Gumboro disease is an avian pathology of viral origin that affects young poultry and can have high mortality. How to prevent and control it?

What is Gumboro disease?

Gumboro disease has also been called Bursa of Fabricius disease because it is the target organ of the virus. This pathology is caused by a virus of the Birnaviridae family, genus Avibirnavirus.

Among the characteristics of the virus causing Gumboro disease, the following stand out:

• Virions are spherical and measure 60 nm.
• It has an icosahedral capsid.
• Its genetic material is composed of two RNA strands.
• Replication of this virus occurs at the cytoplasm level of the cells of the poultry.
• The infected cells are B lymphocytes.

Gumboro disease got its name because it was first discovered in Gumboro, Delaware, in 1962 by Cosgrove.

There are two serotypes of Gumboro disease:

• Serotype 1: Pathogenic
• Serotype 2: Non-pathogenic. Animals with this serotype have protection against serotype 1.

Domestic fowl are the natural hosts of the disease and develop the clinical form of the viral disease. However, ducks and turkeys can also become infected.

Epidemiology of this avian pathology

Gumboro virus disease is distributed worldwide and causes great economic losses to the poultry industry in many countries. Its impact lies in the marked mortality and immunosuppression of infected poultry. Immunosuppression is a condition generated by the virus that predisposes poultry to become ill and die from other infectious agents.

The transmission of Gumboro disease occurs mainly through the oral-fecal route when the birds ingest feces and other contaminated organic materials. There is also vertical transmission through eggs.

For this reason, biosecurity measures and vaccination have been the main strategy for the global control of Gumboro disease. The virus presents certain resistance to environmental conditions such as heat at 60°C for one hour, pH between 3 to 9, making it difficult to control by this method.

Currently, it is a disease of great importance due to the emergence of highly virulent strains that produce clinical cases in vaccinated animals.

Risk factors: Which ones are they?

Gumboro disease affects mainly young poultry that still has the Bursa of Fabricius. It is important to remember that poultry between 2 to 6 weeks of life still have this immune organ and present a marked activity. Therefore, they are susceptible to infection and the development of this viral disease. Birds older than 8 weeks rarely develop Gumboro disease, although cases may occur if the strain involved is highly virulent.

Virus life cycle

Once the virus has entered the poultry orally, macrophages or lymph cells in the small intestine detect it and phagocytize it. Primary virus replication occurs in the duodenum, jejunum, or ileum, or even liver. Then, the virus spreads through the blood to other organs such as the Bursa of Fabricius.

Young poultry has immature B lymphocytes in their bursa of Fabricius, and these cells are the main cells for viral replication. After 13 hours of infection, most of the follicles in the Bursa of Fabricius will already have viral antigens. Thus, 3 hours later, viremia (virus in the blood) will take effect. Clinical signs begin to be observed 64 to 72 hours after infection.

Symptomatology of Gumboro disease

The symptomatology of this avian pathology depends on the strain involved, the breed of the poultry, the age, and the immune status of the animals. The damage generated in the Bursa of Fabricius is severe and permanent, which leads the poultry to have immunosuppression. This immune deficiency makes the poultry susceptible to infections such as Salmonella spp., E. Coli, Coccidiosis, Adenovirus, Mycoplasma, among others. In addition, they do not respond adequately to vaccinations. There are mainly two forms of infection: clinical and subclinical.

Clinical form

– It is of acute course, in poultry from three to six weeks of age.

– Severe lesion of the Bursa of Fabricius.

– Signs such as depression, anorexia, diarrhea, ruffled feathers, tremors, and dehydration.

Subclinical form

– In poultry under three weeks of age, it causes severe immunosuppression.

– Chicks usually have no signs due to their passive immunity that manages to control the effect of the virus.

– In poultry older than three weeks it rarely causes clinical signs, since they produce antibodies against the virus.

Differential diagnoses for Gumboro disease are Marek’s disease, mycotoxicosis, coccidiosis, hemorrhagic syndrome, infectious bronchitis.

How is Gumboro disease diagnosed?

The diagnosis has a wide range of possibilities that can be used together to arrive at a more accurate answer about the health status of a poultry farm.

Necropsy and histopathology

Findings during necropsy and later under the microscope give good evidence for the diagnosis of Gumboro disease. In this case, the following can be observed:

– Atrophy, edema, transudate of the bursa of Fabricius.

– Enlarged kidneys with the accumulation of urate and immunocomplexes in the renal glomeruli.

– Lesions in the thymus, spleen, and bone marrow if the strain is highly virulent.

– Petechiae in pectoral muscles

– Edema in the liver

– Increased mucus in intestines

When the virus enters a farm where the poultry has never been exposed before, mortality can reach 90%. However, after the virus becomes established, mortality is between 20-30%. In cases where there is no mortality, the poultry recover from the disease in five to seven days and become immune.

Viral antigens

The antigens of this Avibirnavirus can be detected by immunofluorescence, immunohistochemistry, agar gel precipitation, or enzyme-linked immunosorbent post-tests.

Biological test

For the diagnosis of this viral disease, inoculation of embryonated eggs that are free of antibodies against Gumboro disease can be performed.

Serology

The ELISA test can detect antibodies created by animals exposed to the virus. On the other hand, Seroneutralization can differentiate the two serotypes and indicate which one is involved in a case.

RT-PCR

The reverse transcriptase PCR test has shown great diagnostic utility to quickly identify the virulence of the strain involved.

How to prevent Gumboro disease?

The control and prevention of Gumboro disease has two main axes: vaccination and biosecurity. Due to the nature of the virus and its resistance to the environment, it is difficult to control; it can resist up to four months in the environment.

Vaccination is carried out in chicks during the first weeks of life. In addition, passive immunity of the chicks through the egg must be guaranteed. For this purpose, mothers are vaccinated with the inactivated virus at 18 weeks of life and revaccinated annually. This generates antibodies that can be transferred to the chicks.

There are numerous factors that can lead to vaccine failure, so a booster vaccination and, in general, to the immunity of the birds, is a highly recommended practice. There are immunostimulant pronutrients that enhance vaccine protection by increasing the number of antibodies produced. These antibodies are a key component in the protection against Gumboro virus, which decreases discards and significantly reduces mortality.

Pronutrients are molecules of botanical origin that stimulate the physiological activity of cells. They act as a stimulus that activates and enhances the activity of certain target cell genes related to specific cell functions. Pronutrients of the immunostimulant class act on the cells of the bird’s immune system, activating them to physiological levels, which allows maintaining the animal’s defenses in an optimal state.

Their administration in the feeding or drinking water in small doses has shown to be able to activate, up to physiological levels, the innate and adaptive immune system, so that the birds are prepared to face any infectious agent. They are also capable of improving the response to vaccination with the objective of obtaining a greater protection against specific diseases, as is the case of vaccination against Gumboro, increasing the synthesis of specific antibodies against this disease.

For vaccines, it is recommended to use highly attenuated strains to achieve effective immunity and avoid risks of subclinical presentation of the disease.

Biosecurity in poultry is an indispensable element to minimize the impact of viruses. The all-in-all-out principle is a biosecurity component that ensures keeping the virus out of the premises and preventing its circulation. On the other hand, Good Poultry Husbandry Practices have key tips at every stage of production to control viruses.