A few years ago, many people felt that new production techniques and disease control strategies were going to put swine veterinarians out of business. Obviously, that has not been the case as we continually see old diseases presented in new ways. And, new diseases are enteringthe picture. One of the relatively new diseases caused by a virus is Postweaning Multi-Systemic Wasting Syndrome (PMWS).
PMWS is caused by a circovirus. There are two different strains of circovirus. The other strain is responsible for "Shaker Pig" symptoms in nursing pigs.
PMWS is usually characterized by wasting, rough hair, pneumonia and sometimes diarrhea. The syndrome primarily affects pigs 8-20 weeks of age. It may affect up to 50% of the group, but usually affects less than 10%. Affected pigs will usually die.
Iowa State University's Veterinary Diagnostic Laboratory diagnosed one case in 1996. The number of cases increased to 111 in 1998 and they are on course to have nearly 200 in 1999.
Diagnosis can be difficult because it is common to find other infections along with PMWS, such as porcine reproductive respiratory syndrome (PRRS), swine influenza virus (SIV), salmonellosis, haemophilus parasuis and streptococcus suis. A thorough diagnostic work-up by a veterinarian is needed to correctly identify circovirus infection. Many times diseases are blamed for management shortfalls, so it is also important to evaluate management issues such as feed and water intake and pig comfort.
Case Study No. 1 This herd has consistently experienced wasting pigs resulting in nursery death loss ranging from 3% to 18%. The farm also experienced high death loss in the early grower stages. The farm is a 450-sow, farrow-to-finish farm on one site. Pigs are raised in all-in, all-out (AIAO) nurseries, by room, with a common hallway. Pigs are then moved to a finishing barn that is a double-curtain-sided barn, also managed AIAO, by rooms.
Multiple postmortems were performed and laboratory work-ups were done in our laboratory as well as in state diagnostic laboratories. Results ranged from mild PRRS infection to Streptococcus suis, meningitis and arthritis.
Multiple antibiotics were used to try to reduce the death loss and incidence of disease but there was little or no response.
Based on research reports from Canada indicating similar symptoms, we submitted tissues to the diagnostic laboratory looking specifically for the circovirus infection. The laboratory identified microscopic changes as well as isolation of a circovirus. Based on these results, we concluded that circovirus was involved in the farm's high death loss.
Now the challenge was to outline a treatment and control protocol to a virus that we know little about. We felt that it was important to follow good pig raising techniques such as strict AIAO pig flow, improving washing and disinfection methods, as well as separating and euthanizing pigs that appear to be chronically affected. We also felt it was important to limit crossfostering to the first 48 hours following birth.
Although it is too early to claim success, we have seen a decline in the death loss of the nursery and early grower. We are not sure how much our management techniques have helped but we feel it is the best approach available for control of the viral spread. We also are hopeful that the sow herd is developing some natural immunity, which is resulting in less sow to piglet transmission.
Case Study No. 2 Our second farm is a 750-sow operation that has three-site production. The nursery is managed AIAO by room as is the finisher. However, the nurseries have a common hallway.
The quality of pigs at weaning was excellent, as was the performance in the finishing barn.
The nursery performance was good for the pigs that survived, but the mortality rate ranged from 2% to 15%. The pigs in the nursery generally started falling behind within the first week. The pigs that were affected in that first week slowly continued to fall back and eventually accounted for 75% of the nursery death loss.
Based on recent press reports about PMWS, the producer was convinced that this must be the problem in his nursery. We were called to the farm to evaluate the death loss and do a diagnostic work-up. We took temperatures of a large number of pigs as well as submitted pigs to a diagnostic laboratory. There were nofevers present, no microscopic lesions supportive of a circovirus infection and there was no virus isolated.
Some management problems were identified and corrected, such as improving air flow, water flow and feed access.
We encouraged the producer to try to increase feed consumption the first 3-4 days, hoping to reduce the number of waste aways.
This farm is slowly responding to some of the management changes and we continue to look for an infectious cause of the problem. We do not feel that circovirus is involved.