Basic information about the farms and their contacts was compiled by the NFSA during initial outbreak investigations. In addition, farm visits were made, and the herd-specific eradication plans were reviewed and discussed with the farmers. The farm veterinarian was interviewed on the phone about the health status of the pigs.
Farm A was a multiplier breeding herd. It ran a 7-, 7- and 8-weeks batch system based on a sow cycle of 22 weeks (116 days gestation 33 days lactation and 5 days from weaning to insemination). Every batch comprised 32 sows and their offspring. The farm self-recruited Norwegian Landrace maternal breeding line as the basis for their production of Topigs Norsvin 70 (TN70) hybrid gilts. All breeding was done by artificial insemination using fresh semen purchased from Norsvin. Gilts were sold as replacement stock to the central unit of a sow pool system, and the remaining growers were sold to a single finisher farm at an age of 10 to 12 weeks.
Farm B was a finisher pig herd that bought grower pigs from farm A. Farm B has three rooms each containing 15 pens with space allowance for thirteen to fifteen pigs, altogether 195 to 225 finisher pigs per room. The farm ran an all in - all out operation on room level, sending pigs for slaughter thirteen to fourteen weeks after arrival. Following the batch system of farm A, they filled an empty and clean room with pigs every seven to eight weeks.
According to herd health records, both farms had low use of antimicrobials, with treatments only initiated on medical indication and administered as individual pig treatments. In farm A, on average 2 sows/batch (6%) were treated for PPDS (mainly injectable non-steroidal anti-inflammatory drugs (NSAIDs)), and 8% of suckling piglets were treated for infectious arthritis (using IM injections benzyl penicillin procaine 60 mg/kg q 24 h for 3–7 days). Neonatal piglet diarrhea occurred on average in some to all piglets in one litter/batch, and affected animals were treated (using per os 60 mg/kg neomycin mixture q 24 h for 3 days). In farm B, 1–2% of the finishing pigs were treated for infectious arthritis or tail lesions (using IM injections of benzyl penicillin procaine 40 mg/kg q 24 h for 3–5 days or amoxicillin 7 mg/kg q 24 h for 3–5 days). Antibacterials (including zinc oxide) were not used prophylactically in either farm.
Based on notification to the NFSA of detection of MRSA in persons with contact to live pigs in the sow pool system, a wider follow-up testing of all pig farms in the sow pool system was initiated. This also included sampling the supplying multiplier breeding herd (farm A). As a multiplier breeding herd, farm A was scheduled for bi-annual MRSA testing in the surveillance program (30) with the earliest sample collection due in April, however this was rescheduled to January as a part of the contact tracing.
The initial sample collection in herd A included 5 swab cloths; three pooled swab cloths from pigs and two pooled swab cloths from the environment. The sampling, submission and bacteriological analysis including verification of MRSA and typing was performed as previously described (21). MRSA CC7 t091 was detected in the pooled samples of the environment of the farm and the NFSA put sanctions on the farm.
Based on the detection of MRSA in environmental samples, further sampling was performed (21) (Appendix 1) using three sterile swab cloths on the environment and 11 cloths from pigs covering all three houses containing pigs and the different rooms in each house. MRSA was found in two of the three environmental samples and in six of the eleven samples from pigs and typing demonstrated MRSA CC7 t091.
To investigate whether MRSA CC7 t091 had the ability to persist and spread in the herd, and as such met the criteria to be defined as LA-MRSA, herd A was resampled two times with an interval of 25 days. Sixty-eight pooled cloth samples were collected, of which 61 were pooled skin swabs of approximately 10–20 pigs per cloth and seven were pooled environmental samples with approx. 15 contact points per swab cloth. Four additional cloth samples were taken in the last sample collection: three from animals in previously unsampled groups of pigs and one from the environment. The number of MRSA positive samples was higher in the second round of sampling (Table 1).
Table 1
Results of longitudinal MRSA-sampling of pigs in a Norwegian pig herd (case farm A) sampled with an interval of 25 days.
| Number of samples from pigs | Number of samples from the environment | Number (percent) of MRSA positive samples from pigs | Number (percent) MRSA positive samples from the environment | Number (percent) MRSA positive samples in total |
First sampling | 61 | 7 | 23 (38%) | 2 (29%) | 25 (37%) |
Second sampling original sample size | 61 | 7 | 29 (48%) | 3 (43%) | 32 (47%) |
Second sampling original sample size plus four new samples | 64 | 8 | 32 (50%) | 3 (38%) | 35 (49%) |
Based on the high prevalence of positive samples and the numeric increase in prevalence from the first to second comparable sampling in farm A, it was concluded that the MRSA CC7 t091 was livestock associated.
Farm B was sampled as a part of the contact tracing after the MRSA findings in the case multiplier herd from where it bought its grower pigs. A total of 15 pooled cloth samples from the skin of the pigs and 3 pooled cloths from the environment were collected. MRSA was detected in 4 (27%) of the pooled skin samples. Further typing demonstrated MRSA CC7 t091.
According to the control policy for LA-MRSA in pig farms in Norway, the NFSA then imposed measures to eradicate MRSA CC7 t091 in both case farms.
According to the national LA-MRSA guidelines (18), the farmers had to develop detailed plans for depopulation and subsequent measures to eradicate MRSA from the farm environment within two months of detection of MRSA. The farm-specific plans had to be compliant with the official LA-MRSA Guidelines (18) and approved by the NFSA. Veterinary swine health consultants employed by the slaughterhouse assisted the farmers in making these plans.
The plans made and the measures taken to eradicate the MRSA were different in the two farms (Table 2). The measures taken in farm A was based on removing, discharging and renewing all internal surfaces of the pig houses. In farm B the pig house was washed and disinfected as it was. The oldest of three houses containing pigs in farm A was emptied, washed and then demolished.
Table 2
Measures taken to eradicate MRSA in two Norwegian pig herds.
Measures taken to eradicate MRSA on farm level | Farm A | Farm B |
Depopulation. All pigs slaughtered or culled. | X | X |
Functional pest control programs running | X | X |
The manure was collected by a local entrepreneur and applied on nearby fields before it was incorporated in the topsoil using plough and/or harrow. Tractors and equipment used for this work was washed and disinfected after the work on the case farms. | X | X |
Miscellaneous, like tools, manure scrapes, boots, piglet creep heat lamps, boxes and cans, was removed from all rooms and discarded. | X | |
Miscellaneous were removed from all rooms and washed and disinfected. Boots and manure scrapes were discarded. | | X |
Rooms were first soaked in water and then washed using water high-pressure washers to remove most of visible dirt from the floors, inventory, walls and ceilings. | X | X |
Detergent was applied to all surfaces and high-pressure washers was again used to remove the rest of the visible dirt. | X | X |
Internal surfaces were rinsed off with water and standing water in puddles, troughs and manure canals was drained. | X | X |
Rooms were left to dry. If low temperatures and/or high humidity prolonged the time needed for drying, extra heat sources was used to dry the rooms more effectively. | X | X |
All interior dismantled and discarded -Pen walls -Piglet creeps -Troughs -Feeding system -Water supply -Smoke detecting system -Slatted floors -Ventilation system -Indoor roofs with its insulation | X | |
The plastic, one-piece pen divider walls were dismantled, and the bottom of the walls were filled in with acryl to prevent organic matter to build up inside the walls. | | X |
All rooms washed a second time | X | X |
Repaired pen walls were reinstalled | | X |
New roofs and all new inventory/interior installed | X | |
All rooms washed a third time | X | X |
All surfaces disinfected using the commercial disinfectant Virocid® according to the manufacturer’s instructions | X | X |
All rooms were disinfected using mobile fogging units dispersing a 1,5% Virocid® solution | X | X |
The NFSA inspected the premises after the LA-MRSA eradication plan had been effectuated (Fig. 1). Before restocking the farms, the environmental samples had to be MRSA negative and the NFSA had to approve the cleanliness of the farm.
The NFSA did not approve the cleanliness of farm B after inspection during week 29, especially noting a problem with organic matter seeping out from under the pen walls. This led to additional dismantling of the pen walls in farm B (Table 2). Also, during a second inspection by the NFSA in week 42, restocking was not allowed based on the finding of unsatisfactory general cleanliness. The extra rounds of washing imposed on farm B are shown in Table 2.
In farm A, pig house one was cleared for restocking in week 130 and house two in week 140. The restocking had to be from a NFSA approved MRSA negative pig farm. The negative MRSA test result on week 150, 12 weeks after the introduction of new pigs in farm A, was needed to be allowed to sell growers to NFSA approved finisher pig farms.
The post-eradication sample results for both case farms are shown in Table 3.
Table 3
Timeline and number of negative MRSA samples from the environment and pigs in two Norwegian pig herds after completing MRSA eradication.
Timeline weeks | 29 | 55 | 72 | 130 | 140 | 150 | 162 | 176 |
Farm A environment/pigs | | | | 13/0 | 9/0 | 3/17 | 4/14 | 2/15 |
Farm B environment/pigs | 18/0 | 21/0 | 13/10 | | | | | |
The direct costs of the measures taken to eradicate MRSA from farm A was 10.8 million Norwegian Crowns (NOK) (approx. 1 mill EUR) and a 100.000 NOK (approx. 10.000 EUR) in farm B. The loss of revenue from pig production and the cost of purchasing replacement stock was not included in these costs.