DNA Day 2020: Understanding Zoonotic Diseases in the Era of COVID 19

Author: Naliaka Odera

Peris Ambala is a virologist,  zoonotic disease specialist, and a 2018 Mawazo PhD Scholar whose research is helping improve Kenya’s capacity to detect, prevent and control for the spread of zoonotic viruses. In her work, Peris uses molecular tools to study the characteristics of filoviruses, which are a group of viruses, including Ebola and Marburg, that are known to cause hemorrhagic fever in humans. Her research, which recently earned her a post-graduate National Research Fund grant from the Government of Kenya, involves examining the ribonucleic acid (RNA) genes of filoviruses, learning how they mutate and their potential to make the leap from animal to human (as in Ebola). In light of DNA Day, celebrated annually on April 25th, Mawazo sat down with Peris to discuss her timely research on zoonotic diseases. 

Let’s start with the most basic question, what is a zoonotic disease?

I would define a zoonotic disease as a disease that can be transmitted from animals to humans. Those animals can include, both large, and small mammals, and also birds. Over 60% of known human diseases originated in animals (WHO, 2018). While it has always been true that the majority of diseases among humans came from animals, humans have increased how much we interact with animals through  hunting of wild animals, encroachment into forested areas, domestication, and more.    

Are there certain animals that more commonly transmit diseases to humans?

We mostly get diseases from primates (monkeys), because they are the closest animals related to humans genetically. We actually share most diseases with primates (Locatelli, 2012). Every once in a while, we can get diseases from bats, but that is very rare. After non-human primates, we get a lot of diseases from domesticated birds like chickens, parrots etc. Other than viral zoonoses the other types of zoonoses include bacterial, fungi, and parasitic zoonoses. Zoonotic diseases are not all the same. They may cause mild to severe diseases in humans.

COVID-19, which is on everybody’s mind right now, is a zoonotic virus, right? Do we know its origin?

Yes, it is a new zoonotic RNA virus, belonging to a family of viruses known as coronaviruses. There is a lack of consensus on where COVID-19 originated from. At present, we believe that it is a combination of both bat coronavirus and snake coronavirus. There is a leading theory that says that the virus might have come from an animal market in Wuhan, China. In other words, the first person might have been infected from an animal market. Most probably, that person came in contact with infected animal meat. Another theory suggests that COVID-19 originated from pangolins which is an animal whose scales are widely traded in China (Nuwer, 2020).

What are the ways in which viruses can be transferred to humans?

Zoonotic viruses can be transmitted in different ways.  If we group them into two broad categories, we have direct transmissions and indirect transmissions. Direct transmission is where an individual gets into direct contact with the virus particle, as well as horizontal transmissions, from mother to child during pregnancy, and vertical transmissions through sexual contacts. With indirect transmissions, people can get infected from contact with contaminated surfaces, faecal material, and through vectors such as mosquitos.

How can you tell the likelihood of a virus transferring from animals to humans?

This is when we start talking about genomes. Viruses are divided into two groups; DNA viruses and RNA viruses, which is all genomic material. Depending on which virus you are targeting, you either look for its DNA or RNA, which is like the fingerprint of the virus. Once we have this, we compare and look at the similarity between the genes of known human viruses that have been documented to those seen in animals. If the genes seen in animals are closely related to what has already been documented in humans, then virus jump to humans, or transmission of the virus to humans, is very likely.

To make this genetic comparison, we target conserved regions of the genomic material. These are regions that do not mutate very easily and are thus more reliable to test. For example, in my work with the Ebola virus, I am targeting the L gene of the virus which can be used to map all known Ebola viruses and Marburg viruses. In testing for COVID-19, researchers are targeting the R Gene of the virus, which is a conserved region. This varies from virus to virus.

Looking at human DNA, is it possible that there are some groups of people more susceptible to catching zoonotic diseases?

Not particularly no. In terms of immunology, humans do not have specific genes that cover all zoonotic diseases. There might be a specific gene that is tied to a specific zoonotic disease, but it would be impossible for one demographic to be more susceptible to all zoonotic diseases based on their DNA.

The thing that makes this work so interesting is that viruses tend to mutate rapidly, especially once they have been transmitted to humans. For this reason, we cannot know for sure how humans will react to a specific virus that has been found in animals until the first human is infected with it. The genomic comparison is key in predicting whether the virus is likely to jump from animal to human, but not necessarily how the human will react to it.

It seems that the significance of your work is in preventing disease outbreaks. Could you discuss that more?

The work I do is all about control and prevention. For example, the issue of risk factors for zoonotic diseases, or conditions that increase the probability of disease occurring, is something that is incorporated in my research. In observing the environment, in my research for example, we noted that humans in the area being studied would use untreated water straight from the river, which we came to find that wild animals were also using.  These are the type of risk factors that can be shared with  government actors and measures can be put in place to decrease the risk factor.

The information that zoonotic disease specialists like myself gather (CDC 2020) then becomes imperative in advising governments about how to prevent or control the spread of disease. For example, we can suggest measures to improve hygiene, control vectors like mosquitoes, safehandling of bushmeat and animal products, and other aspects of human wildlife interaction that could help deter an outbreak.

Ultimately, once we are aware of the specific diseases that exist in wildlife, we are able to take the appropriate measures to prevent human transmission. For example, sometimes isolating or separating animals that carry harmful diseases from humans, is an effective way to prevent outbreaks. If we detect viruses early enough in the environment or in our wildlife, we can be more deliberate about human wildlife interaction and potentially prevent the next COVID-19.