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y serotypes S. Infantis and particularly S. Agona prevailed among certain cattle
for years. Serotype S. Enteritidis was only isolated in individual cases over the
years, but even this has had a tendency to remain within a herd for a long. After
becoming infected by S. Typhimurium, cattle are generally cleaned of infection
within a few months. No multi-resistant strains of Typhimurium DT 104 were
isolated at cattle farms after 1997. Infection with Typhimurium DT 41, typical
for wild birds and particularly seagulls, did not appear to very easily spread to
cattle; generally, this has no longer been isolated from repeated samples, and
disinfection of infection with Typhimurium DT 41 appears to rapidly take effect.
A large proportion of other individual serotypes have also rapidly disappeared
and have often only been isolated once. Serotype Poona, causing human infection
via raw milk in 1996 to 1997, has repeatedly been isolated from fur-animal
feedstuffs. Cattle or pig farms may be located in the vicinity of fur farms or be
run by the same owner, and the risk of spread of disease must then be taken
into account at these at farms.
The expanding unit sizes among cattle farms, as well as increasiang frequency
of freestall dairy barns and three-stage rearing units in meat production have
presented new challenges in the prevention of Salmonella. Animals moving
freely in freestall barns run a greater risk of becoming infected under disease
conditions and their disinfection may then be more difficult than for cows in tie
stall barns. Hence, disease prevention must receive particular attention.
Calves may arrive at calf-rearing units from 30 to 40 farms. Isolating the original
source of Salmonella infection is then laborious, expensive and often impossible.
Disinfection of these farms is also demanding because of the risk of repeated
infection if no separate facilities are available where decontaminated animals
can be transferred to. Even then, while samples are being analyzed for Salmonella,
disinfected animals may become re-infected before being transferred to a
separate place when the results are ready. In addition, the planning of sampling
requires a great deal of thought when the number of individuals is large.
While the National Salmonella Control Programme has been in effect, Salmonella
has only been isolated in swine as individual cases. However, Salmonella has
more often been detected in lymph nodes from pigs than in faecal samples from
farms. Lymph nodes have also carried out three times the number of serotypes
in relation to faecal samples. Generally, as pigs excrete little Salmonella in their
faeces, finding infections in live animals is very difficult, and analysis of faeces
will not always reveal infections. Analysis of lymph nodes is therefore more efficient
than faecal sampels for controlling Salmonella infections in pigs. In EU
countries, where infection is abundant, survey research and efforts to reduce
occurrences are applying analysis of meat fluids through serological methods
carried out at slaughterhouses. Although these are considered cost-efficient methods
for screening, serotype data are necessary for epidemiological monitoring
and hence, to that end, bacteriological isolations are necessary.
As pig-producing units are also increasing in size, quantifying the number of
animals to be extended increasingly demands evaluation to reveal subliclinical
infections, particularly because of the poor secretion in faeces. Symptomless
infections in holdings of hundreds of sows may quickly spread infection to several
fattening units. This has so far been avoided, and preventive actions are
of essential importance. Through efficient cleaning and disinfecting actions, the
few Salmonella-positive herds have mostly been cleaned relatively rapidly. In
locations where infection has prevailed for longer, deficiencies in the implementation
of the disinfection plan have been observed.
Salmonella control and occurence of Salmonella from 1995 to 2004