Amphibians, especially ground dwelling species, can come into direct contact with various bacteria and fungi constantly which will be living in the soil or water or present on the insects they eat. If the frog or toad is healthy, these "environmental" pathogens will not cause any problems. But when the animal is stressed or these pathogens build up in an enclosed environment (such as a keeper's tank in captivity), these bacteria and fungi can overwhelm the animal and cause infection.
Frogs have a habit of shedding the outer cuticle layer of their skin, rubbing it forward on the body, then consuming it. This is probably some form of recycling energy or proteins, but in a disease filled environment, it is probably something which is more detrimental than it is useful.
The skin of an amphibian is protective to the body and keeps out many of these environmental pathogens, but when that skin is breached by injury, a scratch, or an ulcer, this allows bacteria and fungi to enter the body and cause systemic infection and death if not treated.
There are a variety of symptoms which can point to a bacterial infection but all amphibians are slightly different and a symptom seen in one species is not necessarily the same symptom that will appear in another species. But there are some things to look for, especially in the green coloured tree frog species.
We have seen an unidentified problem on frogs which we are calling "skin rot" until better identified. Some limited lab work resulted in a diagnosis of "Aeromonas and pseudomonas" but the rest of the testing we requested was not done. This problem resembles leprosy in that it starts out attacking the skin but rapidly becomes systemic. We can only treat this in the very early stages - once advanced, as in the photo below, the same antibiotic seems to cause anaphylactic shock instead of working against the pathogen!
The problem starts out as an army green, rounded discolouration in the skin, usually on the back of the thighs but sometimes other places on the back, and then turns blueish. As it progresses, the patches get darker until they are black and new greenish/blue ones appear elsewhere on the back. By the time the skin is blackened (necrotic), the bacteria has eaten through the skin and some bleeding could be present.
There are some other flesh-eating bacteria and fungi which are extremely rapid and can eat away skin by a cm per hour - there will be inflamation and bleeding at the edge of the skin (these need veterinary attention immediately!). Thankfully these cases are very rare. The last one we received has been sent to a lab but we are still waiting on results (unforuntately, a lot of labs that we have sent specimens to have never provided us with results - were they lost in the mail or did somebody not want us to have proof of what was going on with these animals???).
Bacterial and fungal problems on frogs need to be treated quickly before they become systemic. If the affected frogs are in captivity, their enclosures need to be dismantled and thorougly disinfected and rinsed well before being setup again with new plants, substrate, etc. A tip for reducing the problems caused by environmental pathogens are to use leaves from your shrubs and trees as your substrate for tree frogs instead of fancy mosses and soils. River sand that has been thorougly rinsed and soaked for several days can be used for burrowing species as this can be easily rinsed out to keep clean whereas soils can't.
The other side of the same coin is to ask why your animals are stressed enough to become ill. Is it their setup, weather conditions outside (such as flooding or drought), change in food supply or setup, etc.
There is another disease group which has been common to captive frogs when they are experiencing stress but wild caught frogs and toads with soil and water bacteria have also become common in this region - especially since the wet season of 2007/08. There are several bacteria which usually fall into the overall category of "gram negative" or "gram positive" but there are exceptions of course. Many bacteria are treated with specific drugs which don't work on other bacteria so identifying which infection is important so that the right antibiotic can be administered. Our page on environmental bacteria and fungi will describe the problems wild caught frogs are coming in with. This page is devoted to two of the more contagious bacterial pathogens in amphibians - Pseudomonas (which might also be known as "dropsy") and Aeromonas ("Red leg").
"Red leg" (Aeromonas hydrophilla)
Aeromonas can devastate captive collections as it has both contact and airbourne transmission, but it does occasionally cause outbreaks in the wild, as it did in the UK after they already had an outbreak of ranavirus. The common name of "Red leg" is given because the disease will cause a pinky-red flush on the underside of the thighs which can also spread to the belly area above the vent. Any bacterial problem in amphibians can cause a pinky flush in this area so this symptom alone is not enough to indicate Aeromonas. There are other symptoms as well which demonstrate the pathogen's attack on the skin such as a slimy pasting occuring all over the body or mostly underneath (the ventral surface) and ulcers in the skin which will be concentrated on the feet, legs and sides of the body. The frog may lose weight quickly, become lethargic, and it might also become paler than usual.
If Aeromonas is suspected in your frogs, you can contact us to discuss the symptoms and treatment procedures we use. You will need the antibiotic Baytril (enrofloxacin) from a vet but it needs to be diluted before use on amphibians. We can provide you with the dilution rate and dosage when you contact us.
Preventing this problem in your animals requires clean conditions in the animals' enclosures but you can also protect your animals even more with a medical air filter. Aviculturists in North America routinely have such filters since they and their birds (especially cockatoos which produce powder in their feathers) are locked up indoors together throughout the winter. This leads to a much greater incidence of respiratory problems and allergies, which are eliminated by the air filters. Air filtration for frog owners with large or valuable collections is another protective step you can take to reduce airbourne problems circulating around your tanks.
This disease is unfortunately a treatment resistant problem. It is an aggressive tissue-eater and extremely painful. It is fast and can kill a frog in only a couple days once clinical signs appear. The frog will become very bloated, become lethargic, change to a very dark body colouration (darker than a Hass avocado!). Very few antibiotics will work against Pseudomonas - Gentamycin is one and ciprofloxacin is another. There is no time to waste if Pseudomonas should appear so we would suggest that if you keep frogs - especially the Common Green/White's - that you might consider either having gentamycin on hand in your refridgerator or that you have regular contact with a vet that can dispense the medication immediately if it is needed. Both gentamycin and 'cipro' are nasty antibiotics so extended use of these is not recommended. Depending on where you are, your vet might not even be allowed to dispense ciprofloxacin. With painful conditions such as this, painkillers should be used on amphibians to relieve suffering and reduce stress so that the antibiotic MIGHT have a chance to succeed. Pseuodmonas is a fluorescent bacteria. If you have a Wood's lamp (blacklight), you can scan the frog's body with this lamp in a dark room. The Pseudomonas will glow green. It is a simple way to quickly identify that you have the nasty Pseudomonas present so you can start immediate treatment and pain relief.
Why Would Your Animals Get Sick?
If your animals are stressed enough to become ill, then you need to also look at their setup and any conditions which are affecting their health such as the onset of breeding season, enclosure is too small, recent flooding or very severe storm activity in your area, introduction of a new animal which was not quarantined first, insufficient hiding opportunities, wrong lighting, poor nutrition, etc.
Another protective step is to restrict the contact visitors have to your animals. Aeromonas is likely to be carryed on clothing so a visit by another frog keeper who has recently had sick animals might result in something turning up in your animals. Always wash your hands with an antibacterial before and after contact with your animals or use disposable gloves when you handle them. Have a simple "hospital tank" on hand to immediately separate any sick looking animals from the others (preferably into another room) and handle these with disposable gloves.
The Rise of 'Environmental Pathogens'
The term 'environmental pathogens' refers to species of fungi and bacteria that live in an environment (such as soil or water) and are supposed to be there. These species are involved in the breakdown of materials (such as dead plants and animals or rotting food) so that the nutrients they contain can be taken up by living things. These bacteria and fungi are non-specific so they will just as happily convert a piece of fruit on the ground or the roots of a dead plant or the decomposing body of animal into basic components that will be eaten by earthworms or absorbed by living plant roots, etc - it is all part of the cycle of recycling that helps keep living things healthier. Environmental pathogens are also known as "opportunistic" in that they will not attack a living thing (such as us or a fish or a bird, for example) unless that living thing has a compromised immune system which doesn't defend it against attack, or the living thing has something else already attacking and weakening it such as an open wound or a serious infestation of parasites. We have been doing rescue and rehab work with amphibians for over 12 years and this has allowed us to see various patterns in what is attacking frogs, when these problems are just background issues or when they cause outbreaks, and how each new problem interacts with the problems that were already there. We have noticed that frogs in this region have been affected by environmental pathogens for some time but these pathogens took a big step forward in the period between January 2008 and April 2010. Not only did the numbers of frogs affected (especially from soil pathogens) increase but the range of nasty bacteria that turned up in the cultures we obtained from DPI were noticeably widened. Below is a short list of pathogens which have been cultured from some of our frog cases since January 2008. It is not a complete list of everything that has been found on frogs over the years but represents environmental pathogens we hadn't seen on our cases earlier. It is presented as listed on the DPI reports to make sure that we don't misinterpret the correct full name for the abbreviations. All the pathogens listed here have been found on the frogs' skin. This leads to two concerns:
With the gram positive pathogens in particular, they are generally more cryptic on the frogs than the gram negative ones are. Only some of the amphibians you find might have any of these on its skin - but you won't know when they do or don't. This is why we strongly encourage anyone handling a wild caught amphibian or a captive one which is ill to always wear disposable gloves and change them between each frog.
- Streptococcus sp. (not the species that would cause Strep throat - this refers to invasive or Group A and B strep)
- Ochrobactrum anthropi (this is one of the species that causes bacterial meningitis)
- Corynebacterium sp.
- Clostridium sp. (DPI says that it was not botulism, tetanus or difficile ...)
- Prov. rettgeri
- Ps. cepacia
- Ps. maltophilia
- Ps. paucimobulis
- Achromobacter sp.
- Acinetobacter sp.
- Pr. mirabilis
- S. marcescens
- Cit. freundii
- Penicillium sp.
- Aspergillus candidus
- Aspergillus glaucus
- Paecilomyces lilacinus
- Scopulariopsis sp.
- Geotrichum sp.
- Candida tropicalis
- Raoultella terrigena
- Ustilago sp. (cane smut) in the gut and this was specific to post-cyclone Larry (IDEXX lab, Brisbane)
Note: Streptococcus pyogenes and Staphylococcus sp. were identified using impression smears on the skin.
Why does something that was always there cause problems for frogs now?
Environmental pathogens have always been there and the frogs have evolved with them, but things are obviously changing. The pathogens being found on the frogs suggests one of two things:
All three could be working in tandem but our money is mostly on the third reason. The rest of this page will discuss the subject of amphibian immune system failure based our own observations from the cases we have received over the past 12 years and other related information we have seen about diseases in other wildlife.
One key reason why amphibian immune systems might be more affected now is the sheer amount of chemical use by a whole range of users, including farmers, councils, revegetation volunteers, pest control businesses, homeowners, mining companies, and so on. There is a definite insufficiency in toxicology and scientific investigation when it comes to exactly what these chemicals will do in an integrated ecological system - but they are marketed, distributed and heavily relied upon nonetheless. If there is less wildlife around, it is hardly noticed (a sign of "progress") and even when noticed, is too complicated to prove WHICH of the many chemicals used in an area is THE one that is causing the decline. (In Australia, we call this "being thrown into the "'too hard' basket".).
One recent area where chemical pollution has been proven to wipe out an entire taxon is the rapid and severe global decline in bee populations. This decline can threaten the global food supply so it was taken extremely seriously and resources were made available for a thorough investigation. The culprit was identified as a new neonicotinoid pesticide manufactured by Bayer. Some European countries have already banned this chemical but others like the US and UK are resisting a ban. (See the Avaaz.org website and many others for more information.)
If all the chemicals in widespread use (including herbicides) were extensively researched, as was done for the bees, we would have a wealth of new information which will undoubtedly show that these chemicals are not making our lifes easier or more convenient - they are causing a slow rot of our basic life supporting systems!
Another piece of the puzzle (in our view) is that researchers themselves seem to have little interest in investigating "home grown" opportunistic diseases. There is far more glamour and prestige it seems in going after globally-wandering emerging diseases instead of those which could be right under our feet and which would provide much more broad-spectrum information about what is happening to our planet. In simple terms, this is like treating a symptom to get rid of it rather than looking at why the symptom has appeared and what caused it so that the cause can be addressed rather than just controlling the symptom!
If the amphibian immune system is failing or being compromised, what could this be telling us?