The two most common zoonotic diseases around the world are campylobacteriosis and salmonellosis, in that order. Salmonella is a bacteria that can cause serious gastrointestinal disease in human beings. As it is a zoonotic disease, it can be transmitted directly or indirectly between animals and human beings through contaminated food. It is most often found in raw eggs and meat, mainly pork, turkey and chicken. In its most recent report, the EFSA confirms that Salmonella enteritidis is the most prevalent serotype in laying hen flocks in the EU.
In the EU, more than 91,000 cases of salmonellosis are recorded every year in humans, which represents a ratio of 20 cases per 100,000 inhabitants. It [has been] estimated that the global cost of human salmonellosis could total €3 billion per year (EFSA data).
In 2003, the EU established a zoonotic disease control programme, which focused on controlling salmonella in poultry, setting reduction targets for salmonella in laying hens, broiler chickens and turkeys. These control programmes set a series of restrictions on the trade of products from infected flocks.
This integrated focus for controlling salmonellosis in the EU helped to reduce cases of salmonellosis by half in a five-year period (2005-2009).
According to the Annual Report on Sources and Trends of Zoonoses published by the EFSA and the European Centre for Disease Prevention and Control (ECDC), cases of salmonellosis have stabilised in recent years in the EU, after a long period of downward trend.
The EFSA publishes an annual report on the status and prevalence of zoonotic diseases in the EU. The last data published was from 2019, stating that the 26 members of the EU that have salmonella control programmes for poultry had similar rates of Salmonella enteritidis as in 2017-2018.
- Of the 26 member states, 18 met the reduction targets, while eight did not meet at least one (five countries did not meet them in breeding hens, four in laying hens, one in broiler chickens and one in broiler turkeys).
- Of the target control serotypes in the national control programmes, Salmonella enteritidis had the highest prevalence in breeding hens and laying hens. For broiler chickens, the prevalence of S. enteritidis and S. typhimurium were similar, while in turkey production (both broilers and breeding hens), S. typhimurium had a higher prevalence.
Salmonella prevalence in the EU in breeding hens
In 2019, salmonella was isolated in 2.34% of flocks sampled in the EU, which was higher than previous years (2.03% in 2018 and 1.89% in 2017).
The prevalence of flocks positive for any of the five serotypes targeted by the salmonella control programmes (S. enteritidis, S. typhimurium (including the monophasic variant), S. virchow, S. infantis and S. hadar) was 0.62% in 2019, somewhat higher than in 2018 (0.54%). In other words, 26.56% of positives for salmonella reported in breeding hen flocks were serotypes targeted by the salmonella control programmes.
Poland had the highest prevalence of the five target serotypes of the salmonella control programmes, with 1.5%
In 2019, S. enteritidis was the serotype with the highest prevalence in breeding hens in the EU.
Salmonella prevalence in the EU in laying hens
According to the 2019 EFSA report, salmonella was found in 3.9% of flocks sampled, a slightly higher number than in 2018 (4.04%).
In laying hens in the EU, the prevalence of the target serotypes of the national salmonella plans was 1.25%, slightly higher than the prevalence in 2018 (1.1%)
This means that 32% of positives for salmonella were serotypes targeted for control, with Salmonella enteritidis having the highest prevalence (0.95% in Europe).
Prevalence in Spain.
The National Salmonella Control Plan sets a series of controls to monitor for salmonella on farms, and specifically differentiates between self-monitoring and official monitoring.
Self-monitoring can be done by the farm itself by sending samples to laboratories officially authorised for this purpose. The samples are collected at different times during the chicks' lifetimes:
- One-day-old chicks
- Chicks 2 weeks after transfer to the laying house
- Every 15 weeks during the laying period (starting at 24+2 weeks).
Meanwhile, official controls are performed by official Ministry veterinarians. The samples are taken from all farms with more than 1,000 birds, at least one flock per farm and year, and from adult breeding hens. There may be more sampling in certain situations where there is suspicion or where there has been salmonella in previous flocks.
The data on prevalence in 2019 in laying hens was 2.34% (source: Ministry of Agriculture, Fisheries and Food), exceeding the target set by the National Plan (2%).
It is worth noting the large difference between the results of self-monitoring (0.5%) and official monitoring (7.4%)
If we look at the various production systems for laying hens, the highest prevalence occurred in caged chickens and in cage-free chickens (2.4% in both cases), followed by free-range chickens (2.3%) and, to a lesser degree, in organic chickens (0.8%). We cannot draw a definitive conclusion on prevalence and production systems, since the opposite was true in previous years, where the highest prevalence was observed in organic systems.
If we look at the different serotypes found in laying hen flocks, we see that Salmonella enteritidis had the highest prevalence, with 16.8% of the total, followed by S. infantis (9%). Salmonella typhimurium made up only 4.3% of the total and monophasic S. typhimurium 2.1%
Conclusion
According to the European Food Safety Authority (EFSA) and the European Centre for Disease Prevention and Control (ECDC), salmonellosis continues to be the second most commonly reported gastrointestinal infection after campylobacteriosis, and a major cause of foodborne outbreaks.
In the EFSA 2019 report, it was determined that S. enteritidis was the serotype that most often caused these infectious outbreaks in humans.
It was also found that Salmonella enteritidis was the predominant serotype in breeding hen and laying hen flocks, while in broiler hens the prevalence is similar to that of S. thyphimurium.
According to the EFSA, these data indicate the importance of prioritising the control of Salmonella enteritidis, as it is the most predominant serotype on farms and the one with the highest risk of transmission to people, especially in laying hens, where its importance is underestimated in some EU countries.