Asymptomatic encephalitis in calves experimentally infected with bovine herpesvirus-5.

This study demonstrated that bovine herpesvirus 5 (BoHV)-5 infected calves can develop encephalitis and remain asymptomatic. Seven calves were infected intranasally and monitored for 30 days. Cerebrospinal fluid (CSF) analysis was performed from the onset of neurological signs. Multiple sections of brain and the trigeminal ganglion were submitted to histopathology. Virus detection (PCR and isolation) was performed on CSF and tissues. Four calves developed signs of neurologic disease and died. Three calves remained asymptomatic and were euthanized 30 days post-infection. Cerebrospinal fluid mononuclear pleocytosis occurred in symptomatic and asymptomatic calves. BoHV-5 was isolated and viral DNA was detected in multiple areas of the encephalon of all calves. The viral DNA was detected in the CSF of 2 calves showing neurological signs. Histologically, inflammation was noted in the brain of all calves and confirmed that the encephalitis caused by BoHV-5 may be mild and asymptomatic.

Hematological and cerebrospinal fluid changes in cattle naturally and experimentally infected with the bovine herpesvirus 5

Bovine herpesvirus 5 (BoHV-5) meningoencephalitis is one of the main causes of mortality by encephalopathy in Brazilian cattle herds. However, the neurological signs observed are common to several encephalopathies and do not contribute decisively to a diagnosis. In order to verify hematological and cerebrospinal fluid (CSF) changes, blood and CSF samples from naturally and experimentally infected bovines were evaluated. In natural cases (n=17), the samples were collected only once, and in experimental cases (n=7), the samples were sequentially obtained throughout disease progression. While routine methods were used to examine the samples, BoHV-5 infection was confirmed by a PCR assay. Blood analyses did not reveal any consistent hematological alterations and the leukogram results occasionally showed increases in leukocyte and segmented neutrophil. Hyperfibrinogenemia was noted in all experimentally infected calves and in half of the natural cases. Pleocytosis with mononuclear cells was a remarkable finding in CSF collected from both groups of animals and was present even in experimentally infected calves that remained asymptomatic. Therefore, CSF evaluation can be used as an auxiliary method in ante-mortem BoHV-5 diagnosis.

A meningoencefalite determinada pelo herpesvírus bovino 5 (BoHV-5) é considerada uma das principais causas de mortalidade por encefalopatia em bovinos no Brasil. O diagnóstico clínico da infecção é difícil de ser realizado pois os sinais neurológicos ocasionados pela infecção com o BoHV-5 são comuns aos observados em encefalopatias bovinas de diferentes etiologias. Com o objetivo de determinar as alterações hematológicas e do líquido cefalorraquidiano, foram avaliadas amostras de sangue total e líquor colhidas de animais infectados tanto naturalmente quanto experimentalmente. Nos casos naturais da doença (n=17), as amostras foram coletadas apenas uma vez. Nos casos de infecção experimental (n=7), as amostras foram obtidas sequencialmente durante a evolução clínica da doença. Enquanto na análise das amostras clínicas foram empregadas metodologias rotineiras, a infecção pelo BoHV-5 foi confirmada em todos os animais incluídos nesse estudo por meio da técnica de PCR. As análises hematológicas não revelaram alterações consistentes e os resultados obtidos a partir do leucograma mostraram aumento ocasional de leucócitos e neutrófilos segmentados. A hiperfibrinogenemia pôde ser observada em todos os bezerros infectados experimentalmente e em metade dos casos naturais da doença. Diferentemente, a pleiocitose com predomínio de células mononucleares foi considerada um achado marcante nas amostras de líquor coletadas em ambos os grupos de animais, encontrando-se presente até mesmo nos bezerros infectados experimentalmente que permaneceram assintomáticos. Os resultados do presente estudo, obtidos tanto em condições de infecções naturais quanto experimentais, demonstraram que a avaliação do líquor cefalorraquidiano pode ser utilizada como método auxiliar para o diagnóstico ante-mortem da infecção pelo BoHV-5.