Short Communication Diagnosis of clinical cases of the nervous form of Maedi-Visna in 4- and 6-month-old lambs Julio Benavides, Carlos Garcı ´a-Pariente, M. Carmen Ferreras, Miguel Fuertes, J. Francisco Garcı ´a-Marı ´n, Valentı ´n Pe ´rez * Departamento de Patologı ´ a Animal, Medicina Animal (Anatomı ´a Patolo ´ gica), Facultad de Veterinaria, Universidad de Leo ´n, Campus de Vegazana s/n, 24071 Leo ´ n, Spain Accepted 17 October 2006 Abstract The nervous form of Maedi-Visna (MV) infection was diagnosed in four lambs aged 4 and 6 months, belonging to three different Assaf flocks that were managed intensively for milk and meat production. The animals presented with hindleg ataxia that rapidly pro- gressed to complete recumbency. Lesions consisted of a moderate to severe non-purulent encephalitis affecting mainly the cerebellar peduncles. MV virus was demonstrated in the damaged tissues by immunohistochemistry and polymerase chain reaction. The investiga- tion demonstrated that the clinical presentation of the nervous form of MV which is reported to occur in adult sheep can also be observed in young animals. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Maedi-Visna; Lentivirus; Nervous; Sheep Maedi-Visna (MV) is a multisystemic chronic infection of sheep that can affect the lungs, mammary gland, central nervous system and joints (Dawson, 1980) with a lymphoid proliferation and mononuclear interstitial infiltration. It is caused by MV virus (MVV), a retrovirus belonging to the lentiviral subfamily. The nervous form, or visna, was first described in Ice- land as a chronic progressive paralytic disease of adult sheep (Sigurdsson et al., 1957). It is characterized by a non-suppurative demyelinating encephalitis that affects the white matter, composed of an infiltrate of lymphocytes with macrophages and glial cells in the brain parenchyma, together with mononuclear perivascular cuffs (Sigurdsson et al., 1957, 1962). Other than the Icelandic epidemics, visna has been reported only rarely, usually accompanying the respiratory form (Pa ´lsson, 1990; Watt et al., 1992; Prit- chard et al., 1995) and always in sheep older than two years. However, in the Castilla y Leo ´n region of Spain, numerous cases of visna have been recently diagnosed, mostly in the Assaf breed (Benavides et al., 2006). In caprine arthritis-encephalitis virus (CAEV) infection, a disease of goats similar to MV and caused by a lentivirus closely related to MVV, an encephalomyelitis similar to that of visna appears in adult animals although it can also occur in kids aged 2–6 months (Callan and Van Metre, 2004). The objective of the present study was to describe four clinical cases of visna in Assaf sheep aged 4 and 6 months, to characterize the lesions and to demonstrate the presence of MVV by immunohistochemistry (IHC) and polymerase chain reaction (PCR) methods. Four sheep, aged 4 (n =3) and 6 (n = 1) months pre- sented with rapid onset locomotor disorders that were con- sidered likely to be a nervous disease. The earliest sign was a stumbling gait due to hindleg weakness and ataxia (Fig. 1). The animals were alert and ate when helped to gain access to food. The status of the animals worsened and their condition progressed over 4–6 days to complete recumbency with rhythmic movements of the four legs. No response to sonorous or visual stimulus could be 1090-0233/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.tvjl.2006.10.014 * Corresponding author. Tel.: +34 987 291327; fax: +34 987 291103. E-mail address: dmavpp@unileon.es (V. Pe ´rez). www.elsevier.com/locate/tvjl Available online at www.sciencedirect.com The Veterinary Journal 174 (2007) 655–658 The Veterinary Journal