Essential guides on swine health and production. Control of swine salmonellosis

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BROCHURE

ESSENTIAL GUIDES ON SWIN HEALTH AND PRODUCTION

Salm nella control in swine farms Raúl C. Mainar Jaime • Eva Creus

ESSENTIAL GUIDES ON SWINE HEALTH AND PRODUCTION

Salmonella control in swine farms

ESSENTIAL GUIDES ON SWIN HEALTH AND PRODUCTION

Salm nella control in swine farms Raúl C. Mainar Jaime • Eva Creus

AUTHORS: Raúl C. Mainar Jaime, Eva Creus FORMAT: 17 × 11 cm.

NUMBER OF PAGES: approx. 80 NUMBER OF IMAGES: to be determined.

BINDING: hardcover, wire-o.

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In industrialized countries salmonellosis is considered one of the most prevalent bacterial infections transmitted to humans via contaminated food. Although in the last years a decrease in the incidence of salmonellosis cases has been noted in the European Union, mainly associated to a reduction of the serotype Enteritidis and thanks to the success of control programmes of avian salmonellosis, the incidence S. Typhimurium has increased. Pigs are considered a major reservoir of this serotype and the second most important source of salmonellosis in humans in Europe.

This handbook thoroughly addresses diverse issues related to the epidemiology and control of swine salmonellosis.

Salmonella control in swine farms

Presentation of the book The present book thoroughly reviews in a handy way the expertise currently available about this infection in swine, the difficulty to control Salmonella spp. is discussed from a full perspective, and possible actions in order to reduce its incidence from feedstocks to carcass processing are posed. A first section addresses the general aspects of the infection reviewing its importance both to the pig’s health, the main characteristics of the Salmonella genus, as well as its pathogenesis and ways of transmission. The existing diagnostic methods are then detailed, with their pros and limitations, in addition to the understanding of how should the lab results be interpreted. A third section looks into the control of contamination by Salmonella spp. in the feedstock manufacturing, and the main feeding strategies directed to control the infection in swine. The next section is dedicated to the epidemiology and control of infection at swine operations, goes into the main risk factors, their dynamics and transmission, and which strategies can be applied in farms to try and control this pathogen. Finally, the importance of transport and slaughter is proposed as risk stages for carcass contamination with Salmonella spp., analysing the different risk factors associated to its presence in carcasses and slaughterhouse facilities as well as the connection between the infection in animals and contamination of carcasses and meat.

The authors RaĂşl C. Mainar Jaime PhD in veterinary medicine at the Complutense University of Madrid (1995), he earned a diploma de facto at the National Public Health School in 2004. He has worked as researcher and professor at the universities of California (19961998), LeĂłn (1998-2002) and Saskatchewan, Canada (2002-2006), as well as at the Research and Food Technology Centre (CITA) of the government of AragĂłn (2006-2012).

He currently performs his educational work at the microbiology and immunology unit at the Veterinary School of the University of Zaragoza. He is specialised in veterinary epidemiology and is particularly interested in the study of the zoonotic diseases transmission in field conditions. He has participated in more than a dozen of research projects being the main investigator in half of them, as has written more than 30 peer-reviewed articles in international journals as well as many outreach articles for national journals. In the last years he has focused his research activity in the study of the infection dynamics and control of swine salmonellosis in farms. He has also developed works on the serological and microbiological tests precision to diagnose brucellosis, toxoplasmosis and salmonellosis. He has been director of three PhD theses and is currently directing two more.

Salmonella control in swine farms

Eva Creus Graduated in veterinary medicine at the Autonomous University of Barcelona, UAB (2002) and PhD in 2007 at the same university. She completed her thesis in the study of strategies to control Salmonella spp. in the swine production chain, a research field she has been dedicated to for more than ten years through her own consulting and teaching practice.

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Her experience -both scientific and technical- about swine salmonellosis, and her knowledge of the swine sector has taken her to participate as speaker in many congresses and technical workshops, to publish more than 20 outreach articles on the topic and to organise numerous training courses for veterinary surgeons and producers. She has actively collaborated with various national universities and research centers in research projects related to the study of feeding strategies to control this infection in swine. She has also participated with many working groups in the sector with the goal to know the levels of prevalence and risk factors of Salmonella spp. in swine facilities in Spain and to design effective control programmes of the infection both regional and nationally.

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ESSENTIAL GUIDES ON SWIN HEALTH AND PRODUCTION

Salm nella control in swine farms Raúl C. Mainar Jaime • Eva Creus

Table of contents 1. Infection in pigs: characteristics and importance Characteristics of the genus Salmonella spp.

Characteristics of the infection

by Salmonella spp. in swine

2. Methods of diagnosis Bacterial culture

4. Epidemiology and control of infection in swine herds Epidemiology and risk factors Dynamics and transmission of infection Control measures

5. Transport and slaughter Control of Salmonella spp. in further stages to farm

Molecular methods

Characteristics and risk factors to Salmonella spp. contamination at slaughter

Others

Control measures

Serology

3. Role of animal feeding Hygiene of feedstocks: importance, risk factors and control measures Feeding practices to control infection

6. Development of control plans in a productive structure Difficulties in Salmonella spp. control Stage 1: Design Stage 2: Implementation Stage 3: Evaluation

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The infection process

Control of swine salmonellosis

Characteristics of the genus Salmonella Salmonellosis in an infection caused by bacteria of the genus Salmonella (family Enterobacteriaceae).

General characteristics: ◗ Gram-negative.

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◗ Facultative anaerobe ◗ Non-spore-forming. ◗ Rod-shaped. ◗ Usually mobile (flagella).

THE INFECTION PROCESS

Classification The genus Salmonella is split into two main species: S. enterica. and S. bongori. Salmonella enterica is further divided into six subspecies: enterica, salamae, arizonae, diarizonae, houtenae and indica (Fig. 1). Most (99.5 %) of the Salmonella strains that have been isolated and are relevant to health belong to the species S. enterica.

5 Species Salmonella enterica Family Enterobacteriaceae

Genus Salmonella

Subspecies enterica (I) salamae (II) arizonae (IIIa)

Salmonella bongori (V)

diarizonae (IIIb) houtenae (IV) indica (VI)

Figure 1. Classification of the genus Salmonella (the old subgenus annotations are shown in brackets).

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The infection process

Control of swine salmonellosis

Each subspecies is subdivided into serogroups, according to the composition of their bacterial cell wall antigens (somatic (O) polysaccharide) (Fig. 2). Approximately 50 different serogroups have been identified to date. Each serogroup is further subdivided into serovars or serotypes, according to the classification of the flagellar H antigen and the capsular Vi antigen. This gives rise to a specific antigenic formula for each serotype, based on the combination of somatic antigen (O) and flagellar antigen (H) (Fig. 3). The S. enterica species includes over 2,600 Salmonella serovars or serotypes, approximately 1,500 of which belong to the enterica subspecies, according to the White–Kauffmann–Le Minor classification.

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Some serotypes (mainly Typhimurium and Enteritidis) can be distinguished even further by their phagotype, a classification based on the susceptibility to a particular set of bacteriophages (viruses that attack bacteria).

THE INFECTION PROCESS

Subspecies Somatic O Ag. (cell wall LPS) Serogroups

E.g.: A, B (Typhimurium), C, D1 (Enteritidis) 7

Flagellar H Ag. Capsular Vi Ag. Serotypes

E.g.: Typhimurium, Rissen

Bacteriophages Phagotypes

E.g.: DT104

Figure 2. Simplified diagram of how the genus Salmonella serogroups and serotypes are defined.

Ag. = antigen LPS = lipopolysaccharides

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The infection process

Control of swine salmonellosis

Abbreviated name: Salmonella Typhimurium.

Full name: Salmonella enterica subsp. enterica serovar Typhimurium.

1,4,[5],12 : i :1,2 Somatic antigens

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Phase 2 flagellar antigens Phase 1 flagellar antigens

Figure 3. Example of an antigenic formula (Salmonella Typhimurium).

THE INFECTION PROCESS

Although some Salmonella serotypes are adapted to certain hosts (Table 1), most can survive in a wide range of species. Pigs can be infected by pig-adapted serotypes, such as Salmonella Choleraesuis, but also by many other serotypes that are not specific to pigs, mainly Salmonella Typhimurium, but also Rissen, Derby, and Anatum, amongst others.

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Table 1. Specificity of some Salmonella serotypes.

Serotype Typhi Paratyphi A Abortusovis Abortusequi Choleraesuis Gallinarum Pullorum

Human . .

Pig

Sheep

Horse

Poultry

. . . .

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The infection process

Control of swine salmonellosis

Characteristics of Salmonella spp. infection in pigs Transmission

Airborne route (- common but + rapid) By dust, aerosols, etc.

Excretion in faeces

Oral route (+ common) Contact with faeces from infected animals

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Figure 4. Main routes of infection.

THE INFECTION PROCESS

Pathogenesis Subclinical form Currently, the subclinical form is the most common form. Pigs mainly carry Salmonella spp. in their tonsils, gastrointestinal tract, and mesenteric lymph nodes (Fig. 5). These asymptomatic carriers tend to excrete Salmonella spp. in the faeces at a low level and intermittently.

Types of subclinical carriers: ◗ Active: infected (or reactivated) recently and shedding the bacteria. ◗ Silent: no bacteria in the intestine, but infection present in lymph nodes. Can shed bacteria at times of stress. ◗ Passive: Salmonella spp. in the faeces, but no infection present.

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1

The infection process

Control of swine salmonellosis

Gastrointestinal tract

Tonsils

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Mesenteric lymph nodes

Figure 5. Subclinical form.

THE INFECTION PROCESS

SUBCLINICAL

Oral ingestion (105-106 bacteria) Colonisation of the gut Invasion of M cells and Peyer's patches Mesenteric lymph nodes

Clinical form Any Salmonella that survives the acid environment of the stomach, the bacteriostatic effect of peptides and bile salts, and the animal’s immune defences, will reach the ileum, where most colonisation by Salmonella spp. occurs. After adhering to the intestinal wall, the bacteria pass through it and invade the mesenteric lymph nodes, where they usually remain. If levels of infection are high, or the animal is young or immunodeficient for example, the bacteria can avoid intracellular defences, pass into the bloodstream, multiply in the macrophages, and cause generalised infection and septicaemia.

CLINICAL

Blood Multiplication in macrophages (liver and spleen)

Figure 6. Subclinical and clinical forms of Salmonella spp. infection in pigs.

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1

The infection process

Control of swine salmonellosis

Clinical signs and lesions 90 % of the clinical cases of salmonellosis in pigs are caused by Salmonella Choleraesuis and Salmonella Typhimurium.

Salmonella Choleraesuis (septicaemia) ◗ Incubation period: 24–36 h.

◗ Delayed diarrhoea, appearing at 5–7 days

◗ Morbidity: 10–20 %.

◗ Cyanosis of the extremities and abdomen.

◗ Mortality: > 90 %.

◗ Necrotic foci in the spleen or liver (Fig. 7).

◗ Poor appetite, lethargy, and fever.

◗ Colitis and ulcerated mucosa (Fig. 8).

◗ Respiratory problems (shallow breathing, productive cough, pneumonia).

◗ Inflamed lymph nodes and hepatomegaly.

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THE INFECTION PROCESS

Figure 7. Liver with necrotic foci of a pig. Image courtesy of R. Baselga and I. Albizu.

Figure 8. Necrotic colitis with perforation of the colon wall and peritonitis. Image courtesy of R. Baselga and I. Albizu.

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2

Diagnostic methods

Control of swine salmonellosis

The subclinical nature of most of the infections by Salmonella spp. in pigs is the main barrier to diagnosis.

Results of diagnostic tests will vary depending on the type of test and the nature of the infection itself.

Types of diagnostic tests: ◗ Direct: bacteriology (Fig. 10), sandwich ELISA, etc.

◗ Indirect: indirect ELISA (Fig. 11), indirect immunofluorescence, etc. ◗ These tests enable the individual body’s specific response to the pathogen to be detected, such as the production of specific immunoglobulins (IgG, IgM, etc.)

◗ These tests enable the pathogen or some of its components to be isolated from body samples of the animal. ◗ A positive result indicates that the animal is definitely infected.

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◗ A positive result indicates that the animal has come into contact with the pathogen, but it is not necessarily infected at the time of testing.

◗ There is the possibility of false negatives.

◗ There is the possibility of false positives (e.g. cross-reactions) and false negatives.

DIAGNOSTIC METHODS

a

b

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Figure 10. (a) Colonies of Salmonella spp. on XLD medium. (b) Growth of Salmonella spp. on a semisolid medium Rappaport– Vassiliadis (MSRV).

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Diagnostic methods

Control of swine salmonellosis

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Figure 11. Indirect ELISA to detect antibodies against Salmonella spp.

DIAGNOSTIC METHODS

Various situations may be encountered, depending on the nature of the infection: ◗ Serotype involved and infectious dose: certain serotypes (e.g. S. Typhimurium and S. Derby) are more able to invade tissues (ileal mucosa and lymph nodes) than others (e.g. S. Cubana). ◗ Type of response: probably associated with invasive ability of serotypes, as some cause stronger serological responses (higher antibody levels) and shed for longer periods. ◗ Time of infection in relation to testing: animals that have recently been infected tend to excrete large numbers of bacteria in the faeces, but they later become intermittent shedders, excreting smaller numbers. Antibody production also takes an average of 10–14 days in primary infections, so recent infections are not usually detected by indirect testing. ◗ Potential serological cross-reactions: usually with other Enterobacteriaceae (e.g. E. coli) which have epitopes that are similar to the lipopolysaccharide (LPS) of the bacterial cell wall.

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