Abstract Background How different ways of assessing suicidal ideation influence its prevalence, correlates and predictive validity among patients with major depressive disorder (MDD) remains unclear. ...Methods Within the Vantaa Primary Care Depression Study (PC-VDS, 91 patients) and the Vantaa Depression Study (VDS, 153 psychiatric out-and 41 inpatients), suicidal ideation was assessed with the Scale for Suicidal Ideation (SSI), Hamilton Depression Scale (HAM-D) item 3 and Beck Depression Inventory (BDI) item 9, and by asking whether patients had seriously considered suicide during the episode. The positive and negative predictive values (PPV, NPV) for suicide attempts during a six-month follow-up were investigated. Results Depending on the setting, 56–88% of patients had suicidal ideation in some of the assessments, but only 8–44% in all of them. Agreement ranged from negligible to moderate (kappa 0.06–0.64), being lowest among primary care patients. The correlates of suicidal ideation overlapped. No assessment had optimal sensitivity, specificity, PPV and NPV. Nevertheless, PPVs ranged up to 43%. Conclusions Which MDD patient is classified as having suicidal ideation depends strongly on the method of assessment, with the greatest variation likely in primary care. Differences in assessments may cause inconsistency in risk factors. Predicting suicide attempts is difficult, but not futile.
Ecological changes affect pathogen epidemiology and evolution and may trigger the emergence of novel diseases. Aquaculture radically alters the ecology of fish and their pathogens. Here we show an ...increase in the occurrence of the bacterial fish disease Flavobacterium columnare in salmon fingerlings at a fish farm in northern Finland over 23 years. We hypothesize that this emergence was owing to evolutionary changes in bacterial virulence. We base this argument on several observations. First, the emergence was associated with increased severity of symptoms. Second, F. columnare strains vary in virulence, with more lethal strains inducing more severe symptoms prior to death. Third, more virulent strains have greater infectivity, higher tissue-degrading capacity and higher growth rates. Fourth, pathogen strains co-occur, so that strains compete. Fifth, F. columnare can transmit efficiently from dead fish, and maintain infectivity in sterilized water for months, strongly reducing the fitness cost of host death likely experienced by the pathogen in nature. Moreover, this saprophytic infectiousness means that chemotherapy strongly select for strains that rapidly kill their hosts: dead fish remain infectious; treated fish do not. Finally, high stocking densities of homogeneous subsets of fish greatly enhance transmission opportunities. We suggest that fish farms provide an environment that promotes the circulation of more virulent strains of F. columnare. This effect is intensified by the recent increases in summer water temperature. More generally, we predict that intensive fish farming will lead to the evolution of more virulent pathogens.
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.
Rainbow trout,
Oncorhynchus mykiss, were infected concomitantly with
Argulus coregoni and
Flavobacterium columnare and their survival was compared with that of fish infected with either the parasite ...or the bacterium alone. The mortality of fish challenged with
A. coregoni was negligible while infection with
F. columnare alone led to significantly lower survival. However, compared with single infections, the mortality was significantly higher and the onset of disease condition was earlier among fish, which were concomitantly infected by
A. coregoni and
F. columnare. This data presents, for the first time, experimental support for the hypothesis that an ectoparasite infection increases susceptibility of fish to a bacterial pathogen.
Aims: Colony morphology variants of fish pathogenic Flavobacterium columnare were studied to clarify the role of colony morphology change in the virulence of the bacterium. Typical rhizoid colony ...(Rz) variants are virulent and moderately adherent, nonrhizoid rough (R) colony variants are nonvirulent and highly adherent, and soft colony (S) variants are nonvirulent and poorly adherent. Methods and Results: Chondroitin AC lyase activity, adhesion to polystyrene at different temperatures and after modification of bacterial surface, and lipopolysaccharide (LPS) profiles of the variants were studied. The chondroitinase activity was significantly higher in the virulent, rhizoid variants than in the rough variants of the same strain. Temperature significantly increased the adhesion of rhizoid variants up to 20°C. Modification of bacterial surface suggested that adhesion molecules contain both carbohydrates and proteins. LPS did not differ between the variants of the same strain. Conclusions: The results suggest that in Fl. columnare both rhizoid colony morphology and high chondroitinase activity are needed for virulence and that temperature may promote the adhesion of the virulent variants to surfaces at fish farms. Significance and Impact of the Study: New information is produced on the virulence mechanisms of Fl. columnare and the reasons behind the survival of the bacterium at fish farms.
Trophically transmitted parasites may predispose infected hosts to predation by altering host behaviour, which can be either an adaptation of the parasites to enhance transmission to the next hosts ...in the life cycle or a nonadaptive side-effect of infection. In an experimental study, we investigated host manipulation by
Diplostomum spathaceum (Trematoda), an eye fluke of fish, to evaluate its adaptive value as a parasite strategy to increase transmission efficiency to bird hosts. The parasite induces cataract formation in the lenses of fish eyes, and predisposes fish to predation by reducing their escape response. We examined the effect of developmental stage and the number of parasites on parasite-induced cataract formation and the susceptibility of rainbow trout,
Oncorhynchus mykiss, to simulated predation (capture by dip-net). We found that the catchability of fish increased with the coverage of parasite-induced cataract. Furthermore, cataract formation was most intensive after eye flukes had completed their development, and host manipulation took place only when parasites were infective to birds and thus capable of being transmitted. Intensity of infection, however, did not affect vulnerability of fish to capture by dip-net. These findings suggest that the ability of the parasite to manipulate fish behaviour by impairing its vision may have resulted from selection preferring parasite genotypes with higher transmission efficiency.
Fish lice (Argulus spp.) are obligate ectoparasites, which contrary to most aquatic parasites, retain the ability to swim freely throughout the whole of their life. In fish farms, they can quickly ...increase in numbers and without effective control cause argulosis, which results in the reduced growth and survival of their fish hosts. The morphology of Argulus spp, including their sensory organs, is suitable for both parasitism and free-swimming. By spending a considerable amount of time away from their host, these parasites risk being excessively dispersed, which could endanger mating success. Here we present a review of recent studies on the behaviour of Argulus spp, especially the aggregative behaviour that mitigates the dilution of the parasite population. Aggregation of parasites, which is especially important during the period of reproduction, occurs on different scales and involves both the aggregation of the host and the aggregation of the parasites on the host. The main behavioural adaptations of Argulus spp, including searches for hosts and mates, host manipulation and host choice, are all focused on the fish. As these ectoparasites repeatedly change hosts and inflict skin damage, they can act as vectors for fish pathogens. The development of environmentally friendly measures for the control and prevention of argulosis needs to take into account the behaviour of the parasites.
We examined the parasite-induced cataract formation in rainbow trout (Oncorhynchus mykiss) using slit-lamp microscopy to determine the relationship between cataract intensity and number of ...Diplostomum spathaceum parasites that were established in the lens. Cataract intensity increased significantly with parasite burden, but was also affected by the pattern of exposure to the parasite cercariae. The slit-lamp methodology proved useful in scoring the cataracts since it provides a 3-dimensional view into the lens and gives an actual picture of the location and intensity of the cataracts, which allows detailed investigations of mechanisms underlying cataract formation in various fish species. Potential applications of the method in fish farming and parasitological studies are discussed.
Manipulation of host phenotype (e.g. behaviour, appearance) is suggested to be a common strategy to enhance transmission in trophically transmitted parasites. However, in many systems, evidence of ...manipulation comes exclusively from laboratory studies and its occurrence in natural host populations is poorly understood. Here, we examined the potential for host manipulation by Diplostomum eye flukes indirectly by quantifying the physiological effects of parasites on fish. Earlier laboratory studies have shown that Diplostomum infection predisposes fish to predation by birds (definitive hosts of the parasites) by reducing fish vision through cataract formation. However, occurrence of cataracts and the subsequent potential for host manipulation in natural fish populations has remained poorly explored. We studied the occurrence of eye fluke-induced cataracts from 7 common fish species (Gymnocephalus cernuus, Rutilus rutilus, Leuciscus leuciscus, Alburnus alburnus, Osmerus eperlanus, Coregonus lavaretus and Gasterosteus aculeatus) from the Bothnian Bay in the Baltic Sea. We found that the parasite-induced cataracts were common in fish and they also reached high levels which are likely to predispose fish to predation. However, we observed such cataracts only in species with the highest parasite abundances, which suggests that only certain hosts may be strongly affected by the infection.
This paper examines the efficiency of acquired resistance in protecting the fish host, rainbow trout (Oncorhynchus mykiss), against the trematode parasite Diplostomum spathaceum, and the hypothesis ...that fish recognize areas where infective stages are aggregated and show avoidance behaviour. We found that when fish with a low level of infection were held in restricted cages in natural conditions they became infected and developed cataracts as a result of this infection. This suggests that acquired resistance is insufficient in protecting fish against the parasite or the deleterious effects of infection in conditions where fish could not avoid the parasite. Behavioural experiments in the laboratory showed that fish reacted to the parasite cercariae by avoiding the infection source, which decreased the rate of parasite establishment. We conclude that by using a combination of behavioural avoidance and physiological resistance, fish could defend against the parasite more effectively.
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