ESAVI POR VACUNA INFLUENZA ESTACIONAL

The main factors influencing Salmonella contamination of finishing pig reported in the

literature are (Balœil et al., 2004):

1) Level of hygiene:

- washing hands;

- controlling for birds, flies and rodents;

- handling of manure.

2) Herd management:

Francesca Piras - “Salmonella spp. In Sardinian slaughter pigs: prevalence, serotypes and genotypic characterization” - Tesi di dottorato in “Produzione e sicurezza degli alimenti di origine animale”- Università degli Studi di Sassari

- batch production system;

- housing (type of pen partitions and wall separation).

3) Feeding practices:

- groundness and pH of feed;

- type of feeding (wet versus dry).

4) Health disorders:

- parasite infestation;

- use of antibiotics;

- health status of the herd.

Salmonella infections can be managed by strict application of all-in/all-out procedures

including cleaning and disinfections (Balœil et al., 2004).

At the herd level, controlling birds, flies and rodents in the stables and storage facilities

as well as keeping pets such as cats and dogs out of the pig house, will help to prevent

the introduction of Salmonella from the environment (Lo Fo Wong et al., 2002).

The herd is a complex factor that also includes all related factors, such as the frequency

of introduction of animals, the number of supplier herds, the size of the production area,

Francesca Piras - “Salmonella spp. In Sardinian slaughter pigs: prevalence, serotypes and genotypic characterization” - Tesi di dottorato in “Produzione e sicurezza degli alimenti di origine animale”- Università degli Studi di Sassari

Only few studies have confirmed that an increased herd size imposes an increased risk

of Salmonella infection (Dahl, 1997; Carstensen and Christensen, 1998). However, an

increase in herd size does not necessarily mean an increase in pig density at the pen

level. In most countries, pen density is restricted by legislation and larger herds

basically are comprised of more epidemiological units. In fact, larger operations might

have the resources necessary for the implementation of effective biosecurity measures

and good manufacturing practice (Lo Fo Wong et al., 2004). This was supported by a

study conducted by van der Wolf et al. (2001b), who found an increased risk for

Salmonella in small-to-moderate-size herds (<800 finishers) compared to large herds.

Herds are subject to the introduction of feed and new stock, and as such are exposed to

potential sources of infection. In a risk factor study carried out by Lo Fo Wong et al.

(2001), it was found that the more supplier herds supplying animals to a finishing herd,

the larger the probability of testing animals seropositive in the receiving herd.

To guard against the co-introduction of Salmonella through purchased animals,

Salmonella-free breeding flocks should be identified or established through a

certification system or through weaning in a clean environment. In addition, the number

Francesca Piras - “Salmonella spp. In Sardinian slaughter pigs: prevalence, serotypes and genotypic characterization” - Tesi di dottorato in “Produzione e sicurezza degli alimenti di origine animale”- Università degli Studi di Sassari

and disinfection procedures between batches in combination with the use of a hygienic

lock, i.e. sanitary facilities for washing hands and changing clothes and boots, should be

made standard operating procedures for all (indoor) pig production to avoid the

introduction and/or spread of Salmonella, as well as other pathogens, in pig herds (Lo

Fo Wong et al., 2002).

The type of floor, was examined by some authors (Davies et al., 1997; Nollet et al.,

2004): a fully slatted floor resulted to be protective because the faeces from pigs housed

on this type of floor immediately flows away in the manure pit, so pigs cannot have a

lot of contact with faeces.

As said, faecal-oral transmission is the most-likely mode of transmission of virulent

salmonellae (Boyen et al., 2008).Dahl et al. (1996) showed that closed pen separations

posed a barrier which prevented faecal contact between adjacent pens and thereby

spread of infection. It was demonstrated that snout contact is significantly associated

with seropositivity (Lo Fo Wong et al., 2002 and 2004).

As regards to feeding management, the main variable taken into account are:

Francesca Piras - “Salmonella spp. In Sardinian slaughter pigs: prevalence, serotypes and genotypic characterization” - Tesi di dottorato in “Produzione e sicurezza degli alimenti di origine animale”- Università degli Studi di Sassari

- feeding meal.

The protective effect on Salmonella seroprevalence of non-pelleted feed compared to

pelleted feed was reported in several studies (Dahl, 1997; Harris et al., 1997; Lo Fo

Wong et al., 2002 and 2004; Hautekiet et al., 2008): coarsely ground grain digests

slower than more finely ground pelleted feed. As a result, some parts of the

carbohydrates of non pelleted-feed will be fermented in the large intestine, forming

volatile fatty acids. These provides a hostile microbiological ecosystem for Salmonella.

The beneficial effect of wet feed was demonstrated by several studies (Van der Wolf et

al., 2001b; Balœil et al., 2004; Hautekiet et al., 2008), and is probably due to the

production of lactic-acid producing bacteria as a result of the natural fermentation

process. These acids lower the pH of the feed to a level at which Salmonella bacteria do

not multiply.

Various concurrent infections might favour Salmonella infection: respiratory viruses,

such as porcine reproductive and respiratory syndrome virus (PRRSV), could induce

immunodepression which could facilitate Salmonella contamination and multiplication

Francesca Piras - “Salmonella spp. In Sardinian slaughter pigs: prevalence, serotypes and genotypic characterization” - Tesi di dottorato in “Produzione e sicurezza degli alimenti di origine animale”- Università degli Studi di Sassari

observed experimentally by Wills et al. (2000). Enteric health problems caused by

pathogens (e.g. Lawsonia intracellularis) might predispose to subclinical salmonellosis

due to a disturbance of the ecological balance of the gut flora (Balœil et al., 2004).