with weakened immune systems (CDC, 2020a).

Since Salmonella can survive in various environmental conditions and has a wide host range, it is difficult to control once it spreads (White et al., 1997). In addition, some serotypes of Salmonella are resistant to antimicrobials or antibiotics (Bearson et al., 2017), making treatment challenging.

The bacteria rarely cause clinical illness in birds and can exist undetected, making Salmonella a significant challenge in the poultry industry.

Salmonella is Often Commensal in Poultry

A blue carton of six white eggs
Chicks recently hatched

Poultry are an easy vector for the transmission of the bacteria into the food supply because birds carry Salmonella without symptoms. It is critical to understand how and when poultry transmit Salmonella and the factors influencing individual susceptibility or resistance to the bacteria.

There are many opportunities in which poultry can become infected throughout their lifetime (Bearson et al., 2017). If Salmonella is present in a hen’s reproductive tract, it can be vertically transmitted through deposition into the egg yolk (ovum) released from the ovary during egg development (USDA-FSIS, 2019). Salmonella deposition onto the surface of the eggshell also occurs during oviposition (egg laying) by contact with fecal matter or the outside environment. Eggshells are porous and bacteria can enter through these pores into the egg albumen (USDA-FSIS, 2019). In the United States, washing table eggs is a common and effective practice but comes with its share of disadvantages. The chemicals can sterilize and reduce bacteria load but also damage the cuticle (protective layer of the eggshell), increasing Salmonella’s ability to penetrate the shell (Gole et al., 2014). As a result, it is critical to refrigerate washed table eggs.

Numerous interactions between the bird, the bacteria, and their environment can impact a bird’s susceptibility to Salmonella colonization. For example, younger birds have immature immune systems and are less resistant to infection (Oakley et al., 2014). Newly hatched chicks have little to no microflora in their gastrointestinal tracts, including commensal microbes. This lack of competition puts the chicks at a higher risk of Salmonella colonization (White et al., 1997).

Clean Hatchery and Brooding Environments are Important Control Points to Reduce the Presence and Spread of Salmonella

Once infected, bacteria are shed through the bird’s feces, contaminating the environment. Horizontal transmission of Salmonella can occur when birds consume litter, feed, or water contaminated with the bacteria (White et al., 1997). Colonization can also occur when a bird ingests contaminated feed or water, which can result from improper storage of feed, contact with feces, or contact by vectors (insects, mice, and other pests). Table 1 provides a summary of bird, host, and environmental factors that can influence Salmonella colonization in poultry.

Table 1. Host (bird), agent (bacteria or Salmonella), and environmental factors that can influence the colonization of Salmonella in poultry. Source: Adapted from White et al., 1997; Heyndrickx et al., 2002; Oakley et al., 2014; Alhenaky et al., 2017.
Bird Agent Environment
  • Age
  • Diet
  • Physiological status
  • Immune/health status
  • Genetic background
  • Stress
  • Medication
  • Intestinal integrity
  • Ability to survive in the digestive system
  • Competition in gut
  • Ability to colonize
  • Environmental hygiene
  • Food/water cleanliness
  • Interaction with other animals, vectors, or feces
  • Biosecurity standards
  • Stressors
  • Temperature, humidity
  • Stocking density (overcrowding)

While Salmonella is generally not harmful to poultry, in some cases it may negatively impact a bird’s production and welfare. Broiler chickens with Salmonellosis can have diarrhea, fever, and reduced feed intake, leading to lower body weight (Xie et al., 2000). Salmonella can also indirectly impair a bird’s welfare by inducing immune stress. Invasion and colonization of the bacteria can result in an inflammatory response in the intestines (Gomes et al., 2014). Immune stress can negatively affect broiler energy usage and feed consumption (appetite), leading to reduced growth and performance (Liu et al., 2014). As such, a symptomatic bird may also experience lethargy, poor hygiene, and a decreased mobility between food and water or to escape predators.

Environmental stress can also facilitate the transmission of bacteria between birds and increase shedding of the pathogen (Burkholder et al., 2008). Heat and other environmental stressors impair intestinal development and functionality in birds, which can lead to leaky gut (Alhenaky et al., 2017). Leaky gut occurs when the tight junctions of intestinal epithelial cells are loosened, allowing pathogens to pass through and enter the intestines. Fasted birds also showed greater Salmonella attachment in the gut (Burkholder et al., 2008) and overcrowding from high stocking density can increase flock susceptibility to Salmonella (Gomes et al., 2014). Salmonella infection in poultry may also result from existing poor welfare conditions due to insufficient biosecurity and hygiene practices.

Biosecurity is Important to Prevent and Control Salmonella Spread

Hen eating at feeder

Contamination can occur at many points throughout the process of poultry production. Effective hygiene and biosecurity programs must incorporate multifaceted intervention approaches to control the presence and spread of Salmonella (White et al., 1997). Control of Salmonella at the hatchery and in the early weeks of life is particularly critical because this is when chicks are most vulnerable to infection (White et al., 1997).

Another increasingly popular method of reducing the risk of Salmonella in poultry is the regulation of gut microbiota through probiotics and prebiotic supplements in poultry feed. These products improve pathogen resistance by either introducing beneficial microflora to the gut (probiotics) or providing the existing microflora with nutrients to support their growth (prebiotics). Probiotics have proven beneficial on numerous accounts and when administered to chickens, have shown improved control over some bacterial infections, including Salmonella as reported in experimental settings (Brisbin, 2011).

A field trial involving broiler chickens showed a successful reduction of Campylobactor in the gastrointestinal tract after consuming a probiotic-supplemented feed (Smialek et al., 2018). This study also reported a reduction in carcass contamination by Campylobacter, which may lead to increased food safety. Table 2 provides a summary of practices and strategies to control Salmonella on-farm.

Table 2. Practices and strategies to aid in controlling Salmonella in poultry. Source: White et al., 1997; Hayes et al., 2000; Moyle et al., 2014; USDA-APHIS, 2018, 2019, 2020
Sanitation Standards Use effective chemicals and sanitation practices Scrub dirty tools and surfaces with water and detergent from top to bottom and rinse. Apply a disinfectant registered by the U.S. Environmental Protection Agency (EPA) that is effective against poultry diseases.
Wash eggs Use polyhexamethylene biguanide, hydrochloride, hydrogen peroxide, and phenolic compounds to safely wash eggs designated for hatch.
Disinfect the environment and materials Thoroughly clean and disinfect buildings and equipment immediately following flock removal and prior to introduction of a new flock.

In hatching cabinets, use UV light, peroxide, and ozone to disinfect the air.

Use bacteriologic and quantitative tests to ensure enterobacteria counts are below 103 cells per 25cm².
Biosecurity Programs Prevent horizontal transmission in the hatchery Ensure eggs come from Salmonella-free flocks and avoid mixing Salmonella positive and negative eggs. Use different incubators when able. Keep infected and uninfected chicks separate at all times.
Actively control pests Pests can carry Salmonella and transmit between poultry houses and flocks. Rodent-proof the facilities and use rodent traps and toxic baits to restrict spread and reduce risk of litter contamination. Ensure rodents and wild birds cannot enter the facilities.
Monitor litter and use effective management strategies Keep litter from becoming too wet. Reduce water activity index to below 0.84 and maintain a moisture content between 20%-25% to limit Salmonella presence and growth.
Utilize effective and biosecure production strategies All-in-all-out can help minimize the movement of birds, people, and equipment, and limit the spread of pathogens.
Avoid contact between poultry and wild birds Wild birds, particularly migratory waterfowl, can carry Salmonella and other diseases.
Monitor cleanliness of feed and water Use pelleted or other heat-processed feed when able (the heat kills Salmonella cells). Ensure feed is transported and stored in enclosed or covered spaces and keep feed off the floor. Clean up and monitor feed spills as they occur.

Inspect water routinely for bacteria and use chlorination to prevent microorganism spread and growth in water.
Monitor the movement of people, vehicles, and materials (fomites) between farms People, vehicles, and materials can transmit pathogens from farm to farm. Limit entry to farm workers and select visitors and disinfect vehicle tires prior to entering the farm.
Wear biosecure clothing and proper personal protection equipment (PPE) Shower and change into fresh clothing and shoe-cover before entering a new farm and between flocks - clean and disinfect. Wear fresh PPE and discard when done.

Appropriate PPE includes but is not limited to, shoe-cover (boots, booties), disposable suit or coveralls, a hairnet, mask, and disposable gloves.
Ensure all employees are trained in biosecurity standards Train farm employees in appropriate biosecurity protocol. Follow all rules of hygiene, including washing hands and changing clothing, footwear, and PPE. Use hand sanitizer when entering and leaving houses. Employees should not interact with birds outside of the farm where they are employed.
Dispose of birds safely Plan procedures ahead of time for bird disposal of both healthy and sick bird carcasses according to methods approved locally and at the State and Federal levels. Dispose onsite if able.

Check birds daily and collect carcasses as soon as possible. Ensure their storage or disposal doesn’t attract insects or other animals by using tight lids or adequate covering. Avoid cross contamination with equipment and vehicles.
Nutritional Strategies Yeast Provide a yeast-type preparation to hatching chicks. Salmonella prefers attachment to the yeast cell wall and can then be easily removed through host defense mechanisms.
Probiotics Provide other commensal microbes for long-term protection from gastrointestinal pathogen infection. Commensal microbes reduce pathogen colonizing ability in the gut through competition.

 

Your Responsibility is to Prevent Spread

A person washing hands

It is important to take precautions to prevent the spread of Salmonella when handling live poultry and poultry products. Avoid eating or drinking around poultry and keep live poultry out of the kitchen and other areas where human food is stored or prepared (CDC, 2020a). Clean and sanitize poultry environments and materials that come in contact with poultry or poultry litter (CDC, 2020c). When preparing products, you should always follow the CDC’s guidelines for safe food handling: Clean, Separate, Cook, and Chill (CDC, 2020d).

References

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  • Bearson, B. L., S. M. D. Bearson, T. Looft, G. Cai, and D. C. Shippy. 2017. Characterization of a Multidrug-Resistant Salmonella enterica Serovar Heidelberg Outbreak Strain in Commercial Turkeys: Colonization, Transmission, and Host Transcriptional Response. Frontiers in Veterinary Science 4:156.
  • Brisbin, J. T. 2011. Regulation of the chicken immune response by the intestinal microbiota. PhD Dissertation. The University of Guelph. Ontario, Canada.
  • Burkholder, K. M., K. I. Thompson, M. E. Einstein, T. J. Applegate, and J. A. Patterson. 2008. Influence of Stressors on Normal Intestinal Microbiota, Intestinal Morphology, and Susceptibility to Salmonella Enteritidis Colonization in Broilers. Poultry Science 87:1734–1741.
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