While sitting in home isolation today with rest of India, I was surfing on social media and looked at the different comments and reactions from people with different backgrounds. Most have not been able to fathom what exactly has happened and are either just following the guidelines or forwarding millions of suggestions on Whatsapp or Facebook which they think are factual. Many of us are not aware about zoonoses and its relation with wildlife and destruction of nature.
Human population are expanding and going into new geographic areas, urbanisation is replacing wilderness taking humans closer to wild animal populations. And when habitats are destroyed, displaced animals will come in contact with humans or when they are caught for wildlife trade for human consumption then they come in contact with humans and then chances of transmitting new infections are very real. By destroying wilderness and habitats we are opening our defenses to these infections and probably we will perish as we knowingly keep destroying these defenses and natural barriers which protect us.
As David Quammen writes in his book Spillover, “As globalisation spreads and as we destroy the ancient ecosystem, we encounter strange and dangerous infections that originate in animals but that can be transmitted to humans, diseases that were contained are being set free and results are potentially catastrophic” I think this is a perfect time to remember this.
With my little background in wildlife research and management of zoonotic diseases, I thought of putting some perspective to these discussions and take it to a more informative platform. I think we need to be more proactive in our approach to this subject and accept that there is always a chance that one of these infections can create a serious problem for our survival as a species.
The present 2019 nCoV pandemic has proven this right. Regular surveillance of such infections in wild animal populations and their potential to infect humans need to be studied regularly to prevent such events. There is also chance of human infections or domestic animal infections jumping into wild population and threaten species survival.
Now going back to zoonotic diseases (Zoonoses), what are those?
Zoonotic diseases are the ones which are naturally transmissible from vertebrate animals to humans, these infections can be viral, bacterial, parasitic or Fungi. The best examples of such infections are, Malaria, Dengue, Leptospirosis, Zika, Ebola, Scrub Typhus, SARS, MERS and the present 2019 nCoV (Covid 19).
Animals play an essential role in maintaining zoonotic infections in nature. Probably it’s a nature’s way to keep these checks and balances.
These zoonotic diseases can be transmitted through variety of pathways:
1) Direct contact – coming in contact with the saliva, blood, urine, mucous, faeces or other body fluids of infected animal, through handling, petting, touching, bites and scratches.
2) Indirect contact – coming in contact with areas or surfaces where these animals live and roam.
3) Vector borne – being bitten by ticks or insect like mosquitoes, fleas or sand flies.
4) Food borne -contaminated food, eating something unsafe like uncooked food, non-pasteurized milk or fruits & vegetables contaminated with faeces, urine or saliva from an infected animal.
5) Water borne – drinking water contaminated with faeces, urine or saliva from an infected animal.
Depending on the type of an infective agent, the pathway and development cycle varies. In case of Malaria or Dengue, where infective agent is in human and mosquitoes transmit them from human-to-human. In Leptospirosis, the infective agent is in the kidneys of a variety of mammals specifically in rodents and transmitted through their urine. In Scrub Typhus, it’s natural infection of rodents which is transmitted by arthropods. So zoonoses infections have a complex mechanism and it’s not easy to predict or control them.
There are many infective agents within the animal kingdom, and many of them are species specific. But the spillover events keep occurring in nature, an infective agent can mutate or adopt or come in contact with humans through unpredictable events and crosses species barrier to infect other species. Take an example of KFD (Kyasanur Forest Disease) or Monkey Fever, which is a viral hemorrhagic fever transmitted from monkeys to humans via arthropods, prevalent in some districts of Karnataka. Small outbreaks of this keeps happening over the years. There is also an example of 2018 Nipah virus outbreak in Kerala, which is transmitted from bats to humans.
Now let’s get back to Corona Viruses (CoVs), these are important pathogens for humans and animals, usually associated with Gastro intestinal and respiratory infections. Until 2002, they were considered minor pathogens, this completely changed with the emergence of highly pathogenic zoonotic diseases, SARS (Severe Acute Respiratory Syndrome), caused by SARS-CoV. It originated in 2002 at Guongdong in Southern China and spread in many countries became a global concern. With a very strong global response, with quarantine methods, tracing of contact and controlling potential source of infections, SARS did not become pandemic at that time. Sero-epidemiology investigations identified Masked Palm Civet sold in animal markets as a possible source of infection. However further studies suggested that Masked Palm Civet was acting as intermediate hosts between an unknown animal reservoir and humans. These several CoV sequences are identified in bat population, suggesting the hypothesis that bats are natural reservoir of CoVs and SARS CoV originated in bats. Overall, Molecular biology and phylogenetic studies of CoVs highlights plasticity of their genomes. Therefore an ability to originate new viral variants can promote jumps from bats to other Sylvatic (Sylvans means forest dwelling animals) animals, adaptation to new host and then transmission to other domestic animals or humans.
Nearly 10 years after the outbreak of SARS, a new corona virus jumped from animals to humans, causing MERS (Middle East Respiratory Syndrome). It was first identified in the Kingdom of South Arabia. As compared to SARS, MERS is still active and sporadic outbreaks keep happening. This is quite a severe disease and fatality rates are 35% in all cases. Epidemiology studies indicate that MERS is CoV transmitted through camels or camel products. Interestingly MERS CoV, like viruses, have been isolated from bat population suggesting that bats probably are natural reservoir of this CoV as well. Again Sero-epidemiology studies on samples collected from camels suggest that passage from Bats to camels may have happened 30 years before. We need more studies to confirm the probabilities and these suggestive hypotheses.
In 2009, there was another zoonotic virus which created fear, commonly called as Swine Flu (H1N1v). This influenza pandemic lasted between 2009 to 2010. This was a second influenza pandemic after the 1918 Spanish Flu pandemic, which killed millions. This swine flu virus jumped from pigs to humans. Though data suggests that this is combination of Avians, Pigs and Human viruses.
At the end of 2019, the present Corona Virus, provisionally called 2019 nCoV emerged, it was linked to Huanan Sea food Market in Wuhan city, China. Over the 2-3 months it became a pandemic threatening our existence and Governments have to act with extraordinary measures.
Due to technological advances of the last decade in Genome research, Genome sequence of 2019 nCoV was immediately available allowing development of molecular tests for the correct epidemiological picture as well as identifying animal hosts. Preliminary report suggested possibility of snakes as origin of Novel Corona Virus, the current consensus within scientific community support hypothesis of involvement of mammals or bird. The phylogenetic analysis of 2019 nCoV suggest the close lineage with CoVs found in Bats. Overall the data collected on 2019 nCoV strongly suggest that this new Betacoronavirus probably jumped from Bats to humans through one or more intermediate hosts.
With such outbreaks of SARS and MERS and present pandemic of 2019 nCoV, it is imperative that we focus on identifying such new CoVs within animal populations and evaluate their zoonotic potential. Studies on emerging infectious diseases of zoonotic origin need to be increased.
In our conservation models and wildlife research, we hardly touch this subject, I know a few of our researchers and conservation fraternity members have contacted such diseases like Scrub Typhus, Malaria and Leptospirosis while they were in wilderness. Surveillance of such infective agents within mammal and bird populations in wild, predominantly bat and rat populations for Viral loads will be crucial to predict the next spillover event. Other than Nipah surveillance in fruit bats species in India, done by National Institute of Virology, we do not conduct regular researches on these Sylvatic infections. We also do not observe ecological changes which support such transmissions.
When any infrastructure project is launched and environmental impact assessment studies are done, we need to also include probable spillover event with existing pathogens present in wild population and how destruction of habitat can put us in real danger of situation like present 2019nCoV pandemic.
Closing down all wild meat markets may be the first step and surveillance of wild population as well as intermediate hosts like poultry and pig farms will help in long run. Bridging the gaps between Wildlife research, Veterinary research and Epidemiological research, connecting them to the probability models and prevention practices, may show the way forward. Our conservation practices need to include economic value of wilderness and undisturbed habitats as a defense from such infections. The present pandemic is a call for awakening to stop destroying nature.
As a global action plan, organisations like WHO & CDC now talk about One Health, which is an approach where interconnection between people, animals, plants and their shared environment is recognised. Health issues are dealt with Human-animal-Environment interface. This approach is gaining more support worldwide now.
So when we destroy nature, it has enough weaponry at its disposal to fight back and the present pandemic is just one such fight back from nature. As we destroy it further we will face many more such events which probably will end this human dominated era on earth.
Reference for information on corona virus –
Coronaviruses: a paradigm of new emerging zoonotic diseases
Cristiano Salata, Arianna Calistri, Cristina Parolin, Giorgio Palù
Pathogens and Disease, Volume 77, Issue 9, December 2019.