Egg drop syndrome, 1976 (EDS'76)

Studies on the persistence and excretion of egg drop syndrome 1976 virus in chickens

EDS virus strain 127 did not induce clinical signs or gross lesions in susceptible chicks of various age groups and in adult cocks. Virus persistence in various internal organs and the rate of excretion of virus by experimentally-infected chicken declined rapidly with increasing age. Virus 127 was detectable in organs of young chicks up to 5 weeks post-infection and in their faeces up to 2 weeks post-infection. In adult birds virus 127 persisted in tissues for about 3 weeks and was excreted with faeces for only 1 week post-infection. Vaccination of adult cocks with an inactivated vaccine resulted in intermittent shedding of virus only within the first 4 days post-challenge; thus, in comparison to non-vaccinated chickens, vaccination reduced virus excretion in faeces to a major extent.

Close phylogenetic relationship between egg drop syndrome virus, bovine adenovirus serotype 7, and ovine adenovirus strain 287

A cloned egg drop syndrome (EDS) virus genomic DNA fragment containing the protease gene has been identified and the complete nucleotide sequence of the protease and partial nucleotide sequence of the hexon genes has been determined. Phylogenetic analysis of the protease gene has revealed EDS virus to be genetically more closely related to bovine adenovirus type 7 (BAV-7) and ovine adenovirus isolate 287 (OAV287) than either of these two viruses are to other members of the genus Mastadenovirus or EDS virus is to an other member of the Aviadenovirus genus. The three viruses share further similarities in that they have a high percentage AT content in their genome and are characterized by having more compact genomes than other adenoviruses. The protease gene from all three viruses contained the active site residues (H55-D72-C122 triad) and C104 (providing a disulfide bond to cofactor pVIc). However, P137, found in all other members of the Mastadenovirus genus, and thought to be involved in trafficking, was missing from the protease of the EDS virus, BAV-7, and OAV287. These results suggest that EDS virus should be classified along with BAV-7 and OAV287 in a separate taxon.

Gordon Memorial Lecture. Chicken anaemia virus--a glimpse of the future?

This paper uses background information about chicken anaemia virus as a guide to how the study and control of virus diseases of poultry may develop in the future. It is predicted that "new' viruses will be discovered in poultry, many of which will be difficult to grow in vitro and whose pathogenicity may appear uncertain. When new diseases/syndromes arise in the future, it should be a priority activity to define their pathology. The limitations of currently available virus diagnostic methods are highlighted. The possibility of vaccinating against economically important subclinical disease is discussed, as is the use of recently developed technologies in differentiating virus strains and in developing new vaccines.

Occurrence of haemagglutination-inhibition antibodies against egg drop syndrome 1976 virus in broilers

From a total of 22 broiler flocks 347 serum samples were screened by the haemagglutination inhibition (HI) test and 114 (32.9%) were positive for antibodies to egg drop syndrome 1976 (EDS'76). The HI titres of the serum samples ranged from 2 to 9 log2 and the overall geometric mean titre was 3.9 log2. Of the serum samples 82.5% showed HI titres between 2(2) to 2(5) and the most frequent titre was 2(3). All the flocks were positive and the flock prevalence of HI antibodies ranged from 13.3 to 46.6 per cent. The age distribution of HI antibodies and their titres have also been recorded. The widespread prevalence of EDS'76 virus infection in broilers and its likely significance are discussed.

Epidemiological and clinical investigations into big liver and spleen disease of broiler breeder hens

The epidemiological and clinical features of big liver and spleen disease (BLS) in flocks on two broiler breeder farms were investigated by serology and gross pathology. The most common necropsy findings on farm 1 were splenomegaly and hepatomegaly, with kidney enlargement in some birds. In one flock (farm 1), a decline in egg production began at 40 weeks of age and lasted for 9 weeks. Seroconversion to BLS antigen was first detected at 45 weeks (3.1% of birds) and increased to 72% at 50 weeks, which coincided with clinical recovery in the flock. Antigen was detected before antibody at 44 weeks and persisted at low incidence (< 15%). Farm egg production statistics and serology indicated that the disease affected all flocks on the farm. In three of eight flocks, seroconversion was detected in birds before peak production. The birds in the remaining sheds did not seroconvert or become sick until after peak production. On the second farm, sampling began within a flock already experiencing BLS. Clinical signs and pathology were similar to those seen in flocks on farm 1. However, the lesions that were seen in the pancreas in 15% of birds have not been reported previously. BLS antibody was detected in 78%, and circulating antigen in 14%, of sick birds.

Involvement of spleen components of mature fowl in the primary and secondary humoral antibody response following experimental EDS'76 virus infection

Cellular changes in spleens of mature fowl in relation to both the primary and secondary humoral antibody response following experimental EDS'76 virus infection were studied. The influence of splenectomy on humoral antibody response was also examined. Experimental fowl had been naturally infected with fowl adenovirus (FAV) but did not possess precipitins to these viruses at the time of EDS'76 virus infection. Since EDS'76 infection provokes a recall of the group antibody to FAV, this infection simultaneously induces a primary response against EDS'76 virus and a secondary response due to the recall of the group antibody to FAV. HI and precipitating antibody to EDS'76 virus (primary response) were first detected at 6 and 8 days p.i. respectively. Curves of HI, precipitating and neutralising antibody titres were biphasic; the first peak (IgM peak) occurred at 10-11 days p.i., the second (IgG peak) at 16-28 days p.i. Precipitating antibodies to FAV (secondary response) were demonstrated from 4 days p.i. The curve of these antibody titres was also biphasic, with peaks at the same times as in the primary response. Based on HI and AGP testing of primary and secondary immune response in both splenectomised and non-splenectomised fowl it is concluded that in the primary response the spleen of the adult fowl is involved significantly in only IgM secretion, while in the secondary response it is likely that both IgM and IgG are secreted in considerable amounts. Clusters of lymphoblasts and plasmablasts were observed at 3 days p.i. in the red pulp. It is very likely that antigen-antibody complexes are formed from that time and circulate bound to the surface of lymphocytes. These antigen-loaded lymphocytes are 'picked up' from the blood stream by -red pulp macrophages, leading to enhanced formation of lymphoblasts in the red pulp. Great numbers of these cells (which are very probably IgM secreting cells) were present on days 6 and 7 p.i., but were no longer detectable after day 10 p.i. -macrophages of the macrophagal ellipsoidal corona (MEC), leading to significant enlargement of the periellipsoidal lymphoid tissue (PELT) by an increase of the number of lymphocytes observed from days 4-12 p.i. The MEC was significantly enlarged from 7-12 days p.i., very likely due to an increased number of macrophages. Following deposition of antigen in the white pulp, formation of follicles begins. The number of small, intact follicles including follicle precursors increased from 6 days p.i.(ABSTRACT TRUNCATED AT 400 WORDS)

Serological examination and egg production of progeny of fowl experimentally infected with egg drop syndrome 1976 virus

Following EDS'76 virus (BC14 virus) infection of breeder chickens by the conjunctival route, vertical transmission occurred in the first week after infection. In the progeny which had been infected with EDS'76 virus by the vertical route, increasing haemagglutination inhibiting (HI) titres to BC14 virus and increasing numbers of birds with HI titres were observed from 3 weeks to 15 weeks of age. Sixty-one per cent of the hens and 77 per cent of the cocks had 2 log HI BC14 virus titres exceeding 4 at an age of 15 weeks. Some birds which han been serologically negative throughout the rearing period, seroconverted between 25 and 28 weeks of age. This phenomenon occurred in hens as well as in cocks. Simulation of stress twice during the laying period by injection of corticosteroid hormone did not increase the number of birds serologically positive to EDS'76 virus. EDS'76 was observed in the group of hens that was vertically infected, since egg production was significantly depressed between 28 and 34 weeks of age. Probably this was mainly the results of a production drop in the hens showing serconversion at 27 or 28 weeks of age. In this group of fowl vertically infected with EDs'76 virus, serologically positive birds appeared to be protected for the greater part to BC14 virus challenge at 50 weeks of age, while negative birds seemed to be fully susceptible. Chicks hatched from eggs collected in the third and fourth week after infection of the dams had maternal antibodies. Fertility and hatchability of apparently normally shelled eggs seemed not to be affected after BC14 virus infection of the dams. Intensive contact with contaminated faeces is probably an indispensable condition for lateral transmission of the virus.

Incidence of EDS'76 virus infection in fowl in 1980 in the Netherlands in comparison with the incidence in 1976-1978

Serological examinations demonstrated that Egg Drop Syndrome 1976 (EDS'76) virus infection was of no significance in the Dutch poultry industry in 1980, in contrast to the situation in 1976-1978 when this infection was of widespread occurrence. The conclusion was reached that the sharp decrease in the incidence of EDS'76 virus infection was due to large scale vaccination in 1978 and 1979. The results of this study show that there is no further need for general EDS'76 vaccinations. However, continuous serological monitoring is necessary to detect flocks for which vaccination is indicated.