This disease is also called “syndrome of the flap of the egg” and EDS/76. It is known in English as Egg Drop Syndrome.

Egg-drop syndrome 76 is an infectious, contagious disease that is transmitted both vertically and horizontally. It tends to become chronic and is characterized by a sudden drop in egg production, accompanied by noticeable abnormalities in the eggs, and is caused by an adenovirus.

There are a number of well-known factors that cause a decrease in egg production, such as viral and bacterial infections, management and nutritional factors.

In light of current research, it has become clear that, in addition to these already known factors, there were previously unknown factors responsible for the decline in egg production.

Since 1975, many Western European countries have had to contend with serious outbreaks that they considered to be among the most significant problems facing the poultry industry.

It was established that the contagion, although atypical, it was real.

Economic importance:

The primary cause of economic losses is believed to be the decline in egg production resulting from a drop in production during the peak laying period, accompanied by a decrease in egg quality and, in the case of brown eggs, a change in their color.

It is common to find eggs in clusters, with thin shells and depigmented yolks; the white of these eggs may be watery, and the yolk is sometimes cloudy.

This drop in production can reach up to 40%, and it takes 4 to 8 weeks to return to normal production levels; generally, production levels remain permanently below normal.

In addition to these production losses, we must also factor in expenses for medication and labor.

Geographical distribution:

It was in 1975 when the farmers from Europe began to see a production not usual eggs with shells fine white or accompanied by severe falls after sunset.

The syndrome was first recognized in the Netherlands in 1975; later, in 1976, the causative agent was identified as the EDS/76 virus in Northern Ireland. The disease has gradually spread, and its contagious nature is evident.

Once this observation was made, research centers were alerted; they readily ruled out general diseases, such as Newcastle disease and encephalomyelitis, as causes of this syndrome.

For some time, infectious bronchitis was suspected to play a role, but Van Eck et al. (1976) and many others since then have refuted this hypothesis.

The problem needed to be framed in clear terms—symptoms, lesions, transmission—to guide the researchers.

This new entity was named the “Syndrome of the fall of the start-76” by the researchers.

It was agreed to refer to it as a syndrome, since a syndrome is a cluster of symptoms that occur simultaneously in a number of different diseases; and, given that many aspects of this condition remain unknown, it is prudent to speak of a syndrome rather than a disease.

The number 76 to catalog this set nosológico described by several authors without ambiguities on the observed data.

This syndrome has been reported in Great Britain, Belgium, Spain, Central and South America, possibly Mexico, and Japan.

Etiology:

The virus producer of the syndrome of the fall of the setting (EDS) is considered by ms. baxendale (1977) morphologically similar to the adenovirus.

The EDS is caused by adenoviruses of the duck. The infection is spread in chickens by means of vaccines grown in cells of ducks or in embryos infected with the virus, EDS.

This virus exhibits icosahedral symmetry, consisting of 252 capsomeres (composed of proteins) arranged in 20 faces or equilateral triangles and 12 fibers or spicules; the spicules are often destroyed during viral preparation. The virus’s diameter appears rounder, unlike that of adenoviruses.

The drop-off virus contains a deoxyribonucleic acid (DNA) strand in its genome; this was demonstrated using a specific inhibitor of DNA synthesis, iododeoxyuridine. This is a feature it shares with adenoviruses and a distinguishing characteristic compared to infectious bronchitis viruses, for example.

The test into the ether (chloroform) was performed to determine the presence or absence of a sheath.

The ether dissolves this nature primarily lipid and the virion lost the ability to multiply.

For verification, equal volumes of ether and virus are mixed and allowed to come into contact for 7 hours at 40 °C; a sample of this mixture is then applied to a cell culture.

In the essay, does not demonstrate the reduction of the cytopathic effect after the action of the ether, but allows confirming the absence of wrap for the virus; this case is equal to the adenovirus.

Density and sedimentation coefficient (s) are determined by ultracentrifugation in a cesium chloride gradient.

Regarding the effect of ultracentrifugation, the different particles migrate to a zone where they are in density equilibrium; these zones appear as whitish bands. The density of the virus in these bands was 1.34 in cesium chloride, a finding confirmed by electron microscopy.

The sedimentation constant (s) for the virus corresponds to the rate at which the virus moves under the influence of centrifugation in a linear sucrose gradient; this rate depends on the shape and size of the virus. The values obtained for this virus are 950 s.

The egg-drop syndrome virus has shown high stability across a pH range of 3–10. The virus is equally resistant to temperature; these characteristics are also common to adenoviruses.

Antigenic analysis of the virus was performed using agarose gel; this qualitative technique was applied to the antigenic properties of virus 127 using various antisera. The results of this test showed positive reactions with antibodies 127, BC 14, and 3877, and negative reactions with antisera BI and adenovirus (CELO type).

Below is Melnik’s (1982) viral classification, which outlines its main characteristics.

• Family: Adenoviridae
• Genus: Adenovirus
• Virion diameter: 70–90 nm
• Number of capsomeres: 252
• Reaction to the ether: resistant
• Site of maturation of the capsid: core
• Virion: naked
• Capsid symmetry: cubic

Other characteristics of the virus that causes drop-egg syndrome include its agglutinating ability; it is capable of agglutinating red blood cells from chickens and ducks, but not those from rabbits, sheep, or horses.

This power hemagglutinating is an important property because it allows to put in evidence the virus in a cell culture by performing a hemagglutination directly with the supernatant fluid of the culture.

We can summarize some characteristics of the virus producer of this syndrome:

It causes hemagglutination of red blood cells from chickens, ducks, and turkeys.

—According to the AGP test, it does not share any major antigens with other avian adenoviruses.

There is no neutralization against other avian adenoviruses in hemagglutination, inhibition, and plaque reduction assays.

Immunofluorescence reveals a certain antigenic relationship with other adenoviruses.

The virus replicates well in chicken embryos, although SPF chicken embryo liver cells (chicken embryo hepatocytes) or duck cells are preferred for culture.

—When culturing in chicken embryo fibroblasts, the cells must be harvested at 9 and 14 days of age.

For the cultivation of kidney cells, the cells must be harvested from the kidneys of 1- to 3-week-old SPF chickens.

—It appears that duck cells are more susceptible than fibroblasts. The virus hardly replicates in kidney cells. The BC-14 virus was isolated by Baxendale from white blood cells, and McFerran was able to isolate virus 127 from the nasal and pharyngeal mucosa of a hen.

Virus 3877 has been isolated from the liver of a laying chicken.

Susceptible species:

Birds can become infected at any stage of their lives. Hens between 26 and 35 weeks of age are most susceptible, with egg production losses of up to 30%; birds recover after 3–4 weeks, but egg production will remain below normal in most flocks.

Exceptionally, birds between 50-55 weeks may show clinical signs.

It is believed that the birds most susceptible to this syndrome are those that lay brown eggs, while those that lay white eggs are less susceptible.