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Biomedical subjects

O Seppälä

Publications and source records attributed to O Seppälä.

14 recordsLinked to original sources
PubMed2006

Ecological divergence of closely related Diplostomum (Trematoda) parasites.

Parasite life-cycles present intriguing model systems to study divergence in resource use and ecology between parasite taxa. In ecologically similar taxa, consistent selective forces may lead to convergence of life-history traits, but resource overlap and similarity of life-cycles may also promote divergence between the taxa in (1) use of host species or (2) specific niche within a host. We studied the life-history characteristics of 2 sympatric species of Diplostomum parasites, D. spathaceum and D. gasterostei, concentrating particularly on differences in intermediate host use and characteristics of the infective stages between the species. This group of trematodes is a notoriously difficult challenge for morphological taxonomy and therefore any information on the ecology of these species can also be helpful in resolving their taxonomy. We observed that these species indeed had diverged as they used mainly different snail and fish species as intermediate hosts and in controlled experiments infected different regions of the eye (lens and vitreous body) of a novel fish host. Interestingly, cercarial characteristics (activity and life-span) were similar between the species and the species were difficult to separate at the cercarial stage unless one observes their swimming behaviour. The release of cercaria from the snail hosts was higher in D. spathaceum, but when cercarial numbers were proportioned to the volume of the snail host, the production was higher in D. gasterostei suggesting differences in the rate of snail host exploitation between the parasite species. These results corroborate the prediction that closely related parasite taxa which are competing for the same resources should have diverged in their life-history characteristics and host use.

Animals↗
PubMed2005

Susceptibility of eye fluke-infected fish to predation by bird hosts.

Host manipulation by trophically transmitted parasites may predispose infected hosts to predation and in this way enhance parasite transmission. In most study systems, however, the evidence comes from laboratory studies, and therefore knowledge of the effect of manipulation on parasite transmission efficiency in the wild is still limited. Here we examined the effect of Diplostomum spathaceum (Trematoda) eye flukes on the susceptibility of fish intermediate hosts to predation by bird definitive hosts. Our earlier studies have shown that the parasite alters fish phenotype and increases their susceptibility to artificial predation under laboratory conditions. In the present field study, we allowed wild birds to feed on fish from cages placed into a lake, and found that predation vulnerability of infected fish did not differ from that of controls. However, we suggest that the experimental set-up likely affected the result because the cages allowed gulls, which caught most of the fish in the study, to feed on fish in an easy, unnatural manner by standing on the edges of the cages. Nevertheless, considerable predation was observed, which provides important initial evidence of how this question should be addressed in the wild.

Analysis of Variance↗
PubMed2005

Intestinal distribution and fecundity of two species of Diplostomum parasites in definitive hosts.

This paper investigated the intestinal distribution and fecundity of 2 species of Diplostomum parasites, D. spathaceum and D. pseudospathaceum, in 2 species of definitive hosts, herring gull (Larus argentatus) and common gull (L. canus), using both empirical field data and experimental infections. At the level of individual hosts, the parasite species occupied different parts within the intestine, but the fecundity of the worms, measured as the number of eggs in the uterus, did not differ between the parasite species except in wild common gulls. Interestingly, egg numbers in individual hosts were positively correlated between the parasite species suggesting that some birds provided better resources for the parasite species. At the host population level, fecundity of the worms did not differ between the host species or between adult birds and chicks. Both parasite species were also aggregated to the same host individuals and it is likely that aggregation is transferred to gulls from fish intermediate hosts. Individual differences in suitability and parasite numbers between hosts provide important grounds and implications for epidemiological model-based parasite prevention strategies.

Animals↗
PubMed2004

Parasite resistance and avoidance behaviour in preventing eye fluke infections in fish.

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.

Animals↗
PubMed2004

Eye fluke-induced cataract formation in fish: quantitative analysis using an ophthalmological microscope.

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.

Animals↗
PubMed1984

Glutathione and selenium in rheumatoid arthritis.

The concentration of selenium in serum (S-Se) was studied in 20 patients and glutathione in erythrocytes (E-GSH) in 16 patients with rheumatoid arthritis (RA) at onset and after 3 and 6 months of antirheumatic therapy with aurothiomalate (19 cases) or with D-penicillamine (one case). The values were compared to those of age and sex matched healthy controls. S-Se was significantly (p less than 0.01) lower in RA patients at the onset of the trial, but increased to the level of the controls during the follow-up. On the other hand, there was no difference in E-GSH between the patients and their controls before the onset of antirheumatic medication but the increase in E-GSH of RA patients during the trial was highly significant (p less than 0.001). Nevertheless, neither S-Se nor E-GSH correlated to changes in clinical or laboratory indicators of disease activity or to the development of new erosions in X-ray. It is concluded that changes in rheumatoid activity or disease progress occur independently of changes in S-Se or E-GSH.

Adult↗
PubMed1978

Acetylation phenotype in rheumatoid arthritis.

The acetylation rate of INH was studied in 39 patients with RA; 20 patients with cardiac arrhythmia served as controls. Statistically, no significant difference was observed between the groups. The percentages of rapid acetylators in the RA and control groups were higher (59 and 55%, respectively) than the reported incidence in the Finnish population, 44% (11). The polymorphic acetylation phenotype was not correlated with either clinical parameters of RA or with sensitivity to gold salts.

Acetylation↗