Value of screening for intestinal and urinary parasites in non-resident permanent students in Tunisia

In order to fight digestive and urinary parasitoses, a national program of surveillance has been founded. The screening of these parasitoses among the non permanent resident students in Tunisia (ENRPTS) is one of the main actions of this program. Among 2560 ENRPTS tested in the laboratory of Parasitologie of Institut Pasteur of Tunis, between 1998 and 2002, 674 were infected by parasites, which represents a global prévalence of 26.3%. The intestinal protozoa constitute the majority of parasites identified (87.4%). Entamoeba histolytica has been isolated in 89 cases, essentially from students from tropical African countries. Urinary bilharziosis has been diagnosed in 25 cases. These results confirm the utility of the control of the ENRPTS. The precocious tracking permits to avoid the introduction and the dissemination of parasites already absent or rare in our country.     

Defense behavior of fish against predators and parasites

This paper is a review of empirical and theoretical studies of the behavioral mechanisms and ecological consequences of the anti-predator and anti-parasite activities of teleost fishes. While the individual and cooperative behaviors used by fish to protect themselves from predators have received marked attention from researchers in the fields of ecology, ethology and applied fish biology, the behaviors by which fish protect themselves from parasites have been poorly investigated. Generally, free-swimming parasites, which are difficult to distinguish, do not elicit any marked behavioral response from fish prior to contact. We hypothesize that the behaviors by which fish avoid parasites are much more efficient for fish in groups than they are for solitary fish. Early avoidance of predators and parasites is compared with the behavioral tactics fish use when such enemies are in close proximity. Individual versus cooperative tactics, as well as the role of learning, are also analyzed. Learning is more important for behaviors which protect fish from predators than those which they use against parasites, especially at the level of individual fish. Finally, we briefly discuss the importance of coordination of anti-predator and anti-parasite activities, which present the most complicated tasks for fish and intriguing problems for researchers.     

Host–parasite interactions in vector-borne protozoan infections

Protists embrace many species, some of which may be either occasional or permanent parasites of vertebrate animals. Between the parasite species, several of medical and veterinary importance are vector-transmitted. The ecology and epidemiology of vector-borne parasitoses, including babesiosis, leishmaniasis and malaria, are particularly complex, as they are influenced by many factors, such as vector reproductive efficiency and geographical spread, vectorial capacity, host immunity, travel and human behaviour and climatic factors. Transmission dynamics are determined by the interactions between pathogen, vector, host and environmental factors and, given their complexity, many different types of mathematical models have been developed to understand them. A good basic knowledge of vector-pathogen relationships and transmission dynamics is thus essential for disease surveillance and control interventions and may help in understanding the spread of epidemics and be useful for public health planning.     

Efficacy of ivermectin (Ivomec) against intestinal capulariosis in falcons

52 captive falcons out of 3,988 (1.3 %) raptors microscopically examined for intestinal parasites in the Middle East proved infested with hairworms (capillariid parasites). 26 of these (50 %) showed concurrent parasitoses. In the group of 26 falcons diagnosed with capillariosis as sole infestation (50 %) compatible clinical signs such as anorexia, weight loss, weakness, dyspnoea, regurgitation of food and blood, diarrhoea and dark tarry faeces, were recorded. These birds were treated intramuscularly with ivermectin at doses of 2 mg/kg. In fecal samples examined 10-15 days later, the eggs of capillariid parasites had disappeared, in association with complete clinical recovery.     

Altered trophic pathway and parasitism in a native predator (Lepomis gibbosus) feeding on introduced prey (Dreissena polymorpha)

Populations of invasive species tend to have fewer parasites in their introduced ranges than in their native ranges and are also thought to have fewer parasites than native prey. This ‘release’ from parasites has unstudied implications for native predators feeding on exotic prey. In particular, shifts from native to exotic prey should reduce levels of trophically transmitted parasites. We tested this hypothesis in native populations of pumpkinseed sunfish (Lepomis gibbosus) in Lake Opinicon, where fish stomach contents were studied intensively in the 1970s, prior to the appearance of exotic zebra mussels (Dreissena polymorpha) in the mid-1990s. Zebra mussels were common in stomachs of present-day pumpkinseeds, and stable isotopes of carbon and nitrogen confirmed their importance in long-term diets. Because historical parasite data were not available in Lake Opinicon, we also surveyed stomach contents and parasites in pumpkinseed in both Lake Opinicon and an ecologically similar, neighboring lake where zebra mussels were absent. Stomach contents of pumpkinseed in the companion lake did not differ from those of pre-invasion fish from Lake Opinicon. The companion lake, therefore, served as a surrogate “pre-invasion” reference to assess effects of zebra mussel consumption on parasites in pumpkinseed. Trophically transmitted parasites were less species-rich and abundant in Lake Opinicon, where fish fed on zebra mussels, although factors other than zebra mussel consumption may contribute to these differences. Predation on zebra mussels has clearly contributed to a novel trophic coupling between littoral and pelagic food webs in Lake Opinicon.     

Epidemiological analyses on animal parasitoses: recent activity of the I.M.I.P.P.V

The paper presents a selected review of the epidemiological analyses performed in recent years (1984-1988) in the Institute of Malattie Infettive, Profilassi e Polizia Veterinaria of the University of Bologna on animal parasitoses, with special reference to the evaluation of some risk factors of bovine, swine and canine helminthoses, and to the validity of the coprological test for some parasites of the red fox.     

Parasitism and evolution: opposing versus balancing strategies

Parasitism refers to a particular symbiosis (deBary 1879) of organisms that live at the cost of their hosts. Virulent microbes (viruses and bacteria) proliferate unlimited causing toxic infections that end either by the host's death or its protective immunity. By this opposing survival strategy, via the population density, i.e. the contact rate, finally results a sequence of epidemic and endemic periods. The host population is kept at a reasonable level to resources, but host and pathogenic agent are wasted in the evolutionary arms race. Sparing such losses, eukaryotic proto- and metazoan parasites induce in natural hosts a delayed infection course by self-controlled propagation and avoid protective immunity. Hosts are ‘immunized but not immune’ and parasites propagate simultaneously with them. Metazoic and some protozoic parasitoses end with the parasite's natural death, pathogenic effects remain irrelevant. Nevertheless, the host's fitness becomes reduced by multiple re-infections and/or by increasing parasite loads. This balancing survival strategy controls host populations at lower costs. A network of parasitoses offers considerable selection advantages and explains the polyphyletic origin of eukaryotic parasites. Parasitism and other kinds of symbioses contribute to the stability of ecosystems and to stasis in long-term evolution but are invisible in the fossil record.     

Toxic pollution and parasitism in freshwater fish

As aquatic habitats throughout the world are increasingly contaminated with toxic chemicals, toxicologist strive to determine what impact these substances will have an biological systems. So far, the effects of this type of pollution on fish parasites has received little attention, despite their important status as determinants of fish health. Robert Poulin discusses the many ways in which toxic pollution may affect infections of metazoan parasites in freshwater fish. Effects on fish immunity, parasites survival and intermediate host populations are not independent, and currently the outcome of toxic pollution and parasitism in fish is impossible to predict. Future research will have to answer several questions if we are to understand and forecast pollution-mediated changes in parasitism, an urgent challenge for ecotoxicologists and fish parasitologists alike.     

The Behavioral Response of Larval Amphibians (Ranidae) to Threats from Predators and Parasites

Organisms are exposed to strong selective pressures from several sources, including predators and pathogens. Response to such interacting selective pressures may vary among species that differ in life history and ecology in predictable ways. We consider the impact of multiple enemies (fish predators and trematode parasites) on the behavior of larvae of three anuran species (Lithobates ( = Rana) sylvaticus, L. clamitans and L. catesbeianus). We show that the three ranid species differ in response to the trade-off imposed by the simultaneous presence of fish predators and trematode parasites in the environment. Two more permanent pond breeders (L. clamitans and L. catesbeianus), which commonly encounter parasites and fish, increased activity when in the combined presence of parasites and a fish predator, resulting in a relatively lower parasite encystment rate. In contrast, the temporary pond breeder (L. sylvaticus), which does not commonly encounter fish in the wild, decreased activity in the combined presence of a fish predator and parasites similar to when only the predator was present. For L. sylvaticus, this suggests that the presence of an unknown predator poses a greater threat than parasites. Further, the presence of fish along with parasites increased the susceptibility of both L. sylvaticus and L. clamitans to trematode infection, whereas parasite infection in L. catesbeianus was unaffected by the presence of fish. Unpalatability to fish may allow some species to respond more freely to attacking parasites in the presence of fish. The results from this study highlight the importance of considering multiple selective pressures faced by organisms and how this shapes their behavior.     

Vulnerability and diet breadth predict larval and adult parasite diversity in fish of the Bothnian Bay

Recent studies of aquatic food webs show that parasite diversity is concentrated in nodes that likely favour transmission. Various aspects of parasite diversity have been observed to be correlated with the trophic level, size, diet breadth, and vulnerability to predation of hosts. However, no study has attempted to distinguish among all four correlates, which may have differential importance for trophically transmitted parasites occurring as larvae or adults. We searched for factors that best predict the diversity of larval and adult endoparasites in 4105 fish in 25 species studied over a three-year period in the Bothnian Bay, Finland. Local predator–prey relationships were determined from stomach contents, parasites, and published data in 8,229 fish in 31 species and in seals and piscivorous birds. Fish that consumed more species of prey had more diverse trophically transmitted adult parasites. Larval parasite diversity increased with the diversity of both prey and predators, but increases in predator diversity had a greater effect. Prey diversity was more strongly associated with the diversity of adult parasites than with that of larvae. The proportion of parasite species present as larvae in a host species was correlated with the diversity of its predators. There was a notable lack of association with the diversity of any parasite guild and fish length, trophic level, or trophic category. Thus, diversity is associated with different nodal properties in larval and adult parasites, and association strengths also differ, strongly reflecting the life cycles of parasites and the food chains they follow to complete transmission.     

Do Larval Damselflies make Adaptive Choices When Exposed to Both Parasites and Predators?

The importance of multiple enemies from different trophic levels on investment in defence by prey has, with some exceptions, received little attention. Some defences may make the victim more susceptible to other enemies; this latter situation applies to predators and parasites of larval damselflies. Baker and Smith [Oecologia 109 (1997) 622) showed that larval damselflies were as active in the presence of both mites and fish as they were when only mites were present, an apparently maladaptive behaviour that results in higher fish predation. In this paper, we further examine this maladaptive behavioural response to multiple enemies (fish predators and mite parasites) and test whether their defence responses are a result of the order in which they experience the parasite or predator, and/or if behavioural ‘personalities’ exist, such that some individuals show anti‐predator behaviours and other show anti‐parasite behaviours. Order of experience did not affect the four main behaviours (groom, crawl, turn and swim) exhibited when larval damselflies were simultaneously exposed to fish and mites. Grooming levels increased in response to mites, decreased in response to fish and when exposed to both mites and fish were similar to when they were exposed to mites alone. Duration of the other three behaviours was lower in the presence of both mites and fish. The crawling ‘personalities’ were evident. The apparently maladaptive response of high grooming levels in the presence of mites and fish is not a result of order of experience or ‘personalities’. It may be a result of relatively high encounter rates with mite parasites, compared with the encounter rates with fish. Lower encounter rates can result in diminishing investment in defence against an enemy.     

A comparison of the parasite fauna of young whiting, Odontogadus merlangus (L.) (Gadidae) from an inshore and an offshore location off the Isle of Man

The occurrence of 12 helminth and 4 crustacean parasites on young whiting 0–2 years old from an inshore (Port Erin Bay) and an offshore (off Bradda Head) area of the Isle of Man were compared. No parasites were found on whiting 4.5–15 mm long and the intestinal digenean Lecithaster gibbosus Rudolphi together with the larvae of the copepod Caligus rapax M. Edwards were the first parasites to appear in whiting 15–42 mm long. This appears to be the only time during the life history of the whiting that C. rapax is of importance as a parasite. In whiting 6 months-2 years old from off Bradda Head such helminths as the acanthocephalan Echinorhynchus gadi Muller and the digeneans Podocotyle atomon Muller and Cryptocotyle lingua Creplin (metacercariae) were found in significantly fewer fish than in an equivalent group from Port Erin Bay. The differences are correlated with the availability of intermediate hosts and the different food spectra of the two groups of fish and are used to support the theory that inshore and offshore whiting of these age groups form separate populations and that the offshore fish may be more important than the inshore fish in replenishing stocks of older whiting.     

Accumulation of plerocercoids of Triaenophorus crassus in the second intermediate host Coregonus lavaretus and their effect on growth of the host

Patterns of accumulation of Triaenophorus crassus in its second intermediate host whitefish Coregonus lavaretus s.l. were studied between 1991 and 1996 from two host populations in two separate areas of Lake Saimaa, Finland. Whitefish were infected commonly with several T. crassus plerocercoids and the parasites were aggregated into the oldest hosts. In one host population the annual parasite accumulation was 0·9 parasites in all host age groups between 3 and 8 years. In the other host population the annual accumulation was 1·6 parasites in 3–5-year-old fish, but increased up to 3 to 4 parasites per year in fish over 5 years old. The increase did not coincide with the period of maturation or any increase in whitefish growth, both of which could alter the food intake of the fish. The sharp increase in the annual accumulation suggests a threshold intensity above which the probability of acquiring further parasites increases. In spite of a heavy aggregation of parasites there was no evidence of parasite-induced host mortality. The annual increase in mean abundance was not correlated with the mean annual weight increase in 2–4-year-old fish within cohorts. However, evidence of a negative effect of parasites on whitefish growth was revealed by back-calculation of lengths of uninfected and infected whitefish and correlations between length or weight of fish and intensity of infection with fish age. Both analyses suggested that larger young fish harboured more parasites than the smaller ones while in older fish the reverse was true, a pattern that has not been shown earlier for parasitized fish.     

The importance of fish stocking in the dissemination of parasites throughout a group of reservoirs

In view of the known importance of anthropochore movements of fish in disseminating their parasites, it was hypothesized that local movements of fish between neighbouring water bodies for stocking and management purposes would similarly disseminate their parasites, resulting in a high degree of similarity in the parasite communities of fish in water bodies that have been linked by fish transfers. This hypothesis was tested by comparing the helminth parasite communities in brown trout, Salmo trutta Linnaeus and rainbow trout, Oncorhynchus mykiss (Walbaum), in reservoirs in south west England. In one group of six reservoirs there is a recent history of transfers of rainbow trout, and in the second group of four there have been no transfers over the last decade. There was no difference in mean similarity, using Jaccard's Coefficient and a Percentage Similarity Index, between the helminth faunas of trout in the reservoirs linked by transfers and those not so linked, and the distribution of several individual species of helminths was not consistent with their having been disseminated in the course of fish stockings. The hypothesis is thus rejected and it is concluded that anthropochore transfers of trout between reservoirs have been of little or no significance in the dispersal of parasites throughout the reservoirs or in the transfer of helminths from one reservoir to another. The reasons for this unexpected conclusion are discussed in the light of indications that factors unrelated to fish transfers were important determinants of helminth community composition in individual reservoirs.     

Vertebrate diets derived from trophically transmitted fish parasites in the Bothnian Bay

Parasites that are transmitted through predator–prey interactions may be used as indicators of trophic relationships between organisms. Yet, they are rarely used as such in the construction of topological (predator–prey) food webs. We constructed food webs of vertebrate trophic interactions using observed diet alone, trophically transmitted parasites alone, and the combination of the two based on data from 31 species of fish from the Bothnian Bay, Finland. The fish food web contained 530 links derived from observed diet, 724 links inferred from parasitism, and 1,058 links calculated from a combination of both stomach contents and parasites. This sub-web constructed from stomach contents had a mean of 17.1 links per fish species, while that using parasites had 23.4 links per fish. Combining the two diet indicators yielded 34.1 links per fish species, illustrating the complementarity of the two methods. Mean number of prey species per fish species was 12.5 using observed diet items, 15.8 using parasites, and 24.5 using both measures together. Mean number of predators per fish species was 7.4 using observed diet, 11.7 using parasites and 15.0 using both. A positive correlation was found between the mean number of parasites and the number of prey taxa in the diet among the fishes. Omnivorous fish had the highest diversity of both parasite species and prey items, while benthophagous fish had among the lowest. Mean total abundance and mean total prevalence of parasites correlated positively with fish size, with piscivores being the largest with the highest abundance and prevalence, while planktivores and benthivores had the lowest. Trophically transmitted parasites may be used to help construct vertebrate sub-webs and derive information about food web processes. Parasites alone provided equivalent if not more information than observed diet. However, resolution is improved by using parasites and observed diet together.     

Interactions among co-infecting parasite species: a mechanism maintaining genetic variation in parasites?

Individuals of free-living organisms are often infected simultaneously by a community of parasites. If the co-infecting parasites interact, then this can add significantly to the diversity of host genotypexparasite genotype interactions. However, interactions between parasite species are usually not examined considering potential variation in interactions between different strain combinations of co-infecting parasites. Here, we examined the importance of interactions between strains of fish eye flukes Diplostomum spathaceum and Diplostomum gasterostei on their infectivity in naive fish hosts. We assessed the infection success of strains of both species in single-strain exposures and in co-exposures with a random strain of the other species. Parasite infection success did not consistently increase or decrease in the co-exposure treatment, but depended on the combinations of co-infecting parasite strains. This disrupted the relative infectivity of D. spathaceum strains observed in single-strain exposures. The infection success of D. gasterostei strains was independent of exposure type. These results suggest that interactions among parasite species may be strain specific and potentially promote maintenance of genetic polymorphism in parasite populations.     

Parasitic diseases in marine cage culture--an example of experimental evolution of parasites?

Rapid development of fish culture in marine cages has been associated with an emergence of parasitic diseases. There is a general trend to an increase in infections with ectoparasites with direct life cycles and a reduced diversity of parasites in aquaculture. Some mariculture creates conditions that are similar to serial passage experiments, which are used to study adaptation during experimental evolution of pathogens. In particular, increased density of fish, repeated introduction of naive hosts, homogenous host populations, fast growth and a potential decrease in genetic diversity are attributes of both aquaculture and serial passage experiments. Some free-living organisms, for example Neoparamoeba spp. and Uronema spp. parasitise fish in culture, but have not been reported from wild populations. Farming fish in marine cages can increase the risk of outbreaks of parasitic diseases, including those caused by opportunistic parasites. However, aquaculture has the potential to control parasitic diseases through selective breeding, vaccination and general fish health management.     

Patterns of interactions of a large fish-parasite network in a tropical floodplain

1.?Describing and explaining the structure of species interaction networks is of paramount importance for community ecology. Yet much has to be learned about the mechanisms responsible for major patterns, such as nestedness and modularity in different kinds of systems, of which large and diverse networks are a still underrepresented and scarcely studied fraction. 2.?We assembled information on fishes and their parasites living in a large floodplain of key ecological importance for freshwater ecosystems in the Paraná River basin in South America. The resulting fish-parasite network containing 72 and 324 species of fishes and parasites, respectively, was analysed to investigate the patterns of nestedness and modularity as related to fish and parasite features. 3.?Nestedness was found in the entire network and among endoparasites, multiple-host life cycle parasites and native hosts, but not in networks of ectoparasites, single-host life cycle parasites and non-native fishes. All networks were significantly modular. Taxonomy was the major host's attribute influencing both nestedness and modularity: more closely related host species tended to be associated with more nested parasite compositions and had greater chance of belonging to the same network module. Nevertheless, host abundance had a positive relationship with nestedness when only native host species pairs of the same network module were considered for analysis. 4.?These results highlight the importance of evolutionary history of hosts in linking patterns of nestedness and formation of modules in the network. They also show that functional attributes of parasites (i.e. parasitism mode and life cycle) and origin of host populations (i.e. natives versus non-natives) are crucial to define the relative contribution of these two network properties and their dependence on other ecological factors (e.g. host abundance), with potential implications for community dynamics and stability.     

南极鱼类后生动物寄生虫研究进展: 线虫、绦虫与桡足类

极端的环境造就了南极独特的生物群体, 其中鱼类是南大洋生态系统中最具多样性的脊椎动物, 也是许多寄生虫的中间或终末宿主。南极鱼类寄生虫种类丰富, 是南大洋海洋生物多样性的重要组成部分。探究南极鱼类及其寄生虫的营养关系可为阐释南极海洋生态系统功能及其变动提供重要的生态数据。虽然关于南极鱼类寄生虫的研究已有一百多年的历史, 但这些研究主要集中在寄生虫的种类鉴定、区系调查和组织病理等方面。由于南极鱼类寄生虫研究跨度时间长、地域范围广, 相关研究较为零散。文章综述了南极鱼类寄生线虫、绦虫以及桡足类的种类组成、宿主范围和地理分布等方面的研究, 并对今后开展南极鱼类寄生虫研究工作提出了展望。     

Parasites of recruiting coral reef fish larvae in New Caledonia

Recruiting coral reef fish larvae from 38 species and 19 families from New Caledonia were examined for parasites. We found 13 parasite species (Platyhelminthes: Monogenea, Cestoda and Trematoda) but no acanthocephalan, crustacean or nematode parasites. Over 23% of individual fish were infected. Didymozoid metacercariae were the most abundant parasites. We conclude that most of the parasites are pelagic species that become ‘lost’ once the fish larvae have recruited to the reef. Larval coral reef fish probably contribute little to the dispersal of the parasites of the adult fish so that parasite dispersal is more difficult than that of the fish themselves.