A micro‐scale serum neutralisation test for the detection and titration of antibodies to chicken anaemia agent ‐ prevalence of antibodies in Danish chickens

Humoral and cellular immune responses in adult geese induced by an inactivated vaccine against new type gosling viral enteritis virus

To assess the immunogenicity of an inactivated new type gosling viral enteritis virus (NGVEV) vaccine, we investigated 3 different doses of the inactivated vaccine and the inactivated vaccine in conjunction with 3 different doses of recombinant goose interleukin-2 (rGoIL-2) adjuvant. A virus concentration of 10(5) 50% embryo infective dose/mL was subcutaneously inoculated into adult geese divided into 6 groups. The dynamic changes of the humoral and cellular immunity responses elicited by the vaccines in the adult geese postvaccination (PV) were investigated using ELISA, virus neutralization test, and lymphocyte proliferation assay. The clearance of virus from the intestines of geese (175 d PV) was studied by histopathological examination and indirect immunofluorescence assay after virulent NGVEV challenge. This study showed that the inactivated NGVEV vaccine elicits strong humoral and cellular responses in the vaccinated adult geese. The absorbance values of specific anti-NGVEV antibodies, the neutralization antibody titer, and the lymphocyte proliferation index rapidly increased, peaked at about 28 d PV, progressed to the plateau stage, and then decreased slightly. The rGoIL-2 adjuvant enhanced the immune response, and this adjuvant in conjunction with the inactivated NGVEV vaccine induces a significantly higher specific anti-NGVEV antibody absorbance value, neutralization antibody titer, and lymphocyte proliferation index than the non-adjuvant-inactivated NGVEV vaccine (P < 0.05). The inactivated NGVEV vaccine conferred adequate efficient ability to clear NGVEV in vaccinated geese even in the last phase of the vaccination period (175 d PV). The inactivated NGVEV vaccine (0.5 mL/goose) with 1,000 units of rGoIL-2 adjuvant/goose is the most effective dose, thereby eliciting the strongest humoral and cellular immunity responses and providing the most efficacious clearance of NGVEV in vivo.

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.

Serologic evidence of chicken infectious anemia in commercial chicken flocks in southwest Nigeria

Sera samples from seven poultry farms in southwest Nigeria consisting of 7 broiler, 10 pullet, 1 layer, 1 cockerel, and 1 broiler breeder flocks were tested for the presence of chicken infectious anemia virus (CIAV) antibodies using a commercial enzyme-linked immunosorbent assay kit. Eleven of the 20 flocks (55%) and six out of seven (86%) farms were positive for CIAV antibodies. The seroprevalence largely depended on the age of the flocks. Seroprevalence was higher within the older pullet and layer flocks (83%-100%) than in the younger broiler flocks (0%-83%). In essence, all flocks older than 6 to 8 wk became infected. This is the first report of serologic evidence of CIAV in Subsaharan Africa. Since Southwest Nigeria is the main port of entry of imported chicken and the hub of major poultry breeders, the disease can probably be found throughout the country and beyond. Further studies are necessary to assess economic losses due to CIAV and the cost benefit of countermeasures.

Real-time quantitative PCR-based serum neutralization test for detection and titration of neutralizing antibodies to chicken anemia virus

Detection and titration of chicken anemia virus (CAV)-neutralizing antibodies has relied on tedious, time-consuming passaging of infected cells, or subjective recognition of cytopathic effect in individual cells, because CAV replicates in culture only in lymphoblastoid cell lines, and thus generates no plaques. This paper describes a rapid method, in which CAV genomes in infected cells are quantitated by qPCR 3-4 days postinfection (p.i.), without passaging cells. Three sera, weakly positive with a commercial CAV ELISA kit, from broiler chickens immunized with a commercial CAV vaccine, were used to develop the assay. Virus neutralization titers of these sera were determined using two different CAV-susceptible cell lines (MDCC-MSB1 and MDCC-CU147) by the conventional method of passaging cells infected with 10,000 TCID(50) CAV per well, and by qPCR-based methods using cells infected with 100 or 10,000 TCID(50) per well in 24-well or 96-well plates. The method was also adapted to conventional PCR. The positive sera exhibited virus neutralization activity at dilutions ranging from 1:10 to 1:320 by the various assays. Although virus neutralization titers differed somewhat depending on the assay conditions used, the relative order of the titers of the three positive sera was the same for all assays. The qPCR-based assays are as sensitive and more rapid for detection of neutralizing antibody than the conventional assay based on passaging infected cells, and more sensitive for detection of low-level CAV antibodies than a commercial blocking ELISA.

Prevalence of antibody to chicken anaemia virus (CAV) in Swedish chicken breeding flocks correlated to outbreaks of blue wing disease (BWD) in their progeny

A serological survey for antibody to Chicken Anaemia Virus (CAV) was performed on broiler breeders as well as layer breeding birds in Sweden at the end of their rearing period. Grandparents (GP) of both types leaving quarantine were in 21 out of 26 cases free from antibody to CAV, but often became infected soon thereafter. A total of 10 outbreaks of blue wing disease (BWD) in 3 series were recorded in the broiler and layer parent generation, all of which were progeny of 3 late seroconverting GP-flocks. All but one of 22 layer parent flocks had been infected and had seroconverted during the rearing period. Subsequently BWD was not recorded from commercial layers. Broiler parent flocks were more protected from CAV infection during rearing. Eighteen out of 94 broiler parent flocks had not developed antibody to CAV before coming into lay. Outbreaks of BWD were reported in progeny flocks from all these broiler breeders, with the exception of those that had been vaccinated. Good hygienic routines along with isolation of the birds delayed the seroconversion to CAV in broiler breeders and vaccination of these breeders protected their progeny from outbreaks of BWD. Broiler flocks in houses where BWD had occurred recently had always antibodies to CAV at slaughter. It was possible to eradicate the infection from the house and prevent the infection between flocks by proper cleaning and disinfection of the broiler houses.

Serological survey on the prevalence of chicken anaemia virus infection in Hungarian chicken flocks

A serological survey on the prevalence of chicken anaemia virus (CAV) infection was performed by using the indirect immunofluorescence (IF) and the virus neutralization (VN) tests in commercial Hungarian chicken populations. By the indirect IF test, a total of 846 serum samples from 13 meat-type parent flocks of two breeds were investigated between 10 and 62 weeks of age. All flocks were found to be positive for anti-CAV antibodies, and the rates of antibody-positive birds among flocks ranged from 40 to 93.3% and with an average of 73.3%. From nine 1-day- to 9-week-old progeny broiler flocks, 96 serum samples were tested. In the 3 flocks, sampled at the hatchery, 75 to 100% (average 86.4%) of the 22 tested birds were antibody positive. From the 6 flocks, tested between 4 to 9 weeks of age, 3 were antibody negative at 4 and 5 weeks of age, whereas in the 3 remaining 6- to 9-week-old flocks 10 to 20% (average 13.5%) of the birds were antibody positive. In egg-laying parent flocks of 14 and 35 weeks old, 54.4 and 71.7% of the tested 79 and 46 birds had antibodies to CAV, respectively. By the VN test, a total of 670 serum samples from 9 meat-type parent flocks aged between 11 and 37 weeks were investigated. The rate of antibody positivity in flocks was always over 80% and averaged 90.9%. From 7 progeny broiler flocks, 261 serum samples were tested between one day and 7 weeks of age, and the rates of seropositivity in flocks were between 93.3 to 100% and averaged 96.9%. In an egg-laying parent flock, 89.2% of the tested 102 birds had neutralizing antibodies to CAV at 35 weeks old. It was concluded that CAV is widespread in Hungarian commercial chicken populations. Though, according to simultaneous examination of 195 flock sera, the VN test revealed 11.3% more antibody-positive birds, the indirect IF test was found suitable for serological surveys at flock(s) level, provided that sufficient numbers of individual chicks were tested.

Influence of subclinical virus infections and other factors on broiler flock performance

1. The influence of subclinical infections with infectious bursal disease virus, adenoviruses, REO viruses and chicken anaemia virus and of various production variables on broiler flock performance was investigated. 2. A significant effect could not be demonstrated of any of the viral infections either alone or in combination. 3. The production results were profoundly influenced by several other factors, that is, breed, diet, stock density and contents of whole wheat grain in the food. 4. The incidence of horizontally-transmitted subclinical chicken anaemia virus infection in Danish broilers has decreased significantly during the period 1988-89 to 1992-93, probably because of improved hygiene and management. The incidence of adeno- and REO virus infections did not change during the same period. 5. It is concluded that factors other than subclinical viral infections presently have an economic impact on performance observed in the Danish broiler production.

Chicken anemia agent

Chicken anemia agent (CAA) is a small, spherical, non-enveloped virus containing a circular single-stranded DNA genome. CAA remains unclassified and probably should be classified in a new virus family. The chicken is the only recognized natural host for CAA. CAA was initially isolated in Japan and the associated disease chicken infectious anemia described in 1979. The virus has a world-wide distribution and is common in intensive poultry raising areas. Chicken infectious anemia is not a new disease but a newly recognized disease. CAA is now thought to play a key role in several multiple etiology disease syndromes; hemorrhagic syndrome; aplastic anemia, gangrenous dermatitis, hemorrhagic anemia syndrome, hemorrhagic aplastic anemia syndrome, anemia dermatitis and blue wing disease. The pathogenesis of chicken infectious anemia is described. Vertical transmission appears to be more important than horizontal spread. A yellow fatty bone marrow is the most characteristic lesion and thymic atrophy is the most consistent finding in CAA infection. Thymic and bone marrow intranuclear inclusion bodies occur with infection but are of limited value diagnostically and are very transient and rarely seen. Five different disease-producing scenarios that lead to clinical CAA infection in young chickens are presented.