Prof Shakil Ahmad Wani
Smallest bits of life
Viruses are the smallest living entities known to mankind with one exception of Prions. Their size is too small (in nanometers) to be visualised under any ordinary microscope and lakhs of them can be accommodated on the tip of a needle. The viruses are unique in storing and deciphering their genetic information as they have either DNA or RNA, contrary to rest of the living organisms which have both. The RNA viruses have tendency to mutate at the rate of 10-3 to 10-4. The viruses are handicapped in many ways. They are very primitive and have no sense, no legs, no eyes. They can’t replicate of their own and are completely dependent on a living cell of the host organism.
Viruses are not affected by antibiotics. Prophet Muhammad said that there is no disease that Allah has created devoid of cure (Bukhari: 5678). Edward Jenner (1749-1823), an English physician, successfully demonstrated this when he exploited the cowpox virus as vaccine against smallpox, both being the members of same family of DNA viruses. Going briefly into the history of virology, it is clear that the Creator has kept many of the viruses away from us at safe distances. This we should not disrespect. We approached the unsafe viruses through unnatural ways. In 1957, the Kyasanur Forest disease (KFD) caused by an RNA virus was reported in Karnataka. The extensive deforestation for farming had led to viral transmission to humans. Another 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. Here also, the “bush meat trading” and hunting of chimpanzees were responsible for the transmission to humans. By the end of the year (1981), 270 cases of AIDS were 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 and sundry viruses
Hendra virus, again an RNA virus, was discovered in 1994 when it killed 13 horses and one trainer in Hendra, Brisbane. Bats (flying fox) were found to be natural hosts of the virus. Then a lady veterinarian lost her husband after the couple conducted the post-mortem of the 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 millions of pigs to stop its spread. In 2001, Siliguri (West Bengal) witnessed the NIV outbreak where in 10 days, 45 of 61 patients lost their life. The spread of the disease was due to close contact with infected persons, pigs and bats, or drinking raw date palm sap. The same virus hit 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 an outbreak in 2014-16 in Africa. Human encroachment into forests and direct contact with wildlife (consumption of bush meat) were the likely sources of infection. Before all this, a strain of Influenza A, an RNA virus, caused a 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, it had no human-to-human spread and this acted as a natural check. This was followed by swineflu (H1N1) originating in USA in 2009. Its mode of transmission was similar to that of the present coronavirus. The behaviour of these influenza viruses was according to calculations of virologists who had been predicting them for decades.
The present Severe Acute Respiratory Syndrome-Coronavirus-2 (SARS-COV-2) is an enveloped virus containing a positive (+) sense single-stranded RNA wrapped in several molecules of a protein. The +sense RNA makes it an infectious molecule itself and akin to mRNA of the host cells for further translation and multiplication. Thus, it makes full use of host cell resources. This advantage is not with Negative (-) sense RNA viruses which have to have their own (transcriptase) enzyme initially to get converted to +sense RNA. So, +RNA viruses are a step ahead in multiplication and in attacking the host cells. Though this virus spreads very fast, it has less mortality rate. This is again a natural check which we should use to boost our morale.
Coronaviruses (CoVs) cause a range of respiratory, enteric, and neurological diseases in humans and animals. Two already known coronaviruses have caused world-wide outbreaks in the past two decades, namely SARS-CoV in 2002–2003, and Middle East respiratory syndrome coronavirus (MERS-CoV) (2012–present) with high mortality rates. Both are of zoonotic origin. MERS-CoV often moves from camels to humans. SARS-CoV moved from civet cats to humans.
With the advent of gene sequencing technology and phylogenetic analysis method, we are now understanding better the origin, evolution, routes, and sources of infection of these viruses. Real time diagnosis is critical for efficient control of infectious diseases. Given the frequent association of corona family viruses with severe diseases, a more comprehensive description of their diversity, especially in animals with frequent human contact, becomes an important objective before the experts.
Thus far, the U.S. Center for Disease Control and Prevention (CDC) and other health agencies insist that primary route of transmission for SARS-CoV-2 is through the larger respiratory droplets, up to 1mm across, that people expel when they cough and sneeze. Gravity grounds these droplets within 1 or 2 meters, although they deposit the virus on surfaces and fomites, from which people can pick it up and infect themselves by touching their mouth, nose, or eyes. But if the coronavirus can be suspended in the ultrafine mist that we produce when we exhale, protection becomes more difficult, and requires people to wear masks in public. Home-made cotton masks should frequently be ironed to decontaminate them by heat.
An Ambitious Virus
The limited investigations in China and Singapore have indicated that about 33% to 50% spread of Covid-19 virus is by pre-symptomatic individuals and about 18% spread is by asymptomatic individuals. This shows that the virus is more ambitious to attract the next victim than producing symptoms in the already infected one. Contamination of surfaces, which could be door handles, water taps, ATMs, mobiles, door curtains, desks, etc, contribute to the spread. Viruses reach a close one but without producing any smell, sound, taste or prick. This explains why it is often reported that an infected person had no travel or contact history. That is why we are being asked to follow social distancing.
Will the virus go away?
It’s now clear that humanity won’t be rid of Covid-19 as it did with SARS in 2003, says Mark Woolhouse, an epidemiologist at the University of Edinburgh. Keeping it at bay might require locking down society for many months, at least until a vaccine is available. Some are of the opinion that immunity can be built by relaxing the lockdowns for brief spells. Some say that suppressing the virus by combining all available measures, especially lockdowns and social distancing of the entire population, is the “only viable strategy at the current time.”
The writer is former Head, Veterinary Microbiology, and former Director Education, SKUAST-Kashmir.