Aspectos epidemiológicos e clínicos da infecção neurológica associada ao herpesvírus eqüino 1 (ehv-1) em cavalos que morreram com sinais nervosos no Estado de Minas Gerais, Brasil

During the period of October 2004 until February 2006, 75 samples of central nervous system (CNS) obtained from horses that died with neurological signs in the state of Minas Gerais were sent to the Laboratory of Compared Virology in ICB/UFMG for diagnosis of equine herpesviruses. All samples were previously diagnosticated negative for rabies virus by the Laboratório de Saúde Animal of the Instituto Mineiro de Agropecuária (IMA). Among the analyzed samples, 39 (52%) were positive for the equine herpesvirus 1 (EHV-1) through the polymerase chain reaction assay (PCR). In most cases, the histopathological examination of the CNS revealed a mild vasculitis with perivascular mononuclear cuffing, congestion, arterial thrombosis and degeneration of nervous tissue. The positive CNS samples for EHV-1 were obtained from horses. sampled from 30 municipalities of Minas Gerais state. The cases occurred in an isolated form in different periods of the year, not presenting a seasonal character. The clinical course duration was acute, varying between one and four days. The most frequently observed neurological signs were ataxia, unsteadiness in the hind limb, paralysis of hind limbs and recumbency. According to information provided by IMA, the infections caused by EHV-1 were as frequent as the ones caused by rabies virus in horses of Minas Gerais state during the studied period. Hence, it became important to include EHV-1 encephalitis in the differential diagnosis from other diseases of the central nervous system in horses of Minas Gerais state.Durante o período de Outubro de 2004 a Fevereiro de 2006, 75 amostras de sistema nervoso central (SNC) oriundas de eqüinos que morreram com sinais neurológicos no estado de Minas Gerais foram enviadas ao Laboratório de Virologia Comparada no ICB/UFMG para o diagnóstico de herpesvírus eqüino. Essas amostras foram previamente diagnosticadas negativas para o vírus da raiva através dos testes de imunofluorescência direta e inoculação em camundongos, no Laboratório de Saúde Animal (LSA) do Instituto Mineiro de Agropecuária (IMA). Dentre as amostras analisadas, 39 (52%) foram positivas para o herpesvírus eqüino 1 (EHV-1) através da técnica de reação em cadeia pela polimerase (PCR). Na maioria dos casos, o exame histopatológico do SNC revelou uma discreta vasculite com infiltrado perivascular de células mononucleares, congestão, trombose arterial e degeneração do tecido nervoso central. As amostras de SNC positivas para o EHV-1 foram coletadas de eqüinos oriundos de 30 municípios de Minas Gerais. Os casos de EHV-1 ocorreram de forma isolada não apresentando caráter sazonal. Na maioria dos casos (71,8%), a evolução dos sinais clínicos foi aguda, sendo que os sinais clínicos observados com mais freqüência foram ataxia, instabilidade dos membros posteriores, paralisia dos membros posteriores e decúbito. De acordo com informações relatadas pelo IMA, as infecções causadas pelo EHV-1 foram tão freqüentes como as infecções causadas pelo vírus da raiva em eqüinos no estado de Minas Gerais durante o período estudado. Portanto, torna-se importante a inclusão da encefalite pelo EHV-1 no diagnóstico diferencial de outras doenças do SNC de eqüinos no estado de Minas Gerais

Isolation of saint louis encephalitis virus from a horse with neurological disease in Brazil.

St. Louis encephalitis virus (SLEV) is a causative agent of encephalitis in humans in the Western hemisphere. SLEV is a positive-sense RNA virus that belongs to the Flavivirus genus, which includes West Nile encephalitis virus, Japanese encephalitis virus, Dengue virus and other medically important viruses. Recently, we isolated a SLEV strain from the brain of a horse with neurological signs in the countryside of Minas Gerais, Brazil. The SLEV isolation was confirmed by reverse-transcription RT-PCR and sequencing of the E protein gene. Virus identity was also confirmed by indirect immunofluorescence using commercial antibodies against SLEV. To characterize this newly isolated strain in vivo, serial passages in newborn mice were performed and led to hemorrhagic manifestations associated with recruitment of inflammatory cells into the central nervous system of newborns. In summary this is the first isolation of SLEV from a horse with neurological signs in Brazil

Analysis of the envelope (E) gene sequence of SLEV.

<p>Phylogenetic tree was constructed using partial E gene sequence by neighbor-joining (NJ) method (using p-distance) of 1,000 bootstrap replicates using Mega 4.0.2. Boostraps values above 60% are shown. The scale bar represents 5% nucleotide sequence divergence. WNV, JEV and DENV-1 were used as the out group.</p

Central nervous system from newborn mice infected with SLEV.

<p>(A) Cerebral cortex from a newborn mouse at the 4^th viral passage with mild hyperemia and mild lympho-histiocytic perivascular cuffs, HE, 600×. (B) Choroid plexus from a newborn mouse at the 4^th viral passage, focally extensive hemorrhage in the ventricular cavity, HE, 200×. (C) Heart from a newborn at the 5^th viral passage, with moderate hyperemia and mild multifocal hemorrhage in the myocardium, HE, 200×. (D) Liver from a newborn at the 6^th viral passage, with severe hyperemia and focal hemorrhage, HE, 200×. (E) Lung from a newborn at the 7^th viral passage, with severe hyperemia, HE, 200×.</p

Viral strains included in phylogenetic analysis.

*<p>Designation according to country or state (in the case of USA) and year of virus isolation. Abbreviations: CA, California; TX, Texas; NM, New Mexico; TN, Tennessee; FL, Florida; MD, Maryland; PAN, Panama; MEX, Mexico; GUA, Guatemala; ARG, Argentina; BRA, Brazil; WNV, West Nile Virus; JEV, Japanese Encephalitis Virus; and DENV, Dengue Virus.</p

Survival rate and frequency of clinical signs in newborn mice inoculated with SLEV.

<p>Uninfected control mice (control), first (P1), second (P2), Third (P3), 4^th (P4), 5^th (P5), 6^th (P6), and 7^th (P7) passages are indicated in the X axis.</p

Newborn mice inoculated with SLEV presenting neurological and circulatory disorders at the 3^rd viral passage.

<p>(A) Bending of the spine (thoracic kyphosis), and limited mobility. (B) Front limb flexed characterizing loss of proprioception and apathy. (C) Necrosis of the distal extremity of the hind limbs and at the tip of the tail. (D) Hyperemia and extensive areas of hemorrhage in the meninges at the rostral part of the brain.</p