Introduction
The giant African land snail, Achatina (Lissachatina) fulica Bowdich, 1822, is an invasive species of terrestrial gastropod native to East Africa. Vijayan et al. (Reference Vijayan, Suganthasakthivel, Sajeev, Soorae, Naggs and Wade2020), provide a brief history of the worldwide invasion of A. fulica, which shows that this species began to disperse from the African continent in around 1800, primarily through human activities, first reaching the islands of Mauritius or Madagascar, and from there, the Comoros, Seychelles and Reunion archipelagos. In around 1847, the species was introduced from Mauritius to India, where it spread subsequently throughout the Asian continent during the first half of the twentieth century, in particular during the Second World War, when it reached many Asian countries and several islands in the Pacific and Indian Oceans (Vijayan et al., Reference Vijayan, Suganthasakthivel, Sajeev, Soorae, Naggs and Wade2020). Achatina fulica arrived in South America in the 1980s, being first recorded in Brazil (Darrigran et al., Reference Darrigran, Agudo-Padrón and Baez2020). During this same period, the species was also recorded in the West Indies (Fontanilla et al., Reference Fontanilla, Sta Maria, Garcia, Ghate, Naggs and Wade2014), and there are two records of its introduction into the United States, in Hawai'i in 1936 (Mead, Reference Mead1961) and Florida in 1966 (Roda et al., Reference Roda, Nachman, Weihman, Yong Cong and Zimmerman2016). Achatina fulica is now present in Africa, the Americas, East and South Asia and Oceania (Thiengo et al., Reference Thiengo, Farraco, Salgado, Cowie and Fernandez2007), with records from 52 countries around the world (Vijayan et al., Reference Vijayan, Suganthasakthivel, Sajeev, Soorae, Naggs and Wade2020).
Achatina fulica is considered to be a synanthropic species, that is, an organism found typically in environments modified by humans (Simião & Fischer, Reference Simião and Fischer2004; Fischer & Colley, Reference Fischer and Colley2005; Silva et al., Reference Silva, Santos, Melo and Jeraldo2020), although it can also occur in tropical forests, where it competes for food and space with the endemic fauna (Raut & Barker, Reference Raut, Barker and Barker2002; Simião & Fischer, Reference Simião and Fischer2004). In urban zones, A. fulica is found primarily in humid and shaded environments that lack adequate sanitation, often in direct contact with trash and sewage outlets, which are also conditions that favours the ocurrence of synanthropic rodents (Silva et al., Reference Silva, Thiengo, Menezes, Melo and Jeraldo2022). These are anthropogenic conditions, which are invariably found observed in urban areas, and favourthe proliferation of A. fulica (Silva et al., Reference Silva, Santos, Melo and Jeraldo2020, Reference Silva, Thiengo, Menezes, Melo and Jeraldo2022).
Given its accelerated population growth, self-fecundation and high rates of dispersion, A. fulica is capable of colonizing many novel types of environments (Dickens et al., Reference Dickens, Capinera and Smith2018; Lima et al., Reference Lima, Cruz, Samasquini, Mesquita, Medeiros, Pacheco and Souza2020). This snail is also resistant to warmer and drier periods, and is most active during cooler, rainy days, especially at night (Eston et al., Reference Eston, Menezes, Antunes, Santos and Santos2006; Almeida et al., Reference Almeida, Pereira and Lima2016). In fact, the active presence of A. fulica in the environment is related directly to rainy days and more humid conditions (Silva et al., Reference Silva, Santos, Melo and Jeraldo2020). This snail also has an extremely diverse diet that includes approximately 500 different plant species, which may reduce the availability of resources for the native fauna, as well as impacting agricultural crops (Thiengo et al., Reference Thiengo, Farraco, Salgado, Cowie and Fernandez2007; Fischer & Costa, Reference Fischer and Costa2010).
Grewal et al. (Reference Grewal, Grewal, Tan and Adams2003) reported that terrestrial molluscs, including A. fulica, are associated with many different species of nematodes, generally acting as the intermediate host, with part of the life cycle of the parasite being completed in the snail or slug. In other cases, the mollusc may be the definitive host, with the juvenile nematode developing in the body cavity or tissue of the foot muscle, and the adults living freely. Some nematodes may even complete their life cycle in the mollusc, which in some cases may lead to the death of the host (Grewal et al., Reference Grewal, Grewal, Tan and Adams2003). The molluscs may even act as paratenic hosts, transporting a larval stage from one host to the next without undergoing any type of development (Anderson, Reference Anderson2000).
Given the current global distribution of A. fulica, and the threats that the presence of this snail pose to public health, local biodiversity, and agriculture, we carried out a comprehensive literature review to identify the nematode species that have been found in association with A. fulica in different countries around the world. We also summarize the principal methods used to extract and to identify these species of nematodes, the larval stages of the nematodes found in A. fulica, as well as the type of environment occupied by this molluck and the specimen collection methods.
Material and methods
The present study was based on a comprehensive and integrated literature search, which was descriptive, exploratory and qualitative. This approach permits the systematic analysis of the data available on a specific topic based on the summarization of the results of previous studies (Soares et al., Reference Soares, Hoga, Peduzzi, Sangaleti, Yonekura and Silva2014). The present study focused on the following question: ‘Worldwide, which nematodes of interest to public health or veterinary medicine have been found parasitizing A. fulica?’.
The papers were selected according to specific criteria of both inclusion and exclusion. The inclusion criteria were full scientific papers that describe nematodes found infecting A. fulica naturally anywhere in the world, and include the key words presented below. The exclusion criteria included personal communications, abstracts of congresses and other events, reviews and studies that did not focus specifically on the themes or topics proposed for this review.
The literature search focused on five online databases: Scientific Electronic Library Online (SciELO); Scopus (Elsevier); LILACS (Latin American and Caribbean Life Sciences Literature); PubMed; and Google Scholar. The search was based on the following key words (in Portuguese and English): (a) Achatina fulica AND nematode OR zoonosis; (b) Achatina fulica AND nematode; (c) Achatina fulica AND Nematoda; (d) Achatina fulica AND parasite; and (d) Achatina fulica AND parasitosis. The Boolean operator AND was used to recuperate papers that contained both key words, while OR was used to amplify the search and guarantee the inclusion of the different key words selected for the study. The literature search was conducted between March and June 2021.
Once the papers were identified, the primary studies were selected based on the proposed research question and the inclusion criteria defined above. The papers were initially analysed according to the search criteria, being identified by the contents of their titles and abstracts, as defined in each database. The papers were then processed manually to eliminate duplicates, before being read in full to determine their eligibility and the data they contained. This identified the papers that would make up the final (analytical) sample. A set of information was extracted from each study and standardized for analysis, being presented in tables. This information included the locality from which the A. fulica specimens were collected, the procedure used to extract the nematodes from the mollusc, the method used to identify the nematode species (morphology, histology and molecular biology), the nematode development stage (larva/adult), the type of environment in which the molluscs were found (anthropogenic or sylvatic) and the method used to capture the specimens.
A few papers were added manually, including full articles that identified the infection of A. fulica by some nematodes but were not found during our previous search (table 1 – online supplementary appendix table S2). The remaining papers were not complete, but as they presented reports of A. fulica being infected by Angiostrongylus cantonensis in countries not identified in our search, they were included in the production of the map (countries in which A. fulica specimens infected naturally with nematodes have been collected), but not in table 1 or online supplementary appendix table S2.
Table 1. Methods used to extract and identify the nematode larvae released from Achatina fulica in the papers surveyed.
a AC = Acre; AM = Amazonas; AP = Amapá; BA = Bahia; ES = Espírito Santo; GO = Goiás; MG = Minas Gerais; MS = Mato Grosso do Sul; MT = Mato Grosso; PA = Pará; PE = Pernambuco; PR = Paraná; RJ = Rio de Janeiro; SC = Santa Catarina; SE = Sergipe; and SP = São Paulo.
* Articles and countries manually included.
** It was not specified whether it was artificial digestion by HCl or pepsin.
The selected papers for analysis were read and evaluated independently by two different groups of reviewers, in order to better select the most appropriate studies for inclusion in the analysis and to better evaluate information obtained from them.
The data were analysed in the Statistical Package for the Social Sciences (SPSS) 22.0, with the results being summarized as absolute and relative frequencies. The variation in the frequency of studies (a) using the different methods for the detection of the nematodes, (b) capturing snails during the daylight or nighttime periods, and (c) reporting different nematode species was evaluated using Pearson's Chi-square, with a P < 0.05 significance level being considered in all cases.
Results
Characteristics of the studies
The literature search identified a total of 20,690 papers based on the data analysed, with a subsample of 168 files selected for further analysis after analysis of all titles and abstracts. One hundered of these papers were read in full, of which, five were manually included. After that, thrity papers were excluded because they did not satisfy the inclusion criteria, that is, they did not provide an adequate approach to the primary question raised in the present study. This left 70 papers, which were analysed completely, according to the inclusion criteria (fig. 1). The earliest paper was published in 1965, and the most recent, in 2021, with a progressive increase in the number of papers published after 2010, reaching a peak (n = 8) in 2019. The studies identified in this search were concentrated in Southeast Asia, the Americas and the basins of the Pacific and Indian Oceans (Robinson, Reference Robinson2000), with the largest number of publications (25) being from Brazil (Caldeira et al., Reference Caldeira, Mendonça and Goveia2007; Thiengo et al., Reference Thiengo, Fernandez, Torres, Coelho and Lanfredi2008; Barbosa et al., Reference Barbosa, Thiengo and Fernandez2020; Silva et al., Reference Silva, Santos, Melo and Jeraldo2020; Ramos-de-Souza et al., Reference Ramos-de-Souza, Maldonado, Vilela, Andrade-Silva, Barbosa, Gomes and Thiengo2021) (table 1) fig. 2.
Fig. 1. Flowchart of the procedural steps of the present study.
Fig. 2. Number of papers included in the present study.
Nematodes found infecting A. fulica and their geographical distribution
Significant variation (P = 0.001) was found in the number of papers published on the different species of nematode found infecting A. fulica, with the largest number of papers referring to A. cantonensis (Chen, 1935), primarily in the countries of Asia (n = 14) and South America (n = 15). In Asia, A. fulica infected with A. cantonensis were recorded in Taiwan, Thailand, Japan, Malaysia, Indonesia, Philippines, China and Singapore (Lim & Heyneman, Reference Lim and Heyneman1965; Bisseru, Reference Bisseru1971; Stafford et al., Reference Stafford, Sukeri and Sutanti1976; Lv et al., Reference Lv, Zhang and Liu2009; Hu et al., Reference Hu, Du, Tong, Wang, Liu, Li and He2011; Deng et al., Reference Deng, Zhang, Huang and Jones2012; Yang et al., Reference Yang, Qu and He2012; Constantino-Santos et al., Reference Constantino-Santos, Basiao, Wade, Santos and Fontanilla2014a; Kim et al., Reference Kim, Hayes, Yeung and Cowie2014; Song et al., Reference Song, Wang, Yang, Lv and Wu2016; Peng et al., Reference Peng, He and Zhang2017) while in South America, this nematode has been recorded in Brazil, Colombia and Ecuador (Thiengo et al., Reference Thiengo, Maldonado and Mota2010; Giraldo et al., Reference Giraldo, Garzón, Castillo and Córdoba-Rojas2019; Solórzano-Alava et al., Reference Solórzano-Alava, Sánchez-Amador and Valverde2019). Angiostrongylus cantonensis was also recorded in Cuba and Guadalupe (n = 3) in the Caribbean (Vázquez & Sanchez, Reference Vázquez and Sánchez2015; Dard et al., Reference Dard, Piloquet, Qvarnstrom, Fox, M'kada, Hebert, Mattera and Harrois2017), in Florida, (n = 6) in North America (Smith et al., Reference Smith, Howe, Dickens, Stanley, Brito and Inserra2015) and in Hawai'i, in the Pacific Ocean (n = 1), and in the Mariana Islands (Wallace & Rosen, Reference Wallace and Rosen1969; Kim et al., Reference Kim, Hayes, Yeung and Cowie2014), Papua New Guinea (Scrimgeour & Welch, Reference Scrimgeour and Welch1984), French Polynesia (Fontanilla & Wade, Reference Fontanilla and Wade2012) and Micronesia (Kim et al., Reference Kim, Hayes, Yeung and Cowie2014) in Oceania. There were also four records from Africa – Nigeria, Cameroon, and the French island dependencies of Mayotte and Réunion (Picot et al., Reference Picot, Lavarde and Grillot1976; Epelboin et al., Reference Epelboin, Blondé and Chamouine2016; Igbinosa et al., Reference Igbinosa, Isaac, Adamu and Adeleke2016; Meffowoet et al., Reference Meffowoet, Kouam, Tchakounte and Kana2020) (fig. 3, table 1).
Fig. 3. The countries in which Achatina fulica specimens infected naturally with nematodes have been collected.
Note: Indonesia, Taiwan, the Mariana Islands (USA), Micronesia, the Ogasawara Islands and Okinawa are all mentioned in the appendix of Kim et al. (Reference Kim, Hayes, Yeung and Cowie2014) and Réunion Island is mentioned by Picot et al. (Reference Picot, Lavarde and Grillot1976).
Other metastrongylid species were also recorded infesting A. fulica, including Aelurostrongylus abstrusus (Railliet, 1898), in Brazil, Argentina and Colombia (n = 8) (Thiengo et al., Reference Thiengo, Fernandez, Torres, Coelho and Lanfredi2008; Oliveira et al., Reference Oliveira, Torres, Maldonado, Araujo, Fernandez and Thiengo2010; Andrade-Porto et al., Reference Andrade-Porto, Souza, Cárdenas, Roque, Pimpão, Araújo and Malta2012; Valente et al., Reference Valente, Diaz, Salomón and Navone2017; Lima & Guilherme, Reference Lima and Guilherme2018; Penagos-Tabares et al., Reference Penagos-Tabares, Lange, Vélez, Hirzmann, Gutiérrez-Arboleda, Taubert, Hermosilla and Chaparro Gutiérrez2019), Angiostrongylus vasorum (Baillet, 1866) in two studies from Colombia (Lange et al., Reference Lange, Penagos-Tabares, Vélez, Gutiérrez, Hirzmann, Chaparro-Gutiérrez, Piedrahita, Taubert and Hermosilla2018; Penagos-tabares et al., Reference Penagos-Tabares, Lange, Vélez, Hirzmann, Gutiérrez-Arboleda, Taubert, Hermosilla and Chaparro Gutiérrez2019) and Angiostrongylus malaysiensis Bhaibulaya and Cross 1971 in two studies from Thailand and one in Malaysia (Lim et al., Reference Lim, Lim, Cheah and Yap1976; Dumidae et al., Reference Dumidae, Janthu, Subkrasae, Dekumyoy, Thanwisai and Vitta2019; Jakkul et al., Reference Jakkul, Chaisiri, Saralamba, Limpanont, Dusitsittipon, Charoennitiwat, Chan and Thaenkham2021). No records of natural infection by Angiostrongylus costaricensis Morera and Céspedes, 1971 were found in any of the papers examined in the present study.
A number of other nematode species were found in association with A. fulica (fig. 3; table 1), such as Cruzia tentaculata (Rud, 1819), which was recorded in Brazil (Ramos-de-Souza et al., Reference Ramos-de-Souza, Maldonado, Vilela, Andrade-Silva, Barbosa, Gomes and Thiengo2021), Ancylostoma caninum (Ercolani, 1859), found in both the Philippines and Brazil (Constantino-Santos et al., Reference Constantino-Santos, Basiao, Wade, Santos and Fontanilla2014a; Orico et al., Reference Orico, Barbosa, Luca, Soares and Gregori2019) and Strongyluris sp., with 11 records in Brazil and Argentina (Franco-Acuña et al., Reference Franco-Acuña, Pinheiro, Torres, Lanfredi and Brandolini2009; Maldonado et al., Reference Maldonado, Simões, Oliveira, Motta, Fernandez, Pereira, Monteiro, Torres and Thiengo2010; Oliveira et al., Reference Oliveira, Torres, Maldonado, Araujo, Fernandez and Thiengo2010; Lima & Guilherme, Reference Lima and Guilherme2018; Oliveira & Santos, Reference Oliveira and Santos2018; Ramos-de-Souza et al., Reference Ramos-de-Souza, Thiengo and Fernandez2018; Oda et al., Reference Oda, da Graça, Lima, Alvarenga and Takemoto2020). In addition, some larvae were also reported in the faeces of A. fulica, not actually configuring mollusc infection. Some examples are: Rhabditis sp. found in faeces and mucus of A. fulica in five studies in Italy and Brazil (Oliveira et al., Reference Oliveira, Gentile, Maldonado, Lopes Torres and Thiengo2015; d’Ovidio et al., Reference d'Ovidio, Nermut, Adami and Santoro2019; Silva et al., Reference Silva, Santos, Melo and Jeraldo2020); Trichuris sp., eggs of Ascaris sp. (n = 2) and larvae of Strongyloides stercoralis Bavay, 1876 (n = 02) found in faeces of A. fulica in Venezuela (Amaya et al., Reference Amaya, Fajardo, Morel, Blanco and Devera2014; Meffowoet et al., Reference Meffowoet, Kouam, Tchakounte and Kana2020); larvae of Strongyloides sp. recorded in faeces of A. fulica in Ecuador (Cuasapaz-Sarabia , Reference Cuasapaz-Sarabia2016); and larvae of Oslerus osleri (Cobbold, 1879) in the Philippines (Constantino-Santos et al., Reference Constantino-Santos, Santos, Soriano, Dy and Fontanilla2014b). In most cases (n = 42), the nematodes were present in larval stage L3.
Methods used to collect and identify the nematodes
Artificial digestion was the method most used in 39 studies, making this method significantly (P < 0.031) more frequent than any other (table 1). This technique involves the digestion of the A. fulica tissue in a solution of hydrochloric acid (HCl), with the resulting liquid being sedimented in a Baermann funnel for the isolation of the nematode larvae (Lim & Heyneman, Reference Lim and Heyneman1965; Maldonado et al., Reference Maldonado, Simões, Oliveira, Motta, Fernandez, Pereira, Monteiro, Torres and Thiengo2010; Thiengo et al., Reference Thiengo, Maldonado and Mota2010; Zanol et al., Reference Zanol, Fernandez, Oliveira, Russo and Thiengo2010; Rollins et al., Reference Rollins, Cowie, Echaluse and Medeiros2021; Souza et al., Reference Souza, Santos and Alves2021). Other methods were also used to extract the nematodes, including artificial digestion with pepsin (n = 19 studies), which was most frequent (n = 14) in Asia (Noda et al., Reference Noda, Uchikawa, Matayoshi, Watanabe and Sato1987; Tujan et al., Reference Tujan, Angelica, Fontanilla and Paller2016; Lange et al., Reference Lange, Penagos-Tabares, Vélez, Gutiérrez, Hirzmann, Chaparro-Gutiérrez, Piedrahita, Taubert and Hermosilla2018; Penagos-Tabares et al., Reference Penagos-Tabares, Lange, Vélez, Hirzmann, Gutiérrez-Arboleda, Taubert, Hermosilla and Chaparro Gutiérrez2019; Jakkul et al., Reference Jakkul, Chaisiri, Saralamba, Limpanont, Dusitsittipon, Charoennitiwat, Chan and Thaenkham2021). These two techniques, in a solution of HCl or pepsin were also more frequently used in South America, being significantly more used (P < 0.001) when compared to other methods. However, it was observed that articles generally do not report the activity of HCl and pepsin, which prevents any reliable standardization and evaluation of the effectiveness of the digestive solution. The parasitological examination of the mucous and faeces was also used in three studies (Amaya et al., Reference Amaya, Fajardo, Morel, Blanco and Devera2014; Morocoima et al., Reference Morocoima, Rodríguez, Rivas, Coriano, Rivero, Errante, Mitchell, Herrera and Urdaneta-Morales2014; Silva et al., Reference Silva, Santos, Melo and Jeraldo2020). The application of saline to the mantle (Deng et al., Reference Deng, Zhang, Huang and Jones2012; Vázquez & Sánchez, Reference Vázquez and Sánchez2015) was most used in North America (n = 4) and once in Malaysia (table 1).
In a majority of the studies (50 papers), the nematodes were identified based on the analysis of their external morphology (table 1), with 13 of these studies employing experimental infection (Lim & Heyneman, Reference Lim and Heyneman1965; Thiengo et al., Reference Thiengo, Maldonado and Mota2010; Oliveira et al., Reference Oliveira, Gentile, Maldonado, Lopes Torres and Thiengo2015; Tomaz et al., Reference Tomaz, Gentile, Garcia, Teixeira and Faro2018) and three, morphometry (Maldonado et al., Reference Maldonado, Simões, Oliveira, Motta, Fernandez, Pereira, Monteiro, Torres and Thiengo2010; Smith et al., Reference Smith, Howe, Dickens, Stanley, Brito and Inserra2015; Guerino et al., Reference Guerino, Pecora, Miranda, Aguiar-Silva, Carvalho, Caldeira and Silva2017). Molecular methods (polymerase chain reaction (PCR) and the sequencing of molecular markers) were also used (n = 29 papers), in particular in Brazil (Caldeira et al., Reference Caldeira, Mendonça and Goveia2007; Thiengo et al., Reference Thiengo, Maldonado and Mota2010; Carvalho et al., Reference Carvalho, Scholte, Mendonça, Passos and Caldeira2012; Guerino et al., Reference Guerino, Pecora, Miranda, Aguiar-Silva, Carvalho, Caldeira and Silva2017; Orico et al., Reference Orico, Barbosa, Luca, Soares and Gregori2019; Barbosa et al., Reference Barbosa, Thiengo and Fernandez2020).
Habitats, methods and the period during which the A. fulica specimens were collected
The infected giant African land snails were collected principally in anthropogenic environments (both urban and rural), with specific characteristics, such as the front and back gardens of houses (peri-domestic environment), public parks, vacant lots and abandoned sites containing piles of trash and building rubble (Smith et al., Reference Smith, Howe, Dickens, Stanley, Brito and Inserra2015; Vázquez & Sánchez, Reference Vázquez and Sánchez2015; Epelboin et al., Reference Epelboin, Blondé and Chamouine2016; Dard et al., Reference Dard, Piloquet, Qvarnstrom, Fox, M'kada, Hebert, Mattera and Harrois2017; Meijides-Mejías & Robledo, Reference Meijides-Mejías and Robledo2019; Pérez et al., Reference Pérez, Mejías, Robledo, del Vallín, Viel, Pérez, González, Contreras and Robles2019). Only a few studies (n = 7) refer to the capture of A. fulica specimens in the rural zone (Lim & Heyneman, Reference Lim and Heyneman1965; Noda et al., Reference Noda, Uchikawa, Matayoshi, Watanabe and Sato1987; Lv et al., Reference Lv, Zhang and Liu2009; Hu et al., Reference Hu, Du, Tong, Wang, Liu, Li and He2011; Andrade-Porto et al., Reference Andrade-Porto, Souza, Cárdenas, Roque, Pimpão, Araújo and Malta2012; Tujan et al., Reference Tujan, Angelica, Fontanilla and Paller2016; Oda et al., Reference Oda, da Graça, Lima, Alvarenga and Takemoto2020), where the snails were collected from plantations of rice (Oryza sp.), rubber trees (Hevea brasiliensis (Willd. ex A. Juss.) Müll. Arg.) (Lim & Heyneman, Reference Lim and Heyneman1965), sugarcane (Saccharum sp.) (Noda et al., Reference Noda, Uchikawa, Matayoshi, Watanabe and Sato1987), cassava (Manihot esculenta Crantz) and papaya (Carica papaya L.) (Andrade-Porto et al., Reference Andrade-Porto, Souza, Cárdenas, Roque, Pimpão, Araújo and Malta2012) (supplementary file table S2).
In most studies (n = 58), A. fulica was captured manually, with no detailed description being provided on the search time or the area surveyed. In a few cases (n = 6), the snails were captured manually in fixed plots (Lv et al., Reference Lv, Zhang and Liu2009; Moreira et al., Reference Moreira, Giese, Melo, Simões, Thiengo, Maldonado and Santos2013; Oliveira et al., Reference Oliveira, Gentile, Maldonado, Lopes Torres and Thiengo2015; Vázquez & Sánchez, Reference Vázquez and Sánchez2015; Córdoba-R et al., Reference Córdoba-R, Patiño-Montoya A and Giraldo2017; Silva et al., Reference Silva, Santos, Melo and Jeraldo2020) or capture rates were presented per unit of sampling effort (n = 3) (Cuasapaz-Sarabia, Reference Cuasapaz-Sarabia2016; Solórzano-Alava et al., Reference Solórzano-Alava, Sánchez-Amador and Valverde2019; Silva et al., Reference Silva, Santos, Melo and Jeraldo2020) (online supplementary file table S2).
Significantly (P = 0.007) more studies were based on the collection of specimens during the daylight period (n = 14 papers), in particular in South America (Moreira et al., Reference Moreira, Giese, Melo, Simões, Thiengo, Maldonado and Santos2013; Peng et al., Reference Peng, He and Zhang2017; Bechara et al., Reference Bechara, Simões, Faro and Garcia2018; Ramos-de-Souza et al., Reference Ramos-de-Souza, Thiengo and Fernandez2018; Silva et al., Reference Silva, Santos, Melo and Jeraldo2020; Souza et al., Reference Souza, Santos and Alves2021), with only five surveys being conducted at night (Lim & Heyneman, Reference Lim and Heyneman1965; Morocoima et al., Reference Morocoima, Rodríguez, Rivas, Coriano, Rivero, Errante, Mitchell, Herrera and Urdaneta-Morales2014; Cuasapaz-Sarabia, Reference Cuasapaz-Sarabia2016; Peng et al., Reference Peng, He and Zhang2017; Bechara et al., Reference Bechara, Simões, Faro and Garcia2018), and thirty-two studies did not specify the collection period (online supplementary file table S2). Five studies referred to the collection of specimens during the rainy season (Caldeira et al., Reference Caldeira, Mendonça and Goveia2007; Vitta et al., Reference Vitta, Nateeworanart and Tattiyapong2011; Andrade-Porto et al., Reference Andrade-Porto, Souza, Cárdenas, Roque, Pimpão, Araújo and Malta2012; Cuasapaz-Sarabia, Reference Cuasapaz-Sarabia2016).
Discussion
The present study identified reports of the infection of A. fulica by nematodes between 1965 and 2021, which reflect, in part, the history of the progressive invasion and dispersion of the species in many parts of the world. The earliest studies that reported the association of A. fulica with nematodes were conducted in Asia and Oceania (Malaysia, Papua New Guinea and Japan) between 1965 and 1987, based on the experimental infection of the snail with A. cantonensis. In the Americas, where A. fulica was introduced in the late 1980s, the first study to confirm natural infection with a nematode was published only in 2007 in Brazil, and also involved A. cantonensis. This was also the first report of the occurrence of this nematode in Brazil, where it was also found in a number of terrestrial molluscs. This also coincides with the territorial expansion of A. fulica in Brazil (Thiengo et al., Reference Thiengo, Farraco, Salgado, Cowie and Fernandez2007; Maldonado et al., Reference Maldonado, Simões, Oliveira, Motta, Fernandez, Pereira, Monteiro, Torres and Thiengo2010), and the concomitant growth in the number of studies about this mollusc, especially in Brazil (25 papers), where publications peaked after 2019 (n = 12). Despite 11 nematode species have been recorded parasitizing A. fulica, a majority of the reports refer to A. cantonensis, throughout the world, that is, in Asia, the Americas, Africa and Oceania, and, principally, in Brazil (Caldeira et al., Reference Caldeira, Mendonça and Goveia2007; Thiengo et al., Reference Thiengo, Maldonado and Mota2010) (fig. 4).
Fig. 4. Distribution of the nematodes associated with Achatina fulica in Brazil.
Achatina fulica is believed to have been introduced into Brazil on at least three independent occasions. Two, possibly intentional introductions are known to have occurred, one in Curitiba, in Paraná state, in 1989, and the other in 1998 in Santos, in São Paulo state, for the commercial production of the animals (Teles & Fontes, Reference Teles and Fontes2002; Fischer & Costa, Reference Fischer and Costa2010). There is also a less well documented case from 1975, when a resident of the city of Juiz de Fora, in Minas Gerais state, reported having bought A. fulica breeding stock from an open-air market in an undetermined foreign country (Zanol et al., Reference Zanol, Fernandez, Oliveira, Russo and Thiengo2010). The large distribution of A. cantonensis in Brazil is probably a result of repeated introductions through rat vectors during the colonial period, given the intense trade between this country and both Africa and Asia during this period (Maldonado et al., Reference Maldonado, Simões, Oliveira, Motta, Fernandez, Pereira, Monteiro, Torres and Thiengo2010). It seems likely that the tropical and subtropical climate of Brazil, together with the lack of any adequate intervention for the control of the spread of A. fulica have favoured its role as an intermediate host of nematodes (Maldonado et al., Reference Maldonado, Simões, Oliveira, Motta, Fernandez, Pereira, Monteiro, Torres and Thiengo2010; Thiengo & Fernandez, Reference Thiengo and Fernandez2016). This process would have been accelerated by socio-economic problems, in particular a lack of public sanitation environmental education, which results in the inadequate disposal of domestic residues and effluents.
Achatina fulica has now been recorded in all 26 of the Brazilian states and the Federal District, with the highest infestation rates being recorded in the states of Goiás, São Paulo, Paraná, Rio de Janeiro, Mato Grosso, Espírito Santo and Minas Gerais (Thiengo et al., Reference Thiengo, Farraco, Salgado, Cowie and Fernandez2007). The species was only recently reported in Rio Grande do Sul (RS), where a juvenile specimen was found in the garden of a residential condominium in the city of Porto Alegre (Arruda & Santos, Reference Arruda and Santos2022). The dissemination de A. cantonensis in Brazil is a major public health problem due to the widespread occurrence of infected rats and snails (Thiengo et al., Reference Thiengo, Simões, Fernandez and Maldonado2013). In addition, this parasite is an aetiological agent of eosinophilic meningitis (EM) in humans (Zanol et al., Reference Zanol, Fernandez, Oliveira, Russo and Thiengo2010), with the parasite being transmitted primarily through the ingestion of molluscs infected with L3 larvae (Vitta et al., Reference Vitta, Srisongcra, Thiproaj, Wongma, Polsut, Fukruksa and Dekumyoy2016), which migrate to the brain, where they transform into stage L4 and then die. The reaction to this process provokes serious neurological damage, which may result in coma and even death, in some cases (Graeff-Teixeira et al., Reference Graeff-Teixeira, da Silva and Yoshimura2009; Thiengo et al., Reference Thiengo, Simões, Fernandez and Maldonado2013). Worldwide, more than 2800 human cases of EM caused by A. cantonensis have been reported from more than 30 countries (Wang et al., Reference Wang, Lai, Zhu, Chen and Lun2008) since the first report, from Taiwan, in 1945 (Beaver & Rosen, Reference Beaver and Rosen1964). Eosinophilic meningitis is considered to be an emerging disease in Brazil, with approximately 40 confirmed and 84 suspected cases between 2007 and 2020 (Morassutti et al., Reference Morassutti, Thiengo, Fernandez, Sawanyawisuth and Graeff-Teixeira2014; Cunha, Reference Cunha2017; Barbosa et al., Reference Barbosa, Thiengo and Fernandez2020). In Brazil cases of the disease have been reported in the states of Pernambuco, Espírito Santo, Paraná, Rio de Janeiro, Rio Grande do Sul, São Paulo, Sergipe and Amapá (Caldeira et al., Reference Caldeira, Mendonça and Goveia2007; Thiengo et al., Reference Thiengo, Fernandez, Torres, Coelho and Lanfredi2008, Reference Thiengo, Maldonado and Mota2010; Lima et al., Reference Lima, Mesquita, Santos, Aquino, Rosa, Duarte, Teixeira, Costa and Ferreira2009; Espírito-Santo et al., Reference Espírito-Santo, Pinto, Mota and Gryschek2013; Morassutti et al., Reference Morassutti, Thiengo, Fernandez, Sawanyawisuth and Graeff-Teixeira2014; Cunha, Reference Cunha2017; Ramos-de-Souza et al., Reference Ramos-de-Souza, Thiengo and Fernandez2018; Barbosa et al., Reference Barbosa, Thiengo and Fernandez2020).
Angiostrongylus cantonensis has also been found in association with A. fulica on islands, such as the Hawaiian archipelago (Kim et al., Reference Kim, Hayes, Yeung and Cowie2014) and French Polynesia, in the Pacific Ocean (Fontanilla & Wade, Reference Fontanilla and Wade2012), Mayotte Island, in the Indian Ocean (Epelboin et al., Reference Epelboin, Blondé and Chamouine2016) and the Ilha Grande in Brazil(Oliveira & Santos, Reference Oliveira and Santos2018), in the Atlantic Ocean. This nematode has also been recorded in Ecuador (Solórzano-Alava et al., Reference Solórzano-Alava, Sánchez-Amador and Valverde2019), Cuba (Meijides-Mejías & Robledo, Reference Meijides-Mejías and Robledo2019), Colombia (Giraldo et al., Reference Giraldo, Garzón, Castillo and Córdoba-Rojas2019), the contiguous United States, in Florida (Kwon et al., Reference Kwon, Ferguson, Park, Manuzak, Qvarnstrom, Morgan, Ciminera and Murphy2013; Rollins et al., Reference Rollins, Cowie, Echaluse and Medeiros2021), Thailand (Dumidae et al., Reference Dumidae, Janthu, Subkrasae, Dekumyoy, Thanwisai and Vitta2019; Jakkul et al., Reference Jakkul, Chaisiri, Saralamba, Limpanont, Dusitsittipon, Charoennitiwat, Chan and Thaenkham2021), China (Lv et al., Reference Lv, Zhang and Liu2009), Japan (Matayoshi et al., Reference Matayoshi, Noda and Sato1987; Noda et al., Reference Noda, Uchikawa, Matayoshi, Watanabe and Sato1987), Malaysia (Lim & Heyneman, Reference Lim and Heyneman1965) and the Philippines (Tujan et al., Reference Tujan, Angelica, Fontanilla and Paller2016). In Europe, the single record from Italy was obtained from a study of snails being raised as pets, which evaluated the potential for the transmission of parasites from the animals to humans, and found snails infected with Rhabditis sp. (d’Ovidio et al., Reference d'Ovidio, Nermut, Adami and Santoro2019).
Other studies of the nematodes associated with A. fulica have been conducted on oceanic islands that are French overseas territories, including Guadalupe (Dard et al., Reference Dard, Piloquet, Qvarnstrom, Fox, M'kada, Hebert, Mattera and Harrois2017), Mayotte (Epelboin et al., Reference Epelboin, Blondé and Chamouine2016), French Polynesia (Fontanilla & Wade, Reference Fontanilla and Wade2012) and Réunion (Picot et al., Reference Picot, Lavarde and Grillot1976). Achatina fulica is believed to have played an important role in the introduction of parasites into all these different regions, as well as other areas of the Indian Ocean and many Pacific islands (Alicata, Reference Alicata1966; Robinson, Reference Robinson2000). The dispersal of A. fulica and synanthropic rodents around the world has also contributed to the propagation of A. cantonensis (Civeyrel & Simberloff, Reference Civeyrel and Simberloff1996; Espírito-Santo et al., Reference Espírito-Santo, Pinto, Mota and Gryschek2013). The explosive and uncontrolled expansion of A. fulica populations in Brazil and other parts of the world may have led to a major increase in the number of diseases that are potentially spread by this species (Thiengo et al., Reference Thiengo, Maldonado and Mota2010).
The present study was unable to verify any reports of the natural infection of A. fulica by A. costaricensis. This may be related to the reduced susceptibility of A. fulica to this nematode, given that experimental trials have found low infection rates and a reduced parasite load (Neuhauss et al., Reference Neuhauss, Fitarelli, Romanzini and Graeff-Teixeira2007).
One other nematode that was reported frequently in association with the giant African land snail was A. abstrusus, with records from Brazil (Oliveira et al., Reference Oliveira, Torres, Maldonado, Araujo, Fernandez and Thiengo2010), Colombia (Penagos-tabares et al., Reference Penagos-Tabares, Lange, Vélez, Hirzmann, Gutiérrez-Arboleda, Taubert, Hermosilla and Chaparro Gutiérrez2019) and Argentina (Valente et al., Reference Valente, Diaz, Salomón and Navone2017). This parasite causes severe pneumonia in both wild and domestic felines (Thiengo et al., Reference Thiengo, Fernandez, Torres, Coelho and Lanfredi2008). Lima et al. (Reference Lima, Cruz, Samasquini, Mesquita, Medeiros, Pacheco and Souza2020), recently reviewed the epidemiological evidence on A. abstrusus in Brazil, and identified nine studies that described an association between this nematode and molluscs which were, in all cases, A. fulica. According to Rodrigues et al. (Reference Rodrigues, Gomes, Montresor, Ramos-de-Souza, Barros, Fernandez and Thiengo2022), there is an intense association between this nematode and A. fulica, with 99% of the snails of this species collected from some municipalities of the state of Rio de Janeiro, Brazil, being infected with A. abstrusus.
Two papers recorded A. malaysiensis, which is also considered to be a source of EM, in association with A. fulica in Thailand (Dumidae et al., Reference Dumidae, Janthu, Subkrasae, Dekumyoy, Thanwisai and Vitta2019) and Malaysia (Lim et al., Reference Lim, Lim, Cheah and Yap1976). This nematode was initially identified as a Malaysian strain of A. cantonensis, given the morphological similarities of their larval stages (Jakkul et al., Reference Jakkul, Chaisiri, Saralamba, Limpanont, Dusitsittipon, Charoennitiwat, Chan and Thaenkham2021), although diagnostic differences in their morphology are present in the adult phase (Bhaibulaya, Reference Bhaibulaya1979).
Two reports, both from Colombia, recorded an association between A. fulica and the nematode A. vasorum (Lange et al., Reference Lange, Penagos-Tabares, Vélez, Gutiérrez, Hirzmann, Chaparro-Gutiérrez, Piedrahita, Taubert and Hermosilla2018; Penagos-Tabares et al., Reference Penagos-Tabares, Lange, Vélez, Hirzmann, Gutiérrez-Arboleda, Taubert, Hermosilla and Chaparro Gutiérrez2019). Other papers, based on experimental infection, reported that A. vasorum is a parasite of the pulmonary arteries of wild and domestic canids (Pereira et al., Reference Pereira, Coaglio, Capettini, Becattini, Ferreira, Costa and Lima2020). The reduced number of records of A. vasorum infecting A. fulica naturally may be related to the snail's phenoloxidase enzyme, which may inhibit infection by this nematode, although further research is needed to better define this defence mechanism (Coaglio et al., Reference Coaglio, Mozzer, Corrêa, de Jesus Pereira and dos Santos Lima2016). Angiostrongylus vasorum has been found in other gastropods examined in urban environments (Hicklenton & Betson, Reference Hicklenton and Betson2019), based on PCR sequencing, which detected the presence of the DNA of this nematode in 4.1% (4/97) of the snails and 9.1% (4/44) of the slugs examined.
Geohelminths, such as Caenorhabditis sp. and Rhabditis sp., have also been reported to be associated naturally with A. fulica (Guerrero et al., Reference Guerrero, Rincon-Orozco and Delgado2018; d’Ovidio et al., Reference d'Ovidio, Nermut, Adami and Santoro2019). These helminths may use A. fulica as a phoretic host, by attaching themselves to the snail's mucus to reach new environments or becoming attached accidentally when the snail secretes mucus as it moves. Given this, it is important to note the potential presence of ancylostomids or species of the genus Strongyloides when examining the mucus, faeces or even the digestive tract of molluscs. Protozoa, platyhelminths and bacteria mays also be detected during the examination of the mucus and faeces of these animals (Amaya et al., Reference Amaya, Fajardo, Morel, Blanco and Devera2014; Morocoima et al., Reference Morocoima, Rodríguez, Rivas, Coriano, Rivero, Errante, Mitchell, Herrera and Urdaneta-Morales2014), although the presence of nematodes is not considered to be a natural component of the ecological relationships of these organisms (Ferreira et al., Reference Ferreira, Chieffi and Araujo2012). In most cases, the nematodes are free-living, and normally feed on decomposing organic matter, where they may be ingested accidentally by foraging molluscs. Achatina fulica is a generalist that may exploit any available food source, including fruit and other decomposing matter, in which nematodes are common (Silva et al., Reference Silva, Santos, Melo and Jeraldo2020). The coprological technique may be appropriate for the extraction of some nematode species, but when the animal ingests the nematodes, irrespective of the developmental phase of the parasite, the extraction of these organisms from the faeces does not necessarily imply that the snail plays some role in the life cycle of the nematode, reinforcing the need to distinguish parasitism from phoresia (Ferreira et al., Reference Ferreira, Chieffi and Araujo2012). Larvae in the L3 stage are mentioned most often because of their more developed morphological structures, which are easier to visualize, allowing comparison with published references, but also because experimental infection and morphometry are possible at the L3 stage.
The artificial digestion methods used to extract the nematodes in the papers identified in the present study can be divided into those that used pepsin and those that did not use this enzyme. When HCl is used on its own, the samples must be immersed in the solution for longer to ensure the rupture of the snail tissue to release the nematode larvae (Coaglio et al., Reference Coaglio, Mozzer, Corrêa, de Jesus Pereira and dos Santos Lima2016). The use of pepsin guarantees the more rapid extraction of the larvae, as long as the process occurs at an ideal temperature for enzymatic activity, that is, 37°C (Thiengo et al., Reference Thiengo, Fernandez, Torres, Coelho and Lanfredi2008; Lv et al., Reference Lv, Zhang and Liu2009). Under these conditions, while digestion with pepsin may release the larvae more rapidly, digestion in a 0.7% solution of HCl is effective at room temperature, even though this process takes much longer (Graeff-Teixeira & Morera, Reference Graeff-Teixeira and Morera1995). This procedure is also more cost-effective than methods that use pepsin. One other approach to the extraction of the nematodes was the use of saline solution, although this method is much less effective because it does not dissolve the mollusc tissue (Graeff-Teixeira & Morera, Reference Graeff-Teixeira and Morera1995). The adequate extraction of the larvae is essential for a reliable parasitological analysis of A. fulica, in order to determine the prevalence of the nematodes and the parasite load, as well as the identification of the nematode species. Despite the properties of the solutions used for artificial digestion, such as their acidity, the nematodes, in particular the gastrointestinal forms, are relatively more resistant than the mollusc tissue, and are often extracted alive with no structural damage (Carvalho et al., Reference Carvalho, Scholte, Mendonça, Passos and Caldeira2012).
Most of the studies recorded here identified the nematodes based on their morphology (Lim & Heyneman, Reference Lim and Heyneman1965; Guerino et al., Reference Guerino, Pecora, Miranda, Aguiar-Silva, Carvalho, Caldeira and Silva2017), even though many of the larval characteristics used to diagnose the species are shared by most of the taxa of a given genus (Spratt, Reference Spratt2015), which hampers reliable identification. Some studies also used morphometric parameters and movement patterns to identify the nematodes (Meijides-Mejías & Robledo, Reference Meijides-Mejías and Robledo2019), as a complement to the morphological identification. In this case, an adequate diagnosis requires the analysis of both the males and the females (Oliveira et al., Reference Oliveira, Torres, Maldonado, Araujo, Fernandez and Thiengo2010; Silva et al., Reference Silva, Santos, Melo and Jeraldo2020), which may require the experimental infection (Bechara et al., Reference Bechara, Simões, Faro and Garcia2018) of the definitive host to obtain the largest possible number of diagnostic characteristics. However, it takes approximately 30 days to obtain the adult forms and, ideally, they should be identified by a taxonomic specialist (Carvalho et al., Reference Carvalho, Scholte, Mendonça, Passos and Caldeira2012; Bechara et al., Reference Bechara, Simões, Faro and Garcia2018). The examination of cysts was also used in some cases (Oliveira & Santos, Reference Oliveira and Santos2018), although this may not be adequate for the identification of species, given that some species of different genera may present similar characteristics in the intermediate host. According to many authors such as Valente et al. (Reference Valente, Robles and Diaz2020), the morphological characteristics of the larvae of the genus Angiostrongylus are insufficient for the reliable identification of species. Molecular techniques were used in some studies to identify the nematode species found in A. fulica, using different markers, such as cytochrome c oxidase subunit I (Barbosa et al., Reference Barbosa, Thiengo and Fernandez2020), internal transcribed spacer 1, (Rollins et al., Reference Rollins, Cowie, Echaluse and Medeiros2021), internal transcribed spacer 2 (Thiengo et al., Reference Thiengo, Maldonado and Mota2010) and cytochrome B (Peng et al., Reference Peng, He and Zhang2017). This approach is undoubtedly the most reliable for the identification of the larvae.
In most studies, A. fulica was found in anthropogenic environments, in particular in household gardens, vacant lots and sites with accumulated trash or debris, which favour the proliferation of the snail (Cuasapaz-Sarabia, Reference Cuasapaz-Sarabia2016; Silva et al., Reference Silva, Santos, Melo and Jeraldo2020). Overall, few of the papers identified in the present study referred to the standardization of collection procedures, such as the fixed plot method (Moreira et al., Reference Moreira, Giese, Melo, Simões, Thiengo, Maldonado and Santos2013; Oliveira et al., Reference Oliveira, Gentile, Maldonado, Lopes Torres and Thiengo2015; Córdoba-R et al., Reference Córdoba-R, Patiño-Montoya A and Giraldo2017; Silva et al., Reference Silva, Santos, Melo and Jeraldo2020) or capture per unit of effort (Cuasapaz-Sarabia, Reference Cuasapaz-Sarabia2016; Solórzano-Alava et al., Reference Solórzano-Alava, Sánchez-Amador and Valverde2019; Silva et al., Reference Silva, Santos, Melo and Jeraldo2020). The standardization of sampling procedures is important to ensure the most effective possible evaluation of the impact of A. fulica in a given environment through the systematic comparison of different study sites using indices of abundance and diversity, and the evaluation of environmental parameters. In most cases, in addition, the paper did not specify the period or season of the specimen collection, although a small number did define daylight or nighttime collecting, or searches during the rainy season (Moreira et al., Reference Moreira, Giese, Melo, Simões, Thiengo, Maldonado and Santos2013; Peng et al., Reference Peng, He and Zhang2017).
In addition to being an intermediate host of nematodes that infect domestic animals, A. fulica may also be an intermediate host of the parasites of wild animals, which implies a threat to the local wildlife (Thiengo et al., Reference Thiengo, Fernandez, Torres, Coelho and Lanfredi2008). In particular, Ramos-de-Souza et al. (Reference Ramos-de-Souza, Maldonado, Vilela, Andrade-Silva, Barbosa, Gomes and Thiengo2021), reported the natural infection of A. fulica by C. tentaculata, a parasite of the opossums of the genus Didelphis Linnaeus, 1758.These authors also concluded that larvae of Strongylus sp., which were previously reported infecting terrestrial mollusks in Brazil are actually larvae of C. tentaculata.
Overall, then, the findings of the present study highlight the potentially significant role of the giant African land snail, A. fulica, in the transmission of parasites to both humans and animals, as well as the importance of understanding the relationship between this snail and the environment, its parasites, and their definitive hosts. The present study showed that these parameters are closely related, and should be considered carefully for the best possible diagnosis and control of areas that may be epidemiologically vulnerable, which is consistent with the ‘One Health’ concept, in which human and animal health are seen as interdependent and linked by the local environment (Lerner & Berg, Reference Lerner and Berg2015). The study also provides important insights for the diagnosis of the nematodes found in association with A. fulica, which is fundamentally important for the development of adequate measures for the control and prevention of zoonoses.
Financial support
Coordination of Superior Level Staff Improvement (CAPES), The Brazilian National Council for Scientific and Technological Development (CNPq) and Oswaldo Cruz Foundation (Fiocruz).
Conflicts of interest
The authors declare that they have no conflict of interestrelated to the publication of this manuscript.
Ethical standards
This study fully satisfies the ethical criteria and norms.
Authors’ contributions
Guilherme Mota da Silva: substantial contribution to the concept and design of the study, data collection, data analysis and interpretation, manuscript preparation, contribution to critical revision and adding intellectual content. Silvana Carvalho Thiengo, Verônica L. S Jeraldo and Suzete R. Gomes: substantial contribution to the concept and design of the study, critical revision and adding intellectual content. Matheus I. F. Rego, Alexandre. B. P. Silva and Paulo S. Rodrigues: contribution to data collection, data analysis and interpretation, manuscript preparation, contribution to data analysis and interpretation. All the authors reviewed and approved the definitive version of the manuscript.
Supplementary material
To view supplementary material for this article, please visit https://doi.org/10.1017/S0022149X22000761.
