Infectious bursal disease

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Medicina pediĂĄtrica en pequeĂąos animales

Presentation brochure



Infectious bursal disease

Author: Emmanuel Baraza Sasita. Co-authors: William Olaho-Mukani, Sabenzia

Nabalayo Wekesa, Romona Ndanyi, Messo Watson.

Format: 17 x 11 cm. Number of pages: 76. Binding: Wire-o.

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Atlas entirely dedicated to infectious bursal disease based on a practical and graphic approach of the topic. This handbook has been carried out by highly experienced authors closely involved with this disease in Africa, where its prevalence and incidence are significant. This updated work has been carefully developed including the most essential contents, so that it depicts a valuable tool to cope and control this virus as far as possible. On the other hand, many helpful tips and visual graphic resources (among other things, a distribution map worldwide and high quality images from characteristic macroscopic lesions) provided by the authors enrich and turn this atlas into a reference in its field. Furthermore, diagnosis and vaccination have been thoroughly explained, highlighting vaccination programmes and types of vaccines. The atlas format helps to make the contents understandable and affordable for the readers.


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Infectious bursal disease

Presentation of the book Infectious bursal disease (also known as Gumboro disease) is a highly contagious viral disease caused by a small, hardy Avibirnavirus belonging to the family Birnaviridae which causes significant economic losses due to mortality, reduced performance and immunosupression that lead to increased susceptibility to other diseases. The virus is resistant to a wide range of temperature and pH, although can be removed by most disinfectants. It is rapidly spread by direct contact between birds and can survive for extended periods of time on inanimate objects, contaminated feed, etc. Currently, the disease has a worldwide prevalence and therefore it is not completely controlled. It is essential to know its main features to minimise the great economic impact which represents for poultry farming. Thus, as veterinary surgeons have to face with this condition in their daily work, this handbook performs a thorough review where the authors, highly qualified and experienced in dealing with this disease, supply visual resources (images, tables, flowcharts, etc.) accompanied by short pieces of text to describe the topic in an understandable and simple way. Therefore, the information included in this handbook helps the veterinarians to get an overview of the topic so as to tackle it successfully day after day.


The author Emmanuel Baraza Sasita BSc, MSc, PhD (currently involved).

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Bachelor of Science in Biomedical Laboratory Technology and MSc in Molecular Biology and Biotechnology both from the Faculty of Veterinary Medicine of Makerere University. Currently, he is pursuing his PhD in virology. He has done recently a publication related to the prevalence of infectious bursal disease in local chickens around Kampala (Uganda). Besides, he works as academic writer, editor and reviewer. He works for academiaresearch based in USA as well as all writers based in UK. He reviews manuscripts with Microbiology Research International (www.netjournals.org). Currently, he is working in a project about contagious caprine pleuropneumonia at International Livestock Research Institute.


Infectious bursal disease

Co-authors William Olaho-Mukani BVM, MSc, PhD. EAC Regional Veterinary Governance Project Coordinator for the African Union. Member of the Editorial Board of the African Journal of Animal and Biomedical Sciences, Journal of Camel Practice and Research, the Bulletin of Animal Health and Production.

Sabenzia Nabalayo Wekesa BVM, MSc, PhD. Researcher and Senior Assistant Director of Veterinary Services (SADVS) in the ministry of Agriculture in Kenya, based at the National Foot and Mouth Disease (FMD) laboratory, Embakasi (Nairobi).

Romona Ndanyi BVM, MSc. Researcher at the Kabete Veterinary Research Laboratories, Kangemi (Nairobi).

Messo Watson BVM, MSc. Working in a fully integrated poultry company in East and Central Africa.


Communication services Web site Online visualisation of the sample chapter. Presentation brochure in PDF format. Author´s CV. Sample chapter compatible with iPad.

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Table of contents 1. Aetiology

3. Epidemiology

Overview

Distribution and persistence

IBD virus (IBDV)

Geographical distribution

Classification

Serological survey

Viral protein structure and function

IBD status

IBDV particle

New epidemiological situation

Genome

Morbidity and mortality

Gene expression

Characteristics in the environment

Replication

2. Importance

4. Pathology Type of birds at risk

History

Transmission

Current status in the world

Incubation period

Economic significance

Pathogenesis

Poultry production and its contributions

Potential risk of spread through trade

Effects on poultry Impact on food security How IBDV causes disease and death


5. Clinical signs

7. Prevention and control

Factors influencing disease severity

Disinfection

Clinical signs associated with acute disease

Vaccination

Classical form Immunosuppressive form Acute form What next after subclinical infection Relationship between clinical signs and diagnosis

6. Diagnosis and treatment Clinical and differential diagnosis Histological diagnosis Post-mortem examination Serological diagnosis Molecular identification and characterization Sampling

Vaccination programmes Routes of vaccine administration Categories of IBD vaccines Advices for vaccinating chickens

8. Actions to take Measures taken to reduce morbidity and mortality during an outbreak Recommended actions after an outbreak

9. References


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Aetiology

Infectious bursal disease

Viral protein structure and function » VP1: key role in virus particle encapsulation. » VP2: encodes major virus antigenic determinants.

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» VP3: intermediary which interacts with VP1 and VP2. » VP4: non-structural and minor polypeptide. » VP5: regulatory function.

AETIOLOGY

IBDV particle » Non-enveloped, single-shelled T = 13 icosahedral symmetry capsid (70 nm in diameter).

VP2 dsRNA A VP3

» 260 VP2 trimers with radial projections of spikes from the capsid.

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dsRNA B

» The pre-VP2 terminal derived cleavage peptides remain linked within the virion.

VP1/Vpg

» VP3 forms a ribonucleoprotein complex with the genomic RNA. Few VP1 are as well incorporated in the virion.

T = 13

Figure 3. IBDV structure (Swiss Institute of Bioinformatics, 2009).


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Epidemiology

Infectious bursal disease

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Acute and immunosuppressive forms reported. Immunosuppressive form reported.

Figure 12. Worldwide geographical distribution of IBDV (Van Den Berg, 2000).

EPIDEMIOLOGY

Serological survey Serological surveys

Acquired through

Passively trasmitted to offspring 25

High IBDV antibodies in breeder flocks

Vaccination or subclinical infection

Protect against clinical disease


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Epidemiology

Infectious bursal disease

IBD status Before 1987

After 1987

Most parts of the world

Vaccine failures

Subclinical

Highly contagious

Subclinical

Controlled by vaccination

Less than 5 % mortality

Slight increase in mortality

Incriminated strains

Imunosuppression

Highly contagious

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Up to 60 % (layers) and 20 % (broilers) mortality

Specific mortality

EPIDEMIOLOGY

New epidemiological situation USA

Important antigenic variation

Slight increase in virulence

No strict import controls 27

Antigenic and molecular characterization

Europe and Asia

Classical serotype 1 strains

Marked increase in pathogenicity

Strict import controls

Japan

Hypervirulent

Highly pathogenic

Strict import control


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Clinical signs

Infectious bursal disease

Relationship between clinical signs and diagnosis » Clinical disease is normally diagnosed by combining post-mortem lesions and clinical signs.

» Laboratory confirmation of disease or subclinical infection detection can be un-

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dertaken by humoral immune response demonstration in unvaccinated chickens or by detecting the viral genome or viral antigen in tissues.

» Histological examination of the bursa may be helpful when these tests are absent.

CLINICAL SIGNS

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Figure 22. Haemorrhages in the muscles of 7-weeks-old broiler chicken.


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Diagnosis and treatment

Infectious bursal disease

Histological diagnosis » Based on modifications detected in the bursa. » The capacity of causing histological lesions in non-bursal lymphoid organs, like the spleen, bone marrow or thymus (Inoue et al., 1994) is considered a potential characteristic of hypervirulent IBDV strains.

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» The histological approach is advantageous because it is possible to diagnose both the subclinical or chronic and acute forms of the disease.

DIAGNOSIS AND TREATMENT

Post-mortem examination » Pathological changes vary due to the disease severity as well as secondary infections or other diseases, but generally it is found enlarged bursa of Fabricius with yellowish oedema (most important), probably haemorrhages that vary from small haemorrhages to completely “cherry red” bursas.

Figure 24. Enlarged bursa.

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Diagnosis and treatment

Infectious bursal disease

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Figure 25. Haemorrhages in the gizzard.

Figure 26. Congested proventriculus.

DIAGNOSIS AND TREATMENT

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Figure 27. Petechial haemorrhages in the muscle.

Figure 28. Echymotic haemorrhages in the muscle.


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Prevention and control

Infectious bursal disease

Table 2. Characteristics of ideal, killed and live vaccines. Ideal Vaccine Easy delivery system such as oral Easy to be manufactured

Vaccine type

Live vaccine (attenuated strain)

Killed vaccine

Immune complex and recombinant vector vaccine Summary

Good immunity at all ages Affordable

Advantages

Long-lasting protection

Disadvantages

Admin. route

Mild vaccine causes limited bursa damage None cause immunosuppression in over 14 days old birds

Intermediate plus causes lymphoid depletion in the

hatched from IBD immune parents Intermediate plus are able to overcome low MDA levels Long-lasting protection Fewer doses needed Production of humoral plus cellular immunity

May revert to pathogenicity but rarely Its production is very complex Might be more reactogenic

Able to stimulate uniform and high antibody levels in parent

They must be used in chickens sensitised by primary

chickens so that the progeny will have high and uniform MDA levels Will not revert or multiply to pathogenicity Easier to produce

exposure, either live vaccine or field virus Requires multidose (booster) series for full protection Low production of cellular immunity

Manufactured in oil emulsion adjuvant and given by injection

Standardised production and appropriate field stability can

Theoretical safety risks (oncogenesis, autoimmunity) Not easily produced for multigene products such as

Subcuteneous route

be predicted Production of cellular plus humoral immunity

Spray or DW

bursa

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carbohydrate capsular antigen

High MDA levels can be generated in breeder birds by giving live vaccine at about 3-4 weeks of age, followed by killed vaccine at about 12-14 weeks of age

PREVENTION AND CONTROL

Advices for vaccinating chickens » Attempt to prevent mixing chickens derived from different flock parent stock flocks, with different immunity levels against IBD.

» When given in the DW: it is critical to use appropriate quality of DW and properly cleaned drinkers to avoid virus neutralization.

» Allow the birds become thirsty for a while, and then give enough DW containing the vaccine for 1-2 hours.

» To check the DW vaccination technique, water soluble dyes could be used. » Skimmed milk powder of 2 % could be added to the water to keep the vaccine (virus) stable in the water and not to lose its antigenic properties (before the vaccine vial has been opened).

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