Lateral transmission of egg drop syndrome‐76 virus by the egg

Development of a new real-time polymerase chain reaction assay to detect Duck adenovirus A DNA and application to samples from Swiss poultry flocks

Between 2008 and 2012, commercial Swiss layer and layer breeder flocks experiencing problems in laying performance were sampled and tested for infection with Duck adenovirus A (DAdV-A; previously known as Egg drop syndrome 1976 virus). Organ samples from birds sent for necropsy as well as blood samples from living animals originating from the same flocks were analyzed. To detect virus-specific DNA, a newly developed quantitative real-time polymerase chain reaction method was applied, and the presence of antibodies against DAdV-A was tested using a commercially available enzyme-linked immunosorbent assay. In 5 out of 7 investigated flocks, viral DNA was detected in tissues. In addition, antibodies against DAdV-A were detected in all of the flocks.

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.

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.

Egg Drop syndrome '76 in Bolivia

Four outbreaks of Egg Drop Syndrome '76 (EDS '76) were diagnosed between April 1993 and July 1993 in the Santa Cruz Department of Bolivia, around the department capital Santa Cruz. Three outbreaks involved commercial laying birds and the fourth a broiler breeder unit. Clinical signs were typical of EDS '76 with decreases in egg production of up to 55% being recorded as well as the production of thin shelled and shell-less eggs. A total of 183 serum samples from the 4 farms were tested for the presence of antibodies to the EDS '76 virus using a haemagglutination inhibition test, with titres of 16 or above being considered as a positive result. Of 63 samples from groups of birds showing signs of EDS '76, 58 (92.1%) had positive titres, and 88 out of 90 samples (97.8%) from unaffected groups of birds had negative titres. Out of 30 samples from birds not yet in lay from the affected farms 28 (93.3%) had tires below 16. EDS '76 had not been reported in Bolivia prior to these outbreaks and vaccination was not practised. The most probable source of virus was from day old chicks imported from South American countries which had recorded outbreaks of EDS '76 before April 1993. The source of the virus, its spread and the control measures implemented in the Santa Cruz area are discussed.

EDS 76 HI antibodies in a flock of free-range layers

An investigation of poor laying performance in a flock of free-range hens revealed high levels of serum antibodies to EDS 76 in the flock initially examined and in another, older flock on the same farm. These flocks had contact with ducks on a farm dam and were supplied with untreated drinking water from the dam. Serological evidence indicated that another flock supplying the same egg packing station had been infected with EDS 76 virus. Little serological evidence of EDS infection was detected from five other flocks supplying the packing station, parent breeders or the ducks resident on the dam. Therefore, the source of the EDS 76 virus remains conjectural.