From Poultry Hub

Salmonella in layer flocks - Does a broom a day keep Salmonella away?

By George Arzey (NSW DPI)

There should be little doubt that some Salmonella enteritidis (SE) phage types are endemic in Queensland. Yet, despite abundant epidemiological links between NSW/Victorian egg Industry and the Queensland Industry, SE has not been found in any of the participating layer farms in NSW or Victoria since the program of monthly or trimonthly sampling was introduced in 1996.

Among birds in SE positive flocks, in 56% of flocks SE was detected in less than 1% of birds (Ebel Schlosser 2000, Hogue et al 1997)

Among eggs from infected flocks the prevalence of SE ranged between 0.001% and 0.1% on the shell. The finding of SE even in known infected flocks is a challenge and the Joint NSW Vic SE Monitoring & Accreditation Program uses drag swabs of the environment. Assuming an average of 12 swabs per layer farm (4 swabs/shed x 3 shed farm) and that one swab is equivalent to culture or serology on 50 - 60 birds (Kingston, 1981), this sampling regime provides a 95% confidence of detecting a within-flock prevalence of 0.5% in layer flocks.

A by product of the program is the detection of other Salmonella serovars. This is an important element that provides quality assurance and useful information. Since 1996 the number of serovars and phage types on monitored layer farms has increased from 10 in 1996 to 44 in 2006.

Changes in the serovar profile were also observed between 1996-2000 and 2001-2006. Mbandaka and Infantis came to prominence between 2000 and 2005 and in 2006 Mbandaka is continuing to be the most prominent serovar.

Analysis of the Salmonella typhimurium serovars over this 10 year period also reveals a dramatic increase in the number of Typhimurium phage types in the last 5 years.

A close examination of the data from individual farms also reveals that on most farms the appearance of Salmonella of a certain serovar was transient and the serovar was not detected in subsequent sampling in the same year. Nevertheless, on a minority of farms environmental persistence of specific Salmonella serovars was evident (chart below).

In 2002 investigations of an incident of human food poisoning traced to a layer farm identified poor sanitation and lack of hygiene at the egg production level as an issue. The serovars found were Salmonella Agona, Salmonella Infantis and S. Broughton The abundance of serovars (environmental contamination) was linked to the poor hygienic status on the farm (CDI N0 4 2003).

A recent combined investigation of NSW DPI and NSW FA on a layer farm with high standards of hygiene, well constructed modern sheds (controlled environment) found an abundance of Salmonella serovars in the environment (Egg rinse** shed 4 & shed 6 - Salmonella Ohio, Faeces / drag swabs / egg conveyor- S Havana, S Senftenberg, S Ohio, S Agona, S Sub 4;12;d, S Singapore (6).

Other recent investigations on a barn/FR layer farm with less than optimal management and hygienic standards found a predominance of STM 108 (170) and one additional serovar (Sub 1:16) in the environmental samples in and out the shed on 3 separate visits.

In a market retail survey in the UK (2003) “There was no statistically significant difference between the prevalence of egg shell Salmonella contamination in samples purchased in England, Scotland, Wales or Northern Ireland; or between the prevalence of Salmonella contamination in samples from different egg production types or between eggs that were stored chilled or at ambient temperature”.

Does a broom a day keeps Salmonella away?