Evaluation of anatomopathological, serological, immunological responses and protection in broilers vaccinated with live infectious bursal disease vaccines

ABSTRACT The study was divided into three experiments. In the first one, broilers were distributed into six groups and vaccinated against infectious bursal disease at 14 days of age: T1-not vaccinated, T2-Lukert1 (intermediate), T3-Lukert2 (intermediate plus), T4-228E, T5-V877 and T6-Winterfield 2512 (hot strains). Bursas of Fabricius (BF) were collected at 17, 21, 28 and 35 days to measure BF relative weight (BFRW), diameter, histological examination and image processing analysis (IPA). At one, 14, 21, 28 and 35 days of age, samples of blood taken from eight birds from each group for serology analysis by ELISA test. Hot strains vaccines induced reduction of BFRW and BF diameter, higher histological score lesion degree, more lymphocyte depletion on the BF follicles and higher IBD antibody titer. In the second experiment, 16 birds from groups T1 to T6 were isolated and challenged with a very virulent strain of IBDV (vvIBDV) at 25 days of age. Only groups T4, T5 and T6 were totally protected against vvIBDV challenge. In the third experiment, the immunosuppressive potential of each vaccine was determined by examining the ability of IBDVvaccinated birds to respond to Newcastle disease (ND) vaccination and challenge. None of the vaccines was found to be immunodepressive.

RESUMO O estudo foi dividido em três experimentos. No primeiro, frangos foram distribuídos em seis grupos e vacinados contra a Doença Infecciosa da Bursa (IBD) aos 14 dias de idade: T1-não vacinados, T2-Lukert1 (intermediária), T3-Lukert2 (intermediária plus), T4-228E, T5-V877 e T6-Winterfield 2512 (cepa forte). As bursas de Fabrícius (BF) foram colhidas aos 17, 21, 28 e 35 dias para mensurar o seus pesos relativos da BF (BFRW), diâmetros, exames histológicos e processamento de imagem imagens(IPA). Ao primeiro, 14, 21, 28 e 35 dias de idade, foram colhidas amostras de sangue de oito aves de cada grupo para a realização de sorologia através do método ELISA indireto. As vacinas cepa forte induziram redução do BFRW peso e do diâmetro da BF, maior grau de lesão histológica e depleção linfocitária e títulos mais elevados de anticorpos. No segundo experimento, 16 aves dos grupos T1 ao T6 foram isoladas e desafiadas com o vírus muito virulento da IBD (vvIBDV) aos 25 dias de idade. Somente os grupos T4, T5 e T6 foram completamente protegidos do desafio com vvIBDV. No terceiro experimento, o potencial imunossupressor de cada vacina foi determinado através da capacidade das aves vacinadas responderem à vacinação contra a Doença de Newcastle (ND) e posterior desafio. Nenhuma vacina apresentou-se imunossupressora.

Anticorpos Para o Vírus da Anemia das Galinhas (CAV) em Matrizes de Corte no Brasil

Although the isolation and identification of CAV as well as other recent diagnosis of the virus in broiler flocks have provided evidence for chicken anemia virus, Brentano & Ottati (1999), the prevalence of CAV had not yet been determined in Brazil. Since the knowledge of the prevalence of the virus and the level of antibodies against CAV in breeders flocks provide key information for designing control measures against chicken infectious anemia, we conducted a serological survey in broiler breeders of different ages, in five States with intensive commercial broiler flock production. Of a total of 2,355 sera tested by a commercial ELISA assay, 89% were found positive for antibodies to CAV, indicating a high prevalence of the virus in Brazil, in all the surveyed states. The analysis of antibodies to CAV in 6 to 70 week-old breeders showed that flocks between 6 and 18 weeks of age have the highest number of seronegative and low antibody titer chickens, thus representing the age group with the most uneven level of immunity against CAV. Chickens with negative or low antibody titers were still detected until 24 weeks of age, whereas at 25 weeks there was a 100% seroconversion to CAV and a reduction to less than 2,5% in the number of chickens with low antibody titers. These results provide evidence for a gradual and progressive virus spread in broiler breeder flocks, with the occurrence of a small percentage of chickens with low antibody titers at beginning of lay and therefore susceptible to inadequate transfer of passive immunity and vertical transmission of CAV to their progeny.

Apesar do diagnóstico da anemia infecciosa e mais evidências recentes de infecção em campo (Brentano & Ottati, 1999), não havia até hoje dados disponíveis da prevalência do vírus da anemia das galinhas (CAV) no Brasil. Uma vez que o conhecimento da prevalência do vírus e da distribuição de anticorpos nos lotes de matrizes é essencial para o delineamento de estratégias de controle da doença, realizamos um levantamento em 5 Estados com produção comercial intensiva de linhas de corte, abrangendo lotes de aves com diferentes idades. De 2.355 soros testados por ELISA, 89% foram positivos, indicando a alta prevalência do CAV no Brasil, em todos os Estados testados. A análise do soro de aves das 6 até as 70 semanas de idade demonstrou que lotes de 6 a 18 semanas apresentam desuniformidade na imunidade ao CAV, caracterizada por títulos de anticorpos abaixo dos níveis considerados protetores e aves ainda negativas para o CAV. A desuniformidade nos títulos de anticorpos e a ausência dos mesmos são evidentes ainda, mas em menor proporção também até as 24 semanas, enquanto que apenas partir das 25 semanas há 100% de soroconversão, acompanhada de significativa redução da desuniformidade no título de anticorpos das matrizes para menos de 2,5% das aves. Esses resultados fornecem evidência de uma progressiva disseminação do vírus em matrizes de corte, mas com riscos da presença de aves ainda susceptíveis à transmissão vertical e inadequada transferência de imunidade passiva no início do período de postura, que podem culminar em surtos da doença na progênie.

Anticorpos Para o Vírus da Anemia das Galinhas (CAV) em Matrizes de Corte no Brasil

Although the isolation and identification of CAV as well as other recent diagnosis of the virus in broiler flocks have provided evidence for chicken anemia virus, Brentano & Ottati (1999), the prevalence of CAV had not yet been determined in Brazil. Since the knowledge of the prevalence of the virus and the level of antibodies against CAV in breeders flocks provide key information for designing control measures against chicken infectious anemia, we conducted a serological survey in broiler breeders of different ages, in five States with intensive commercial broiler flock production. Of a total of 2,355 sera tested by a commercial ELISA assay, 89% were found positive for antibodies to CAV, indicating a high prevalence of the virus in Brazil, in all the surveyed states. The analysis of antibodies to CAV in 6 to 70 week-old breeders showed that flocks between 6 and 18 weeks of age have the highest number of seronegative and low antibody titer chickens, thus representing the age group with the most uneven level of immunity against CAV. Chickens with negative or low antibody titers were still detected until 24 weeks of age, whereas at 25 weeks there was a 100% seroconversion to CAV and a reduction to less than 2,5% in the number of chickens with low antibody titers. These results provide evidence for a gradual and progressive virus spread in broiler breeder flocks, with the occurrence of a small percentage of chickens with low antibody titers at beginning of lay and therefore susceptible to inadequate transfer of passive immunity and vertical transmission of CAV to their progeny.

Apesar do diagnóstico da anemia infecciosa e mais evidências recentes de infecção em campo (Brentano & Ottati, 1999), não havia até hoje dados disponíveis da prevalência do vírus da anemia das galinhas (CAV) no Brasil. Uma vez que o conhecimento da prevalência do vírus e da distribuição de anticorpos nos lotes de matrizes é essencial para o delineamento de estratégias de controle da doença, realizamos um levantamento em 5 Estados com produção comercial intensiva de linhas de corte, abrangendo lotes de aves com diferentes idades. De 2.355 soros testados por ELISA, 89% foram positivos, indicando a alta prevalência do CAV no Brasil, em todos os Estados testados. A análise do soro de aves das 6 até as 70 semanas de idade demonstrou que lotes de 6 a 18 semanas apresentam desuniformidade na imunidade ao CAV, caracterizada por títulos de anticorpos abaixo dos níveis considerados protetores e aves ainda negativas para o CAV. A desuniformidade nos títulos de anticorpos e a ausência dos mesmos são evidentes ainda, mas em menor proporção também até as 24 semanas, enquanto que apenas partir das 25 semanas há 100% de soroconversão, acompanhada de significativa redução da desuniformidade no título de anticorpos das matrizes para menos de 2,5% das aves. Esses resultados fornecem evidência de uma progressiva disseminação do vírus em matrizes de corte, mas com riscos da presença de aves ainda susceptíveis à transmissão vertical e inadequada transferência de imunidade passiva no início do período de postura, que podem culminar em surtos da doença na progênie.

Experimental infection of swine by Isospora suis Biester 1934 for species confirmation.

A survey of Isospora suis performed in 177 faecal samples from 30 swine farms detected thin wall type I. suis oocysts in seven samples. This type of oocyst measuring 23.9 by 20.7 microns had a retracted thin wall similar to that of the genus Sarcocystis. This type of oocysts, isolated from four different faecal samples, was inoculated in four-five-days-old piglets free of contamination in order to verify the life cycle and pathogenicity of the species. The pigs were kept in individual metal cages and fed with cow milk. Daily faecal collections and examinations were performed until the 21st day after infection. MacMaster and Sheather's methods were used for oocyst counting and identification. Infected piglets produced yellowish-pasty diarrhoea with slight dehydration. The prepatent and patent periods were respectively from 6 to 9 and 3 to 10 days after infection. Oocyst elimination was interrupted on the 10th and 11th days after infection with biphasic cycles. Thin and thick wall oocysts were detected in the same faecal samples. Thin walls were not observed in unsporulated oocytes. The observations suggest that this type of oocysts could appear in specific strains which occur in the later stages of their development. These oocysts seem to be responsible for clinical and pathogenic signs of neonatal isosporosis in pigs.

Prevalence of porcine neonatal isosporosis in Brazil.

The prevalence of Isospora suis and clinical signs of isosporosis were observed in 33 swine farms from 20 sites in the southeastern state of São Paulo, Brazil. The study was performed by collecting 177 faecal samples from nursing and weaned piglets. A history of clinical neonatal isosporosis, as well as the type of farrowing and nursery houses and the pig management in the farms were correlated to the prevalence of I. suis oocysts. Six faecal samples were collected in each of the farms (two from groups of 10- to 19-day-old piglets, two from groups of 20- to 29-day-old and another two from groups of 30- to 50-day-old pigs). Faecal consistency was also registered at the time of their collection. Chi-square tests were used for statistical analysis. Oocysts were more prevalent in farms with a history of neonatal isosporosis than in those without previous cases. Faecal consistency was not related to oocyst elimination. In farms with a history of clinical isosporosis, faecal samples from groups of 10- to 19-day-old piglets showed a higher prevalence of oocysts than the groups of other ages studied. There was no difference in the prevalence of oocysts between nursing and weaned piglets. Oocysts were more prevalent in faecal samples collected from dirty-cemented floors than from self-cleaning floors in the farrowing houses. Types of floor and pig management in nursery houses were not associated with the presence of oocysts in weaned pigs.