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Volume 20, Number 12—December 2014


Zoonotic Baylisascaris procyonis Roundworms in Raccoons, China

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Technical Appendices


Suggested citation for this article

To the Editor: Baylisascaris procyonis, an intestinal roundworm that infects raccoons (Procyon lotor), causes fatal or severe neural larva migrans in animals and humans (1,2). Globally, ≈130 species of wild and domesticated animals are susceptible (2). Infections in humans typically occur in children who have the disorders pica or geophagia and ingest B. procyonis eggs in items contaminated with raccoon feces (3). Clinical manifestations include ocular disease, eosinophilic encephalitis, and eosinophilic cardiac pseudotumors; severe infection can lead to death. Since 1984, ≈24 cases of B. procyonis–related human neural larva migrans have been reported, mainly in the United States (1,3–5; K.R. Kazacos, pers. comm.). Despite few cases among humans, lack of effective treatment and widespread distribution of infected raccoons in close association with humans make B. procyonis a potentially serious public health threat (2,6). The current distribution of B. procyonis is poorly recorded in Asia (2,7), except for Japan (8). We describe B. procyonis infections among raccoons in China as part of a series of ongoing surveys of helminthic zoonoses linked to captive exotic animals in zoologic gardens (ZGs) in China.

More than 90% of raccoons in China (n >320) are raised as exotic ornamental animals in 18 ZGs. During 2011–2013, we collected 2×308 fecal samples (i.e., 1 repeat within each sampling) from 277 raccoons in 12 randomly selected ZGs (Technical Appendix [PDF - 776 KB - 4 pages] Figure 1). Samples were stored in individual plastic bags at –20°C until use. We examined raccoons (n = 31) at the Sichuan ZGs twice, in June 2012 and May 2013. We identified B. procyonis eggs in feces using morphologic and molecular analyses (1,2,9). The nuclear first internal transcribed spacer (428 bp) and mitochondrial cytochrome c oxidase subunit 1 (cox-1, 938 bp) genes in each sample were PCR-amplified and sequenced. B. procyonis infection was confirmed by sequencing and phylogenetic analyses of both genes (7,9). We reexamined ≈60% of fecal samples to validate results. Prevalence (95% CI) was calculated for the overall population and independently for female, male, juvenile, and adult raccoons. We determined differences between the tested ZG prevalence and prevalence by sex or age of raccoons using χ2 or Fisher exact tests in SAS (SAS Institute, Cary, NC, USA); p values <0.05 were considered significant.

Building on egg-based morphologic characterization and internal transcribed spacer 1 and cox-1 gene-based phylogenies using neighbor-joining trees (Technical Appendix [PDF - 776 KB - 4 pages] Figure 2), we found B. procyonis in raccoon feces from 5/12 ZGs (42%; 95% CI 14%–70%), including 2 in the most densely populated provinces, Henan and Sichuan. More infections were found in western than central and eastern ZGs (4/6 and 1/6, respectively; Table, Technical Appendix [PDF - 776 KB - 4 pages] Figure 1) (p = 0.079). Fecal samples of 35 raccoons (13%; 95% CI 9%–17%) tested positive for B. procyonis. The mean intensity of egg shedding was 5,000 eggs per gram (range 800–11,200 eggs per gram; data not shown). No significant difference was observed in the intensity of shedding by comparing sex and age of animals, and no significant differences were noted in the mean prevalence between female and male raccoons (12% versus 14%; p = 0.677) or between adult and juvenile animals (13% versus 10%; p = 0.536).

This investigation documents the presence and prevalence of B. procyonis among raccoons in China. The findings imply that raccoons harboring this parasite have the potential for spreading it to humans. One reason is that captive raccoons adapt readily to humans and easily take food offered by hand; another is that communal raccoon latrine sites in ZGs are usually close to areas where humans gather, so ZG visitors may be exposed to large numbers of eggs (Technical Appendix [PDF - 776 KB - 4 pages] Figure 3). These eggs can remain viable and infective for years (2), and latrines are recognized as primary sources of transmission of B. procyonis to humans (4). Current public health initiatives to prevent B. procyonis infections in humans rely on the education of veterinary and human health care professionals, who in turn inform the public (1,6,10). Thus, veterinarians, clinicians, and public health officials in China should be more informed about this pathogen, especially in regions with large raccoon populations.

Because of a lack of clinical awareness of this illness and subsequent lack of early diagnosis and effective treatment, prevention of B. procyonis infection by education is essential. In addition, a strategy for eradication is needed. Heat, in the form of boiling water, steam-cleaning, or fire, is the optimal tool for killing B. procyonis eggs (2) and therefore can be used to decontaminate areas surrounding latrines. Within heavily contaminated areas, removing and then sterilizing the top few inches of surface soil with heat would be effective and practical (1,2). Among captive raccoon populations, particularly in China, regular deworming is also likely to be helpful in reducing novel and existing sources of infection (13).

Finally, although no cases of human infection have been reported in China to our knowledge, physicians should consider including B. procyonis infections in their differential diagnoses of patients with indicative features: clinical (eosinophilic encephalitis, ocular disease), epidemiologic (raccoon exposure), radiologic (white matter disease), and laboratory results (blood and CNS eosinophilia) (1,10). This study lays the foundation for future steps to educate the population of China about B. procyonis infection and to create programs to prevent the spread of this disease to humans.

Yue Xie, Xuan Zhou, Mei Li, Tianyu Liu, Xiaobin Gu, Tao Wang, Weimin Lai, Xuerong Peng, and Guangyou YangComments to Author 

Author affiliations: Sichuan Agricultural University, Ya’an, Sichuan, China


We thank Bo Zhao and Lili Niu for their coordination and help in collecting fecal samples from zoologic gardens of China. We also thank Kevin R. Kazacos for reviewing the manuscript and providing helpful comments.

This study was supported by grants from the Program for Changjiang Scholars and Innovative Research Team in University (PCSIRT) (grant no. IRT0848) and the Research Fund for the Chengdu Research of Giant Panda Breeding (project no. CPF2012-13).


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Technical Appendix

Suggested citation for this article: Xie Y, Zhou X, Li M, Liu T, Gu X, Wang T. Zoonotic Baylisascaris procyonis roundworms in raccoons, China [letter]. Emerg Infect Dis. 2014 Dec [date cited].

DOI: 10.3201/eid2012.140970

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Table of Contents – Volume 20, Number 12—December 2014


Please use the form below to submit correspondence to the authors or contact them at the following address:

Guangyou Yang, Department of Parasitology, College of Veterinary Medicine, Sichuan Agricultural University, 46 Xinkang Rd, Ya’an, Sichuan, 625014, People’s Republic of China

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