Key Determinants in the Pathogenesis of Equine Herpesvirus 1 and 4 Infections

Equine Herpesvirus Type 1 Myeloencephalitis in the Brazilian Amazon

An investigative and epidemiological study was carried out for equine herpesvirus type 1 (HVE-1) in 10 outbreaks of neurological disease from different farms in the state of Pará, Brazil. 25 horses were studied: six male and 19 females, aged between one and 13 years. A necropsy of six horses was performed, and the others recovered either with or without treatment (T1-vitamin B1 + dexamentasone; T2-vitamin B1 + flunixim meglumine). Animals that received treatment recovered after eight days. The main clinical signs observed were motor incoordination, progressive paresis, thoracic and/or pelvic limbs abducted after induction of clinical examination, knuckling of the hind fetlocks, sagging and swaying of the hindquarters while standing or walking and paresis. All animals were positive: 88% (22/25) in nested PCR and 72% (18/25) in serum neutralization (including three negatives in serology). Focal brownish areas compatible with hemorrhage were found in the white and gray matter of the spinal cord of two animals. On histological analysis, there were perivasculitis and neutrophilic vasculitis in the gray matter of the spinal cord and brain. Based on the evidence, this work proves the circulation of HVE-1 in the Amazon biome, mainly in the state of Pará, Brazil.

Molecular detection of equid herpesvirus in bronchoalveolar lavage fluid from asymptomatic horses in Southern Brazil

Background and Aim

Molecular approaches to diagnose respiratory viruses have provided an opportunity for early and subclinical pathogen detection, particularly in samples from the upper respiratory tract. This study aimed to investigate the presence of herpesviruses, particularly equid herpesvirus (EHV)-2 and EHV-5, in samples from the lower respiratory tract of healthy racehorses from Southern Brazil.

Materials and Methods

Samples from the lower respiratory tract (i.e., bronchoalveolar lavage fluid [BALF]) were assessed by video endoscopy, cytological evaluation of BALF, and tracheal aspirates (TA), along with quantitative polymerase chain reaction (qPCR), to detect equine herpesvirus infection in the lower respiratory tract samples and compare corresponding cytological and endoscopic findings.

Results

At least one abnormality per horse during endoscopy examination was observed, including, but not limited to, mucous secretion in the airways and pharyngeal lymphoid hyperplasia. The presence of EHV-2 and/or EHV-5 was detected by qPCR in 3/10 animals. One horse was positive for EHV-2 alone, one for EHV-5 alone, and one for both.

Conclusion

To the authors' knowledge, this is the first molecular detection of EHV-2 and EHV-5 in Brazilian thoroughbred horses. These findings may provide new insights into the epidemiology of EHV-2 and EHV-5 in Brazilian horses, evidencing the importance of the molecular investigation, early detection, and prevention of respiratory diseases.

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): infection with Equine Herpesvirus-1

Equine Herpesvirus-1 infection has been assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of: Article 7 on disease profile and impacts, Article 5 on the eligibility of the disease to be listed, Article 9 for the categorisation of the disease according to disease prevention and control measures as in Annex IV and Article 8 on the list of animal species related to Equine Herpesvirus-1 infection. The assessment has been performed following a methodology composed of information collection and compilation, and expert judgement on each criterion at individual and collective level. The outcome is the median of the probability ranges provided by the experts, which indicates whether the criterion is fulfilled (66-100%) or not (0-33%), or whether there is uncertainty about fulfilment (33-66%). For the questions where no consensus was reached, the different supporting views are reported. According to the assessment performed, Equine Herpesvirus-1 infection can be considered eligible to be listed for Union intervention according to Article 5 of the Animal Health Law with 33-90% certainty. According to the criteria as in Annex IV of the AHL related to Article 9 of the AHL for the categorisation of diseases according to the level of prevention and control, it was assessed with less than 1% certainty that EHV-1 fulfils the criteria as in Section 1 (category A), 1-5% for the criteria as in Section 2 (category B), 10-66% for the criteria as in Section 3 (category C), 66-90% for the criteria as in Section 4 (category D) and 33-90% for the criteria as in Section 5 (category E). The animal species to be listed for EHV-1 infection according to Article 8(3) criteria are the species belonging to the families of Equidae, Bovidae, Camelidae, Caviidae, Cervidae, Cricetidae, Felidae, Giraffidae, Leporidae, Muridae, Rhinocerontidae, Tapiridae and Ursidae.