Post weaning multisystemic wasting syndrome: clinical and histopathological findings in a follow up of sick animals isolated in a lazaret

Post weaning multisystemic wasting syndrome is a new infectious disease complex of swine wasting of growing pigs is the major clinical sign associated with a tremendous increase of the mortality rate. PCV2 is at the moment recognised as the main agent of the disease. In a 200 sows farrow to finish unit where the disease exists for 2 years, in a batch of 300 piglets 2 six weeks old not sick yet are euthanasied and are considered as negative control. 3 weeks later 9 sick pigs of the same batch are isolated and identified in a confortable lazaret on the farm. At do all the 9 pigs are bled and 2 are euthanasied for post mortem examinations. Between d0 and d42 Living pigs are bled at d21 and d42 and the 3 living pigs are euthanasied on d42. (Pigs numbers 1, 2 and 7). Post mortem and lab examinations are : gross lesions, histology in situ hybridization (ISH) on sera urea, transaminases activities, hemograms, free aminoacid concentrations, creatinine and bilirubin. PRSS and experimental Ploufragan PCV2 serology tests are done on the last blood sample of the pig. All the signs described in the previous references are found on these pigs : wasting, dyspenea, cough, icterus, pale and ulcers. Surviving pigs at d21 (n degrees 1, 2, 7) have completely physically recover at d42. Considering the gross and histological lesions what ever the day of the death, looking of the piglet are still the same : intersticial pneumonia, lymphoid cuffing and lymphoid depletion, lymphoid node enlargement, icterus, kidney enlargement with nephrititis. Pancreas lesions are frequent. ISH positive tests decreased with the living of sick piglets, and is negative on piglets sacrified at d42 in spite of gross and histological lesions. Biochemistry on transaminases, bilirubin urea, seems to be of a limited value. Hemograms are more interesting, with an inversion on sick pigs with a deep lymphopenia. For the surviving pigs with a normal look, we have noticed and increase of beta and gama globulins, and a slight sere conversion on PRSS and PCV2. In conclusion this study shows that sick piglets isolated in a lazaret can recover a physical normal look in 40 % of cases, in spite of specific lesions still present on euthanasied pigs. ISH is a useful tool on early diagnosis on the opposite PCV2 Elisa test is late and not complete. Deep lymphopenia is a bad pronostic, but when the number is above 8000 lymphocits/mm(3) pronostic is good. Are the pigs at d42 negative on ISH carriers of the virus ? What are the mechanisms which save apparently the pig ? These questions need to be deepened in a further study.