BioQuakes

AP Biology class blog for discussing current research in Biology

Author: mrnaposada

Intermediate Host of COVID-19 Found to be Pangolins

COVID-19 had intermediate animal hosts before beginning to infect humans. It is not uncommon for viruses and illnesses to have animal hosts that have the ability to transmit it to other organisms, one such example being mosquitoes and various illnesses such as malaria and the West Nile virus. It has been proven that bats are carrier of SARS-CoV-2, but scientists have been trying to discover how exactly it got from bats to humans. This knowledge matters because understanding where the virus originated and how it came to infect humans could prove crucial to future treatment and control.

It was originally suggested that snakes were the intermediate host due to a genome study; however, it had a lot of scientific criticism for a few reasons, one such being the fact that the coronavirus has only been known to infect mammals and birds. Meanwhile, another unrelated study comparing the spike proteins to that of HIV-1, discovered a few unexpected similarities. Due to the rise of conspiracy theories and rumors, a scientist by the name of Yang Zhang, along with some colleagues, decided to conduct a more in-depth study on SARS-CoV-2 sequences.

Yang Zhang and his colleagues uncovered the error in the analysis that claimed snakes were the intermediate host. Additionally, they analyzed and compared DNA and protein sequences from pangolin tissues in order to try to find those similar to SARS-CoV-2. They were able to identify protein sequences that were 91% identical to those found in the human virus’ proteins. The spike protein found in pangolins only had 5 differences in the amino acids as compared to the 19 differences in the bat viral proteins which is further evidence that pangolins are the intermediate host. However, researchers say that it is possible for other intermediate hosts to exist.

A pangolin, now suspected to be an intermediate host of the coronavirus

So how does an illness transfer from animals to humans? One belief is that rapid mutation is the main factor that allows viruses to adapt to overcome a new hosts barriers and immunological defenses. Another proposed theory is host similarity as explained by Gary McCracken, a professor at the University of Tennessee. They tested this theory by analyzing hundreds of rabies viruses in various species of bats. They found that the more genetically similar species of bats had these cross-species viruses.

As more tests have been conducted, it has been found that some animals, other than bats and pangolins, are also able to be infected with the coronavirus. João Rodriguez from Stanford University and some colleagues used computers to simulate and investigate how the spike protein interacts with different animal cells ACE2 receptors. The better the viral “key” fit into the receptor “lock”, the more susceptible that species was to SARS-CoV-2. Therefore, by applying this knowledge (as well as McCracken’s theory) to other situations, it would make sense that humans could be infected by a cross-species virus, particularly from other mammals.

This connects to what we learned in class about receptors and cell signaling. ACE2 receptors are found on cells throughout the body, most notably in this case, in the lungs. ACE2 receptors help regulate blood pressure, wound healing, and inflammation. Once a message (a signaling molecule or such) is received by the receptor, cell signaling moves into the next stage of transduction which ultimately produces a response. Therefore when something (in this case COVID-19) interferes, the proper signaling becomes changed or altered leading to the symptoms we have come to recognize as COVID-19.

Zebrafish: The Cure to Vision Loss?

Sight is one way in which we, along with many animals, interact with the world. Unfortunately, some people are unable to interact with the world in that same manner. Whether it is hereditary blindness or vision loss due to a neurodegenerative disease, vision loss and eye damage is difficult to fix, especially at a neurological level.

Neurons are present throughout the body and are connected via the nervous system. Their function is to transmit information to the brain and the rest of the body. They do this by signaling other cells by what is called neuronal firing. Individual nerve cells send electrical impulses to others allowing the message to reach other parts of the body. Simply put in the case of eyes and sight, the lens collect and bend the light and that information is sent through the optic nerve to the brain which then processes the information to produce an image. Therefore, if the neurons in the eye are damaged, that information cannot be collected and sent to the brain.

One such eye problem is Macular Degeneration which targets the macula. The macula is the central part of the retina that collects details images from the center of one’s field of vision. Damage to the macula results in a loss of central vision. Those who have it still retain their peripheral vision, but if the case is severe enough, they are deemed legally blind. As of now, there is no known cure.

However, Johns Hopkins Medicine researchers have been studying some animals’ ability to regrow neurons. Fish, along with other cold-blooded animals have the ability to repair eye neurons after injury, and for a long time it was thought that these genes were not present in mammals. According to Seth Blackshaw, professor of neuroscience at John Hopkins University, “[there is] the potential for regeneration is there in mammals, including humans, but some evolutionary pressure has turned it off” (ScienceDaily.com).

Blackshaw’s team has been studying the supportive cells in the back of the eye in zebrafish. These cells, known as the Müller glia, are able to repair the retina by growing neurons. Blackshaw’s team examined the retinal damage and repair of zebrafish, chickens, and mice. They found that while chicken and mice both have the capacity and gene pathways to generate neurons, the transcription factors were blocked so that the neurons don’t regenerate. Blackshaw suspects that the inability to regenerate neurons is due to the fact that animals that are more prone to disease in the brain, or other neurological tissue, may have lost this regenerative ability in order to protect other brain cells.

All of this is very exciting news and I think it is fascinating that studying cells from a fish could potentially help people who suffer from vision loss. I never would have thought that an animal that seems so different from us could help solve a problem that people have been dealing with for centuries. However, I think it is the fact that perhaps we aren’t so different from animals, at least on a biological level, that we are able to study them in order to better understand ourselves. For example, as Blackshaw and his team has discovered, we have those same gene pathways that allow zebrafish to regenerate neurons. And while ours don’t work the same way as of now, they are still present despite years and years of evolution. In the end, I think that the similarities we share with other animals is something to think about.

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