On the basis of these results, we hypothesize that sow milk could represent a possible (and potentially major) route for the vertical transmission of PEDV from sow to suckling piglet. This hypothesis could be indirectly verifi ed by our fi eld observation that piglet death rates decreased as a result of fostering (data not shown). Our fi ndings show that PEDV was identifi ed not only in fecal samples from sick piglets, as expected, but also in the milk of the sow, which suggests vertical transmission of the virus. Differential Seroprevalence of Human Bocavirus Species 1-4 in Beijing, China BACKGROUND: Four species of human bocaviruses (HBoV1-4) have been identified based on phylogenetic analysis since its first report in 2005. HBoV1 has been associated with respiratory disease, whereas HBoV2-4 are mainly detected in enteric infections. Although the prevalence of HBoVs in humans has been studied in some regions, it has not been well addressed globally. METHODOLOGY/PRINCIPAL FINDINGS: Cross-reactivity of anti-VP2 antibodies was detected between HBoV1, 2, 3, and 4 in mouse and human serum. The prevalence of specific anti-VP2 IgG antibodies against HBoV1-4 was determined in different age groups of healthy individuals aged 0-70 years old in Beijing, China, using a competition ELISA assay based on virus-like particles of HBoV1-4. The seroprevalence of HBoV1-4 was 50%, 36.9%, 28.7%, and 0.8%, respectively, in children aged 0-14 years (n = 244); whereas the seroprevalence of HBoV1-4 was 66.9%, 49.3%, 38.7% and 1.4%, respectively, in healthy adults (≥15 years old; n = 142). The seropositive rate of HBoV1 was higher than that of HBoV2, HBoV3, and HBoV4 in individuals older than 0.5 years. Furthermore, IgG seroconversion of HBoV1 (10/31, 32.3%), HBoV2 (8/31, 25.8%), and HBoV3 (2/31, 6.5%) was found in paired sera collected from children with respiratory tract infections who were positive for HBoV1 according to PCR analysis. CONCLUSIONS/SIGNIFICANCE: Our data indicate that HBoV1 is more prevalent than HBoV2, HBoV3, and HBoV4 in the population we sampled in Beijing, China, suggesting that HBoV species may play differential roles in disease. Human bocavirus (HBoV), a member of the Parvoviridae family, is a potential etiologic agent of respiratory disease and of acute gastroenteritis [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] . Based on phylogenetic analysis of viral genomes, four species of HBoVs (HBoV1-4) have been identified [1, [7] [8] [9] . HBoV1 is associated with respiratory tract diseases [1, 2, [12] [13] [14] . HBoV2 and 3 have been detected in the respiratory tract, but are associated mainly with stool samples [8] [9] [10] [11] 15, 16] . HBoV4 has been detected in enteric infections [9] . However, as HBoVs are frequently co-detected with other viral infections in patients with respiratory or enteric infections, the exact roles of HBoVs in pathogenicity are unclear.