Animal models for research in human infectious diseases. CMI editorial policy
Authors: I.C. Gyssens
Journal: Clinical Microbiology and Infection (2019)

Animal models have contributed substantially to unravelling the physiopathology of infection and host–pathogen interactions in infectious diseases. Experimental studies on animals provide information on intervention strategies with drugs, invasive procedures and vaccines at a preclinical level. CMI publishes manuscripts presenting the results of original research in clinical microbiology, infectious diseases, bacteriology, mycology, virology and parasitology, including immunology and epidemiology as related to these fields. At the last CMI editorial board meeting, the question was raised whether CMI should publish experimental animal studies. In the last 5 years, CMI has infrequently published original articles using animal models, approximately 1 or 2 per year [1Zeng X. Gu H. Cheng Y. Jia K.R. Liu D. Yuan Y. et al.A lethal pneumonia model of Acinetobacter baumannii: an investigation in immunocompetent mice.Clin Microbiol Infect. 2019; 25: 516.e1-516.e4Abstract Full Text Full Text PDF Scopus (15) Google Scholar, 2Chia J.H. Wu T.S. Wu T.L. Chen C.L. Chuang C.H. Su L.H. et al.Clostridium innocuum is a vancomycin-resistant pathogen that may cause antibiotic-associated diarrhoea.Clin Microbiol Infect. 2018; 24: 1195-1199Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar, 3Cameron D.R. Lin Y.H. Trouillet-Assant S. Tafani V. Kostoulias X. Mouhtouris E. et al.Vancomycin-intermediate Staphylococcus aureus isolates are attenuated for virulence when compared with susceptible progenitors.Clin Microbiol Infect. 2017; 23: 767-773Abstract Full Text Full Text PDF PubMed Scopus (18) Google Scholar]. All studies were conducted in mice. Reasons for such low numbers could be the reluctance of authors to submit their work to CMI due to the absence of a clear position on animal studies in the scope of CMI author guidelines. Experimental animal studies are well within the scope of CMI. This Editorial note formulates a CMI policy relating to experimental animal research. Guidance for ‘humane experimental technique’ goes back to the 1950s. The ‘3R principles of animal experimentation’, namely reduce, refine and replace were formulated by Russell & Burch [[4]Russell W.M.S. Burch R.L. The principles of humane experimental technique. Methuen, London1959Google Scholar]. Reduction includes methods that minimize the number of animals used per experiment. Refinement refers to methods that minimize animal suffering and improve welfare. Replacement corresponds to methods that avoid or replace the use of animals. The 3R principles are still the basis of ethical and responsible use of animals. Details can be found on the UK funded National Centre for the Replacement Refinement & Reduction of Animals in research (NC3Rs) website https://nc3rs.org.uk. With regard to these principles, since the 1980s, several scientific groups have regularly reported concerns about the quality of reporting methods and results of animal experiments. Despite an abundance of guidelines, the awareness and their implementation in the research community has been variable [[5]Osborne N. Avey M.T. Anestidou L. Ritskes-Hoitinga M. Griffin G. Improving animal research reporting standards: HARRP, the first step of a unified approach by ICLAS to improve animal research reporting standards worldwide.EMBO Rep. 2018; 19: e46069Crossref PubMed Scopus (35) Google Scholar]. European legislation is available and the EU Directive 2010/63/EU should be complied with. The ARRIVE (Animal Research: Reporting of in vivo experiments) guidelines https://www.nc3rs.org.uk/arrive-guidelines issued by the NC3Rs in 2010 were intended to improve the reporting of research using animals – maximizing information published and minimizing unnecessary studies [[6]Kilkenny C. Browne W.J. Cuthill I.C. Emerson M. Altman D.G. Improving bioscience research reporting: the ARRIVE guidelines for reporting animal research.PLoS Biol. 2010; 8: e1000412Crossref PubMed Scopus (4737) Google Scholar]. The process of these guidelines' development paralleled the process of the CONSORT guidelines for clinical trials. ARRIVE guidelines cover all sections of a manuscript, from title to discussion. They come with a 20-item checklist https://www.nc3rs.org.uk/sites/default/files/documents/Guidelines/NC3Rs ARRIVE Guidelines Checklist (fillable). pdf to be used when submitting manuscripts. The USA National Institutes of Health (NIH) has proposed its own guidelines, the Principles and Guidelines for Reporting Preclinical Research (NIHPG), with similar objectives as ARRIVE. The six ‘core’ reporting items found in the NIHPG are similar to the corresponding items (sub-items) in the ARRIVE checklist [[7]Moher D. Avey M. Antes G. Altman D.G. The National Institutes of Health and guidance for reporting preclinical research.BMC Med. 2015; 13: 34Crossref PubMed Scopus (24) Google Scholar]. In addition, the International Council for Laboratory Animal Science (ICLAS) working group has produced a somewhat ‘light’ version of eight harmonized animal research reporting principles (HARRP), published in a European Molecular Biology Organization (EMBO) report [[4]Russell W.M.S. Burch R.L. The principles of humane experimental technique. Methuen, London1959Google Scholar]. CMI accepts reports on animal studies that include host–pathogen interaction and pathogen virulence, close to practice in humans (for example see [1Zeng X. Gu H. Cheng Y. Jia K.R. Liu D. Yuan Y. et al.A lethal pneumonia model of Acinetobacter baumannii: an investigation in immunocompetent mice.Clin Microbiol Infect. 2019; 25: 516.e1-516.e4Abstract Full Text Full Text PDF Scopus (15) Google Scholar, 2Chia J.H. Wu T.S. Wu T.L. Chen C.L. Chuang C.H. Su L.H. et al.Clostridium innocuum is a vancomycin-resistant pathogen that may cause antibiotic-associated diarrhoea.Clin Microbiol Infect. 2018; 24: 1195-1199Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar, 3Cameron D.R. Lin Y.H. Trouillet-Assant S. Tafani V. Kostoulias X. Mouhtouris E. et al.Vancomycin-intermediate Staphylococcus aureus isolates are attenuated for virulence when compared with susceptible progenitors.Clin Microbiol Infect. 2017; 23: 767-773Abstract Full Text Full Text PDF PubMed Scopus (18) Google Scholar]). In vaccine development animal models can optimize vaccine formulation (antigen, adjuvant), route of administration (e.g. intramuscular vs. mucosal) and effective and safe vaccine dosage. The induced immune response can be assessed to find immune correlates of protection. This preclinical research maximizes the chances that a vaccine candidate will be protective and safe before it is applied to humans [[8]Kaser T. Renois F. Wilson H.L. Cnudde T. Gerdts V. Dillon J.R. et al.Contribution of the swine model in the study of human sexually transmitted infections.Infect Genet Evol. 2018; 66: 346-360Crossref PubMed Scopus (19) Google Scholar]. Animal models have proven useful to design and minimize the risk of subsequent clinical trials on antimicrobial drugs [[9]Andes D.R. Lepak A.J. In vivo infection models in the pre-clinical pharmacokinetic/pharmacodynamic evaluation of antimicrobial agents.Curr Opin Pharmacol. 2017; 36: 94-99Crossref PubMed Scopus (24) Google Scholar]. The study of pharmacokinetics/pharmacodynamics (PK/PD) in specific, well-standardized models such as the mouse thigh infection model has led to the formulation of indices and targets that determine optimal drug exposures. These results can be translated from the in vivo model to humans, because the antimicrobial target is in the microorganism and not the host. Exposure relative to the MIC provides a normalization across host species [[9]Andes D.R. Lepak A.J. In vivo infection models in the pre-clinical pharmacokinetic/pharmacodynamic evaluation of antimicrobial agents.Curr Opin Pharmacol. 2017; 36: 94-99Crossref PubMed Scopus (24) Google Scholar]. The murine model is most frequently used in infection research. In contrast to other rodents and non-human primates, mice are small, easy to handle and transport in the laboratory setting. With their short generation time they provide large numbers of animals quickly at relatively low cost [[10]Masopust D. Sivula C.P. Jameson S.C. Of mice, dirty mice, and men: using mice to understand human immunology.J Immunol. 2017; 199: 383-388Crossref PubMed Scopus (147) Google Scholar]. Besides the thigh model for the study of PK/PD, the mouse is also the predominant animal model for the preclinical study of urinary tract infections [[11]Barber A.E. Norton J.P. Wiles T.J. Mulvey M.A. Strengths and limitations of model systems for the study of urinary tract infections and related pathologies.Microbiol Mol Biol Rev. 2016; 80: 351-367Crossref PubMed Scopus (34) Google Scholar], different types of pneumonia [[12]Bielen K. Jongers B. Malhotra-Kumar S. Jorens P.G. Goossens H. Kumar-Singh S. Animal models of hospital-acquired pneumonia: current practices and future perspectives.Ann Transl Med. 2017; 5: 132Crossref PubMed Scopus (22) Google Scholar] and sepsis [[13]Osuchowski M.F. Ayala A. Bahrami S. Bauer M. Boros M. Cavaillon J.M. et al.Minimum quality threshold in pre-clinical sepsis studies (MQTiPSS): an international expert consensus initiative for improvement of animal modeling in sepsis.Shock. 2018; 50: 377-380Crossref PubMed Scopus (102) Google Scholar]. Differences between animal and human immune systems have on the one hand led to more immunological research in human ex vivo cell systems replacing animals; on the other hand due to immunological differences between humans and mice, swine models have been developed due to their similarities with humans in terms of anatomy, genetics, immunology and physiology, their manageable behaviour and size, and the general public acceptance of using pigs for experimental purposes [[8]Kaser T. Renois F. Wilson H.L. Cnudde T. Gerdts V. Dillon J.R. et al.Contribution of the swine model in the study of human sexually transmitted infections.Infect Genet Evol. 2018; 66: 346-360Crossref PubMed Scopus (19) Google Scholar]. As an example, the swine model has been successful in the study of several human sexually transmitted infections [[8]Kaser T. Renois F. Wilson H.L. Cnudde T. Gerdts V. Dillon J.R. et al.Contribution of the swine model in the study of human sexually transmitted infections.Infect Genet Evol. 2018; 66: 346-360Crossref PubMed Scopus (19) Google Scholar]. However, the development of so-called ‘humanized mice’ to correct for immunological differences is more in line with the above-mentioned Refinement principle. Humanized mice, defined as mice engrafted with functional human cells or tissues, are suitable for the study of immune responses to various pathogens and for the development of novel therapeutic and prophylactic approaches. This applies to viral pathogens that have a narrow human tropism and target components of human immune system such as human immunodeficiency virus or epstein barr virus, but also to bacteria such as Salmonella spp. or Neisseria meningitidis, which have specific cellular tropism [[14]Ernst W. Humanized mice in infectious diseases.Comp Immunol Microbiol Infect Dis. 2016; 49: 29-38Crossref PubMed Scopus (29) Google Scholar]. Recently, much smaller Refined experimental organisms such as the nematode Caenorhabditis elegans infected with human pathogens have shown their usefulness for the study of mechanisms of host immunity and pathogen virulence [[15]Marsh E.K. May R.C. Caenorhabditis elegans, a model organism for investigating immunity.Appl Environ Microbiol. 2012; 78: 2075-2081Crossref PubMed Scopus (112) Google Scholar] as well as for investigating the efficacy of antibacterial agents in vivo at an early stage [[16]Eissa I.H. Mohammad H. Qassem O.A. Younis W. Abdelghany T.M. Elshafeey A. et al.Diphenylurea derivatives for combating methicillin- and vancomycin-resistant Staphylococcus aureus.Eur J Med Chem. 2017; 130: 73-85Crossref PubMed Scopus (32) Google Scholar]. Other examples include zebrafish (Danio rerio) larvae, which present a fully functional innate immune system with macrophages and neutrophils that mimic mammals. This model is also increasingly used in preclinical drug development and toxicity testing [[17]Torraca V. Mostowy S. Zebrafish infection: from pathogenesis to cell biology.Trends Cell Biol. 2018; 28: 143-156Abstract Full Text Full Text PDF PubMed Scopus (83) Google Scholar]. In conclusion, CMI encourages authors to submit their preclinical experimental animal work applying the standards on reporting, and to upload a completed ARRIVE checklist with their manuscript. CMI invites authors to submit with the checklist a 3R supplementary document, justifying the use of animals for their study and how the 3Rs were addressed. Authors need to take the reporting standards into account when planning and conducting their experiments; otherwise, it will require additional effort to collect the details required on submission. CMI Editors will recommend peer reviewers to use the guidelines/checklist during their manuscript review assessment. Verification by the editorial team of author adherence to the policy will further guarantee transparency and reproducible preclinical research reports in CMI. The author declares no conflict of interest. The CMI editors and Jerónimo Pachón are acknowledged for their critical reading of the manuscript.