Experimental infection of sheep, goats and cattle with a bluetongue virus serotype 4 field strain from Bulgaria, 2014
Schulz, C. | Sailleau, C. | Bréard, E. | Flannery, J. | Viarouge, C. | Zientara, S. | Beer, M. | Batten, C. | Hoffmann, B.
In 2014, a new bluetongue virus serotype 4 (BTV‐4) strain was detected in southern Greece and spread rapidly throughout the Balkan Peninsula and adjacent countries. Within half a year, more than 7,068 outbreaks were reported in ruminants, particularly in sheep. However, the reported morbidity and case fatality rates in ruminants varied. The pathogenesis of a Bulgarian BTV‐4 strain isolated from sheep during the BTV‐4 epizootic was studied in different species. Therefore, four sheep, three goats and three cattle were experimentally infected with the isolate BTV‐4/BUL2014/15 and monitored for clinical signs up to several weeks. Serum and whole‐blood samples were collected at regular intervals and subjected to serological and virological analyses. In this context, BTV‐4‐specific real‐time RT‐PCR assays were developed. The infection kinetics were similar to those known for other traditional BTV serotypes, and only mild BT‐like clinical signs were observed in goats and sheep. In cattle, no obvious clinical signs were observed, except a transient increase in body temperature. The study results contrast with the severe clinical signs reported in sheep experimentally infected with an African BTV‐4 strain and with the reports of BT‐like clinical signs in a considerable proportion of different ruminant species infected with BTV‐4 in the Balkan region and Italy. The discrepancies between the results of these animal trials and observations of BTV‐4 infection in the field may be explained by the influence of various factors on the manifestation of BT disease, such as animal breed, fitness and virus strain, as described previously.
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