A young, male harbor seal (Phoca vitulina), approximately one year of age, was stranded on the Dutch coast and admitted to the Seal Rehabilitation and Research Centre (SRRC) in the Netherlands in 2012 (rehabilitation number 12-410). Upon arrival at the centre, the seal displayed left-sided hemiparesis. Despite treatment with antibiotics and anti-inflammatory medication for several weeks, the seal developed severe central nervous system (CNS) disorders including episodes of unconsciousness. Since no recovery was observed, the seal was euthanized.
At necropsy, severe multifocal, cutaneous nodular lesions were observed. In addition, in the lungs multifocal, dark, firm areas were present. No further abnormalities were detected. Samples of brain, lungs, liver, spleen, kidney and bladder were collected and stored at either -70°C or fixed in 10% neutral buffered formalin. Furthermore, the complete head of seal 12-410 was stored at -20°C for several weeks until further analysis by magnetic resonance imaging (MRI).
On histological examination, multiple inclusion bodies were found in the skin consistent with Seal poxvirus infection.1 In the lungs, a moderate, multifocal, parasitic bronchopneumonia was present, which is a major cause of disease among harbor seals of this age in this population.2 In the cerebrum, a moderate to severe, multifocal, non-suppurative meningoencephalitis was observed. MRI images of the brain showed subdural areas with a hypointense signal in all sequences, compatible with air due to postmortem preparation. No gross abnormalities were found within the brain parenchyma.
The observed histological lesions in the brain suggested a viral infection, but no morbillivirus or herpesvirus could be detected by PCR. In addition, other main causes of the neurological signs (e.g., tumor or trauma) could be excluded by MRI. Therefore, samples of the seal were analysed by random PCR in combination with next-generation sequencing. Using this technique a novel parvovirus was detected in the brain of the seal. In addition, two novel viruses belonging to the family Anelloviridae were detected in the lungs of this animal. Phylogenetic analysis of the coding sequence of the VP2 gene of the novel parvovirus, tentatively called Seal parvovirus, indicated that this virus belongs to the genus Erythrovirus, to which also human parvovirus B19 belongs. Although no other seals with similar signs were rehabilitated at the SRRC in recent years, a prevalence study of tissues of seals from the same area collected in the period 2008–2012 indicated that the Seal parvovirus has circulated in the harbor seal population at least since 2008.
The presence of the Seal parvovirus in the brain was confirmed by real-time PCR and in situ hybridization, showing for the first time that a parvovirus of the genus Erythrovirus can be present in the Virchow-Robin spaces and in the brain parenchyma adjacent to the meninges. These findings show for the first time that a parvovirus of the genus Erythrovirus can be involved in central nervous system infection and inflammation, as has also been suspected but not proven for human parvovirus B19 infection.3-5
This work was financially supported by the EU FP7 project EMPERIE. The authors thank the SRRC staff members and volunteers who participated in the sample collection.
* Presenting author
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