Longitudinal studies on the egg drop syndrome 1976 (eds‐76) in the fowl following experimental infection at 1‐day‐old

Avian Viruses that Impact Table Egg Production

Eggs are a common source of protein and other nutrient components for people worldwide. Commercial egg-laying birds encounter several challenges during the long production cycle. An efficient egg production process requires a healthy bird with a competent reproductive system. Several viral pathogens that can impact the bird's health or induce reversible or irreversible lesions in the female reproductive organs adversely interfere with the egg industry. The negative effects exerted by viral diseases create a temporary or permanent decrease in egg production, in addition to the production of low-quality eggs. Several factors including, but not limited to, the age of the bird, and the infecting viral strain and part of reproductive system involved contribute to the form of reproductive disease encountered. Advanced methodologies have successfully elucidated some of the virus-host interactions relevant to the hen's reproductive performance, however, this branch needs further research. This review discusses the major avian viral infections that have been reported to adversely affect egg productivity and quality and aims to summarize the current understanding of the mechanisms that underlie the observed negative effects.

Epidemiology of egg drop syndrome virus in ducks from South Korea

Egg drop syndrome virus (EDSV) is an important pathogen of poultry that decreases egg production in chickens and causes respiratory disease in goslings. In 2011, we obtained serum samples from 139 domestic Pekin ducks, 416 one-day-old Pekin ducklings, and 75 wild ducks (67 mallards and 8 pintails) to survey their exposure to EDSV. A total of 123 of 139 sera (88.5%) from Pekin ducks, 396 of the ducklings (95.2%), and 16 of 67 mallards (23.9%) were positive. Field cases of EDSV in wild and domestic ducks were investigated. Six cases from domestic Pekin ducks were identified by PCR detection and were used for virus isolation and molecular analysis. Phylogenetic analyses of the partial hexon and full fiber genes showed that the D11-JW-012 and D11-JW-017 strains among 6 isolates belonged to different clusters compared with other known strains including the 127 strain. We assessed cell growth efficiency by hemagglutination (HA) titers and cytopathic effects in duck embryo liver cells and chicken embryo liver (CEL) cells to investigate host adaptation. The D11-JW-017 strain propagated more in chicken embryo liver than the D11-JW-012 strain and the field isolate from chickens. Our results demonstrate the high prevalence of EDSV in wild and domestic ducks in South Korea and provide information on EDSV from ducks that showed variable adaptability in chickens.

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.

No evidence for adaptation of current egg drop syndrome 1976 viruses to chickens

In order to determine whether the current field strains of egg drop syndrome (EDS) 1976 viruses adapt to chickens, we compared the growth efficiency of three Japanese field strains (PA-1/79, AWI/98, Gifu/01) in chicken and duck embryo liver cells. The growth efficiency in chicken or duck embryo liver cells was almost similar in these strains. The fiber protein may carry the type-specific antigen and the hemagglutination activity, and hexon protein may contain the subgroup-specific antigenic determinants. Therefore, the fiber head and hexon loop 1 DNA domain sequences of the six Japanese field strains UPA-1/79, ME/80, 44/81, Kyoto/91, AWI/98, Gifu/01) were compared, but these DNA domains were identical among the six field strains. Our data suggested that the EDS virus was maintained without discernible changes for the last two decades in the field.

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.

Egg drop syndrome 1976 (EDS-76) virus infection in inadequately vaccinated chickens

Experiments were carried out to study the epizootiology of the egg drop syndrome 1976 virus infection in chickens that were not adequately protected by vaccination. Virus excretion was demonstrated when chickens vaccinated at the recommended level were challenged within 10 days of vaccination and when chickens were challenged 6 weeks after administration of low doses of vaccine. In the latter experiment, those chickens which shed virus had all shown a poor haemagglutination inhibition antibody response to vaccination but had high serum neutralisation antibody titres when challenged.

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.