Untersuchungen zur Wirksamkeit einer Mannheimia-haemolytica-Adsorbatvakzine in Beziehung zur Immunitätslage von Mastkälbern aus dem Institut für Bakteriologie und Mykologie der Veterinärmedizinischen Fakultät der Universität Leipzig (140 S., 15 Abb., 18 Tab., 407 Lit.) Die Enzootische Bronchopneumonie des Rindes stellt einen der zentralen und wirtschaftlich bedeutsamsten Krankheitskomplexe in der Rinderaufzucht und –mast dar. Unter den Bedingungen der konzentrierten Stallhaltung größerer Tierpopulationen verursachen respiratorische Erkrankungen jährlich weltweit ökonomische Verluste in Höhe von mehreren Mrd. Dollar. In der vorliegenden Arbeit wurde unter Feldbedingungen in zwei Kälbermastbeständen die Wirksamkeit der Mannheimia-haemolytica-Adsorbatvakzine PRESPONSE? getestet. Anhand der erhobenen klinischen, bakteriologischen und serologischen Befunde konnten zudem Betrachtungen hinsichtlich des Zusammenhanges zwischen Transportbelastung und Gesundheits- bzw. Immunstatus der Tiere gemacht werden. In die Untersuchungen waren 123 Kälber aus einem Betrieb mit Zukauf und 162 Kälber sowie 57 hochtragende Kühe aus einem Bestand mit eigener Reproduktion involviert. Die Ergebnisse der 790 bakteriologischen Nasentupferuntersuchungen erbrachten keinen Nachweis von impfstoffinduzierten Modifikationen in der Zusammensetzung der Nasenschleimhautflora der Kälber. Andererseits verdeutlichten die Untersuchungsbefunde, daß insbesondere der Nachweis von Mannheimia-haemolytica-A1-Stämmen und toxischen Pasteurella-multocida-Stämmen eng mit dem respiratorischen Erkrankungsgeschehen im jeweiligen Bestand korrelierten. Die Dominanz dieser beiden Vertreter auf den Nasenschleimhäuten erkrankter Kälber unterstreichen deren ätiologische Bedeutung. Die ermittelten bestandsabhängigen Unterschiede im klinischen Ausprägungsgrad der respiratorischen Symptomatik akzentuierten ein weiteres Mal, daß Crowding und Transportstreß wesentliche nichtinfektiöse Faktoren im Pathogeneseprofil der EBP des Rindes repräsentieren. Das Spektrum der blutserologischen Untersuchungen umfaßte die Parameter Mannheimia-haemolytica-Antikörpertiter, Antikörperstatus pneumotrope Viren, IgG-Anti-Lipid-A sowie C-reaktives Protein. Im Verlauf der blutserologischen Untersuchungen konnten bei den Jungtieren keine signifikanten vakzineassoziierte Effekte nachgewiesen werden. Für die Betrachtungen zum Immunstatus der Kälber wurden vorrangig die Daten der IgG-Anti-Lipid-A- sowie der CRP-Bestimmungen herangezogen. Unter Berücksichtigung der altersspezifischen Konstellationen des juvenilen Immunsystems konnte anhand der erzielten Untersuchungsergebnisse nachgewiesen werden, daß diese beiden Parameter für die Einschätzung der Immunkompetenz von Kälbern geeignet sind. Insbesondere auf der Grundlage korrelativer Betrachtungen spiegelten sie deutlich die differenzierte Befähigung der Jungtiere zur Auseinandersetzung mit gramnegativen Infektionserregern wider. / Studies of the efficacy of adsorbed Mannheimia haemolytica vaccine in relation to the state of immunity of fat stock from the Insitute of Bacteriology and Mycology, Faculty of Veterinary Medicine, Leipzig University, Germany (140 pages, 15 figures, 18 tables, 407 references) Enzootic bronchopneumonia in cattle represents one of the crucial and economically important disease of breeding-calves and fat stock. Under the circumstances of concentrated mass production of cattle respiratory disease annually cause worldwide economic losses of several billions of dollars. In the thesis presented here the effectiveness of Mannheimia haemolytica adsorbed vaccine “Presponse TM” was tested under field conditions in two fat stock farms fattening calves. From the gained clinical, bacteriological and serological findings conclusions could be drawn concerning the connections between stress factors connected with transportation and health-/immune-state of the animals. 123 calves from a farm purchasing their new calves and 162 calves plus 57 highly pregnant cows from a farm with own reproduction were included in this study. The results of 790 bacteriologically examined nose swabs gave no hints to vaccine – induced modifications in the composition of the calves nasal mucosal flora. On the other hand the results make clear that specially the presence of Mannheimia haemolytica A1 strains and toxic Pasteurella multocida strains strongly correlates with respiratory disease cases in the concerned farms. The dominance of these two bacteria in the nasal mucosa of calves fallen ill emphasizes their aetiological importance. The results achieved showing the differences in the grades of clinical symptoms make evident that crowding and stress factors connected with transportation represent important non infectious factors in the pathogenetic profile of enzootic bronchopneumonia in cattle. The range of the accomplished bloodserological examinations included the following parameters: titer of antibodies against Mannheimia haemolytica, antibodies against pneumotropic viruses, IgG-anti-lipid-A as well as C-reactive protein. In the course of the bloodserological examinations no significant effects associated with vaccination were found in young cattle. For the consideration of the state of immunity of the calves mainly the data of the IgG anti lipid A and the CRP determinations were used. Under consideration of the age-specific constellation of the juvenile immune system from the achieved data it could be concluded that these two parameters are suitable for the appreciation of the immune competence of calves. Specially on the base of correlative considerations they reflect the differenciated ability of young cattle to deal with gram negative infectious agents.

Freie Universiẗat, Diss., 2004--Berlin. / Dateiformat: zip, Dateien im PDF-Format. Erscheinungsjahr an der Haupttitelstelle. 2004.

Bovine respiratory disease (BRD) is the leading cause of morbidity in feeder and stocker cattle, resulting in large impacts on economics of stocker and feedlot operations. One of the most effective means of controlling BRD is the mass administration of antimicrobials (AM) at arrival or “metaphylaxis”, potentially leading to increased antimicrobial resistance (AMR). Mannheimia haemolytica (MH), the most commonly isolated bacterial pathogen in BRD cases in feedlot cattle, has been shown to have integrative-conjugative elements (ICE), which are mobile genetic elements that have the ability to integrate themselves in the host genome. Notably, these ICE have been shown to contain multiple antimicrobial resistance genes (ARG) conferring resistance to antimicrobial classes used for BRD treatment. ICE have also been shown to be transferred between different genera. Since these ICE contain genes for resistance to multiple AM classes, administration of one AM could increase pressure for bacteria to transfer ICE for resistance to multiple drug classes; therefore, mass administration of AM may lead to increased isolation of multidrug resistant (MDR) MH and increase presence of resistance genes in the metagenome. Many NGS studies to date have used low numbers of cattle or pooled samples due to cost. Pooling is an acceptable strategy to increase number of units sampled, however sequencing depth per individual sample is decreased, and there is little evidence comparing pools to individual samples. In a trial involving high risk stocker cattle, tulathromycin metaphylaxis was associated with increased isolation of MDR MH, and this was associated with ICE related genes. Using pooled DNA extracted from NPS in these animals, which were shown to be acceptable for group level comparisons, metaphylaxis also increased ARG richness and diversity in these heifers; however, BRD treatment and time had a greater effect on the mircrobiome and resistome. Further work is needed to improve MH strain classification. These finding highlight the complexity of AMR research, because though tulathromycin had a clear effect on odds of isolation of MDR MH, metaphylaxis’ effects on the resistome and microbiome were more complex, and time and BRD contributed to greater change.

A Mannheimia haemolytica é uma importante bactéria relacionada ao Complexo Doença Respiratória dos Bovinos e a essa atribui-se uma evolução para uma forma grave de pneumonia fibrinonecrótica. É considerada um habitante comensal da nasofaringe que em situações de comprometimento da resposta imune adquire um perfil oportunista. O presente estudo buscou observar por meio de modelo de infecção experimental, as possíveis alterações locais e sistêmicas causadas pela M. haemolytica em bezerros experimentalmente inoculados. Dessa forma seria possível de maneira longitudinal, acompanhar a dinâmica dos principais aspectos de defesa das vias aéreas posteriores durante a infecção e após o tratamento com o antimicrobiano norfloxacina associado ou não à flunexina meglumina. Avaliou-se por exame físico acrescido de broncoscopia, alterações funcionais das células de defesa e mediadores inflamatórios, tanto séricos quanto locais e a atividade in vitro da norfloxacina sobre a função dos fagócitos sanguíneos e do lavado broncoalveolar (LBA). Para tal foram utilizados 12 bezerros sadios que foram experimentalmente infectados por M. haemolytica dos quais foram avaliadas as alterações clínicas e, quantitativamente e funcionalmente, as populações leucocitárias no sangue e no LBA, assim como o efeito da norfloxacina sobre a atividade funcional dos fagócitos no sangue e no LBA. Os resultados do presente estudo demonstraram o sucesso da infecção experimental por M. haemolytica pelos achados clínicos, broncoscópicos e citológicos. Ademais, a infecção experimental por M. haemolytica foi associada a alterações nas subpopulações de linfócitos T CD8+ e уδ, na produção intracelular de espécies reativas de oxigênio (ERO), fagocitose e viabilidade pelas células CD14+ sanguíneas e do LBA e granulócitos do sangue e, expressão de L-selectina pelos leucócitos polimorfonucleares do sangue. Nenhuma alteração evidente foi observada na expressão de citocinas IL-1β, IL-8 e TNF-α nas células sanguíneas e do LBA. O tratamento com antimicrobiano associado ou não ao anti-inflamatório foi capaz de curar a infecção e reestabelecer os parâmetros avaliados à sua condição basal. Portanto, não se observou benefícios com a utilização adicional do anti-inflamatório no reestabelecimento do quadro clínico e da resposta imune neste experimento. Contudo, apesar de algumas alterações na resposta sistêmica durante o quadro infeccioso, as alterações locais foram mais perceptíveis. Outro aspecto importante encontrado foi o efeito in vitro da norfloxacina na produção intracelular de ERO, fagocitose bacteriana pelas células CD14+ sanguíneas e do LBA e em leucócitos polimorfonucleares no sangue. Conclui-se que as alterações funcionais dos fagócitos apresentaram papel importante na patogenia da mannheimiose, que foram condizentes com os achados clínicos da mannheimiose e da evolução do tratamento quando realizado no início do processo nosológico. / Mannheimia haemolytica is an important bacterial pathogen associated with Bovine Respiratory Disease Complex (BRDC) and it is believed to be the predominant cause of the disease’s evolution into a fibrinonecrotic pneumonia. A commensal inhabitant of the nasopharynx, M. haemolytica acts as an opportunist when host defenses are compromised. This study used an experimental infection model to investigate the possible local and systemic changes caused by M. haemolytica in inoculated calves. It sought to linearly follow the dynamics of the lower respiratory tract defense mechanisms, during the course of infection and after treatment with the antibacterial norfloxacin, which was administrated both with and without the anti-inflammatory flunixin meglumine. With clinical examination followed by bronchoscopy, this study evaluated the physiological modifications in defense cells and mediators of inflammation, and the in vitro influence of norfloxacin on phagocytes from the peripheral blood and Bronchoalveolar Lavage Fluid (BLF). Twelve (12) healthy calves were infected with M. haemolytica and posteriorly physically examined, and had samples of white cells from the peripheral blood and BLF analyzed for changes in count and physiology, further, the norfloxacin effect on phagocytes from the peripheral blood and BLF was also studied. The experimental infection proved itself to be successful based on clinical, bronchoscopic and cytological findings. Furthermore, the M. haemolytica experimental infection was associated with modifications in the subpopulations of lymphocytes CD8+ and уδ T cells, in intracellular production of Reactive Oxygen Species (ROS), viability and phagocytosis activity of CD14+ cells from the peripheral blood and BLF and granulocytes from the peripheral blood. No obvious change was observed in the expression of cytokines IL-1β, IL-8 e TNF-α by cells from the peripheral blood or BLF. The treatment with the antibacterial agent, with or without the anti-inflammatory, was proved to be successful in curing the disease, thus, the addition of an anti-inflammatory was considered unnecessary to revert the clinical infection and in the immune response. Although there was a systemic response during the course of infection, the local response was more noticeable. Another key finding of the present study was the in vitro effect of norfloxacin on the intracellular production of ROS and on phagocytosis activity of CD14+ cells from the peripheral blood and BLF and granulocytes from the peripheral blood. In conclusion, the functional changes in phagocytes play an important role in the pathogenesis of pulmonary infection caused by M. haemolytica, as they were consistent with the clinical findings of mannheimiosis and with the treatment when it was administrated in the beginning of the infection.

A Mannheimia haemolytica é uma importante bactéria relacionada ao Complexo Doença Respiratória dos Bovinos e a essa atribui-se uma evolução para uma forma grave de pneumonia fibrinonecrótica. É considerada um habitante comensal da nasofaringe que em situações de comprometimento da resposta imune adquire um perfil oportunista. O presente estudo buscou observar por meio de modelo de infecção experimental, as possíveis alterações locais e sistêmicas causadas pela M. haemolytica em bezerros experimentalmente inoculados. Dessa forma seria possível de maneira longitudinal, acompanhar a dinâmica dos principais aspectos de defesa das vias aéreas posteriores durante a infecção e após o tratamento com o antimicrobiano norfloxacina associado ou não à flunexina meglumina. Avaliou-se por exame físico acrescido de broncoscopia, alterações funcionais das células de defesa e mediadores inflamatórios, tanto séricos quanto locais e a atividade in vitro da norfloxacina sobre a função dos fagócitos sanguíneos e do lavado broncoalveolar (LBA). Para tal foram utilizados 12 bezerros sadios que foram experimentalmente infectados por M. haemolytica dos quais foram avaliadas as alterações clínicas e, quantitativamente e funcionalmente, as populações leucocitárias no sangue e no LBA, assim como o efeito da norfloxacina sobre a atividade funcional dos fagócitos no sangue e no LBA. Os resultados do presente estudo demonstraram o sucesso da infecção experimental por M. haemolytica pelos achados clínicos, broncoscópicos e citológicos. Ademais, a infecção experimental por M. haemolytica foi associada a alterações nas subpopulações de linfócitos T CD8+ e уδ, na produção intracelular de espécies reativas de oxigênio (ERO), fagocitose e viabilidade pelas células CD14+ sanguíneas e do LBA e granulócitos do sangue e, expressão de L-selectina pelos leucócitos polimorfonucleares do sangue. Nenhuma alteração evidente foi observada na expressão de citocinas IL-1β, IL-8 e TNF-α nas células sanguíneas e do LBA. O tratamento com antimicrobiano associado ou não ao anti-inflamatório foi capaz de curar a infecção e reestabelecer os parâmetros avaliados à sua condição basal. Portanto, não se observou benefícios com a utilização adicional do anti-inflamatório no reestabelecimento do quadro clínico e da resposta imune neste experimento. Contudo, apesar de algumas alterações na resposta sistêmica durante o quadro infeccioso, as alterações locais foram mais perceptíveis. Outro aspecto importante encontrado foi o efeito in vitro da norfloxacina na produção intracelular de ERO, fagocitose bacteriana pelas células CD14+ sanguíneas e do LBA e em leucócitos polimorfonucleares no sangue. Conclui-se que as alterações funcionais dos fagócitos apresentaram papel importante na patogenia da mannheimiose, que foram condizentes com os achados clínicos da mannheimiose e da evolução do tratamento quando realizado no início do processo nosológico. / Mannheimia haemolytica is an important bacterial pathogen associated with Bovine Respiratory Disease Complex (BRDC) and it is believed to be the predominant cause of the disease’s evolution into a fibrinonecrotic pneumonia. A commensal inhabitant of the nasopharynx, M. haemolytica acts as an opportunist when host defenses are compromised. This study used an experimental infection model to investigate the possible local and systemic changes caused by M. haemolytica in inoculated calves. It sought to linearly follow the dynamics of the lower respiratory tract defense mechanisms, during the course of infection and after treatment with the antibacterial norfloxacin, which was administrated both with and without the anti-inflammatory flunixin meglumine. With clinical examination followed by bronchoscopy, this study evaluated the physiological modifications in defense cells and mediators of inflammation, and the in vitro influence of norfloxacin on phagocytes from the peripheral blood and Bronchoalveolar Lavage Fluid (BLF). Twelve (12) healthy calves were infected with M. haemolytica and posteriorly physically examined, and had samples of white cells from the peripheral blood and BLF analyzed for changes in count and physiology, further, the norfloxacin effect on phagocytes from the peripheral blood and BLF was also studied. The experimental infection proved itself to be successful based on clinical, bronchoscopic and cytological findings. Furthermore, the M. haemolytica experimental infection was associated with modifications in the subpopulations of lymphocytes CD8+ and уδ T cells, in intracellular production of Reactive Oxygen Species (ROS), viability and phagocytosis activity of CD14+ cells from the peripheral blood and BLF and granulocytes from the peripheral blood. No obvious change was observed in the expression of cytokines IL-1β, IL-8 e TNF-α by cells from the peripheral blood or BLF. The treatment with the antibacterial agent, with or without the anti-inflammatory, was proved to be successful in curing the disease, thus, the addition of an anti-inflammatory was considered unnecessary to revert the clinical infection and in the immune response. Although there was a systemic response during the course of infection, the local response was more noticeable. Another key finding of the present study was the in vitro effect of norfloxacin on the intracellular production of ROS and on phagocytosis activity of CD14+ cells from the peripheral blood and BLF and granulocytes from the peripheral blood. In conclusion, the functional changes in phagocytes play an important role in the pathogenesis of pulmonary infection caused by M. haemolytica, as they were consistent with the clinical findings of mannheimiosis and with the treatment when it was administrated in the beginning of the infection.

Doctor of Philosophy / Department of Diagnostic Medicine/Pathobiology / Robert L. Larson / Brad J. White / The diagnosis and prevention of bovine respiratory disease (BRD) is challenging due to the multifactorial nature of the disease. Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni are gram negative bacteria that are commonly considered three of the most important bacterial agents involved in the etiology of BRD; all three are also commensals in the upper respiratory tracts of healthy cattle. However, despite decades of study, questions still remain regarding the transmission dynamics and characterization of these bacteria, the ability of diagnostic sampling methods to accurately portray the causative bacteria, and ways to mitigate the effects of risk factors for BRD such as long-distance transportation. Through our research, we have demonstrated how variable the culture results of a single nasopharyngeal swab can be and the challenges of using an individual culture to truly represent animal M. haemolytica status. Additionally, comparison of the diagnostic performance of two antemortem sampling methods, nasopharyngeal swabs (NPS) and bronchoalveolar lavages (BAL), revealed high agreement, high negative predictive values of NPS for the presence of M. haemolytica, P. multocida, and H. somni in the lungs, and the potential for different susceptibility profiles from paired NPS and BAL samples. As agreement and predictive values can vary with disease prevalence, interpretation of diagnostic test results should be done carefully and with due consideration of the sample population in which the test is being applied. An investigation into cattle behavior following a relatively innocuous handling procedure indicated that some behaviors are altered after handling and restraint in a squeeze chute. Additionally, we demonstrated that cattle with different temperament scores may have different activity levels and spend different amounts of time within 1 m of the hay bunk, grain bunk, waterer, and shed after handling. Consequently, there is also the potential to improve upon disease detection algorithms by incorporating behavioral changes that may occur after handling events and the need for careful trial design when behavioral parameters are a trial outcome. Additionally, this study indicated that some behaviors may vary for calves that react differently when handled, which also has potential implications when behavior is considered a variable of interest. Examination of the potential for 1 mg/kg oral meloxicam administered pre-transport to mitigate the effects of long-distance transportation revealed that meloxicam did not have a statistically significant effect on the maintenance of leukocyte function or the reduction of inflammation during or after long-distance transportation in healthy steers. Finally, a report on two separate experiments regarding the effects of 1 mg/kg oral meloxicam administered pre-transport on the movement, feeding, and drinking behaviors and performance of transported and non-transported calves demonstrated that there was a significant day effect on behaviors in transported calves but meloxicam did not affect behavior or performance. However, meloxicam did modify the effect of day on daily distance traveled in non-transported calves but there were no significant within-day comparisons between non-transported meloxicam and non-transported control calves. These results do not provide evidence for the benefit of administering a single dose of 1 mg/kg oral meloxicam prior to long-distance transportation.

Frankfurt (Main), Universiẗat, Diss., 2008. / Dateien im PDF-Format.

Doctor of Philosophy / Department of Diagnostic Medicine/Pathobiology / Derek A. Mosier / The bovine respiratory disease complex (BRDC) is a major concern for cattle producers in the United States and worldwide. One of the most costly and deadly components of BRDC is bovine pneumonic pasteurellosis (BPP) caused by Mannheimia haemolytica. The initial pulmonary inflammation associated with BPP is a characteristic serofibrinous exudation into the lung, which is believed to be induced by M. haemolytica virulence factors such as lipopolysaccharide (LPS) and leukotoxin (LKT) and host cytokines and chemokines such as tumor necrosis factor – α, interleukin – 1β, and interleukin – 8. However, these pulmonary changes often occur before virulence factors or cytokines are substantial components of the pulmonary microenvironment. Other proinflammatory molecules such as substance P (SP) may be involved in the pathogenesis of the peracute serofibrinous exudation of BPP. SP is an 11 amino acid long neuropeptide that is a neurotransmitter of pain that can be released from sensory nerves into tissues to cause neurogenic inflammation. Neurogenic inflammation is characterized by serofibrinous exudation and leukocyte activation. SP-like immunoreactivity was present in the airways, alveolar septa, macrophages, endothelium, and peribronchial nerves in both pneumonic and normal bovine lung; however, SP-like immunoreactivity was increased in pneumonic compared to normal bovine lung due to increased immunoreactivity in macrophages. SP and the combination of SP with histamine and LPS increased the permeability of a calf pulmonary arterial endothelial cell line to Evans blue dye labeled albumin by 12.34%, 13.57%, and 22.03%, respectively compared to a cell control. Similarly, SP and the combination of SP and histamine increased the monolayer permeability of a bovine adrenal gland capillary endothelium by 8.27% and 16.69% compared to a cell control. The increase in permeability was due to endothelial cell shape change and the formation of intercellular gaps rather than cell death. However, SP does not increase the surface expression of the β2 integrin CD18 (the M. haemolytica LKT receptor) on bovine neutrophils nor does it increase LKT-induced leukocytotoxicity of bovine peripheral blood leukocytes. These findings indicate that SP may be a contributor to BPP in association with other cytokines.

Bovine respiratory disease (BRD) is the principal cause of morbidity and mortality among feedlot cattle. Mannheimia haemolytica is consistently implicated in this condition, but treatment options are diminishing with the rise of antimicrobial resistance and intensifying consumer pressure to reduce reliance on conventional therapies. Thus, sustainable alternatives like vaccination are required. In this study, the phenotypic and genotypic diversity of BRD pathogens were examined with the objective to identify vaccine targets using reverse vaccinology, an innovative approach to identify antigens via genomic sequence. Preliminary surveillance confirmed M. haemolytica serotype 2 isolates were predominant in healthy animals (75.5%) while serotypes 1 (70.7%) and 6 (19.5%) were common in diseased animals. Pathogens of BRD, including M. haemolytica, Pasteurella multocida and Histophilus somni were also isolated from North American BRD mortalities, and compared using pulsed-field gel electrophoresis and antimicrobial susceptibility. Concurrently, polymerase chain reaction detection of bacterial and viral agents confirmed that M. haemolytica with bovine viral diarrhea virus were the most prevalent. Whereas isolates from live cattle were found to have a relatively low level of resistance, several pathogens from the mortalities were found to contain integrative conjugative elements (ICE) conferring resistance to seven antimicrobial classes. These ICEs were transferred via conjugation to other bacterial species, emphasizing the need for alternative antimicrobial therapies. Collectively, data from these investigations informed the selection of 11 diverse M. haemolytica strains for whole genome sequencing and comparative analyses. Several bacteriophage associated genes and CRISPR-Cas regulated gene expression systems were identified and are likely contributing to virulence in M. haemolytica. Coding sequences across all genomes were screened using pan-genome analysis, identifying 291 candidates with cell-surface associated signatures. Using a cell-free translation system and enzyme-linked immunosorbent assay the candidates were screened against serum from cattle challenged with serovar 1, 2 or 6 of M. haemolytica, and ranked according to immunogenicity. The top five vaccine candidates included Ssa1, ComE, a solute binding protein, an outer membrane protein, and the periplasmic component of an ABC transporter. With further characterization, these unique antigenic candidates could be developed into a vaccine to effectively reduce the dependence on antimicrobial therapies.

La lechiguana es una enfermedad de los bovinos definida como una paniculitis fibrogranulomatosa proliferativa. Se caracteriza por una tumoración subcutánea de crecimiento rápido, con marcada proliferación de tejido fibroso que puede ocasional la muerte del animal. El objetivo de este trabajo fue confirmar la hipótesis de que la lechiguana es una enfermedad causada por una asociación entre el parasitismo de la Dermatobia hominis y la presencia de Mannheimia granulomatis.