Porcine parvovirus 4 linked to wasting syndrome in Brazilian pigs

A study of pigs in southern Brazil has found that porcine parvovirus 4 (PPV4) is strongly associated with postweaning multisystemic wasting syndrome, or PMWS, a wasting disease of young pigs driven by porcine circovirus 2 (PCV2). The research, published in the journal Discover Viruses, used polymerase chain reaction (PCR) to search for PPV4 and two porcine bocaviruses, PBoV1 and PBoV3, in tissue and serum samples from pigs with and without the syndrome on commercial farms in the state of Rio Grande do Sul.

The most striking result came from serum analysis. The frequency of PPV4 DNAemia, meaning detectable viral DNA in the bloodstream, was six times higher in PMWS-affected pigs than in age-matched healthy controls: 41.2 percent versus 6.7 percent, a difference the authors report as statistically significant at p ≤ 0.0001.

PMWS is the main clinical manifestation of porcine circovirus associated disease. Infection with PCV2 is a necessary condition for the syndrome to develop, but it is not sufficient on its own to trigger clinical disease, which is why researchers continue to search for co-factors that tip subclinical infection into overt wasting. Consistent with this established concept, PCV2 was detected in all tissue samples from every PMWS-affected animal in the study, while quantitative data from the team’s earlier work on the same cohort showed significantly higher PCV2 DNA loads in diseased animals than in non-affected ones. No sample from a non-PMWS animal exceeded a load of 10^4.4 copies per 100 nanograms of DNA, reinforcing the idea that high tissue viral load is a critical determinant in the transition from subclinical infection to disease.

The PMWS-affected group comprised 94 pigs aged five to eight weeks, from which tissue samples of spleen, liver, lymph nodes, lungs and kidneys were collected during necropsy, yielding 379 individual DNA extracts of sufficient quality. Diagnosis was based on established pathological criteria for PCV2-systemic disease, including clinical signs such as dyspnea, enlarged inguinal lymph nodes, pallor, jaundice and diarrhea, along with macroscopic and histopathological lesions such as lymphoid depletion and the presence of PCV2 antigen within lesions demonstrated by immunohistochemistry. The control tissue group consisted of samples from eleven healthy pigs at slaughter age of 16 to 18 weeks. Serum comparisons drew on 102 samples from affected piglets and 187 control samples, including 89 from healthy piglets aged one to two months, allowing age-matched comparison of DNAemia.

In contrast to PPV4, neither bocavirus showed any association with the syndrome. PBoV1 DNA was detected in serum at almost identical frequencies in PMWS-affected and unaffected animals, 33.3 percent and 34.7 percent respectively, with no significant difference, leading the authors to conclude that PBoV1 DNAemia is not associated with the development of PMWS. In tissues, however, PBoV1 was found in 40 percent of the PMWS-affected animals in at least one of the five organs examined, with a marked tropism for lymphoid tissues: detection in lymph nodes was three times higher than in the other tissues analyzed. PBoV1 DNA was not detected in any tissue from the adult slaughter-age animals, although viral DNA did appear in roughly 10 percent of serum samples from adult animals, a discrepancy the authors attribute to possible transient or low-level viremia in younger individuals within the six-to-19-month adult age range.

PBoV3 presented a different pattern altogether. The virus was widely distributed across multiple organs in both PMWS-affected and healthy pigs, with tissue detection rates in diseased animals ranging from 27.4 percent in lung to 54.8 percent in lymph nodes, and with lymph nodes from healthy animals showing a remarkably high detection rate of 81.8 percent. Yet serum analysis revealed only low-level DNAemia: 4.9 percent in PMWS-affected pigs, 11.2 percent in healthy piglet controls and just 2 percent in adults, none of these differing significantly. The authors interpret this contrast between high tissue prevalence and minimal viremia as evidence of strong viral tropism for and replication within solid tissues, with only limited spillover into the bloodstream, and they note that it aligns with serological evidence from China where PBoV3 seroprevalence reached 90 percent in tested herds, indicating near-ubiquitous and predominantly subclinical exposure.

Both bocaviruses displayed a consistent predilection for immune tissues, echoing the well-established characteristic of bocaviruses to replicate primarily in lymphoid organs such as lymph nodes, spleen and tonsils. The authors also report, to the best of their knowledge, the first detections of both PBoV1 and PBoV3 in pigs in Brazil and anywhere in South America, despite prior documentation of PBoV1 circulation in Africa, North America, Europe and Asia. Given that PBoV1 has been reported at higher rates in PMWS-affected pigs in some earlier studies, including a detection rate of 88 percent in affected versus 46 percent in non-affected animals, while other studies found no significant differences between healthy and diseased pigs, the Brazilian team frames these viruses as potential opportunistic, or two-in-one, pathogens that may cause disease under specific conditions such as immunosuppression or co-infection, or persist as subclinical infections.

PPV4 told a more complex epidemiological story. Although viral DNA was found across all examined organs in PMWS-affected pigs without statistically significant predominance in any single tissue, trends toward higher detection in the spleen at 15.8 percent and liver at 13.2 percent were observed. More revealing was the age pattern: healthy adult pigs showed a DNAemia prevalence of 40.8 percent, similar to that of the diseased piglets, along with high detection rates in kidneys at 36.7 percent and spleen at 27.3 percent. The shift from low DNAemia in young healthy pigs to high DNAemia in healthy adults suggests, in the authors’ view, that PPV4 establishes chronic, persistent infection over time. They propose a plausible molecular mechanism: unlike the linear genomes of other porcine parvoviruses, PPV4 can form circular or head-to-tail concatemer DNA structures often associated with episomal maintenance and persistence in host cells.

The authors are careful to acknowledge the limitations of their design. The study lacked age-matched healthy tissue controls: diseased pigs were five to eight weeks old while tissue controls were roughly five months old, an age gap that confounds direct comparison of tissue tropism and viral load, since viral distribution and persistence can change substantially during this period of rapid growth and immune maturation. The modest size of the healthy tissue control group, just eleven animals, also limits statistical power for comparative tissue analyses, underscoring the preliminary nature of the tissue distribution patterns reported for PPV4. Importantly, however, the team notes that these limitations do not affect the core epidemiological findings on DNAemia, which rest on comparisons of age-matched young pigs and remain the robust conclusions of the work.

Taken together, the results delineate what the authors describe as a hierarchy of viral involvement in PMWS-affected herds: PCV2 as the essential pathogen, ubiquitous and present at high load in diseased animals; PPV4 as a potential exacerbating co-factor linked to viremia and capable of persistent infection; and the bocaviruses as common bystanders or agents of subclinical infection. The detection of PPV4 in Brazil is consistent with earlier reports from Argentina and Brazil, and with findings of the virus in boar semen, sow reproductive tissues and the lungs of pigs with respiratory disease in China, underscoring its broad tissue tropism. The authors call for future studies employing techniques such as in situ hybridization to localize the bocaviruses within histopathological lesions, experimental models to reproduce disease, and work to elucidate the mechanisms of PPV4 persistence, its potential synergism with PCV2, and its impact on reproductive performance. They also recommend that surveillance of these silently circulating agents be integrated into established swine pathogen monitoring programs, a consideration of particular relevance given the global scale of Brazilian swine production.

Subject of Research: Associations of porcine parvovirus 4 and porcine bocaviruses 1 and 3 with postweaning multisystemic wasting syndrome in Brazilian pigs

Article Title: Detection and association of porcine bocaviruses 1 and 3 and porcine parvovirus 4 with postweaning multisystemic wasting syndrome (PMWS) in Brazil

Article References: Cibulski, S. P., Teixeira, T. F., Varela, A. P. M., Dezen, D., Scheffer, C. M., dos Santos, H. F., & Roehe, P. M. (2026). Detection and association of porcine bocaviruses 1 and 3 and porcine parvovirus 4 with postweaning multisystemic wasting syndrome (PMWS) in Brazil. Discover Viruses, 3(1), Article 5. https://doi.org/10.1007/s44370-026-00038-z

Image Credits: AI Generated

DOI: 10.1007/s44370-026-00038-z

Keywords: porcine parvovirus 4, porcine bocavirus 1, porcine bocavirus 3, PMWS, PCV2, swine, Brazil, DNAemia, lymphoid tropism, viral persistence, PCR, swine health