| Human paramyxovirus influenza virus-1(HPIV-1), an enveloped-ssRNA virus, was one of the important pathogen that frequently causes infant respiratory disease and6% hospitalization rates every year. The main clinical symptoms include rhinitis, pharyngitis, otitis media, laryngitis, bronchitis, pneumonia, etc. At present, there were no efficacious drugs and vaccines available for treatment, as well as appropriate small animal model for research. Sendai virus (SeV) which mainly infected rodents has highly similar genome sequence with HPIV-1. They have protective cross immunity. They also have the similar transmission route and tissue tropism. Therefore, SeV was considered to be the optimal animal model for HPIV-1research and the ideal candidate vaccine for HPIV-1.Paramyxovirus Tianjin strain is the virus with high haemagglutination titer. which was isolated from the lung tissues of the dead common cotton ear marmoset with the severe lower respiratory infection. It was identified a new genotype of SeV with440nucleotides and110amino acid residues alteration according to genome sequencing (GenBank accession number EF679198) and phylogenetic analysis. SeV naturally infect rodents, however, Paramyxovirus Tianjin strain presented highly pathogenic to common cotton ear marmosets. During the outbreak, no mouse was infected in the experiment animal center. The strains of mice mainly included Kunming and BALB/c strain. In order to make clear the pathogenicity of Paramyxovirus Tianjin strain to the other strains of mice beside BALB/c strain and look for the most suitable rodent animal as research model which was more susceptible to Paramyxovirus Tianjin strain, we try four mice strains which were chosen to be infected by Paramyxovirus Tianiin strain.Firstly, in the prophase work, the Paramyxovirus Tianjin strain was propagated for72h in9-11day-old chicken embryos. The virus titer of1:1280in the harvested allantoic fluid was detected by hemagglutination assay; it was aslo detected to be3×109PFU/ml by plaque assay. Four strains of mice,129Sv, DBA/2, Kunming and BALB/c were intranasally inoculated with1.5×10’PFU in5μl and30μl virus solution. The weight loss of mice was monitored in the consecutive12days and the survival rate was observed. The maximum percentage of average weight loss of129Sv, DBA/2, Kunming and BALB/c were-13.0%,-4.7%,6.6%and6.3%with100%survival rate of each mouse strains when129Sv, DBA/2, Kunming and BALB/c were inoculated with5μl virus solution, while the maximum percentage of average weight loss reached-21.7%,-30.3%,-16.7%and-9.7%with the survival rate20%,0%,80%and100%when the mice were inoculated with30μl virus solution. The weight loss and survival rate suggest the order of susceptiblility is DBA/2>129Sv>Kunming> BALB/c.Next, in order to detect the susceptibility to Paramyxovirus Tianjin strain, the nasopharynx, tracheal and lung tissues from the four strains of mice were isolated to detect the viral replication. Paramyxovirus Tianjin strain is the virus that which naturally infect the respiratory tract in the rodent animals. In the experiment, the129Sv, DBA/2, Kunming, BALB/c were intranasally inoculated with30μl virus solution with3×105PFU, they were killed in the first, thirth, fifth, seventh, ninth, eleventh day postinfection, that is to say, six mice were sacrificed in each mouse strain every day. The tracheal. nasal, right lung tissues were isolated from the sacrificed mice. The tissues were homogenated into the suspension in lml precooling PBS and then were frozen in-80℃refrigerator. These specimens were detected virus titer with the plaque Assay. The left lungs were fixed in4%formalin for the histopathologic examination. These left lungs tissues were used to make slice to for the observation of the different pathological changes in lungs.To sum up,(1) the four strains of mice present the distinguishing susceptibility to Paramyxovirus Tianjin strain. Though virus replication level was different in four strains of mice, the virus titer curve trends similar as the increase at first followed the decline.(2) Both the peak time of viral titer and the viral replication level were different. The peak time of virus titer in lung, nasal, trachea in DBA/2appeared in the fifth day postinfection which was similar with129Sv mice in lung and nasal tissues. The peak time of virus titer was delayed to the seventh day in the trachea of129Sv mice. Paramyxovirus Tianjin strain showed the different replication level in the three tissues of Kunming mice. The seventh day was the peak time in lungs, the third day in the nasal tissues, and the fifth day in trachea. The virus titer peak time in BALB/c lung and nasal was the fifth day, trachea was in the third day. These results indicate the susceptiblility in four strains of mice ranks DBA/2>129Sv>Kunming>BALB/c.(3) DBA/2was the earliest virus that show+++pathology change in four strains of mice. The histopathology result showed that lungs of DBA/2mice were the most serious damaged, lymphocytes were observed to accumulate in lung stroma; meanwhile there were a large number of neutrophils, and macrophages. A large amount of exudate were deposited in the alveolar, the hyperplasia appeared in the submucosa and the, injury was severe in the airway epithelial cells. The necrotic cells were visible. There is no integral alveolar structure in the whole vision. Lung injury in129Sv ranked the second. Although pathology changes also appeared+++change, the peak time was delayed, which appeared in the ninth day. The pathology process of lung injury in129Sv mice was slower than DBA/2. The lung injury in Kunming and BALB/c mice were relatively not severe. Although the most serious pathological classification in two strains of mice were++, Kunming mice appeared earlier and longer than BALB/c mice. BALB/c mice showed most mild the lung pathological changes in four strains of mice, not only lung injury delayed, but also last shorter. We got the conclusion that the order of susceptiblility might be DBA/2>129Sv>Kunming>BALB/c.According to the weight loss, survival rate, and viral replication in tissues, as well as the pathological changes, four strains of mice showed the different susceptibility to the infection of Paramyxovirus Tianjin strain. We got the conclusion that DBA/2>129Sv>Kunming>BALB/c from susceptibility to resistance.The DBA/2and129Sv were considered to be the optimal small animal model as researching for vaccine and pathogenicity. |
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