A Mouse Model For Study Of Porcine Circovirus Disease

Tischer, a Germany scholar, had found Porcine Circovirus type 1 (PCV1) from PK-15 cells since 1974, up to1991 the pathogenicity of PCV2 and post-weaning multisystemic wasting syndrome (PMWS) were reported. From then, PCV2 as the main pathogen of PMWS was reported in many counties over the world. PCV2 infection could cause immunosuppression which usually results in secondary infection by other pathogens. Therefore, the direct and indirect economic losses caused by PCV2 is very difficult to be estimated.The main pathogen of PMWS is PCV2, but a severe infection caused by PCV2 which develops into the PMWS in pig still needs many factors, such as co-infection of pathogens (bacteria, PRRS, PPV), immunostimulation and so on. Researches regarding PCV2 and PCV2 associated-deseases encounter many difficultes due to these uncertain factors. So, to further study the pathogeny of PCV2, it is necessary to select a suitable experimental animal and develop a good animal model for PCV2. In this study, Kunming mice were used as the experimental animals to study:the infection methods of PCV2; PCV2 distribution and viral lesions in infected mice; PCV2 associated reproductive syndrome and pathological lesions in mice co-infected with PCV2 and bacteria. The aim of this study was to develop a Kunming mouse model for PMWS.1 The methods of PCV2 infection in miceForty-eight 6-week-old mice were divided into two groups, inoculated intraperitoneally (n= 24) and intranasally (n= 24) respectively with four different doses of PCV2 (10000 TCID50?1000 TCID50?100 TCID50 and 10 TCID50),6 mice for each dose. All mice were sacrificed on day 21 post infection (21 dpi), the infection status of mice was evaluated by histopatholigical lesions and PCV2 replication. The results showed that PCV2 could infect Kunming mice by intraperitoneal and intranasal infection, and the optimal virus challenge dose was 1000 TCID502 Viral distribution and lesions in mice experimentally infected with PCV2A total of 35 Kunming mice were intraperitoneal infected with PCV2 of 1000 TCID50. After PCV2 infection,5 mice were sacrificed on the 3,7,14,21,28,35,42 dpi, respectively. Lesions were observed in virus-infected mice and characterized by pulmonary hemorrhage, liver focal necrosis, spleen congestion, lymphadenctasis, and cells apoptosis or necrosis in the spleen, lymph node, thymus, heart, liver, lung, kidney, brain, uterus and testicle, particularly in lymphoid tissues. Immunohistochemical staining showed that PCV2 antigen signals were observed in lymphocytes, macrophages, alveolar epithelial cells, renal tubular epithelial cells, neurocytes, hepatocytes, spermatogonia and follicular granulosa cells.3 Ultra-microscopic Lesion in Mice Inoculated with PCV2Ten mice were injected intraperitoneally with (containing virus 1000 TICD50) viral cell cultures,0.1 mL per mouse. On 14 dpi, tissues from all euthanatized mice were collected for preparation for Transmission Electron Microscopy (TEM) and PCR assay. The results showed that ultra-microscopic lesions in PCV2-infected mice were characterized by apoptosis or cytonecrosis in parenchymal cells of lymphoid organ, heart, liver, lung, kidney, brain and intestine; mitochondrial edema, endoplasmic reticulum dilatation within these cells; and capillary congestion, inflammatory cells infiltration in interstitial tissues. Inclusion bodies of PCV2 were found in lymphocytes and macrophages of lymphoid organ, as well as in hepatocytes, podocytes and neurocytes. PCV2 DNA could be detected by PCR in all of the tissues ofPCV2-infected mice.4 PCV2-related productive failure in miceSixteen female mice were infected with PCV2 through intraperitoneal injection on day 10 before gestation (n= 7), or after day 7 (n= 4) and day 14 (n= 5) of gestation. The results showed that PCV2 caused one death, one difficult delivery and one abortion. Among the 123 newborn mice, there were 24 mice with undergrowth and 4 mice died during lactation. Histopathological observation showed that typical viral lesions were found in maternal mice as well as in their babies, and PCV2 could be detected in tissues of these mice too.5 Pathological studing of mice co-infected by PCV2 and bacteriaIn order to study the synergistic effect on pathogenicity in mice caused by PCV2 and bacteria, mice were co-infected PCV2 and haemophilius parasuis (HPS) or streptococcus type C (Strep.C) in this experiment. The results showed that the disease was more severe in mice of co-infected with PCV2 and bacteria than those infected with PCV2 or bacteria alone, manifested as a higher morbidity and mortality; histopathological observation indicated that severe lesions including cytonecrosis and inflammatory exsudation were obseved in co-infection mice while the lesions were moderate in mice with single factor infection. So, PCV2 associated with HPS or Strep. C had obvious synergistic effect on pathogenicity in mice.Conclusion:PCV2 can replicate in Kunming mice, and PCV2-associated lesions in mice that are similar to lesions of PMWS in pigs; PCV2 associated with bacteria had obvious synergistic effect on pathogenicity in mice. It is possible to use Kunming mouse as an animal model for PMWS research.