[Hydranencephaly in a newborn calf after intrauterine BTV-3 infection in a beef cattle herd in Saxony/Germany].

During the 2024/25 outbreak of bluetongue disease caused by serotype 3 of the bluetongue virus (BTV-3) in Germany, 6 newborn calves in a beef cattle herd in Saxony exhibited neurological abnormalities immediately after birth. This case study aims to describe the clinical findings in these 6 calves, the pathological and histological lesions observed in one of them, as well as the virological test results from the herd. The affected calves showed disorientation, absent reflexes, and poor suckling. In the necropsied calf, marked bilateral-symmetric loss of the cerebral cortex with fluid-filled cavities in the neuroparenchyma and dilated lateral ventricles consistent with hydranencephaly was observed. Histologically, cortical hypo- and dysplasia, cystic defects, micro- and astrogliosis, and dystrophic calcifications were present. In all 3 examined calves, BTV-3 RNA was detected in blood via RT-PCR, and high antibody titers were found, as well as in their dams and most of the herd. Evaluation of the herd's epidemiological situation suggests a possible intrauterine BTV-3 infection around day 120 of gestation. The demonstration of hydranencephaly in this case supports the general principle that detailed morphological characterization of the lesions can substantially aid in distinguishing this condition from other, particularly viral causes of CNS malformations in calves.