A host choosy gill parasite (Dactylogyrus spp.) in fish: an insight into host-parasite interaction for developing control strategies

Dactylogyrosis is caused by more than 900 reported species of Dactylogyrus (gill fluke), mostly in Cyprinoidei fish leading to low to severe mortality in different culture systems and also in rivers/lakes. Dactylogyrus has been reported worldwide where Cyprinoidei is endemic. In recent years, incidents of infection and infectivity of different species of Dactylogyrus have increased many-fold due to several predisposing factors like intensification of culture, environmental quality, climatic change, poor quality fish seed, etc. These parasites are host choosy, either generalist or specialist. Dactylogyrus infection causes major changes in the anatomy and physiology of gill function. Necrosis, hyperplasia and hypertrophy of gill lamellae are the common pathologies observed during infection, which in turn invites other secondary pathogens leading to heavy mortalities. Currently, very few drugs or chemicals are available for controlling dactylogyrosis. Very few attempts have been made to develop vaccines against this important parasite. Here, we review the innate and adaptive immune responses modulated by Dactylogyrus infection and a hypothetical immunological model has been proposed to understand host-pathogen interaction based on our findings. The information collected and analysed in this review on the biology and host-pathogen interaction will help in the development of prophylactic and other sustainable management measures to reduce the loss associated with dactylogyrosis.