Immunohistopathological response against anisakid nematode larvae and a coccidian in Micromesistius poutassou from NE Atlantic waters.

A survey on Anisakis simplex (sensu stricto (s.s.)) from blue whiting, Micromesistius poutassou, in the north-eastern Atlantic Ocean revealed the occurrence of high infection levels of third larval stages in visceral organs and flesh. Larvae were genetically identified with a multilocus approach as A. simplex (s.s.). Histochemical, immunohistochemical and ultrastructural observations were conducted on 30 M. poutassou specimens. Gonads, pyloric caeca and flesh harboured encapsulated larvae of A. simplex (s.s.) but no intense host reaction was encountered around the parasite in the above organs. In the liver, the most infected organ, the larvae co-occurred with the coccidian Goussia sp. Within the granuloma around the A. simplex (s.s.) larvae, two concentric layers were recognized, an inner mostly comprising electron-dense epithelioid cells and an outer layer made of less electron-dense epithelioid cells. Macrophages and macrophage aggregates (MAs) were abundant out of the granulomas, scattered in parenchyma, and inside the MAs, the presence of engulfed Goussia sp. was frequent. In liver tissue co-infected with Goussia sp. and A. simplex (s.s.), hepatocytes showed cytoplasmic rarefaction and acute cell swelling. Results suggest that the host-induced encapsulation of A. simplex (s.s.) larvae is a strategic compromise to minimize collateral tissue damage around the larval infection sites, to facilitate the survival of both parasite and host.

Reviewing biodiversity and epidemiological aspects of anisakid nematodes from the North-east Atlantic Ocean.

This review provides an inventory of the biodiversity of the anisakid species identified so far from fish and marine mammals of the NE Atlantic Ocean. The paper reviews and discusses various taxonomical and epidemiological aspects related to biodiversity assessment, with emphasis on: (1) taxa recognized as 'biological species' based on molecular/genetic markers; (2) current molecular/genetic approaches to identify the species at different developmental stages; (3) ecological data related to the actual geographical distribution and definitive host preferences of the species; (4) their distribution in various, commercially important fish species in northern European waters; (5) their possible occurrence in farmed fish; and, finally, (6) an update of their zoonotic potential as causative agents of anisakidosis in humans.

No more time to stay 'single' in the detection of Anisakis pegreffii, A. simplex (s. s.) and hybridization events between them: a multi-marker nuclear genotyping approach.

A multi-marker nuclear genotyping approach was performed on larval and adult specimens of Anisakis spp. (N = 689) collected from fish and cetaceans in allopatric and sympatric areas of the two species Anisakis pegreffii and Anisakis simplex (s. s.), in order to: (1) identify specimens belonging to the parental taxa by using nuclear markers (allozymes loci) and sequence analysis of a new diagnostic nuclear DNA locus (i.e. partial sequence of the EF1 α-1 nDNA region) and (2) recognize hybrid categories. According to the Bayesian clustering algorithms, based on those markers, most of the individuals (N = 678) were identified as the parental species [i.e. A. pegreffii or A. simplex (s. s.)], whereas a smaller portion (N = 11) were recognized as F1 hybrids. Discordant results were obtained when using the polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLPs) of the internal transcribed spacer (ITS) ribosomal DNA (rDNA) on the same specimens, which indicated the occurrence of a large number of 'hybrids' both in sympatry and allopatry. These findings raise the question of possible misidentification of specimens belonging to the two parental Anisakis and their hybrid categories derived from the application of that single marker (i.e. PCR-RFLPs analysis of the ITS of rDNA). Finally, Bayesian clustering, using allozymes and EF1 α-1 nDNA markers, has demonstrated that hybridization between A. pegreffii and A. simplex (s. s.) is a contemporary phenomenon in sympatric areas, while no introgressive hybridization takes place between the two species.

IgE sensitization to the fish parasite Anisakis simplex in a Norwegian population: a pilot study.

The reports on fish parasite Anisakis simplex allergy have increased in countries with high fish consumption in the last decade. In Norway, a high consumption country, the prevalence of immunoglobulin E (IgE) sensitization to A. simplex was still unknown. Thus, our objective was to investigate the sensitization prevalence in this country. At the Haukeland University Hospital, Bergen, Norway, two main groups of surplus serum samples were collected: one from newly recruited blood donors (BDO) and the other from the Allergy laboratory (ALL) after analysing IgE and IgE antibodies. The latter was divided into three series: one containing unsorted sera and two sorted by either Phadiatop(®) ≥0.35 kU(A)/l or total IgE ≥1000 kU/l. The sera were analysed for total IgE and IgE antibodies against A. simplex, shrimp, house dust mite (HDM), cod and cross-reactive carbohydrates (CCDs). The prevalence of IgE sensitization to A. simplex was 2.0%, 2.2% and 6.6% in BDO, the unsorted and Phadiatop(®) positive serum groups, respectively. A considerable degree of cross-sensitization to shrimp and HDM is further suggested. Unspecific binding because of high total IgE or by binding to CCDs seemed to play a minor role. The prevalence of IgE sensitization to A. simplex appears to be lower in a Norwegian population than in other high fish-consuming countries, but might still be overestimated owing to cross-sensitization.

Occurrence of postmortem myoliquefactive kudoosis in Atlantic mackerel, Scomber scombrus L., from the North Sea.

Members of the myxosporean genus Kudoa occur in various marine teleosts worldwide. Several species are of concern to the fishery and aquaculture industries as they may produce unsightly cysts in the fish host's musculature or are associated with postmortem myoliquefaction of the fish muscle, commonly referred to as 'soft flesh'. This study describes the occurrence and effects on a host of a Kudoa species in Atlantic mackerel, Scomber scombrus, from the northern North Sea. Generalized postmortem myoliquefaction associated with Kudoa sp. occurred in 0.8% of the examined fish, i.e. 11 of 1339 mackerel developed 'soft flesh'. There was a significant difference in the prevalence of myoliquefaction between medium sized (400-600 g) and large mackerel (>600 g). The prevalence reached 8.9% in the latter host size group. No subclinical infections of Kudoa sp. were detected when examining fresh muscle (n = 103) and blood (n = 165) samples for spores using light microscopy. Affected mackerel developed generalized myoliquefaction after 38-56 h post-catch. No inflammatory host response was associated with the presence of plasmodia within single body muscle fibres of 'soft flesh' affected fish. Based on comparison of myxospore dimensions and analysis of the nuclear small subunit (SSU) ribosomal DNA, the present Kudoa species is assigned to Kudoa thyrsites. However, due to the species' apparently very wide geographical distribution and host range, its varying effect on different fish host species, together with the still unknown life cycle of Kudoa spp., the taxonomic status of K. thyrsites appears not to be fully resolved.

Selection pressure towards monoxeny in Camallanus cotti (Nematoda, Camallanidac) facing an intermediate host bottleneck situation.

This paper describes the ability of the Asian fish nematode Camallanus cotti to carry out both heteroxeny, i.e. an indirect life-cycle using copepods as intermediate host, and monoxeny, i.e. direct infection and development in the definitive fish host. C. cotti occurs naturally in various freshwater teleosts in Asia. During the past decades it has been disseminated into closed or semi-closed aquaculture systems and aquaria around the world, mainly due to the ornamental fish trade. Under such conditions the species may frequently face a bottleneck situation with regard to the availability of copepods. It is known that C. cotti may reproduce and persist in copepod-free aquaria for several months. In order to investigate whether C. cotti has selected towards monoxeny in water systems lacking copepods, in contrast to the opposite selection pressure when copepods are present, 2 separate infection trials were run. It was shown that the parasite can infect the fish host both indirectly via copepods, and directly. However, C. cotti has significantly higher fitness, expressed as survival to maturity, when transmitted indirectly compared to the direct transmission mode. We suggest that the ability of aquarium populations of C. cotti to carry out a direct life-cycle is favoured by selection in order to avoid extinction whenever copepods are absent. It still remains unknown, however, whether the parasite shows the same characteristics in the wild.