Salmonella

Salmonella Enteritidis, Salmonella Typhimurium

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Salmonella are the pathogens of the disease Salmonellosis, and are among the most important bacteria to cause infections in humans and animals worldwide. They appear in high numbers of serotypes and strains, many of which can cause zoonoses. Salmonella are rod-shaped bacteria; many of them are motile featuring flagella and being about 2-5 µm long in size. They live in human and animal intestines, but can survive for weeks outside the human or animal body.

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Salmonella are the pathogens of the disease Salmonellosis, and are among the most important bacteria to cause infections in humans and animals worldwide. They appear in high numbers of serotypes and strains, many of which can cause zoonoses. Salmonella are rod-shaped bacteria; many of them are motile featuring flagella and being about 2-5 µm long in size. They live in human and animal intestines, but can survive for weeks outside the human or animal body.

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Transmission

An infection is caused by ingesting Salmonella with food. Types of food that are more likely to contain Salmonella are eggs and egg products, poultry, meat and meat products, dairy products and ice cream (there is hardly any food in which Salmonella had not been detected). An infection is usually caused after ingesting a relatively substantial amount of bacteria (>105). This initial number is easily reached when food is not stored properly, as Salmonella can reproduce very rapidly within a few hours at room temperature.

Situation in Foods

Foods in which Salmonella strains were detected in 2013 included: in 10 % (16 out of 167) of raw chicken meat samples tested; in 9 % (6 out of 69) of raw turkey meat and turkey meat preparations; and in 12 % (15 out of 131) of fresh poultry meat (poultry type not disclosed). One of 92 beef samples tested was contaminated with Salmonella, but Salmonella was found in none of the 217 raw pork samples that were examined, none of the 472 fresh meat and meat preparations (from other animals, game or mixed) and none of the 266 ready-to-eat samples of meat, cold meats and sausages that were examined.

None of the 591 samples of milk, dairy products and cheese tested (31 samples of unpasteurised milk and 111 samples from cheeses and other dairy products) contained Salmonella. Two of 136 noodle and pasta samples and one of 158 spices and herbs samples were contaminated by Salmonella. However, none of the 2,207 samples taken from foods, such as 114 samples from eggs produced solely for consumption, 78 egg product samples, 140 fish or fish product samples, fruit, vegetable and other samples, showed any evidence of Salmonella.

Symptoms

Following an incubation period (= time between exposure to the pathogens and the first apparent symptoms) of 6 to 72 hours, patients suffer from acute gastroenteritis (infectious diarrhoea) with mainly watery, but not bloody, stools. Body temperature can rise to 39 °C and 40 °C in some cases. In severe cases, there is a strong feeling of unwellness and circulation problems. While the symptoms subside mostly within one to two days, the illness may last for several days in some cases. The infection may end fatally – luckily, this is very rare in Austria – even on the first day or on subsequent days due to heart or circulatory problems. In newborns and babies, this can also be caused by severe systemic diseases originating in the intestine, such as sepsis and meningitis, in addition to intestinal infections. The same applies to patients with compromised immune systems and elderly individuals. In such cases, infections may already be caused by a smaller number of pathogens.

In the majority of cases it is enough to treat the symptoms through additional fluid and electrolyte intake, thanks to the self-limiting nature of the gastroenteritis. Treatment with antibiotics is only considered in exceptions. Newborns and babies are also treated with antibiotics because they are at a higher risk of suffering from meningitis. The same applies to toddlers suffering from generally weak health and patients with a compromised immune system and very old people. Antibiotics must be used for extraintestinal Salmonella conditions (e.g. Salmonella infections outside the intestine).
 
A total of 1,433 laboratory-confirmed infections were reported in 2013. This was a decrease of 83 % compared to 2002 (2002: 8,405 first isolates). The spectrum of the most common Salmonella serovars that cause human infections has slightly changed in recent years. S. Stanley, the monophase variety of S. Typhimurium found predominantly in turkey flocks (probable reservoir: swine) and S. Infantis; the most common serotype in broilers, are gaining in prominence.

Animals

Animal-based food is the most important source of Salmonella infections in humans. Standardised basic studies have been carried out in various animal populations across the EU over the past 3 years to record their significance as reservoirs for Salmonella. These studies showed that eggs and poultry play the most important role in Salmonella infections in humans in Austria, while all other animal species tested are only occasional carriers of Salmonella. The EU has defined limits for each Member State, specifying the maximum contamination of such poultry flocks with S. Enteritidis and S. Typhimurium: 2 % for laying hens, 1 % for broilers and turkeys and 1 % for parent animals of chickens (here S. Infantis, S. Virchow and S. Hadar are also part of the target requirements, in addition to S. Enteritidis und S. Typhimurium).

The Member States compile an annual report on the share of Salmonella-positive flocks for the various livestock of poultry, breeding hens, laying hens, chicken and turkey broilers as part of the EU-wide programme to combat Salmonella. The data gathered by the Poultry Health Data PHD are evaluated and used for national reports and then sent to the relevant authorities and to the European Food Safety Agency (EFSA), as part of the EU zoonosis report.  

The data processed showed a similar, slightly regressive Salmonella prevalence in flocks of breeding hens, laying hens and broiler hens and a strongly declining prevalence in turkeys in 2014 as compared to previous years. The EU targets were achieved in all categories of poultry listed in the combating programmes in regards to serovars that are relevant to the control programme. A prevalence of 0 % of control relevant serovars was reached for breeding hens and turkeys and a prevalence of under 0.5 % for laying and broiler hens.

The successful fight against Salmonella infections requires a rather complex approach.  The goal is to reduce Salmonella infection pressure and create and maintain Salmonella-free livestock, in addition to treating infected animals. This can only be achieved with complex, long-term control programmes. These objectives have already been introduced in Scandinavia to the point at which Salmonella is very rare in livestock. It has been possible to decrease the number of Salmonella-infected poultry flocks in Austria drastically in recent years. The number of positive groups in other livestock is very small.

Salmonella Infections in Animals

Salmonella infections can be detected in almost all animal species. Reptiles are particularly exposed to latent infections from a wide range of serovars.
Salmonellosis in cattle: S. Dublin is adapted to the animal, but also other serovars can cause general infections with severe clinical symptoms. Calves that are in their second week or older are the most susceptible. The most common symptoms are diarrhoea, general health problems and pneumonia, which get milder as the calf gets older. However, serious infections with diarrhoea, decline in milk production and miscarriages can occur in cows.
Salmonellosis in swine: adapted bacteria species are S. Choleraesuis und S. Typhisuis. Non-adapted serovars cause far fewer infections, in particular infections with diarrhoea. The infection affects pigs that are stopping weaning and young pigs up to 60 kg. The infection usually progresses to a feverish general disease with lung symptoms, occasionally with diarrhoea. Sows may have miscarriages.

Salmonellosis in sheep: S. Abortusovis is adapted solely to sheep and one of the most important pathogens causing miscarriages. Oral infection or infection during mating is followed by a septicaemic general infection. Miscarriages in the 4th or 5th month of pregnancy are the most typical symptom, in addition to puerperal complications and general diseases across all age groups. Non-adapted serovars cause latent infections, diarrhoea and miscarriages in sheep.

Salmonellosis in horses: S. Abortusequi is the adapted type. An oral infection or infection during mating is followed by a general infection that can lead to miscarriages in the 4th month of pregnancy. Very weak foals may be born. Mares develop immunity after the miscarriage. Non-adapted serovars may cause asymptomatic infections including the shedding of pathogens or mild to severe infections and even septicaemia.

Salmonellosis in cats and dogs:  these animal species are more resistant to Salmonellae and there are no adapted serovars. Latent infections were observed in most cases, but diarrhoea, vomiting and fever were also observed under specific conditions.

Salmonelloses in chickens: S. Gallinarum has adapted to chickens, but can also occur in turkeys and a few other bird species. Mammals are not susceptible. This serovar is found in two biovars: Biovar Pullorum is responsible for Pullorum disease and results in acute septicaemic infections in chicks up to the 3rd to 6th week of life. Biovar Gallinarum is the cause for so-called fowl typhoid, which occurs predominantly in chickens. Infections with non-adapted types do rarely cause disease in chickens, but mostly cause latent infections. However, these latent infections are a primary source of food-borne infections, thus receiving lots of attention. The most important serovar in this context in Austria is S. Enteritidis, followed by S. Typhimurium.

Salmonelloses in water fowl: water fowl were identified as a potential source of infection in humans long before chickens. Thus, there have long been special rules in place for the consumption of duck eggs. These animals are exposed to higher infection pressure as they live in standing waters. Young animals are, in particular, affected with diarrhoea and septicaemia (Keel Disease: infected animals swim on their backs).

Feedstuffs

Feedstuffs are part of a permanent monitoring programme in Austria. Salmonella was detected in five out of 323 farm animal feed samples examined in 2013, as displayed in Image 4. The most important Salmonella source is protein-rich oil oilseed meal (by-product of oil extraction). This is how Salmonellae are imported into the feedstuff chain, where they can contaminate the mixed feed that is made out of these products. A total of 54 samples of pet food and pet chew toys were tested by the authorities in the reporting year 2014. Pet food and chew toys, in particular, have been considered risk materials for several years. It is recommended very strongly to wash your hands after feeding the dog or cat and also after intensive contact through stroking and touching the animals.

The feed industry decided to compile recommendations for self-monitoring to control Salmonella contamination of feedstuffs together with AGES, after S. Agona was found in larger quantities in imported soybean meal in 2011 and 2012. The objective was to develop useful guidelines to introduce concrete directives for self-monitoring programmes and enable coordinated action across the industry, but also create better awareness in terms of hygiene and a proactive approach to solving problems.

Outbreaks

EU-Wide Salmonella Enteritidis Outbreak Solved

There was an accumulation of food-borne infections caused by the diarrhoea pathogen Salmonella Enteritidis Phagotype (PT) 14b in Austria, France, Germany and the UK between June and October 2014. An egg producer/egg packaging centre in southern Germany could be identified as the source, thanks to examinations and investigations carried out by the European Centre for Disease Prevention and Control (ECDC), the European Food Safety Agency (EFSA) and national authorities.

Surveys conducted by AGES showed that there had been an Austria-wide accumulation of Enteritidis PT14b infections from June -- a type that corresponded exactly to that detected in patients and food samples (eggs) in France. AGES was commissioned to investigate this outbreak as it had spread across many Austrian provinces: "For 51 out of 61 cases in Tyrol, the consumption of food that had been prepared in the kitchen of a social service provider and was delivered to three retirement homes and individuals via a delivery service (Meals on Wheels) could be established as the connecting factor. The eggs used in the kitchen came from the aforementioned egg packaging centre in southern Germany, which was also connected to other infection cases in France and Germany." (Source: AGES press release 28.08.2014 - in German)

The outbreak affected a total of 151 individuals in seven Austrian provinces (no cases in Burgenland and Vorarlberg). Tyrol reported 69 cases. One patient died as a result of the outbreak. Battery eggs from Germany were identified as the infection vehicle, carrying the strain mentioned. The analytic-epidemiologic study proved that the ingestion of meals that were prepared with the eggs in question were associated with the infections (Source: Lebensmittelbedingte Krankheitsausbrüche/Foodborne Outbreaks 2014 - in German).

Research via a European-wide network (EPIS FWD) showed that there were other cases caused by exactly the same Salmonella type in France, Germany, the Netherlands and the UK.

The identification of the outbreak source was made possible by close cooperation between the Austrian and European authorities, as well as cooperation between service providers and patients with the AGES epidemiologists. Linking of the results of the evaluation of the incoming RASFF notifications, the examinations carried out by the authorities on site and the interviews on symptoms with the menu plans provided led to the identification of eggs as the source. The bacterium’s DNA finger printing (Salmonella Enteritidis Phagotype 14b) confirmed the suspicion: the bacteria isolated from the patients showed the same pattern as the isolates taken from the food from a moleculargenetic perspective. (Source EFSA/ECDC: Multi-country outbreak of Salmonella Enteritidis infections associated with consumption of eggs from Germany)

S. Stanley

Infections caused by Salmonella Stanley have been registered in growing numbers in Europe and Austria since 2011. This strain of Salmonellae was very rare in Europe up to then. It is a more common pathogen for diarrhoea illnesses caused by Salmonellae (Salmonelloses) in Southeast Asia. Cases in Europe were mainly traced back to journeys to these regions before 2011. This has changed quite drastically: the majority of infections have occurred in Europe since 2012.

Studies in several European countries (Hungary, Austria, Germany, the UK, Belgium, Czech Republic, Sweden, Italy, Slovakia and Greece) indicate strongly that the cause of the outbreak can be found in the production chain of turkey meat. Both the European Food Safety Agency (EFSA) and the European Centre for Disease Prevention and Control (ECDC) believe that there will be further sporadic outbreaks in the future, even in countries that have not been affected so far. Infections with Salmonella Stanley have also increased considerably in Austria since 2011: meanwhile, S. Stanley is the third-most common strain found in Salmonellosis patients.

Information on infections caused by Salmonella Stanley


 

 


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