Virus/host specificity

In cases where uptake of nucleic acids by competent cells is not specific, transfection can be attempted with a wide range of virus nucleic acids. Transfections with nucleic acids from viruses which normally cannot infect such cells may yield information about mechanisms of intracellular restriction which determine virus/host specificity. 

Baculovimses, especially nuclear polyhedrosis viruses (NPV) and granulosis viruses (GV), appear to be exceptionally well suited for IPM because of their extreme insect specificity. They are stomach poisons and are slow-acting. In vitro production is difficult and the products are more expensive than the bacterial insecticides. Their high host specificity is viewed as a commercial disadvantage, and improvements in formulations and appHcation techniques are needed. 

J he abundance of organic materials that occur in the plant kingdom offer an opportunity for searching for specific compounds interfering with virus replication in plants. It is hoped that such compounds, if discovered, could be used efficiently for virus control and also serve as tools for our understanding of the complex virus-host system. 

Attachment There is a high specificity in the interaction between virus and host. The most common basis for host specificity involves the attachment process. The virus particle itself has one or more proteins on the outside which interact with specific cell surface components called receptors. The receptors on the cell surface are normal surface components of the host, such as proteins, polysaccharides, or lipoprotein-polysaccharide complexes, to which the virus particle attaches. In the absence of the receptor site, the virus cannot adsorb, and hence cannot infect. If the receptor site is altered, the host may become resistant to virus infection. However, mutants of the virus can also arise which are able to adsorb to resistant hosts. 

The endoparasite C. sonorensis has evolved with the ability to generate extrachromosomal genetic elements in the form of multiple double-stranded, superhelical DNA molecules. These DNA molecules are amplified in the calyx cell nucleus, packaged into viruses, and secreted in a complex process of viral maturation, which also provides a complex double viral envelope. One viral envelope is assembled in the cell nucleus, and the other is obtained during budding from the calyx cell surface into the oviduct lumen. Viral envelopes, which are derived from cellular membranes, may mediate species-specific virus host cell and tissue interactions. This could be one important aspect of the species-specific endoparasite-host relationship fundamental to parasite survival. 

Viruses, like all pathogens, show host specificity, usually infecting only one or a restricted range of host species. The initial basis of specificity is the ability of the virus particle to attach to the host cell. If the amount of infectious virus is measured over a period of time in the host, it is seen to fall, after an initial lag period, remain low for a period of time, and then rise to even higher levels. The period during which the amount of virus is low is referred to as the eclipse period. The virus infection cycle can be divided into several events. 

Interferon. Any of a family of glycoproteins that exert virus-nonspecific but host-specific antiviral activity by inducing the transcription of cellular genes coding for antiviral proteins that selectively inhibit the synthesis of viral RNA and proteins. Interferons have immunoregulatory functions and can inhibit the growth of nonviral intracellular parasites. 

The infectivity of host cells varies considerably between viruses. A specific virus may have a great diversity of host ceils, while another may be capable of infecting only one type of cell. The sensitivity defines the capacity of the cell or animal to be infected. 

Bilimoria SL, Demirbag Z, Ng FI (1992), Abortive cell culture infections of nuclear polyhedrosis viruses as model systems for host specificity, Pesquisa Agropecuaria Brasileira 27 123-141. 

Parvoviridae is a family of small icosahedral, nonenveloped animal viruses that contain a linear ssDNA genome of approximately 5000 bases with short unique terminal palindromic sequences that fold back on themselves to form hairpin duplexes (van Regenmortel et al, 2000). They are further classified into two subfamilies, Parvcwirinae and Densovirinae, and various genera depending on host specificity, strand specificity of the genomic ssDNA, and on whether helper viruses are required for productive infection (dependoviruses). Members of the Parvoviridae... 

Amino-5-iodo-2, 5 -dideoxyuridine [56045-73-9] (13) C9H12IN304, was synthesized in 1975 (27) and was found effective against herpes keratitis in rabbits (28). This compound is markedly less cytotoxic than IdU, indicating that it may have a safer and more specific mode of antiviral activity. A potential limitation of this group of nucleosides is their specificity, for they fail to inhibit all strains of herpes viruses. The specific antiviral activity of (13) is considered to be a result of the incorporation of the 5 -IV-phosphate into both viral and host DNA in infected cells, but not into the DNA of normal cells. Phosphorylation of (13) occurs only in herpes virus-infected cells, brought about by a virus-induced thymidine kinase (29). 

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