The threat of Gumboro disease (IBD)
Gumboro is an infectious viral disease affecting broilers and pullets (layers and breeders) worldwide. The virus targets the bursa of Fabricius, the organ responsible for the development of immunity in young chicks.
Depending on the virus strain and the time of infection, the disease presents itself in different ways. When the infection occurs before the third week of age, it causes immunosuppression, low mortality, and drop in performance. If infection occurs after three weeks, it normally causes high mortality, immunosuppression, depression, ruffled feathers, and diarrhoea.
In Zambia, the disease is endemic, which means that this is an ever-present threat. Most of the outbreaks are caused by very virulent strains, which infect young birds quite early.
Protection
As mentioned in our previous article of ProAgri Zambia, issue 71 (Blanco 2021), control of the disease is achieved by means of biosecurity and vaccination.
Traditionally, there are four types of vaccines:
Live vaccines
They are administered on farm via drinking water in the first weeks of life. They protect the bird in two ways. If given at the right time the vaccine virus can enter the bursa of Fabricius and block the field strain from entering by means of “competitive exclusion”. The vaccine strain then multiplies and produces an antibody immune response that can destroy any circulating field strain virus in the body.
The challenge we face with live vaccines is that they can be inactivated by varying levels of IBD antibodies that the chick gets from the hen (MDAs). The MDAs are meant to protect the young chick from field challenge but, unfortunately, they can also kill the vaccine virus.
Field strains, especially very virulent ones, can “break through” high levels of MDAs while many vaccine strains have much lower “breakthrough” levels, allowing the field strain to enter the bursa before the vaccines can. There are, however, some vaccine strains (for example TAbic MB) that are able to break through quite high MDA levels and can, therefore, be applied earlier and offer better protection against virulent field strains.
To get the best results from a live vaccination programme it is important, therefore, to know what the MDA levels are in the day-old chick, as well as the expected breakthrough level of the vaccines, to allow you to apply the vaccine at the optimal time.
Inactivated vaccines
They are given to pullet breeders to create enough antibodies that will pass to their chicks (MDAs), protecting them from early infection.
Recombinant vaccines
Vaccines in which a carrier virus has “fractions” of proteins of the Gumboro virus on its surface, against which the bird generates antibodies. They are administered at the hatchery.
Immune complex vaccines
The vaccine virus is covered with antibodies in laboratory conditions and injected to embryos or chicks at the hatchery. As the MDA levels in the chicken drop, the vaccine virus is released to reach the bursa.
In Zambia, where very virulent Gumboro strains are present, MB strain is the best option to protect broilers and pullets against infection. As discussed in ProAgri Zambia Issue 71 (Blanco, 2021), MB is a Gumboro Intermediate Plus vaccine strain. This means it can reach the bursa of Fabricius faster than most of the current available vaccines, allowing to obtain a quicker protection against field viruses. Furthermore, because of its higher genetical similarity with the very virulent strains of Zambia, it confers better protection than other vaccines in the market.
MB-1, the latest good news for protection against Gumboro
Using a derivative of the MB strain, Phibro has developed MB-1. This new vaccine is injected at the hatchery, either in-ovo (at 18,5 days of incubation) or right after hatching. Instead of killing the MB virus, the MDAs form a protective coating around the virus (formation of immune complex, not in a lab but inside the chicken), which is slowly broken down to release the vaccine, allowing it to enter the bursa (Figure 1).
Clik here to view.
Once in the bursa, the vaccine virus prohibits the entry of any other viruses, multiplies, and stimulates the development of active immunity by the bird (Figure 1). This is particularly useful in flocks with very variable levels of MDAs, since the release of the MB-1 as the maternal antibodies drop results in an immune response that is “tailored” to each chicken.
According to scientific publications, MB-1 reaches the bursa before immunocomplex vaccines do, conferring earlier protection by colonising the bursa (Ashash et al, 2019; De Wit et al, 2021), which is essential when very virulent field viruses are present. It also induces the production of antibodies earlier than immunocomplex vaccines and recombinant vaccines (Figure 2) (Ashash, 2021; Ashash et al, 2019; De Wit et al, 2021).
Clik here to view.
Finally, the multiplication of MB-1 in the bursa does not induce immunosuppression, as demonstrated in field and laboratory trials. In those trials, birds vaccinated with MB-1 produced an immune response to Newcastle disease vaccination not different from birds receiving an immunocomplex vaccine (Ashash et al, 2019).
Several studies have proven that MB-1 is safe to be used in broilers, breeders, and layers. It can be diluted in any Marek’s vaccine diluent. It is compatible with any other injectable and spray vaccines, vitamins, and antibiotics that are applied at the hatchery.
MB-1 constitutes a unique tool for the control of Gumboro in Zambia, where very virulent Gumboro strains are endemic, and the levels of MDAs are sometimes very variable. If you require more information about MB-1, speak with your consulting veterinarian, or contact the local Phibro representative.
Clik here to view.
References
Ashash, A. (2021) A new approach to controlling Gumboro Disease, Asian Poultry Magazine, February 2021, Pp. 38 – 40.
Ashash, A. et al. (2019) In-ovo and day-of-hatch application of a life infectious bursal disease virus vaccine in commercial broilers, Avian Diseases, 63(4): 713 – 720.
URL: https://doi.org/10.1637/aviandiseases-D-19-00087
Blanco, O. (2021) Gumboro Disease and the MB strain. ProAgri Zambia, Issue 71, December 2021.
De Wit, S. et al. (2021) In-ovo application of a live infectious bursal disease vaccine to commercial broilers confers proper immunity. Avian Pathology, URL: https://doi.org/10.1080/03079457.2021.1986618
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