The cost benefit of vaccinating broiler flocks against subclinical infectious bursal disease

In an attempt to reduce economic losses due to subclinical infectious bursal disease (IBD), broilers reared in 23 houses known to have been infected with IBD virus were vaccinated with live, attenuated IBD virus vaccine at 20 days of age. Vaccination of either one, two or three consecutive flocks resulted in significant increases in net income and average bird weight, and in a decrease in mortality. An improvement in broiler performance was not restricted to vaccinated flocks, but was also apparent for at least 1 year following placing of the first vaccinated flock in subsequent flocks reared in the same houses.     

Improved performance in commercial broiler flocks with subclinical infectious bursal disease when fed diets containing increased concentrations of vitamin E

The economic effects of increased vitamin E supplementation in 79 commercial broiler flocks incorporating over 1.5 million birds was assessed. Approximately half of the flocks were fed on either a high (178 IU/kg) or normal (48 IU/kg) vitamin E-containing diet. In addition, in approximately half of the flocks subclinical infectious bursal disease (IBD) was present. Analysis of the performance data demonstrated that flocks with subclinical IBD were consistently worse (P< 0.001) for net income, feed conversion ratio and average weight per bird than flocks without the subclinical disease. The trial also indicated that the average net income of flocks with subclinical IBD and fed a high vitamin E-containing diet was 10% better (P < 0.05) than flocks with subclinical IBD and fed a normal vitamin E-containing diet. However, the trial also demonstrated that the difference between the average net income achieved by flocks without subclinical IBD and being fed on either a high or a normal vitamin E-containing diet was only 2% and not significantly different. It is suggested that the increased improved performance from high vitamin E-containing diets recorded in flocks with subclinical IBS is due to enhanced immunocompetence and increased resistance to disease. It is also suggested that under field conditions, high dietary inputs of vitamin E are most beneficial where there is a challenge to the host's defence system and significantly improved performance will occur more predictably under such conditions.     

Concurrent outbreak of staphylococcal pneumonia with infectious bursal disease in broiler chickens

Concurrent outbreak of staphylococcal pneumonia with infectious bursal disease (IBD) occurred in 29-day-old broiler chickens. The outbreak started after a flock of 279 birds was decongested by moving 121 birds to another pen. The birds were depressed and weak before death and carcasses were cyanotic. At necropsy, the lungs were dark red, congested and consolidated; the bursa of Fabricius (BF) was enlarged; the liver was pale and the intestinal mucosa was hyperaemic. Histopathological examination of the lungs, BF and liver revealed fibrinopurulent pneumonia, purulent inflammation of the BF and hepatic lipidosis, respectively. Staphylococcus aureus was isolated from the teased tissue of the lungs. The mortality was 35.8% within 5?days of the outbreak. The circumstances of the outbreak suggested that immunosuppression due to stress associated with crowding and transferring of the birds from one pen to another and poor seroconversion to previous infectious bursal disease virus vaccination, favoured the clinical establishment of the bacterial and IBD viral infections.     

Concurrence of nephrosis-nephritis due to infectious bronchitis virus and infectious bursal disease in broiler chickens

A condition showing nephrosis-nephritis caused by infectious bronchitis virus (IBV) and atrophy of the bursa of Fabricius attributable to infectious bursal disease virus (IBDV) occurred with a mortality rate of 6.4%, 7.4% and 8.5% in young broiler chickens in three flocks on a poultry farm. Eighteen birds from the outbreaks were studied histologically and ultra-structurally. Nephrosis-nephritis appeared initially as degenerative changes of the convoluted tubules, followed by inflammatory reactions in the affected parenchyma and interstitium. Virus particles similar to IBV were demonstrated in the epithelial cells and lumens of the convoluted tubules. The bursa of Fabricius revealed lesions characteristic of infectious bursal disease and virus particles identical to IBDV were found in the reticulo-epithelial cells of the follicles. Two-thirds of the birds examined had the same histological lesions in the larynx and trachea as those seen in infectious bronchitis. The possibility existed of a pathogenetic interaction between IBV and IBDV infections.     

An overview of infectious bursal disease

Infectious bursal disease (IBD) is a viral immunosuppressive disease of chickens attacking mainly an important lymphoid organ in birds [the bursa of Fabricius (BF)]. The emergence of new variant strains of the causative agent [infectious bursal disease virus (IBDV)] has made it more urgent to develop new vaccination strategies against IBD. One of these strategies is the use of recombinant vaccines (DNA and viral-vectored vaccines). Several studies have investigated the host immune response towards IBDV. This review will present a detailed background on the disease and its causative agent, accompanied by a summary of the most recent findings regarding the host immune response to IBDV infection and the use of recombinant vaccines against IBD.     

Immunosuppressive effect of infectious bursal disease virus on vaccination against infectious bronchitis

Groups of broiler chicks hatched with parental antibodies to infectious bursal disease virus (IBDV) and infectious bronchitis virus (IBV) were vaccinated against IBV at 1 day of age via the oculonasal routes and inoculated with virulent IBDV at 1, 5, 10, 15 or 20 days of age. While the non-IBDV inoculated birds were solidly immune against IBV challenge at an age of 29 days, immunity in the IBDV infected birds was depressed. This depression, which was most serious in the birds IBDV inoculated at 1 or 5 days of age, coincided with a delayed infiltration of the Harderian gland by lymphocytes and immunoglobulin-bearing cells. In the groups inoculated at older ages infiltration did not seem to be delayed but moderate destruction of plasma cells was observed 7 to 14 days later. The neutralisation index to IBV, which was significantly higher in the non-IBDV infected than in the infected birds at the day of challenge, increased sharply after challenge in the IBDV infected but not in the non-infected birds. All IBDV-inoculated birds developed typical lesions when 17 to 26 days old whereas precipitins reappeared when birds were 29 to 33 days old.     

Pathogenesis of infectious bursal disease in cyclophosphamide-treated chickens

Broiler chickens inoculated with cyctophosphamide showed atrophic bursae and severe immuno-suppression. Infectious bursal disease virus (IBDV) inoculation of the birds at 5 weeks of age caused neither clinical signs nor gross lesions. IBDV was re-isolated from some bursae samples. Cyclophosphamide non-treated (CYNT) chickens inoculated with IBDV showed bursal enlargement followed by atrophy. Examination of sections of the organ showed severe lymphocytic necrosis and depletion. IBDV was re-isolated from the bursa and spleen. The geometric mean titres of the IBDV serum neutralizing antibodies for infected cyclophosphamide treated (CYT) and CYNT chickens were 4.3 and 955.4, respectively. The above observations show that CYT chickens did not develop clinical IBD in the presence of infection and severe immunosuppression. They confirm the hypothesis that a healthy bursa is essential for the development of clinical IBD in chickens within the susceptible age range.     

Risk factors associated with the introduction of acute clinical infectious bursal disease among Danish broiler chickens in 1998

The objective of the present study was to investigate risk factors associated with the introduction of acute clinical infectious bursal disease (IBD) among Danish broiler chickens in 1998. Data on 218 flocks were collected from hatcheries, abattoirs, farmers and veterinarians; 49 of the flocks had experienced acute clinical IBD (cases), 169 were unexposed (controls). The study was carried out using a case-control design. Cases were defined as the first flock on each premises to experience acute clinical IBD, and these were compared with non-diseased, non-IBD-vaccinated control flocks chosen randomly from each unaffected farm. The resulting numbers of cases and controls used for statistical analyses were 16 and 61, respectively. Statistically significant associations were seen between the initial 16 Danish cases of acute clinical IBD in 1998 and certain hatcheries, age of parent birds and a certain feed mill.     

Genomic sequence analysis of a new reassortant infectious bursal disease virus from commercial broiler flocks in central China

We report the complete nucleotide sequence of a reassortant infectious bursal disease (IBD) virus (IBDV) HN isolate from commercial broiler flocks in central China. The genome consisted of 3,232 and 2,652 nucleotides in the coding regions of segments A and B, respectively. Alignment of both nucleotide and deduced amino acid sequences and phylogenetic analysis revealed that the genome segments A and B of HN were derived from the attenuated strain B87 and the VV strain OKYM. This is a new reassortant IBDV strain that has emerged in nature, involving segment A of a cell-culture-adapted attenuated vaccine strain B87.     

Isolation of infectious bursal disease virus from turkeys

A virus, which is morphologically identical and antigenically related to two previously known isolates of infectious bursal disease (IBD) virus, was isolated from pooled faeces of 6-week-old turkeys with diarrhoea. It is concluded that this virus, designated TY89, is an isolate of IBD virus. The isolation of TY89 was heavily dependent upon the use of electron microscopy and the immunofluorescence technique. Antibody to TY89 virus was detected by both indirect immunofluorescence and serum neutralisation tests in 28 of 95 (29%) sera collected from 20-week-old turkeys. The available evidence suggests that this virus has only recently been introduced into turkeys in Northern Ireland. It is believed that this is the first report of natural infection of turkeys with IBD virus.     

Comparison of vaccines against infectious bursal disease.

A comparative study was undertaken of 9 products from 7 different sources intended for use as vaccines against infectious bursal disease of chickens (IBD). A range of properties was found in laboratory tests for safety, efficacy and immunosuppressive effect. No vaccine caused clinical disease after administration to chicks at 7 days of age, but one caused a significant impairment of weight gain, and when given to day-old chicks caused some morbidity and deaths.Most vaccines affected the bursa of Fabricius and histological examination of this organ revealed varying degrees of tissue damage which correlated with the reduction in size of this organ. The effects with the different products ranged from no damage to damage almost as rapid and severe as that produced by a fully virulent field strain of the agent.Selected products which differed in their effect on the bursa were tested for their immunosuppressive properties by assessing the response to live Newcastle disease vaccine administered after the IBD vaccine. The effect on the response to Newcastle disease vaccine was found to be correlated with the degree of tissue damage.Variations in the ability of the vaccines to protect against IBD challenge were also found, but these did not depend on the degree of damage to the bursa.These studies enable proposals for standard tests for IBD vaccines to be formulated in respect of safety, potency and lack of immunosuppressive effect. Only 2 of the 9 vaccines tested satisfied these standards.     

Current status of vaccines against infectious bursal disease

Infectious bursal disease virus (IBDV) is the aetiological agent of the acute and highly contagious infectious bursal disease (IBD) or “Gumboro disease”. IBD is one of the economically most important diseases that affects commercially produced chickens worldwide. Along with strict hygiene management of poultry farms, vaccination programmes with inactivated and live attenuated viruses have been used to prevent IBD. Live vaccines show a different degree of attenuation; many of them may cause bursal atrophy and thus immunosuppression with poor immune response to vaccination against other pathogens and an increase in vulnerability to various types of infections as possible consequences. Depending on their intrinsic characteristics or on the vaccination procedures, some of the vaccines may not induce full protection against the very virulent IBDV strains and antigenic variants observed in the last three decades. As chickens are most susceptible to IBDV in their first weeks of life, active immunity to the virus has to be induced early after hatching. However, maternally derived IBDV-specific antibodies may interfere with early vaccination with live vaccines. Thus new technologies and second-generation vaccines including rationally designed and subunit vaccines have been developed. Recently, live viral vector vaccines have been licensed in several countries and are reaching the market. Here, the current status of IBD vaccines is discussed.     

Reassortant infectious bursal disease virus isolated in China

Infectious bursal disease virus (IBDV) is a bi-segmented, double-stranded RNA virus which belongs to the genus Avibirnavirus of the family Birnavirideae. In this study, we determined the complete nucleotide sequences of a reassortment IBDV strain TL2004 with segments A and B derived from attenuated and very virulent strains of IBDV. This strain is pathogenic to SPF-embryonated eggs and chickens, although it is not as virulent as very virulent strain. Genomic sequence in GenBank analysis showed that both types of natural genetic reassortment of infectious bursal disease virus emerged in China. Our findings, which strongly suggest genetic exchange between attenuated and very virulent strains of IBDV, emphasizes the risk of generating uncontrolled chimeric viruses by using live attenuated vaccines.     

Pathogenesis of infectious bursal disease in embryonally bursectomised chickens

Embryonally bursectomised and nonbursectomised chickens were infected with infectious bursal disease virus (IBDV) at 36 days of age. Neither clinical signs nor gross lesions were observed in the infected, bursectomised (IB) chickens. No significant changes were observed in carcass, thymus or spleen weights of IB and noninfected bursectomised chickens. A mild lymphocytic necrosis and depletion were found in the spleen, thymus and caecal tonsil of the IB chickens. Neither precipitating nor serum neutralising antibodies were detected in the sera but IBDV was reisolated from the spleen and thymus. Infected, nonbursectomised (IN) chickens developed severe depression with diarrhoea and high mortalities. Haemorrhages were found in the muscles of the breast and thigh, proventriculus and intestines. Significant changes were observed between the carcass, thymus and bursa weights of the IN and noninfected, nonbursectomised chickens. There was severe lymphatic necrosis of the bursa, thymus, spleen and caecal tonsil. Both precipitating and neutralising antibodies were detected in the sera and the virus was reisolated from the bursa, thymus and spleen. It is concluded that the bursa of Fabricius is not essential for the establishment of an IBDV infection but is required for the clinical infection.     

Identification of serotype ii infectious bursal disease virus proteins

Polyacrylamide gel electrophoresis (PAGE) of serotype II IBDV (OH and MO strains) purified from infected Vero cells resolved a previously undetected major viral polypeptide, VP2. The molecular weight (MW) of VP2 was different between the two strains of serotype II. It was 43.5 kDa in strain OH and 44 kDa in strain MO. This was higher than the MW of VP2 in SAL strain of serotype I IBDV which was 41 kDa. VPX (50 kDa), VP3 (33 kDa) and VP4 (30.5 kDa) were similar in both serotype II virus strains but were also of higher MW than VPX (48 kDa), VP3 (32 kDa) and VP4 (30 kDa) of SAL virus. VP1 (80 kDa) had the same MW in both serotypes.     

Rapid detection of infectious bursal disease antibodies by counterimmunoelectrophoresis

Counterimmunoelectrophoresis was used to detect infectious bursal disease virus-specific precipitating antibodies in chicken sera. The method was found to be sensitive, simple, reproducible and rapid - detecting precipitins after 45 min. Results could be read visually, without staining, and they compared favourably with results obtained with the agar-gel precipitation test.