Biology And Genome Characteristics Of A Highly Pathogenic Chicken Infectious Anemia Virus

Chicken anemia virus (CAV) is widely distributed in the world and is one the most important pathogens in chiken industry. CAV causes transient severe aplastic anemia due to destruction of erythroblastoid cells and generalized lymphoid atrophy with a concomitant immunosuppression.CAV causes considerable economic losses in poultry industry as a result of a co-infection and a secondary affection after its infection. So it is important to reaserch CAV systematically.In this study,we systematically Research CAV in aspects of Detection methods,epidemiology and genetic variation and pathogenicity of a pandemic strain.According to the genomic sequences of VP1 gene of Chicken anemia virus (CAV) published in Genbank,one pairs of primers were designed for amplifying the fragment in PCR experiments. The PCR product was labeled with digoxigenin by PCR as DNA probe for detection of CAV. The dot blot hybridization assay result of specificity showed CAV was positive, but other nucleotide extracted from REV,MDV,REOV were negative. The sensitivity result showed that as few as 1 pg DNA amount of CAV could be detected by DIG-labeled probe.So the DIG-labeled probe could be used to detect the CAV.The spleen samples of 384 chickens with clinical performance from 3 strains chicken flocks of different ages were collected in eight cities of Shan dong province, including 105 portion partridge chickens,185 portion broilers,94 portion egg chickens. By dot blot hybridization assay , the detection result of CAV in 384 portion spleen samples showed that total detection rate was 27.9%(107/384). Test results of 3 strains chickens showed that detection rate of partridge chickens was 37.1%(39/105); detection rate of broilers was 31.3%(58/185);detection rate of egg chickens was 11.7%(11/94). Tthe experiments indicated that detection rate of broilers and partridge chickens was significantly higher than egg chikens.Test results of 3 ages chickens showed that detection rate of 1-20 old-day ages was 6.4%(7/110); detection rate of 20-60 old-day ages was 45.6%(93/204);detection rate of after 60 old-day ages was 10.0%(7/70). The experiments indicated that detection rate of 20-60 old-day ages was significantly higher than 1-20 old-day ages and after 60 old-day ages, 20-60 old-day ages was the peak disease prases.Extract DNA from spleen,thymus and bone marrow of disease chicken suspected infection with CAV from a 20 day-old broiler flock with growth runting syndromes, dot blot hybridization showed CAV positive, A field strain SDLY08 of chicken infectious anemia virus (CAV) was isolated by 1 day-old Specific-pathogen-free(SPF) chicken and 7 day-old Specific-pathogen-free (SPF) chicken embryo inoculation. The viral genomic DNA was amplified by PCR in 3 overlapped fragments and PCR products were cloned into T-vecor plasmid for sequencing. The sequencing results indicated that the total genome of SDLY08 strain CAV was 2298nt, it contained 3 overlapped ORF and 1 non-coding regulation fragment. Its whole genome had 96.6%-99.0% of homogeneity to other 8 published CAV reference strains. There were some mutations in 3 amino acid sequence which were encoded by 3 genes VP1, VP2 and VP3. VP1 was less conservative than VP2 and VP3. the homogeneity was 96.6%-99.0%.In this study, Specific-pathogen-free(SPF) chickens were inoculated of a chicken infectious anemia virus field isolate CAV-SDLY08 with 104.5 mean embryo infective dose(EID50) at 1,7,21 day of age to elucidate the pathogenicity of CAV- SDLY08.SPF chickens at different ages of 1,7,21 day were challenged with the virus by oral administration and intramuscular injection. Ratios of thymuses, spleens and the Bursa to body weight, several blood parameters were examined and compared to controls 12 days after infectons with CAV.The reaserch of weight show that the weight of 1-day-old and 7-day-old chickens was significantly lower than control group (P<0.05) 12 days after infectons with CAV,the differences in two infective methods were not significant statistically(P>0.05). The infective group of 21-day-old chickens was also lower than control group,but differences were not significant statistically(P>0.05) ,the differences in two infective methods were not significant statistically.The reaserch of immune organ show that there was splenomegaly in different ages, the differences were significant statistically in the oral administration group and the injection group of 1-day-old chickens compared to control group(P<0.05). The differences were not significant statistically in 7-day-old chickens group and 21-day-old chickens group compared to to control group(P>0.05).There was no differences in two infective methods.The infection of 3 ages could all cause severe atrophy of thymus, the differences were very significant statistically in different infective ages and different infective methods compared to control group(P<0.01).The reaserch of blood index show that, white blood cells decrease after infection of 12 day, the differences were very significant statistically in the oral administration group and the injection group of 1-day-old chickens compared to control group(P<0.01). With infection of 7-day-old chickens group and 21-day-old chickens group, the injection group was significantly lower than oral administration group and control group (P<0.05),there was no significant differences in oral administration group and control group (P>0.05).Infection of CAV strain SDLY08 at all 3 ages could cause significantly decrease of red blood cells, the differences were very significant statistically in the oral administration group and the injection group compared to control group(P<0.01) and the differences of two methods infection were significant statistically(P<0.05). The haematocrit decrease significantly compared to control group(P<0.01), the differences were very significant statistically in the oral administration group and the injection group of 1-day-old chickens and 7-day-old chickens compared to control group(P<0.01), significant in 21-day-old chickens (P<0.05).Results indicated that challenges of CAV strain SDLY08 at all 3 ages could cause growth retardation, severe atrophy of thymus and spleen megaly, significant decrease of red blood cells,white blood cells and the haematocrit. It was also demonstrated that 1-day-old and 7-day-old SPF chickens were more sentitive to SDLY08 than 21-day-old chickens, chickens were more sensitive to challenges by intramuscular injection than oral administration. Results also showed that this CAV strain can also cause significant pathogenicity in 21-day-old chickens...