Commercial Layer Flocks Research Articles

Sensitivity of environmental sampling methods for detectingSalmonellaEnteritidis in commercial laying flocks relative to the within-flock prevalence

The objective of this study was to estimate the sensitivity of three different sampling/testing methodologies for the detection of Salmonella Enteritidis in commercial egg-laying flocks relative to the within-flock prevalence. The following methods were compared on 21 farms: (1) The European Union (EU) baseline survey method (five faecal and two dust samples); (2) an in-house method that involved collecting 10 dust and 10 faecal samples into jars with buffered peptone water, and (3) a method involving single samples of pooled faeces and dust that has been adopted as a monitoring method for the National Control Programme across the EU (the NCP method). Testing of individual bird ovaries/oviduct and caeca was carried out on each flock, and the sensitivity of each sampling method was estimated relative to the within-flock prevalence using Bayesian methods. Results showed that the sensitivity of all the sampling methods increased as the within-flock prevalence increased, and that all were more efficient than individual bird sampling for detection of S. Enteritidis in commercial flocks. The in-house method was the most sensitive of the methods compared, with a 98% power to detect a 0.1% prevalence, and the NCP method the least sensitive, with a 93% power to detect a prevalence of 20%.

Detection of avian leukosis virus (ALV) in albumen of Shiraz commercial and local layer flocks using ELISA and RT-PCR

Summary Avian leukosis viruses (ALVS) cause different types of tumours in poultry and can affect the health and egg production of the birds. To investigate the presence of the virus in chicken layer flocks in Shiraz, 222 egg albumen from local layer breeder (25 eggs), local layer grand parent (30 eggs), broiler breeder (60 eggs), commercial layer (46 eggs) and broiler grand parent (61 eggs) were tested by antigen-capture enzyme-linked immunosorbent assay (AC-ELISA). The results showed that 3.33, 76 and 80% of commercial broiler breeder, local layer breeder and local layer grand parent were positive, respectively. Thirty-five albumen samples were randomly selected and tested by RT-PCR using PU1/PU2 and PA1/PA2 primer sets. The samples with ELISA S/P ratio equal or more than 0.17 were positive by RT-PCR using PA1/PA2 primers. This is the first report of the presence of the ALV in egg albumen samples of chicken layer flocks in Shiraz.

Short Communication: DIazinon toxicity in a commercial layer flock on the University of Ibadan farm, Nigeria

No Abstract Bulletin of Animal Health and Production in Africa Vol. 54 (4) 2006: pp. 298-301

Salmonella Enteritidis in commercial layer flocks in Europe: legislative background, on-farm sampling and main challenges

BACKGROUNDDuring 2006 there were 160,645 reported human cases ofsalmonellosis in the then 25 Member States of the European Union(equivalent to an incidence of 35.4 cases per 100,000 population (EFSA,2007a), making Salmonella the second most commonly reportedgastrointestinal zoonotic infection across the EU. However, this figureis likely to be a considerable underestimate of the true incidence ofdisease. In the EU there are five serovars that account for the majorityof cases of Salmonella in humans. These serovars are S. Enteritidis (SE),S. Typhimurium (ST), S. Infantis, S. Hadar, and S. Virchow, and weredesignated by the European Commission (EC) as ‘serovars of publichealth significance’. However, in Europe, SE is by far the predominantserovar (59-62%), followed at a distance by ST (13-17%) (EFSA, 2007a;Fisher, 2004). The rise of SE over the last few decades can be rightlydescribed as an epidemic. The number of human cases of SE started toincrease dramatically in most countries of western Europe during themid - to late eighties, and a similar phenomenon had been observed insome US regions a few years before (Saeed, 1999). This ‘SE epidemic’involved mostly phage type (PT) 4, although in some European countriesand the USA PT8 was initially predominant. In the UK, for example, atthe peak of the SE epidemic (1996/97) PT 4 isolates made up 75% of allSE human isolates. Animal surveillance data suggested a rapid spreadin commercial layers across the EU and beyond. The rapid spread of PT4 worldwide suggests that the epidemic may have originated frominfected grandparent breeding stock, and was subsequently amplifiedthrough hatcheries and disseminated globally. A notable exception tothis phenomenon in western Europe was seen some Nordic countrieswith very strict Salmonella control programmes.Epidemiological investigations demonstrated that contaminated eggsproduced by infected laying hens were the main source of humaninfection with SE (Coyle et al., 1988; Gillespie & Elson, 2005; Gillespieet al., 2005; Rabsch et al., 2001). SE shows an affinity for internal organsof the chicken and (in the case of laying hens) for the ovary and oviduct,leading to internal contamination of eggs prior to being laid (Guan etal., 2006; Humphrey et al., 1989; Poppe, 1999). However, the egg mayalso become contaminated in the shell when the poultry houseenvironment is highly contaminated with SE. In the EU, washing of eggsis not permitted, and irradiation is not regarded as acceptable by thegeneral population.Because the European Union functions as a single market, theEuropean Commission has played a major role in harmonising and co-ordinating monitoring and control programmes and ultimately aimingto reduce the prevalence of Salmonella in primary production of poultryacross member states (MS). A key piece of EU legislation is the EuropeanCommission (EC) Regulation No. 2160/2003, which requires that MS

Detection and Localization of Naturally Transmitted Avian Leukosis Subgroup J Virus in Egg‐type Chickens by In situ PCR Hybridization

Avian leukosis virus (ALV) subgroup J (ALV-J) is an exogenous ALV and causes myeloid leukosis in meat-type chickens. We have previously reported the isolation and identification of ALV-J in commercial layer flocks from 12 farms in northern China. In this report, we further characterized this virus by in situ polymerase chain reaction (PCR) hybridization in various affected organs of chickens from six of the 12 farms. A routine method for hybridization of nucleic acid uses radioactive probe, such as a P32-labelled probe. We found that the non-radioactive digoxigenin (DIG) probe is sensitive enough to detect the nucleic acid of virus in chicken tissues. We used a pair of published primers (H5/H7) specific to the gp85 envelope gene and 3' region of pol gene of prototype ALV-J strain HPRS-103. The total RNA extracted from tumour, bone marrow, oviduct, liver and spleen of the diseased chickens from six commercial flocks, and cDNA was successfully amplified. Using the primers and cDNA, we obtained an ALV-J-specific cDNA probe of 545 bp in length by PCR. In situ PCR with H5/H7 primers was carried out in the paraffin sections from tissues of the diseased chickens, followed by in situ hybridization using the DIG-labelled cDNA probe. Positive hybridization signals were detected in the cytoplasm of paraffin sections of tumours and other organ tissues. The intensity of the signals was documented using an image analysis system measuring integral optical density (IOD). The IOD values for tissue sections treated by in situ PCR hybridization are significantly higher than that by in situ hybridization alone (P < 0.01). These data taken together suggest that in situ PCR hybridization is a more sensitive technique for detection of ALV-J in tissue sections.

Persistence of Salmonella on Egg Conveyor Belts Is Dependent on the Belt Type but Not on the rdar Morphotype

Commercial caged layer flocks in Alberta, Canada, are commonly monitored for Salmonella enterica serovar Enteritidis (SE) and S. enterica serovar Typhimurium (ST) by environmental sampling. In one recent case, a SE strain isolated from the egg conveyor belt was a source of persistent infection for the flock. This study was undertaken to examine Salmonella colonization on egg conveyor belts and to determine whether the rdar morphotype, a conserved physiology associated with aggregation and long-term survival, contributed to persistence. Four woven belts constructed of natural or nonnatural fibers and a 1-piece belt made of vinyl were tested with rdar-positive ST and SE strains and a rdar-negative ST DeltaagfD reference strain. The type of egg belt was the most important factor influencing Salmonella colonization and persistence. The vinyl belt, with the least surface area available for colonization, had the fewest Salmonella remaining after washing and disinfection, whereas the hemp-plastic belt, with the greatest surface area, had the most Salmonella remaining. Real-time gene expression indicated that the rdar morphotype was involved in colonizing the egg belt pieces; however, it was not essential for persistence. In addition, rdar-positive and rdar-negative strains were equally similarly to disinfection on the egg belt pieces. The results indicate that Salmonella can persist on a variety of egg belts by mechanisms other than the rdar morphotype, and that using egg conveyer belts with reduced surface area for bacterial colonization can lessen contamination problems.

Survey of the prevalence of Salmonella species on commercial laying farms in the United Kingdom

A survey of salmonella infection on 454 commercial layer flock holdings in the uk was carried out between October 2004 and September 2005. Fifty-four (11·7 per cent, 95 per cent...

Detection and Seroprevalence of Infectious Bronchitis Virus Strains in Commercial Poultry in Pakistan

This study was conducted to investigate the incidence of infectious bronchitis virus (IBV) in commercial broiler and layer flocks in Pakistan. Serum samples from 16 layers and 9 broiler flocks were screened against M-41, D-274, D-1466, and 4-91 strain antigens using hemagglutination inhibition assay. Overall, 88% of the flocks were seropositive for M-41 antibodies, whereas 40, 52, and 8% of the flocks were positive for D-274, D-1466, and 4-91 IBV strains, respectively. The M-41 antigen was also detected in lungs and tracheal tissues of the clinically positive infectious bronchitis cases. Phospholipase C treatment of the lung and tracheal tissue homogenates from IBV-positive chickens increased the detection limit for M-41 strain from 1.3% positive samples in simple hemagglutination assay to 30.6% positivity when the same samples were treated with phospholipase C. Similarly, reverse transcription-PCR was a much better M-41 detection tool as compared with the classical agar gel precipitation assay utilized to screen tissue homogenates from IBV-positive chickens. In conclusion, this survey clearly demonstrates that several strains of IBV are prevalent in poultry flocks in Pakistan. By utilizing such diagnostic techniques it is possible to conduct a detailed epidemiological study to determine the full economic impact of this disease.

A longitudinal study of environmental salmonella contamination in caged and free-range layer flocks

The environmental contamination by salmonella was examined over a 12-month period in 74 commercial layer flocks from eight farms in the UK, which previously had been identified as being contaminated with salmonella. Samples of faeces, dust, litter, egg belt spillage and wildlife vectors were taken, plus swabs of cages, feeders, drinkers, floors, egg belts and boots. Some sampling was performed in each month of the year. Numerous serovars were detected but Salmonella enterica serotype Enteritidis was the only persistent serotype found among single-age flocks. There was a significant correlation between qualitative environmental samples and semi-quantitative faeces samples. The level of environmental contamination increased significantly over time. There were significant temperature and seasonal effects upon contamination. Wildlife vectors proved to be sensitive samples for the detection of salmonella. The efficacy of cleaning and disinfection upon residual salmonella contamination, and upon subsequent flock contamination, was highly variable between and within premises. The variability between detected prevalences over time and between flocks indicates a need for regular, sensitive monitoring of flocks for salmonella to permit targeting of control measures aimed at eliminating contamination of the layer environment by salmonella. There is substantial scope for improvement of cleaning and disinfection procedures.

Comparison of the Reveal Test, the U.S. Food and Drug Administration Culture Method, and Selective Media for Recovery of Salmonella Enteritidis from Commercial Egg Layer Flock Environments

Salmonella is the leading cause of foodborne illnesses in the United States, and Salmonella Enteritidis (SE) is the second most frequently isolated Salmonella serovar. Egg products are most often associated with outbreaks of SE infection. To prevent SE contamination of eggs, many producers are implementing flock inspections for SE at their facilities. A rapid and simple method for detecting SE in poultry environmental samples is critical for effective control of SE. In this study, the Reveal test for SE was compared with the conventional U.S. Food and Drug Administration (FDA) culture method for detecting SE in naturally contaminated environmental samples. The efficacy of two enrichment media, tetrathionate broth (TT) and Rappaport-Vassiliadis medium (RV), and three selective plating media, brilliant green agar with novobiocin (BGN), xylose lysine tergitol 4 agar (XLT4), and bismuth sulfite agar (BS), also were compared for SE isolation. One hundred twenty-eight environmental drag swab samples were collected from two previously identified SE-positive chicken flocks in two U.S. states and analyzed in parallel using the Reveal test and the FDA culture method. Twenty-five samples (19.5%) yielded SE when the Reveal test was used, and 23 samples (18.0%) were positive for SE by the FDA culture method. No significant difference in efficacy (P = 0.527) was found between the two methods. The Reveal test had a sensitivity, specificity, and accuracy of 83, 94, and 92%, respectively. Overall, a significantly greater number of positive samples was obtained after enrichment in RV compared with TT. XLT4 and BGN were more efficient than BS for isolating SE. However, no single method or medium successfully recovered SE from all SE-positive environmental samples.

Susceptibility of Various Parental Lines of Commercial White Leghorn Layers to Infection with a Naturally Occurring Recombinant Avian Leukosis Virus Containing Subgroup B Envelope and Subgroup J Long Terminal Repeat

Chickens from seven different parental lines of commercial White Leghorn layer flocks from three independent breeders were inoculated with a naturally occurring avian leukosis virus (ALV) containing an ALV-B envelope and an ALV-J long terminal repeat (LTR) termed ALV-B/J. Additional groups of chickens from the same seven parental lines were inoculated with ALV-B. Chickens were tested for ALV viremia and antibody at 0, 4, 8, 16, and 32 wk postinfection. Chickens from all parental lines studied were susceptible to infection with ALV-B with 40%-100% of inoculated chickens positive for ALV at hatch following embryo infection. Similarly, infection of egg layer flocks with the ALV-B/J recombinant virus at 8 days of embryonation induced tolerance to ALV with 86%-100% of the chickens viremic, 40%-75% of the chickens shedding virus, and only 2/125 (2%) of the chickens producing serum-neutralizing antibodies against homologous ALV-B/J recombinant virus at 32 wk postinfection. In contrast, when infected with the ALV-B/J recombinant virus at hatch, 33%-82% of the chickens were viremic, 28%-47% shed virus, and 0%-56% produced serum-neutralizing antibodies against homologous ALV-B/J recombinant virus at 32 wk postinfection. Infection with the ALV-B/J recombinant virus at embryonation and at hatch induced predominately lymphoid leukosis (LL), along with other common ALV neoplasms, including erythroblastosis, osteopetrosis, nephroblastomas, and rhabdosarcomas. No incidence of myeloid leukosis (ML) was observed in any of the commercial White Leghorn egg layer flocks infected with ALV-B/J in the present study. Data suggest that the parental line of commercial layers may influence development of ALV-B/J-induced viremia and antibody, but not tumor type. Differences in type of tumors noted in the present study and those noted in the field case where the ALV-B/J was first isolated may be attributed to differences in the genetics of the commercial layer flock in which ML was first diagnosed and the present commercial layer flocks tested in the present study.

Persistence of Immunity in Commercial Egg-Laying Hens Following Vaccination with a Killed H6N2 Avian Influenza Vaccine

The California poultry industry experienced an outbreak of H6N2 avian influenza beginning in February 2000. The initial infections were detected in three commercial egg-laying flocks and a single noncommercial backyard flock but later spread to new premises. The vaccination of pullet flocks with a commercially prepared, killed autogenous vaccine prior to their placements on farms with infected or previously infected flocks was used as a part of the eradication programs for some multiage, commercial egg production farms. The purpose of this study was to follow three vaccinated flocks on two commercial farms to track the immune responses to vaccination. The antibody-mediated responses of the three flocks followed in this study were markedly different. One flock achieved 100% seroconversion at 12.5 wk of age, but by 32 wk of age, all of the hens were seronegative by agar gel immunodiffusion (AGID). In contrast, at 32 wk of age, flocks from the other farm (flocks 2A and 2B) were 95% and 72% seropositive by AGID, respectively. Of the differences that were identified between the vaccination protocols on the two farms, the distinction that could explain the level of disparity between responses is the delivery of the second dose of vaccine with a bacterin on the first farm, which may have interfered with the persistence of immunity in this flock. Hens from flocks 2A and 2B were experimentally challenged at 25 wk of age with H6N2 avian influenza virus. Hens from flock 2A did not transmit virus to naive contact-exposed hens, but hens from flock 2B did. At 34 wk of age, hens from flock 2A were again challenged and naive contact-exposed hens were infected in this second trial. These challenge experiments served to demonstrate that despite detectable antibody responses in flocks 2A and 2B, the birds were protected from infection for less than 21 wk after the second vaccination.

Detection of Antibodies Against Serotypes 1 and 2 Infectious Bursal Disease Virus by Commercial ELISA Kits

Two distinct serotypes of infectious bursal disease virus (IBDV) are recognized in chicken and turkey flocks in the United States. Serologic testing of chicken flocks for serotype 1 viruses is routinely performed to monitor disease status and vaccination. Earlier studies indicated that enzyme-linked immunosorbent assay (ELISA) test detects antibodies to both serotypes of the virus, while the virus neutralization (VN) test is serotype specific. It is useful to evaluate currently available commercial ELISA kits for their ability to differentiate between antibodies elicited by the two serotypes. Three trials were performed in which chickens were orally inoculated with either a high or a low dose of serotype 1 STC or serotype 2 OH strains of IBDV. Sera collected at 0, 7, 14, and 21 days from these chickens and antisera procured from naturally infected broiler (n=20) and layer (n=30) flocks were tested with five different commercial ELISA kits and by VN. All ELISA kits detected different levels of antibodies elicited against serotype 1 of the virus and moderate and high levels of antibodies against serotype 2 virus. A correlation existed between the ELISA and the VN titers of experimentally infected chickens. All serum samples tested from the commercial layer flocks and 65% of the broiler flocks had antibodies against the OH strain. However, no correlation between the VN titers and ELISA titers was observed for the commercial broilers and layers sera by the majority of the kits. The results indicated that currently available commercial ELISA kits detect antibodies elicited by the two serotypes of IBDV. Hence, the prevalence of serotype 2 antibodies in the flocks should be considered while determining antibody profiles of the flocks against serotype 1 viruses.

Differentiation of Infectious Laryngotracheitis Virus Isolates by Restriction Fragment Length Polymorphic Analysis of Polymerase Chain Reaction Products Amplified from Multiple Genes

Infectious laryngotracheitis (ILT) has been identified in most countries around the world and remains a threat to the intensive poultry industry. Outbreaks of mild to moderate forms of ILT are common in commercial layer flocks, while sporadic outbreaks of ILT in broiler flocks have also been recognized as an emerging problem in several countries. Examination of viral isolates using restriction fragment length polymorphism of polymerase chain reaction (PCR-RFLP) from individual ILTV genes has suggested that some of these outbreaks were caused by vaccine strains. In this study, PCR-RFLP of a number of ILTV genes/genomic regions including gE, gG, TK, ICP4, ICP18.5, and open reading frame (ORF) B-TK was used to examine a number of historical and contemporary Australian ILTV isolates and vaccine strains. PCR-RFLP of gE using restriction endonuclease EaeI failed to distinguish between any of the isolates including the vaccine strains. PCR-RFLP of gG, TK, and ORFB-TK using restriction endonucleases MspI and FokI, respectively, divided all the isolates into two groups. PCR-RFLP of ICP18.5 and ICP4 using restriction endonuclease HaeIII separated the isolates into three different groups with some field isolates only able to be distinguished from vaccine strains by PCR-RFLP of ICP18.5. A combination of groupings including gG, TK, ICP4, ICP18.5, and ORFB-TK PCR-RFLP classified the ILTV isolates under investigation into five different groups with most isolates distinguishable from vaccine strains. Results from this study reveal that to achieve reliable identification of strains of ILTV, the examination of multiple gene regions will be required, and that most of the recent ILT outbreaks in Australia are not being caused by vaccine strains.

Survival of Exotic Newcastle Disease Virus in Commercial Poultry Environment Following Removal of Infected Chickens

During the first weeks of 2003, after exotic Newcastle disease (END) was confirmed in commercial layer flocks in Southern California, it became apparent that the virus survival information in the literature varied widely and was difficult to extrapolate to current local conditions. The END Task Force used the information available in the literature and the recommendations of research scientists to establish protocols for safely handling manure from infected and depopulated premises. In an attempt to gain more applicable knowledge in the management of contaminated poultry manure in the course of the END outbreak, this virus survival study was designed and implemented. Environmental drag swabs were tested for END virus from two of the early-infected commercial ranches that consisted of several houses following immediate removal of the infected flocks. A total of 293 samples, composed of 168 manure drag swab pools, 72 dropping board swab pools, and 38 compost swab pools from 3 houses (ranch 1), and 180 manure belt scraper swab pools from ranch 2 were analyzed for ND virus isolation and characterization for 21 consecutive days postdepopulation. Thirteen manure drag swab pools (from houses 1 and 3) and two manure dropping board swab pools (from house 3) collected from ranch 1 were positive for END virus at 0, 1, 2, 3, 4, 7, 10, 12, and 16 days postdepopulation. No END virus was isolated after the 16th day following depopulation from any of the samples. All samples from ranch 2 were negative during the entire observation period.

Evaluation of methods for the identification of Salmonella enterica serotype Typhimurium DT104 from poultry environmental samples

An increase in the prevalence of Salmonella enterica serotype Typhimurium DT104 has been reported worldwide. This study examined the prevalence of this microorganism in poultry environmental samples from commercial layer flocks and pullet environments as well as the sensitivity and specificity of a PCR-based method, and multiple antibiotic resistance profile of Salmonella serogroup B isolates in relation to the serotype and phagetype reference method for the identification of Salmonella Typhimurium DT104. A total of 435 Salmonella isolates were obtained from poultry house environmental samples tested during a 20-month period representing a prevalence of 5.5%. Of these, 313 (72%) isolates were identified as Salmonella serogroup B isolates. These isolates were tested by a PCR-based assay, and for resistance to five antibiotics: ampicillin, chloramphenicol, streptomycin, sulfonamides, and tetracycline (ACSSuT) for the rapid identification of Salmonella Typhimurium DT104. Upon comparing the antibiotic resistance and PCR results with serotype and phage type data, the sensitivity and specificity for the identification of Salmonella Typhimurium DT104 of both methods were found to be 100%, and 99.6%, respectively. Both methods can be completed within 24 h after obtaining an isolate, while serotyping and phagetyping required more than 5 days to complete.

Welfare implications of avian osteoporosis

Cage layer fatigue was first noticed after laying hens began to be housed in cages in the mid-20th century. Hens producing eggs at a high rate were most susceptible to the disease. Early research revealed that cage layer fatigue was associated with osteoporosis and bone brittleness. Severe osteoporosis leads to spontaneous bone fractures commonly in the costochondral junctions of the ribs, the keel, and the thoracic vertebrae. Vertebral fracture may damage the spinal cord and cause paralysis. Osteoporosis appears to be inevitable in highly productive caged laying hens. The condition can be made worse by metabolic deficiency of calcium, phosphorus, or vitamin D. Hens in housing systems that promote physical activity tend to have less osteoporosis and rarely manifest cage layer fatigue. Genetic selection may produce laying hens that are less prone to bone weakness. The welfare implications of osteoporosis stem from pain, debility, and mortality associated with bone fracture. The chicken has well-developed neural and psychological systems specialized to respond to pain associated with trauma and inflammation. Although studies on the chicken have not focused on pain due to bone fracture, physiological and behavioral similarities to other species allow inference that a hen experiences both acute and chronic pain from bone fracture. There is little information on osteoporosis in commercial caged layer flocks, however, evidence suggests that it may be widespread and severe. If true, most caged laying hens suffer osteoporosis-related bone fracture during the first laying cycle. Osteoporosis also makes bone breakage a serious problem during catching and transport of hens prior to slaughter. Estimates of mortality due to osteoporosis in commercial caged layer flocks are few, but range up to a third of total mortality. Many of these deaths would be lingering and attended by emaciation and possibly pain. Osteoporosis-related bone breakage during processing has reduced the marketability of spent caged laying hens, contributing to the need to develop humane on-farm killing methods to support alternative means of spent hen disposition. Overall, the evidence indicates that cage layer osteoporosis is a serious animal welfare problem. A determined effort must be made to make the laying hen no longer susceptible to the harmful effects of excessive bone loss.

Occurrence of avian leukosis virus subgroup J in commercial layer flocks in China

Mortality from myeloid leukosis was observed in commercial layers from 12 farms in northern China. Affected chickens were extremely thin and dehydrated, bleeding occurred in feather follicles and claws, combs were pale and anaemic, phalanges were swollen, and many yellowish–white tumours were seen on the visceral surface of the sternum. Focal tumour cells, with spherical eosinophilic granules in the cytoplasm, were found in the liver, spleen, kidney, ovary, oviduct, lung, bone marrow, proventriculus and gut by histopathological examination. Immunohistochemical studies with a monoclonal antibody to gp85 of avian leukosis virus subgroup J (ALV-J) revealed antigen in all organs examined. Polymerase chain reaction tests using a pair of ALV-J-specific primers H5/H7 (Smith et al., 1998) produced a 545 basepair fragment. The sequence of the Polymerase chain reaction product was compared with that of the ALV-J HPRS-103 prototype strain. The identity of nucleotides and predicted amino acids was 97.4% and 96.1%, respectively. On this basis the disease in the egg-type chickens was diagnosed as an ALV-J infection. This is the first report of field cases of myeloid leukosis caused by ALV-J in commercial egg-type chickens.

Low-pathogenicity avian influenza virus (H6N2) in chickens in California, 2000-02.

During 2000, 2001, and January 2002, avian influenza virus was isolated from chickens from 12 different locations in California. All the isolates were typed as H6N2 and determined to be of low pathogenicity for chickens. Nine of the isolates came from commercial layer flocks; one from a backyard flock; one from a mixed age flock, where ducks and squabs were also present; and one from a primary broiler breeder. Although a drop in egg production and increased mortality were among the disease signs reported in the layer flocks, the pathological changes observed in the early cases were primarily associated with mild respiratory infections. It was not until August 2001 that yolk peritonitis was observed; this has been a feature of all the remaining cases through 2001 and 2002. All the isolates clustered as a unique group separate from other influenza viruses based upon sequence data of the H6, neuraminidase (N2), and matrix (MA) genes, indicating a common ancestor for these three gene segments. However, sequencing of the nonstructural (NS) gene indicates introductions from two separate origins. With the first isolate CK/CA/431/00 as the index case, the N2, MA, and NS genes are more closely related to North American isolates, as is the NP gene of CK/CA/650/00. In contrast, the H6 gene is more closely related to a Eurasian influenza isolate. Comparison of amino acid sequences of the N2 and MA genes of these isolates with available type A influenza viruses identified two unique changes in the MA gene and nine in the N2 gene, as well as four progressive changes. These results are discussed in relation to available clinical and epidemiological data.

The occurrence of avian influenza A subtype H6N2 in commercial layer flocks in Southern California (2000-02): clinicopathologic findings.

Between February 2000 and February 2002, the California Animal Health and Food Safety Laboratory System diagnosed 26 cases of low-pathogenic H6N2 avian influenza from 12 commercial egg-laying farms. The most common gross and histologic lesions observed in infected chickens were fibrinous yolk peritonitis, salpingitis, oophoritis, and nephritis. Edema of the mesentery of the oviduct and pale, swollen kidneys were also observed. Mortality in infected flocks ranged from 0.25% to 3%, and egg production dropped 7% to 40%.