Talking about enveloped vs. non-enveloped viruses, and the first thing that comes to mind is the outer protective covering surrounding enveloped viruses. Often referred to as the lipid envelop, it is absent in non-enveloped viruses. Here’s more…
Did You Know?
Some enveloped viruses have spikes (glycoprotein) that protrude from the envelop surface.
A virus is a microscopic organism capable of causing serious infections. Presently, over 5,000 species of viruses have been identified. They are 10 to 100 times smaller than bacteria, and so cannot be viewed without an optical microscope. However, unlike bacteria, viruses require a host cell for replication.
Every virus has a genome (nucleic acid) that is enclosed within a protein coat, referred to as a capsid. Based on their outer structure, viruses are categorized into two types: enveloped and non-enveloped. Apart from the dissimilarities in their structure, viruses in both the groups exhibit different characteristics too.
Non-enveloped Viruses Vs. Enveloped Viruses
♦ Non-enveloped viruses are surrounded by a protein coating, commonly referred to as a capsid. The capsid does the job of attaching to host cells.
♦ Enveloped viruses too have a protein coat, but this capsid is encased within an outer lipid membrane. It is a lipid envelop that allows the virus to firmly stick to its target cell.
♦ Adenovirus usually causes upper respiratory tract infections, but sometimes is also blamed for gastroenteritis, urinary tract infections, and cystitis. Poliovirus, rotavirus, and norovirus are other examples of non-enveloped viruses.
♦ The influenza virus that causes seasonal flu symptoms, such as a runny nose, fever, sore throat, and muscle aches. The herpes simplex virus, the chickenpox virus, and even the recent ebola virus, are considered as enveloped viruses.
♦ They display excellent heat-resistant properties, and moreover, can easily withstand a dry and acidic environment. In fact, the virus is more powerful and proliferates rapidly in an acidic environment. They can also survive in some disinfection processes. This essentially means that the virus remains active and infectious in these harsh conditions too.
♦ They cannot tolerate hot temperatures or acidic environment. Moreover, they are also sensitive to dry conditions. This means that they no longer remain active in these conditions.
♦ Non-enveloped viruses can easily withstand the harsh conditions of the gastrointestinal (GI) tract. Hence, usually, intestinal infections are caused by these viruses.
♦ Enveloped viruses cannot bear the conditions encountered within the gastrointestinal tract. Bile salts in the GI tract tend to show detergent-like activity, which can destroy these viruses.
♦ Due to their complex outer structure and low resistance to harsh environment, they are less stable, and therefore survive for a shorter time in the host as well as outside the host environment.
♦ Enveloped viruses tend to show higher stability, and moreover, survive longer due to their adaptability to different environmental conditions.
♦ Non-enveloped viruses are difficult to sterilize, as they can easily adjust to changes in temperature.
♦ As enveloped viruses do not show much resistance to desiccation and heat treatment, they are easier to sterilize.
♦ Non-enveloped viruses usually do not cause recurrent infections.
♦ Enveloped viruses are potent at attacking the immune system, as they can quickly change their ‘surface protein’ to disguise themselves; hence, they can cause recurrent infections.
How Enveloped Viruses Get Their Envelope?
As aforementioned, a viral envelop refers to the outer wrapping that encircles the protein coat (capsid). Contrary to popular belief, the viral envelop is not present in a newly formed virus. It acquires from the cell to which it is attached. Following attachment, there are virus-host cell membrane interactions, which leads to the development of a viral envelope. So, the viral envelop that shows a distinct lipid composition is essentially a host-derived membrane.