Isolation of Histophilus somni from the nasal exudates of a clinically healthy adult goat

Histophilus somni disease conditions with simultaneous infections by ovine gammaherpesvirus 2 in cattle herds from Southern Brazil

This report investigated the cause of cattle mortality in two farms in Southern Brazil. The tissues of one animal from each farm (animals #1 and #2) respectively were used in pathological and molecular investigations to determine the possible cause of death. The principal pathological findings observed in animal #1 were pulmonary, myocardial, and encephalitic hemorrhages with vasculitis, and lymphoplasmacytic interstitial pneumonia with proliferative vascular lesions (PVL). The main pathological findings observed in animal #2 were purulent bronchopneumonia, hemorrhagic myocarditis, and lymphoplasmacytic interstitial pneumonia with PVL. An immunohistochemical assay detected intralesional antigens of a malignant catarrhal fever virus (MCFV) from multiple tissues of animal #2 while PCR confirmed that the MCFV amplified was ovine gammaherpesvirus 2 (OvGHV2), genus Macavirus, subfamily Gammaherpesvirinae; OvGHV2 was also amplified from multiple tissues of animal #1. Furthermore, PCR assays amplified Histophilus somni DNA from multiple fragments of both animals. However, the nucleic acids of Mannheimia haemolytica, Pasteurella multocida, Mycoplasma bovis, bovine respiratory syncytial virus, bovine alphaherpesvirus virus 1 and 5, bovine coronavirus, and bovine parainfluenza virus 3 were not amplified from any of the tissues analyzed, suggesting that these pathogens did not participate in the development of the lesions herein described. These findings demonstrated that both animals were concomitantly infected by H. somni and OvGHV2 and developed the septicemic and encephalitic manifestations of H. somni. Furthermore, the interstitial pneumonia observed in cow #2 was more likely associated with infection by OvGHV2.

Transferrin Binding Protein B and Transferrin Binding Protein A2 Expand the Transferrin Recognition Range of Histophilus somni

The bacterial bipartite transferrin receptor is an iron acquisition system that several important human and animal pathogens require for survival. It consists of the TonB-dependent transporter transferrin binding protein A (TbpA) and the surface lipoprotein transferrin binding protein B (TbpB). Curiously, the Tbps are only found in host-specific pathogens and are themselves host specific, meaning that they will bind to the transferrin of their host species but not to the transferrins of other animal species. While this phenomenon has long been established, neither the steps in the evolutionary process that led to this exquisite adaptation for the host nor the steps that could alter it are known. We sought to gain insight into these processes by studying Tbp specificity in Histophilus somni, an economically important pathogen of cattle. A past study showed that whole cells of H. somni specifically bind bovine transferrin but not transferrin from sheep and goats, two bovids whose transferrins share 93% amino acid sequence identity with bovine transferrin. To our surprise, we found that H. somni can use sheep and goat transferrins as iron sources for growth and that HsTbpB, but not HsTbpA, has detectable affinity for sheep and goat transferrins. Furthermore, a third transferrin binding protein found in H. somni, HsTbpA2, also showed affinity for sheep and goat transferrins. Our results suggest that H. somni TbpB and TbpA2 may contribute to broadening the host transferrin recognition range of H. somni IMPORTANCE Host-restricted pathogens infect a single host species or a narrow range of host species. Histophilus somni, a pathogen that incurs severe economic losses for the cattle industry, infects cattle, sheep, and goats but not other mammals. The transferrin binding proteins, TbpA and TbpB, are thought to be a key iron acquisition system in H. somni; however, despite their importance, H. somni TbpA and TbpB were previously shown to be cattle transferrin specific. In our study, we find that H. somni TbpB and another little-studied Tbp, TbpA2, bind sheep and goat transferrins, as well as bovine transferrin. Our results suggest that TbpB and TbpA2 may allow for host range expansion and provide a mechanism for how host specificity in Tbp-encoding pathogens can be altered.

Histophilus somni-associated syndromes in sheep from Southern Brazil

Histophilus somni is a Gram-negative bacterium that is associated with a disease complex (termed histophilosis) that can produce several clinical syndromes predominantly in cattle, but also in sheep. Histophilosis is well described in North America, Canada, and in some European countries. In Brazil, histophilosis has been described in cattle with respiratory, reproductive, and systemic disease, with only one case described in sheep. This report describes the occurrence of Histophilus somni-associated disease in sheep from Southern Brazil. Eight sheep with different clinical manifestations from five farms were investigated by a combination of pathological and molecular diagnostic methods to identify additional cases of histophilosis in sheep from Brazil. The principal pathological lesions were thrombotic meningoencephalitis, fibrinous bronchopneumonia, pulmonary abscesses, and necrotizing myocarditis. The main clinical syndromes associated with H. somni were thrombotic meningoencephalitis (n = 4), septicemia (n = 4), bronchopneumonia (n = 4), and myocarditis (n = 3). H. somni DNA was amplified from multiple tissues of all sheep with clinical syndromes of histophilosis; sequencing confirmed the PCR results. Further, PCR assays to detect Pasteurella multocida and Mannheimia haemolytica were negative. These findings confirmed the participation of H. somni in the clinical syndromes investigated during this study, and adds to the previous report of histophilosis in sheep from Brazil.

Histophilus somni-induced infections in cattle from southern Brazil

The sudden death of three calves, one diarrheic calf, and one aborted fetus from four farms in southern Brazil was investigated. Two Histophilus somni-associated syndromes were identified: systemic histophilosis (n = 4) and abortion (n = 1). The principal pathological findings included vasculitis, meningoencephalitis with thrombosis, necrotizing myocarditis, renal infarctions, hepatic abscesses, and bronchopneumonia. PCR assays were used to amplify specific amplicons of the ovine herpesvirus 2, bovine herpesvirus 1 and −5, Listeria monocytogenes, H. somni, and pestivirus; bovine group A rotavirus (BoRV-A) and bovine coronavirus (BCoV) were investigated in calves with diarrhea. H. somni DNA was amplified in tissues from all calves and the brain of the aborted fetus with pathological alterations consistent with histophilosis. All other PCR assays were negative; BoRV-A and BCoV were not identified. These findings confirm the participation of H. somni in the pathological alterations observed in this study and represent the first description of histophilosis in cattle from Brazil.

Two outer membrane lipoproteins from Histophilus somni are immunogenic in rabbits and sheep and induce protection against bacterial challenge in mice

Histophilus somni is an economically important pathogen of cattle and other ruminants and is considered one of the key components of the bovine respiratory disease (BRD) complex, the leading cause of economic loss in the livestock industry. BRD is a multifactorial syndrome, in which a triad of agents, including bacteria, viruses, and predisposing factors or "stressors," combines to induce disease. Although vaccines against H. somni have been used for many decades, traditional bacterins have failed to demonstrate effective protection in vaccinated animals. Hence, the BRD complex continues to produce strong adverse effects on the health and well-being of stock and feeder cattle. The generation of recombinant proteins may facilitate the development of more effective vaccines against H. somni, which could confer better protection against BRD. In the present study, primers were designed to amplify, clone, express, and purify two recombinant lipoproteins from H. somni, p31 (Plp4) and p40 (LppB), which are structural proteins of the outer bacterial membrane. The results presented here demonstrate, to our knowledge for the first time, that when formulated, an experimental vaccine enriched with these two recombinant lipoproteins generates high antibody titers in rabbits and sheep and exerts a protective effect in mice against septicemia induced by H. somni bacterial challenge.