- An animal model is a non-human species that is used in experiments that would not be feasible or ethical to conduct in humans.
- Animal models are particularly useful in research that focuses on complex systems that involve multiple cell types or organ structures, such as the immune system or the brain. Currently, these environments cannot be accurately recreated using cell lines or in vitro systems.
- Commonly used animal models include:
-Caenorhabditis elegans (roundworm)
-Drosophila melanogaster (fruit fly)
-Danio rerio (zebrafish)
-Mus musculus (mouse)
-Rattus norvegicus (rat)
-Macaca mulatta (Rhesus monkeys)
- The safety of drugs and therapies can be tested on animals of different sexes at various stages of development before moving to clinical trials in humans.
- Research can be conducted efficiently and economically on sizable cohorts of animals, increasing the statistical power of the research.
- The effects of drugs and therapies can be observed in a variety of tissues/organs and at multiple time points without performing invasive procedures on humans.
- The life cycles and gestation periods of model organisms are shorter than in humans; experiments can proceed more quickly and address all life stages. Additionally, genetic modifications can be made and refined more quickly in models with shorter generation times.
- The choice of animal model is dependent on several factors:
-the similarity of the animal gene/protein/cell/organ to its human counterpart
-genetic uniformity (to minimize experimental variations)
-background knowledge (genome sequences, previously published research)
-experimental tools (transgenics, humanization, cell/tissue/organ grafting)
-cost and availability (larger animals or those with complex needs are more expensive to purchase and care for)
-ethical considerations (particularly for non-human primates)
- Multiple animal models may be used in the drug testing process because the effects of the drug may vary between species. For instance, thalidomide does not cause limb defects in mice and rat embryos, but it does in humans, monkeys, rabbits, chicks, and zebrafish.
- Some diseases are difficult to study in animal models, and it can take a long time to establish an effective animal model. For example, HIV has traditionally been studied using macaques and either SIV or an SIV/HIV hybrid virus (SHIV). Humanized mouse models (engrafted with human immune cells) have also been developed for HIV research.
- Researchers should always attempt to apply the “3Rs” (Replacement, Reduction and Refinement) in their research with animal models. They should also utilize the recommendations found in the ARRIVE Guidelines and strive to adhere to the strictest ethical guidelines in their field.
What to watch for
- When you read a scientific manuscript, note if any animal models were used. Examine previously published manuscripts in the same area of study to determine if similar animal models are commonly used across the field. If a different model organism is used, try to discover why it was chosen and if it is appropriate.
- Try to determine how many animals were used; if it appears that the research involved unusually large or small numbers of animals, you may wish to scrutinize the data more closely. Remember that it is more difficult and expensive to utilize larger animal models (such as livestock) or those with complex needs (such as non-human primates); these studies often involve smaller numbers of animals.
- If unusual procedures or husbandry practices are described in the manuscript, investigate further to determine if they are standard for the field. Animal ethics standards are constantly reviewed and updated, and if a study does not align with current guidelines, there may be other serious issues with the research or the journal that publishes it.
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