Infectious Bursal Disease remains one of the most significant viral threats to poultry worldwide. Both very virulent and variant strains circulate, with many causing subtle or subclinical infections that reduce growth, worsen feed conversion and weaken the immune system of birds.
Because outbreaks can lead to long-term performance losses, vaccination is the central strategy recommended for both breeders and broilers. The page emphasises the importance of early vaccination in hatcheries, consistent program design and proper application techniques to ensure flock uniformity and protection.
When correctly implemented, vaccination reduces disease pressure, improves productivity and supports sustainable poultry production.
Key points
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Gumboro disease, also known as Infectious bursal disease (IBD), is a highly contagious disease of young chickens caused by infectious bursal disease virus (IBDV).
Despite the wide use of vaccines and increased biosecurity, however, it is still very much present and ranks among the top five diseases in almost all countries globally. The World Organization for Animal Health (OIE) listed IBD as a notifiable disease with importance in 2017.
After the initial outbreak in the US, clinical IBD was reported in many other countries. More virulent forms were later reported around the same time that had a very immunosuppressive form of IBD.
Today, the very virulent form is predominant in most countries, and variant strains of IBD are present in several countries, leading to sub-clinical forms of the disease.
The cost of IBD has been very well documented in different publications in the last decade. It has a direct impact on mortality, from 5% to 30%, depending on the degree of protection of the birds and the form of the disease (Rosenberger et al., 1986; Van den Berg, 1991).
In subclinical cases, it can reduce the income per flock by up to 14%, with a 11% reduction in yield and a 10% reduction in profit due to weight loss and increased FCR (McIlroy, 1992).
Recently, interesting calculations have been performed especially focused on the subclinical variant IBD strains. Researchers have identified a positive correlation between serological IBD titers with increased lesions and condemnations during processing.
IBD is caused by an Avi-birnavirus which replicates and damages the bursa of Fabricius. The Infectious Bursal Disease Symptoms vary, and basically presents 3 different clinical forms: immunosuppressive, clinical and subclinical.
The intensity and extension of the lesions explain the clinical symptoms of infection. Although this is not fully understood, these symptoms depend on several factors including:
All these possible factors of variation associated with the extreme variability of the virus and the often indirect pathogenic process easily explains the variability of the symptoms.
It’s difficult to describe Gumboro Disease in a simple and unequivocal manner. It is however useful to recognise three main theoretical forms of Gumboro Disease
The immunosuppressive form is the consequence of the infection of chickens aged less than 2 weeks by any pathogenic IBD virus. During this time, the organ where B-lymphocytes are produced needs to mature to become functional and provide the chickens with effective humoral immune response capabilities.
The symptoms of immunosuppression varies according to age at infection (the earlier the age, the worse the infection) as well as the type of virus. When compared to more ‘classical’ strains, it has the capacity to create extensive and persistent depletion of the follicles and consequently, dramatically reduce the size of the bursa.
Since IBD is a very persistent virus, it is capable of prevailing for a long time in the farms.
The Transmission of Infectious Bursal Disease can occur from one bird to another, or from one flock to another. The presence of variant or vvIBDV in previous flocks, can lead to an outbreak if new birds are placed in the same houses.
The Gumboro virus is extremely resistant and it is often unrealistic to imagine eradicating it from a farm. The characteristics of this challenge in chickens (age of birds, severity, consequences, etc.), might vary from house to house, but the challenge will definitely occur at some point in time.
In contrast to other diseases such as NewCastle disease, Infectious Bronchitis or Avian Influenza, which are epizootic diseases (non-resident virus), the Gumboro disease is an enzootic disease, which means that the virus is resident in poultry houses.
Conversely, use of built-up litter management systems increases virus pressure. As there is a higher load of virus, the transmission will increase as well.
However, the strict application of biosecurity measures and thorough cleaning and disinfection will play a critical role in reducing virus pressure and prevent the emergence of new variant viruses. Successful vaccination should protect the chickens and prevent disease challenges.
Gumboro disease, as a resident disease, is already present inside the farm, in the litter, or before the day-old chicks are released onto the floor, so the probability of challenges for most farms is very high.
Vaccination should aim at both protecting the chickens and preventing the challenge from getting out of control, therefore ‘controlling’ the Gumboro Disease.
The objectives of a Gumboro vaccination program must be:
These last two points are the consequences of the ‘protection against shedding’. In other words, the objectives of a sound Gumboro vaccination program should aim to stop the Gumboro cycle.
To achieve the control of the Gumboro disease, the vaccination program should be tailored to the farm and the flock. Several Types of Gumboro Vaccines are available in the market and can be classified into 3 categories:
Other factors that should be observed for optimal short-term and long term control of Gumboro Disease include biosecurity, cleaning & disinfection, and achieving passive immunity.
Biosecurity measures, such as cleaning and disinfection methods are important to suppress the virulent virus and will help to speed up the process of displacement of the field strains to the vaccine strain, in cases where a live IBD vaccine as Immune-complex is used.
The most dramatic consequences of Gumboro Disease challenges are observed in cases where the chick is very young. As the vaccine doesn’t take effect for the first two weeks, only passive immunity which is transferred from the breeder to the chick by yolk can be effective at this stage, highlighting its fundamental role and the need to take it into account.
This is why the breeders should also be injected with inactivated IBD vaccines containing IBDV strain, before the laying period, so that the passive protection is transmitted to the progeny.
When the subclinical form of Gumboro disease is present, a vaccination failure means the chickens will be infected by the field virus. This may not necessarily cause an immediately perceptible negative effect, but it will create the opportunity for the field virus to multiply, naturally produce variants and spread, with two very important consequences that will impair the future sanitary and/or economical performance of the poultry house or farm:
In terms of performance and economical impact, it is well established that Gumboro disease can result in the decrease of weight gain, as well increase the feed conversion, secondary infections, slaughterhouse condemnations, mortality and morbidity, leading to losses and decreased profitability.
Below you will find the economical analysis of the cost of infection in some situations:
Several publications, showed the impact on the performance as described above:
As the most common form of Gumboro disease is named “sub-clinical” Gumboro Disease, where the clinical signs are not perceptible, it is important to monitor all the links in the production chain, including the slaughterhouse.
Some publications demonstrate the cost of the sub-clinical form in the slaughterhouse:
In conclusion, the Gumboro disease can have several different faces depending on the form (immunosuppressive, clinical or subclinical), but in all cases it will impact the performance, and the profits of the poultry producer.
As a resident disease, it needs to be controlled through vaccination. Hence, a very successful vaccination program against Gumboro disease, whether clinical or subclinical, should not only ensure the ‘protection’ of the chickens against clinical signs following infection, but should also ensure the ‘prevention’ of the disease by decreasing the population of Gumboro virus shed – so that the virus pressure in the poultry house does not increase – and will significantly reduce the risk of emergence of a variant virus. ‘Protection’ and ‘Prevention’ are the two objectives assigned to a Gumboro vaccination program aiming for true ‘Control’ of the disease. This should be undertaken as part of a long-term action plan.