In December 2024, a parvovirus closely related to one discovered in red fox (Vulpes vulpes) feces in the Netherlands (fox parvovirus, Protoparvovirus carnivoran4) (Appendix Figure 1) (1) caused a large multifarm outbreak involving >80 pig herds in the Netherlands (2). Pigs infected with fox parvovirus had exophthalmos, erythema, and other nonspecific clinical signs. In June 2026, similar signs, including exophthalmos, strabismus (Appendix Figure 2), weakness, erythema, and alopecia, were noted in 1.5%–2% of piglets and recently weaned pigs from a herd of 920 sows in Denmark. Follow-up inspections revealed exophthalmos in 20% of pigs 2 weeks of age, 40% of recently weaned pigs, 60%–80% of pigs 2 weeks after weaning, and 0.5% of pigs 6 weeks after weaning. Among pigs 2 weeks after weaning with exophthalmos, ≈50%–60% also had erythema and low body condition scores. The herd tested free from porcine pathogens that are routinely surveyed annually (Appendix). Antimicrobial drugs were administered to recently weaned pigs but were ineffective (Appendix).

The farmer selected 6 weak piglets (1–2 weeks of age) with exophthalmos for euthanasia and subsequent necropsy. Examination revealed mucus in the nasal cavities of all 6 piglets and mild exophthalmos, eyelid edema, and eyelashes adhered by remnants of ocular discharge in 4 piglets. We observed consolidation of the lobus medius (≈7% of lung tissue) and serous fluid in 1 bulla tympanica in 1 piglet. Two piglets had minimal stomach content; the others had moderate milk amounts. Two piglets had increased synovial fluid in several joints, and we cultured streptococci from 1 elbow joint. We also noted swelling of the liver, spleen, and kidneys, possibly from euthanasia with pentobarbital. We collected liver and kidney samples from all 6 pigs and tested them for fox parvovirus by seminested PCR (Appendix). All samples were PCR-positive. The animals were coccidia-negative, and no other specific diagnostic tests were performed.

We screened for fox parvovirus DNA previously isolated from wild animals sampled throughout Denmark during 2018–2024 (3) (Appendix Figure 3). We detected fox parvovirus DNA in 1 of 2 fecal samples from red foxes, supporting previous results by Bodewes et al. and Lojkić et al., who found this virus in fox stool samples in the Netherlands and Croatia (1,4). In addition, we detected fox parvovirus DNA in 2 (2.5%) of 80 spleen samples from red foxes (2022–2023) but none in 27 spleen samples from other wild carnivorans (Appendix). The 2 foxes positive for fox parvovirus had no pathologic signs of disease (Appendix), but 1 fox was also amdoparvovirus-positive (3).

We obtained the full viral genome sequence from the PCR-positive fox fecal sample (XFM39) by using metagenomic sequencing (18,876 reads with an average coverage of 558×, range 29×–782×), as previously described (5). In addition, we performed Sanger-based complete genome sequencing of fox parvoviruses from 1 PCR-positive fox spleen sample (FFM99) and 2 PCR-positive pig liver samples (FPP1 and FPP4) (Appendix). We obtained partial fox parvovirus sequences from all other PCR-positive samples: the sequence from the second positive fox spleen sample was identical to XFM39, and sequences from the other 6 pig samples were identical to FPP1 and FPP4.

Figure 1

Figure 1. Phylogenetic analysis of fox parvoviruses from study of emerging protoparvovirus in pigs and wildlife, Denmark. Midpoint-rooted maximum-likelihood phylogenetic tree (left) was built with a concatenated alignment of nonstructural protein 1...

Figure 2

Figure 2. Complete genome comparisons of fox parvoviruses from study of emerging protoparvovirus in pigs and wildlife, Denmark. Sequence identities across complete genomes of fox parvoviruses from pigs and foxes were compared...

Maximum-likelihood phylogenies (6) showed that the virus from the outbreak in the Netherlands was the closest relative to the ones from the Denmark pig farm. The parvoviruses from the pig farm outbreaks in Denmark and the Netherlands shared 99.9% genomic identity (2 nonsynonymous substitutions in the nonstructural protein gene) (Figures 1, 2; Appendix Figure 4). Those viruses clustered in a clade that also included fox viruses from Croatia and the Netherlands (Figure 1). Viruses from foxes in Denmark shared <95% identity with all other viruses and formed a distinct clade (Figures 1, 2; Appendix Figure 4).

Our study supports the hypothesis that this parvovirus is a porcine pathogen and reports its detection in Denmark. Clinical signs resembled those observed in herds in the Netherlands. Controlled and epidemiological studies are needed to establish viral association with disease and viral prevalence and diversity in pig farms across countries.

Detecting fox parvovirus in fox organs suggests that this virus is not simply carried in feces but can infect and replicate in carnivorans, similar to other protoparvoviruses (7). However, its pathogenic role in wildlife remains unknown. Viruses from pig farms in the Netherlands and Denmark were more closely related to each other than to wildlife viruses from their respective countries, suggesting an epidemiologic link between farm outbreaks and possible multicountry spread after a single introduction into pigs. Although fox parvovirus detection in foxes preceded the recognition of the pig syndrome, definitively concluding whether foxes and pigs were infected by the same source or the virus originated from wild animals and was introduced into farms, or vice versa, was not possible because previous farm outbreaks might have gone undetected. Given the environmental stability of parvoviruses (7), we hypothesize an environmental-related transmission between wild and farmed animals (e.g., through contaminated material introduced into farms or exposure to contaminated farm-originating biological byproducts).

Our study was limited to cases from a single farm, lacked histopathologic evaluation, and included few recently collected wildlife samples. Larger-scale studies are needed to determine virus origin and spread among pig farms and wildlife globally and to clarify pathogenicity and ecology, including identifying maintenance and spillover hosts, host range, and transmission routes.

In summary, the close genetic relationship between viruses from pig outbreaks in Denmark and the Netherlands suggest a farm-related international epidemiological link. Those findings support additional surveillance of fox parvovirus among domestic pigs and wildlife.

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Suggested citation for this article: Canuti M, Høeg FJ, Vedsted Hammer AS, Jensen TK, Quaade ML, Ryt-Hansen P, et al. Emerging protoparvovirus in pigs and wildlife, Denmark. Emerg Infect Dis. 2026 Dec [date cited]. https://doi.org/10.3201/eid3212.261184