Introduction
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.
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:
- To ensure continuous protection of the chickens against infection by the Farm IBDV, from delivery of the day-old chicks until departure to the slaughtering plant or laying house (‘viral protection’).
- The chickens should be protected against the clinical consequences of infection (‘clinical protection’).
- To prevent or significantly reduce the amount of virus shed (‘protection against shedding’).
- To prevent the build-up of a higher virus pressure, cycle after cycle
- To stop the evolution of the IBD virus towards a form that could escape the prevention program.
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:
- Immune Complex vaccines
- Vector HVT-IBD vaccines
- Conventional field vaccines
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.
Passive Immunity
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:
- The virus pressure (the amount of virus to which the chickens of the next cycle will be exposed) will increase
- An opportunity will be created for a variant virus to colonise the farm. The Gumboro viruses that multiply are then more able to surmount passive protection (from the breeders program) and active protection (from vaccination).
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:
- In a situation where 10% of the flocks has the subclinical infection, there will be a 10% decrease in feed conversion;
- Increase of general feed conversion, from 1,60 to 1,61, or to 1,63, or to 1,65.
- Increase of 0,5% of mortality (example from 4% to 4,5%)
Several publications, showed the impact on the performance as described above:
- CANADA (Tata Zachar et al., 2016): Increase of mortality & condemnations;
- EUROPE (Van den Berg et al. 1991): Mortality 25-30% in broilers
- NORTHERN IRELAND (McIlroy 1992): -10% Income in subclinical IBD, when compared with uninfected flocks reduction in weight higher FCR;
- JAPAN (Nunoya et al., 1992): Mortality between 50-60% in layers
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:
- USA (Shane et al., 1994): 10% Rise in production costs
- CANADA (Amini, 2015): Titers for Variant-E strains correlated with increased hepatic lesions and condemnations in the slaughterhouse
- CANADA (Kurukulsuriya, 2016): 1,6 higher risk to develop E. coli septicemia in case of an existing subclinical IBD infection
