Infectious bursal disease (IBD, Gumboro disease) is an acute contraceptive disease of chickens characterized by a lesion of the factory bag, diarrhea, nephrosis, intramuscular hemorrhages.
For the first time the disease was registered in 1957 in the town of Gumboro, (USA), which gave the disease a second name.
Currently, the disease is registered in all countries of the world. The contamination of herds ranges from 2 to 100% and is manifested by outbreaks of the disease. Economic damage consists of losses associated with the death of chickens, forced culling of poultry, reduced meat productivity of young animals, as well as the costs of preventive measures and a low level of vaccination response due to immunodepression caused by bursa pathology.
Characteristics of the pathogen. The causative agent of IBB is a virus belonging to the family Birnaviridae (from English bi - double, rna - ribonucleic acid), the genus Avibirnavirus. The virions of the virus are shellless, are spherical particles with a diameter of 55 and 18-22 nm. They consist of a core containing double-stranded linear RNA, and a protein, an icosahedral capsid, constructed from 92 capsomers.
Resistance to physical and chemical influences. The virus is resistant to ether, chloroform, changes in pH (2-11), UV irradiation. When exposed to a 0.5% formalin solution, it is inactivated in 6 hours, 0.5% chloramine in 10 minutes.
Antigenic structure. Five proteins have been found in virion structures. One of them is responsible for group-specificity, the other for type-specificity and the induction of neutralizing antibodies.
Antigenic variability. The virus has antigenic variability: one serotype with six subtypes is pathogenic for chickens, two serotypes pathogenic for turkeys. The presence of antigenic variability of the virus requires the use of a strain with the maximum degree of antigenic homology with the epizootic strain as a vaccine.
Hemagglutination properties. Not installed.
Virus cultivation. The IBB virus can be propagated in chicken embryos free of maternal antibodies to a number of viruses, including the IBB virus. When infected into the allantoic cavity or the yolk sac, embryos die on the 3rd-8th day after infection. Signs of reproduction of the virus in the chicken embryo - necrosis and hemorrhages on the body of the embryo, liver, kidneys. The virus is well reproduced in the culture of kidney cells and chicken embryo fibroblasts, causing on the 3-5th day after infection with the JRS. It is possible to cultivate it on SPF-chickens (free from pathogenic flora) 21-25 days of age.
Clinical signs. In chickens of 3-6 weeks of age, the disease is acute, but depending on the immune state of the population, a subacute course or death is possible. The incubation period is 1-3 days, and the disease lasts 5-7 days.
In diseased chickens, diarrhea is manifested with the discharge of watery, whitish-yellowish litter, then head and neck tremor, deep prostration appear. Morbidity and mortality increase rapidly and reach a maximum on the 3-4th day of illness, then it usually diminishes within 5-7 days. Distinctive signs of the disease - suddenness, high level of damage and rapid recovery. Mortality is 6-37%. Subclinical infection is mainly expressed as growth retardation. When an adult bird is ill, there is only a slight decrease in the percentage of viability of the embryos.
Pathological changes. They are different at different stages of the disease. Initially, hypertrophy of the bursa and petechiae in its mucous membrane is noted, exudate with fibrin flakes between its folds, hemorrhages in the pectoral muscles and leg muscles, and serous membranes. After a week, the lesions become different: serofibrous pericarditis, hepatitis and nephritis. One month after the infection, the bursa atrophies and is 3-4 times smaller than in healthy birds of the same age. Microscopic changes characteristic of IBB are found in a factory bag of sick birds. They are mainly represented by lymphoid necrosis and hyperplasia of reticuloendothelial cells, thickening of interfollicular connecting partitions, formation of glandular structures instead of follicles.
Virus localization. The virus penetrates the digestive tract and infects lymphoid tissue. After 24-28 hours, it is localized in a fabric bag. The most sensitive to the virus are lymphocytes, on the surface of which IgM are fixed. Therefore, the main target for the virus is a subclass of B lymphocytes, especially their immature forms. In addition, the lymphocytes of the spleen, the cecal glands of the blind processes, etc. are destroyed. The immunodepressive effect caused by the virus is due to the defeat of the lymphoid tissue.
CPD of immune complexes, including lymphocytes infected with a virus, antibodies, complement, leads to the appearance of hemorrhagic lesions in skeletal muscles, liver and other organs. Deposition of immune complexes in the glomeruli and convoluted tubules of the kidneys reduces their filtration capacity, and urates accumulate in the kidneys.
Diarrhea in IBD develops due to the reproduction of the virus in intestinal epithelium cells, which leads to dehydration. The weakening of the immune status of the bird leads to additional infection with viruses and bacteria.
Source of infection - sick bird. The pathogen is transmitted with infected feed, water, aerogenic, as well as with inventory and through the egg. Helminths and lice are considered direct transmission vectors. Wild birds can be direct and indirect vectors. In natural conditions IBB only chickens are sick, namely chickens of 2-15 weeks of age. However, it was possible to isolate the virus from poults, bats and mosquitoes.
Diagnostics. Only with a typical course of the disease is relatively easy to diagnose on clinical and pathological signs. Laboratory studies are needed in the early stages or in the subclinical course.
Laboratory diagnosis. For laboratory tests, birds taken from factories that have fallen or been killed during the first 7 days of illness take a factory bag, a liver, and kidneys.
Virus detection in pathological material it is possible to establish by express methods: an indirect variant of ELISA, REEF and PCR.
Virus isolation carried out by bioassay with subsequent isolation of the virus in chicken embryos, in cell culture and infection of chickens. It is not always possible to isolate the virus from the affected organs, therefore a more reliable method for diagnosing IBD is serodiagnosis. Blood serum is also examined for asymptomatic disease. Important in the prevention of IBD is systematic monitoring of the immune state of the herd. Such control is carried out by studying paired serum.
Identification isolated virus is carried out with the help of PH on chicken embryos, in REEF and RDP.
Antibody Detection to IBD virus in the blood serum of sick and ill birds is carried out in PH, RNGA, RDP, ELISA.
Neutralizing antibodies reach maximum titers by the seventh day after infection and persist in the body of the bird for up to three months. Serum with a high titer of neutralizing antibodies is usually positive in the RDP. RNGA detects antibodies already on the 3-5th day after infection, with their maximum titers on the 3-4th week. For a wide serological study used ELISA.
Differential diagnostics. IBB must be differentiated from infectious bronchitis of chickens, Newcastle disease, Marek's disease, Rous sarcoma, coccidiosis, nephritis, vitamin A deficiency. However, only the detection of antibodies does not allow diagnosis, it is necessary to isolate the virus, determine its serotype, subtype and virulence.
Immunity and specific prevention. When carrying out measures of specific prevention, it is necessary to take into account factors that negatively affect the formation of persistent immunity in birds. This is primarily the type of antigen, the method and frequency of its use in the vaccination process, the degree of attenuation or inactivation.
When immunizing against IBD with a live vaccine, it is necessary to establish the conformity of the drug used with the epizootic strain circulating among birds. In addition, vaccination should take into account maternal antibodies.
Currently, live vaccines are widely used from naturally attenuated strains, as well as weakened by passaging on CE and in cell culture. In birds of different age groups, the intensity and duration of post-vaccination immunity are not the same. The level of specific antibodies in chickens corresponds to the concentration of virus-neutralizing antibodies in adult chickens-mothers during the laying period.
Currently used dry live vaccine strains D-78 and "Winterfield 2512" orally and in the form of a spray.
Inactivated vaccine is prepared from virus propagated in EC and in cell cultures. The virus is inactivated by formalin or β-propiolactone, aluminum hydroxide is added. The vaccine is used subcutaneously or intramuscularly, introducing it at the age of 2-4 months. The titers of post-vaccination antibodies are studied in ELISA and PH.
Numerous names of the disease, such as Gumboro disease, infectious neurosis, infectious bursitis, IBD, express a high degree of damage to the vital organs of the chicken herd in a short time.
The primary goal of the virus is to destroy leukocytes in the organs of the immune system:
- factory bag
- almond shape.
They increase and acquire a color from light gray to dark brown, urates (uric acid stones consisting of crystals of uric acid salts) fill the tubules and ureters. A distinctive feature of the pathogen is its stability and duration of exposure in the environment.
Water, food, bird droppings save it for up to 56 days, utility equipment, infected clothing of contacting personnel, etc. - more than 120 days. The duration of the disease is 5–6 days, but it seizes a large number of livestock (40–100%) for a short period of time. Mortality reaches 20–40%. The suppression of leukocytes leads to the destruction of immunity and, as a consequence, the risk of other deadly diseases: colibacteriosis, coccidiosis, enteritis.
Sources of infection
The seriousness of the infection lies in the extremely rapid transmission of viral material between contactors (in this case birds), as well as through food, water, litter and inventory devices for the maintenance of chickens. Poultry farmers themselves can become peddlers of the virus.
It is revealed that the carriers of the virus and at the same time its carriers in their natural habitat can be birds: ducks, turkeys, geese, guinea fowls, quails, sparrows and pigeons. Infection occurs by alimentary means, mucous membranes of the mouth and nose, conjunctiva of the eyes are involved. The carriers of the virus will be fluffy meals that have fallen on a hen, for example, from an infected sparrow that has accidentally flown into the chicken yard.
Diseased chickens become a source of infection, as they emit the pathogen with droppings, infect food, water, bedding material, ancillary equipment.
Infected feeds are transported throughout the room (and further) not only by chickens, but also by pests (mice, rats), which makes it difficult to localize the source of infection. Keep the feed quality and purity.
It is important to note that Gumbore’s disease has two types of illness:
- subclinical (hidden).
Symptoms of infectious bursitis include:
- severe diarrhea whitish-yellow
- ruffled plumage
- weakness and depression of birds (depression),
- significant loss of appetite (refusal of feed),
- signs of incoordination (in some cases),
- severe itching around the cloaca (frequent),
- susceptibility to pathogens.
- growth retardation
- immunity immunity sick birds.
Yet the final diagnosis can be confirmed only by laboratory tests that are aimed at detecting the virus, identifying it, and detecting antibodies in the blood.
The causative agent of IBB is relatively stable to aggressive environmental factors. Laboratory tests established his death only at 70 ° C in 30 minutes. Lower temperatures require a longer time to maintain the temperature. The virus is immune to chloroform, trypsin, ether. Destruction is observed when processing 5% formalin, chloramine, caustic soda solution. There is no special treatment for infectious bursitis. Vaccination is indicated as the main method of counteracting undesirable outbreaks. Apply live and inactivated vaccines. The primary condition for success in combating the disease is timely detection of the outbreak and isolation of sick stock. The weakest sick birds must be destroyed.
The remaining diseased chickens determined in another room. Infected territory is cleaned and several times treated with formalin, phenol and other special means. Garbage material (bedding, food residues) must be destroyed. The disease does not depend on the breed and age of chickens, occurs at any time of the year and is manifested in different climatic conditions.
With the threat of the spread of Gumbore disease, vaccination is of paramount importance. The most common vaccines consider:
- inactivated vaccine from strain BER-93,
- virus vaccine from strains UM-93 and VG-93,
- Gallivac IBD (France)
- inactivated vaccines N.D.V. + I.B.D + I..B. and quadratin N.D.V. + I..B.D + I..B. + Reo and NECTIV FORTE (Israel).
Preventive measures help to prevent the outbreak of infectious bursitis, or to minimize possible losses during infection. A number of actions include:
- periodic sanitary and hygienic measures, in accordance with existing standards,
- limiting contacts of birds of different ages,
- conducting preventive vaccination in disadvantaged farms,
- food quality and purity standards,
- carrying out activities for the destruction of rodents and parasitic insects (lice, peroed, etc.),
- sick representatives are immediately isolated in a separate room or destroyed.
It is important not only to strive for profit, but to meticulously and closely monitor the chicken population, ensuring proper living conditions for it, and the results of hard work will soon appear in the form of tasty and healthy products derived from this bird.
The first symptoms of the disease are diarrhea, accompanied by the discharge of watery whitish-yellow litter, sudden loss of appetite, trembling of the legs and head, and sudden death. Morbidity and mortality increase rapidly and reach a maximum at the 3-4th day of illness. After the virulence of the virus decreases, the number of deaths decreases, usually after 8–9 days.
Unlike the clinical form of the disease, the subclinical form is observed in chickens less than 4 weeks old, when the immune system is most susceptible to damage. The early manifestation of IBD is characterized by the absence of clinical signs and the defeat of the fabric bag, where the number of B-lymphocytes sharply decreases and immunosuppression develops. It should be noted that the recovered bird becomes very sensitive to other diseases.
Hemorrhage in the Fabric Bag
Muscle hemorrhage in Gumboro disease
В начале болезни отмечают воспаление фабрициевой сумки, ее увеличение, отек, гиперемию и кровоизлияния. 5 days after the onset of the disease, a rapid decrease in the bursa and its atrophy is observed. Histological examination observed the death of lymphoid elements, necrobiosis of lymphocytes.
Hemorrhages are observed in various muscle groups (usually chest and hip), on the mucous membrane of the glandular stomach and in the tonsils of the cecum. The kidneys are enlarged, from light gray to dark brown, with a clear pattern of filling the tubules and ureters with urates.
In a typical form, infectious bursitis is easily diagnosed by clinical and pathological signs. The early stages of the disease or atypical course can be established by laboratory research, which is based on the isolation of the virus, its identification, the detection of antibodies in the blood serum, and the formulation of a biological test on susceptible chickens.
In the differential diagnosis, it is first necessary to exclude infectious bronchitis, sulfonamide poisoning, mycotoxicosis, as well as Newcastle disease, nephrosis nephritis, lymphoid leukemia, Marek's disease, and fatty toxicoses.
Treatment and Prevention
For specific prophylaxis of IBD, vaccines are used, which can be divided into 4 types according to antigenic activity:
- Soft - from attenuated virus, not causing significant changes in the bursa. Effective in chickens that do not have maternal antibodies. Such vaccines are also used to reduce the pathogenicity of the field virus, when the disease is asymptomatic.
- Vaccines intermediate type of virus of moderate virulence. They are effective in conditions of acute outbreak of infection and in stationary disadvantaged farms, since such vaccines are able to form immunity in chickens with maternal antibodies and create the necessary protection in earlier periods. Intermediate vaccines include VirusWall against IBD from the strain "Winterfield 2512".
- Virulent vaccines from a weakly attenuated virus causing acute changes in the Fabric bag. These are “hot vaccines” that cause a clinical re-illness of the bird, but with less waste up to 2%. They are able to form immunity in chickens with maternal antibodies. The disadvantage of such vaccines is their pronounced residual virulence, the ability of vaccine viruses to persist in the environment and cause an immunosuppressive effect.
- Inactivated vaccines provide a more intense immunity in repairing young animals and chickens of the parent flock, which, thanks to maternal immunity in chickens, helps protect young birds from IBD disease in the early period of their life.