Mortality attributable to bluetongue virus serotype 8 infection in Dutch dairy cows.
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.
Santman-Berends
I M G A
IM
Animal Health Service, P.O. Box 9, 7400 AA Deventer, The Netherlands. I.berends@gddeventer.com
van Schaik
G
G
Bartels
C J M
CJ
Stegeman
J A
JA
Vellema
P
P
D000818:Animals; D000831:Animals, Newborn / Q000821:virology; D001819:Bluetongue / Q000401:mortality* / Q000821:virology; D001820:Bluetongue virus / Q000145:classification / Q000472:pathogenicity*; D002417:Cattle / Q000821:virology*; D002418:Cattle Diseases / Q000401:mortality / Q000821:virology*; D058872:Epidemics / Q000662:veterinary*; D009426:Netherlands