Virus

Virus adalah parasit berukuran mikroskopik yang menginfeksi sel organisme biologis. Virus hanya dapat bereproduksi di dalam material hidup dengan menginvasi dan mengendalikan sel makhluk hidup karena virus tidak memiliki perlengkapan selular untuk bereproduksi sendiri. Istilah virus usually refers to those particles that infect eukaryotes (multi-celled organisms and many single-celled organisms), whilst the term bacteriophage or phage is used to describe those infecting prokaryotes (bacteria and bacteria-like organisms lacking a nucleus). Typically these particles carry a small amount of nucleic acid (either DNA or RNA, but not both) surrounded by some form of protective coat consisting of proteins, lipids, glycoproteins or a combination. Importantly, viral genomes code not only for the proteins needed to package its genetic material, but for proteins needed by the virus during its life cycle

Organisme subselular yang, karena ukurannya sangat kecil, tidak hanya dapat dilihat dengan menggunakan mikroskop elektron. Ukurannya lebih kecil daripada bakteri.

Size, structure, and anatomy

Virus particles comprise a nucleic acid genome that may be either DNA or RNA, single- or double-stranded, and positive or negative sense. This is surrounded (encapsidated) by a protective coat of protein called a capsid. The viral capsid may be either spherical or helical and is composed of proteins encoded by the viral genome. In helical viruses, the capsid protein (frequently called the nucleocapsid protein) binds directly to the viral genome. For example, in the case of the measles virus, one nucleocapsid protein binds every six bases of RNA to form a helix approximately 1.3 micrometers in length. This complex of protein and nucleic acid is called the nucleocapsid, and, in the case of the measles virus, is enclosed in a lipid "envelope" acquired from the host cell, in which virus-encoded glycoproteins are embedded. These are responsible for binding to and entering the host cell at the start of a new infection. Spherical virus capsids completely enclose the viral genome and do not generally bind as tightly to the nucleic acid as helical capsid proteins do. These structures can range in size from less than 20 nanometers up to 400 nanometers and are composed of viral proteins arranged with icosahedral symmetry. Icosahedral architecture is the same principle employed by R. Buckminster-Fuller in his geodesic dome, and it is the most efficient way of creating an enclosed robust structure from multiple copies of a single protein. The number of proteins required to form a spherical virus capsid is denoted by the "T-number" whereby 60t proteins are necessary. In the case of the hepatitis B virus, the T-number is 4, therefore 240 proteins assemble to form the capsid. As in the helical viruses, the spherical virus capsid may be enclosed in a lipid envelope, although frequently spherical viruses are not enveloped, and the capsid proteins themselves are directly involved in attachment and entry into the host cell. The complete virus particle is referred to as a virion. A virion is little more than a gene transporter, and components of the envelope and capsid provide the mechanism for injecting the viral genome into a host cell.

Virus sering diperdebatkan statusnya sebagai makhluk hidup karena ia tidak dapat menjalankan fungsi biologisnya secara bebas. Karena karakteristik khasnya ini virus selalu terasosiasi dengan penyakit tertentu, baik pada manusia (misalnya virus influenza dan HIV), hewan (misalnya virus AI/flu burung), atau tanaman (misalnya virus mosaik tembakau/TMV).

Struktur virus sangat sederhana. Ia hanya terdiri dari seberkas bahan genetik (DNA atau RNA) yang dibungkus oleh protein. Karena sederhana, virus sangat mudah bermutasi sehingga mampu beradaptasi dengan perubahan lingkungan secara cepat.

Bahan genetik kebanyakan virus hewan dan manusia berupa DNA, dan pada virus tumbuhan kebanyakan adalah RNA yang beruntai tunggal.

Partikel virus disebut virion, yang pada umumnya dibagi menjadi dua golongan berdasarkan bentuk strutur nukleokapsidnya: (1) berbentuk heliks dan (2) berbentuk polihedron. Pada banyak virus hewan dan manusia nukleokapsid mempunyai selubung atau amplop yang terdiri atas lipida.

Human viral diseases

Examples of diseases caused by viruses include the common cold, which is caused by any one of a variety of related viruses; smallpox; AIDS, which is caused by HIV; and cold sores, which are caused by herpes simplex. Other connections are being studied such as the connection of HHV-6 in organic neurological diseases such as Multiple Sclerosis and Chronic Fatigue Syndrome. Recently it has been shown that cervical cancer is caused at least partly by papillomavirus (which causes papillomas, or warts), representing the first significant evidence in humans for a link between cancer and an infective agent. There is current controversy over whether borna virus, previously thought of primarily as the causative agent of neurological disease in horses, could be responsible for psychiatric illness in humans. The relative ability of viruses to cause disease is described in terms of virulence.

The ability of viruses to cause devastating epidemics in human societies has led to concern that viruses will be weaponized for biological warfare. Further concern was raised by the successful recreation of a virus in a laboratory. Much concern revolves around the smallpox virus, which has devastated numerous societies throughout history, and today is extinct in the wild.

Native American populations were devastated by contagious diseases, particularly smallpox, brought to the Americas by European colonists. It is unclear how many Native Americans were killed by smallpox after the arrival of Columbus in the Americas, but it may have been very large. The damage done by this disease may have significantly aided European attempts to displace or conquer the native population. Jared Diamond argued in his book Guns, Germs, and Steel that highly contagious diseases develop in agricultural societies and regularly aid those societies when they expand into the territories of non-agricultural peoples.

Of all types of virus, the most deadly are known as filovirus. The Filovirus group consists of Marburg, first discovered in 1967 in Marburg Germany, and ebola. Filovirus are long, worm-like virus particles that, in large groups, resemble a plate of noodles. As of April 2005, the Marburg virus is attracting widespread press attention for an outbreak in Angola. Beginning in October 2004 and continuing into 2005, the outbreak, which now appears to be coming under control, is the world's worst epidemic of any kind of hemorrhagic fever.

Laboratory diagnosis of pathogenic viruses

Detection and subsequent isolation of viruses from patients is a very specialised laboratory subject. Normally it requires the use of large facilities, expensive equipment, and highly trained specialists such as technicians, molecular biologists, and virologists. Often, this effort is undertaken by state and national governments and shared internationally through organizations like WHO.

Prevention and treatment of viral diseases

Because they use the machinery of their host cells to reproduce, viruses are difficult to kill. The most effective medical approaches to viral diseases, thus far, are vaccination to provide resistance to infection, and drugs that treat the symptoms of viral infections. Patients often ask for antibiotics, which are useless against viruses, and their misuse against viral infections is one of the causes of antibiotic resistance in bacteria. That said, sometimes, in life-threatening situations, the prudent course of action is to begin a course of antibiotic treatment while waiting for test results to determine whether the patient's symptoms are caused by a virus or a bacterial infection.

Etimologi

Walaupun virus ditemukan oleh ahli biologi Rusia Dmitry Ivanovsky pada tahun 1892, nama virus baru digunakan kemudian. Nama tersebut berasal dari kata Latin virus yang berarti racun.