The biological control of snail intermediate hosts of schistosomiasis by fish

Summary The use of molluscivorous fish for biological control of snail intermediate hosts of schistosomiasis is a regularly reappearing theme in the literature on schistosomiasis control. The effectiveness of this control method has not yet been demonstrated, and conclusive field evidence is lacking. In this article the literature on snail control by fish is critically reviewed. Special attention is paid to the cichlid fish Astatoreochromis alluaudi that has been used in well-documented field trials in Kenya and Cameroon. After some small initial success, after a longer period the fish appeared to be ineffective in snail control. Moreover, the fish reproduces at a pace too slow to be of use in large-scale biocontrol trials. Laboratory observations on foraging behaviour and anatomy of the fish give essential cues to explain the failure of the fish in snail control. An observed reduction in the fishes' pharyngeal jaw apparatus, used to crush snails shells, results in a lower profitability of snails. As predicted by a simple foraging model, the prey preference of the fish shifts towards other more profitable prey items, such as benthic and pelagic macrofauna. Although eradication of snails by fish will not be feasible in most cases, the role of natural predators of snails cannot be neglected, and may still be of importance in integrated control efforts.     

The role of birds as definitive hosts and intermediate hosts of heteroxenous coccidians

Sarcocystis-like oocysts-sporocysts were found in four species of owls (Asio otus, Bubo bubo, Strix aluco, and Tyto alba) and in five species of predatory birds (Accipiter gentilis, Accipiter nisus, Buteo buteo, Circus aeruginosus, Falco tinnunculus). In addition, the muscles of 15 of 41 (36.5%) pheasants (Phasianus colchicus) and one of two jays (Garrulus glandarius) were found to harbor three types of Sarcocystis. Three of 15 (20%) infected pheasants had type I cystozoites (6-8 X 2 microns) in muscle homogenates, but sarcocysts were not seen whereas the other 12 infected pheasants had type II cystozoites (16 X 2-3 microns) and sarcocysts (90 X 600 microns) in their muscles. The one infected jay had type III cystozoites (8-10.5 X 2.5-3 microns) and sarcocysts (35-40 X greater than 770 microns) in its muscles.     

Alkali denaturation of oxyhaemoglobins of some digenetic trematodes and their hosts

Oxyhaemoglobins of six digenetic trematodes,--Srivastavaia indica, Gastrothylax crumenifer, Gigantocotyle explanatum, Fasciolopsis buski, Gastrodiscoides hominis, Isoparorchis hypselobagri, and of their 3 vertebrate hosts, Bubalus bubalis, Sus scrofa, Wallago attu, were subjected to alkali denaturation at a pH of 12.4. All oxyhaemoglobins from trematodes and their hosts differ from each other in the rate and extent of alkali denaturation which may be explained due to variations in the amino acid sequences of a particular haem protein in addition to other factors.     

Review of oribatid mites as intermediate hosts of tapeworms of the Anoplocephalidae

A list of oribatid mites acting as intermediate hosts of tapeworms of the Anoplocephaldae is provided. to date, 127 species of oribatids included in 27 families, are implicated as intermediate hosts of the 14 genera and 27 species of anoplocephalid tapeworms. The most cited mites families are Oribatulidae with 35 species, Galumnidae with 22 species and Ceratozetidae with 15 species. Scheloribates laevigatus (Oribatulidae) is the species that demonstrated most susceptibility, both natural and experimental, to develop larval forms of anoplocephalid tapeworms. A theoretical-methodological model for parasitology based on the trophic characteristics of the intermediate and definitive mammalian hosts is reviewed.     

Small-sized fish as possible seed dispersers: disclosing novel fish and plant species interactions in the Pantanal wetland

ABSTRACT

Seed dispersion is a critical process to vegetation dynamics which is particularly complex in mosaic-like landscapes as the Pantanal wetlands. We analyzed some aspects of ichthyochory in the Pantanal flooded grasslands. The fish were collected and had their whole intestinal contents removed and submitted to suitable germination conditions for 179 days. We collected 661 specimens belonging to 40 species. Feces from Astyanax lacustris, Poptela paraguayensis, Moenkhausia sanctafilomena and Moenkhausia bonita produced 15 seedlings of herbaceous plant of the species Ludwigia inclinata, Ludwigia leptocarpa and a non-identified monocotyledon. A total of 30.4 g of fecal mass was recovered with a rate of 0.49 seedling.gram^?1. There is a positive relation between the number of seedlings obtained and the amount of fish fecal mass (g). Currently, Pantanal landscape dynamics is under rising pressure of field compartmentalization due to man-made roads which restrains fish transit.     

Infection dynamics of Centrocestus armatus cercariae (Digenea: Heterophyidae) to second intermediate fish hosts

The infection dynamics of Centrocestus armatus cercariae with respect to second intermediate fish hosts were investigated using cercariae collected from naturally infected Semisulcospira libertina. Cercariae survival and infectivity were recorded at 2-hr intervals. Survival remained constant but decreased abruptly at 30 hr of age. An age-dependent model presented the best-fit curve for the survival data (r2 0.936), implying that cercariae tended to allocate resources equally among themselves and then died once those resources were depleted. Cercariae infectivity remained constant over the first 10 hr of life and then declined; an age-dependent model also provided a better fit (r2 = 0.956). The transmission rate of C. armatus cercariae to the fish host was relatively low near the time of emergence from the snail host but peaked at 85% after 1 hr and then maintained a plateau period until 5 hr of exposure to fish. The pattern of transmission was also investigated initially at varying densities of cercariae and then by maintaining a constant cercariae density but varying the total number. Results revealed that the pattern of transmission was frequency-dependent.     

Freshwater fishes of thailand as experimental intermediate hosts for Capillaria philippinensis

Bhaibulaya M., Indra-Ngarm S. and Ananthapruti M. 1979. Freshwater fishes of Thailand as experimental intermediate hosts for Capillaria philippinensis. The International Journal for Parasitology9: 105–108. Nine species of freshwater fishes from Thailand have been exposed to infection with embryonated eggs of Capillaria philippinensis. The eggs were fed to fishes with food or through a polyethylene tube. After 10–30 days larvae capable of establishing intestinal capillariasis in Mongolian gerbils were recovered from six fish species: Cyprinus carpio, Puntius gonionotus, Aplocheilus panchax, Gambusia holbrookii, Rasbora borapelensis, and Trichopsis vittatus. Larvae were not recovered from Tilapia nilotica, Osteochilus hasseltii and Trichogaster trichopterus. Five human cases of intestinal capillariasis have been reported from widely scattered areas of Thailand and the natural intermediate and definitive hosts remain to be determined.     

The suitability of several aquatic snails as intermediate hosts for Angiostrongylus cantonensis.

Sixteen species of aquatic snails of four families were tested by quantitative technique under standardized conditions for their suitability as intermediate hosts for Angiostrongylus cantonensis. These species were the planorbid snails Biomphalaria glabrata, Biomphalaria alexandrina, Planorbis planorbis, Planorbis intermixtus, Bulinus truncatus, Bulinus contortus, Bulinus africanus, Bulinus tropicus and Helisoma sp.; the lymnaeid snails Lymnaea natalensis, Lymnaea tomentosa, Lymnaea stagnalis, and Stagnicola elodes; the physid snail Physa acuta (an Egyptian and a German strain) and the ampullariid snails Marisa cornuarietis and Lanistes carinatus. All these snail species proved to be susceptible to infection with A. cantonensis, and first stage larvae reached the infective third stage in all of them. However, the rate and intensity of infection varied with different species. B. glabrata was the most susceptible snail species with a 100% infection rate and an average percentage recovery of third stage larvae of 26.1. This was followed by S. elodes and B. africanus, with a 100% infection rate and an average percentage recovery of third stage larvae of 15.6 and 14.6 respectively. The rest of snail species proved to be less susceptible. For comparative evaluation of the suitability of the various snail species as intermediate hosts of A. cantonensis a "Capacity Index" was determined. This index should provide a useful method for the evaluation of the suitability of various snails as intermediate hosts of nematode parasites under standardized conditions in the laboratory.     

Ants as first intermediate hosts of Mesocestoides on San Miguel Island, USA

This study tested the hypotheses that ants (Formicidae) function as a first intermediate host of Mesocestoides (Cestoda: Mesocestoididae) and that deer mice (Peromyscus maniculatus) develop metacestode infections after ingesting cysticercoid or procercoid-infected ants. Field studies were conducted at an island fox (Urocyon littoralis littoralis) breeding facility located on San Miguel Island, California Channel Islands National Park, USA, where > 40% of captive foxes were infected with adult Mesocestoides. Eight percent (8%) of deer mice at the fox pen site were infected with Mesocestoides metacestodes while none were infected at a distant site where foxes were absent (campground), thereby indicating the potential localized presence of a first intermediate host. To test whether ants from San Miguel Island contained Mesocestoides DNA, a polymerase chain reaction (PCR)-based diagnostic assay was developed using nested primers that could detect a single hexacanth larva within pooled samples of ten ants. Ants (Lasius niger and Tapinoma sessile) collected near the fox breeding facility were tested using the nested-PCR assay. Seven of 223 pooled samples of L. niger (3.1%) and 2 of 84 pooled samples of T. sessile (2.4%) tested positive for Mesocestoides DNA, while none of the ants were positive at the campground site. Positive samples were sequenced and found to match DNA sequences from Mesocestoides obtained from island fox and deer mice. Finally, to determine whether ants function as a first intermediate host for Mesocestoides, colony-raised deer mice (n = 47) were fed L. niger (n = 3860) or T. sessile (n = 339) collected from the San Miguel Island fox breeding facility. No mouse became infected with Mesocestoides metacestodes after ingesting ants. While both L. niger and T. sessile from SMI were positive for Mesocestoides DNA, they were not infective to deer mice in the laboratory.     

Internal movement of estuarine digenetic trematodes through their intermediate snail host Cerithidea californica

The ability of free-swimming larval parasites to control emergence from their hosts can be critical in increasing the chances of successful infection transmission. For a group of estuarine trematodes, emergence of cercariae from their snail hosts is known to match favorable temperature, tidal activity, and light intensity. How the larvae time this behavior is not well understood, but the pathway that the larvae take through their host may play a role. Through video and histological analysis, we were able to identify the snail's anus as the emergence point and the peri-intestinal sinus dorsal to the intestines as the route by which they reach that point. By moving through this open sinus, the larvae have an energetically efficient pathway to reach their emergence point while minimizing damage to the host. Most importantly, it allows control over emergence to be maintained by the parasite, not the host, thus increasing the chances of the larva successfully reaching its intended destination.     

Mucous cell types in the branchial epithelium of the euryhaline fish Poecilia vivipara

On transfer to sea water for 45 days, the return of appetite was later and growth rates tended to be lower for triploid Atlantic salmon, Salmo salar , reared together with diploid Atlantic salmon. All mortalities comprised of triploid salmon (29%) and were attributable to failed smolt syndrome. No correlation was found between the growth of diploid or triploid fish in fresh water and their subsequent growth on transfer to sea water.     

Community assembly of a euryhaline fish microbiome during salinity acclimation

Microbiomes play a critical role in promoting a range of host functions. Microbiome function, in turn, is dependent on its community composition. Yet, how microbiome taxa are assembled from their regional species pool remains unclear. Many possible drivers have been hypothesized, including deterministic processes of competition, stochastic processes of colonization and migration, and physiological ‘host‐effect’ habitat filters. The contribution of each to assembly in nascent or perturbed microbiomes is important for understanding host–microbe interactions and host health. In this study, we characterized the bacterial communities in a euryhaline fish and the surrounding tank water during salinity acclimation. To assess the relative influence of stochastic versus deterministic processes in fish microbiome assembly, we manipulated the bacterial species pool around each fish by changing the salinity of aquarium water. Our results show a complete and repeatable turnover of dominant bacterial taxa in the microbiomes from individuals of the same species after acclimation to the same salinity. We show that changes in fish microbiomes are not correlated with corresponding changes to abundant taxa in tank water communities and that the dominant taxa in fish microbiomes are rare in the aquatic surroundings, and vice versa. Our results suggest that bacterial taxa best able to compete within the unique host environment at a given salinity appropriate the most niche space, independent of their relative abundance in tank water communities. In this experiment, deterministic processes appear to drive fish microbiome assembly, with little evidence for stochastic colonization.     

Oribatid mites as intermediate hosts of Anoplocephala manubriata, cestode of the Asian elephant in India

Anoplocephala manubriata (Cestoda: Anoplocephalidae) is a tapeworm that parasitizes both African (Loxodonta africana) and Asian (Elephas maximas) elephants. Its life cycle has not yet been completely elucidated nor have intermediate hosts been previously reported. Soil and substrate was collected in the Kodanadu Forest Range, Ernakulum District and Guruvayur Devaswom Temple grounds, Thrissur District, in Kerala, India. Oribatid mites (Acari: Oribatida) were collected from dung piles near captive elephants' bedding and examined for immature stages of the tapeworm. Five species of oribatids were found to contain at least one immature life stage of A. manubriata: Galumna flabellifera orientalis Hammer 1958, Scheloribates latipes (C.L. Koch 1844), S. praeincisus (Berlese 1913), Protoribates seminudus (Hammer 1971), and P. triangularis (Hammer 1971).