Caractérisation biologique de Schistosoma haematobium, S. bovis et leurs hybrides chez l’homme et chez les mollusques Bulinus truncatus naturellement infestés, au Centre et Nord de la Côte d’Ivoire.

Objectif : Identifier les espèces Schistosoma haematobium, S. bovis et leurs hybrides et, évaluer la compatibilité des schistosomes avec les mollusques hôtes intermédiaires et la souris blanche (Mus musculus albinos), hôte définitif, en infestation expérimentale. Méthodologie et résultats : Des schistosomes ont été obtenus à partir de bulins infestés naturellement ou expérimentalement avec des miracidiums provenant des urines de l’homme. Ils ont permis d’étudier la compatibilité de quatre populations de Bulinus truncatus avec deux souches du groupe S. haematobium. La chronobiologie cercarienne a été étudiée à partir de quatre tranches horaires : 6-10h, 10-12h, 12-15h et 15- 18h. Des souris blanches infestées expérimentalement, ont été perfusées pour dénombrer les vers adultes. Une meilleure compatibilité schistosome-mollusque a été observée au niveau des infestations sympatriques. Le pic d’émergence cercarienne pour les mollusques naturellement infestés a été observé entre 6-10h, 10h15h et à 15-18h, tandis que celui des bulins infestés expérimentalement a été majoritairement observé entre 10-15h. En termes de nombre de vers collectés, les souris blanches ont été plus permissives aux schistosomes provenant des mollusques naturellement infestés. Conclusion et application des résultats : Les pics d’émergence cercarienne précoce (6-10h) et tardif (15-18h) pourraient être liés à S. bovis, tandis que celui de 10-15h correspondrait à S. haematobium. De même, en raison de la très faible compatibilité connue entre Mus musculus albinos et S. haematobium, les schistosomes auxquels les souris blanches ont été plus permissives sont fort probablement des S. bovis et/ou hybrides S. bovis x S. haematobium. Ainsi, les espèces anthropophiles et celles zoophiles du groupe Schistosoma haematobium peuvent être distinguées de manière routinière par deux approches. La première, en disséquant des souris de laboratoire (Mus musculus albinos) 4 mois après leur mise au contact de l’eau contenant des cercaires obtenues après exposition à la lumière de mollusques infestés prélevés sur le terrain ; la seconde en comparant les profils obtenus après dénombrement des cercaires émises au cours de quatre tranches horaires bien choisies. Mots clés : Bulinus truncatus, Schistosoma haematobium, Schistosoma bovis, Caractérisation, Chronobiologie. Glitho et al., J. Appl. Biosci. 2021 Caractérisation biologique de Schistosoma haematobium, S. bovis et leurs hybrides chez l’homme et chez les mollusques Bulinus truncatus naturellement infestés, au Centre et Nord de la Côte d’Ivoire. 16341 ABSTRACT Objective: Identify the species Schistosoma haematobium, S. bovis and their hybrids; to evaluate the compatibility of schistosomes with intermediate host snails and the white mouse (Mus musculus albinos), the definitive host for experimental infestation. Methodology and results: Schistosomes have been obtained from naturally or experimentally infested snails with miracidiums from human urine. The compatibility of four populations of Bulinus truncatus with two strains of the S. haematobium group was studied. The chronobiology of cercariae was studied in four time slots: 6- 10h, 10-12h, 12-15h and 15-18h. Experimentally infested white mice were perfused and adult worms were collected. A better schistosome-snail compatibility was observed in sympatric infestations. The peak of cercarial emergence for naturally infested snails was at 6-10h, 10h-15h and 15-18h, while that of the snails experimentally infested was mostly observed at 10-15h. In terms of number of worms collected, white mice were more permissive to schistosomes from naturally infested snails. Conclusion and application of results: Early (6-10h) and late (15-18h) cercarial emergence peaks can be related to S. bovis, while the 10-15h peak correspond to S. haematobium. Due to the reported low compatibility between the white mice Mus musculus albinos and S. haematobium, the observed schistosomes permissive to the white mice are most likely S. bovis and/or hybrids S. bovis x S. haematobium. Therefore, anthropophilic and zoophilic species of the Schistosoma haematobium group can be routinely distinguished by two approaches. The first, dissecting laboratory mice (Mus musculus albinos) 4 months after their contact with water containing cercariae obtained after exposure to light from infested snails collected in the field; the second by comparing the profiles obtained after enumeration of cercariae emitted during four well-chosen time slots. Keywords: Bulinus truncatus, Schistosoma haematobium, Schistosoma bovis, hybrid, Characterization, Chronobiology.

A month for the mission: using a sentinel approach to determine the transmission window of digenean cercariae in the subarctic White Sea

In the digenean life cycle the cercaria ensures an important transmission stage, from the first intermediate host to the second or the definitive host. In regions with pronounced seasonality, this process occurs within a certain interval, the transmission window. In high latitudes, the size of transmission window has previously been determined only by comparing data on seasonal dynamics of infection level in various categories of hosts or extrapolating the results of laboratory experiments on cercarial biology to natural conditions. In this study, we evaluated the dynamics of infection of the second intermediate hosts (mussels Mytilus edulis) with cercariae of two digenean species, Himasthla elongata (Himasthlidae) and Cercaria parvicaudata (Renicolidae), at a littoral site at the White Sea by exposing cages with uninfected mussels during the warm season. This is the first such study in a subarctic sea. Mussel infection was observed from May to mid-September, but its intensity was the greatest only for approximately a month, from some moment after 10 July to mid-August, when water temperature was within the optimal range for cercarial emergence in both studied species (15‒20°C). During this time, the mussels accumulated 66.3 ± 6.2% metacercariae of H. elongata and 79.7 ± 5.3% metacercariae of C. parvicaudata out of the total number accumulated during the experimental period. We suggest that climate warming at high latitudes may prolong the period when the water temperatures are optimal for cercariae emergence, thereby intensifying digenean transmission in coastal ecosystems.

Morphological Characterization of Emerging Cercariae among Lymnaeid Snails from Barangay Cawongan, Padre Garcia, Batangas, Philippines

Background and Objectives. Lymnaeid snails are the known intermediate hosts of the liver fluke Fasciola spp. and therefore play an important role in the parasite’s life cycle. The study is conducted to determine specificity of snail host-parasite interaction and to determine the snail-trematode infection rate by cercarial emergence, characterizing the emerging larvae using standardized key. Materials and Methods. A total of 750 snails were collected from a rice field in Barangay Cawongan, Padre Garcia, Batangas, from November 2016 to March 2017 (n=150/month). Preliminary snail identification was based on morphological features of the shell. Each snail was acclimatized for 24 hours in a 50-ml capacity container before being exposed to strong artificial light. The 150 snails collected per month were grouped into 5 batches (n=30/batch) with each batch receiving different number of light exposures. Emerging cercariae were described and characterized using photo-referencing and standardized keys. All statistical tests were performed at p<0.05 level of significance using SPSS ver. 20. Results. The total cercarial shedding rate of the snails studied, as a measure of the infected snails, was found to be 35.6% and was positively associated with the length of the snail shell [OR = 1.809; 95% CI: 1.471–2.225; p<0.001], but not with the weight [OR = 0.003; 95% CI: 0.00–0.275; p=0.012] and width of the shell [OR = 0.937; 95% CI: 0.672–1.305]. The rates varied from 29.3% to 38.0% based on the frequency of 6-hour light exposure. Appearance of encysted forms increased with increasing number of light exposures [OR = 10.27, 95% CI: 3.04–34.76, p<0.001]. Three distinct cercariae were identified, namely, echinostome, longifurcate-pharyngeate distome cercariae (Strigea cercariae), and the virgulate xiphidiocercaria, with 26.4%, 2.27%, and 0.67% infection monitored by cercarial emergence, respectively. Conclusion. Local lymnaeid snails were infected with a single type of trematode larvae and coinfection with multiple larvae was rare but was encountered.

Effect of temperature changes on the cercarial-shedding rate of two trematodes

ABSTRACT Since temperature is a key condition in the initiation of cercarial emergence, the objective of the work reported here was to evaluate the effect of that variable on the shedding of two morphologic and taxonomic types of cercariae. Bioassays were accordingly performed with snails naturally infected with either monostome or pleurolophocercous cercariae because those two cercarial types were found to be the most prevalent in the environment under study. The snails were placed in 6-ml circular plastic dishes with soft plastic stoppers containing 3 ml of reconstituted water and then sequentially exposed for 24 h to a 14:10-h light:dark cycle at 20, 25, or 30 °C. The data were analyzed at a significance level of p <0.05 by means of the InfoStat program. The optimum temperature for cercarial emergence was typically in the range of 25 °C and decreased significantly at 30 °C. We observed no significant difference in the number of cercariae emerging between the two morphologic types.