Postweaning Multisystemic Wasting Syndrome (PMWS) in pigs with particular emphasis on the causative agent, the mode of transmission, the diagnostic tools and the control measures. A review

Porcine Circovirus type 2 - Systemic disease on pig farms and associated knowledge of key players in the pig industry in Central Uganda

Porcine Circovirus type 2 (PCV2) infections and associated diseases have been rarely studied in Africa. There is no report of PCV2 infection-associated morbidity and the level of awareness of stakeholders has never been investigated in Uganda. This cross sectional survey investigated the occurrence of Porcine Circovirus type 2 - systemic disease (PCV2-SD) among pigs and the associated level of awareness of stakeholders in Central Uganda. Data were collected using questionnaires, Focus Group Discussions (FGDs), key informant interviews and laboratory investigations. All respondents (n = 131) and farmers attending FGDs (n = 31) had never heard of PCV2-SD and only 16.7% (n = 2) of the interviewed animal health workers (n = 12) knew about the disease. Among the farms, 20 piglets presenting with a chronic wasting and a persistent diarrhea were detected and sampled for laboratory investigations. Severe lymphoid depletion with histiocytic and macrophage infiltration in lymphoid organs (n = 8), shortening of intestinal villi (n = 9), abscesses in various organs (n = 15) and granulomatous pneumonia (n = 2) were the major histopathological lesions described. Immunohistochemistry and PCR assays on organs with implicating lesions confirmed PCV2 infection in 25% (n = 5) of the 20 pigs. The study confirmed the occurrence of PCV2 infections among piglets with persistent diarrhea on pig farms in central Uganda and revealed a low level of associated knowledge among farmers and veterinary practitioners. The study arouses the need for systematic studies on prevalence of PCV2 infections and sensitization of stakeholders on occurrence of PCV2 infections in Uganda.

Exposure to environmental stressors result in increased viral load and further reduction of production parameters in pigs experimentally infected with PCV2b

•

Environmental stress increases viral load of PCV2b in serum and tissue.

•

Environmental stress exacerbates PCV2b induced weight loss.

•

Environmental stress and PCV2b reduce ADG and impact negatively on FCR.

Porcine circovirus type 2 (PCV2) has been identified as the essential, but not sole, underlying infectious component for PCV-associated diseases (PCVAD). Several co-factors have been suggested to convert an infection with PCV2 into the clinical signs of PCVAD, including co-infection with a secondary pathogen and the genetic background of the pig. In the present study, we investigated the role of environmental stressors in the form of changes in environmental temperature and increased stocking-density on viral load in serum and tissue, average daily weight gain (ADG) and food conversion rate (FCR) of pigs experimentally infected with a defined PCV2b strain over an eight week period. These stressors were identified recently as risk factors leading to the occurrence of severe PCVAD on a farm level. In the current study, PCV2-free pigs were housed in separate, environmentally controlled rooms, and the experiment was performed in a 2 × 2 factorial design. In general, PCV2b infection reduced ADG and increased FCR, and these were further impacted on by the environmental stressors. Furthermore, all stressors led to an increased viral load in serum and tissue as assessed by qPCR, although levels did not reach statistical significance. Our data suggest that there is no need for an additional pathogen to develop PCVAD in conventional status pigs, and growth retardation and clinical signs can be induced in PCV2 infected pigs that are exposed to environmental stressors alone.

Antimicrobial use in Danish pig herds with and without postweaning multisystemic wasting syndrome

A retrospective cohort study was performed on 130 pig herds in Denmark, to assess the effect of PMWS on the use of antimicrobial drug. The study comprised 65 herds diagnosed with PMWS during 2003-2004, and matched by the veterinary practitioner with 65 herds free from PMWS. Information on antimicrobial use 1 year before and 1 year after the diagnosis was achieved from the National Prescription Medicine Monitoring Database, VetStat, and summarized on quarter within age group and herd. The multiple linear regression analysis comprised antimicrobial use as the outcome variable with (1) quarter relative to diagnosis of PMWS in the positive herd (same date for the negative match), (2) diagnosis of PMWS (same date used for matched PMWS(-) herd), (3) season and (4) temporal trend as fixed effects. Relative to the unaffected herds, the antimicrobial use in the sow units in the PMWS(+) herds was elevated significantly by 35% in the last quarter and 43% in the fourth quarter before positive diagnosis in the herds (p<0.05). In weaner pigs, the antimicrobial use increased significantly two quarters before, and one quarter after the positive diagnosis, by 68%, 91% and 124% respectively. In weaner pigs, effects were seen of herd size and season. The study support that increased morbidity occur for an extended period prior to the diagnosis of PMWS, both in the sow units and the weaner pig units and further indicate that the syndrome cease after the diagnosis, with a decrease in need for antimicrobial treatment.

Pig-major acute phase protein and haptoglobin serum concentrations correlate with PCV2 viremia and the clinical course of postweaning multisystemic wasting syndrome

The aim of the present longitudinal study was to assess the evolution of two acute phase proteins (APPs), pig-major acute phase protein (pig-MAP) and haptoglobin (HPT), in serum from pigs that developed postweaning multisystemic wasting syndrome (PMWS) in comparison to healthy and wasted non-PMWS affected pigs. In addition, evidence of infection with other pathogens and its relation with variations in APPs concentrations was also assessed. Fourteen independent batches of 100-154 pigs were monitored from birth to PMWS outbreak occurrence in 11 PMWS affected farms. Pigs displaying PMWS-like signs and age-matched healthy controls were euthanized during the clinical outbreak. PMWS was diagnosed according to internationally accepted criteria and pigs were classified as: (i) PMWS cases, (ii) wasted non-PMWS cases and (iii) healthy pigs. At the moment of PMWS occurrence, pig-MAP and HPT concentration in PMWS affected pigs were higher than in healthy ones (p<0.0001). No differences in APPs serum concentrations between subclinically PCV2-infected pigs and healthy non-PCV2-infected pigs (based on quantitative PCR on serum results) were detected. Results showed a significant correlation between PCV2 loads and both pig-MAP (R=0.487-0.602, p<0.0001) and HPT (R=0.326-0.550, p<0.05-0.0001) concentrations in serum of PMWS affected pigs, indicating that the acute phase response in PMWS affected pigs occurred concomitantly to PCV2 viremia. No other pathogen, apart from PCV2, was consistently related with variations in APPs concentrations. A ROC analysis, made to determine the capacity of discrimination of both APPs between PMWS affected and non-affected pigs, showed higher sensitivity and specificity values using pig-MAP compared to HPT. These results suggest that pig-MAP might be a better indicator of PMWS status than HPT. Moreover, the fact that APR occurred some weeks before the start of clinical signs suggests that APPs could provide valuable prognostic information for PMWS development.

Virucidal efficacy of nine commercial disinfectants against porcine circovirus type 2

A number of commercially available disinfectants are commonly used on pig breeding farms and are authorised by the French Agricultural Ministry. However, the efficacy of these disinfectants is unknown with regard to the emergent porcine circovirus type 2 (PCV2). The virucidal efficacy of nine disinfectants was evaluated by testing a suspension of PCV2 isolated in France. The assays were performed at 20 degrees C and the efficacy determined after 30 min contact time between virus and disinfectant. After this time, the mixture was passed through a detoxification column and then diluted to remove compounds toxic to the virus and the porcine kidney cell line. The filtrate was serially diluted and inoculated onto cell culture. The infectivity of PCV2 was determined by an immunoperoxidase monolayer assay. No reduction in PCV2 titre was demonstrated with iodine and phenolic products. Significant PCV2 titre reductions (1.61 log(10)) were noted for the seven other products. For five disinfectants, namely a product composed of potassium monopersulfate, two products comprising a quaternary ammonium with one or three aldehyde(s), sodium hypochlorite, and sodium hydroxide, the concentration that significantly reduced the PCV2 titre was equal or 1.5-4 times lower than the authorised use concentration. Only two disinfectants, one composed of potassium monopersulfate, the other containing peracetic acid with hydrogen peroxide, reduced the PCV2 titre with a product concentration at best equal or two times higher than the authorised use concentration.