Molecular characterization of zoonotic anisakid Contracaecum spp. larvae in some fish species from Lake Nasser, Egypt

Abstract

Infections with zoonotic anisakid nematode larvae Contracaecum spp. were detected in five fish species from Lake Nasser, Egypt: three tilapia species (Oreochromis niloticus, Sarotherodon galilaeus and Tilapia zillii) and two catfish species (Malapterurus electricus and Heterobranchus bidorsalis). Severely infected fish displayed general body emaciation and distended abdomen. The overall prevalence of infection was 30% (tilapia species 24.17% and catfish 41.67%). The larvae were morphologically identified as third stage larvae of Contracaecum. The internal transcribed spacer sequences of nuclear ribosomal DNA (ITS-1 and ITS-2) were used for molecular characterization, resulting in the submission of six new sequences to the GenBank database and confirming that the present larvae were members of the C. multipapillatum complex (C. multipapillatum and C. quadripapillatum). The phylogenetic analysis corroborated the molecular results and demonstrated Contracacum's polyphyletic nature. The larvae aggressively bore into the heart ventricle of tilapia species (Heartworm Disease), causing severe pathological changes such as myocardial fibre atrophy, interstitial haemorrhage, pericarditis with eosinophilic granular cells infiltration and intravascular thrombosis, and impairing heart function, whereas in catfish, the larvae encapsulated in the abdominal cavity and caused little harm. As a result, they are the causative agent of Heartworm Disease.