PESQUISA VETERINÁRIA BRASILEIRA

Abstract in English:

ABSTRACT.- Millar P.R., Alves F.M.X., Teixeira V.Q., Vicente R.T., Menezes E.M., Sobreiro L.G., Pereira V.L.A. & Amendoeira M.R.R. 2012. Occurrence of infection with Toxoplasma gondii and factors associated with transmission in broiler chickens and laying hens in different raising systems. Pesquisa Veterinária Brasileira 32(3):231-236. Laboratório de Toxoplasmose, Instituto Oswaldo Cruz, Fiocruz, Avenida Brasil 4365, Manguinhos, Rio de Janeiro, RJ 21040-900, Brazil. E-mail: amendoei@ioc.fiocruz.br Toxoplasmosis is a zoonotic disease caused by the protozoan Toxoplasma gondii. The aim of the present study was to determine the occurrence and identify the risk factors associated with transmission of T. gondii to chickens raised in different systems (free-ranged and confined) to produce eggs or meat. The 810 animals were allocated in two experimental groups according to the production system purpose: 460 broiler chickens (Group 1) and 350 layer chickens (Group 2). In order to analyze the possible factors involved in T. gondii infection in the chickens, an epidemiological questionnaire was developed for all properties.The serological detection of anti-Toxoplasma gondii antibodies was performed by Indirect Immunofluorescence (IFAT) and by Enzime Linked Imunossorbent Assay (ELISA). Since the agreement index (kappa) between these two serological techniques was considered high, 21.2% of the 810 animals were considered reactive. In Group 1, 12.2% (56/460) were positive, while in the Group 2 the positivity rate was 33.1% (116/350). The production system may be influencing the seropositivity of the animals in both groups. However, only in Group 2 it was possible to notice a statistically significant relationship between the breeding system and the frequency of positive sera. This result indicates that, at least for laying hens, the production system is directly involved in T. gondii infection. The contact with cats in Group 1 did not influence the distribution of seroreactive animals, but in Group 2 a significant relationship was observed. The occurrence of anti-T. gondii antibodies was high in both groups (broiler and posture chickens). Free-ranged chickens raised for egg production proved to be the most exposed group to the T. gondii infection. This can be related to the fact that these animals stay for longer periods in the farms, in direct contact with possibly contaminated soil by the presence of domestic cats.

• Toxoplasma gondii

Abstract in Portuguese:

RESUMO.- Millar P.R., Alves F.M.X., Teixeira V.Q., Vicente R.T., Menezes E.M., Sobreiro L.G., Pereira V.L.A. & Amendoeira M.R.R. 2012. Occurrence of infection with Toxoplasma gondii and factors associated with transmission in broiler chickens and laying hens in different raising systems. Ocorrência da infecção por Toxoplasma gon- dii e fatores associados à sua transmissão em aves de corte e postura produzidas em diferentes tipos de criação. Pesquisa Veterinária Brasileira 32(3):231-236. Laboratório de Toxoplasmose, Instituto Oswaldo Cruz, Fiocruz, Avenida Brasil 4365, Manguinhos, Rio de Janeiro, RJ 21040-900, Brazil. E-mail: amendoei@ioc.fiocruz.br A toxoplasmose é uma zoonose causada pelo protozo- ário Toxoplasma gondii. O objetivo deste estudo foi determinar a ocorrência e identificar os fatores de risco associados à transmissão de T. gondii para frangos criados em diferentes sistemas (caipira e confinado) para produzir ovos ou carne. Os 810 animais foram divididos em dois grupos experimentais de acordo com o propósito do sistema de produção: 460 frangos de corte (Grupo 1) e 350 galinhas poedeiras (Grupo 2). A fim de analisar os possíveis fatores envolvidos na infecção pelo T. gondii nas galinhas, um questionário epidemiológico foi respondido por todos os proprietários. A detecção sorológica de anticorpos anti-Toxoplasma gondii foi realizada pela técnica de imunofluorescência indireta (RIFI) e Enzime Linked Assay Imunossorbent (ELISA). Uma vez que o índice de concordância (kappa) entre estas duas técnicas sorológicas foi considerada alta, 21,2% dos 810 animais foram considerados reativos. No Grupo 1, 12,2% (56/460) foram positivos, enquanto no Grupo 2 a taxa de positividade foi de 33,1% (116/350). O sistema de produção pode estar influenciando a soropositividade dos animais em ambos os grupos. No entanto, apenas no Grupo 2, foi possível notar uma relação estatisticamente significativa entre o sistema de produção e da freqüência de soros positivos. Este resultado indica que, pelo menos para as galinhas poedeiras, o sistema de produção está diretamente envolvido na infecção pelo T. gondii. O contato com os gatos no Grupo 1 não influenciou a distribuição dos animais sororreagentes, mas no Grupo 2 uma relação estatisticamente significativa foi observada. A ocorrência de anticorpos anti-T. gondii foi alta nos dois grupos (frangos de corte e postura). Galinhas cairpiras criadas para produção de ovos provou ser o grupo mais exposto à infecção T. gondii. Isto pode estar relacionado ao fato de que estes animais ficam por períodos mais longos nas fazendas, em contato direto com o solo possivelmente contaminado pela presença de gatos domésticos.

Abstract in English:

ABSTRACT.- Arenhart S., Bauermann F.V., Oliveira S.A.M., Weiblen R. & Flores E.F. 2009. [Shedding and transmission of bovine viral diarrhea virus by persistently infected calves.] Excreção e transmissão do vírus da diarréia viral bovina por bezerros persistentemente infectados. Pesquisa Veterinária Brasileira 29(9):736-742. Departamento de Medicina Veterinária Preventiva, Centro de Ciências Rurais, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS, Brazil. E-mail: eduardofurtadoflores@gmail.com Persistently infected (PI) calves born to cows infected with non-cytopathic bovine virus diarrhea virus (BVDV) represent the main reservoir of the virus in nature. We herein report an investigation on the patterns of virus shedding and transmission by five PI calves produced experimentally through inoculation of pregnant cows with Brazilian BVDV isolates. Five calves that survived intrauterine infection were born healthy, lacking neutralizing antibodies to BVDV and harboring virus in the blood. After weaning - and following the disappearance of colostral antibodies - PI calves were monitored for virus in serum and body secretions (ocular, oral, nasal and genital) at weekly intervals for up to 150 days. For each animal, the virus titers in serum showed minor variations throughout the collections (with one exception that presented an increase late in infection), yet the titers varied widely among animals (from 102 to 106TCID50/mL). Virus shedding in secretions was detected steadily during all the observation period with minor titer variations for each particular animal. The highest titers were generally detected in nasal and ocular secretions (titers 104 to 106TCID50mL) whereas genital and oral secretions usually contained low amount of virus (102 to 103TCID50mL). To evaluate the kinetics of virus transmission by these animals, one PI was introduced on a group of 10 seronegative calves maintained with a high animal density simulating the conditions of an intensive management. All 10 contact calves seroconverted to BVDV by day 30. Another PI calf was introduced into a 48-head herd kept under a low animal density, extensive grass management. Among these animals, 8/48 (16.6%) seroconverted by day 10, 26/48 (54.1%) by day 40 and 37/48 (77%) were seropositive at day 100, when the monitoring was discontinued. These results show that continuous viremia and virus shedding in high titers in secretions by PI animals assure an efficient and rapid virus transmission to contact animals, being the kinetics of transmission much faster under intensive conditions.

• Bovine viral diarrhea virus BVDV vírua da diarréia viral bovina

Abstract in Portuguese:

RESUMO.- Arenhart S., Bauermann F.V., Oliveira S.A.M., Weiblen R. & Flores E.F. 2009. [Shedding and transmission of bovine viral diarrhea virus by persistently infected calves.] Excreção e transmissão do vírus da diarréia viral bovina por bezerros persistentemente infectados. Pesquisa Veterinária Brasileira 29(9):736-742. Departamento de Medicina Veterinária Preventiva, Centro de Ciências Rurais, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS, Brazil. E-mail: eduardofurtadoflores@gmail.com Bezerros persistentemente infectados (PI) nascidos de vacas infectadas com amostras não-citopáticas do vírus da diarréia viral bovina (BVDV) se constituem nos principais reservatórios do vírus na natureza. Este trabalho relata uma investigação do padrão de excreção e transmissão viral por cinco bezerros PI produzidos experimentalmente pela inoculação de vacas prenhes com isolados brasileiros do BVDV. Cinco bezerros que sobreviveram a infecção intrauterina nasceram saudáveis, soronegativos e com a presença de vírus no sangue. Após o desmame - e desaparecimento dos anticorpos colostrais - os bezerros PI foram monitorados semanalmente durante 150 dias para a presença de vírus e títulos virais no soro e em secreções (ocular, oral, nasal e genital). Os títulos virais no soro de cada animal apresentaram pequenas variações durante o período (com exceção de um animal que apresentou um aumento de título tardiamente), mas os títulos variaram amplamente entre os animais (entre 102 e 106TCID50/ml). O vírus também foi excretado continuamente nas secreções de todos os animais, com pequenas variações de título entre as coletas. Os maiores títulos virais foram geralmente detectados nas secreções nasais e oculares (títulos de 104 a 106TCID50/mL), enquanto as secreções orais e genitais usualmente continham títulos virais baixos (102 a 103TCID50/mL). Com o objetivo de avaliar a dinâmica de transmissão viral, um bezerro PI foi introduzido em um grupo de 10 bezerros soronegativos, mantido com uma alta densidade animal e submetido a manejo diário para simular as condições de manejo semi-intensivo. Após 30 dias de convívio com o bezerro PI, todos os demais animais haviam soroconvertido ao BVDV. Para investigar a transmissão viral sob condições extensivas, outro bezerro PI foi incorporado a um rebanho de 48 animais mantido a campo, com baixa densidade animal e submetido a manejo extensivo. Dentre estes animais, 8/48 (16,6%) foram soropositivos para anticorpos no dia 10, 26/48 (54,1%) no dia 40 e 37/48 (77%) haviam soroconvertido no dia 100, quando encerrou-se o monitoramento. Estes resultados demonstram que a viremia e excreção viral contínua em altos títulos por animais PI assegura a transmissão rápida do BVDV a animais mantidos em contato, sendo a transmissão notadamente mais rápida em condições intensivas e de alta densidade animal.

Abstract in English:

Garmatz S.L., Irigoyen L.F., Rech R.R., Brown C.C., Zhang J. & Barros C.S.L. 2004. [Malignant catarrhal fever in cattle in Rio Grande do Sul, Brazil: Experimental transmission to cattle and characterization of the etiological agent.] Febre catarral maligna em bovinos no Rio Grande do Sul: transmissão experimental para bovinos e caracterização do agente etiológico. Pesquisa Veterinária Brasileira 24(2):93-106. Depto Patologia, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS, Brazil. E-mail: claudioslbarros@uol.com.br Two oubreaks of malignant catarrhal fever (MCF) occurring in cattle on two farms (A and B) in the municipality of Santiago, state of Rio Grande do Sul (RS), Brazil, and the transmission of the disease to susceptible calves as well as the detection of ovine herpesvirus-2 (OvHV-2) in tissues of affected cattle are reported. The two epizootics occurred from November 2001 to February 2002 (Farm A) and in January-February 2003 (Farm B). Numbers of cattle at risk, morbidity and letality rates were respectively 170, 10.59% and 83.33% for Farm A and 500, 2.4% and 100% for Farm B. Contact between affected cattle and sheep was detected in both farms, but lambing ewes were present only in farm A. Duration of clinical courses, gross findings and histopathology were the same for the affected cattle in both farms. Most affected cattle died or were euthanatized in extremis after a clinical course of 2-8 days. Clinical signs included fever (40.5 and 41.5°C), nasal and ocular discharge, corneal opacity, conjunctivitis, drooling, erosions and ulcerations of the mucosae, diarrhea, hematuria, and neurological disturbances. Eleven necropsies (9 on Farm A, 2 on Farm B) were performed. Gross lesions included erosions and ulcers affecting the mucosae of nasal turbinates, oral cavity, gastrointestinal and urogenital tracts; hemorrhage and necrosis of the tip of the buccal papillae, lymph node enlargement, multifocal white foci in renal cortex, and hyperemia of leptomeninges. Microscopically, there were arteritis and fibrinoid degeneration in medium and small arteries and arterioles of multiple organs and tissues, necrosis and inflammation in several mucosal surfaces, keratitis, conjunctivitis, uveitis, intersticial nephritis, and encephalitis. Transmission experiments were attempted in five calves (E1-E5) by inocculating each of them intravenously with 500 ml of whole heparinized blood from a MCF affected cow. The transmission was suscessful in at least three (E1-E3) of the experimental calves which became sick after an incubation period of 15-27 days. Four experimental calves either died or were euthanatized in extremis after a clinical course which varied from 3 days to 8 weeks. The remaining experimental calf (E5) recovered from a mild disease and was euthanatized 14 weeks after inocculation. Necropsies were performed in all five calves. Clinical signs, necropsy and histopathological findings of three calves (E1-E3) were characteristic of MCF. OvHV-2 viral DNA was detected by the polimerase chain reaction (PCR) test in paraffin embedded tissues from seven cattle out of the 11 spontaneous MCF cases and from three experimental calves (E1-E3). PCR tests resulted negative in the remaining four of the 11 spontaneous MCF cases tested and in two (E4,E5) of the five experimental calves. Immunohistochemistry performed in sections of lymphoid tissue from calf E4 failed to detect BVD virus antigen. The experimental transmission of MCF and the characterization of the etiological agent as OvHV-2 were successfully attempted in cattle for the first time in Brazil.

• Infectious diseases malignant catarrhal fever viral diseases diseases of cattle pathology polimerase chain reation.

Abstract in Portuguese:

Garmatz S.L., Irigoyen L.F., Rech R.R., Brown C.C., Zhang J. & Barros C.S.L. 2004. [Malignant catarrhal fever in cattle in Rio Grande do Sul, Brazil: Experimental transmission to cattle and characterization of the etiological agent.] Febre catarral maligna em bovinos no Rio Grande do Sul: transmissão experimental para bovinos e caracterização do agente etiológico. Pesquisa Veterinária Brasileira 24(2):93-106. Depto Patologia, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS, Brazil. E-mail: claudioslbarros@uol.com.br Two oubreaks of malignant catarrhal fever (MCF) occurring in cattle on two farms (A and B) in the municipality of Santiago, state of Rio Grande do Sul (RS), Brazil, and the transmission of the disease to susceptible calves as well as the detection of ovine herpesvirus-2 (OvHV-2) in tissues of affected cattle are reported. The two epizootics occurred from November 2001 to February 2002 (Farm A) and in January-February 2003 (Farm B). Numbers of cattle at risk, morbidity and letality rates were respectively 170, 10.59% and 83.33% for Farm A and 500, 2.4% and 100% for Farm B. Contact between affected cattle and sheep was detected in both farms, but lambing ewes were present only in farm A. Duration of clinical courses, gross findings and histopathology were the same for the affected cattle in both farms. Most affected cattle died or were euthanatized in extremis after a clinical course of 2-8 days. Clinical signs included fever (40.5 and 41.5°C), nasal and ocular discharge, corneal opacity, conjunctivitis, drooling, erosions and ulcerations of the mucosae, diarrhea, hematuria, and neurological disturbances. Eleven necropsies (9 on Farm A, 2 on Farm B) were performed. Gross lesions included erosions and ulcers affecting the mucosae of nasal turbinates, oral cavity, gastrointestinal and urogenital tracts; hemorrhage and necrosis of the tip of the buccal papillae, lymph node enlargement, multifocal white foci in renal cortex, and hyperemia of leptomeninges. Microscopically, there were arteritis and fibrinoid degeneration in medium and small arteries and arterioles of multiple organs and tissues, necrosis and inflammation in several mucosal surfaces, keratitis, conjunctivitis, uveitis, intersticial nephritis, and encephalitis. Transmission experiments were attempted in five calves (E1-E5) by inocculating each of them intravenously with 500 ml of whole heparinized blood from a MCF affected cow. The transmission was suscessful in at least three (E1-E3) of the experimental calves which became sick after an incubation period of 15-27 days. Four experimental calves either died or were euthanatized in extremis after a clinical course which varied from 3 days to 8 weeks. The remaining experimental calf (E5) recovered from a mild disease and was euthanatized 14 weeks after inocculation. Necropsies were performed in all five calves. Clinical signs, necropsy and histopathological findings of three calves (E1-E3) were characteristic of MCF. OvHV-2 viral DNA was detected by the polimerase chain reaction (PCR) test in paraffin embedded tissues from seven cattle out of the 11 spontaneous MCF cases and from three experimental calves (E1-E3). PCR tests resulted negative in the remaining four of the 11 spontaneous MCF cases tested and in two (E4,E5) of the five experimental calves. Immunohistochemistry performed in sections of lymphoid tissue from calf E4 failed to detect BVD virus antigen. The experimental transmission of MCF and the characterization of the etiological agent as OvHV-2 were successfully attempted in cattle for the first time in Brazil.

Abstract in English:

Whole blood, plasma and peripheral blood leukocytes from an adult cow with antibody to gp55 of bovine leukosis vírus (BL V), whose cultured leukocytes produced numerous type-C viral particles, and pools of milk from BLV-free and BLV-infected cows were assayed for infectivity in experimental transmission studies utilizing a calf bioassay. During an observation period of 6 months, the development of antibody to gp55 in the inoculated calves was considered as evidence of acquired infection with BLV. Whole blood inoculated subcutaneously in quantities that varied from 0.5ml to 8.0ml transmitted BLV to almost 50% of the calves. Peripheral blood leukocytes inoculated in quantities of 103, 104 and 105 per calf did not transmit BLV. However, 1 of every 2 calves inoculated with 106 and 107 leukocytes acquired the infection. Calves inoculated with plasma as well as uninoculated control calves did not become infecte d. Calves bom to BL V-free dams remained serologically negative after being inoculated intra-abdominally with a pool of milk from BLV-free cows and type-C viral particles were not observed in cultures of their leukocytes. Similar calves inoculated with a pool of milk from BLV-infected cows were all infected 3 months later and their cultured leukocytes contained small numbers of type-C viral particles. Four of 5 calves bom to BLV-infected dams remained serologically negative after the inoculation of a pool of milk from BLV-free cows. Conversely, 5 of 7 calves also bom to BLV-infected dams developed antibody to gp55 after being inoculated with a pool of milk from BLV-infected cows. It is concluded that BLV can be transmitted iatrogenically through the inoculation of fresh blood, that lymphocytes from infected animals produce type-C viral particles and are probably the cells responsible for infectivity, that there is no true viremia as shown by the lack of infectivity of plasma and that the milk from infected cows contains infectious BLV.

• Enzootic bovine Jeukosis virus transmission blood milk

Abstract in Portuguese:

Foi testada a infectividade de sangue total, plasma e leucócitos periféricos de uma vaca adulta com anticorpos para gp55 do vírus da leucose bovina (VLB), cujos leucócitos em cultura produziram numerosas partículas virais de tipo-C, e de misturas de leite de vacas livres e infectadas com o VLB, utilizando-se um bioensaio em bezerros. Durante um período de observação de 6 meses, o desenvolvimento de anticorpos para gp55 nos bezerros inoculados foi considerado como evidência de infecção adquirida com o VLB. Sangue total inoculado subcutaneamente, em quantidades variando entre 0,5ml e 8,0ml, transmitiu o VLB a quase 50% dos bezerros. Leucócitos do sangue periférico inoculados em quantidades de 103, 104 e 105 por bezerro não transmitiram o VLB, porém, 1 de cada 2 bezerros inoculados com 106 e 107 leucócitos adquiriram a infecção. Os bezerros inoculados com plasma assim como os bezerros testemunhas não inoculados não adquiriram a infecção. Bezerros nascidos de vacas livres do VLB permaneceram sorologicamente negativos após a inoculação intra-abdominal de mistura de leite de vacas isentas do VLB e não foram observadas partículas virais de tipo-C em culturas dos seus leucócitos. Bezerros similares inoculados com uma mistura de leite de vacas infectadas com o VLB estavam todos infectados 3 meses mais tarde e seus leucócitos em cultura continham um pequeno número de partículas virais de tipo-C. Quatro de 5 bezerros nascidos de vacas infectadas com o VLB permaneceram sorologicamente negativos após a inoculação de mistura· de leite de vacas livres do VLB. Por outro lado, 5 de 7 bezerros também nascidos de vacas infectadas com o VLB desenvolveram anticorpos para gp55 após a inoculação de mistura de leite de vacas infectadas com o VLB. Conclue-se que o VLB pode ser transmitido iatrogenicamente através da inoculação de sangue fresco, que os linfócitos de animais infectados produzem partículas virais de tipo-C e são provavelmente as células responsáveis pela infectividade, que não existe uma viremia verdadeira como foi determinado pela falta de infectividade do plasma e que o leite de vacas infectadas contém o VLB em estado infeccioso.

• Leucose enzoótica bovina vírus transmissão sangue leite

Abstract in English:

Egg albumens from hens belonging to nine commercial laying stocks and one broiler stock, obtained from five poultry breeders, were tested for the presence of the group-specific (gs) antigen oflymphoid leukosis viroses (LLV). The congenital transmission rates in the laying stocks ranged from 6.7 to 24.7 percent, while the rate in the broiler stock tested was found to be 1.3 percent. The significance of these findings in relation to the eradication of LLV is discussed.

• Avian leukosis vírus congenital transmission groupspecific antigen

Abstract in Portuguese:

Albuminas de ovos de galinhas, pertencentes a nove linhagens comerciais de postura e uma de corte, obtidas de cinco granjas de matrizes, foram testadas pela presença do antígeno específico de grupo (gs) dos vírus da leucose linfóide aviária (LLV). As taxas de transmissão congênita nas linhagens de postura variaram entre 6, 7 e 24, 7 por cento, enquanto que a taxa na linhagem de corte testada foi de 1,3 por cento. O significado destes achados em relação à erradicação dos LLV é discutido.

• Vírus da leucose aviária transmissão congênita antígeno específico de grupo

Abstract in English:

White Leghorn hens from two commercial lines were identified as shedders or non-shedders of the lymphoid leukosis virus (LL) using the micro-complement fixation test. This test detected the group-specific antigen (gs-ag) of the leukosis/sarcoma group of viruses when used directly on the albumen of unincubated fresh eggs. It was found that 21.4% of line A hens and 17.2% of line B hens eliminated gs-ag into their eggs. Sequential studies of the elimination of the gs-ag, demonstrated that infected hens can be either intermittent or consistent shedders of this antigen in their eggs. Electron microscopy studies demonstrated the presence of type-C viral particles in the pâncreas and in the magnum of the oviduct of hens that had consistently shed the gs-ag in the egg albumen. The indirect immunofluorescence test detected gs-ag in the cytoplasm of peripheral blood leucocytes and was used to detect infected roosters that were utilized as semen donors. Artificial insemination of non-shedder hens with semen obtained from infected rooters resulted in the shedding of gs-ag into the eggs of one of the hens. Moreover, there was seroconversion in 11 of the 26 hens from both lines, inseminated with semen from the infected roosters. In was concluded that LL virus infection could be introduced, through insemination, to non-infected hens using sêmen from infected roosters.

• Congenital transmission virus avian lymphoid leukosis

Abstract in Portuguese:

A microprova de fixação do complemento permitiu a identificação de galinhas Leghorn brancas das linhagens A e B infectadas com o vírus da leucose linfóide aviária (LL). Esta prova detectou o antígeno específico (ag-gs) do vírus do grupo leucose/sarcoma aviário quando foi utilizada diretamente na albumina de ovos frescos não incubados. Encontrou-se que 21,4% das galinhas da linhagem A e 17,2% das galinhas da linhagem B do plantel geral eliminavam ag-gs nos seus ovos. Foi demonstrado também que as galinhas infectadas podem eliminar ag-gs nos ovos, constantemente ou intermitentemente. Estudos realizados com o microscópio eletrônico demonstraram a presença de partículas virais do tipo C no pâncreas e na porção do magnum do oviduto de galinhas que tinham eliminado ag-gs do vírus da LL cons-tantemente na albumina dos ovos. A técnica de imunofluorescência indireta detectou ag-gs no citoplasma de leucócitos de aves portadoras e foi utilizada para identificar galos infectados a serem usados como doadores de sêmen. A inseminação de galinhas não eliminadoras de ag-gs do vírus da LL com sêmen de galos portadores resultou na eliminação de ag-gs nos ovos de uma das galinhas inseminadas. Mais ainda, houve uma conversão sorológica, em 11 das 26 galinhas das linhagens A e B após serem inseminadas com sêmen de galos portadores, demonstrando-se assim a participação do galo como introdutor da infecção via sêmen.

• Transmissão congénita vírus leucose linfóide aviária