Don’t Let It Get Under Your Skin! – Vaccination Protects the Skin Barrier of Common Carp From Disruption Caused by Cyprinid Herpesvirus 3

Abstract

Vaccination is the best form of protecting fish against viral diseases when the pathogen cannot be contained by biosecurity measures. Vaccines based on live attenuated viruses seem to be most effective for vaccination against challenging pathogens like Cyprinid herpesvirus 3. However, there are still knowledge gaps how these vaccines effectively protect fish from the deadly disease caused by the epitheliotropic CyHV-3, and which aspects of non-direct protection of skin or gill integrity and function are important in the aquatic environment. To elucidate some elements of protection, common carp were vaccinated against CyHV-3 using a double deletion vaccine virus KHV-T ΔDUT/TK in the absence or presence of a mix of common carp beta-defensins 1, 2 and 3 as adjuvants. Vaccination induced marginal clinical signs, low virus load and a minor upregulation of cd4, cd8 and igm gene expression in vaccinated fish, while neutralisation activity of blood serum rose from 14 days post vaccination (dpv). A challenge infection with CyHV-3 induced a severe disease with 80-100% mortality in non-vaccinated carp, while in vaccinated carp, no mortality was recorded and the virus load was >1,000-fold lower in the skin, gill and kidney. Histological analysis showed strongest pathological changes in the skin, with a complete destruction of the epidermis in non-vaccinated carp. In the skin of non-vaccinated fish, T and B cell responses were severely downregulated, inflammation and stress responses were increased upon challenge, whereas vaccinated fish had boosted neutrophil, T and B cell responses. A disruption of skin barrier elements (tight and adherence junction, desmosomes, mucins) led to an uncontrolled increase in skin bacteria load which most likely exacerbated the inflammation and the pathology. Using a live attenuated virus vaccine, we were able to show that increased neutrophil, T and B cell responses provide protection from CyHV-3 infection and lead to preservation of skin integrity, which supports successful protection against additional pathogens in the aquatic environment which foster disease development in non-vaccinated carp.

The influence of viral infection on cell line characteristics: Lessons learned from working with new cell lines from common carp

“…This is a further indication that no infection of the cells with CEV occurred. In previous studies, CyHV‐3 did not induce a strong type I IFN response in infected cells or tissues (Adamek et al, 2012, 2019, 2022), while the paramyxovirus CCPV induced an upregulation of this response (Adamek, Davies, et al, 2021). Likewise, CyHV‐3 did not induce high type I IFN responses, while CCPV induced high responses in CCAbre, CCAcar and CCApin cells but no response in CCAgill cells.…”

“…Furthermore, in infected cell monolayers, transcript levels of the virus‐induced interferon (IFN) a2 protein were analysed using the RT‐qPCR protocol from Adamek et al (2012) as a surrogate for inducing an innate immune response. The transcription of the genes of common carp were quantified using a standard curve prepared from 10 1 to 10 7 copies of recombinant DNA plasmids of the respective gene as described by Adamek et al (2022). For normalizing the expression, the gene encoding the 40S ribosomal protein S11 was used as reference gene.…”

“…For normalizing the expression, the gene encoding the 40S ribosomal protein S11 was used as reference gene. The level of expression is shown as number of the gene normalized against 1 × 10 5 copies of the reference gene (normalized copy number) as described by Adamek et al (2022).…”

“…The alloherpesvirus CyHV‐3 infects all organs of carp and koi, but mainly skin, gills, kidney, and brain and therefore was regarded as partly epitheliotrophic (Hanson et al, 2011). In carp, the infection initiates in skin, which develops severe alterations, including mucus hypersecretion, peeling away of the epithelium, scale loss and fin erosion (Adamek et al, 2013, 2022; Costes et al, 2009). Important histopathological changes also occur in gills, including hyperplasia of the gill epithelium, a subsequent degeneration of branchial epithelial cells and fusion of secondary lamellae leading to gill necrosis (Pikarsky et al, 2004).…”

Tilapia Lake Virus Vaccine Development: A Review on the Recent Advances

“…Indeed, this ability to proliferate or enter the host stimulates greater cellular responses both innate and adaptive, which in turn lead to a potent and lasting immune response [ 33 ]. Given their usually high efficacy, the use of an adjuvant to enhance the vaccine efficacy of live vaccines is not always required and a single dose might therefore be enough to stimulate a heightened immune response and RPS reaching 100% [ 34 ].…”