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Dispatch
Hepatitis E Virus Transmission
from Wild Boar Meat
Tian-Cheng Li,* Katsumi Chijiwa,† Nobuyuki Sera,† Tetsuya Ishibashi,†
Yoshiki Etoh,† Yuji Shinohara,‡ Yasuo Kurata,‡ Miki Ishida,§ Shigeru Sakamoto,¶
Naokazu Takeda,* and Tatsuo Miyamura*
*National Institute of Infectious Diseases, Tokyo, Japan; †Fukuoka Institute
of Health and Environmental Sciences, Fukuoka, Japan; ‡Tagawa Health,
Welfare, and Environment Office, Fukuoka, Japan; §Fukuoka Prefectual Government,
Fukuoka, Japan; and ¶Iizuka Hospital, Fukuoka, Japan
Suggested
citation for this article
We investigated
a case of hepatitis E acquired after persons ate wild boar meat. Genotype
3 hepatitis E virus (HEV) RNA was detected in both patient serum and
wild boar meat. These findings provided direct evidence of zoonotic
foodborne transmission of HEV from a wild boar to a human.
Hepatitis E virus (HEV), a causative agent of human hepatitis E, is a
single-stranded positive-sense RNA virus recently classified as the sole
member of the genus Hepevirus in the family Hepeviridae
(1,2). HEV is transmitted primarily by the fecal-oral
route through contaminated drinking water. However, recent studies have
demonstrated that various animal species have serum antibodies to HEV,
suggesting that hepatitis E is a zoonotic disease (3).
In Japan, 4 hepatitis E cases have been linked directly to eating raw
deer meat (4), and several cases of acute hepatitis E
have been epidemiologically linked to eating undercooked pork liver or
wild boar meat (5,6). These cases provide convincing
evidence of zoonotic food-borne HEV transmission. We report direct evidence
of HEV transmission from a wild boar to a human.
The Study
A 57-year-old woman came to Iizuka Hospital on March 12, 2005, with malaise
and anorexia. Although she was a healthy hepatitis B virus carrier and
negative for serologic markers of hepatitis A and C, testing upon admission
showed elevated levels of liver enzymes (alanine aminotranferase 752 IU/L,
aspartate aminotransferase 507 IU/L, and γ-glutamyl transpeptidase
225U/L). A serum sample collected on March 16 was positive for both immunoglobulin
M (IgM) and IgG antibodies to HEV when tested by an antibody enzyme-linked
immunosorbent assay using recombinant viruslike particles (7).
This led to the diagnosis of hepatitis E. The hepatitis was typical, acute,
and self-limiting, and the patient recovered by the end of March.
The patient's husband traditionally hunted boar for food 3 or 4 times
a year, and she had eaten boar meat on 2 occasions. With her husband,
she ate the meat as part of a hot pot on December 28, 2004, 11 weeks before
her illness, and again, grilled, on January 19, 2005, along with 10 other
people (including her husband) 8 weeks before her illness. Disease did
not develop in the other 10 people. Except for this wild boar meat, the
patient had not eaten meat or liver from other wild animals. Since she
had not traveled abroad in the past 30 years, transmission must have occurred
in Japan. Two portions of meat from the wild boar (meats 1 and 2) eaten
on December 28, 2004, and 1 portion from the other wild boar (meat 3)
eaten on January 19, 2005, remained and were frozen.
Juice was obtained from the sliced meat by centrifugation at 10,000 ×
g for 15 min. The supernatant was used for RNA extraction. A nested
reverse transcription–polymerase chain reaction (RT-PCR) was conducted
to amplify part of open reading frame 2 (ORF2), which corresponds to nucleotides
(nt) 5939–6297 of the genotype 1 HEV genome (GenBank D10330), with external
sense primer HEV-F1 (5´-TAYCGHAAYCAAGGHTGGCG-3´) and antisense
primer HEV-R2 (5´-TGYTGGTTRTCRTARTCCTG-3´). A nested PCR was
conducted with internal sense primer HEV-F2 (5´-GGBGTBGCNGAGGAGGAGGC-3´)
and internal antisense primer HEV-R1 (5´-CGACGAAATYAATTCTGTCG-3´).
This procedure allows amplification of HEV 1, 3, and 4 genotypes. A PCR
product of 359 bp including the primer sequences was obtained from meat
3 by nested PCR. However, meats 1 and 2 were negative. HEV RNA was not
detected in the patient's serum by the same amplification method. This
may have resulted from an extremely small amount of RNA.
New primers for the nested RT-PCR were designed for a region within the
359 base region based on the meat 3 sequences, which corresponded to nt
5983–6243. The first PCR was performed with external sense primer HEV-WB-F1
(5´-ACCTCTGGCCTGGTAATGCT-3´) and antisense primer HEV-WB-R2
(5´-GAGAAGCGTATCAGCAAGGT-3´). The nested PCR was performed
with internal sense primer HEV-WB-F2 (5´-TATTCATGGCTCTCCTGTCA-3´)
and internal antisense primer HEV-WB-R1 (5´-ACAGTGTCAGAGTAATGCCT-3´).
These primers allowed amplification of 281 nt, including the primer sequences
from the patient serum collected on March 16, 2005. In contrast, meats
1 and 2 were negative with these new primers.
To further analyze the RNA in the patient serum and meat 3, RNA genomes
encoding an entire ORF2 were amplified as overlapping segments, nucleotide
sequences were determined, and phylogenetic analysis was carried out with
avian HEV as an outgroup. Avian HEV is a causative agent of chicken hepatitis-splenomegaly
syndrome (8). Two sequences, 1 from the patient (DQ079629)
and the other from meat 3 (DQ079630), were classified into genotype 3
(Figure). Only 1 nt difference was observed in the
1,980 nt of the entire ORF2; the nucleotide sequence identity was 99.95%.
The difference was not accompanied by any amino acid changes. These data
demonstrated that HEV infection was transmitted from the wild boar meat
to the patient on January 19, 2005.
Conclusions
Currently, deer, pig, and wild boar are suspected sources of foodborne
zoonotic transmission of HEV in Japan, and genotypes 3 and 4 of HEV are
believed to be indigenous (4–6,9,10). Direct evidence
for transmission of genotype 3 HEV from animals to humans was observed
in acute hepatitis in 4 persons who had eaten uncooked deer meat that
contained ≈107 copies of HEV RNA (4).
However, the rare finding of HEV antibody-positive deer in Japan suggest
that deer are not the major zoonotic reservoir of HEV in this country
(11). In contrast, high antibody-positive rates in domestic
pig and wild boar, including HEV genotypes 3 and 4, have been frequently
detected, suggesting that persons who eat uncooked meat are at risk for
infection with HEV (12,13). This report is the first
to provide direct evidence of zoonotic foodborne genotype 3 HEV transmission
from wild boar to a human.
Acknowledgments
We thank Tomoko
Mizoguchi for secretarial assistance.
This study was supported
in part by grants on emerging and reemerging infectious diseases, hepatitis,
and food safety from the Ministry of Health, Labor and Welfare, Japan.
Dr Li is a senior
researcher at National Institute of Infectious Diseases in Tokyo, Japan.
His research focuses on epidemiology, expression of viral proteins,
and the three-dimensional structure of hepatitis E virus.
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Suggested citation
for this article:
Li T-C, Chijiwa K,
Sera N, Ishibashi T, Etoh Y, Shinohara Y, et al. Hepatitis E virus transmission
from wild boar meat. Emerg Infect Dis [serial on the Internet]. 2005 Dec
[date cited]. Available from http://www.cdc.gov/ncidod/EID/vol11no12/05-1041.htm
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