Specific Pathogen Free Leghorn Research Articles

Virulence of Low Pathogenicity H7N2 Avian Influenza Viruses from the Delmarva Peninsula for Broiler and Leghorn Chickens and Turkeys

The virulence of low pathogenicity (LP) type A H7N2 avian influenza virus (AIV) isolates recovered from chickens in Delaware and the eastern shore of Maryland in 2004 was evaluated. Three-week-old leghorn- and broiler-type chickens and turkeys were inoculated via the conjunctival sac with 10(3.5)-10(4.0) 50% embryo infections dose (EID50) of virus per bird with A/ chicken/Delaware/Viva/04, A/chicken/Delaware/Hobo/04, and A/chicken/Maryland/Minh Ma/04. In broilers, the viruses produced respiratory signs, airsacculitis, and microscopic lesions in the trachea and lung. In contrast, signs and lesions were less severe in turkeys, and they were rarely observed in specific-pathogen-free (SPF) leghorns. In broilers and SPF leghorns, AIV peaked on day 3 postinoculation (PI), based on virus isolation and real-time reverse transcription-polymerase chain reaction, and antigen capture testing. Infection in turkeys peaked on day 7 PI. Serum antibodies generally were detected earlier in broilers (day 7 PI) than in turkeys or SPF leghorns (day 14 PI) using agar gel immunodiffusion, hemagglutination-inhibition, and the enzyme-linked immunosorbent assay. A second trial was performed to further examine the disease susceptibility of the leghorn chicken given the comparatively mild responses noted in the first trial. A 10-fold higher dose of 10(4.5)-10(5.0)EID50 per chick given via the conjunctival sac was used. In addition, commercial-type leghorns were tested as were chicks from the SPF leghorn source. The higher AIV dose resulted in more rapid and consistent rates of infection and higher serum antibody responses in both types of leghorn chickens. However, as observed in the first trial, clinical signs and microscopic lesions in both types of leghorns were infrequent and very mild. These findings indicate leghorn-type chickens, which are commonly used for pathogenicity assessments because of their availability, may not be the most suitable host for evaluating the virulence potential of LP AIV.

Multi-centric histiocytosis: Experimental induction in broiler and specific pathogen-free leghorn chickens

Seventy-five 3-day-old broiler chicks and twenty specific pathogen-free leghorn chicks were injected with 0.5 ml of a homogenate, prepared from organs from broilers diagnosed with naturally-occurring multicentric histiocytosis (MH). Equal numbers of uninjected broiler and leghorn chicks (controls) were maintained in adjacent pens. Ten weeks later, nine broilers had well-developed gross and microscopic MH lesions. The distribution and histological appearance of lesions in these experimental chicks was similar to lesions described in naturally occurring field cases. Six leghorns had gross lesions similar to those found in their broiler counterparts; however, in the leghorns, the cellular masses contained more lymphocytes and, additionally, masses were found in the gizzard musculature. One gizzard contained a sarcoma. Broiler chickens with MH weighed less than their control counterparts and were more likely to be anaemic. Sequences specific for reticuloendotheliosis viruses (REV) were found in the MH homogenate, in organs from most affected experimental leghorns and broilers, and in organs from a control broiler. However, REV were not isolated from these tissues, nor were specific antibodies for REV or avian leukosis/sarcoma viruses (ALV) found in chick serum. Leukosis/sarcoma viruses were isolated from some MH-affected experimental leghorns and broilers. Sequences specific for Marek's disease herpesvirus were not identified by polymerase chain reaction. The aetiology of MH remains unknown.

Attenuation of Lentogenic Newcastle Disease Virus Strain B-1 by Cold Adaptation

The Hitchner B-1 strain of Newcastle disease virus was plaque-cloned and then serially passaged 36 times in specific-pathogen-free (SPF) chicken embryos incubated at two different temperatures. Virus passaged at a reduced temperature (29 C) was identified as cold-adapted (Ca) and virus passaged at the normal temperature (37 C) was designated non-cold-adapted (non-Ca). The Ca and non-Ca B-1 viruses were compared with the parent B-1 and a commercial B-1 vaccine. In vitro Ca B-1 characteristics included adaptation for more rapid growth at 29 C and the aquisition of temperature sensitivity indicated by substantially reduced growth at 41 C, properties not seen with non-Ca B-1. Embryo mean death times for the Ca virus (140 hr) were longer than for non-Ca B-1 (107 hr) and parent B-1 (121 hr) viruses. The Ca virus retained a rapid (< 2 hr) hemagglutination (HA) elution rate but lost the property of binding the monoclonal antibody AVS-I typical of other B-1 strains. The pathogenicity of the Ca B-1 strain was compared to the non-Ca B-1, parent B-1 strain, and a commercial B-1 strain vaccine in 1-day-old broiler-type chickens. Pathogenicity was evaluated by assessing the severity of respiratory disease signs and the incidence of airsacculitis, perihepatitis, and pericarditis lesions in inoculated chicks. A respiratory disease index was calculated for each B-1 strain based on daily observation scores that determined the presence or absence of disease signs (coughing, rales, labored breathing, death) from 1 to 14 days following intratracheal inoculation with 10(6) 50% egg infective doses of virus per chick. The lower respiratory disease index obtained for the Ca B-1 strain (0.075) indicated it was less pathogenic than the commercial B-1 vaccine (0.296) and the non-Ca (0.478) and parent (0.521) B-1 strains. Ca B-1-infected chicks had only a 5% incidence of air sac lesions, compared to chicks given non-Ca (65%), Hitchner B-1 (65%), or a commercial B-1 vaccine (30%). Immunogenicity tests performed in 1-week-old SPF leghorn chickens demonstrated that Ca B-1 induced complete protection when administered intraocularly as a single entity. However, when Ca B-1 was given in combination with a modified live infectious bronchitis virus vaccine, chickens were only partially protected (60-75%) against Texas GB strain-induced neurotropic velogenic Newcastle disease.

Bordetella avium: An Opportunistic Pathogen in Leghorn Chickens

Experiments were conducted in order to produce bordetellosis in specific-pathogen-free (SPF) leghorn chickens. In the first and second of three experiments, young turkeys and chickens, respectively, were allotted into groups and challenged at 2 weeks of age with one of seven different isolates of Bordetella avium and two isolates of B. avium-like bacteria. Isolates of B. avium with the smooth colony type were pathogenic in turkeys but not in chickens. The B. avium-like bacteria and B. avium isolates with rough colonial morphology were nonpathogenic. In the third experiment, SPF leghorn chicks were vaccinated at 1 day of age with infectious bronchitis virus, Newcastle disease virus, or both and then challenged with B. avium at 7 days of age. Chickens vaccinated and then challenged with B. avium showed clinical signs and lesions similar to bordetellosis in turkeys. No clinical signs were observed in unchallenged chickens. Thus, we conclude that B. avium is an opportunistic pathogen in SPF leghorn chickens.

Comparisons of Packed Cell Volumes (PCVs) from So-Called Chicken Anemia Agent (CAA; A Virus)-Free Broilers to PCVs from CAA-Free Specific-Pathogen-Free Leghorns

Packed cell volumes (PCVs) from 3-, 7-, 14-, 21-, 28-, and 35-day-old clinically healthy chicken anemia agent (CAA)-free and specific-pathogen-free (SPF) leghorn chicks were compared with PCVs from age-matched clinically healthy CAA-free broiler chicks. The PCVs of the SPF chicks regressed significantly (F = 20.6, df = 2/3, P < 0.025) on age in a linear fashion. The PCVs of the broiler chicks regressed significantly (F = 9.56, df = 2/3, P < 0.05) on age in a cubic parabola. The mean PCVs of the broiler chicks were significantly (P < 0.05) higher than PCVs of SPF chicks at every tested time interval. Results indicate that PCV values are higher in broiler chicks than in SPF leghorn chicks, and that PCVs increase as chicks age. Clinicians, diagnosticians, and investigators who intend to work with chicken blood must be aware of these differences.