Borna disease virus 1 (BoDV‐1) is the causative agent of Borna disease, an often fatal neurologic condition of domestic mammals, including New World camelids, in endemic areas in Central Europe. Recently, BoDV‐1 gained further attention by the confirmation of fatal zoonotic infections in humans. Although Borna disease and BoDV‐1 have been described already over the past decades, comprehensive reports of Borna disease outbreaks in domestic animals employing state‐of‐the‐art diagnostic methods are missing. Here, we report a series of BoDV‐1 infections in a herd of 27 alpacas (Vicugna pacos) in the federal state of Brandenburg, Germany, which resulted in eleven fatalities (41%) within ten months. Clinical courses ranged from sudden death without previous clinical signs to acute or chronic neurologic disease with death occurring after up to six months. All animals that underwent necropsy exhibited a non‐suppurative encephalitis. In addition, six apparently healthy seropositive individuals were identified within the herd, suggesting subclinical BoDV‐1 infections. In infected animals, BoDV‐1 RNA and antigen were mainly restricted to the central nervous system and the eye, and sporadically detectable in large peripheral nerves and neuronal structures in other tissues. Pest control measures on the farm resulted in the collection of a BoDV‐1‐positive bicoloured white‐toothed shrew (Crocidura leucodon), while all other trapped small mammals were negative. A phylogeographic analysis of BoDV‐1 sequences from the alpacas, the shrew and BoDV‐1‐positive equine cases from the same region in Brandenburg revealed a previously unreported endemic area of BoDV‐1 cluster 4 in North‐Western Brandenburg. In conclusion, alpacas appear to be highly susceptible to BoDV‐1 infection and display a highly variable clinical picture ranging from peracute death to subclinical forms. In addition to horses and sheep, they can serve as sensitive sentinels used for the identification of endemic areas.

Borna disease is a progressive meningoencephalitis caused by spillover of the Borna disease virus 1 (BoDV-1) to horses and sheep and has gained attention due to its zoonotic potential. New World camelids are also highly susceptible to the disease; however, a comprehensive description of the pathological lesions and viral distribution is lacking for these hosts. Here, the authors describe the distribution and severity of inflammatory lesions in alpacas ( n = 6) naturally affected by this disease in comparison to horses ( n = 8) as known spillover hosts. In addition, the tissue and cellular distribution of the BoDV-1 was determined via immunohistochemistry and immunofluorescence. A predominant lymphocytic meningoencephalitis was diagnosed in all animals with differences regarding the severity of lesions. Alpacas and horses with a shorter disease duration showed more prominent lesions in the cerebrum and at the transition of the nervous to the glandular part of the pituitary gland, as compared to animals with longer disease progression. In both species, viral antigen was almost exclusively restricted to cells of the central and peripheral nervous systems, with the notable exception of virus-infected glandular cells of the Pars intermedia of the pituitary gland. Alpacas likely represent dead-end hosts similar to horses and other spillover hosts of BoDV-1.

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