الفهرس 
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Abstract
The purpose of this study was to investigate the effect of E. tenella on the (vv) IBDV infection as well as on the course of vaccination in balady chicken. Different immune parameters were examined more closely along with other consideration as clinical signs, postmortem lesion, histopathological changes, serological and hematological analysis, mortality rate, parasitological parameters (lesion score, dropping score, oocysts count) and growth parameters.
A local E. tenella isolate which was obtained from a field outbreak of caecal coccidiosis on broiler flock from Matrouh, propagated and sporulated along with histopathological examination to ensure purified isolate (single oocysts) then it was preliminary experimented for pathogenicity in twenty-one day old thirty SPF birds, in three groups (n=10) inoculated with three doses of sporulated oocysts (25x103 , 40x103 and 60x103 oocysts per bird intra-crop route ) and birds were observed for seven days for mortality rate and bloody dropping score , on the basis of that, the infective dose of two experiments was chosen.
IBDV isolate was isolated from bursa of a naturally infected flock from Behera were prepared for bursal homogenate 10% and inoculated in 10th day ECEs for 5 days with daily candling and embryo mortality percent was recorded then the suspension tested by (RT-PCR) which was positive for presence of IBDV genetic material then sorted as very virulent IBDV during sequencing analysis revealed that (MN832712 IBD Alex 2019) very close to very virulent GIZA 2008 strain. Virus had titer was pronounced as the 50% embryo infective dose (EID50) per ml. Challenge birds with vvIBDV was performed at age of 25th days with a challenge dose of 106.5 EID50/ml (200µl /bird: 100 µl by the nasal route and 100 µl applied via eye drop, while negative-control group were given PBS.
Balady chickens were inoculated with E. tenella in two different doses of sp. oocysts either high dose (50x103 oocysts) or low dose (15x103 oocysts) to represent clinical and subclinical coccidiosis, respectively.
For experiment 1 at which E. tenella sp. oocysts by two different doses were inoculated to four groups at 11th day of age (two groups further vaccinated with D78 at 15th day of age and two groups remained without D78 vaccination), while another group of chicken were vaccinated only with a single dose of intermediate live attenuated vaccine of IBDV (D78) at 15th day of age and group of chicken remained uninfected as control negative group and another group of birds challenged with vvIBDV at 25th day of age as a control positive group, furthermore, all groups except for control negative group were challenged with vvIBDV at 25th day of age with a challenge dose of 106.5 EID50/ml.
E. tenella inoculation caused mortality percent ranged from 5% to 10% (in groups 3 and 6) with caecal lesions and bloody droppings in surviving birds ,in addition to significant decrease in the distribution and replication of IBD vaccine strain (D78) than birds vaccinated only without receiving E. tenella before vaccination, in which bursal samples tested for Real-time PCR examination at 3rd and 7th day post- D78 vaccination. As well as, the significant reduction in ELISA antibody titers for IBD post vaccination while increased after vvIBDV challenge in groups receiving E. tenella and consequently lowering in protection percentage against challenge with vvIBDV.
Thus, Eimeria may be the one of the reasons of the reduction in humeral immunological reaction of balady chicken after vaccination with commercial vaccines.
For experiment two at which E. tenella inoculated to four groups of chickens in two different doses (15x103 and 50x103 sp. oocysts) at 21st day of age in which two groups further challenged with vvIBDV at 25th days of age and two groups remained without IBDV challenge, while group of chickens remained uninfected as a control negative group and another group of birds challenged only with vvIBDV at 25th day of age as a control positive group.
vvIBDV-challenged birds showed mortality percent 10% in group (B) at 2nd day post vvIBDV challenge with lower bursal index at 7th day post and lower positive viral titer from fecal swab examination by Real-time PCR compared to groups previously inoculated with E. tenella. On the other hand, mortality percent in group (E) at 6th day post E. tenella inoculation was 5% along with surviving birds showed more oocysts output in E. tenella inoculated groups with vvIBDV than alternative without vvIBDV.
This study clearly confirmed an immunosuppressive effect of E. tenella on birds further infected with vvIBDV or vaccinated with commercial IBD vaccine as it led to increase in viral replication which consequently lead to more execration and shedding of IBDV in environment. On the other hand, the modulatory effect of vvIBDV on the reproductive potential and severity of E. tenella was illustrated through parasitological parameters (lesion score, dropping score, oocysts count), thus we speculated that two pathogens affect each other.
Although in Eimeria inoculated groups only, the dose differences of sporulated oocysts pointed to the paying attention to subclinical coccidiosis infection which is the dormant risk endanger poultry industry in which birds shed more oocysts lead to spread infection in intensive farming furthermore development of culls due to failure to achieve normal weight and interfere with routine vaccination schedule and further may provoked to develop clinical picture of pathogens so that it is reasonable for early protection of the flock against coccidiosis.