As we approach the end of 2020 and look back on the year that has felt like a lifetime, it is clear we have learned a lot in the past six months. Among the lessons is that humans are not distinct from the rest of the animal kingdom.
Nearly three-quarters of emerging infectious human diseases actually originate in animals, according to the CDC. In the specific instance of coronavirus, it is a family of viruses that is very common in birds and mammals—including humans. This knowledge provides researchers additional means to study new therapeutic strategies by taking advantages of similarities across different viral strains in different species. A study published recently in mBio found that a COVID-19 vaccine based on the parainfluenza virus 5 (PIV5)—one cause of kennel cough in dogs—protected mice from the lethal Middle East respiratory syndrome (MERS) virus, which is also a coronavirus. Other investigators recently identified a novel nidovirus in Pacific Salmon that causes localized infections of the gills. Nidoviruses are evolutionarily similar to coronaviruses, and by examining similarities and differences in respiratory disease resulting from this viral family across a range of species, we can start to understand more about how different species respond to infection, and apply those learnings to find new ways to improve human health.
The linkage between animal genomics and human health
Given that we share approximately 90% of our genes with other mammals, it’s time that we begin to consider diverse animal models not from a perspective of simply modeling human disease, but from a perspective of novel discovery and leveraging unique biology to find new pathways for therapeutics.
The separation of human and animal diseases is an antiquated notion. Outside of basic physiology and genomics, the linkage between animals and humans affects nearly every aspect of our lives, from the environment to antimicrobial resistance to food security to rare disease biology. Research has shown that cross species conservation is twice as predictive as any other factor in determining if a gene plays a role in disease. It’s important for us to remember that humans are also animals, and by ignoring these key evolutionary relationships, we cannot truly understand ourselves. On the contrary, by studying other animals, we can learn more about disease etiology and find ways to naturally combat and cure disease.
Recently, investigators studying hibernating ground squirrels discovered that these animals have developed ways to reduce clotting and resist damage from myocardial infarction. While hibernating mammals are a fascinating example of how we can learn from natural biology, researchers are learning more from other species as well. For example, marine mammals can provide clues on extreme changes in metabolism, lipid disorders, resistance to hypoxia, and cardiac disease. The development of additional resources for more mechanistic studies, such as cell lines derived from these unique species, will give investigators more tools to understand how these animals do what they do and how we can take advantage of that knowledge to improve human health.
Animal insights to reveal treatments
Despite many attempts over the years, the mystery of what sends animals into hibernation has never been solved. It is believed this knowledge could help advance treatments for traumatic brain injury (TBI) in humans. These animals experience long-term suspended animation in torpor and receive cerebral blood flow at only 10% of the normal rate, yet they are able to protect their brains from ischemia and subsequent reperfusion upon arousal. Because ischemia and TBI share common pathologies including inflammation, oxidative stress, excitotoxicity, and perturbation of calcium homeostasis, adaptations in hibernators may also be useful in protecting against TBI in humans if we can gain a better understanding of the pathways utilized by hibernators to protect brain tissue from injury.
In another study, researchers revealed evidence of this built-in survival mode dating back 250 million years. They found evidence of torpor in the tusks of Lystrosaurus, which are early Triassic mammalian predecessors. An analysis of their ancient tusks revealed long periods of stress associated with torpor, which indicated the organism lowered its metabolism at regular intervals.
Our mission: To gain a better understanding
We now know that all animals can be models, and nearly every human disease can be modeled in one or more species. It’s a matter of finding the right model. It’s time to remember that humans are animals and by ignoring many of our relatives, we cannot truly understand ourselves.