Viruses are not considered as living organism. They are metabolically inert outside the living cells and lack metabolic properties enabling them simpler life form to survive and replicate autonomously. They are thus called as obligate parasites.
The size of viruses ranges from 20 nm to 40 nm (Nanometer) and contain only one type of nucleic acid either DNA or RNA. Some of the DNA viruses are Herpes virus, Pox virus, Hepa DNA, Parvovirus etc. and RNA virus are Paramyxo (Para influenza, Measeals, Mumps), Orthomyxo (Influenza A, B, C), Corona virus, Rabies, Sandfly, Hanta, Ebola virus, Dengue, Rubella etc. We have seen how some of the deadly virus causing havoc in human civilization in the past ( see pandemic history) and how we won over them.
Here are different ways in which viruses can be detected, treated and defeated.
Controlling the reservoir
Early diagnosis of virus can be done by detection of viral genetic material by PCR (Polymerase Reaction Chain), Antibody Assays (Rapid Diagnostic Test, RDT), Cell culture and isolation.
Notification and situational awareness is another step of tackling virus.
Isolation is one of the oldest communicable disease control methods which is practiced in almost every corner of the world. Isolation can be achieved by RING-Immunization, i.e. encircling the infected person with the barrier of immune persons through which the virus infection is unable to spread. Also, there is distinct nature of isolation in diseases like Diphtheria, Cholera, Plague. However, they indicate presence of defense against virus without severe clinical features.
Quarantine: It means limitation of freedom of movement of people or animals exposed to communicable diseases for a period of time not longer than the longest usual incubation of the disease to prevent effective contact those not so exposed.
Interruption of transmission
Steps like hand-washing, good sanitation practice, adequate cooking, and use of barriers like masks, physical distance, gloves, etc. interrupt the viral transmission.
Host Resistance to Disease
It can be attained as an immunity against viral infection by circulating antibodies especially Immunoglobulin (IgA, IgG, IgM). Furthermore, cell-mediated immunity via activated lymphocytes also has a role in resisting the virus. Injection of normal Immunoglobulin and specific human immunoglobulin (obtained from recovered patients) is a common practice to treat the patient affected with virus.
Specific anti-viral drugs are also used with limited efficacy.
In addition, immunization is a common practice which aims to achieve artificial resistance sufficient to prevent a clinical attack of infection without ill-effect of recipient. Vaccines can be live attenuated for the viruses which have antigenicity but lacks toxicity. It mimics the natural infection with anti-body production but without symptoms.
Also, killed (inactivated) vaccines are used as a resistance technique to control the effect of virus.
The target of vaccination is to gain herd immunity. It is the level of resistance of a community or group of people to a particular disease in its environmental setting. Elements to achieve herd immunity are:
Immunization of the human; in context of COVID-19, vaccine is not available till date.
Herd structure includes population, vectors, environments and social factors that favors or inhibit spread of infection.
Occurrence of clinical and sub-clinical infection: In context of countries like Nepal, cases with positive antibody assay (RDT) and negative in PCR indicate defense against virus leading intact immune status. However, limited number of tests hinder above facts. The basic reproduction rate (Ro) of an infection is the expected number of cases directly generated by one case. Roughly, Ro of COVID-19 is 2 to 5, which means one case can generate 2 to 5 new cases. In absence of vaccine, elevating herd immunity without morbidity is not possible. Hence, exposure to pathogens resulting clinical and subclinical manifestation leads to herd immunity which is not a preventive method but is rather a natural post pandemic scenario.
Finally, physical distance, personal hygiene, immune system enhancing, ring immunization, effective treatment, along with surveillance and containment are the tools to defeat this human catastrophe. Development of vaccines will be a magic wand which unfortunately, is not found yet.