Coronary artery ectasia (angiographic and clinical findings of our patients)

Abstract

For the last 70 years, long before the virus nature of the tristeza disease was recognized, Citrus tristeza virus (CTV), genus Closterovirus, family Closteroviridae, was considered as a serious threat to citrus production. The costs of CTV infections varied geographically and temporally, especially since growers worldwide have recognized the grave consequences of CTV epidemics. A variety of control measures including replacing sensitive rootstocks, prevention of spread with propagation material, and wide scale use of cross-protection for handling stem pitting-related problems are now commonly used in attempts to control the range of CTV diseases.Despite these efforts, the virus which apparently originated in Asia continued its spread and its now present throughout most citrus growing areas of the world, with only a few of the Mediterranean basin countries, and some Western USA areas still free of massive infections. However, even these areas are now under a serious threat due to the recent spread of the most efficient aphid vector to nearby areas. CTV is naturally transmitted in a semipersistent mode by several aphid species. The brown citrus aphid (Toxoptera citricida) is the most efficient vector because of its great abundance on citrus trees and its high efficacy of vectoring highly pathogenic isolates. The symptoms of CTV depend on the nature of the invading isolate and the sensitivity of the citrus host. The most dramatic symptom referred to as ‘quick decline’ results from rapid death of trees grafted onto sour orange rootstocks. Other CTV-related diseases such as ‘stem pitting’ of grapefruit or sweet orange trees are not related to a specific rootstock and do not result in death, but are often associated with stunting and poor productivity. Symptomless CTV isolates are used to provide protection (‘cross-protection’) against stem pitting, but not against the quick decline.The virions of CTV are long flexuous particles (2000 × 12 nm) with an unusual architecture that results from two different coat proteins, the major coat protein (CP), and minor coat protein (CPm) encapsidating approximately 97% and 3%, respectively, of the helically structured particles. Two additional viral proteins, p61 and p64 (a HSP70 homolog), are required for efficient assembly. The 19.3 kbp single-stranded RNA genome is the largest among the plant viruses. Genomic analyses showed a division into 12 open reading frames (ORFs), the organization of which is conserved among isolates. The ORF1a encodes a 349 kDa polyprotein containing two papain-like protease domains plus methyltransferase-like and helicase-like domains. Translation of the polyprotein is thought occasionally to continue through the polymerase-like domain (ORF1b) by a =1 frameshift. Ten 3′ ORFs are expressed by 3′ co-terminal subgenomic messenger RNAs. Infected cells contain a myriad of other subgenomic RNAs. In addition, most CTV isolates contain one or more defective RNAs of different sizes and genomic rearrangements. Among the CTV translation products, at least three function as RNA-silencing repressors, which are correlated with unusual difficulty in conferring pathogen-derived resistance to transgenic citrus plants.