[Coronaviruses as the cause of respiratory infections]

Hintergrund

Es gibt sechs humanpathogene Coronaviren (CoV), die vornehmlich respiratorische Infektionen auslösen. Im klinischen Alltag ist es hilfreich, Relevanz und Besonderheiten dieser Erreger zu kennen.

Fragestellung

Praxisnahe Darstellung der Epidemiologie, Klinik und Unterschiede humanpathogener CoV. Hinweise zu Diagnostik und Umgang mit Patienten bei Verdacht auf eine CoV-Infektion.

Material und Methoden

Selektive Literaturrecherche, Darstellung und Diskussion von Grundlagenarbeiten und Expertenempfehlungen einschließlich der Veröffentlichungen der Weltgesundheitsorganisation (WHO), des Europäischen Zentrums für die Prävention und die Kontrolle von Krankheiten (ECDC) und des Robert Koch-Instituts.

Ergebnisse

Die weltweit endemischen CoV (HCoV-NL63, -229E, -OC43 und -HKU1) sind häufige Ursache von leichteren respiratorischen Infektionen. Zwei epidemische, zoonotische Coronaviren (SARS- und MERS-CoV, MERS „Middle East respiratory syndrome“, SARS „severe acute respiratory syndrome“ [schweres akutes Atemwegssyndrom]) können schwere Pneumonien hervorrufen. SARS-CoV ist seit 15 Jahren nicht mehr im Menschen nachgewiesen worden. MERS-CoV zirkuliert seit 2012 hauptsächlich auf der Arabischen Halbinsel. Eine spezifische Therapie oder zugelassene Impfung existiert noch für keines der sechs humanpathogenen Coronaviren.

Schlussfolgerung

Eine Erregerdiagnostik mittels Polymerase-Kettenreaktion aus respiratorischem Material ist für alle CoV möglich, für die vier endemischen allerdings selten notwendig. SARS-CoV hat aktuell keine Relevanz in der Klinik, da es seit 15 Jahren nicht mehr im Menschen nachgewiesen wurde. Der Verdacht auf eine MERS-Infektion sollte hingegen bei entsprechender Symptomatik und Reiseanamnese differenzialdiagnostisch in Betracht gezogen werden. Hier sind eine schnelle Diagnosesicherung und allgemeine Hygienemaßnahmen zur Verhinderung der Verbreitung entscheidend.

Rodent animal models of delayed bone healing and non-union formation: a comprehensive review

Despite the growing knowledge on the mechanisms of fracture healing, delayed healing and non-union formation remain a major clinical challenge. Animal models are needed to study the complex process of normal and impaired fracture healing and to develop new therapeutic strategies. Whereas in the past mainly large animals have been used to study normal and impaired fracture healing, nowadays rodent models are of increasing interest. New osteosynthesis techniques for rat and mice have been developed during the last years, which allowed for the first time stable osteosynthesis in these animals comparable to the standards in large animals and humans. Based on these new implants, different models in rat and mice have been established to study delayed healing and non-union formation. Although in humans the terms delayed union and non-union are well defined, in rodents definitions are lacking. However, especially in scientific studies clear definitions are necessary to develop a uniform scientific language and allow comparison of the results between different studies. In this consensus report, we define the basic terms "union", "delayed healing" and "non-union" in rodent animal models. Based on a review of the literature and our own experience, we further provide an overview on available models of delayed healing and non-union formation in rats and mice. We further summarise the value of different approaches to study normal and delayed fracture healing as well as non-union formation, and discuss different methods of data evaluation.

Small animal bone healing models: standards, tips, and pitfalls results of a consensus meeting

Small animal fracture models have gained increasing interest in fracture healing studies. To achieve standardized and defined study conditions, various variables must be carefully controlled when designing fracture healing experiments in mice or rats. The strain, age and sex of the animals may influence the process of fracture healing. Furthermore, the choice of the fracture fixation technique depends on the questions addressed, whereby intra- and extramedullary implants as well as open and closed surgical approaches may be considered. During the last few years, a variety of different, highly sophisticated implants for fracture fixation in small animals have been developed. Rigid fixation with locking plates or external fixators results in predominantly intramembranous healing in both mice and rats. Locking plates, external fixators, intramedullary screws, the locking nail and the pin-clip device allow different degrees of stability resulting in various amounts of endochondral and intramembranous healing. The use of common pins that do not provide rotational and axial stability during fracture stabilization should be discouraged in the future. Analyses should include at least biomechanical and histological evaluations, even if the focus of the study is directed towards the elucidation of molecular mechanisms of fracture healing using the largely available spectrum of antibodies and gene-targeted animals to study molecular mechanisms of fracture healing. This review discusses distinct requirements for the experimental setups as well as the advantages and pitfalls of the different fixation techniques in rats and mice.

Time kinetics of bone defect healing in response to BMP-2 and GDF-5 characterised by in vivo biomechanics

This study reports that treatment of osseous defects with different growth factors initiates distinct rates of repair. We developed a new method for monitoring the progression of repair, based upon measuring the in vivo mechanical properties of healing bone. Two different members of the bone morphogenetic protein (BMP) family were chosen to initiate defect healing: BMP-2 to induce osteogenesis, and growth-and-differentiation factor (GDF)-5 to induce chondrogenesis. To evaluate bone healing, BMPs were implanted into stabilised 5 mm bone defects in rat femurs and compared to controls. During the first two weeks, in vivo biomechanical measurements showed similar values regardless of the treatment used. However, 2 weeks after surgery, the rhBMP-2 group had a substantial increase in stiffness, which was supported by the imaging modalities. Although the rhGDF-5 group showed comparable mechanical properties at 6 weeks as the rhBMP-2 group, the temporal development of regenerating tissues appeared different with rhGDF-5, resulting in a smaller callus and delayed tissue mineralisation. Moreover, histology showed the presence of cartilage in the rhGDF-5 group whereas the rhBMP-2 group had no cartilaginous tissue. Therefore, this study shows that rhBMP-2 and rhGDF-5 treated defects, under the same conditions, use distinct rates of bone healing as shown by the tissue mechanical properties. Furthermore, results showed that in vivo biomechanical method is capable of detecting differences in healing rate by means of change in callus stiffness due to tissue mineralisation.

Digital image correlation: A technique for determining local mechanical conditions within early bone callus

Local mechanical conditions are known to play a role during the regeneration of musculoskeletal tissues, and histomorphometrical investigations of the time course of healing have enabled specific conclusions regarding the mechanosensitivity of tissue differentiation. However, the mechanism for this influence is not clearly understood. In order to extend this analysis, it is essential to link local histological understanding with direct characterisation of the local mechanical environment. Digital image correlation (DIC) is a computer-based image analysis technique that enables the non-contact measurement of strains on material surfaces and is finding application in many areas of biomechanics. Here we report a DIC technique to investigate the local distribution of mechanical strain within regenerating soft tissue sections. We provide exemplary data from analysis of a section of sheep bone callus. An assessment of displacement measurement accuracy gave an RMS error of 4.2 microm, corresponding to an estimated strain error of 1.4%. The sections showed concentrations of up to four times the applied strain and comparison of the strain patterns with histological analysis confirmed that these concentrations reflected boundaries between hard and soft callus.