New developments

Anisakis simplex and P. decipiens were, until some years ago, regarded as monotypic species; they occur in whales and seals in all cool seas. However, by enzyme electrophoresis, research carried out mainly in Rome, Italy and reviewed by Bullini et al. (1997), the assumed simple A. simplex is shown to be composed of five sibling species, that is, genetically good species that cannot be distinguished on morphology. The same applies to P. decipiens also, with five siblings, three of them in the North Atlantic; their specific identities were resolved by Paggi et al. (2000). The species Contracaecum osculatum in seals also consists of five siblings. Some of the larvae in these genera can by electrophoresis even be identified to sibling species. In an ecological context, the species and their hosts have co-evolved.

Live A. simplex larvae, found in marinated herring, were shown on German TV in 1987, leading to instant reduced demand for fish. The public became aware of possible anisakid larvae in food fishes, and the German authorities established rules for permissible statistical numbers of larvae in imported fish. Other countries tightened control with fish products crossing their borders. A strange situations resulted - lorries loaded with fish were detained on the Italian border, while any housewife in Rome could buy fresh local fish teeming with A. simplex larvae. H. Möller in Kiel, Germany convened a special workshop on the nematode problems in North Atlantic fish in 1989 (Möller 1989). Ukraine and Byelorussia import frozen round herring from Norway. Their food inspection service demands that the herring shall be free of any parasites - which is impossible to guarantee. As the public in other countries are becoming aware of the possible presence of nematode larvae in fish, exporters, importers, and their customers are asking for basic information, such as is presented in this chapter.

Also, in Spain the public is becoming aware of anisakid worms in fish, and in 1997 this subject has almost daily been given attention in the media. It is worth noting that most of the allergy work referred to above is done in Spain.

When fish die, and are left ungutted, they will become 'soft in the belly' and due to autolysis larvae may start to wriggle out of their decomposing capsules. There are several papers on the number of A. simplex larvae in fish viscera and in fish muscles and it is almost an axiom that they migrate from viscera into the muscles as soon as the host dies (Smith and

Page 167

Woothen 1974). Thus, it may be imperative that fish should be gutted soon after capture to avoid the larvae moving into the flesh. However, in modern fisheries, large number of fish are either caught in trawls or in purse seines; and are by the ton lifted/hoisted out of the water. This means that almost all fish are exposed to heavy mechanical pressure, which very likely disrupt or damage the connective capsules surrounding the larvae. Roepstorff et al. (1993) handled small samples of live herring very gently and kept them ungutted for several days on ice; there was no significant post-mortem migration of Anisakis larvae.

The anisakid nematodes dealt with in this chapter have complicated life cycles. Knowledge of their taxonomy and biology, including their host ranges, is essential. When man interferes in the normal life cycle by consuming raw intermediate hosts, fish and squids, with live larvae, their ensuing attempt to develop in an abnormal hosts represent a zoonosis. Armed with basic biological knowledge, we should be able to minimize human cases of anisakidosis.

0 0

Post a comment