3.1 Angiostrongylus cantonensisoutbreaks in Taiwan

Instances of human infection by Angiostrongylus cantonensis have been reported in Taiwan and details of those cases including clinical manifestation, diagnosis and treatments are provided in Table- 1, including whether direct or indirect involvement of gastropod species was reported. The first outbreak in this review occurred during 1968-1969 (Table 1) among whom many patients displayed severe manifestations. Three patients suffered from permanent sequelae from the infection including blindness, and there were four deaths (Yii, 1976). Sequelae were noted in only two other reports; one toddler among the 37 cases presented in Tseng et al. (2011) with weakness in lower limbs, and a 15-year old with pica disorder who presented with urine retention (Hsueh et al., 2013). In addition, a case study of a 66-year old homeless man who presented with neuroangiostrongyliasis in 2022 mentioned transfer of the patient to long term care post-treatment, however the reason for transfer was not clear (Luo et al., 2023).
Children appeared to be more vulnerable to severe manifestations, as well as had greater chances of parasite recovery from the CSF, as seen in the 87 cases of children reviewed by Hwang et al. (1994). They were found to be more likely to get infected, and quicker to manifest symptoms than adults. This implies the large populations of invasive gastropod vectors, including Achatina fulica and Pomaceaspp. pose a high infection risk to children.
Mode of infection appeared to be highly variable among cases (Table 1), where direct consumption of raw Pomacea sp. alone or with wine (Tsai et al., 2001; Wang et al., 2011) as well as boiled Pomaceasp. (http://www.mohw.gov.tw/), and even raw vegetable juice without any apparent involvement of a host (Tsai et al., 2004) have resulted in cases of neuroangiostrongyliasis. Involvement of paratenic hosts in causing infection, such as the Eastern Golden Frog Rana plancyi , which was consumed as Chinese medicine by a 70-year old man, have also been reported (Lai et al., 2007). Interestingly, in a case reported by Wan and Weng (2004), a 10-year old boy displayed intermittent headache, low grade fever, and blurred vision after raisingPomacea spp. as pets, suggesting an indirect infection route.
Since the first reported case in 1945, there has been a number of neuroangiostrongyliasis cases in Taiwan, including four outbreaks. While recently within the past three decades, there have been relatively fewer cases reported, there is still a high risk of infection from consuming raw or undercooked snails, or even through close contact with infected gastropod hosts (Tsai et al., 2013). As seen in Table- 1, a considerable number of cases have resulted from infection through handling or consuming gastropods such as Pomacea canaliculata andAchatina fulica , which may be attributed to the prevalence of these snails in Taiwanese cuisine, or to the large population sizes of these invasive snails. This implies a high prevalence of A. cantonensis among the gastropod species in Taiwan (Banerjee et al., unpublished data).