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SARS, MERS and COVID-19 (Zoonotic Viruses) and their Wild Animal Hosts

Dr. Lakshmi Unnithan
Dr. Lakshmi Unnithan

Zoonotic infections are not new. Their Origin has always been from domestic animals, poultry and livestock. Zoonotic viruses have always been in the forefront of causing human epidemics like anthrax, tuberculosis, plague, yellow fever and influenza.  Recently Wildlife is seen to be emerging as the primary source of the human pandemics according to WHOAvian influenza and rabies, are well established, while others have only recently emerged or have only recently been linked to wildlife reservoir species. 

The recent century is seeing several zoonotic outbreaks in humans, like the Dengue, Chikungunya, Nipah, SARS1, along with the recent outbreak of COVID 19, which is seriously acclaiming several lives. It was found to be originated in Wuhan in China  is severely linked to a human transmission from bats to human hosts.. The increasingly globalized society is the main reason for contributing to the apparently increased transmission of pathogens to humans over the past decades. Increasing population and its associated changes, exploitation of the environment and hence losing the biodiversity are all contributory factors.  

A large number of other paramyxoviruses, coronaviruses, astroviruses, adenoviruses and herpesviruses have been reported across literatures. It is always necessary to place these under judicious watch since the public health threat of these viruses is unknown. These are a group of RNA viruses that are predominantly responsible for acute respiratory diseases and are usually transmitted by airborne droplets. The paramyxoviruses include the agents of mumps, measles (rubeola), RSV (respiratory syncytial virus), Newcastle disease, parainfluenza, Hendra Virus and Nipah. Coronaviruses are a group of related viruses that cause diseases in mammals and birds. In humans, coronaviruses cause respiratory tract infection   that can be mild, such as some cases of the common cold   and others that can be lethal, such as SARS,MERS and COVID-19. Reston virus is known to cause disease in nonhuman primates and pigs, but not in people.  Ebola virus was first discovered in 1976 near the Ebola River in what is now the Democratic Republic of Congo. Since then, the virus has been infecting people from time to time, leading to outbreaks in several African countries.

The Hendra virus which came into first detection in 1994 appears to have been circulating in Australian flying foxes for a long time. In a Primary Outbreak of Hendra virus (HeV) disease in Australia, twenty horses and two humans were affected in two weeks. Hendra virus is supposed to be the close relative of Nipah virus (NiV) & many other emerging zoonotic viruses. Nipah virus, is very infectious and was first detected in humans and commercially farmed pigs exhibiting respiratory and neurological disease. NiV, a slightly different nipah emerged in  Bangladesh & India in 2001 and continues to cause regular outbreaks of fatal encephalitis in humans, with evidence of direct bat-to-human and human-to-human transmission and mortality of between 70% and 100% reported by Lang and Grameri in 2014. The Ebola virus, which was also causing severe outbreak  is also recently linked to cave-dwelling bats in Africa. 

As of 17 July 2018, according to WHO, a total of 19 Nipah virus (NiV) cases, including 17 deaths, were reported from Kerala State: 18 of the cases were laboratory-confirmed and the deceased index case was suspected to have NiV but could not be tested. The outbreak was localized to two districts in Kerala State: Kozhikode and Malappuram. No new cases or deaths have been reported since 1 June 2018 and, as of 30 July, human-to-human transmission of NiV has been contained in Kerala State.  

At present we are deeply concerned both by the alarming levels of spread and severity and this increase in the COVID-19  infection is all across the globe ,COVID -19 has infected almost all continents except Antartica and Brazil. Human race is proud of the advances in scientific technology and scope of disease detection and diagnostic capability. However, we are also terribly late in identifying pathogens and still it goes o undetected if it does not cause a significant disease outbreak. Until and Unless these viruses affect a human population and  the population acquires antibodies for the disease it is very difficult to contain them at the outbreak times. 

There should be Collaborative efforts from multiple disciplines which will work proactively globally to keep a tab on these merging zoonotic viruses as they are a threat to the humans and the environment at large. The destruction of the Mother Earth which goes beyond all powers of the human races and just political vindictiveness should be rules out and Have a thought that there is no Planet B and there is one Earth and it is our duty to keep it protected. If we did had a slight  thought about the forests which act as a reservoir  protecting the humans and are keepers of wildlife and the zoonotic viruses,  we wouldn’t have reached at this point of spilling over. 

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