The Pathogenicity Of Bovine Adenovirus Type3and Bovine Parainlfuenza Type3to Laboratory Animals

Bovine respiratory disease complex is the major clinical manifestation of bovine respiratoryinfectious disease, which causes serious economic losses for the global cattle industry annually, andbovine adenovirus type3and bovine parainfluenza type3are the most important pathogen. A ChineseBAV-3strain HLJ0955was first isolated in2009in Heilongjiang Province, China.4BPIV3strains werefirst isolated in Shandong Province by our laboratory in2008, the4BPIV3strains were different fromthe previously reported genotypes. Natural infections with BAV-3or BPIV3in calves are very popularand result in difficulties of acquiring the suitable calves for experimental infection. Therefore specificpathogen free animals might be a useful animal infection model for studies on the pathogenesis ofBAV-3and BPIV3isolates.The present study used virus isolation, real-time PCR and immunohistochemistry staining to detectbovine adenovirus type3in tissues from experimentally infected BALB/c mice and guinea pigs. As afirst step, the infected lungs and other organs of2week old and4week old female BALB/c mice werecollected on different time post inoculation (105.2TCID50) for subsequent tests. BAV-3replicates wellin the lungs of2week old BALB/c mice, no virus could be isolated by day5PI, but IHC results showedthat the antigen of BAV-3in the alveolar epithelial cells can be detected from1to11days PI. ViralDNAs were detectable in the lungs of experimentally infected BALB/c mice during7days ofobservation by real-time PCR. Infection of BALB/c mice causes an interstitial pneumonia characterizedby hemorrhage, alveoli septa thickening, alveolar epithelial cell proliferation. On the other hand, thehistological lesions in the lungs of4week old BALB/c mice inoculated with BAV-3were less severeand their lasting time was shorter. All of the infected guinea pigs had apparently elevated rectaltemperatures (39.2℃–39.9℃), consolidation and petechial hemorrhage were observed in guinea pigsexperimentally infected with the HLJ0955. Viral replication was detectable by virus isolation andtitration and IHC in the lungs of guinea pigs as early as24hr PI. Viral DNA was detectable in the lungsof infected guinea pigs during11days of observation by real-time PCR. Virus neutralization antibodiesagainst BAV-3were detectable from11days PI. Histopathological changes were the same as thechanges in mice.An experimental infection of SPF guinea pigs with the Chinese BPIV3strain SD0835of thegenotype C was performed. Sixteen guinea pigs were intranasally inoculated with the suspension ofSD0835(3.55×106TCID50). The virus-inoculated guinea pigs displayed a few observable clinical signsthat were related to the respiratory tract disease and two experimentally infected guinea pigs died, thegross pneumonic lesions in guinea pigs inoculated with SD0835consisted of dark red, consolidationand atelectasis. Histopathological changes including alveoli septa thickening and focal cellulosepneumonia were also observed in the lungs of guinea pigs experimentally infected with SD0835. Viralreplication was detectable by virus isolation and titration, real-time RT-PCR and immunohistochemistry(IHC) staining in the respiratory tissues of guinea pigs as early as24hours after intranasal inoculation with SD0835. As well, the results of IHC staining implicated that the lungs and tracheas were the majortissues in which SD0835replicated. Virus-specific serum neutralizing antibodies against BPIV3weredetected in virus-inoculated guinea pigs.In conclusion, it is eligible to the BALB/c mice as the animal model for the BAV-3strain HLJ0955infection, and the2week old mice were more sensitive than the4week old mice to HLJ0955infection.However, no clinical sign and gross lesion was observed in BALB/c mice experimentally infected withBAV-3strain HLJ0955. On the contrary, the HLJ0955could replicate in lungs of guinea pigs and causefever and gross and histological lesions in infected guinea pigs. Therefore the guinea pig infectionmodel of BAV-3would serve as a more useful system than BALB/c mice for monitoring the infectionprocess and pathogenesis of the Chinese BAV-3strain HLJ0955. BPIV3strain SD0835of the genotypeC was pathogenic to guinea pigs and could cause a few observable clinical signs, and gross andhistologic lesions in virus-inoculated guinea pigs. Thus guinea pig is an ideal laboratory animalinfection model for BPIV3and would cast more light on the genotype C of BPIV3infection process, invivo tropism and pathogenesis.