Difference Between Parasite and Virus

Parasites and viruses are two types of organisms that can cause diseases in humans and other living organisms. While both can lead to health complications, there are notable differences between parasites and viruses. This essay will explore the differences between parasites and viruses.

What are Parasites?

Parasite is any organism, from unicellular to multicellular organisms, that lives in or on a host, negatively impacting the host to a certain degree since they feed off the host tissue. They can live on a single host, or have complex life cycles which involve different hosts.

There are three kinds of parasites that can live in humans and cause disease: protozoa, helminths, and ectoparasites. Protozoa are unicellular, microscopic organisms that are able to multiply in their host. In some cases, parasites with multiple life stages have a protozoan life stage. Helminths are larger, often visible with the naked eye, worm-like parasites, which include flatworms, thorny-headed worms, and roundworms. Ectoparasites include any parasite that lives or forages off the body surface, including mosquitoes, ticks, lice and so on. These ectoparasites may act as vectors for protozoic parasites as well.

Transmission of parasites from one host to another can occur either by a fecal-oral route or by vector transmission (an organism such as an arthropod in which the parasite can survive to infect another host).

What is Virus?

Virus is a microscopic pathogen (between 15 to 350 nm) that infects cells in living organisms. Viruses are visible only with an electron microscope. They can infect animals, plants, and bacteria.

There are two main forms of the virus:

  • Extracellular (virion) -inactive form, adapted to transfer the nucleic acid from one cell to another. It activates only after it enters a living cell;

  • Intracellular – active form.

Viruses carry a small amount of nucleic acid – DNA or RNA. The nucleic acid can be single or double stranded, protected by a shell containing proteins, lipids, carbohydrates, or a combination thereof.

Structurally, viruses are divided into two types:

  • Simple viruses − made up of nucleic acid (nucleotide) and protein shell (capsid).

  • Complex viruses − in addition to the nucleic acid and protein envelope they have lipoprotein or phospholipoprotein envelope, called peplos.

Depending on the type of the nucleic acid, the viruses are generally divided into RNA viruses and DNA viruses. Examples of RNA and DNA viruses are:

  • DNA − adenovirus, parvovirus, herpesvirus, etc.;

  • RNA − reoviruses, rhabdovirus, retrovirus, etc.

Viruses are unable to reproduce independently, as they do not have their own self-replicating apparatus. They only reproduce by controlling and subordinating living cells. The virus attaches to a living cell and injects its nucleic acid into it. Multiplication of the viral genome occurs through replication, resulting in a huge number of new copies of the viral RNA or DNA. The nucleic acid binds to the ribosomes of the cell and stimulates them to produce viral proteins. The produced molecules bind together to form new viruses.

The host cells are damaged by these processes and are no longer beneficial to the viruses. That is why the newly synthesized viruses leave it and target new cells. The leaving of the host cell from the virus may be rapid, accompanied by complete destruction, or gradual, by budding.

Differences: Parasite and Virus

The following table highlights the major differences between Parasite and Virus:





A parasite is an organism that lives in or on another organism (the host) and feeds on the host's nutrients.

Parasites can cause various diseases in their hosts, including malaria, tapeworms, and giardiasis, among others.

Parasites are categorized into three groups: protozoa, helminths, and ectoparasites.

On the other hand, a virus is a microscopic infectious agent that can only replicate within the cells of a host organism.

Unlike parasites, viruses are not living organisms as they cannot carry out metabolic processes outside the host's cells. Instead, they rely on the host's cellular machinery to replicate and produce new viruses.


Parasites are eukaryotic organisms.

Viruses are not-cellular structures.


From several micrometers (unicellular parasites) to several meters (tapeworms).

Between 15 to 350 nm.


Parasites are able to reproduce by sexual or asexual reproduction.

Viruses are unable to reproduce independently, they only reproduce by controlling and subordinating living cells.


The parasites can parasitize on the surface of the host’s body or inhabit different organs and tissues. They can come in contact with the host only to feed or use it as a permanent habitat.

Viruses are active only in living cells.


Parasites have a complex structure with multiple cells, tissues, and organs. The structure of parasites varies depending on their type, and they can range from microscopic protozoa to large tapeworms that can grow up to several meters in length.

In contrast, viruses have a simple structure that consists of genetic material (DNA or RNA) enclosed in a protein coat called a capsid.

Some viruses also have a lipid envelope that surrounds the capsid, and this envelope is derived from the host's cell membrane.

Mode of Transmission

Parasites can be transmitted through various routes, including ingestion of contaminated food or water, contact with infected animal feces, or through the bites of infected insects.

Some parasites, such as hookworms and schistosomes, can also penetrate the host's skin.

Viruses, on the other hand, can be transmitted through different modes, including direct contact with an infected person, ingestion of contaminated food or water, inhalation of droplets from an infected person, or through the bites of infected insects.

Some viruses, such as the human immunodeficiency virus (HIV), can also be transmitted through blood transfusions, sharing of contaminated needles, or from mother to child during pregnancy, childbirth, or breastfeeding.


Parasites can cause a wide range of symptoms, including fever, diarrhea, abdominal pain, nausea, vomiting, and weight loss, among others.

The symptoms of parasitic infections can vary depending on the type of parasite and the location of the infection in the host's body.

Viruses can cause a wide range of symptoms, including fever, cough, sore throat, body aches, fatigue, and headache, among others.

The symptoms of viral infections can also vary depending on the type of virus and the location of the infection in the host's body.


The treatment of parasitic infections involves the use of antiparasitic drugs, such as albendazole, mebendazole, and praziquantel, among others.

In some cases, surgery may be required to remove the parasites from the host's body.

The treatment of viral infections is usually symptomatic, and there are no specific antiviral drugs available for most viral infections.

However, some antiviral drugs, such as acyclovir, can be used to treat specific viral infections, such as herpes simplex virus (HSV) and varicella-zoster virus (VZV).


The prevention of parasitic infections involves various measures, including practicing good hygiene, avoiding contact with contaminated water or soil, and using insect repellents to prevent insect bites.

Vaccines are also available for some parasitic infections, such as malaria and schistosomiasis.

The prevention of viral infections involves various measures, including practicing good hygiene, avoiding contact with infected people or surfaces, and getting vaccinated.


To conclude, a Parasite is an organism that feeds with parts or vital products from another living organism called host, while a Virus is a microscopic pathogen (between 15 to 350 nm) that infects cells in living organisms.

Updated on: 30-Jun-2023


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