Potential of fish eating birds to spread virulent Aeromonas hydrophila

Aeromonas hydrophila is a Gram-negative, rod shaped, facultative anaerobic bacterium that is ubiquitous to freshwater and slightly brackish aquatic environments and can cause infections in fish, humans, reptiles and avian... [ view full abstract ]

Aeromonas hydrophila is a Gram-negative, rod shaped, facultative anaerobic bacterium that is ubiquitous to freshwater and slightly brackish aquatic environments and can cause infections in fish, humans, reptiles and avian species. Recent severe outbreaks of disease in commercial catfish aquaculture ponds have been associated with a highly virulent Aeromonas hydrophila strain (VAh) that is genetically distinct from less virulent strains. Previous research has shown that Great Egrets, Double-crested Cormorants (Phalacrocorax auritus), American White Pelicans (Pelecanus erythrorhynchos), and Wood Storks (Mycteria americana) can carry and shed viable VAh after consuming fish infected with VAh. These fish-eating birds can serve as a reservoir for VAh and may spread the pathogen while foraging on uninfected catfish ponds.
Therefore, our objectives were to 1. Examine the role of fish-eating birds in the epidemiology and spread of VAh, 2. Evaluate the potential and likely process for colonization of VAh in non- endemic catfish ponds by evaluating transmission using a piscivorous bird (Great Egret, Arde alba) model in experimental ponds. We found that VAh survives passing through the GI tract of Great Egrets and viable VAh can be shed at substantial levels for a limited period when birds consume infected fish. We found that both treatment ponds had positive qPCR results for VAh while the control pond remained negative. VAh was detected in fish, pond water, chironomids, invertebrates, snails and mud from treatment ponds. We conclude that fish eating birds that consume fish infected with VAh can spread the bacteria to naïve ponds and cause a disease outbreak.