Migratory response of European eel (Anguilla anguilla) phagocytes to the eel swimbladder nematode Anguillicola crassus.

The migratory response of peripheral blood granulocytes and monocytes from the European eel Anguilla anguilla (L.) to infective larvae of the swimbladder nematode Anguillicola crassus Kuwahara, Niimi and Hagaki, 1974 was examined by means of light microscopical histology and with an in vitro assay using a modified Boyden chamber. Histological examination of experimentally infected eels revealed that, already 8 days postinfection, an infiltration of inflammatory cells around L3 of A. crassus in the swimbladder tissue can occur. In the Boyden chamber, in presence of infective larvae of A. crassus (L3), neutrophil granulocytes and monocytes showed a higher migration activity than in the absence of L3. In conclusion, infection of European eels with A. crassus leads to an activation of the defence cells resulting in an increased migration activity compared to uninfected eels.

Evaluation of an ELISA and immunoblotting for studying the humoral immune response in Anguillicola crassus infected European eel Anguilla anguilla.

The applicability of an enzyme-linked immunosorbent assay (ELISA) for the detection of anguillicolosis in feral eels was examined using a crude antigen preparation from the body wall of adult Anguillicola crassus. The screening consisted of samples from 100 feral European eels Anguilla anguilla. As a reference the actual status of infection was determined by dissection of the eels' swim-bladders. The ELISA results were compared with a background value calculated from the results obtained from 43 non-infected farm eels. The screened samples had a high prevalence of A. crassus (83 %); however, the specificity and the negative predictive value of the ELISA were low compared to the high positive predictive value. Nonetheless, the reproducibility (precision) of the test was satisfactory, and for the non-infected reference group specificity was 97.7 %. Although the ELISA, as used in the present study, is not applicable for diagnostic purposes, it represents a useful tool for the investigation of the specific humoral immune response of eels against A. crassus under controlled experimental conditions. Immunoblots using crude antigen preparations from different parts of adult A. crassus as well as a crude somatic third-stage (L3) antigen preparation illustrated that only antigens associated with the body wall of adult A. crassus are potentially suitable for diagnostic purposes. Despite the fact that antibodies against Raphidascaris acus cross-reacted with 3 body wall antigens of A. crassus, the most encouraging results were obtained with the antigen preparation from the outer cuticle of adult A. crassus which yielded a conspicuous, broad band at about 100 kDa.

An enhanced humoral immune response against the swimbladder nematode, Anguillicola crassus, in the Japanese eel, Anguilla japonica, compared with the European eel, A. anguilla.

The humoral immune response in the two eel species, Anguilla japonica and Anguilla anguilla against two fractions of antigens in Anguillicola crassus were studied. Within species, both eel species showed significantly elevated titres compared with controls when immunized with antigens from Anguillicola crassus. In interspecific comparison, Anguilla japonica showed significantly elevated titres in comparison with Anguilla anguilla. Immunization of Anguilla anguilla caused a significantly decrease in the plasma levels of protein in comparison with control fish and all groups of Anguilla japonica. In contrast, Anguilla japonica showed significantly lower plasma levels of Ig in all groups compared with Anguilla anguilla. The different susceptibilities to Anguillicola crassus between the natural host, Anguilla japonica, and the naive, Anguilla anguilla, is partly due to differences in the ability of the two eel species to mount a humoral immune response.

Attempts to analyse Anguillicola crassus infection and the humoral host response in eels (Anguilla anguilla) of Lake Balaton, Hungary.

Since the introduction of Anguillicola crassus into Europe, anguillicolosis has been a considerable problem in several countries. From 1991, periodical eel mortality occurred in Lake Balaton, Hungary. However, eels with a worm burden of 20 to 50 parasites did not show severe swimbladder lesions, which observation cast doubts on the primary aetiological role of the parasite in the eel kill. In order to study the pathology of the infection, from the spring of 1996 until October of the same year, 51 eels were collected from two regions of Lake Balaton and examined for swimbladder changes. To detect humoral antibodies, an enzyme-linked immunosorbent assay (ELISA) was performed, using cuticular-oesophageal worm antigen. The results of the test show the applicability of the method. However, no direct correlation was found between antibody levels or the intensity of infection and the swimbladder lesions. The low level of specific antibodies and the increasing severity of swimbladder changes in the autumn suggest that parasite-induced immunity is insufficient to prevent reinfection.