A comprehensive review of viruses in terrestrial animals from the Caribbean islands of Greater and Lesser Antilles

Viruses pose a major threat to animal health worldwide, causing significant mortalities and morbidities in livestock, companion animals and wildlife, with adverse implications on human health, livelihoods, food safety and security, regional/national economies, and biodiversity. The Greater and Lesser Antilles consist of a cluster of islands between the North and South Americas and is habitat to a wide variety of animal species. This review is the first to put together decades of information on different viruses circulating in companion animals, livestock, and wildlife from the Caribbean islands of Greater and Lesser Antilles. Although animal viral diseases have been documented in the Caribbean region since the 1940s, we found that studies on different animal viruses are limited, inconsistent, and scattered. Furthermore, a significant number of the reports were based on serological assays, yielding preliminary data. The available information was assessed to identify knowledge gaps and limitations, and accordingly, recommendations were made, with the overall goal to improve animal health and production, and combat zoonoses in the region. This article is protected by copyright. All rights reserved.

Characterization of the highly immunogenic VP2 protrusion domain as a diagnostic antigen for members of Birnaviridae family

Birnaviridae is a family of viruses (birnaviruses) which consists of four genera, members of which cause diseases in fish, birds, mollusks, and insects. The genome of birnaviruses encodes the highly immunogenic VP2 capsid protein. In order to demonstrate that the VP2 protein can be exploited as a diagnostic antigen for birnaviruses, we developed a lateral flow assay based on the surface-exposed VP2 protrusion domain of a representative birnavirus, infectious bursal disease virus (IBDV) of serotype 1 which causes the highly devastating infectious bursal disease in chickens. The biophysical characterization of the purified domain reveals that the domain predominantly consists of β-sheets, exists in a trimeric form, and remains folded at high temperatures, making it suitable for diagnostic purposes. Owing to its highly immunogenic nature and excellent biophysical properties, we employed the VP2 protrusion domain in a gold nanoparticle-based lateral flow assay for rapid detection of anti-IBDV antibodies in serum samples of infected chickens. Our results indicate that the domain binds anti-IBDV antibodies with high specificity during laboratory testing and on-site testing. The lateral flow assay reported here yields comparable results in a qualitative manner as obtained through a commercial enzyme-linked immunosorbent assay (ELISA). As VP2 is a common capsid protein of birnaviruses, the lateral flow assay can be generalized for other birnaviruses, and members of Tetraviridae and Nodaviridae families which contain homologous VP2 capsid proteins.

New oligonucleotide microarray for rapid diagnosis of avian viral diseases

BACKGROUND

We developed a new oligonucleotide microarray comprising 16 identical subarrays for simultaneous rapid detection of avian viruses: avian influenza virus (AIV), Newcastle disease virus (NDV), infection bronchitis virus (IBV), and infectious bursal disease virus (IBDV) in single- and mixed-virus infections. The objective of the study was to develop an oligonucleotide microarray for rapid diagnosis of avian diseases that would be used in the course of mass analysis for routine epidemiological surveillance owing to its ability to test one specimen for several infections.

METHODS AND RESULTS

The paper describes the technique for rapid and simultaneous diagnosis of avian diseases such as avian influenza, Newcastle disease, infectious bronchitis and infectious bursal disease with use of oligonucleotide microarray, conditions for hybridization of fluorescent-labelled viral cDNA on the microarray and its specificity tested with use of AIV, NDV, IBV, IBDV strains as well as biomaterials from poultry. Sensitivity and specificity of the developed microarray was evaluated with use of 122 specimens of biological material: 44 cloacal swabs from sick birds and 78 tissue specimens from dead wild and domestic birds, as well as with use of 15 AIV, NDV, IBV and IBDV strains, different in their origin, epidemiological and biological characteristics (RIBSP Microbial Collection). This microarray demonstrates high diagnostic sensitivity (99.16% within 95% CI limits 97.36-100%) and specificity (100%). Specificity of the developed technique was confirmed by direct sequencing of NP and M (AIV), VP2 (IBDV), S1 (IBV), NP (NDV) gene fragments.

CONCLUSION

Diagnostic effectiveness of the developed DNA microarray is 99.18% and therefore it can be used in mass survey for specific detection of AIV, NDV, IBV and IBDV circulating in the region in the course of epidemiological surveillance. Rather simple method for rapid diagnosis of avian viral diseases that several times shortens duration of assay versus classical diagnostic methods is proposed.

Simultaneous detection of eight immunosuppressive chicken viruses using a GeXP analyser-based multiplex PCR assay

BACKGROUND

Immunosuppressive viruses are frequently found as co-infections in the chicken industry, potentially causing serious economic losses. Because traditional molecular biology methods have limited detection ability, a rapid, high-throughput method for the differential diagnosis of these viruses is needed. The objective of this study is to develop a GenomeLab Gene Expression Profiler Analyser-based multiplex PCR method (GeXP-multiplex PCR) for simultaneous detection of eight immunosuppressive chicken viruses.

RESULTS

Using chimeric primers, eight such viruses, including Marek's disease virus (MDV), three subgroups of avian leucosis virus (ALV-A/B/J), reticuloendotheliosis virus (REV), infectious bursal disease virus (IBDV), chicken infectious anaemia virus (CIAV) and avian reovirus (ARV), were amplified and identified by their respective amplicon sizes. The specificity and sensitivity of the optimised GeXP-multiplex PCR assay were evaluated, and the data demonstrated that this technique could selectively amplify these eight viruses at a sensitivity of 100 copies/20 μl when all eight viruses were present. Among 300 examined clinical specimens, 190 were found to be positive for immunosuppressive viruses according to this novel assay.

CONCLUSION

The GeXP-multiplex PCR assay is a high-throughput, sensitive and specific method for the detection of eight immunosuppressive viruses and can be used for differential diagnosis and molecular epidemiological surveys.

An in vivo experimental model to determine antigenic variations among infectious bursal disease viruses

Infectious bursal disease virus (IBDV) is a double-stranded RNA virus causing infectious bursal disease in chickens. IBDV undergoes antigenic drift, so characterizing the antigenicity of IBDV plays an important role for identification and selection of vaccine candidates. In this study, an in vivo experimental model was developed to differentiate a new antigenic variant of IBDV. To this end, a hyper-immune serum to IBDV E/Del-type virus was generated in specific pathogen-free chickens and a standard volume of the hyper-immune serum was serially diluted and injected in specific pathogen-free birds via intravenous, subcutaneous, or intramuscular routes. The chickens were bled at different time points in order to evaluate the dynamics of virus neutralization titres. Based on the results, chickens were injected with different serum dilutions by the subcutaneous route. Twenty-four hours later, chickens were bled and then challenged with 100 median chicken infectious doses of the E/Del virus and a new IBDV variant. Chickens were euthanized at 7 days post infection and the bursa of Fabricius was removed for microscopic evaluation to determine the bursal lesion score. The determined virus neutralization titre along with the bursal lesion score was used to determine the breakthrough titre in the in vivo chicken model. Based on the data obtained, an antigenic subtype of IBDV was identified and determined to be different from E/Del. This model is a sensitive model for determination of IBDV antigenicity of non-tissue culture adapted IBDV.

Detection of infectious bursal disease virus isolates with unknown antigenic properties by reverse genetics

Infectious bursal disease virus (IBDV) serotype 1 is the causative agent of a highly contagious immunosuppressive disease of young chickens. In the past, a number of antigenic, as well as pathogenic, subtypes have been described. The determination of the antigenic makeup of circulating strains is of vital interest to the poultry industry because changes in the antigenicity of circulating field strains have an impact on the use of vaccines. To obtain a more comprehensive overview of the relationship between the nucleotide and amino acid sequence and the antigenic makeup of field isolates, a system based on reverse genetics of IBDV was established. Using this approach, a database for field isolates from three different states in the United States (Georgia, Alabama, and Louisiana), consisting of nucleotide sequence, amino acid sequence, and a reaction pattern based on a panel of monoclonal antibodies, was established. The obtained results showed that phylogenic analysis, which is based on the similarity of sequences, would lead to false conclusions regarding a possible antigenic makeup of the particular isolate. Sequences of field samples were divided into three groups: 1) those that grouped with variant strain E/Del sequences but were antigenically different, 2) those that did not group with sequences of E/Del but were similar in their antigenic makeup, and 3) those that did not group with E/Del sequences and were antigenically different. In addition, using the reverse-genetics approach, a number of field isolates showed no reactivity with any of the used monoclonal antibodies, indicating that an unknown, antigenic subtype of IBDV serotype 1 is circulating in the field.

Molecular characterization of field isolates and vaccine strains of infectious bursal disease virus

The present investigation was conducted to study the genetic heterogenicity and molecular polymorphism among the field isolates and vaccine strains of infectious bursal disease virus (IBDV). Samples of bursa of Fabricius from 15 suspected outbreaks of infectious bursal disease (IBD) were subjected to agar gel precipitation test (AGPT), virus isolation and reverse transcription-polymerase chain reaction (RT-PCR) combined with restriction fragment length polymorphism (RFLP). Nine out of 15 samples were found positive in AGPT while 14 were found positive both by virus isolation and RT-PCR. PCR amplified 474bp fragment from the variable region of VP2. Sac I, Stu I, Alu I, Ssp I and Mbo I restriction enzymes were used for characterization of all the 14 IBDV isolates and four reference vaccine strains. Sac I, Stu I, Alu I and Ssp I could differentiate classical virulent IBD (cvIBD) vaccine virus strains from very virulent IBD (vvIBD) field isolates by their varying restriction patterns. Based on above results two field isolates (VPL and VMK) were placed in cvIBD virus group and 12 field isolates were placed in vvIBD virus group. Virus neutralisation test (VNT) using rabbit raised Georgia strain anti-serum, however, could not differentiate between cvIBD virus and vvIBD virus. It was concluded that RT-PCR combined with RFLP assay using restriction enzymes Sac I, Stu I, Alu I and Ssp I can be used for rapid differentiation and classification of field isolates of IBDV.

Molecular characterization of Indian isolates of infectious bursal disease virus from broiler chickens

The present study was undertaken to characterize recent field isolates of infectious bursal disease virus (IBDV) by reverse transcription-polymerase chain reaction (RT-PCR) and partial sequencing of VP2 gene. The virus could be detected in 17 of 20 field samples from broiler chickens in Haryana state, India as well as in all the four vaccine strains. Nucleotide sequences of four field isolates and one vaccine strain were compared with 10 reported IBDV strains from different parts of the world. Nucleotide substitutions at 795G, 827T, 833C, 857C, 897A, 905T, 908T, 1011A and 1094G specific for very virulent (vv) strains, were maintained in all the four field isolates. However, unique nucleotide substitutions at 806A-G, 851 C-T, 1010 T-C, 1019T-C and 1082T-C showed further divergence of these isolates from already reported vvIBDVs. Deduced amino acid substitutions at 222P-A, 256V-I, 279N-D, 294L-I and 299N-S specific for vvIBDV strains were also present in all the four isolates. The vaccine strain showed amino acid change 279D-N, a characteristic of attenuated vaccine strains. Phylogenetic analysis showed that all the field isolates in the present study were closely related to reported UK (UK661) and Japan (OKYM) field isolates. All the four field IBDV strains of the present study were closely related to each other but distinct from already reported vvIBDVs of India. On the basis of nucleotide sequencing and phylogenetic analysis, it is very likely that IBD causing strains in this part of India are of very virulent character and are still undergoing changes at genetic level.

Molecular characteristics of infectious bursal disease viruses from asymptomatic broiler flocks in Europe

Infectious bursal disease virus (IBDV) exists in several different antigenic and pathogenic forms. The immune suppression caused by this virus in young chickens is not always associated with clinical signs of disease. The antigenic variant viruses originally described in the United States typically do not cause clinical signs of disease but can cause a marked immune suppression via the destruction of B lymphocytes. Using a reverse transcription-polymerase chain reaction (RT-PCR) assay we conducted a survey of asymptomatic broiler chicken flocks in Europe for IBDV. Restriction fragment length polymorphisms in the viral protein 2 (VP2) gene of four isolates from Spain and four isolates from France indicated they may be different from the classic and very virulent (vv) IBDV strains found throughout Europe. Nucleotide sequence and phylogenetic analysis of the hypervariable region of the VP2 gene indicated that all eight viruses were more similar to U.S. variant viruses than classic viruses. In two viruses, one from France and one from Spain, threonine was observed at amino acid position 222 and serine was found at position 254. These two substitution mutations are characteristic of Delaware variant viruses. In addition, all eight viruses had mutated amino acid position 318 from glycine to aspartic acid, another substitution mutation commonly found in U.S. variant viruses. Although importation restrictions prevented us from directly testing the antigenicity of these viruses, their nucleotide and predicted amino acid sequences suggest they could be antigenically distinctive compared to classic and vvIBDV commonly found in Europe. Confirmation of the presence of antigenic variant IBDV strains in Europe requires additional immunologic studies to elucidate the exact nature of the viral epitopes. Our data support the need for these immunologic studies.

Restriction fragment length polymorphism typing of infectious bursal disease virus field strains in Turkey

Infectious bursal disease (IBD), also known as Gumboro disease, is a highly contagious, immunosuppressive disease of immature chickens. It is caused by IBD virus (IBDV) and is responsible for major economic losses in the poultry industry worldwide. In this study, 280 bursa samples from 56 commercially reared chicken flocks in Turkey with clinical symptoms of IBD were examined for IBDVs using the reverse transcription (RT)-polymerase chain reaction (PCR)/restriction fragment length polymorphism (RFLP) assay. The assay was conducted on a 743-bp fragment of the VP2 gene with the restriction enzymes BstNI, MboI, and SspI. The results indicate the existence of field isolates with new molecular patterns different from those previously published that may well be unique and specific to geographical regions.

Comparison of Sybr Green I, ELISA and conventional agarose gel-based PCR in the detection of infectious bursal disease virus

The current available molecular method to detect infectious bursal disease virus (IBDV) is by reverse transcriptase-polymerase chain reaction (RT-PCR). However, the conventional PCR is time consuming, prone to error and less sensitive. In this study, the performances of Sybr Green I real-time PCR, enzyme-linked immunosorbent assay (ELISA) and conventional agarose detection methods in detecting specific IBDV PCR products were compared. We found the real-time PCR was at least 10 times more sensitive than ELISA detection method with a detection limit of 0.25pg. The latter was also at least 10 times more sensitive than agarose gel electrophoresis detection method. The developed assay detects both very virulent and vaccine strains of IBDV but not other RNA viruses such as Newcastle disease virus and infectious bronchitis virus. Hence, Sybr Green I-based real-time PCR is a highly sensitive assay for the detection of IBDV.

Detection of Infectious Bursal Disease Virus in Various Lymphoid Tissues of Experimentally Infected Specific Pathogen Free Chickens by Different Reverse Transcription Polymerase Chain Reaction Assays

Infectious bursal disease (IBD) is a worldwide distributed immunosuppressive viral disease in young chickens, controlled by vaccination. Emergence of several strains of IBD virus (IBDV) has created a demand for strain-specific diagnostic tools. In the present experiment, five different reverse transcription polymerase chain reaction (RT-PCR) assays, including two recently developed strain-specific assays, were employed for detection of ribonucleic acid (RNA) from three different IBDV strains in bursa tissue samples from experimentally infected specific pathogen free chickens. The virus strains included vaccine strain D78, classical strain Faragher 52/70, and the very virulent Danish strain DK01. The presence of the virus infection was confirmed by histopathologic evaluation of bursa lesions. The largest number of positive samples was obtained with a strain-specific two-step multiplex (MPX) RT-PCR assay based on iScript enzyme, and the commercially available Qiagen one-step RT-PCR. Between these methods, agreement was obtained for 57 of 59 samples. Because the Qiagen one-step RT-PCR assay was suggested as the more sensitive of these two assays, it was used for detection of IBDV in bone marrow, spleen, thymus, and cecal tonsils from experimentally infected chickens. The identity of the virus strains involved was confirmed by MPX RT-PCR. In conclusion, the MPX RT-PCR represented a reliable assay for detection and differentiation of IBDV strains in selected lymphoid tissues of chickens. All three of the IBDV strains used were detected in bursa tissues, whereas only the two virulent strains were detected in bone marrow, spleen, and thymus.

Development of a multiplex PCR for detection of avian adenovirus, avian reovirus, infectious bursal disease virus, and chicken anemia virus

A multiplex polymerase chain reaction (mPCR) was developed and optimized for the simultaneous detection and differentiation of avian reovirus (ARV), avian adenovirus group I (AAV-I), infectious bursal disease virus (IBDV), and chicken anemia virus (CAV). Four sets of specific oligonucleotide primers were used in this test for ARV, AAV-I, IBDV, and CAV. The mPCR DNA products were visualized by gel electrophoresis and consisted of fragments of 365 bp for IBDV, 421 bp for AAV-I, 532 bp for ARV, and 676 bp for CAV. The mPCR assay developed in this study was found to be sensitive and specific. Detection of PCR-amplified DNA products was 100 pg for both CAV and IBDV, and 10pg for both ARV and AAV-I and this mPCR did not amplify nucleic acids from the other avian pathogens tested. The mPCR demonstrated similar sensitivity in tests using experimental fecal cloacal swab specimens that were spiked with ARV, AAV-1, IBDV, and CAV, and taken from specific pathogen free (SPF) chickens. This mPCR detected and differentiated various combinations of RNA/DNA templates from ARV, AAV-I, CAV, and IBDV without reduction of amplification from feces.

Viral Genotyping of Infectious Bursal Disease Viruses Isolated from the 2002 Acute Outbreak in Spain and Comparison with Previous Isolates

An infectious bursal disease (IBD) outbreak occurred in the east region of Spain in the spring of 2002 and rapidly spread thorough the whole country, although proper vaccination programs were applied. In this report, 33 infectious bursal disease viruses (IBDVs) isolated from this outbreak were characterized by nucleotide sequencing of the VP2 gene hypervariable region and were compared with reference IBD strains and the 1990s Spanish IBDVs in order to determine possible emergence of IBDV isolates with modified antigenic or virulent properties. Moreover, histopathologic and immunohistochemical studies of those cases where bursal tissues were available were carried out. Of the 33 isolates, 23 were identified as very virulent IBDVs (vvIBDVs), whereas the other 10 isolates were classified as attenuated or intermediate virulence classical strains and could possibly be IBDV live vaccine strains used in the immunization of these chickens. Results of this study indicate that wIBDV isolates from the 2002 Spanish outbreak are closely related with those from the 1990s outbreak. However, acute IBD cases have not been reported in Spain during these 10 yr. Genetic, management, and environmental factors likely related with IBD reemergence in Spain are discussed. Moreover, our results indicate that good correlation exists between the IBDV subtype present in the field and the degree of lesions in bursa tissue, as well as the immunohistochemistry staining.

A very virulent genotype of infectious bursal disease virus predominantly associated with recurrent infectious bursal disease outbreaks in Tunisian vaccinated flocks

Outbreaks of infectious bursal disease (IBD) still continue to afflict the Tunisian poultry industry even in those flocks where the vaccination program is strictly applied. To characterize the viruses that circumvent protection provided by vaccination, field isolates of infectious bursal disease virus (IBDV) obtained from vaccinated flocks that have repeatedly experienced IBDV outbreak episodes were analyzed from bursal samples by reverse transcription coupled with polymerase chain reaction and dideoxynucleotide sequencing of the VP2 hypervariable region. Although sequence data were obtained from samples collected from three distinct flocks over a period of 3 years, only limited sequence variation has been observed. The few nucleotide changes were silent and the deduced amino acid sequences were identical. Thus, the virus population that predominates in the field seems to represent a homogeneous antigenic pool. Compared with the VP2 sequences of several IBDV strains, this predominant pool was found to be closely related to the very virulent (vv) IBDV viruses described in Europe and Asia. Sequence and phylogenetic analysis of the precursor polyprotein coding sequence of a representative Tunisian isolate further confirmed its assignment to the vv genotype. The deduced amino acid sequence of the whole polyprotein of the Tunisian isolate was found to be identical to a South Korean IBDV strain. Alignment of the polyprotein amino acid sequence of 35 IBDV strains identified additional mutations outside the VP2 variable domain and which occur frequently in vv strains. Based on this comparative analysis, the set of amino acid residues that should represent a typical vv profile involves Ala222, Ile242, Ile256, Ile294, Leu451, Tyr680, N685, Ser715, Asp751, Val990, and Ala1005. Such a combination of amino acid changes was observed for the majority of vvIBDV strains that define a distinct phylogroup.

Identification of Soybean mosaic virus Strains by RT-PCR/RFLP Analysis of Cylindrical Inclusion Coding Region

A reverse-transcriptase polymerase chain reaction/restriction fragment length polymorphism (RT-PCR/RFLP) was employed successfully for detection and identification of Soybean mosaic virus (SMV) strains. A primer pair amplifying a 1,385-bp fragment of the cylindrical inclusion (CI) coding region was used for RT-PCR and the RFLP profiles of the RT-PCR products were compared after restriction digestion with RsaI, EcoRI, or AccI restriction endonucleases. These enzymes were chosen based on the nucleotide sequences of SMV strains G2, G5, G5H, G7, and G7H in the CI coding region. These five strains, as well as seedborne SMV isolates from local soybean cultivars, could be differentiated by RT-PCR/RFLP analysis. The results correlated well with strain identification by symptom phenotypes produced on differential cultivars inoculated with strains and isolates. The sensitivity of RT-PCR enabled detection of SMV from plants with necrotic symptoms in which the number of virus particles was too low to be detected by enzyme-linked immunosorbent assay.

Characterization of Egyptian Field Strains of Infectious Bursal Disease Virus

The reverse transcriptase-polymerase chain reaction/restriction fragment length polymorphism (RT-PCR/RFLP) technique was used for identification and characterization of Egyptian field strains of infectious bursal disease viruses (IBDVs) that caused severe outbreaks with (30%-60%) mortality rate. Twenty-four bursal samples collected from 24 field outbreaks in commercially reared chicken flocks experiencing signs typical of infectious bursal disease (IBD) were used. Ten of the bursal samples examined were determined to contain IBDV as evidenced by amplification of a 743-bp region of the VP2 gene of IBDV by RT-PCR. The RT-PCR products of the detected viruses were characterized by digestion with three restriction enzymes, BstN, MboI, and SpI. Three different RT-PCR/RFLP profiles were observed. Seven of the detected viruses had RFLP profiles identical to the very virulent European strains of IBDV (vvIBDVs). One virus had a RFLP profile identical to the U.S. classic vaccine strain, and one virus had a unique RFLP profile. The clinical history of the outbreaks and the presence of the SspI site in the 743-bp RT-PCR fragment were the criteria for designating the viruses as belonging to the very virulent (vv) phenotype.

Differentiation of infectious bursal disease viruses isolated in Croatia

Infectious bursal disease viruses (IBDVs) in 26 IBDV-positive bursa samples collected in Croatia during the period 1996-2000 and in two commercially available vaccines were differentiated by the presence or absence of the CfoI, SacI, SspI, StuI, and TaqI restriction sites in the 422-bp fragment of segment A of the VP2 gene (nt 732-1153). The fragments from 14 (54%) field isolates were TaqI+ StuI+ SspI+ and SacI- CfoI-, indicating their very virulent (vv) character. The presence of CfoI restriction site in 10 (38%) field isolates is uncommon for vvIBDV strains. It was detected in only the 88180 vvIBDV strain. Nevertheless, these isolates can be classified as vv strains according to TaqI+ StuI+ SspI+ SacI- restrictions. Two SacI+ StuI+ CfoI+ TaqI- SspI- field isolates (8%) could be classified as non-vvIBDVs. The StuI+ restriction is common to vvIBDV strains. However, the StuI recognition sequence is present in the F52/70 classic European and 002-73 attenuated strains as well. The SacI+ CfoI+ StuI- SspI- restrictions and the lack of the TaqI restriction at nt position 832 show that the IBDV in GUMBOKAL IM-SPF vaccine corresponds to the attenuated and/or vaccine strains. The TaqI restriction at nt position 875 suggests that the IBDV in GUMBOKAL SPF vaccine could belong to the mild strains.

Molecular characterization of infectious bursal disease virus from commercial poultry in the United States and Latin America

From June 1999 to September 2001, 216 bursal samples from broiler farms in the United States and from countries of Latin America were submitted to the Poultry Diagnostic and Research Center at the University of Georgia for the purpose of genotyping field infectious bursal disease viruses (IBDVs). The reverse transcriptase-polymerase chain reaction (RT-PCR) was used to amplify a 248-bp product, encompassing the hypervariable region of VP2 gene. The genotyping was conducted by restriction fragment length polymorphism (RFLP) analysis with six restriction endonucleases, DraI, SacI, TaqI, Sty, BstNI, and SspI. For the 150 samples received from the United States, 125 samples (83.3%) were RT-PCR positive for the presence of IBDV. One hundred positive samples (80%) had RFLP identical to the variant Delaware E strain, whereas 10 samples (8.0%) exhibited a RFLP pattern similar to this antigenic variant. Other IBDV strains such as Grayson Laboratory strain (GLS), Lukert, PBG-98, Delaware A, and the vaccine strains Sal-1 and D-78 were also detected. Two samples exhibited a pattern similar to the standard challenge (STC) strain, and seven strains (5.6%) were not classified by RFLP. Sixty-six bursal samples previously inactivated with phenol were received from Latin American countries. IBDV strains with analyzed genotypes similar to the Lukert strain were predominantly detected in Mexico. IBDV strains similar to variant E were detected in Colombia and Ecuador. Peru and Venezuela exhibited a higher heterogeneity of IBDV strains due to the detection of classic Delaware type as well as GLS variant strains. IBDV strains detected from Brazil and Dominican Republic exhibited RFLP patterns identical to very virulent IBDV strains prevalent in several countries in Europe, Asia, and Africa.

Restriction fragment length polymorphism analysis of the VP2 gene of Australian strains of infectious bursal disease virus

Twenty-four Australian strains of infectious bursal disease virus (IBDV) were characterized by reverse transcription/polymerase chain reaction-restriction fragment length polymorphism and compared with previously published overseas strains. A primer pair designed to amplify a 743 base pair fragment of the VP2 gene was used and restriction fragment length polymorphism profiles were determined for each strain using three restriction enzymes, Bst NI, MboI and SspI. Australian strains comprised 12 molecular groups that were unique and distinct from overseas IBDV strains. A specific SspI site that is used to predict a very virulent IBDV phenotype was absent from all Australian strains, contrary to a previous finding by Jackwood and Sommer (1999). One Australian strain (N1/99) contained an SspI site; however, this was located at a different position than that found in very virulent IBDV strains. The results demonstrate that restriction fragment length polymorphism can be used to rapidly differentiate Australian IBDV strains from overseas strains. However, the existence of a large number of molecular groups might preclude its effectiveness for inter-strain differentiation.

Molecular characterization of Spanish infectious bursal disease virus field isolates

Nine Spanish isolates of infectious bursal disease virus (IBDV) were characterized and classified after reverse transcriptase-polymerase chain reaction of a 248-bp fragment of the VP2 gene hypervariable region and restriction fragment length polymorphism (RFLP). The restriction endonucleases (REs) used were BstNI, Sad, SspI, TaqI, DraI, and StyI. Sequencing of the amplified product and further comparison of these sequences with published sequence data from other IBDV strains were also performed. Very virulent and classic strains were identified. None of the strains identified had molecular characteristics similar to that of the American variant strains. Four very virulent strains (VG-248, 5939, 6145, and 7333) were digested by the TaqI, SspI, and StyI enzymes. The sequences of these strains were closely related to other European and Japanese very virulent IBDV (vvIBDV) strains. Strains VG-311, VG-262, and VG-208 were digested by the BstNI and Sad REs and were classified as classic strains. Strains VG-276 and VG-313 had unique RFLP patterns. VG-276 exhibited the SspI RE site, which has been reported as a characteristic of vvIBDV strains, whereas the VG-313 strain exhibited a Sad and StyI RE site indicative of the classic IBDV Edgar and 52-70 strains. However, nucleotide sequence analysis of the amplified hypervariable region strain VG-276 revealed a higher identity with the classic strains STC, 52/70, and 9109 IBDV strains, whereas strain VG-313 exhibited a higher identity with the vvIBDV strains.

Detection of infectious bursal disease virus in different lymphoid organs by single-step reverse transcription polymerase chain reaction and microplate hybridization assay

A rapid and sensitive method for the detection of infectious bursal disease virus (IBDV) RNA in different chicken lymphoid organs was developed. The method is based on a single-step reverse transcription polymerase chain reaction (RT-PCR) procedure and the enzyme-linked immunosorbent assay (ELISA) detection method of amplified products. Vaccinal IBDV strain and field isolates were used for the optimization of RT-PCR and for the determination of conditions for microplate hybridization and colorimetric detection of the amplicons. With this method, viral RNA could be detected in various stages of infection in samples of different lymphoid organs. Bursas and cecal tonsils were suitable organs for viral RNA detection at different times during IBDV infection. The RT-PCR/ELISA method can be applied for IBDV detection in routine diagnostic tests, which are not usually carried out because of the difficulties involved in isolating the virus.

Measuring infectious bursal disease virus RNA in blood by multiplex real-time quantitative RT-PCR

A quantitative reverse transcription polymerase chain reaction (RT-PCR) protocol for assessing infectious bursal disease virus (IBDV) RNA levels in blood was developed using the ABI PRISM 7700 Sequence Detection System coupled with TaqMan chemistry. To control for variations in sampling and processing between samples 28S rRNA was co-amplified in a multiplex reaction and used to quantify total RNA. Relative quantification and standardisation was achieved using a log10 dilution series of RNA extracted from IBDV stock. A linear relationship was observed between input RNA and cycle threshold values (C(T)) over 5 log10 dilutions for the IBDV-specific product and 6 log10 dilutions for the 28S rRNA-specific product. As a test of the assay it was used to determine whether differences in susceptibility to IBDV observed between inbred lines of chickens could be detected at the level of viral load in the blood. Viral RNA levels peaked 2 days post-infection when there was significantly less viral RNA in the blood of resistant line 6(1) chickens compared with the more susceptible Brown Leghorns (P = 0.01). These results demonstrate that the course of IBDV infection can be monitored by quantifying IBDV RNA extracted from blood of infected chickens using TaqMan technology.

Development of a ssRNA internal control reagent for an infectious bursal disease virus reverse transcription/polymerase chain reaction-restriction fragment length polymorphism diagnostic assay

Infectious bursal disease virus (IBDV), family Birnaviradae, is the etiologic agent of a commercially important, globally distributed, contagious, immunosuppressive disease of young chickens. A restriction enzyme-compatible ssRNA internal control was developed for an IBDV reverse transcription/polymerase chain reaction-restriction fragment length polymorphism (RT/PCR-RFLP) diagnostic assay. An 841-bp bacteriophage-lambda DNA fragment was directionally ligated to 3' and 5' oligonucleotide linkers containing the IBDV RT/PCR target primer sequences. A pGEM-3Zf (+) transcription vector containing the internal control construct was used in an in vitro transcription reaction to produce ssRNA. After RT and PCR amplification, the transcripts produced an 882-bp cDNA product, larger than, co-amplifiable with, and free of the restriction sites used to prepare RFLP patterns of the 743-bp IBDV cDNA target product. The limit of detection of the transcripts in the RT/PCR test is 3.2 femtograms. With the internal control, a test inhibition rate of 7.7% (20/261) was determined for the IBDV RT/PCR assay. By identifying inhibited tests, the assay was improved through a reduction in the number of false-negative results.