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Abstract: In 2007, bluetongue virus serotype 8 (BTV-8) re-emerged in the Netherlands and a large number of farmers notified morbidity and mortality associated with BTV-8 to the authorities. All dead cows in the Netherlands are registered in one of the three age classes: newborn calves <3 days, calves 3 days to 1 year, and cows >1 year. These registrations result in a complete data set of dead cattle per herd per day from 2003 until 2007. In this study, the mortality associated with BTV-8 for the Dutch dairy industry was estimated, based on this census data. Default, mortality associated with BTV-8 was estimated for the confirmed notification herds. Moreover, an additional analysis was performed to determine if mortality associated with BTV-8 infection occurred in non-notification herds located in BTV-8 infected compartments. A multivariable population-averaged model with a log link function was used for analyses. Separate analyses were conducted for the three different age groups. Confirmed notification herds had an increased cow mortality rate ratio (MRR) (1.4 (95% CI: 1.2–1.6)); calf MRR (1.3 (95% CI: 1.1–1.4)); and newborn calf MRR (1.2 (95% CI: 1.1–1.3)). Furthermore, in non-notification herds in BTV-8 infected compartments, mortality significantly increased 1.1 times (95% CI: 1.1–1.1) in cows, 1.2 times (95% CI: 1.2–1.2) in calves and 1.1 times (1.1–1.1) in newborn calves compared with BTV-8 non-infected months. Using objective census data over a 5-year period, the MRRs indicated increased mortality associated with BTV-8 infection not only in herds of which the farmer notified clinical signs but also in non-notification herds in infected compartments. [Copyright &y& Elsevier]

Abstract: In February 2008, evidence was found for transplacental infection of bluetongue virus serotype 8 (BTV-8) in PCR negative, seropositive heifers in Northern Ireland originating from the Netherlands. The relevance of this route of transmission was studied in Dutch cow–calf combinations in the Netherlands of which the calves were born in the same time period of the year as the calves from the exported heifers, the first quarter of 2008. Blood samples were tested from 385 cows and their calves, housed in 43 dairy farms that became naturally infected with BTV-8 for the first time in 2007. All calves were at least 10 days old at the moment of first testing. In total 229 cows tested seropositive for BTV-8. Eight of these cows were still PCR positive. Out of the 229 seropositive cows, 37 calves (16.2%; 95% CI: 11.4–21.0) were tested PCR positive in the first sample taken in April 2008. In the first week of June, 34 out of the 37 PCR positive calves were still available for resampling. Three calves were still PCR positive; one was 5 months old, the other two were 3 months old. One month later, in the first week of July, all initially PCR positive calves, including the three still tested positive 1 month earlier, were PCR negative. We showed that BTV-8 can be vertically transmitted from cow to calf and can result in healthy looking viraemic calves remaining PCR positive for up to 5 months. These PCR positive calves could play a role in the epidemiology, and in particular in overwintering of BT. However, further investigations are needed to evaluate the importance of this route of transmission. [Copyright &y& Elsevier]

Abstract: During 2006 the first outbreak of bluetongue ever recorded in northern Europe started in Belgium and the Netherlands, spreading to Luxemburg, Germany and north-east France. The virus overwintered (2006–2007) reappearing during May–June 2007 with greatly increased severity in affected areas, spreading further into Germany and France, reaching Denmark, Switzerland, the Czech Republic and the UK. Infected animals were also imported into Poland, Italy, Spain and the UK. An initial isolate from the Netherlands (NET2006/04) was identified as BTV-8 by RT-PCR assays targeting genome segment 2. The full genome of NET2006/04 was sequenced and compared to selected European isolates, South African vaccine strains and other BTV-8 strains, indicating that it originated in sub-Saharan Africa. Although NET2006/04 showed high levels of nucleotide identity with other ‘western’ BTV strains, it represents a new introduction and was not derived from the BTV-8 vaccine, although its route of entry into Europe has not been established. [Copyright &y& Elsevier]