Lipid envelope

Viruses are small infectious agents composed of a nucleic acid genome (DNA or RNA) encased by structural proteins and in some cases a lipid envelope. They are the causative agents of a number of human infectious diseases, the most important for public health today being acquired immunodeficiency syndrome (AIDS), hepatitis, influenza, measles, and vituses causing diarrhoea (e.g., rotavirus). In addition, certain viruses contribute to the development of cancer. Antiviral drugs inhibit viral replication by specifically targeting viral enzymes or functions and are used to treat specific virus-associated diseases. 

Flaviviruses Yeiiow fever virus Spherical particles 40 nm in diameter with an inner core surrounded by an adherent lipid envelope The virus is spread to humans by mosquito bites the liver is the main target necrosis of hepatocytes leads to jaundice and fever... 

Filoviruses Ebola virus Long filamentous rods composed of a lipid envelope surrounding a helical nucleocapsid lOOOnm long, 80nm in diameter The virus is widespread amongst populations of monkeys. It can be spread to humans by contact with body fluids from the primates. The resulting haemorragic fever has a 90% case fatality rate... 

Susceptibility of viruses to antimicrobial agents can depend on whether the viruses possess a lipid envelope. Non-lipid viruses are frequently more resistant to disinfectants and it is also likely that such viruses cannot be readily categorized with respect to their sensitivities to antimicrobial agents. These viruses are responsible for many nosocomial infections, e.g. rotaviruses, picornaviruses and adenoviruses (see Chapter 3), and it may be necessary to select an antiseptic or disinfectant to suit specific circumstances. Certain viruses, such as Ebola and Marburg which cause haemorrhagic fevers, are highly infectious and their safe destruction by disinfectants is of paramount importance. 

Most of the bacterial viruses which have been studied in any detail infect bacteria of the enteric group, such as Escherichia coli and Salmonella typhimurium. However, viruses are known that infect a variety of procaryotes, both eubacteria and archaebacteria. A few bacterial viruses have lipid envelopes but most do not. However,... 

Lin and coworkers (Lin et al., 2000) compared light-dependent and light-independent inactivation of dengue-2 and other enveloped viruses by the two regioisomers of carboxyfullerene, and found that asymmetric isomer had greater dark activity (albeit at much higher concentrations than needed for its PDT effect) due to its interaction with the lipid envelope of the virus. 

A retrovirus consists of double-stranded RNA (the genome) and a few proteins within a lipid envelope bilayer and... 

Swartzendruber, D.C., et al. 1987. Evidence that the comeocyte has a chemically bound lipid envelope. J Invest Dermatol 88 709. 

Adenoviruses also have DNA as their genetic material and are smaller than herpesviruses, with diameters of 70 to 100 nm. Adenoviruses do not have lipid envelopes and can survive on inanimate objects. Adenoviral serotypes 3, 7, 8, 19, and 37 cause conjimctivitis and epidemic keratoconjimctivitis. Currently, no antivirals are approved for ocular adenoviral infections. Studies have shown that topical cidofitvir may be effective in lowering the frequency of severe corneal opacities, but additional studies are needed to address corneal toxicity. 

All herpesvirus virions have a characteristic appearance (Fig. ID) with an icosahedral capsid surrounded by a thick ( 500 A) layer of protein designated the tegument (Rixon, 1993 Steven and Spear, 1997). The entire particle is enclosed by a spherical lipid envelope (Szilagyi and Berriman, 1994). The core of infectious virions is believed to consist exclusively of the double-stranded DNA genome without any associated protein (Booy et al, 1991 Zhou et al, 1999). The structures of the tegument and envelope are poorly understood as they are indeterminate in both size and composition and have a limited symmetrical relationship to the capsid (Chen et al, 1999 Zhou et al, 1999). 

The cornified cell envelope is the outermost layer of a corneocyte, and mainly consists of tightly bundled keratin filaments aligned parallel to the main face of the corneocyte. The envelope consists of both protein and lipid components in that the lipid is attached covalently to the protein envelope. The envelope lies adjacent to the interior surface of the plasma membrane. " The corneocyte protein envelope appears to play an important role in the structural assembly of the intercellular lipid lamellae of the stratum corneum. The corneocyte possesses a chemically bound lipid envelope comprised of A-co-hydroxyceramides, which are ester linked to the numerous glutamate side chains provided possibly by both the ot-helical conformation and p-sheet conformation of involucrin in the envelope protein matrix. In the absence of A-oo-hydro-xyceramides, the stratum corneum intercellular lipid lamellae were abnormal and permeability barrier function was disrupted. 

Behne, M. Uchida, Y. Seki, T. Ortiz de Montellano, P. Elias, P.M. Holleran, W.M. Omega-hydroxyceramides are required for corneocyte lipid envelope (CLE) formation and normal epidermal permeability barrier function. J. Invest. Dermatol. 2000, 114, 185-192. 

It has been postulated that transfusion-transmitted virus (TT virus) can be transmitted through heat-treated blood products (16). Transfusion-transmitted virus is a common DNA virus in healthy Japanese, and it lacks a lipid envelope, similar to parvovirus B19 (16,17). Transmission of transfusion-transmitted virus often occurs with blood transfusion and it can cause post-transfusion hepatitis with high postoperative peak alanine transaminase activity (17). No patients with hepatitis due to transfusion-transmitted virus have clinically apparent hepatitis (17). The incidence of transfusion-transmitted virus viremia in patients with hemophiha... 

One of 81 patients with Von Willebrand disease treated with a high-purity factor Vlll/Von Willebrand factor concentrate was infected with parvovirus B19 after infusion of a solvent/detergent-treated formulation. Parvovirus B19 is not lipid-enveloped and is resistant to treatment by solvent detergent (10). 

Viruses do not have a cellular structure. They are particles composed of nucleic acid surrounded by protein some possess a lipid envelope and associated glycoproteins, but recognizable chromosomes, cytoplasm and cell membranes are invariably... 

Flaviviruses Yellow fever virus Spherical particles 40 nm in diameterwith an inner core surrounded by an adherent lipid envelope... 

Filoviruses Ebola virus Long filamentous rods composed of a lipid envelope surrounding a helical nucleocapsid 1000nm long, 80nm in diameter... 

An important hypothesis was put forward in the USA by Klein and Deforest in 1963 and modified in 1983. Essentially the original concept was based on whether viruses could be classified as lipophilic , i.e. those, such as herpes simplex virus, which possessed a lipid envelope or hydrophilic , e.g. poliovirus, which did not contain a lipid envelope. 

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