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Medycyna Weterynaryjna
|
2010
|
tom 66
|
nr 07
s.459-563,rys.,bibliogr.
The article reviews the clinical symptoms and pathogenesis of Bluetongue virus (BTV) infection of domestic and wild ruminants. The clinical signs of BTV infection occur principally in sheep but typical BT signs have also been observed in cattle infected with BTV serotype 8 in North-Western Europe. BTV infection can display a variety of clinical manifestations, ranging from subclinical or mild, to acute or even fatal infections. The lesions of BT differ not only among the animal species but also within breeds of the same species. In sheep the febrile period (41-42°C) lasts about one week. Nasal discharge, salivation, hyperemia, hemorrhages of the oral and nasal mucosa are observed 24-48 hrs after onset of fever. After the next few days edema of lips, tongue, face and ears is developed. At the end of febrile period, when mouth lesions begin to heal, coronitis may occur. The pathogenesis of BTV infection is similar in all species of ruminants. After cutaneous infection of BTV, by inoculation or through the bite of a BTV-infected Culicoides vector, the virus travels along the blood vessels to the regional lymph node, the place of the first replication of BTV. The virus is then disseminated to a variety of tissues throughout the body (particularly lungs and spleen) where replication occurs principally in mononuclear phagocytic and endothelial cells, lymphocytes and other cell types. BTV replicates in endothelial cells, causing cell injury and necrosis and leading to vascular thrombosis, tissue infarction, and, consequently, to a dysfunction of organs.
The article reviews the structure of BTV and the role of capsid proteins in the replication process. The BTV is an icosahedral virus with a genome of approximately 19 200 base pairs and composed of ten linear segments of double-stranded RNA (dsRNA). These RNA segments are packaged in a triple layered protein capsid (88 nm in diameter). The outer shell of capsid is composed of two structural proteins: 60 trimers of VP2, which acting as a hemagglutinin (HA) is responsible for glycoprotein receptor binding, and 120 trimers of VP5 that mediate the release of viral particles from endosomal compartments into cytoplasm and undergo pH dependent conformational changes that allow membrane fusion and syncytium formation. The intermediate layer consists of VP7 - protein the major immunodominant of BTV. This layer surrounds the subcore (54 nm) which consist of 12 decamers of the VP3 protein (role in the structural integrity of the virus core) and three minor structural proteins: VP1 (replicase), VP4 (mRNA capping enzyme) and VP6 (RNA-dependent ATPase and helicase). Moreover, the viral subcore consists of nonstructural proteins: NS1, NS2, NS3 and NS3A, which participate in the control of BTV replication, maturation and export from infected cell.
Basic information, including data about the occurrence and the pathogenesis of Bluetongue (BT), have been presented. These were followed by the main topic of this review, being the characterization of the disease occurrence after August 2006 in Europe. Due to climate change and global warming due to climate change and global warming, from this date on the disease appeared for the first time in areas that include northern Europe. On account of two different virus serotypes there are currently two main ongoing epizootics of BT. One, due to BTV-8, has already spread widely; the other, due to BTV-1, is currently starting to spread northwards. It is stressed in the paper that for the first time the infection of BT spread to the north of the 50th latitude. In these areas, affected by BTV-8 serotype, the main vectors are Culicoides species belonging to the Culicoides obsoletus complex, including Culicoides dewulfi and Culicoides chiopterus. The continuation of the BT epizootic, including winter periods, is explained by the persistence of BTV within surviving adult vectors or in the infected animal - cow or sheep - or additionally, thanks to transplacental transmission from infected cows or sheep to their progeny. A chapter of the paper is devoted to veterinary legislation used in the strategy of disease control. As an essential factor in the control of the disease the use of mass vaccination against sheep and cattle BT is recommended. Possible complications observed in the use of live virus attenuated vaccines are mentioned.
The article reviews the occurrence of bluetongue (BT) in Europe after 2006. In August this year, BT passed the latitude 50şN for the first time and BT outbreaks caused by bluetongue virus (BTV) serotype 8 occurred in several countries of North-Western Europe: the Netherlands, Belgium, Germany, France and Luxembourg. In the years 2007-2008 diseases caused by BTV-8 spread in many other territories of Europe and new, never previously noticed in Europe BTV serotypes 6 and 11 appeared. In Switzerland, a new orbivirus called “Toggenburg Orbivirus” (TOV) was diagnosed in goats, and on the basis of its genetic similarity to BTV was recognized as serotype 25 of BTV. The spread of BTV in those areas could be affected by many factors; among others, climate changes (increase in mean annual temperature and humidity) favor the increasing occurrence of Culicoides vector. Mass vaccination campaigns implemented in Europe in spring 2008 limited the spread of BTV, and, consequently, caused a significant reduction of BT outbreaks in Europe. The number of BTV-8 outbreaks has decreased to 350 in 2009, 19 in 2010 and no cases of BTV-8 disease were reported in North- -Western Europe throughout 2011. BT has never been found on Polish territory and Poland has a status free from BT. However, the results of the virological monitoring studies by real-time RT-PCR method of animals imported to Poland after 15 September 2006 confirmed the presence of BTV RNA in 38 samples of blood collected from German cattle, in one sample from Dutch fallow deer and one sample of blood from a 4-week-old calf born from a serologically and virologically positive German dam.
Artificial insemination is widely used in cattle reproduction all over the world and enables rapid genetic improvement in cattle breeding. The extent and importance of artificial insemination has significantly increased since semen storage in liquid nitrogen was introduced into practice. Semen may be stored for years in this temperature with no negative impact on its quality. However, infectious agents such as viruses also survive for very long time at the temperature of liquid nitrogen. For this reason it is vital to ascertain that breeding bulls are free from viral infections before collecting semen otherwise they could cause a large scale spreading of infectious diseases in cattle populations. The aim of the article is to provide readers with information about the most important cattle viruses which can be transmitted by bull semen.
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