One of the greatest threats to global biodiversity, livelihoods, human and animal health, agriculture, and the local economy are invasive alien species ¹ . The giant African snail, Achatina fulica, (Bowdich 1822) is a gastropod native to Africa and considered one of the 100 worst invasive alien species in the world ^{2, 3} . Currently, this species is widespread in tropical and subtropical areas on all continents due to the growth of international trade and increased transport that facilitate the introduction of this species, accidentally through agricultural or horticultural products or intentionally as a source of food or as a pet ^{2, 4, 5} .

The giant African snail is recognized as an agricultural and garden pest ⁵ . Its great reproductive capacity allows it to reach high densities and biomass in short times ^{3, 5} , and its broad spectrum herbivorous diet allows it to consume more than 50 species of native and agricultural plants, all of which makes this species a serious pest with the ability to modify habitats and displace native species ⁵ . The giant African snail is an intermediate host for various parasites, among which the nematodes Angiostrongylus cantonensis and Angiostrongylus costaricensis stand out, which cause eosinophilic meningoencephalitis and abdominal angiostrongyliasis in humans, respectively ^{6, 7} . Recently, the presence of A. cantonensis in African snails in Colombian territory was confirmed, putting the population on alert due to the exposure of humans to the parasitic load of this snail, leading to the consideration of eosinophilic meningitis as a possible emerging disease in Colombia ⁸ . Risk factors for infection in humans and pets by this and other nematodes include eating infected snails raw or undercooked, or food contaminated by snail slime or feces ^{9, 10} .

In Colombia, the presence of A. fulica was registered for the first time in 2009 ¹¹ , since then the mollusk has been distributed in more than 20 departments, registering in all regions of the country ¹² . Particularly in the Colombian Caribbean Region, the growth of A. fulica populations has been documented in the department of Sucre ^{12– 14} . In Cartagena, Bolívar, journalistic media reported the presence of the giant African snail south of the city in 2016. However, since its appearance, there has been no scientifically documented record of the presence and distribution of this species in urban areas of the city, as well as its impact on human health. Therefore, the objective of this study was to generate the baseline of reference information on the African snail populations present in the Cartagena city, including the assessment of nematode parasites in the specimens.

During the period studied 204 snails were collected, distributed in four zones of four Cartagena neighborhoods, for which the presence of A. fulica was indicated by the community ( Figure 1). The inspected sites where the snails were collected corresponded principally to extensive gardens and other spaces inside of private properties and residential condominiums (Manga, Las Gavias, and Serena del Mar). At these sites the snails were found in different substrates, such as plants, tree roots, grasses, under litter, flowerpots, and ornamental plants; In Zaragocilla, snails were found aggregated in rubble inside an educational institute.

Overall, 50% of the total material collected corresponded to class 2 snails, followed by class 3 (42.64%) and class 4 (7.35%). In particular, in the Zaragocilla and Las Gavias sites, class 3 individuals predominated with 44.11% and 52.33%, respectively, in Manga, class 2 specimens were more abundant with 73.33% ( Table 1).

Mean size and weight per site is shown in Table 2. The Kruskal-Wallis test showed a significant difference between the sizes of the most abundant African snail population groups (Zaragocilla, Manga, and Las Gavias sites) (p<0.01). Likewise, Bonferroni-adjusted pairwise comparisons indicated that differences existed between each site (p<0.01 between each pairing). The population density established in each point, as well as the estimated biomass according to the calculated total weight, is presented in Table 3.

Regarding the parasitological analyzes, all the observed lungs were found healthy (free of cysts), likewise, no free larvae were observed in the slime or the rest of the soft organs, showing that these specimens were not infected with nematode parasites according to the methodology used.

Understanding the populations of giant African snail present in different areas of Colombia is of great ecological, agricultural, and public health importance. The current study constitutes the first scientifically documented record of the presence of the species A. fulica in urban areas of the city of Cartagena.

It is known that the African snail can reach sizes of up to 300 mm in the length of the shell ¹⁹ . In contrast, other studies establish that the size naturally reached by A. fulica is around 100 mm ^{20, 21} . Even so, the mean values reported are usually much smaller and vary between 30 and 60 mm ^{13, 14, 22– 25} . Comparatively, our results from Cartagena agree with these last values, obtaining average sizes between 36.2–69 mm. Patterns in snail size can reflect the age structure of the population in a given area. It has been proposed that the establishment of A. fulica in new areas takes place in three stages: exponential, known as a long phase with vigorous individuals; stable, with a prevalence of a variable shell size among young and adult, and the decline phase, where young individuals are prevalent ²² . This suggests that the populations obtained from A. fulica collected in Cartagena are in the stable phase, presenting a variety of young and adult individuals.

The population density of A. fulica reported in this study was between 0.0019–0.6818 ind/m ², these density values are similar to those obtained by De la Ossa et al. in studies carried out with snails collected in urban areas of the city of Sincelejo and other municipalities of the department of Sucre, these authors reported densities in a range of 0.0031–0.205 ind/m ^{2 13, 14, 24} . Other similar values were reported in a study performed in Ilha Porchat, Brazil, obtaining a density of 0.07 ind/m ^{2 3} . Investigations such as those carried out in Havana, Cuba, showed a considerably lower density of snails (0.00015 ind/m ²) ²⁶ . In contrast, densities of 1.1–4.6 ind/m ² have been reported in different departments of Colombia ²⁷ , 0.06–8 ind/m ² in Northeast Brazil ²⁸ , and an average of 8.4 ind/m ² in Puyo, Ecuador ²² . On the other hand, studies performed in Puerto Iguazú y Corrientes, Argentina, recorded a much higher average density, which reaches 107.6 ind/m ² and 118.6 ind/m ², respectively ^{15, 29} . It has been mentioned that the areas highly affected by the giant African snail present densities of 10 ind/m ² or more ^{12, 30} ; this similarly occurs with regards to biomass, where devastating values of up to 780 kg/ha are estimated for areas which are highly affected ^{12, 31} . If that is the case, the densities and biomasses obtained in the snail populations of Cartagena are not very harmful.

Nematodes such as A. cantonensis and A. costaricensis cause eosinophilic meningoencephalitis and abdominal angiostrongyliasis, respectively, in humans. The life cycle of these nematodes involves rodents as the definitive host and mollusks of various species, including A. fulica, as intermediate hosts ⁷ . The snails examined in this work did not show evidence of infection by nematode parasites, one of the reasons could be the environment in which these snails were found. It has been noted that the African snail prefers sites such as garbage dumps, landfills, and empty lots, places where there is a greater probability of contact with rats, necessary for the nematodes to complete their life cycle ¹⁷ . In our case, more than 80% of the analyzed snails were collected in gardens of remarkably well-kept properties given the exclusivity of the sites, and according to interviews with various neighbors, rodents do not frequent these spaces.

In conclusion, although the densities of A. fulica estimated do not reach values considered highly harmful, the presence of this invasive species in properties and residential areas of Cartagena is worrying. Most of the snails were found associated with gardens, which suggests that the introduction and dispersal of this species within the city are related to the transport of organic fertilizers or other garden products, which could convert this species into a serious pest. Similarly, although no parasites were found in these snails, it is necessary to continue carrying out studies on the effect of this species on human health, as well as training campaigns on the management and control of the giant African snail in the city.

Figshare: Raw data file_African Snail Project.csv, https://doi.org/10.6084/m9.figshare.13288808 ³² .

This project contains the following underlying data:

Data are available under the terms of the Creative Commons Attribution 4.0 International license (CC-BY 4.0).