Zoonotic Disease Potentials of Tropical Fish

Potential Zoonotic Diseases: Aside from food poisonings, the overall incidence of transmission of disease-producing agents from fish to humans is low. There are, however, a number of agents that are found in fish and aquarium water that have the potential to be transmitted to humans. In general, humans contract fishborne disease through ingestion of infected fish tissues or aquarium water, or by contamination of lacerated or abraded skin. An important feature of many bacterial and protozoal organisms is their opportunistic nature. The development of disease in the human host often requires a preexisting state that compromises the immune system. If you have an immune-compromising medical condition or you are taking medications that impair your immune system (steroids, immunosuppressive drugs, or chemotherapy) you are at-risk for contracting a fishborne disease and should consult your physician. The following is a list of known and potential fishborne zoonoses.

Mycobacterium: Organisms in the genus Mycobacterium are nonmotile, acid-fast rods. Two species, M. fortuitum and M. marinum, are recognized as pathogens of tropical fish. Humans are typically infected by contamination of lacerated or abraded skin with aquarium water or fish contact. A localized granulomatous nodule may form at the site of infection, most commonly on hands or fingers. The granulomas usually appear approximately 6-8 weeks after exposure to the organism. They initially appear as reddish bumps (papules) that slowly enlarge into purplish nodules. The infection can spread to nearby lymph nodes. More disseminated forms of the disease are likely in immunocompromised individuals. It is possible for these species of mycobacterium to cause some degree of positive reaction to the tuberculin skin test.

Aeromonas spp :Aeromonad organisms are facultative anaerobic, gram-negative rods. These organisms can produce septicemia in infected fish. The species most commonly isolated is A. hydrophilia. It is found world wide in tropical fresh water and is considered part of the normal intestinal microflora of healthy fish. Humans infected with Aeromonas may show a variety of clinical signs, but the two most common syndromes are gastroenteritis and localized wound infections. Again, infections are more common and serious in the immunocompromised individual.

Other Bacteria and Protozoa: additional zoonotic organisms that have been documented in fish or aquarium water. Human infections are typically acquired through ingestion of contaminated water resulting in gastroenteritis symptoms or from wound contamination.

Gram-negative Organisms: Plesiomonas shigelloides, Pseudomonas fluorescens, Escherichia coli, Salmonella spp., Klebsiella spp., Edwardsiella tarda

Gram-positive Organisms: Streptococcus, Staphylcocccus, Clostridium, Erysipelothrix, Nocardia

Protozoa: Cryptosporidium