Sea Lice (Lepeophtheirus salmonis) Infestation Reduces the Ability of Peripheral Blood Monocytic Cells (PBMCs) to Respond to and Control Replication of Salmonid Alphavirus in Atlantic Salmon (Salmo salar L.).

Amr A A Gamil,Koestan Gadan,Øystein Evensen,Elisabeth Gislefoss

doi:10.3390/v12121450

Amr A A Gamil, Koestan Gadan + Show 2 more

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https://doi.org/10.3390/v12121450

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Journal: Viruses	Publication Date: Dec 16, 2020
Citations: 4	License type: CC BY 4.0

Affiliation: Norwegian University of Life Sciences

Abstract

Here we have studied the impact of lice (Lepeophtheirus salmonis) infestation of donor fish on the ability of isolated peripheral blood monocytes (PBMCs) to control the replication of salmonid alphavirus (SAV) ex vivo. PBMCs were collected by Percoll gradients at eight and nine weeks post copepodid infestation of Atlantic salmon post smolt. Uninfested fish were controls. PBMCs were then infected ex vivo with SAV (subtype 3), and samples were collected for analysis at two, four, and six days post virus infection. Virus titer in the supernatant was assayed in CHH-1 cells, and in addition, the relative expression of the virus structural protein E2 and selected host antiviral genes, IRF9, ISG15, Mx, and IFIT5, were assayed using real-time PCR. Significantly higher virus replication was detected in cells collected from lice-infested fish compared to controls. Higher virus titer coincided with an inability to upregulate the expression of different immune genes, IFIT5, IRF9, and Mx. These findings point towards compromised ability of PBMCs from lice-infested fish to control virus replication, and, to our knowledge, is the first report showing the direct effect of lice infestation on the interplay between viruses and immune cells. There is a possible impact on the dynamic spread of viral diseases in the aquatic environment.

Highlights

Sea lice (Lepeophtheirus salmonis) infestations remain one of the major challenges for the salmon industry, and the annual costs of treatment exceeded 5 billion NOK in 2018 [1,2,3]
We have explored the interplay between lice and salmonid alphavirus (SAV)-3 infection, where salmon were experimentally infested with Lepeophtheirus salmonis copepodids for 8–9 weeks until the lice developed into the pre-adult lice stage
Non-infested fish served as donors of peripheral blood monocytes (PBMCs), and cells were infected with SAV-3

Summary

Introduction

Sea lice (Lepeophtheirus salmonis) infestations remain one of the major challenges for the salmon industry, and the annual costs of treatment exceeded 5 billion NOK in 2018 [1,2,3]. Immune modulation where innate (inflammatory) host responses are downplayed is believed to be one of the main factors that enable the sea lice to stay on the hosts for a prolonged period [5,6,7,8,9,10]. This immune modulation, in addition to the wounds and stress induced by the lice infestation, may facilitate secondary infections and increase the host’s susceptibility to other pathogens. Non-infested fish served as donors of PBMCs, and cells were infected with SAV-3

Ethical Statement

Cell Lines

Virus Propagation

In Vivo Experiment

Ex Vivo Experiments

Graphics and Statistical Analysis

Results