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Egg Drop Syndrome: Causes, Signs and Treatment

Egg Drop Syndrome

Have you noticed a drop in your egg production of about 10 to 40% before or after your hens’ laying period?

Have you seen any thin-shelled or pale, soft-shelled eggs in your trays?

If your poultry birds produce bad-quality eggshells despite looking healthy, chances are you’re experiencing an episode of egg drop syndrome.

But what is egg drop syndrome in chickens, and how does it affect your flock?

In this article, we’ll share with you the:

  • Causes and origin of EDS
  • Signs and symptoms you should look out for, and
  • Prevention tips to prevent the transmission of this disease

So if you want to gain more insights into EDS and ensure you can protect your birds to prevent profit loss, this is for you.

We’ll discuss everything you need to know about this disease and what appropriate actions you should take to keep your flock healthy and happy.

What is Egg Drop Syndrome in Chickens?

Egg drop syndrome in poultry, also known as EDS ’76, is a viral infection that affects laying hens.

It affects the bird’s egg production with an estimated drop of 10 to 40%, and the first infestation in laying hens was recorded in 1976, hence the name egg drop syndrome ’76.

It’s also known as EDS ’76, and it’s often addressed with its full name to distinguish it from ducks’ flaviviral disease, aka “egg drop syndrome in ducks” and “duck egg drop syndrome,” and to avoid confusion.

It’s not easy to detect the early signs of this condition because hens usually eat their shell-less eggs, leaving only the membranes that don’t easily get noticed.

If your hens are suffering from egg drop syndrome, you may not be able to reach the expected production targets.

The ED ’76 cases have been recorded in the US and other countries like Ireland, England, and Brazil.

It affects chickens of all ages and breeds, but it’s more severe in broilers and brown egg-layer breeds.

What Causes Egg Drop Syndrome In Chickens?

The main culprit of egg drop syndrome is the egg drop syndrome virus or duck adenovirus 1.

It’s a double-stranded DNA virus that is resistant to pH ranging from 3 to 10 and heating for about 3 hours at 56°C (or 132.8°F).

Therefore, ducks and geese are the usual hosts of this virus, but they’re usually asymptomatic carriers.

The egg drop syndrome virus multiplies rapidly in the chick-embryo liver cells, but it replicates less well in the chick kidney cells and even more poorly in the chick-embryo fibroblast.

Furthermore, it doesn’t grow in embryonated chicken eggs or mammalian cells.

The Origin of the Egg Drop Syndrome

The egg drop syndrome ’76 virus usually affects wild and domestic ducks and geese.

But there are also cases where it was found in coots, grebes, owls, herring gulls, storks, swans, and quail.

The first recorded case of EDS, which was in 1976, started with a contaminated vaccine of duck-embryo fibroblasts which were also used in the chickens.

And that’s how EDS started in chickens.

Since then, the virus has spread worldwide, caused problems with eggshell quality, and resulted in a loss of saleable and hatchable eggs in affected flocks.

The virus has reached North America, but since 2019, there has been no EDS infection report in laying flocks.

Egg drop syndrome 76

How EDS ’76 Spreads

The virus spreads vertically through their eggs, but birds’ droppings can also contain the virus, which can be horizontally transmitted through an oral route.

We’ll dig deeper into it later in this article.

The EDS Patterns Recognized in Chickens

There are three common EDS patterns recognized in chickens. We’ll uncover each one of them below.

1. Classic EDS ’76

It occurs when the breeding chickens get infected, and the virus spreads vertically through the eggs.

But the virus stays dormant until the infected chick reaches sexual maturity, and at that time, the virus will spread through the eggs and droppings.

Any chicken that comes in contact with their eggs and droppings will contract the virus.

2. Endemic EDS ’76

This refers to the horizontal transmission of the egg drop syndrome virus via contaminated eggs from shared equipment like trays, crates, and trucks.

The personnel who work on the shared egg-packing stations can also be a means of the virus transmission.

3. Sporadic EDS ’76

This route is uncommon. But it occurs when chickens have direct contact with the infected ducks or geese or when they share a water supply that is contaminated by wildfowl droppings.

This eventually leads to an endemic disease.

What Happens After

The virus multiplies to the nasal mucosa’s low titers after the EDSV horizontal transmission.

Then, the viremia, virus replication of the chicken’s lymphoid tissue and pouch shell gland, occurs in a span of 5 days.

It helps with diagnosis that this extensive viral replication takes place in the pouch shell gland following seroconversion.

The virus multiplies in the shell gland’s surface epithelium, causing karyomegaly and basophilic intranuclear inclusion formation.

Squamous and cuboidal cells initially take their place, but gradually the normal pseudostratified ciliated epithelium gets restored.

During the stages of viral replication, the mucosa experiences moderate to severe heterophilic inflammatory infiltration, and small amounts of heterophilic exudate mixed with shed epithelial cells may develop.

It’s worth noting that EDS ’76 survivors may still have sporadic residual oviductal lymphoid masses.

The viral replication in the shell gland and changes to the eggshell occur simultaneously.

Eggs laid between 8 and 18 days after infection have the virus in both the shell and the inside.

The oviduct’s exudate and secretions are full of virus, which passes into the droppings, and may become slightly to moderately watery for two to three days.

EDSV has not been reported to reproduce in the intestinal epithelial cells, in contrast to several aviadenoviruses.

EDS ’76 Diagnosis or Clinical Manifestations

Hens with egg drop syndrome usually appear healthy.

But the problem lies in their eggs; it could be either thin-shelled, soft-shelled, or sometimes it’s completely shell-less.

However, the internal quality of the egg, such as the white and yolk, is usually unaffected.

Another good indicator of EDS is the failure to achieve the predicted production targets.

But you’re lucky if some of your birds have antibodies because it can slow down the spread of the virus in your flock.

The bird may also show mild signs of depression, diarrhea, or both.

If your healthy poultry birds’ eggs have poor-quality eggshells that are at peak production, that’s a sign of EDS ’76.

However, transmission is slow in chickens in caged units. But the signs can easily be overlooked in a small flock.

Sometimes, some chicken keepers may think it’s just a small decrease in their egg yield, which leads to misdiagnosis.

What separates EDS ’76 from Newcastle disease and avian influenza is the absence of illness.

Unlike infectious bronchitis, chickens with ED ’76 will not experience respiratory illnesses.

Furthermore, the absence of poor internal egg quality and ridged or malformed eggs could also indicate egg drop syndrome.

Confirming Diagnosis

To make a definitive diagnosis, vets usually run confirmatory laboratory testings and search for evidence of seroconversion in unvaccinated flocks.

They may need to test hens that have produced affected eggs and see if they’ve developed antibodies.

Vets may also use other tests like serum neutralization and double immunodiffusion test for confirmation.

On top of that, they may also utilize PCR assays and ELISA testing to detect EDSV DNA and the presence of antigens, respectively.

Another way to diagnose EDSV is through isolation.

It’s done through the inoculation of the embryonated duck or goose eggs or the chick-embryo liver cell cultures.

But it’s not easy to identify the virus, especially in non-caged birds.

In fact, feeding affected eggs to the antibody-free hens is a much easier technique.

But it’s also possible to isolate the EDS virus from the chickens’ pouch shell gland.

As for the antigen, it’s hard to detect it using conventional techniques.

Since EDVV strongly agglutinates avian erythrocytes, a hemagglutination-inhibition test is necessary to detect antibodies.

Laying hen

Egg Drop Syndrome Treatment

So, how do you treat egg drop syndrome?

Honestly, there’s no treatment for egg drop syndrome ’76, but good animal husbandry can help prevent the spread of this disease.

But there are some ways you can do to control the endemic form of egg drop syndrome.

How to Prevent Egg Drop Syndrome

You can control and prevent the spread of EDS by having a strict biosecurity plan and restricting visitors’ entry.

You can also control endemic EDS ’76 by using dedicated equipment and trays for each farm and washing and disinfecting your trays regularly.

Another effective way to prevent the spread of sporadic forms of ED ’76 is by separating chickens from waterfowl and other birds that may carry this disease.

Like any other contagious disease, applying strict quarantine rules is necessary to keep your flock safe and protected.

It’d also help if you could chlorinate the contaminated water to avoid transmission through shared water sources.

You may also find inactivated vaccines with oil adjuvant in vet clinics, and if you do, you should avail it to ensure that your flock is fully protected.

Even though they don’t prevent the EDS virus shedding, they can help minimize it.

But when should you administer this vaccine?

It’s best to use it during the chickens’ growing period, specifically during their 14th to 18th week.

You can also safely combine them with other vaccines like those for the Newcastle disease.

Furthermore, induced chicken molting can also help restore their egg production after suffering from egg drop infection ’76.

How Long Does Egg Drop Syndrome Last?

EDS ’76 virus has an incubation period of 3 to 5 days, and the drop in egg production lasts from 4 to 10 weeks.

Since there’s no proven treatment for egg drop syndrome ’76 yet, it’s best to vaccinate and take precautionary measures to avoid the disease and economic losses.

FAQs About Egg Drop Syndrome

To help you get more insights into egg drop syndrome, we answered the most common questions about the disease below.

Do chickens recover from egg drop syndrome?

There’s no available treatment for EDS ’76, but it can recover and return to normal production after over 10 weeks.

However, good animal husbandry practices can help control the spread of this disease, like cleaning and disinfecting egg trays and man more.

Are egg drop syndrome eggs safe to eat?

Since EDSV does not cause any illness in humans, you don’t have to worry if you’ve eaten an egg with EDS.

However, it’s best to avoid consuming eggs that contain the virus and get rid of them safely to avoid the spread of disease because prevention is the key.

How do I know if my chicken has egg drop syndrome?

The most obvious sign of egg drop syndrome is the production of pale, thin, soft, or shell-less eggs of chickens that appear to be healthy.

Your bird may also experience signs of depression, mild diarrhea, or both.

However, conducting laboratory tests is necessary before making a definitive diagnosis.

Is egg drop syndrome contagious?

The horizontal transmission of egg drop syndrome virus occurs when chickens share contaminated trays, crates, and trucks with infected ones.

The virus may also spread through droppings, shared vaccination needles, contaminated water, and direct contact with wild waterfowl.

Egg drop syndrome in chickens

Final Thoughts on Egg Drop Syndrome

EDS ’76 is a serious problem in the poultry industry, but it doesn’t affect the birds’  fertility or the hatchability of the eggs.

Since the risk is higher on broiler chickens, you need to be more careful whether your birds are caged or not.

It requires time and effort to apply strict biosecurity plans to your poultry. But it’s necessary to prevent the egg drop syndrome virus from entering your flock and causing huge loss economic losses.

Although there has been no report regarding the occurrence of EDS ’76 in the US, and it’s well-controlled in areas where endemics are common thanks to existing inactivated vaccines. You should still apply precautionary measures.

How about you?

Did your flock ever experience the egg drop syndrome ’76?

How did you deal with it, and what did you do to help your birds recover?

Share with us your EDS ’76 recovery journey below and help us spread the word about this disease caused by duck adenovirus 1 or EDS virus.

READ NEXT: 9 Reasons Why Your Chickens Stopped Laying Eggs

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