Enzootic angiostrongyliasis in Shenzhen, China.

Abstract

To the Editor: Angiostrongylus cantonensis is a zoonotic parasite that causes eosinophilic meningitis in humans after they ingest infective larvae in freshwater and terrestrial snails and slugs, paratenic hosts (such as freshwater fish, shrimps, frogs, and crabs), or contaminated vegetables. With the increase of income and living standards, and the pursuit of exotic and delicate foods, populations around the world have seen angiostrongyliasis become an important foodborne parasitic zoonosis (1-9).

Full text

Page 1

LETTERS
Address for correspondence: Laura Tomassone,
Dipartmento di Produzioni Animali, Ecologia
ed Epidemiologia, Università di Torino, Italy,
via L da Vinci 44, 10095 Grugliasco, Torino,
Italy; email: laura.tomassone@unito.it
Enzootic
Angiostrongyliasis
in Shenzhen, China
To the Editor: Angiostrongylus
cantonensis is a zoonotic parasite that
causes eosinophilic meningitis in hu-
mans after they ingest infective larvae
in freshwater and terrestrial snails and
slugs, paratenic hosts (such as fresh-
water fi sh, shrimps, frogs, and crabs),
or contaminated vegetables. With the
increase of income and living stan-
dards, and the pursuit of exotic and
delicate foods, populations around the
world have seen angiostrongyliasis
become an important foodborne para-
sitic zoonosis (1–9).
Shenzhen municipality is situated
in the most southern part of main-
land People’s Republic of China be-
tween the northern latitudes of 22°27′
to 22°52′ and eastern longitudes of
113°46′ to 114°37′; it shares a border
with the Hong Kong Special Admin-
istrative Region, China, in the south.
The climate is subtropical, with an av-
erage annual temperature of 23.7 °C.
The city is 1,952.84 km2 and has a
population of 10 million.
Since 2006, thirty-two sporadic
cases of human eosinophilic menin-
gitis caused by consumption of un-
dercooked aquacultured snails have
been documented in Shenzhen (Shen-
zhen Center for Disease Control and
Prevention, unpub. data). To identify
the source of these infections and as-
sess the risk for an outbreak of eo-
sinophilic meningitis, we conducted
a survey to investigate whether A.
cantonensis occurs in wild rats and
snails in Shenzhen.
To examine A. cantonensis infec-
tion in intermediate host snails, 302
terrestrial snails (Achatina fulica)
were collected from 10 investigation
sites across Shenzhen, and 314 fresh-
water snails (Pomacea canaliculata)
were sampled from 6 investigation
sites. We examined the snails for A.
cantonensis larvae by using pepsin
digestion standardized procedures (3).
To survey the prevalence of adult A.
cantonensis in defi nitive host rats, we
collected 187 Rattus norvegicus rats
and 121 R. fl avipectus rats collected
from 4 sites where positive snails pos-
itive for A. cantonensis were found.
These rats were examined for the pres-
ence of adult A. cantonensis in their
cardiopulmonary systems.
A. cantonensis larvae were found
in 96 (15.6%) of 616 examined snails.
Of these, P. canaliculata had an aver-
age infection rate of 20.7% (65/314),
signifi cantly higher (p<0.01) than
that of A. fulica (10.3%, 31/302), an
indication that P. canaliculata may
be the principal intermediate host for
A. cantonensis in Shenzhen. A. can-
tonensis adults were recovered from
the cardiopulmonary systems of 37
(12%) of 308 examined rats. Infec-
tion rate for R. norvegicus rats was
16.6% (31/187), signifi cantly higher
(p<0.01) than that for R. fl avipec-
tus (4.9%, 6/121), an indication that
R. norvegicus may be the principal
defi nitive host for A. cantonensis in
Shenzhen, possibly due to the rat’s
preference for eating snails. Infec-
tion rates were higher for female rats
(25.6% for R. norvegicus and 7.8%
for R. fl avipectus) than for male rats
(8.9% for R. norvegicus, 2.9% for R.
fl avipectus), possibly because female
rats eat more snails to supply proteins
for reproduction. This report of enzo-
otic A. cantonensis infection in wild
rats and snails in Shenzhen demon-
strates the existence of natural origins
of infection with A. cantonensis for
humans in this city.
Persons in Shenzhen eat raw or
undercooked freshwater and terrestri-
al snails and slugs. This practice pro-
vides opportunities for infection with
A. cantonensis, particularly given that
P. canaliculata has been aquacultured
intensively for human consumption.
The prevalence of A. cantonensis in
wild rats and snails in Shenzhen poses
substantial risk for future outbreaks
of human eosinophilic meningitis.
Moreover, public health offi cials,
epidemiologists, researchers, clini-
cal technicians, medical practitioners,
parasitologists, and veterinarians, as
well as the general public, should be
aware of such risks, and integrated
strategies should be taken to reduce or
eliminate such risks.
Acknowledgment
We thank Alasdair Nisbet for his as-
sistance in improving the manuscript.
Project support was provided in part
by a grant from Shenzhen Municipal Bu-
reau of Science and Technology (grant
no. 2007079) to R.-L.Z. and a grant from
the Program for Changjiang Scholars and
Innovative Research Team in University
(grant no. IRT0723) to X.-Q.Z.
Ren-Li Zhang, Mu-Xin Chen,
Shi-Tong Gao, Yi-Jie Geng,
Da-Na Huang, Jian-Ping Liu,
Yuan-Liang Wu,
and Xing-Quan Zhu
Author affi liations: Shenzhen Center for
Disease Control and Prevention, Shen-
zhen, People’s Republic of China (R.-L.
Zhang, M.-X. Chen, S.-T. Gao, Y.-J. Geng,
D.-N. Huang, J.-P. Liu, Y.-L. Wu); and South
China Agricultural University, Guangzhou,
People’s Republic of China (M.-X. Chen,
X.-Q. Zhu)
DOI: 10.3201/eid1412.080695
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Address for correspondence: Xing-Quan Zhu,
Laboratory of Parasitology, College of Veterinary
Medicine, South China Agricultural University,
483 Wushan St, Tianhe District, Guangzhou,
Guangdong Province 510642, People’s Republic
of China; email: xingquanzh@scau.edu.cn
Knowledge about
Avian Infl uenza,
European Region
To the Editor: Since the fi rst iden-
tifi cations of avian infl uenza (H5N1)
in Europe in late 2005 and early 2006,
Eurobarometer survey data obtained
during April–May 2006 have provided
a unique opportunity to examine the
knowledge of respondents across the
European Union, Croatia, and Turkey
about the risks and transmission of
avian infl uenza. The H5N1 strain of
avian infl uenza virus has caused >240
human deaths in central and Southeast
Asia, the Middle East, and Africa (1).
Four of these deaths occurred in Tur-
key in 2006. Understanding gaps in
the public’s knowledge about avian
infl uenza risks and transmission pro-
vides guidance on which issues future
public health information campaigns
may wish to focus. From a public
health perspective, a more informed
general public will be less likely to un-
necessarily alter their travel and food
consumption behavior and more likely
to take appropriate preventive actions.
A 2006 Eurobarometer survey
asked 29,170 residents of the 27 coun-
tries in the European Union, Croatia,
and Turkey about their knowledge of
avian infl uenza risks (2). Eurobarom-
eter surveys are undertaken by the Eu-
ropean Commission to monitor the EU
public’s social and political opinions.
The survey was conducted on a mul-
tistage random sampling basis. There-
fore, the sample is representative of
the whole territory surveyed. Each
country’s population was randomly
sampled according to rural, metropoli-
tan, and urban population densities. A
cluster of addresses was selected from
each primary sampling unit by using
country-dependent resources such as
electoral registers. Addresses were
chosen systematically by using stan-
dard random route procedures, begin-
ning with a randomly selected initial
address. The survey was conducted
by face-to-face interviews in respon-
dents’ homes.
Data were collected from March
27 through May 1, 2006. This period
is especially interesting when looking
at Europeans’ knowledge about avian
infl uenza risk because the fi rst Euro-
pean cases of avian infl uenza (H5N1)
were found in October 2005 in Tur-
key; additional cases were found later
that month in Romania, Croatia, and
the United Kingdom. Therefore, the
period would have included media
coverage about avian infl uenza as well
as any targeted public health efforts to
inform residents about avian infl uenza
risks. By the end of this survey’s fi eld-
work period, 17 of the 29 countries
surveyed had reported infl uenza virus
(H5N1) in birds, 3 in mammals, and 1
in humans (3).
Respondents were asked 7 ques-
tions about their knowledge of the
risks humans face regarding avian
infl uenza (Table). When we looked
at these results with the aim of set-
ting future public health information
campaign objectives, we considered
incorrect or “don’t know” responses
to indicate public health information
campaign failures. Uncertainty regard-
ing avian infl uenza risks appeared to
involve consumption of eggs and vac-
cinated, cooked poultry and whether
the virus can be transmitted between
humans. However, for all questions
asked, more than half of the respon-
dents answered correctly except when
asked about eating poultry that had
been vaccinated against avian infl uen-
za. This question also had the highest
number of “don’t know” responses.
Respondents are most knowledge-
able about the preventive measure of
culling chickens, perhaps because of
the media attention these events at-
tract. The large percentage of correct
answers for some questions points
to successes of previous information
campaigns and media coverage, but
the 40% of respondents answering in-
correctly or “don’t know” to questions
about poultry and egg consumption
1956 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 14, No. 12, December 2008