Persistent infection with chicken anaemia virus and some effects of highly virulent infectious bursal disease virus infection on its persistency

Chicken anaemia virus (CAV) infectivity and the effect of highly virulent infectious bursal disease virus (hv IBDV) infection on CAV's infectivity were examined in chickens inoculated with CAV or inoculated dually with CAV and hv IBDV. Five chickens inoculated dually with hv IBDV at 35 days old and then with CAV at 40 days old exhibited no clinical signs of disease, but showed atrophic bursae of Fabricius when necropsied 4 weeks later. Upon examining the chickens at 7 days postinoculation (dpi) with CAV, it was found that hv IBDV infection had inhibited production of virus neutralising (VN) antibody to CAV, and that it was possible to recover CAV from plasma of these chickens. Although VN antibody to CAV appeared after 14 dpi, CAV was recovered from blood cells (BC s) at high titres ranging from 10(2.5)to 10(5.5)TCID(50)/0.1 ml, 7 to 28 dpi in IBDV -induced immunosuppressed chickens. In addition, CAV was sporadically recovered, using rectal swabs, from the dually inoculated chickens at low titers, ranging from 10(1.0)to 10(2. 0)TCID(50)/0.1 ml). In contrast, although CAV was recovered from BC s in most of the chickens inoculated with CAV alone, the titers were lower (10(1.0)to 10(2.5)TCID(50)/0.1 ml). No CAV was detected from the rectal swabs of these chickens. The results of virus recovery were confirmed by polymerase chain reaction. This study first examined the persistency of CAV in BC s and the effective enhancement of primary CAV infection as a result of immunosuppression caused by hv IBDV infection.     

Detection of chicken anemia virus in the gonads and in the progeny of broiler breeder hens with high neutralizing antibody titers

Previous evidence for the presence of chicken anemia virus (CAV) in the gonads of immune specific-pathogen-free chickens raised the question whether this occurs also in commercial breeders. The presence of CAV was investigated by nested PCR in the gonads and spleens of hens from two 55- and 59-week-old, CAV-vaccinated (flocks 2 and 3), and two 48- and 31-week-old non-vaccinated broiler breeder flocks (flocks 1 and 4). In addition, lymphoid tissues of 20-day-old embryos from these hens were also investigated for the presence of CAV. CAV was detected in the gonads and of 5/6 and 11/22 of the vaccinated hens and in some hens also in the spleen alone. Embryos from 7/8 and 5/18 of these hens were positive. In the non-vaccinated flocks, CAV was detected in the gonads of 11/34 and 10/10 hens in flocks 1 and 4, respectively. In addition, 11 birds in flock 1 had positive spleens. CAV DNA was detected in 3/11 and 2/10 of their embryos. CAV-positive gonads and embryos were detected in samples from hens with moderate as well as high VN antibody titers. Vaccinated chickens positive for CAV in the gonads and in their embryos had VN titers ranging from >1:512 to <1:2048. In non-vaccinated chickens, the VN titers of CAV positive chickens ranged from 1:128 to 1:4096. These results demonstrate that CAV genome can remain present in the gonads of hens in commercial broiler breeder flocks even in the presence of high neutralizing antibody titers that have been associated with protection against CAV vertical transmission. It also suggests that transmission to the progeny may occur irrespectively of the level of the humoral immune response in the hens.     

A study of the epidemiology of infectious bursal disease in poultry in Queensland, 1976–1979

The epidemiology of infectious bursal disease (IBD) was studied by serology and sometimes by visual examination of the bursa of Fabricius in poultry flocks in Queensland during 1976–1979.
Ten flocks, each of approximately 30,000 meat breeding chickens, were surveyed. All chickens had maternally-derived antibody against IBD virus (IBDV) at hatching and active antibody was not detected while the chickens were brooded on rearing farms. When distributed to breeding farms, 7 of the flocks developed antibody when 11 to 25 weeks of age. The remaining 3 flocks were vaccinated by infection of 10% of the birds and within 4 weeks more than 80% of the chickens had developed precipitating antibody to IBDV.
Blood samples of 20 to 30 broiler chickens were collected at slaughter (7 to 9 weeks of age) from each of 312 broiler flocks raised on 37 contract farms. While the samples from 21 flocks were without detectable antibody to IBDV, all serum samples for 263 flocks contained antibody. The ratio of bursal weight to bodyweight was significantly lower in birds from 144 flocks having antibody to IBDV than in birds from 10 flocks that were without detectable antibody. In sequential studies, IBDV antibody became demonstrable in 27 of 30 flocks when the chickens were one to 6 weeks of age and was accompanied by bursal atrophy.
Serological investigation of 4 flocks of layer breeding chickens on a multi-age farm at approximately monthly intervals resulted in antibody to IBDV being detected at every examination.
Serological tests and bursal examinations were carried out weekly in 2 flocks each of 4000 layer chickens between one and 20 weeks of age. Serum antibody developed in one flock at 4 weeks of age and in the other at 17 weeks of age. In both flocks, bursal atrophy occurred concurrently with the development of antibody.     

Immune responses of breeding chickens to trivalent oil emulsion vaccines: responses to infectious bronchitis

Three similar flocks of broiler breeder parent chickens that had been given live infections bronchitis (IB) vaccines during rearing were injected at 20 weeks of age with three different oil emulsion vaccines: a commercial monovalent Newcastle disease (ND) vaccine (flock A); an experimental bivalent vaccine containing ND and infectious bursal disease (IBD) components (flock B); and an experimental trivalent vaccine containing ND, IBD and IB components (flock C). One week after vaccination 40 hens from flock A and 40 from flock C were taken to the laboratory and their egg yields individually recorded. At 37 weeks of age they were challenged by aerosol exposure to virulent IB virus. The egg production dropped significantly in the hens from flock A but not in the hens from flock C. On the farm, flock C showed a higher mean IB virus antibody titre four weeks after vaccination but titres rose in all three flocks indicating the presence of active IB virus infection. No differences in egg yields were found between the three farm flocks.     

THE PATHOGENESIS OF INFECTIOUS AVIAN ENCEPHALOMYELITIS

An association was demonstrated between the development of clinical infectious avian encephalomyelitis (IAE), the persistence and titre of infectious avian encephalomyelitis virus (IAEV) in the brain of the chicken, the duration of detectable viraemia and the age of the chicken at the time of infection with the virus. The older the chicken at the time of infection the milder the disease, the lower the virus titre in the brain and the shorter the period of viraemia. IAEV serum neutralising antibody was produced earlier after infection in older chickens, and its detection was associated with decreasing virus titres in the brain and the cessation of detectable viraemia. Treatment of chickens with testosterone in ova, to inhibit the development of antibody synthesis, prevented the onset of age-associated resistance and testosterone treated birds were as susceptible to clinical IAE as baby chickens. The results suggested that the ability to produce IAEV serum neutralising antibody was an important component of age-associated resistance to IAE.     

Economic effects of clinical chicken anemia agent infection on profitable broiler production.

An outbreak of anemia dermatitis syndrome caused by chicken anemia agent (CAA) occurred in 15 broiler flocks. An average of 29% of chickens in these flocks were derived from a common breeder flock. The breeder flock had no antibody to CAA at 20 weeks of age but had seroconverted by 31 weeks. Diseased broiler flocks were derived from eggs laid by the breeder flock between 25 and 30 weeks of age. CAA infection in the breeder flock was subclinical, with no apparent effects on mortality or performance. A strategic program of therapeutic and/or prophylactic antibiotic therapy was begun in affected broiler flocks as soon as the disease was diagnosed. Nevertheless, when the cost of therapy was taken into account, affected broiler flocks had a net income 17.3% to 19.6% lower than normal flocks. Average bird weights were 3.3% to 3.5% lower in affected flocks than in unaffected flocks, and affected flocks had a significantly greater proportion of lighter birds. Average mortality in affected flocks was 2.0% to 2.3% higher than in normal flocks, with peak mortality occurring in the third week of life. There was no apparent effect on feed-conversion ratio.     

Serological survey of the prevalence of Toxoplasma gondii antibodies in rams in sheep flocks in New South Wales

SUMMARY Serum samples from 5724 rams on 534 farms in New South Wales were tested in the indirect fluorescent antibody test for toxoplasmosis. Nine per cent of rams had titres of 64 or higher and 41% of flocks had either one or more rams with a titre of 64 or higher. There were significant differences in the geographical distribution of infected flocks, ranging from 57.8% of flocks infected on the tablelands to 41% on the slopes and 22.4% on the plains. There were significantly more infected commercial flocks (47.5%) than stud flocks (32.9%). The results indicated that the prevalence of infection was influenced by management, with a higher prevalence of infection in flocks kept under an intensive or semi-intensive system of management.     

核酸探针检测山东省鸡群中马立克病毒、传染性贫血病毒、网状内皮增生病病毒和呼肠孤病毒的流行状况

为对山东家禽业免疫抑制病的流行情况进行调查,从烟台、滨州、临沂、泰安、聊城、青岛大型养殖场共随机收集600只病死鸡的肝脏和脾脏病例组织样品,用斑点杂交的方法检测样品中鸡马立克病毒（Marek’s disease virus, MDV）、传染性贫血病毒（chicken anemia virus,CAV）、网状内皮增生病病毒(reticuloendotheliosis virus,REV)和呼肠孤病毒（reovirus,REOV）的感染情况。结果发现,MDV、CAV、REV、REOV的感染率分别为5.17%、8.17%、1.17%、2.5%,检出率较以前的研究报道有降低趋势,有多种双重感染和三重感染,表明山东家禽业在免疫抑制病方面总体控制较好,但不同的养殖场发病情况差异极显著,管理水平参差不齐,个别地区发病情况严重,检出率超过其他地区的总和。     

我国白羽肉用型鸡群中CAV、REV和REOV感染状况的血清学调查

为了解鸡传染性贫血病毒（CAV）、禽网状内皮增生病病毒（REV）和呼肠孤病毒（REOV）在我国白羽肉用型鸡中的感染状态，在2003—2004年，检测了来自5省市8个公司不同年龄鸡群血清样品中3种病毒抗体的存在状况。结果表明，在送检的75个鸡群中，对CAV、REV和REOV呈现抗体阳性的鸡群分别有64个（85．3％）、36个（48％）和74个（96％）。在总共检测的1764份血清样品中，对这3种病毒的平均抗体阳性率分别为51．4％、9．8％和75．1％。在1日龄雏鸡，对CAV和REOV的平均母源抗体阳性率可达100％和81．1％，但对REV只有7．4％。抗体阳性率随年龄变化的动态分析表明，对REV和REOV的母源抗体在出壳后2～3周内消失，而对CAV的母源抗体则可持续3～4周。对CAV和REOV的抗体从5周龄起再次出现，到20周龄时，所有送检鸡群全部阳性，平均阳性率在90％以上。有近一半送检鸡群对REV呈现抗体阳性，抗体阳性率普遍较低，即使在达到开产年龄后，仍还有很高比例鸡为抗体阴性，即对REV仍为易感鸡。研究表明，我国多数鸡群中都同时存在着这3种病毒的感染，但它们在感染的程度和动态等流行病学特点上显著不同，应根据鸡群中抗体的阳性率分别采取不同的措施。     

Postvaccination viremia in breeding flocks of layers and broilers after vaccination against Marek's disease of fowl

The immunity state after vaccination against Marek's disease (MD) was studied in three multiplier flocks of laying fowl (MFL), five multiplier flocks of broiler fowl (MFB), and one commercial layer flock (CLF). The occurrence and average titres of post-vaccination viraemia in the selected sets of chickens from these flocks, examined at the age of three or twenty weeks, were used as the immunity criterion. The development of post-vaccination viraemia, following the administration of the MARVAK vaccine at the doses of 100 and 1000 PFU per bird in the HX-SL and Shaver layer hybrids, was examined under laboratory conditions at the same time. In the group of birds examined in the third week of age and coming from the MFL vaccinated with the recommended MARVAK vaccine (dose (100 PFU per bird), 64.3% of the chicks were viraemic, the average viraemia titre being 12 PFU/10(7) leucocytes. After the administration of a four-fold vaccine dose, 57.1% of the chicks were viraemic, the average titre being 3.2 PFU/10(7) leucocytes. After the administration of a ten-fold dose of MARVAK vaccine, 80% of the chicks were viraemic and the average titre of viraemia was 8 PFU/10(7) leucocytes. In the MFB vaccinated with the recommended dose of the MARVAK vaccine, the percentage of viraemic chickens was 48.3% and the average titre of viraemia was 6.5 PFU/10(7) leucocytes. In the pullets examined at the age of 20 weeks the number of viraemic birds ranged from 20 to 50% and the average viraemia titres were from 3.8 to 13.1 PFU/10(7) leucocytes. In the flock affected by acute MD, no post-vaccination viraemia was found in the clinically diseases pullets. In the chickens of the HX-SL line vaccinated with the recommended MARVAK vaccine dose, viraemia culminated in the third week after vaccination (31.5 PFU/10(7) leucocytes), and after the use of the dose ten times as high as the recommended one the culmination came a week later (47 PFU/10(7) leucocytes). In the Shaver chicks vaccinated with the recommended dose or with the ten-fold dose of the MARVAK vaccine, the post-vaccination viraemia culminated in the fourth week after vaccination (94.9 and 116.8 PFU/10(7) leucocytes). The post-vaccination precipitation antibodies were first detected in the eighth week after vaccination.     

肉种禽网状内皮增生症、鸡传染性贫血和禽白血病血清学调查

对不同种鸡场不同周龄肉种鸡进行REV、CAV和ALV（A、B亚群）抗体检测。在572份血清样品中，除了一个8．1周龄和15周龄鸡群CAV抗体阳性率分别为13．3％和75％外，其它鸡群无论是否进行CAV疫苗免疫，抗体阳性率均为100％。在212份血清样品中，REV抗体阳性率在16．7％～62．5％之间；ALV（A、B亚群）抗体阳性率在0％～75％之间。本研究结果表明，所检测种鸡群中存在3种免疫抑制性病毒的感染或混合感染。     

A survey for parvovirus-like virus (so-called chick anemia agent) antibodies in broiler breeders

A prospective study to survey for the presence of parvovirus-like virus (PVLV; so-called chick anemia agent) antibody in broiler breeder pullets in Georgia, North Carolina, and Florida was conducted by collecting serum samples from 52 breeder flocks that ranged in age from 1 day to 55 weeks old. Results indicated that PVLV infection was widespread. Ninety-eight percent (51/52) of chicken flocks and 62% (530/861) of chickens had PVLV antibody. Rates of antibody-positive chickens among flocks ranged from 0% to 100% and averaged 76%. Upon initial examination, the percentages of chickens positive for PVLV appeared evenly distributed with respect to several convenient age groups and geographic locations. However, compared with young chickens (less than or equal to 19 weeks old), markedly significantly lower proportions of positives were present among chickens more than 19 weeks old (P = 0.00001) or chickens 30 weeks old or more (P = 0.000004). Also, there were significant (F = 7.7, df = 3/827, P less than 0.001) differences among the rates of PVLV antibody in chickens among various companies. The relatively high rate of PVLV antibody among broiler breeder chickens helps explain the low incidence of clinical disease among their offspring.     

Local chicken production system in Malawi: Household flock structure,dynamics, management and health

Household flocks of scavenging chickens were monitored from August 2002 to August 2003 in 27 villages in Lilongwe, Malawi. The objective was to evaluate the local chicken production system by investigating flock structure, utilization, management and constraints. Farmers and researchers jointly obtained data on household flocks. Mean flock size was 12.9, with a range of 1–61 chickens. The flock dynamics of chickens over 8 weeks old constituted 91% migrating out of flocks and 9% into the flocks. Primary functions based on flock dynamics were, in order of importance, household consumption, participation in socio-cultural ceremonies, selling, exchanging breeding stock and gifts. Of the flock exits, 43.9% were due to losses from diseases, predation and theft. Most flocks (85%) were housed in human dwelling units. Scavenging was the main source of feed. The majority (77.6%) of farmers supplemented their chickens erratically with energy-rich feeds, mostly maize bran. Most supplementation took place during the cold-dry season. Village chicken production offers diverse functional outputs but faces animal health (diseases, parasites, predation) and management (feeding) constraints, which require an integrated intervention approach at community and household level.     

Prevalence of antibodies to pestiviruses in goats in Austria

Serological investigations were carried out to determine the prevalence of pestiviral infections in goats in Austria, and to investigate the possible relations to herd management practices. The prevalence of antibodies to pestiviruses was investigated in 549 goats in 80 flocks from four regions of Austria. The examination for antibodies was performed using an indirect enzyme-linked immunosorbent assay detecting antibodies to the border disease virus (BDV) and bovine viral diarrhoea virus (BVDV). The observed individual prevalence was 11.5% and the flock prevalence was 31.3%. Comparative neutralization studies on the 63 seropositive samples with BVDV-1, BVDV-2 and the BDV yielded in 32 samples higher titres (> or =4-fold) to BVDV-1 and in two samples to BDV. The remaining samples did not show distinct differences in antibody titres against the pestivirus strains tested because of the cross-reactions. There was a significant (P < 0.05) association between the prevalence of antibodies to pestiviruses and the presence of cattle on the farm. Significant (P < 0.05) geographical variations in individual prevalence were obtained, ranging from 3.5% in lower Austria to 20.2% in Vorarlberg.     

Probable infectious stunting syndrome in replacement pullets

Infectious stunting is recorded in detail in three egg-type pullet flocks and one egg-type breeder flock. Three different strains of brown egg birds were involved. The clinical effects were less severe than those usually seen in broilers. Excessive mortality during the first three weeks was a feature of all four flocks. Fibrous atrophy of the pancreas was seen in one flock and could still be found in individual birds at 18 weeks old. Bone disorders were seen in two flocks. Severe anaemia was seen in some birds in one flock. Severe emaciation of the pectoral muscles was an unexplained and prominent feature of all the flocks. As the birds grew the visible and clinical evidence of stunting was much reduced and it appeared that compensatory growth took place so that by 18 weeks old the flocks appeared normal and the culling rate at caging was negligible.     

An enzyme-linked immunosorbent assay for the detection of antibody to avian reovirus by using protein sigma B as the coating antigen

An enzyme-linked immunosorbent assay using the expressed protein sigma B as the coating antigen (sigma B-ELISA) for detecting antibody to avian reovirus (ARV) in chickens was developed and compared with a conventional ELISA. Both ELISA s and a serum neutralisation (SN) test were used to test the sera from experimentally vaccinated and farm chickens. The sigma B-ELISA could clearly distinguish the SN-positive and -negative sera in 38-week-old chickens. The correlation rate between SN and a sigma B-ELISA was 100 per cent (65/65), and that between SN and conventional ELISA was 84 per cent (55/65). With the sigma B-ELISA, all SN-negative sera had low absorbance values (below 0.06), and the absorbance values correlated closely with the SN titres. However, the sera which were antibody-negative by SN had various absorbance values, ranging from 0.07 to 0.39 in the conventional ELISA. Hence, the sigma B-ELISA had lower non-specific binding reactions than the conventional ELISA against sera from ARV -negative birds. Antibody against ARV could be detected by sigma B-ELISA after vaccination. Absorbance values peaked 4 weeks after vaccination at 2 weeks of age and were maintained until the birds were 27 weeks old. The results suggest that the presence of antibody against viral protein sigma B in birds may be used as a good indicator by the sigma B - ELISA for detecting immune status of a chicken flock or to detect chickens infected with ARV.     

Pestiviral infections in sheep and pigs in Northern Ireland

Serological surveys were carried out to determine the prevalence of pestiviral infections in sheep and pigs in Northern Ireland. Sera from 918 ewes in 92 flocks from 10 regions were tested by ELISA for antibodies to border disease virus and positive results were obtained from 49 ewes (5.3 per cent) in 28 flocks (30.4 per cent). There were highly significant geographical variations in its flock prevalence ranging from 0 per cent in the Enniskillen region to 70 per cent in the Coleraine region. There was no significant association between the proportion of seropositive flocks and the presence of cattle on the farm (P = 0.583). In the positive flocks, the average rate of seroprevalence was 17.5 per cent, and the highest was 40 per cent. Comparative neutralisation studies on 14 positive sera with bovine viral diarrhoea virus type I (BVDV I) and border disease virus revealed higher titres (> or = four-fold) to BVDV I in all cases. Only one positive result was obtained when fluids from 186 aborted ovine fetuses were tested for border disease virus by ELISA. Serum samples from 680 pigs in 46 herds were tested for virus neutralising antibodies to border disease virus. Twenty sera (2.9 per cent) were cytotoxic, and only one of the remaining 660 sera gave a positive result. This sample tested negative for classical swine fever by ELISA, and comparative neutralisation studies showed that it had a four-fold higher titre to BVDV I than to border disease virus.     

Protection of broilers against Newcastle disease by hyperimmunisation of the dams

A flock of broiler parents was hyperimmunised against Newcastle disease (ND) by subcutaneous injection of an experimental high-potency inactivated oil emulsion (IOE) vaccine in order to achieve high and long-lasting passive protection in broilers. During the egg production period mean log2 HI ND titre of the parents slowly decreased from 11.6 at 26 weeks of age to 10.0 at 53 weeks of age. Titres of day-old progeny paralleled those of their parents. Mean protection of broilers against mortality following challenge with Herts 33 virus at the ages of 1, 2, 3 and 4 weeks was 86%, 73%, 54% and 44%, respectively. As compared with the current Dutch situation, application of the high-potency IOE vaccine will significantly increase antibody titres in parent flocks and the level and duration of passive protection in broilers. It is concluded that passive ND protection of broilers by hyperimmunisation of the dams is realisable from an economic point of view and is suitable for low-risk areas.     

Development and application of an ELISA for detecting antibodies to Salmonella enteritidis in chicken flocks.

Enzyme-linked immunosorbent assays (ELISAs) were developed for the detection of IgG antibody to Salmonella enteritidis in poultry flocks. A lipopolysaccharide (LPS) and heat-extracted (HE) antigen for use in the ELISA were evaluated together with the rapid slide test (RST), microagglutination test (MT) and the microantiglobulin (MAG) test. In experimentally infected specific pathogen free chickens, good correlation was seen between all tests although, generally, the MT and MAG detected antibody earlier and titres peaked earlier than the ELISAs. The LPS antigen detected antibody earlier than the HE antigen but the latter gave higher titres in the later stages of infection. Cross reactions were seen between S enteritidis and S typhimurium in the ELISAs although homologous reactions were always much higher. Antisera to S montevideo or S senftenberg gave weak positive reactions in both S enteritidis ELISAs. Serological and bacteriological examinations of representative samples from two commercial chicken flocks were carried out. In flock A the HE-ELISA and MAG test detected antibody in nearly all birds. The LPS-ELISA detected antibody in over 60 per cent of birds, while the MT and RST detected few seropositive birds. The whole blood test using the stained S pullorum antigen on the farm detected antibody in just under 25 per cent of the birds. S enteritidis was isolated from the organs of 25 per cent of the birds. All birds in flock B were seronegative by all tests; no salmonellae were isolated from the organs of these birds.     

新城疫单抗ELISA试剂盒监测免疫鸡群中新城疫强毒

应用新城疫（ND）单抗ELISA试剂盒对2个免疫鸡群中ND强毒感染情况及个体感染强毒后排毒动态跟踪监测，并平等测定其HI抗体效价。共采集泄殖腔棉拭子和血液对应样品2317份。结果表明：HI效价2－14之间的个体均可检出强毒，其中HI效价在6以下和11以上的个体强毒检出率都较高。HI效价在6以上的个体仍角感染强毒，强毒感染导致HI抗体水平上升，且感染前低者上升速度较快，幅度亦较大；并且发现排毒个体的高水平抗体是强毒感染所致。个体感染强毒后排毒过程可长达3周，而且感染前抗体水平低者排毒时间相对较长。强毒一旦侵入鸡群便可在群内巡回传播，长期维持下来。