Abstract
Abstract Background Nematodes of the family Anisakidae are parasites of many fishes and aquatic invertebrates which act as intermediate or paratenic hosts, while mammals and fish-eating birds are definitive hosts. Infective L3 larvae may be incidentally taken by human through eating raw or undercooked fish meat, causing anisakidosis. The main purpose of this study is to provide a basis for the future investigations to discover the genetic diversity of this widely distributed parasite nematodes of fishes and fish eating animals and their effect on fisheries and public health in Egypt and worldwide. Results One thousand, one hundred and fifteen specimens belong to nine fish species were collected from Lake Nasser, Egypt, and examined for infection with Anisakid larvae. Four fish species (Oreochromis niloticus, Tilapia galilaea, Lates niloticus, and Hydrocynus forskahlii) were found infected with third stage larvae of Contracaecum spp. No other Anisakid nematodes were detected. Larvae were found in the body cavity adhering to mesenteries by a thin membrane, except in Oreochromis niloticus and Tilapia galilaea were found free in branchial chambers. The highest prevalence was recorded in L. niloticus (100%) and H. forskahlii (82%). The mean intensity of infections were 0.17–4.12 and 5.1–10.3 in L. niloticus and H. forskahlii respectively. For further identification, the internal transcribed spacers (ITS-1 and ITS-2) of nuclear ribosomal DNA from isolated larvae (n = 54) were amplified by PCR, followed by single-strand conformation polymorphism (SSCP) analysis which revealed five possible profiles. Conclusion Light and scanning electron microscope studies revealed that all anisakid larvae in the present study showed the most typical features of the genus Contracaecum. The sequencing (n = 28) and sequence and phylogenetic analyses showed that the present nematode larvae are likely belonging to C. multipapillatum.