Immersion mucoadhesive cationic lipid-based nanovaccine enhances protective efficacy and immune responses in striped catfish (Pangasianodon hypophthalmus) against Edwardsiella ictaluri

Summary 

Striped catfish, scientifically known as Pangasianodon hypophthalmus, has gained significant recognition as a primary whitefish species in aquaculture worldwide. Its production has seen a remarkable increase to meet the global demand for seafood. This species holds crucial importance for many low to middle income countries (LIMCs), especially South-East Asia, as it serves as a vital protein source and generates essential income for numerous low-income families. However, the necessity for intensive farming methods to meet the rising demand has been impeded by several challenges, including substandard fish farming practices, water quality issues, and a surge in infectious disease outbreaks within aquaculture systems. Among these challenges, Bacillary necrosis of Pangasianodon (BNP), a recently identified disease caused by Edwardsiella ictaluri, has emerged as a significant infectious disease concern in intensive striped catfish production. E. ictaluri can affect fish of all ages, but it particularly leads to high mortality rates among fingerling and juvenile fish. During the initial stages of infection, BNP exhibits minimal external symptoms. Clinical signs become apparent shortly before death occurs. Affected fish swim slowly near the water's surface and, upon examination, display pale discoloration on their skin and gills. Additionally, internal examination reveals white spots on the liver, kidney, and spleen. Outbreaks attributed to BNP lead to complete mortality, reaching up to 100%, resulting in significant economic implications. This poses a threat to food security and undermines sustainability in aquaculture. Consequently, the primary approach currently employed to treat BNP is the administration of antibiotics. However, relying on drug application to combat disease outbreaks is expensive and raises significant concerns for both the environment and consumers. It is not a sustainable long-term solution to address the problem. Vaccination is a preferred strategy for managing infectious diseases in aquaculture, as it can effectively prevent disease, reduce economic losses caused by high levels of mortality, and decrease the reliance on antibiotics. Hence, researchers will develop a mucoadhesive cationic lipid-based nano-immersion vaccine for striped catfish (Pangasianodon hypophthalmus) against Edwardsiella ictaluri.

Project Outcomes

Striped catfish (Pangasianodon hypophthalmus) is a key whitefish species in global aquaculture, particularly vital for low- and middle-income countries (LMICs) in Southeast Asia. It serves as an essential source of protein and income but faces significant challenges due to intensive farming practices, poor management, water quality issues, and infectious diseases like Bacillary necrosis of Pangasianodon (BNP), caused by Edwardsiella ictaluri. BNP affects fish of all ages, leading to high mortality rates, especially in fingerlings and juveniles, with symptoms such as pale skin and white internal spots. Outbreaks of BNP can result in up to 100% mortality, posing severe threats to food security and sustainability. Given the high cost and unsustainability of antibiotic treatments, vaccination has emerged as a preferred strategy. This study aimed to develop a mucoadhesive cationic nanoemulsion vaccine, characterize its properties, assess its mucoadhesive abilities, evaluate skin penetration, and determine the efficacy of the vaccine against E. ictaluri infection in striped catfish. Healthy striped catfish were immersed in either formalin-killed sonicated cells (FK-SC), used as a positive control, or in chitosan nanoemulsion (CS-NE) and cetyltrimethylammonium bromide CTAB nanoemulsion (CAT-NE) for 30 minutes, followed by a challenge with E. ictaluri at 30 and 45 days post-vaccination (dpv). Fish survival was monitored for 15 days after each challenge, and specific IgM antibody levels were measured in serum and mucus up to 28 dpv, along with the expression of inflammatory genes. The CS-NE vaccine demonstrated promising characteristics, including a nano-sized (261 nm), positively charged (32.9 mV) structure with a PDI of less than 0.3, ensuring stability at 25°C for 90 days. CS-NE exhibited superior gill fluorescence intensity in striped catfish post-immersion and was the only vaccine to achieve a significant, time-dependent increase in skin penetration, reaching depths of 80 µm and 100 µm after 1 and 5 minutes, respectively. Additionally, CS-NE provided higher relative percent survival (RPS) at 30 and 45 days dpv compared to FK-SC and CAT-NE. Vaccination with CS-NE and CAT-NE also resulted in significantly elevated serum and mucus IgM levels. Significant Differences in the expression of MHC-2 and IL-1 key immune gene marker were observed in gill, kidney and splenic tissues post-vaccination in CS-NE vaccines, highlighting the great adjuvant potential of cationic polysaccharide chitosan potentiating mucosal immune response by triggering and induction of IL-1b secretion in antigen presenting cells.