A avicultura brasileira é atualmente uma atividade de grande sucesso. A utilização de sistemas de planejamento associados a novas tecnologias, reflete-se no extraordinário crescimento da atividade. A produção brasileira de frango ultrapassou a marca anual de 10 milhões de toneladas, em 2007. O Brasil está entre os três maiores produtores de frango no ranking mundial, junto com Estados Unidos e China. Haja vista a importância que a avicultura representa para o país, pela geração de benefícios sociais e econômicos, o risco que a Doença de Newcastle (DNC) constitui para a avicultura brasileira é enorme. Um surto desta doença em um centro de produção avícola representaria um risco à economia e incidiria de forma negativa nos níveis de consumo de proteína de qualidade e economicamente acessível à população. A fim de estabelecermos um monitoramento do vírus da Doença de Newcastle (NDV) em aves selvagens, livres ou de cativeiro, e aves domésticas não vacinadas, residentes em regiões de elevada confluência migratória aviária no Brasil e em pingüins ao redor da Estação Antártica Comandante Ferraz (EACF), coletamos amostras de swabs orais e cloacais para a posterior análise por PCR em Tempo Real (qPCR), além de sangue para testes sorológicos, tendo como objetivos maiores, contribuir para o fortalecimento dos serviços de defesa sanitária animal, aumentar a capacidade de investigação, e finalmente, atualizar e harmonizar normas e procedimentos para a prevenção e controle da DNC, referenciando-se nas recomendações da Organização Mundial de Sanidade Animal (Office International des Epizooties - OIE). Das 1072 aves amostradas em diferentes regiões do Brasil, 8 (0,75%) apresentaram resultado positivo para o NDV por qPCR, sendo 5 (62,5% das positivas) delas provenientes da região Norte, 2 (25% das positivas) do Nordeste e 1 (12,5% das positivas) da região Sul do Brasil. Na Antártica, dos 100 pingüins estudados, 2 apresentaram resultado positivo para o NDV por qPCR e em cerca de 33,3% dos soros testados foi detectada a presença de anticorpo pelo teste de Inibição da Hemaglutinação (HI). Todas as amostras positivas foram re-analisadas por qPCR específico para cepas mesogênicas e/ou velogênicas, resultando negatividade, corroborando os dados que certificam o Brasil como sendo livre da Doença de Newcastle. / Brazilian chicken meat exports ended 2007 with shipments of 3,3 million tons, which represented a 21% increase in comparison with 2006. These results were the best in the history of the poultry sector in Brazil. The production reached 10.2 million tons, a result that kept the country as the worlds largest chicken meat exporter and the third largest producer, only behind USA and China. Thus the risk of an introduction of the Newcastle disease virus (NDV) into domestic poultry is enormous and will play severe consequences for the economy and poltry industries. In order to provide the surveillance of the NDV in wild, free or captive, and non vaccinated domestic birds from some regions of migratory birds confluence in Brazil and in penguins around the brasilian Antarctic Station Comandante Ferraz, we collected oral and cloacal swabs, for the viral detection by Real Time PCR (qPCR), and blood for the serological test (hemaglutination inhibition test HI). A total of 1072 birds were sampled in diferent regions of Brazil, where 8 (0.75%) shown positive results to NDV, in which 5 (62.5% of positive) were from North region, 2 (25% of positive) were from Northeast and 1 (12,5% of positive) was from South. In the Antarctic 100 penguins were studied, in which 2 were detected the NDV (2% of total). HI test showed that 33.3% of penguins were seropositives for NDV, indicating their previous contact with the pathogen. All the positive samples by qPCR were repeated with primers projected to detect only virulent strains and no sample was positive, indicating the absence of velogenic strains in Brazil. The epidemiological profile was richer with the isolament of positive samples in embrioned chiken eggs specific patogen free and latter nucleotidic genomic sequencing of isolate.

The first step of viral infection requires the binding of the viral attachment protein to cell surface receptors. Following binding, viruses penetrate the cellular membrane to deliver their genome into the host cell. For enveloped viruses, which have a lipid bilayer that surrounds their nucleocapsids, entry into the host cell requires the fusion of viral and cellular membranes. This process is mediated by viral glycoproteins located on the surface of the virus. For many enveloped viruses, such as influenza, Ebola, and human immunodeficiency virus, the fusion protein is responsible for mediating both attachment to cellular receptors and membrane fusion. However, paramyxoviruses are unique among fusion promoting viruses because their receptor binding and fusion activities reside on two separate proteins. This unique distribution of functions necessitates a mechanism by which the two proteins can transmit the juxtaposition of the viral and host cell membranes, mediated by the attachment protein (HN/H), into membrane fusion, mediated by the fusion (F) protein. This mechanism allows for paramyxoviruses to gain entry into and spread between cells, and therefore, is an important aspect of virus infection and disease progression. Despite the conservation of receptor binding activity among members of the Paramyxovirinaesubfamily, for most of these viruses, including Newcastle disease virus (NDV), heterologous HN proteins cannot complement F in the promotion of fusion; both the HN and F proteins must originate from the same virus. This is consistent with the existence of a virus-specific interaction between the two glycoproteins. Thus, one or more domains on the HN and F proteins is thought to mediate a specific interaction between them that is an integral part of the fusion process. Therefore, the primary focus of this thesis is the identification of the site(s) on HN that directly contacts F in the HN-F interaction. The ectodomain of the HN protein consists of a stalk and a terminal globular head. Analysis of the fusion activity of chimeric paramyxovirus HN proteins indicates that the stalk region of HN determines its F protein specificity. The first goal of this research was to address the question of whether the stalk not only determines F-specificity, but does so by directly mediating the interaction with F. To establish a correlation between the amount of fusion and the extent of the HN-F interaction, a specific and quantitative co-immunoprecipitation assay was used that detects the HN-F complex at the cell surface. As an initial probe of the role of the HN stalk in mediating the interaction with F, N-glycans were individually added at several positions in the region. N-glycan addition at positions 69 and 77 in the stalk specifically and completely block both fusion and the HN-F interaction without affecting either HN structure or its other activities. However, though they also prevent fusion, N-glycans added at other positions in the stalk also modulate activities that reside in the globular head of HN. This correlates with an alteration of the tetrameric structure of the protein as indicated by sucrose gradient sedimentation analyses. These additional N-glycans likely indirectly affect fusion, perhaps by interfering with changes in the conformation of HN that link receptor binding to the fusion activation of F. To address the issue of whether N-glycan addition at any position in HN would abolish fusion, an N-glycan was added in another region at the base of the globular head of HN (residues 124-152), which was previously predicted by a peptide-based analysis to mediate the interaction with F. HN carrying this additional N-glycan exhibits significant fusion promoting activity, arguing against this site being part of the F-interactive domain in HN. These data support the idea that the F-interactive site on HN is defined by the stalk region of the protein. Site-directed mutagenesis was used to begin to explore the role of individual residues in the stalk in the interaction with F. The characteristics of the F-interactive domain in the stalk of HN are that it is a conserved motif with enough sequence heterogeneity to account for the specificity of the interaction. One such region that meets these requirements is the intervening region (IR) (residues 89-95); a non-helical domain situated between two conserved heptad repeats. Several amino acid substitutions for a completely conserved proline residue in this region impair not only fusion and the HN-F interaction, but also decrease neuraminidase activity in the globular domain and alter the structure of the protein, suggesting that the substitutions indirectly affect the HN-F interaction. Substitutions for L94 also interfere with fusion, but have no significant effect on any other HN function or its structure. Amino acid substitutions at two other positions in the IR (A89 and L90) also modulate only fusion. In all cases, diminished fusion correlates with a decreased ability of the mutated HN protein to interact with F at the cell surface. These findings indicate that the IR is critical to the role of HN in the promotion of fusion and are consistent with its direct involvement in the interaction with the homologous F protein. These are the first point mutations in the HN protein for which a correlation has been demonstrated between the extent of the HN-F interaction and the amount of fusion. This argues strongly that the co-IP assay is an accurate reflection of the HN-F interaction. The second goal of this research was to address the HN-F interaction from the perspective of the F protein by investigating the relationship between receptor binding, the HN-F interaction, and fusion using a highly fusogenic form of the F protein. It has previously been shown that an L289A substitution in NDV F eliminates the requirement for HN in the promotion of fusion and enhances HN-dependent fusion above wild-type (wt) levels. Here, it was shown that the HN-independent fusion exhibited by L289A-F in Cos-7 cells cannot be duplicated in BHK cells. However, when L289A-F is co-expressed with wt HN, enhanced fusion above wt levels is observed in BHK cells. Additionally, when L289A-F is co-expressed with IR-mutated HN proteins previously shown to promote low levels of fusion with wt F, a 2.5-fold increase in fusion was observed. However, similar to wt F, an interaction between L289A-F and the IR-mutated HN proteins was not detected. These results imply that the attachment function of HN, as well as the conformational change in L289A-F, are necessary for the enhanced level of fusion exhibited by HN proteins co-expressed with L289A-F. Indeed, two MAbs detected a conformational difference between L289A-F and the wt F protein. These findings support the idea that the L289A substitution converts F to a form that is less dependent on an interaction with HN for conversion to the fusion-active form. The last goal of this research was to address the cellular site of the HN-F interaction, still a controversial issue based on conflicting data from studies of different paramyxoviruses, using various approaches. This is a particular point of interest, as it speaks to the mechanism by which the HN-F interaction regulates fusion. Thus, NDV HN and F were successfully retained intracellularly with a multiple arginine or KK motif, respectively. The results of Endoglycosidase H resistance and F cleavage studies indicate that the mutated proteins, HN-ER and F-ER, are retained in a compartment prior to the medial-Golgi apparatus and that they are unable to interact with a high enough affinity to co-retain or even cause reduced transport of their wt partner glycoproteins. This is consistent with the HN-F interaction occurring at the cell surface, possibly triggered by receptor binding. In conclusion, this thesis presents evidence to argue that the IR in the stalk of the NDV HN protein directly mediates the interaction with the F protein that is necessary for fusion. Overall, the data presented in this thesis extend the current knowledge of the mechanism by which the paramyxovirus attachment protein can trigger the F protein to initiate membrane fusion. A clear understanding of this process has the potential to identify new anti-viral strategies, such as small molecule inhibitors, aimed at controlling paramyxovirus infection by interfering with early steps in the virus infection cycle.

Newcastle disease virus (NDV) belongs to the Paramyxoviridae, a family of enveloped RNA viruses that includes many important human and animal pathogens. Although many aspects of the paramyxovirus life cycle are known in detail, our understanding of the mechanisms regulating paramyxovirus assembly and release are poorly understood. For many enveloped RNA viruses, it has recently become apparent that both viral and host cellular determinants coordinate the proper and efficient assembly of infectious progeny virions. Utilizing NDV as a model system to explore viral and cellular determinants of paramyxovirus assembly, we have shown that host cell membrane lipid raft domains serve as platforms of NDV assembly and release. This conclusion was supported by several key experimental results, including the exclusive incorporation of host cell membrane raftassociated molecules into virions, the association of structural components of the NDV particle with membrane lipid raft domains in infected cells and the strong correlation between the kinetics of viral protein dissociation from membrane lipid raft domains and incorporation into virions. Moreover, perturbation of infected cell membrane raft domains during virus assembly resulted in the disordered assembly of abnormal virions with reduced infectivity. These results further established membrane raft domains as sites of virus assembly and showed the integrity of these domains to be critical for the proper assembly of infectious virions. Although specific viral protein-protein interactions are thought to occur during paramyxovirus assembly, our understanding of how these interactions are coordinated is incomplete. While exploring the mechanisms underlying the disordered assembly of non-infectious virions in membrane raft-perturbed cells, we determined that the integrity of membrane raft domains was critical in the formation and virion incorporation of a complex consisting of the NDV attachment (HN) and fusion (F) proteins. The reduced virus-to-cell membrane fusion capacity of particles released from membrane raft-perturbed cells was attributed to an absence of the HN – F glycoprotein-containing complex within the virion envelope. This result also correlated with a reduction of these glycoprotein complexes in membrane lipid raft fractions of membrane raft-perturbed cells. Specifically, it was determined that the formation of newly synthesized HN and F polypeptides into the glycoprotein complex destined for virion incorporation was dependent on membrane lipid raft integrity. Finally, a novel virion complex between the ribonucleoprotein (RNP) structure and the HN attachment protein was identified and characterized. Unlike the glycoprotein complex, the detection of the RNP – HN protein-containing complex was not affected by membrane raft perturbation during virus assembly in the cell. The biological importance of this novel complex for the proper assembly of an infectious progeny virion is currently under investigation. The results presented in this thesis outline the role of host cell membrane lipid raft domains in the assembly and release processes of a model paramyxovirus. Furthermore, the present work extends our understanding of how these particular host cell domains mechanistically facilitate the ordered assembly and release of an enveloped RNA virus.

Newcastle disease virus (NDV), an avian paramyxovirus, enters the host cell by fusion of viral and host cell membranes. The fusion of two membranes is mediated by the viral fusion (F) protein. The F protein, like other class I fusion proteins, is thought to undergo major conformational changes during the fusion process. The exact mechanism that leads to major refolding of F protein is not clear. Recently, it has been proposed that disulfide bond reduction in the fusion protein of some viruses may be involved in the conformational changes in fusion proteins. In some viruses, the reduction of disulfide bonds in the fusion protein is mediated by host cell disulfide isomerases belonging to the protein disulfide isomerase (PDI) family. In this study, the role of disulfide bond isomerization in the entry of NDV was analyzed. Using inhibitors of thiol-disulfide isomerases, we found that blocking the reduction of disulfide bonds in the fusion protein inhibited cell-cell fusion as well as virus entry into the host cell. Also, over-expression of isomerases belonging to the PDI family significantly enhanced cell-cell fusion. Taken together, these results suggest that free thiols play an important role in fusion mediated by NDV glycoproteins. Using a thiol specific, membrane impermeable biotin, MPB, we found that free thiols are produced in cell surface-expressed NDV F protein. The production of free thiols was inhibited by inhibitors of thiol-disulfide isomerases. Over-expression of isomerases belonging to the PDI family enhanced detection of free thiols in F protein. In F protein, present in virions or in virus-like particles, free thiols were detected only after the particles were attached to target cells. Taken together, these results suggest that free thiols are produced in F protein and the production of free thiols is mediated by host cell thiol-disulfide isomerases. Using conformation sensitive antibodies, we also studied the conformation of cell surface-expressed F protein in the presence ofthiol-disulfide isomerase inhibitors or in cells over-expressing thiol-disulfide isomerases. In the presence of thiol-disulfide isomerase inhibitors, the cell surface-expressed F protein was in a prefusion conformation while in cells over-expressing thiol-disulfide isomerases the F protein was in a post-fusion conformation. We also correlated the production of free thiols to the conformational changes in F protein. Using temperature-arrested intermediates or F protein with mutations in heptad repeat domains, which are defective in attaining intermediate conformations, we found that free thiols are produced before any of the proposed conformational changes in F protein. Also, the production of free thiols in F protein was found to be independent of its activation by hemagglutinin-neuraminidase (HN) protein. These results suggest that free thiols are probably required for the activation of F protein during membrane fusion.

The final step of paramyxovirus infection requires the assembly of viral structural components at the plasma membrane of infected cells followed by budding of virions. While the matrix (M) protein of some paramyxoviruses has been suggested to play a central role in the assembly and release of virus particles, the specific viral and host protein requirements are still unclear. Using Newcastle disease virus (NDV) as a prototype paramyxovirus, we explored the role of each of the NDV structural proteins in virion assembly and release. For these studies, we established a virus-like particle (VLP) system for NDV. The key viral proteins required for particle formation and the specific viral protein-protein interactions required for assembly and release of particles were explored in chapter 2. First we found that co-expression of all four proteins resulted in the release of VLPs with densities and efficiencies of release (1.18 to 1.16 g/cm3and 83.8%±1.1, respectively) similar to that of authentic virions. Expression of M protein alone, but not NP, F-K115Q or HN proteins individually, resulted in efficient VLP release. No combination of proteins in the absence of M protein resulted in particle release. Expression of any combination of proteins that included M protein yielded VLPs, although with different densities and efficiencies of release. To address the roles of NP, F and HN proteins in VLP assembly, the interactions of proteins in VLPs formed with different combinations of viral proteins were characterized by co-immunoprecipitation. The co-localization of M protein with cell surface F and HN proteins in cells expressing all combinations of viral proteins was characterized. Taken together, the results show that M protein is necessary and sufficient for NDV budding. Furthermore, they suggest that M protein – HN protein and M protein - NP interactions are responsible for incorporation of HN protein and NP proteins into VLPs and that F protein is incorporated indirectly due to interactions with NP and HN protein. Since the vacuolar protein sorting (VPS) system is involved in the release of several enveloped RNA viruses, chapter 3 describes studies which explored the role of the VPS system on NDV particle release. First, we characterized the effects of three dominant negative mutant proteins of the VPS pathway on particle release. Expression of dominant negative mutants of CHMP3, Vps4 and AIP1 proteins inhibited M protein particle release as well as release of complete VLPs. Mutation of a YANL sequence in the NDV M protein to AANA inhibited particle release while replacement of this sequence with either of the classical late domain motifs, PTAP or YPDL, completely restored particle release. The host protein AIP1, which binds YXXL late domain sequences, is incorporated into M protein particles. These results suggest that an intact VPS pathway is necessary for NDV VLP release and that the YANL sequence is an NDV M protein L domain. The sequence and structure of the Newcastle disease virus (NDV) fusion (F) protein are consistent with its classification as a type 1 glycoprotein. We have previously reported, however, that F protein can be detected in at least two topological forms with respect to membranes in both a cell-free protein synthesizing system containing membranes as well as infected COS-7 cells (J. Virol. 2004 77:1951). One form is the classical type 1 glycoprotein while the other is a polytopic form in which approximately 200 amino acids of the amino terminal end as well as the cytoplasmic domain (CT) are translocated across membranes. Furthermore, we detected CT sequences on surfaces of F protein expressing cells and antibodies specific for these sequences inhibited red blood cell fusion to HN and F protein expressing cells suggesting a role for surface expressed CT sequences in cell-cell fusion. In chapter 4, we extended these findings and found that the alternate form of the F protein can also be detected in infected and transfected avian cells, the natural host cells of NDV. Furthermore, the alternate form of F protein was also found in virions released from both infected COS-7 cells and avian cells by Western analysis. Mass spectrometry confirmed its presence in virions released from avian cells. Two different polyclonal antibodies raised against sequences of the CT domain of the F protein slowed plaque formation in both avian and COS-7 cells. Antibody specific for the CT domain also inhibited single cycle infections as detected by immunofluorescence of viral proteins in infected cells. The potential roles of this alternate form of the NDV F protein in infection are discussed. Virus-like particles (VLPs) generated from different viruses have been shown to have potential as good vaccines. Chapter 5 explored the potential of NDV VLPs as a vaccine for NDV or as a vaccine vector for human pathogens. Significant quantities of NDV VLPs can be produced from tissue culture cells. These VLPs are as pure as virions prepared in eggs. In addition, some rules for incorporation of viral proteins into VLPs were also explored. We found that the cytoplasmic domain of the fusion (F) protein is necessary for its incorporation into VLPs. We found that an HN protein with an HA tag at its carboxyl terminus was incorporated into VLPs. We also found that the HN and F proteins of NDV, strain B1, can be incorporated into VLPs with M and NP of strain AV. The demonstration of specific domains required for protein incorporation into particles is important in using NDV VLPs as a vaccine vector for important human pathogens. In conclusion, this dissertation presents results that show that the M protein plays a central role in NDV assembly and release, a finding that is consistent with findings with other paramyxoviruses. More importantly, this work extends the current knowledge of paramyxovirus assembly and release by providing the first direct evidence of interactions between paramyxovirus proteins. These interactions between viral proteins provide a rational basis for incorporation of viral proteins into particles. This work also provides a clearer understanding of the role of the host vacuolar protein sorting machinery in NDV budding. A clear understanding of virus assembly and budding process contributes to the design of strategies for therapeutic intervention and in the development of safer, more economical and effective vaccines.

Desinfektionsmittel sind ein elementarer Bestandteil der Tierseuchenbekämpfung und damit auch der Lebensmittelsicherheit. Die Prüfung chemischer Desinfektionsmittel ist Voraussetzung für deren zuverlässige Wirksamkeit und zielgerichteten Einsatz. In Deutschland geschieht dies nach den Richtlinien der Deutschen Veterinärmedizinischen Gesellschaft e.V. (DVG). Seit der ersten Fassung sind die Richtlinien einem ständigen Anpassungsprozess unterworfen. Im Zuge der europäischen Harmonisierung gilt es nun, sich gesamteuropäischen Richtlinien, verfasst durch das europäische Komitee für Normung (Comité Européen de Normalisation) (CEN) anzupassen. Das Thema dieser Arbeit entwickelte sich im Kontext der derzeitigen Diskussion über Verbesserungsvorschläge zu den bestehenden Richtlinien und deren Anpassung an die europäischen Normen. Es wurden je zwei Testviren für die Bereiche Tierhaltung und tierärztliche Praxis ausgewählt, um sie auf Eignung für die Viruzidieprüfung zu testen und gegebenenfalls zu etablieren. Des Weiteren wurde in einem zweiten Teil, in Anlehnung an die Forderungen der europäischen Normen die Prüfung zu vereinfachen, ein alternatives Zellkulturnachweissystem für das Newcastle-Disease-Virus (NDV) geprüft. Die Prüfung der viruziden Wirksamkeit erfolgte mit fünf verschiedenen Grundsubstanzen, gewählt um ein möglichst breites Spektrum an Desinfektionsmittelwirkstoffen abzudecken. Es wurden Glutaraldehyd, Ethanol, Natronlauge, Natriumhypochlorit und Peressigsäure verwendet. Die Versuche wurden mit einer niedrigen Eiweißbelastung und bei einer Temperatur von 20°C durchgeführt. Um eine praxisnahe Situation zu simulieren wurde auf, bereits in den DVG-Richtlinien, verankerten Stahl- und Holzkeimträgertests zurückgegriffen. Als mögliche Prüfviren für die Tierhaltung wurden das Equine Arteritis-Virus (EAV) und das Bovine Virus Diarrhoe Virus verwendet. Bei beiden Viren handelt es sich um weit verbreitete Tierseuchenerreger mit einer großen epidemiologischen Bedeutung. Die Untersuchung von fünf verschiedenen Desinfektionsmitteln erfolgte im Keimträgertest auf Holz. Sowohl EAV als auch BVD stellen ein weniger geeignetes Prüfvirus dar, da beide Viren enorme Titerverluste im Trocknungsvorgang der Holzkeimträger zeigten. Die Viren ließen sich zwar leicht vermehren, aber die erzielten Ausgangstiter reichten nicht aus um die Trocknungsverluste zu kompensieren und aussagekräftige Ergebnisse zu produzieren. Für den Bereich tierärztliche Praxis wurden das Feline Coronavirus (FCoV) und das Murine Parvovirus (MPV) genutzt. FCoV ist ein weltweit in Hauskatzenpopulationen vorkommendes Virus mit einer hohen Seroprävalenz und wurde daher ausgewählt. MPV wurde als Stellvertreter für die, in der Praxis häufig vorkommenden Parvovirusinfektionen gewählt. Es schien ein ideales Modellvirus aufgrund seiner weiten Verbreitung in der Forschung zu sein. Bei beiden Viren erfolgte die Prüfung auf Stahlkeimträgern. Unter Laborbedingungen konnte FCoV ohne Probleme zu hohen Titern vermehrt werden. Es gab keine nennenswerten Trocknungsverluste. FCoV erwies sich als geeignetes Prüfvirus. MPV hingegen ist bedingt durch die langen Versuchszeiten und schwierig auszuwertenden Zellkulturen, sowie wegen der niedrigen Ausgangstiter weniger geeignet als Modellvirus für die Desinfektionsmittelprüfung. Die Anzucht von NDV in Allantoisflüssigkeit von SPF Hühnereiern erschien sehr aufwendig und mit hohem Eiweißfehler belastet. In den Versuchen konnte ein deutlich höherer Eiweißgehalt als in den vergleichend geprüften, in Zellkultur angezogenen Viren nachgewiesen werden. Infolge der Probleme mit der Kultivierung der LMH-Zelllinie und den damit verbundenen langen Wartezeiten bis zur eigentlichen Versuchsdurchführung kann nur eine teilweise Empfehlung, von auf Zellkultur vermehrtem NDV (NDV (ZK)) gegeben werden. Nach Behebung dieser Probleme ist durchaus eine Ablösung, von in Allantoisflüssigkeit angezüchtetem NDV durch NDV (ZK) zu empfehlen. Die Verfälschung der Ergebnisse durch die höheren Eiweißgehalte bei Desinfektionsmitteln mit deutlichem Eiweißfehler könnten so vermieden werden.

Le déoxynivalénol (DON) est l'une des mycotoxines trichothécènes les plus abondantes et les plus importantes produites par les espèces de Fusarium. Les aliments contaminés par les mycotoxines peuvent affecter négativement la santé des poulets de chair. La présente étude a été menée pour évaluer les effets du déoxynivalénol (DON) sur les performances des poulets de chair, le poids des organes, les paramètres biochimiques sériques, la réponse immunitaire et l'histologie intestinale. L’expérience a permis d’évaluer l'efficacité d'un additif alimentaire commercial, basé sur les synbiotiques (SFA), et ayant la capacité d'oxyder le DON. Au total, six cents poussins mâles d'un jour d'une souche commerciale (Ross 308) ont été vaccinés avec un vaccin vivant combiné contre le virus de la maladie de Newcastle (NDV) et le virus de la bronchite infectieuse (IBV) et ont été répartis de façon aléatoire entre 6 traitements (100 oiseaux dans chaque groupe) pour 5 semaines. Ces groupes ont été nourris avec la même nourritures naturellement contaminés par DON mais à des concentrations différentes : < 0,5 (régime témoin), 1,5 et 3 mg/kg avec et sans SFA à 250 g/tonne. Les paramètres, y compris le poids corporel, la consommation d'aliments, et le taux de mortalité, ont été enregistrés sur une base hebdomadaire. De plus, des échantillons de sang ont été prélevés sur quatre oiseaux de chaque groupe pour déterminer les caractéristiques biochimiques sériques, et les titres d'anticorps contre NDV et IBV. Au cours de la semaine 5, quatre des poulets sélectionnés ont été euthanasiés, et les organes, coeur, foie, rate, bourse de Fabricius, ont été pesés. Des tissus de l'intestin, segments de 2 cm du duodénum, du jéjunum, de l'iléon et du cæcum, et de la bourse de Fabricius et thymus ont été prélevés pour des examens histologiques. Les résultats obtenus démontrent que les oiseaux dont l’alimentation était contaminée au DON présentaient une diminution (P < 0,05) du poids moyen aux jours 28 et 35 par rapport aux groupe témoin et groupes traités avec le SFA. De plus, l'inclusion de DON dans l'alimentation a réduit le titre d'anticorps contre le NDV (P < 0,05) et l'IBV (P < 0,001). Les paramètres biochimiques sériques, et le poids des organes pendant toute la période expérimentale (P > 0,05) n’ont pas montré de différences significatives. De plus, chez les oiseaux nourris avec des aliments contaminés, le DON a provoqué un processus de nécrose au niveau des villosités du duodénum et du thymus. Cependant, cela n'a pas modifié la morphométrie du tissu intestinal et de la bourse de Fabricius. Il a été conclu que les performances des poulets de chair, ainsi que la réponse vaccinale et paramètres histologiques, étaient négativement affectées par une alimentation contaminée par le DON. La supplémentation alimentaire avec un additif alimentaire à base de synbiotiques, serait une alternative pour atténuer les effets causés par cette mycotoxine chez les oiseaux. / Deoxynivalenol (DON) is one of the most abundant and important trichothecene mycotoxins produced by Fusarium species. Mycotoxin-contaminated feeds may negatively affect broiler chickens’ health, a sustainable approach to achieve mycotoxin elimination is necessary. An experiment was conducted to study the effects of deoxynivalenol (DON) on the performance of broilers, organ weights, serum biochemical parameters, immune response, and intestinal histology and to evaluate the efficacy of a commercial feed additive, based on synbiotics (SFA), with the ability to deepoxidize DON. In total, six hundred 1-d-old male broiler of a commercial strain (Ross 308) were vaccinated with combined live Newcastle disease virus (NDV) and infectious bronchitis virus (IBV) vaccine and were randomly allotted to 6 dietary treatments (100 birds in each group) for 5 wk. These groups were fed 3 diets naturally contaminated with DON at concentrations of < 0.5 (control diet), 1.5, and 3 mg/kg with and without SFA at 250 g/ton. The parameters including body weight, feed intake, and mortality rate were recorded on a weekly basis. In addition, weekly blood samples were collected from four birds in each group to determine serum biochemical characteristics and antibody titers to NDV and IBV. In week 5, four selected chickens were euthanized, and organs (heart, liver, spleen, bursa of Fabricius) were weighed. Tissues from intestine (2-cm segments of duodenum, jejunum, ileum, and caecum) and immune system (bursa of Fabricius and thymus) were collected for further histological examinations. The results indicated that DON-challenged birds had decreased (P < 0.05) average body weight (ABW) at days 28 and 35 as compared to control and treated groups with SFA. Furthermore, the inclusion of DON in the diet reduced antibody titer against NDV (P < 0.05), and IBV (P < 0.001). However, there were no significant differences in serum biochemical parameters and organs weight during the whole experimental period (P > 0.05). Moreover, in birds fed contaminated diets, DON caused necrosis in duodenum villus and in the thymus but did not alter the intestinal or the immune system morphometrics. It was concluded that broiler performance, histological, and immunological parameters were adversely affected by feeding diets contaminated with DON. However, the dietary supplementation with Synbiotics as a detoxifying agent would be an alternative to alleviate adverse effects on birds.