The occurrence and clinical importance of infectious stage of Echinocephalus (Nematoda: Gnathostomidae) larvae in selected Australian edible fish.

Cases of gnathostomiasis, an infection caused by consuming infected seafood, have been reported in Australia. However, doubt exists over the validity of these diagnoses as there are no reports of Gnathostoma spp. in Australian teleost fish. Also, the diagnoses in human cases were based on a serological test developed in Thailand. The specificity and sensitivity of this test in non-endemic areas are uncertain. Interestingly, parasites belonging to the genus Echinocephalus, which morphologically are very similar to Gnathostomum, are commonly found in Australian fish and shellfish and can potentially infect humans. The aim of this study was to determine the occurrence of these zoonotic nematodes within commercial fish and to characterise nematode larvae in order to provide insights into the specific identity of the potential causative agents of gnathostomiasis in Australia. Six edible fish species (n = 163) were examined. Gnathostomid-type larvae were found only in Acanthopagrus australis and Rhabdosargus sarba. Detailed examination and sequence data suggested parasite larvae belonged to the genus Echinocephalus. Further investigation of the occurrence of zoonotic nematodes within marine environments and observation of their spatial and temporal patterns will help raise awareness of the significance of this food safety issue within global fishing industries and health sectors. The accurate identification of zoonotic nematodes is a key component of disease surveillance and control. This information can also be used to develop specific and sensitive diagnostic test.

New and known zoonotic nematode larvae within selected fish species from Queensland waters in Australia.

Zoonotic fish-borne nematodes are a significant and growing global health concern. However, in Australia their occurrence and geographical distribution are not well known. Moreton Bay in Queensland, Australia, is a popular tourist destination for domestic and international visitors where seafood is a popular food item. The aim of this study was to determine the occurrence of zoonotic nematodes within four commercially significant teleost fish species from Moreton Bay; Surf Bream, Sea Mullet, Yellow-Fin Tripod fish and Gold-Lined Sea Bream. Overall, 34.03% of fish examined (n = 144) were found to be a host to at least one parasitic nematode. The seasonal dynamics and prevalence of nematode infection was tested by statistical means. Results indicated a significant difference in seasonal infection for Surf Bream (p < 0.005) only. Several potentially zoonotic larval morphotypes were found, including Contracaecum types I and II, and Terranova type II (Family Anisakidae), and Hysterothylacium types VI and XIV and a new Hysterothylacium larval type herein assigned as type XVII (Family Raphidascarididae). ITS sequence data showed that some Contracaecum type II and Hysterothylacium types VI found in the present study are genetically distinct from those previously reported. The new genotypes were assigned to Contracaecum type II Genotype B and Hysterothylacium type VI, Genotypes B and C. This study provides essential information for future research on specific identification and differentiation of infective stages of zoonotic nematoda in edible fish.