Orientogalba, Kruglov & Starobogatov, 1985

Juh, A., asz, Nkolokosa, C., Kambewa, E., Jones, S., Cunningham, L. J., Chammudzi, P., Kapira, D., Namacha, G., Lally, D., Kayuni, S. A., Makaula, P., Musaya, J. & Stothard, J. R., 2024, An alien intermediate snail host in Malawi - Orientogalba viridis (Quoy and Gaimard, 1832) - A new concern for schistosomiasis transmission in Africa?, International Journal for Parasitology: Parasites and Wildlife 23, pp. 100919-100919 : 100919-

2.1. The first encounter with Orientogalba

In May 2023, following a general malacological survey for intermediate snail hosts of schistosomiasis in Chikwawa District, Malawi, Central Africa, an unusual lymnaeid, superficially resembling Galba spp. , was first noted at (S16.02528 ◦, E34.82106 ◦) within a spring-fed rice paddy. Numerous snails were observed on moist mud in between plants ( Fig. 1 ). In total, 12 snails were collected, then placed in 100 ml of mineral water for inspection of shedding trematode cercariae which, later in that day, revealed an alarming presence of a single motile schistosome cercaria. This cercaria could not be readily explained as a contaminating artefact from environmental water, and likely originated from the snails themselves, though we acknowledge a possibility it may have been adhered to a shell. This larva was immediately harvested unto an FTA® card, subjected to DNA barcoding and was later confirmed as Schistosoma haematobium using protocols described by Webster et al. (2013). Inspecting surviving snails (n = 8) the following day for shedding cercariae did not yield any further evidence of patent infection(s).

Alerted to this alarming concern for schistosomiasis transmission, in July 2023, 465 snails were collected around the edges of the same rice paddy. Water temperature was 26.0 ◦ C, pH was 9.5, conductivity (uS) was 737.5 and total dissolved salts (ppm) was 370.5. Collected snails were placed in mineral water for inspection of shedding of trematode cercariae. In total, 25 dissected snails were euthanized by emersion in boiling water for 3 min, loosening the columellar muscle, allowing the soft body to be extracted from the shell with hooked metal forceps. The empty shells were cleaned, dried and preserved at room temperature for shell morphometrics. Snails macroscopically resembled Orientogalba spp .. Under the microscope, all dissected snails proved not to be infected with trematodes and were fully developed adults, according to the maturity of their genital organs. The genital structure was dissected out of the soft body and measured using a stereo microscope ( Fig. 2A, B, C, D ). The buccal mass was dissected out and digested in lactic acid for 48 h to free the radula from snail tissues and then examined under the compound microscope ( Fig. 2E ). A total evidence approach was taken to assess each character against the current lymnaeid literature, as there is no reliable species-specific morphological key.

Figures

Fig. 1. Site photo of the location where O. viridis was first encountered. Numerous snails were found on mud within the rice paddy [large inset] and, of particular note, a single schistosome cercaria of S. haematobium was observed upon microscopy and photographed [small inset] and confirmed by DNA barcoding. This rice paddy was immediately adjacent to a small oxbow lake, where children were seen swimming and numerous Bulinus were found but these snails were not observed to shed schistosome cercariae at the time of first survey in May 2023.

Fig. 2. A) Shell, scale bar: 3 mm; B) mantle pigmentation, scale bar: 3 mm; C) bursa copulatrix, scale bar: 2 mm; D) penis, ratio of penis sheath (ps)/preputium (pp) ~1, overall length 0.5 cm; E) radula, scale bar: 10 μm; F) experimental infection with S. haematobium with miracidia highlighted within red elipses with unaltered swimming around the snail’s body. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)