Enzootic Angiostrongyliasis in Shenzhen, China

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). 
 
Shenzhen municipality is situated in the most southern part of mainland People’s Republic of China between 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 Administrative Region, China, in the south. The climate is subtropical, with an average 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 meningitis caused by consumption of undercooked aquacultured snails have been documented in Shenzhen (Shenzhen Center for Disease Control and Prevention, unpub. data). To identify the source of these infections and assess the risk for an outbreak of eosinophilic meningitis, we conducted a survey to investigate whether A. cantonensis occurs in wild rats and snails in Shenzhen. 
 
To examine A. cantonensis infection in intermediate host snails, 302 terrestrial snails (Achatina fulica) were collected from 10 investigation sites across Shenzhen, and 314 freshwater 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 definitive host rats, we collected 187 Rattus norvegicus rats and 121 R. flavipectus rats collected from 4 sites where positive snails positive for A. cantonensis were found. These rats were examined for the presence 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 average infection rate of 20.7% (65/314), significantly 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. cantonensis adults were recovered from the cardiopulmonary systems of 37 (12%) of 308 examined rats. Infection rate for R. norvegicus rats was 16.6% (31/187), significantly higher (p<0.01) than that for R. flavipectus (4.9%, 6/121), an indication that R. norvegicus may be the principal definitive host for A. cantonensis in Shenzhen, possibly due to the rat’s preference for eating snails. Infection rates were higher for female rats (25.6% for R. norvegicus and 7.8% for R. flavipectus) than for male rats (8.9% for R. norvegicus, 2.9% for R. flavipectus), possibly because female rats eat more snails to supply proteins for reproduction. This report of enzootic A. cantonensis infection in wild rats and snails in Shenzhen demonstrates the existence of natural origins of infection with A. cantonensis for humans in this city. 
 
Persons in Shenzhen eat raw or undercooked freshwater and terrestrial snails and slugs. This practice provides 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 officials, epidemiologists, researchers, clinical 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.


Enzootic Angiostrongyliasis in Shenzhen, China
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 fi sh, 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)(2)(3)(4)(5)(6)(7)(8)(9).
Shenzhen municipality is situated in the most southern part of mainland People's Republic of China between 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 Administrative Region, China, in the south. The climate is subtropical, with an average annual temperature of 23.7 °C. The city is 1,952.84 km 2 and has a population of 10 million.
Since 2006, thirty-two sporadic cases of human eosinophilic meningitis caused by consumption of undercooked aquacultured snails have been documented in Shenzhen (Shenzhen Center for Disease Control and Prevention, unpub. data). To identify the source of these infections and assess the risk for an outbreak of eosinophilic meningitis, we conducted a survey to investigate whether A. cantonensis occurs in wild rats and snails in Shenzhen.
To examine A. cantonensis infection in intermediate host snails, 302 terrestrial snails (Achatina fulica) were collected from 10 investigation sites across Shenzhen, and 314 freshwater 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 positive for A. cantonensis were found. These rats were examined for the presence 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 average 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. cantonensis adults were recovered from the cardiopulmonary systems of 37 (12%) of 308 examined rats. Infection rate for R. norvegicus rats was 16.6% (31/187), signifi cantly higher (p<0.01) than that for R. fl avipectus (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. Infection 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 enzootic A. cantonensis infection in wild rats and snails in Shenzhen demonstrates the existence of natural origins of infection with A. cantonensis for humans in this city.
Persons in Shenzhen eat raw or undercooked freshwater and terrestrial snails and slugs. This practice provides 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, clinical 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.  (1). Four of these deaths occurred in Turkey in 2006. Understanding gaps in the public's knowledge about avian infl uenza risks and transmission provides 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 unnecessarily 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 countries in the European Union, Croatia, and Turkey about their knowledge of avian infl uenza risks (2). Eurobarometer surveys are undertaken by the European Commission to monitor the EU public's social and political opinions. The survey was conducted on a multistage random sampling basis. Therefore, the sample is representative of the whole territory surveyed. Each country's population was randomly sampled according to rural, metropolitan, 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 standard random route procedures, beginning with a randomly selected initial address. The survey was conducted by face-to-face interviews in respondents' 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 European cases of avian infl uenza (H5N1) were found in October 2005 in Turkey; 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 eldwork 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 questions about their knowledge of the risks humans face regarding avian infl uenza (Table). When we looked at these results with the aim of setting future public health information campaign objectives, we considered incorrect or "don't know" responses to indicate public health information campaign failures. Uncertainty regarding avian infl uenza risks appeared to involve consumption of eggs and vaccinated, cooked poultry and whether the virus can be transmitted between humans. However, for all questions asked, more than half of the respondents answered correctly except when asked about eating poultry that had been vaccinated against avian infl uenza. This question also had the highest number of "don't know" responses. Respondents are most knowledgeable about the preventive measure of culling chickens, perhaps because of the media attention these events attract. 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 incorrectly or "don't know" to questions about poultry and egg consumption