Gumboro Disease – Backyard Poultry

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And the poultry immune system.

By Sue Norris

FOR THE SCIENCE NERDS among you, there are lots of biology details in this article.

Gumboro disease, caused by the infectious bursal disease virus (IBDV) in the Birnaviridae family, is a highly contagious virus affecting chicks under 16 weeks of age.

Although named for Gumboro, Delaware, where it was first discovered in 1957, Gumboro affects birds globally (except for in New Zealand) and can cause huge losses for both industrial poultry operators and backyard flock-keepers alike.

Bursa of Fabricius

In order to understand this disease, we need to understand something about the function of the bursa of Fabricius organ in birds and their immune systems. The bursa is located internally above and near the cloaca
and plays an early, vital role in the immune system of the fowl. First noted in the 17th century by Heironymus Fabricius, the organ was thought to be a semen receptor. It wasn’t until the mid-20th century that poultry researchers Bruce Glick and Timothy Chang discovered its real use: The site
where some immature blood cells are made into B lymphocyte cells.

Formed during embryogenesis of the chick, the bursa consists of a round sac containing numerous folds of lymphoid tissue and collagen. During the embryonic stage, days 8 to 15, the bursa sends a signal that starts the process of B cell development and maturation, a process that continues into the first two weeks following hatching. During this time, the bursa builds the framework for a strong immune system utilizing the B cells. At the two-week mark, the bursa is as large as it will get and, in fact, it slowly starts to shrink in size.

Affected chicks should be removed and isolated from the flock as a precaution against the further spread of the virus.

After the B cells are mature, they leave the bursa to “patrol” the body via secondary lymphatic tissues. It’s here they’ll encounter bacteria and viruses that they’ll battle with to keep the bird healthy. Healthy B cells are vital to a functioning immune system. Without these, the chicken is susceptible to infections and viruses. (Other components of the immune system are the thymus and spleen, each with separate but vital roles in a vibrant immune system.)

Dissection of an infected bursa.

Damage to a chick’s bursa during an infection diminishes the organ’s ability to produce sufficient, healthy lymphocytes to fight infection. Affected birds will be performing sub-par for the rest of their lives. The virus will replicate in the B lymphocytes and with the bursa effectively destroyed, the bird has no way to fight against the infection.

Signs and Symptoms

In the 1980s, a very virulent form of the disease made its appearance in Asia, Africa, South America, the Netherlands, and the United Kingdom. This
“very virulent” strain, known as “vvIBDV,” has since made short appearances in the United States — in California in 2008 and in Washington state in 2014.

While infection may result in mortality (deaths) of around 30%, the morbidity (number of birds contracting the virus) can approach 100%.
Although the infected birds may not die from this disease, their immune
system is now severely compromised making them susceptible to further
infections, which may weaken or kill them later in life. Mortality in the very
virulent strain can often reach 100%.

In the clinical disease, chicks between the ages of 3 to 6 weeks will appear lethargic and droopy, with a decreased appetite and exhibiting signs of dehydration, diarrhea, vent pecking, staggering gait, trembling, and depression. The symptoms will appear quite suddenly, and 20% to 30% of the flock may die within a couple of days. Enlist a veterinary examination and necropsy to confirm Gumboro as the cause. During necropsy, areas of hemorrhage are usually found throughout the body due to the destruction of blood cells.

Chicks less than 3 weeks of age can be affected by what is known as a sub-clinical infection. This means they show no outward signs of disease or illness but may be severely immunocompromised for the rest of their lives. Affected chicks should be removed and isolated away from the flock as a precaution against the further spread of the virus.

Chick affected by Gumboro disease.

Prevention and/or Eradication

Good biosecurity and coop cleanliness go a long way toward prevention, but the virus is incredibly resilient once established. The disease is transmitted via the oral-fecal route, so keeping the coop and pens clean is important, especially in hatching and brooder areas. It can survive outside of its host for several months, making it difficult to control or eradicate. It’s also somewhat resistant to many of the commonly used disinfectants used in hen houses.

Darkling beetles (mealworm beetles) and vermin can carry the virus from place to place. Boots, equipment, and tools can do the same. Keeping equipment clean and not loaning anything to other chicken keepers will
help to keep your birds safe. If you get new birds from another source or
The dissection of the infected bursa. exhibit your birds in shows or competitions, quarantine these birds from your flock for 30 days.

Vaccination and Research

Vaccination has been effective against this virus in the past and can continue to be the best weapon against infection especially in a large commercial facility. While some have expressed concern that backyard flocks present the highest risk of Gumboro disease, presumably because vaccination is unlikely, I have found no scientific evidence to back this claim. The cost of the vaccine is in excess of $1,000 for a 200-dose vial. Until the vaccine becomes affordable, the best strategy is cleanliness, good biosecurity, and selective stock purchase.

The virus has a double-strand ribonucleic acid (RNA) capable of mutation.
While only two serotypes were known originally, with the first being the one pathogenic in chickens, recent research has indicated that closer to seven serotypes might exist now due to the virus mutating. The takeaway is
that, while vaccination does mitigate the disease, chicks are not protected against all variations.

Research is ongoing regarding the use of herbal treatments for Gumboro, including ashwagandha, calendula extract, scutellaria, and hibiscus extracts. Results are inconclusive so far.

Many thanks to Nati Elkins at www.PoultryMed.com for invaluable assistance and access to documents and photos.

SUE NORRIS was born and raised in the United Kingdom. She traveled around the world as a registered nurse and settled in New York
State with her partner about 25 years ago. Sue is happily retired and enjoying the serenity of living on 15 rural acres with 40-ish chickens,
four rabbits, two dogs, three cats, and assorted wildlife.


Originally published in the Feb/Mar 2024 issue of Backyard Poultry magazine and regularly vetted for accuracy.



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