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Infectious bursal disease is highly contagious in young birds and destroys lymphoid organs, specifically the bursa of fabricius. Photo: Ramiro Martinez
Infectious bursal disease
INFECTIOUS bursal disease or gumboro is a viral disease affecting the immune system of young chickens.
feathers and dehydration. Presentation of clinical signs depends on the strain of the virus and presence of
poorly to vaccination and are more susceptible to oth- er diseases, making IBD an economically important disease.
North America in 2008. For the latest information on the distribution of IBD, refer to the WAHIS infor- mation database website of the World Organisation for Animal Health or the FAO EMPRESi Global Animal Disease Information Sys-
ly resistant to heat and chemicals and can last four months in contaminated bedding and premises. Clinical disease
Present worldwide, the disease is highly conta- gious in young birds and destroys lymphoid organs, specifically the bursa of fabricius, with symptoms including depression, wa- tery diarrhoea, ruffled
maternal immunity. Chickens less than three
Aetiology
The incubation period in clinical infections is usually very short, approximately 2-3 days.
weeks of age infected with IBD have subclinical infec- tions which can cause se- vere, long-lasting suppres- sion of the immune system.
The virus that causes IBD is a double-stranded non-enveloped ribonucleic acid virus, belonging to the genus avibirnavirus in the family birnaviridae.
tem.
Clinical signs in the acute phase of the disease include anorexia, watery diarrhoea and ruffled feathers.
Chickens that are im- munosuppressed respond
It is very resistant to dessi- cation and can persist in the environment for extended periods.
In Australia, both classi- cal and variant strains are present, but these are ge- netically different from the classical, variant and very virulent strains found over- seas.
Mortality peaks by day four and then subsides, with the surviving chickens re- covering to a state of appar- ent health after about seven days.
Australia
The virus is most easily isolated from the bursa of fabricius.
Australia remains free from vvIBDV.
Vaccination
Infectious bursal disease virus strains are classified into two serotypes but only serotype 1 causes disease in chickens – serotype 2 infec- tions are non-pathogenic.
In Australia, commercial broiler and layer breeder flocks are vaccinated against IBDV so they are antibody positive.
This is dependent on the age and breed of chickens, the virulence of the strain and presence of maternal antibodies.
IBDV has been identified in other avian species and antibodies to the virus have been found in several wild bird species.
Commonly, breeder birds are vaccinated at about 8-12 weeks with a live vaccine, followed by an inactivated vaccine before point of lay.
A prominent characteris- tic of vvIBDV is the ability to induce high mortality.
Wild birds may thus play a role in the spread of IBDV. The serotype 1 strains can be further classified based on phenotypic traits such as
Mortality ranges from 5-25 percent in broilers and 30-70 percent in layers.
virulence and antigenicity. Serotype 1 IBD vi- rus classifications are at- tenuated (vaccine strains), classical (cIBDV), variant (varIBDV) or very virulent
In Australia, chickens less than six-weeks old are usu- ally not vaccinated. Transmission
However, clinical signs are more acute in individ- ual birds and subacute in flocks.
(vvIBDV).
The natural reservoir
The IBDV is spread hori- zontally from infected to healthy chickens via the faecal-oral or respiratory route.
IBDV should be consid- ered when birds present with very high morbidity and severe depression last- ing five to seven days.
hosts of IBD are chickens for serotype 1 and turkeys for serotype 2. Distribution
Disease transmission is by direct contact with excretions from infected birds, or indirect contact with mechanical vectors and fomites.
The rate of mortality is variable depending on the virulence of the IBD virus strain.
Global
Differential diagnoses include Newcastle disease, acute coccidiosis, infectious bronchitis, Marek’s disease, avian influenza, stress, wa- ter deprivation and intoxi- cation, and haemorrhagic
Transfer of maternal an- tibodies to progeny birds usually provide enough protection against the field virus challenges.
Syndromes of clinical dis- ease are similar to classical virulent strains.
Classical serotype 1 IBDV strains are endemic globally.
Two enlarged bursae – yellowish grey (right) and haemorrhagic (left). Photo: Lucien
Mahin
The vvIBDV strain is en- demic in parts of south- ern Asia, Indonesia, Mid- dle East, Africa and South America, spreading to
The virus is extremely re- sistant in the environment, increasing the likelihood of indirect transmission.
Diagnosis
Page 10 – National Poultry Newspaper, March 2022
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The virus is also high-
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