Outbreaks of Eastern equine encephalitis in northeastern Brazil.

This research discusses outbreaks of eastern equine encephalitis that occurred in northeastern Brazil from May 2008 to August 2009, and the symptoms, effects, and genetic sequencing of the virus involved.

Outbreak Details

• Outbreaks of eastern equine encephalitis (EEE) were observed from May 2008 to August 2009 in the Brazilian states of Pernambuco, Ceará, and Paraíba.
• The disease occurred in 93 farms and affected 229 equids (a group that includes horses, donkeys, and zebras).
• The case fatality rate was quite high, at 72.92%.

Clinical Signs and Lesions

• The main clinical signs observed in the affected equids were circular motion, depression or extreme excitability, uncoordinated movements (ataxia), and progressive paralysis.
• These symptoms manifested over a period of 3 to 15 days.
• The dominant histologic (tissue-based) changes were a widespread lymphocytic encephalomyelitis, characterized by inflammation of the brain and spinal cord with neuronal death, satellitosis (cluster of glial cells around a neuron), neuronophagia (destruction of nerve cells), and hemorrhages.
• These lesions were most severe in the cerebral gray matter of the telencephalon, diencephalon, and mesencephalon, which are parts of the brain.
• Some animals also had areas of softening (malacia) in the telencephalon, thalamus, and basal nuclei (areas of the brain),

Virus Identification

• In one case, the virus was isolated through inoculation in mice.
• In 13 other cases, the presence of the Eastern equine encephalitis virus was confirmed using a semi-nested reverse transcription polymerase chain reaction, a technique that amplifies specific DNA sequences to detect the presence of the virus.
• After DNA sequencing of the samples, all were identified as Eastern equine encephalitis through BLASTn analysis, a method of comparing primary biological sequence information.
• However, it was noted that samples from the states of Ceará and Paraíba corresponded to the same cluster (implying they were from the same outbreak or same source), while the sample from Pernambuco belonged to a different cluster.