Aeromonas hydrophila is a common species of gram negative bacteria that often infects captive frogs and salamanders. It is particularly prevalent during the warmer months, when high temperatures stress amphibian immune systems (even tropical species often spend much of their time in cool micro-habitats) and leave them vulnerable to microorganisms that might otherwise have been resisted. Aeromonas infections are usually referred to as “red leg” or “Septicemia”.
Red leg, so named because the red lesions associated with it often first appear on the skin where the rear legs meet the body, is contagious and can be transmitted by contact with infected water, animals, wood, etc. The skin hemorrhages that typically occur become progressively deeper and the skin eventually sloughs off. Afflicted animals may also twitch, convulse, and become comatose. If not treated in its early stages, the condition is almost always fatal.
Improved sanitation is an immediate first step to take. Hands must be washed after handling animals and enclosures, for your own and your collection’s benefit. Environmental conditions such as poor hygiene will contribute to Aeromonas outbreaks, as will overcrowding.
Refrigeration as Treatment
Red leg is sometimes cured or by refrigeration at 39 to 41°F for two weeks. This treatment, pioneered in laboratory colonies of leopard frogs, has also been successfully used with Mexican axolotls. It appears that the immune systems of some amphibians function more effectively at low temperatures, while Aeromonas bacteria does best under warmer conditions.
The beneficial effects of low temperatures are not limited to red leg alone…while working at the Bronx Zoo I twice submitted “dead” salamanders (a mudpuppy and a hellbender) for necropsy, only to find them alive and well after a night in the animal hospital’s refrigerator!
When working with animals afflicted by any type of infection, it is very important that you contact your personal physician for advice concerning possible health risks to you and other members of your household.
While lacerated skin would lead one to believe that Aeromonas is the culprit, a definite diagnosis can only be made by blood culture performed by a veterinarian. This is important because a number of other species of bacteria, including Pseudomonas and Salmonella, may cause similar lesions, and the treatment of each will likely vary. Opportunistic bacteria and fungi, which commonly colonize the open wounds, must also be addressed.
An interesting early case history of a red leg outbreak among captive frogs is posted at https://kb.osu.edu/dspace/bitstream/1811/5136/1/V66N01_087.pdf.