The viruses are the smallest living entities known to themankind with one exception of Prions. Their size is too small (in nanometers)to be visualised under any ordinary microscope and lakhs of them can beaccommodated on the tip of a needle. The viruses are unique in storing anddeciphering their genetic information as they have either DNA or RNA contraryto rest of the living organisms which have both. The RNA viruses have tendencyto mutate at the rate of 10-3 to 10-4. The viruses are handicapped in manyways. They are very primitive yet have the potential to challenge world withcutting-edge technology and pride economy. They have done it earlier also whenthey were not visible to mankind. Small pox and influenza viruses are witnessto it. The viruses have no sense, no legs, no car, no aeroplane, no train or shipto walk to us. They have no eyes and no telescope to see us. They don’t eat, drink or inhale air. Theycan’t replicate of their own and are completely dependent on a living cell ofthe host, may be humans or animals. Whatever limitations the virus has shouldbe considered a natural check and need to be acknowledged. It is we who equipthem to handle us badly. Being senselesscreature has challenged the sensible. It carries itself a lot for philosophersand scientists. It makes us to realise that life on this planet is not smooth,it is made so. So sense it appropriately and act accordingly.
The Viruses are not affected by antibiotics. Thanks to investigators for developing few antiviral drugs especially against the Herpes-, AIDS- viruses and for few others. But these are the vaccines which play major role against the viruses for their eradication, prevention and control. Prophet Muhammad PBUH (571-632) said that there is no disease, that Allah has created devoid of cure (Bukhari: 5678). The Edward Jenner (1749-1823) an English Physician successfully demonstrated it that both run parallel when he exploited cowpox virus as vaccine against smallpox both being the members of same family of DNA viruses and were circulating side by side in animals and humans. This ultimately resulted in eradication of Smallpox across the globe. Subsequently, Alexander Fleming (1881-1955) discovered both (bacterium and penicillin) on same Petri plat-used for growth of bacteria or fungus in the labs. Coronavirus now teaches us that remedy could be effortless and contactless. This needs to be relished by staying at home.
Going briefly in the history of virology. It is clear that Creator has kept many of the viruses away from us at safer distances. This we should not continue to disrespect. We approached them by unnatural ways of greed or luxury. We broke their quarantine frequently and ultimately got quarantined. Why I am looking to history this time when people are concerned with COVID-19 virus only. The reason is “Not to know what happened before you were born is to remain forever a child” Marcus Cicero. “If you don’t know the history you are bound to repeat the mistakes of history”. The viruses do follow the rules of history. In 1957 the Kyasanur Forest disease (KFD) caused by +sense RNA virus was reported in Karnataka. The extensive deforestation for farming etc., led to viral transmission to humans. The other example is the surfacing of AIDS virus in 1981. The virus belongs to a very complex family of Retroviruses harbouring a unique RNA-DNA hybrid and was initially detected in Gay men and drug addicts. Thus four H groups including Homosexuals and Heroin addicts were well known to be at high risk. Here also the “bush meat trading” and hunting of Chimpanzees do count in the history of AIDS virus. By the end of the year (1981) 270 cases of sever immune deficiency was reported among Gay men with 121 deaths in USA. By the year 2005, it achieved the peak by infecting about 35 million people in the world. Hendra virus again an RNA virus was discovered in 1994 when it killed 13 horses and one trainer at a training Complex in Hendra, Brisbane, Australia. Bats (flying fox) were found to be natural reservoirs. Then a lady veterinarian lost the husband after the couple conducted the post-mortem of the dead horse. However, its incidence is very rare now. Another virus of the same family called Nipah virus (NIV) struck in Nipah, Malaysia in 1998 and killed hundreds of humans. Death rate was 50-70% in infected individuals. The Malaysian authorities had to kill then millions of pigs to stop the spread. In 2001 the Siliguri (West Bengal), witnessed the NIV outbreak where in 10 days period 45 of 61 patients lost the life. The spread of the disease was close contact with infected persons, pigs and bats or drinking raw date palm sap. Same hit in Kerala in 2018. Both Hendra and Nipah viruses produced acute respiratory illness and fatal encephalitis. Another RNA virus discovered in 1976 in Zaire known as Ebola virus caused another outbreak in 2014-16 in Africa setting. The encroachment into the forests and direct contact with wildlife (consumption of bush meat) were the likely sources of infection. Before all this a strain of Influenza A again an RNA virus caused a human pandemic in 1918 killing 50 million people across the globe. The first bird flu (H5N1) infection occurred in 1997 in Hong Kong and killed 60 % of the infected persons. However, no human to human spread was the natural check which we need to acknowledge. This was followed by swineflu (H1N1) originating from USA in 2009. Its mode of transmission is similar to present coronavirus. The behaviour of these influenza viruses was in calculation of virologists who predicted decades, before it actually happened owing to their segmented RNA portraying genetic reassortment phenomenon (a process whereby the viruses swap over their genetic material). One lesson which we have not so for learned that these zoonotic diseases need to be tackled on ‘one health’ basis i.e health of humans, animals, plant and environment should be approached as one. Thus the laboratories concerned with all these need to be strengthened to fight these threats efficiently and sufficiently.
The present Sever Acute Respiratory syndrome-Coronavirus-2(SARS-COV-2) popularly known as Coronavirus, is a member of Coronaviridae familyunder genus Betacoronavirus. This virus less than 4 months in visibility is anenveloped virus containing a positive (+) sense single-stranded RNA wrapped in the several molecules of aprotein. The other four proteins are on the surface of its envelope. One ofthese called spike (S) protein like a knob carries the receptor binding domain(RBD) site to bind with the angiotensin-converting enzyme 2 (ACE2)molecule present on human cell to launchthe attack and ring the warning bell. This means it has only one hand (ligand).The other hand called receptor is with us. Who engineered RBD site to bind efficiently to human cell molecule atnano level? This needs an infinite wisdom which can’t be without an infinitewise. The +sense RNA makes it aninfectious molecule itself and akin to mRNA of the host cells for furthertranslation and multiplication. Thus makes full use of host cell resources.This advantage is not with Negative (-) sense RNA viruses which have to havetheir own (transcriptase) enzyme initially to get converted to +sense RNA andonwards. So +RNA viruses are a step ahead in multiplication and attacking thehost cells. Though this virus spreads very fast yet has less mortality rate ascompared to others described above. This is again a natural check which wecannot deny and we should use it to boost our will power.
Coronaviruses (CoVs) cause a range of respiratory, enteric,and neurological diseases in humans and animals. Two already knowncorona-viruses have caused world-wide outbreaks in the past two decades, namelySARS-CoV in 2002–2003 and Middle East respiratory syndrome coronavirus(MERS-CoV) (2012–present) with high mortality rates. Both are of zoonoticimportance. MERS-CoV often moves from camels to humans. SARS-CoV movedfrom civet cats to humans and caused substantial morbidity and mortality beforeit was brought under control. The SARS virus was having high morbidity but lowrate of transmission as compare to COVID-19 Virus. The reason for fast spreadis less generation time of COVID-19 virus as compared to SARAS virus. Oneinfectiousness model suggests that the total contribution to basic reproduction number called R0( is thetypical number of infections caused by an individual in the absence ofwide-spread immunity) from pre-symptomatics is 0.9 (0.2 – 1.1), almost enoughto sustain an epidemic on its own. For SARS, the corresponding estimate wasalmost zero immediately telling us that different containment strategies willbe needed for COVID-19
With the advent of gene sequencing technology andphylogenetic analysis method we are now better understanding the origin,evolution, routes and sources of infection of these viruses swiftlyand precisely as is evidenced by the speed of identification of the COVID-19virus. Real time diagnosis is critical for efficient control of infectiousdiseases. This is particularly of great importance to characterize potentiallyzoonotic viruses in exotic hosts that have not been described yet. Given thefrequent association of Corona family viruses with severe diseases, a morecomprehensive description of their diversity, especially in animals withfrequent human contact, becomes an important objective before the experts.Detailed understanding of how an animal virus crosses the species barriers toinfect humans so productively will help in the prevention of future zoonoticevents.
Prof. Shakil Ahmad Wani, is former Head, Veterinary Microbiology & Former Director Education, SKUAST-Kashmir.