Maximal Predicted Duration of Viremia in Bluetongue Virus—Infected Cattle

Abstract

Abstract. Central to the development of rational trade policies pertaining to bluetongue virus (BTV) infection is determination of the risk posed by ruminants previously exposed to the virus. Precise determination of the maximal duration of infectious viremia is essential to the development of an appropriate quarantine period prior to movement of animals from BTV-endemic to BTV-free regions. The objective of this study was to predict the duration of detectable viremia in BTV-infected cattle using a probabilistic modeling analysis of existing data. Data on the duration of detectable viremia in cattle were obtained from previously published studies. Data sets were created from a large field study of naturally infected cattle in Australia and from experimental infections of cattle with Australian and US serotypes of BTV. Probability distributions were fitted to the pooled empirical data, and the 3 probability distributions that provided the best fit to the data were the gamma, Weibull, and lognormal probability distributions. These asymmetric probability distributions are often well suited for decay processes, such as the time to termination of detectable viremia. The analyses indicated a Ͼ 99% probability of detectable BTV viremia ceasing after Յ 9 weeks of infection in adult cattle and after a slightly longer interval in BTV-infected, colostrum-deprived newborn calves.Bluetongue is an insect-transmitted, noncontagious viral disease of domestic and wild ruminants that is caused by bluetongue virus (BTV). 11,16,26 It is 1 of only 16 diseases included in List A by the Office International des Epizooties (OIE). Diseases included in OIE List A are defined as communicable diseases that have the potential for very serious and rapid spread, irrespective of national borders, that are of serious socioeconomic or public health consequence, and that are of major importance to the international trade of livestock and livestock products. 1 The major adverse economic impact of BTV infection in many regions of the world is its effect on international trade and movement of ruminant livestock and germplasm and not direct losses from bluetongue disease. 16,22,25 Central to the development of rational trade policies pertaining to BTV infection is determination of the risk posed by ruminants previously exposed to the virus. BTV infection of cattle is characterized by prolonged but not persistent viremia. 11 Virus is highly cell associated during viremia, and intimate association of BTV with erythrocytes is responsible for both prolonged viremia as well as infection of the hematophagous vector insects that transmit the virus. 4 Duration of viremia in BTV-infected cattle is related to the lifespan of the bovine erythrocyte, and precise determi-

Duration of Bluetongue Viremia in Experimentally Infected American Bison

“…The pattern of declining virus titers in bison blood, and the lack of infectivity for sheep of bison blood collected from 28 dpi onward, supported this determination. The length of BT viremia in the bison was highly comparable to that in sheep (Katz et al, 1993) and comparable to, or shorter than, the duration of BT viremia in cattle which is reported to range from 7 to 63 days based on virus isolation (Singer et al, 2001). The variability in duration of bluetongue viremia reported for cattle can depend on the virus serotype, blood fraction examined, and virus detection system used.…”

Comparison of bluetongue virus detection and quantitation methods in south India

“…Serological methods fail to detect BTV in the blood of clinically BTV-positive ruminants. However, virus antigen can be detected only in those animals showing a heightened viremia [14]. To overcome these limitations, RT-PCR was developed and evaluated as a suitable diagnostic method for direct detection of BTV in clinical samples [15][16][17].…”

Virological and pathological findings in Bluetongue virus serotype 8 infected sheep

“…Viremia is highly cell-associated as BTV first replicates in dendritic cells, endothelial cells and mononuclear phagocytes (Barratt-Boyes and MacLachlan, 1994;Hemati et al, 2009). However, during the later stages of viremia, BTV is exclusively associated with the red blood cell fraction which results in a prolonged, but not persistent viremia (Barratt-Boyes and MacLachlan, 1995;Singer et al, 2001). In sheep viremia is first detected approximately 3 days post infectionem (d.p.i.)…”