Mice and rats are the most common lab mammals for scientific research, But depending on the question being asked, and if relevant, the intervention being tested, they are not necessarily always the most appropriate animal to use.
When it comes to studying interventions for human diseases, scientists in translational research must usually find animal models in whom the disease acts as similarly as possible to the way it does in humans. For example, when FDA researcher Tod Merkel conducted a study to test the effectiveness of the acellular pertussis vaccine in preventing infection, he used baboons because the disease process of pertussis is similar in baboons as it is in humans. The research cannot be perfectly translated, but it can come close enough to explain trends that researchers had identified in epidemiological data.
But the SARS-CoV2 coronavirus is novel, so scientists need to figure out what animals are best for studying it. An article from Eric Boodman at Stat News March 5 opens with how various the possible animal models might be: “One lab is digging into its freezer to thaw out the archived sperm of SARS-susceptible mice. Another is anesthetizing ferrets, so they don’t sneeze when the new coronavirus is squirted into their nostrils. Yet others are racing to infect macaques, marmosets, and African green monkeys.”
Determining which animal is best is no small task, nor is it quick or cheap. Some of the questions scientists have to explore include:
- What animals can biologically be hosts for the virus? (The virus has to be able to replicate in them.)
- What does an infection look like in these animals? How does their immune system respond to it?
- What clinical symptoms do they display? How do these symptoms compare to those observed in humans?
- What are their outcomes, and how do those outcomes compare to humans?
Even if a mammal is excellent for studying one respiratory disease — even a similar coronavirus, such as SARS — it may not be right for studying this coronavirus. Sure, the chances are higher that animals that were good models for SARS will be suitable for this new virus, but the immune system in humans and animals is incredibly complex — perhaps the most complex system in the body. Even subtle differences in viruses could influence subtle differences in immune systems that could render findings from one animal species meaningless when it comes to humans.
Boodman’s article goes into depth about these challenges and what scientists are working on. Another informative article by from Diane Peters on Undark explores how ferrets, in particular, may play a role in COVID-19 research. Both are worth a read as background for when animal studies on vaccines begin coming out. Reporters will need to consider which animal a vaccine candidate or new treatment was tested on and spend a good portion of any interview with researchers on this important question: Why this animal, and what can it tell us about humans?