Pedro Villegas

Malabsorption syndrome in broiler chickens.

A disease syndrome of broiler chickens is described. Affected birds exhibited poor pigmentation of the shanks, decreased weight gains, elevated feed conversions, poor feathering, enlargement of the proventriculus, and a decrease in the size of the gizzard. Reoviruses were isolated from affected chickens from several farms. Signs and lesions similar to those seen in chickens with the field syndrome were reproduced when these isolates were inoculated into day-old chicks with low levels of maternal antibody against viral arthritis. The pathogenicity of the viral isolates was variable. The incidence of lameness was much higher in those groups of chicks injected with these viruses than in the control groups.

Identification and serological differentiation of several reovirus strains isolated from chickens with suspected malabsorption syndrome.

Five virus strains designated CO8, 43A, 45, 81-5, and 82-9 were isolated from the intestines of 3-to-6-week-old broilers showing signs and lesions consistent with malabsorption syndrome. The strains were identified as reoviruses based on their effect on chicken embryo kidney cells, morphology, chloroform, iododeoxyuridine and heat sensitivity, hemagglutination ability, pathogenicity in embryos, and replication cycle. Relatedness values, determined by cross-neutralization studies, revealed that the strains could be classified into three distinct serotypes. Two of the serotypes did not share antigenic relationship with strain S1133, which has been used in the field to vaccinate chickens against viral arthritis.

Viral diseases of the respiratory system

Abstract Infectious bronchitis, Newcastle disease, infectious laryngotracheitis, avian influenza, and pneumovirus are the viruses that more frequently affect the respiratory tract of chickens. Because of the tendency to change its antigenic properties, infectious bronchitis is currently the viral disease present in most poultry producing areas of the world. New serotypes and variant strains are reported in several countries. Current commercially available vaccines do not always provide protection against new field isolates. Vaccination programs are constantly adjusted in an attempt to improve protection against this disease. Infectious laryngotracheitis has appeared in the broiler industry as a serious disease. Improved vaccines are needed to control the disease in broilers. In the U.S., the control of the highly pathogenic forms of avian influenza and the velogenic forms of Newcastle disease have been achieved by eradication. In other countries, effective vaccines have been used to control Newcastle and avian influenza. Avian pneumovirus infection is also an emerging disease of chickens and turkeys.

Genetic Characterization of Very Virulent Infectious Bursal Disease Viruses from Latin America

Abstract Very virulent infectious bursal disease viruses (vvIBDVs) were detected in phenol inactivated bursal samples obtained from Brazil, the Dominican Republic, and Venezuela.After nucleotide sequence analysis of the hypervariable region of VP2 gene, the vvIBDVs from Brazil and Venezuela exhibited all of the 14 nucleotide changes that are conserved in the European UK-661 and most other vvIBDV strains. However, the vvIBDV from the Dominican Republic presented 11 nucleotide changes that are conserved in vvIBDV strains. After phylogenetic analysis, the Latin American strains were found to be related to other vvIBDV strains from Europe, Asia, and Africa. However, Brazilian and Dominican vvIBDVs clustered in two separate subgroups, while the vvIBDVs from Venezuela were closely related to other strains from other parts of the world. By deduced amino acid sequence, the three conserved amino acid residues in vvIBDV strains (222 Ala, 256 Ile, and 294 Ile) were confirmed in the Latin American viruses, and one amino acid change (300 Ala) was unique to all vvIBDVs from the Dominican Republic. The occurrence of this change in the Dominican vvIBDVs may have an impact in their antigenic makeup. Results of this study indicate that the vvIBDVs detected in Latin America are genetically similar to IBDV strains from other parts of the world. However, vvIBDVs from Venezuela were more similar to the vvIBDV strains from Europe and Asia. Of all the samples analyzed, vvIBDVs from Brazil and the Dominican Republic exhibited more genetic changes. These changes may have emerged as a result of the different management practices and environmental conditions present in each particular geographic area.

Differentiation of vaccine strains and Georgia field isolates of infectious laryngotracheitis virus by their restriction endonuclease fragment patterns.

Seven restriction endonucleases (REs) were used to cleave the DNA from seven vaccine strains of infectious laryngotracheitis (ILT) virus and from six Georgia field isolates of ILT virus. After electrophoresis of the resulting RE fragments, the patterns were compared in order to differentiate strains of ILT virus. The six chicken-embryo-origin (CEO) vaccines were identical with each RE, but the tissue-culture-origin (TCO) vaccine strain differed from the CEO vaccines using five of the REs. Four of the six field isolates were identical by each RE, but two field isolates differed from each other and from the four identical field isolates on the basis of patterns produced by some but not all of the REs. The four identical field isolates could not be differentiated from the CEO vaccine strains by any RE, but the other two field isolates were not identical to either strain of vaccine virus. This work demonstrates that differentiable strains of ILT virus exist in the United States and that viruses other than vaccine viruses are involved in field outbreaks of ILT.

Genetic Characterization, Pathogenicity, and Protection Studies with an Avian Adenovirus Isolate Associated with Inclusion Body Hepatitis

Abstract An avian adenovirus (AAV) was isolated from liver samples of two 2-wk-old broiler-breeder flocks obtained from grandparents vaccinated at 10 and 17 wks of age with an autogenous inactivated vaccine containing the European AAV 8 (8565 strain) and 11 (1047 strain) serotypes (AAV8/11 vaccine). Affected broiler-breeders exhibited clinical signs and macroscopic and microscopic lesions associated with inclusion body hepatitis (IBH). The isolated adenovirus, identified as Stanford, was molecularly characterized as European serotype 9. The pathogenicity of the Stanford strain was confirmed after inoculation of specific-pathogen-free (SPF) chickens at 1–7 days of age, causing 100% and 20% mortality, respectively. The level of protection against IBH was evaluated in two broiler-breeder progenies from AAV 8/11–vaccinated grandparent flocks and a commercial broiler flock by challenge at 1 or 7 days of age with the AAV 8 and 11 serotypes and/or the Stanford strain. The broiler-breeder progenies and the commercial broiler flock exhibited protection against IBH after challenge. No significant differences in mean body weights were observed at 3 wk of age in any of the evaluated groups. We conclude that broiler-breeder progenies from 30- to 50-wk-old grandparents vaccinated with the AAV 8/11 vaccine were adequately protected against challenge with the AAV 8 and 11 serotypes and the Stanford strain.

Efficacy of Single Dose Recombinant Herpesvirus of Turkey Infectious Bursal Disease Virus (IBDV) Vaccination Against a Variant IBDV Strain

Abstract The use of viral vectors for transgenic expression of immunogenic proteins is a current trend in the poultry industry. The objective of this work was to assess the protection against the variant E of infectious bursal disease virus (IBDV), conferred by day-one vaccination with a commercial recombinant herpesvirus of turkey (HVT) vaccine (VAXXITEK®) expressing the immunogenic viral protein 2 from a classical IBDV. In separate trials, 1-day-old specific-pathogen-free (SPF) or broiler chickens were vaccinated by the subcutaneous route and challenged with the variant E strain at 18 or 28 days of age. Bursa/body weight ratio and bursal histopathology were assessed as protection criteria. Protection was demonstrated at both challenge points, bursal indexes in vaccinated SPF and broiler groups were significantly higher than in the challenged controls. The commercial vaccine protected against bursal damage as indicated by significantly lower bursal lesion scores in the vaccinated birds. These experimental results indicate that a single dose of the recombinant HVT-IBDV confers protection against variant E challenge even though the VP2 expressed by the recombinant herpes virus belongs to a standard strain.

Characteristics and Pathogenicity of Two Avian Reoviruses Isolated from Chickens with Leg Problems

Two reoviruses identified as 172 and 176 were isolated from the hock of 2-to-3-week-old broiler breeders exhibiting leg problems. Oral-ocular or intraplantar inoculation of day-old specific-pathogen-free or broiler chickens produced severe mortality (60-100%) within 2 to 6 days. The main lesions observed were tenosynovitis as well as necrosis and congestion of the liver, spleen, kidneys, and bursa of Fabricius.

Molecular Characterization of Infectious Bursal Disease Virus from Commercial Poultry in the United States and Latin America

SUMMARY. 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.

Molecular Characterization of Seven Field Isolates of Infectious Bursal Disease Virus Obtained from Commercial Broiler Chickens

Specific-pathogen-free sentinel birds were used as an initial biological system to isolate infectious bursal disease virus (IBDV) field isolates from commercial broiler farms exhibiting recurrent respiratory problems and poor performance. Reverse transcription (RT)-polymerase chain reaction (PCR) was used to amplify a 248-bp product encompassing the hypervariable region of the IBDV VP2 gene. Restriction fragment length polymorphism (RFLP) analysis of the RT-PCR products was performed with the restriction endonucleases DraI, SadI, TaqI, StyI, BstNI, and SspI. Two isolates (619 and 850) exhibited a RFLP pattern characteristic of Delaware variant E IBDV. Restriction enzyme digestion for four isolates (625, 849, 853, and 11,153) revealed unmatched RFLP patterns when compared with reference IBDV strains. Nucleotide and deduced amino acid sequence analyses of the VP2 hypervariable region for these six isolates revealed identity (96.3% up to 98%) with Delaware E variant IBDV strain. However, serine at position 254, which is characteristic of Delaware variant strains, was substituted by asparagine in these six isolates. The seventh IBDV isolate (9109) also exhibited a unique RFLP pattern, which included the SspI restriction site, which is characteristic of very virulent (vv) IBDV strains. Nucleotide and amino acid sequence analyses of the hypervariable region for this isolate revealed identity (90%) with the standard challenge strain. However, the leucine residue at position 294 was substituted by isoleucine. This substitution corresponds to one of the amino acids that are conserved in the vvIBDV strains. Antigenic index studies of the predicted amino acid sequence of the hypervariable region of VP2 from isolates 619, 625, 849, 850, 853, and 11,153 exhibited a profile almost identical to variant E, whereas the isolate 9109 exhibited a profile characteristic of standard IBDV strains.