Studies on the Ascaridia galli embryonal stages, potential maternal protection and immune response in chicken
von Shayan Rahimian
Datum der mündl. Prüfung:2016-11-04
Betreuer:Prof. Dr. Dr. Matthias Gauly
Gutachter:Prof. Dr. Christoph Knorr
Gutachter:Prof. Dr. Jürgen Hummel
EnglischRegarding to a lack of experimental infection models and different maturation ability of Ascaridia galli egg sources (Worm uteri and faeces) in a first study (Paper 1), A.galli eggs isolated from two different sources were investigated for different embryonic development capacities. The second study (Paper 2) showed no protective maternal immunity against A. galli in chicken. The objective was to investigate whether maternal antibody positive chicks are more resistant to A. galli infection than maternal antibody negative chicks. Free-range chickens are exposed to a high risk of nematode infections. Genetic selection for increased immunity could be an important tool to reduce problems due to infectious diseases - estimating the number of parasite eggs for an infectivity diagnosis can be unreliable in a free-range system. Thus the objectives of a third study (Paper 3) were to estimate genetic resistance to naturally acquired immune systems and infectivity diagnosis by estimating the total specific antibody responses against most prevalent nematodes in the free-range laying hen system. The first experiment (Paper 1) was performed to investigate the embryonation ability of A. galli eggs, isolated from two different sources originating from 12 worm infrapopulations both from faeces of the living host (faecal eggs) and directly from worm uteri after host necropsy (uterine eggs). The isolated eggs from each infrapopulation and source were incubated in Petri dishes (n=24) containing a potassium-dichromate (0.1%) medium for 28 days at room temperature. In ovo larval development was evaluated every second day by examining morphological characteristics of 200 eggs/ Petri dish starting from the day of egg isolation (d0). A total of 72,000 eggs were classified into undeveloped, early development, vermiform 2 or fully embryonated stages. Isolation procedures caused similar damage to uterine and faecal eggs (2.2% and 0.5%, respectively; P=0.180). The first sign of in ovo embryonic development in faecal eggs (7%) was observed during the 24-hour period when faeces were collected. On d28, a higher percentage of uterine eggs remained undeveloped when compared with faecal eggs (58.6% vs 11.0%; P< 0.001). Although a higher (P<0.001) percentage of faecal eggs entered both the early developmental and vermiform stages, which took place primarily within the first two weeks of incubation, there was no time-shift between the development of faecal and uterine eggs. Starting from d10, higher (P<0.05) percentages of faecal eggs completed embryonation compared with uterine equivalents. The second experiment (Paper 2) was demonstrating whether chicks descending from nematode-infected hens are more resistant against Ascaridia galli, a prevalent gastrointestinal nematode, infection than infected offspring from nematode-free mothers. One-day-old chick offspring (N=153) from infected (mab+; maternal antibody+) or uninfected control dams (mab-) were experimentally infected with A. galli at two different concentrations (100 or 1000 eggs/chick). Female chickens exhibited significantly (P<0.05) higher specific antibody concentrations (2.355 ± 0.211). The worm burdens of the chicks were determined at 6 weeks after infection. There was a high correlation (r=0.89, P<0.001) between A. galli-specific antibody concentrations in dam plasma and egg yolk. Dam and chick infection doses interaction had a significant effect (P<0.05) on worm burden and the highest infection rate (21.2 ± 2.95) occurring in mab+ chicks challenged with +1000 A. galli eggs. In chicks, lower doses of infection caused a difference in worm burden between the mab +/ - groups. Chick infection dose had a significant effect on female/ male 3 harvested worms. There was also an interaction effect between maternal infection and chick infection with respect to worm weight. The final study (Paper 3) was conducted on two genotypes of Brown hens (LB classic and LB plus) under practical free-range farm condition. Aims of this study were to describe genetic resistance to immune systems and infectivity diagnosis by estimating total specific antibody concentration (TsAb) against the most prevalent nematodes in free-range chicken systems. Chickens (17 weeks old) of two Lohmann brown genotypes (LB plus/ LB Classic) were examined for a laying period of one and a half years. Individually obtained plasma of the genotypes, LB plus (n= 200) and LB classic (n=200) were used for detecting TsAb via the ELISA test before necropsy. Some birds were subjected to post-mortem parasitological examinations at 79 weeks (LB plus, n= 162) or 88 weeks (LB classic, n=139) of age. There was a significant (P<0.05) difference in total worm burden (TWb) and TsAb in relation to the genetic background of the chickens in their response to naturally acquired nematode infections. Positive phenotypic correlations (r=0.1, P=0.014) of TsAb with the total epg (Tepg) before necropsy and no significant correlation (r=-0.13, P=0.1) with TWb at necropsy were moderated. Slightly fluctuating increases of TsAb by age (weeks) were observed. It is concluded that isolated A.galli eggs from both sources reached a plateau of embryonation by the end of the second week of incubation, with faecal eggs having more than a two-fold higher embryonation ability. Cumulative mortality was higher in uterine eggs (14.3%) when compared to faecal eggs (0.2%). Although lower worm burden in mab- chicks with resistant tendency against A.galli pathogen in maternal antibody positive (mab+) offspring was demonstrated, no protective immunity against A. galli infection was observed. In this free-range chicken system, the LB classic 4 genotype was more susceptible to gastrointestinal nematodes than the LB plus genotype with higher total antibody responses before necropsy and lower total antibody responses at necropsy. Estimating total specific antibody responses is meaningful for infectivity diagnosis in a free-range chicken system.
Keywords: Ascaridia galli; Chicken; Egg development; Egg yolk; Free-range; Genetic; IgY; Incubation; Infection model; Nematode; Protective immunity