Polyomaviridae are a group of DNA viruses without a viral envelope that have a genetic material of DNA and contain a capsid of more than 70 capsomeres. The genus includes viruses such as the human polyomavirus or the BK and JC viruses. Especially da BK virus has now strongly adapted to humans as hosts.
What are polyomaviridae?
The Polyomaviridae correspond to DNA viruses without a viral envelope. Their genetic material consists of DNA. The Polyomaviridae play a role predominantly for vertebrates. The infected organisms suffer from persistent infections of various types. Murine polyomavirus was the first polyomavirus to be documented. This virus causes various types of tumors in newborn mice. The Polyomaviridae primarily includes this genus of polyomaviruses, which in turn includes several subspecies. These species include, for example, baboon polyomavirus 2, human polyomavirus, and bovine polyomavirus, in addition to the guenon polyomavirus. Preliminarily, species such as chimpanzee polyomavirus and Merkel cell polyomavirus have also been classified as species within the genus Polyomavirus.
Occurrence, distribution, and characteristics
The viral ions of a polyomavirus are composed of a naked capsid between 40 and 45 nm in diameter. Each capsid is composed of 72 capsomers. These capsomeres are icosahedrally symmetrical in their arrangement and are formed at their base by five different molecules. The molecules of this pentamer do not lie uniformly to each other, but are skewed. We are therefore talking about twisted icosahedral symmetry. The interior of the capsid is stabilized by capsid proteins VP2 and VP3, which form the VP1 scaffold of the capsid. The individual proteins interact with DNA in the capsid. In some cases, virus particles deviate from this structure and can, for example, correspond to normally structured capsids, appear as microcapsids or have an irregular tube-like structure. VP1 capsid proteins can aggregate and thus form a virus-like particle without the aid of further viral proteins. However, the particles formed in this way are not capable of packaging nucleic acid. Within each capsid lies a covalently closed ring of DNA of the viral genome. As in the genus Papillomaviridae, the ring is twisted several times. Together with cellular histones, the DNA ring forms nucleoprotein complexes with structural similarity to eukaryotic nucleosomes. Environmental stability is one of the most important properties of capsids. Because of this property, polyomaviridae cannot be inactivated using diethyl ether or detergents. This means that washing hands with soap, for example, is not an effective preventive measure against these viruses. Even temperatures can hardly harm them: up to 50 degrees Celsius, they are considered heat-stable for one hour. Only heat in combination with magnesium chloride makes the capsids unstable, since their capsid structure is presumably dependent on divalent cations.
Diseases and ailments
Avian polyomaviruses cause various infections, such as French molt. In people with immunosuppression, BK virus can promote graft loss after kidney transplantation. BK virus is also associated with respiratory infections and, in children, cystitis. Hemorrhagic cystitis often occurs in patients after bone marrow transplants. In patients with kidney transplants, the virus can cause ureteral stenosis. In addition, AIDS patients may develop meningoencephalitis from the virus. The BK and JC viruses persist in the tissues of the kidneys. Infections with the viruses extremely rarely take a fatal course, since the viruses have adapted to humans as hosts and do not want to harm their reservoir host in this way due to their own disadvantages. Humans have also adapted to the virus over the course of generations. Current population infestation with the BK virus is estimated to be as high as 90 percent. However, JC virus can have serious consequences for immunocompromised patients, such as progressive multifocal leukoencephalopathy. PML is further associated with an often fatal course. Several tumor diseases are associated with simian virus 40. Population infestation with these species of the Polyomaviridae is much lower than for the BK viruses.Virus to human and human to virus adaptation is less advanced for this species.
