Salmonella Transmission Studied in Pigs17 May 2010
SWEDEN - All the selected Salmonella serotypes were transmitted to pigs from a contaminated environment although the transmission rate was low in in experiments at the National Veterinary Institute. S. Typhimurium was the most likely to infect pigs in an environment with low contamination, and the results highlight the need for high hygiene standards.
Julia Österberg and colleagues at the National Veterinary Institute in Uppsala have studied the direct and indirect transmission of four Salmonella enterica serotypes in pigs, publishing their paper in Acta Veterinaria Scandinavica.
Feed-borne spread of Salmonella spp. to pigs has been documented several times in recent years in Sweden, they explain. Experiences from the field suggest that feed-associated serotypes might be less transmissible and subsequently easier to eradicate from pig herds than other serotypes more commonly associated to pigs. Four salmonella serotypes were selected for experimental studies in pigs in order to study transmittability and compare possible differences between feed-associated (S. Cubana and S. Yoruba) and pig-associated serotypes (S. Derby and S. Typhimurium).
Direct contact transmission was studied in four groups of pigs formed by six 10-week-old Salmonella-negative pigs commingled with two fatteners excreting one of the four salmonella serotypes. Indirect transmission was studied by putting six 10-week-old Salmonella-negative pigs in each of four salmonella contaminated rooms. Each room had previously housed a group of pigs excreting one of the four selected serotypes. All pigs were monitored for two weeks with respect to the faecal excretion of Salmonella and the presence of serum antibodies.
At the end of the trial, eight samples from inner tissues and organs were collected from each pig at necropsy.
The researchers found that, in the four direct transmission groups, one pig shed Salmonella (S. Cubana) at one occasion. At necropsy, S. Typhimurium was isolated from one pig. In the indirect transmission groups, two pigs in the S. Yoruba room and one pig in each of the other rooms were excreting detectable levels of Salmonella once during the study period of two weeks.
At necropsy, S. Derby was isolated from one of six pigs in the S. Derby room and S. Typhimurium was isolated from four of the six pigs in the S. Typhimurium room. No significant serological response could be detected in any of the 48 pigs.
These results show that all four selected serotypes were able to be transmitted in at least one of these field-like trials, but the transmission rate was low in all groups and no obvious differences between feed-associated and pig-associated serotypes in the transmission to naive pigs and their subsequent faecal shedding were revealed, say Österberg and co-authors. However, the post mortem results indicated a higher detection of S. Typhimurium in the ileo-caecal lymph nodes of pigs introduced into a contaminated environment in comparison with the other three serotypes.
Österberg J., S. Sternberg Lewerin and P. Wallgren. 2010. Direct and indirect transmission of four Salmonella enterica serotypes in pigs. Acta Veterinaria Scandinavica 2010, 52:30. doi:10.1186/1751-0147-52-30
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