This axolotl has saprolegniasis. Photo by Dr. Mark Schrag.
Amphibian saprolegniasis is a skin infection caused by one of a variety of water molds. Owners commonly call it cotton skin. Saprolegniasis is usually seen in two forms, either in a localized form where there are only small patches of infection, or in a more generalized form that affects the entire body. Both forms can cause severe, life-threatening disease by causing breaks in the skin that lead to secondary bacterial infections. This disease is found in both adults and tadpoles, and tadpoles often suffer from infections of the spiracles (breathing tubes), resulting in respiratory dysfunction and death.
The first signs of saprolegniasis that owners typically notice on the aquatic amphibian’s skin are small tufts of white, gray, brown, or green cottony material called a fungal mat; they are like tangled threads. In terrestrial amphibians, they typically see a gray to dull white layer of slime that bleeds when touched or scraped.
White fungal mats suggest an early infection, while gray, brown, or green colored mats indicate an infection that has been around for more than a few days. The skin under the fungal mats is often ulcerated and may be open all the way down to the bone.
A red rash or discoloration, called a septic blush, may be seen on pale areas of the body, such as the belly or the underside of the thighs. Other signs that are often noted may include lethargy, weight loss, gaping, vomiting, and lack of appetite.
Saprolegniasis is common when water temperatures are too cool and husbandry isn’t quite good enough to prevent illness. Outbreaks are common in situations where a tank is overcrowded and the water quality is suboptimal.
Any species of amphibian can be affected. However, it seems that species that are fully aquatic, such as African clawed frogs, some salamanders and axolotls, are more prone to saprolegniasis.
There are a number of other risk factors or captive conditions in amphibians that are associated with getting infected with Saprolegnia:
- Amphibians maintained at or below the correct temperature range for that species but is commonly seen in tanks maintained below 68°F.
- Abrasions or other injuries to the skin from tank mates, rocks and other sharp objects in the enclosure.
- Removal of the slime layer from chemical irritants such as an ammonia spike (due to inadequate biological filtration) or contamination of the enclosure with disinfectants, soaps, or detergents.
- Malnutrition, particularly hypovitaminosis A.
Owners of ill aquatic amphibians should call their veterinarian before coming into the office for the appointment. This is because your veterinarian will often ask you to take some measurements of the water for evaluation. These measurements include the temperature of the water, the pH and the total ammonia nitrogen (TAN) of the water. All of these measurements must be taken directly from the tank and can be obtained using an ammonia and pH test kit designed for freshwater tropical fish tanks. If this is not possible, then an airtight glass jar filled to the top with the aquarium water should be brought into the veterinary office and analyzed as soon as possible.
At the appointment, your veterinarian will start by taking a thorough medical and husbandry history and give your amphibian physical examination. In the vast majority of cases your veterinarian will be able to diagnose saprolegniasis based on the water measurements and the clinical signs.
No other disease has clinical signs that closely resemble the cottony tufts of saprolegniasis. However, early stages seen as discoloration of the skin with ulcers may be mistaken for other diseases that your veterinarian may want to check for.
In the clinic, your veterinarian will likely want to perform a skin scrape (using a slide to collect some surface material) and a look at it under the microscope to look for water molds that cause saprolegniasis, or for protozoa that can cause signs that look like saprolegniasis.
If there is a history of water temperatures that are less than or equal to 68°F, saprolegniasis is a likely diagnosis.
There are a number of treatment options that your veterinarian will discuss with you depending on the species affected and the duration and severity of the disease.
Where practical, raise water temperature to above 68°F. Some species of amphibians may not tolerate warmer temperatures.
For localized or patchy infections, your veterinarian may want to gently pull off the mats (debride) and apply a topical medication to the wounds.
In the case of a more generalized infection that affects most of the skin, a bath in an anti-fungal medication like itraconazole or a salt-solution may be used. These baths last for about 5 to 60 minutes and are often repeated.
If your veterinarian suspects a bacterial septicemia, then antibiotics may be used to treat the infection.
Your veterinarian will also review husbandry, paying particular attention to water filtration and other sanitation practices. Husbandry may be a contributory factor.
Appropriate water quality and stocking densities are key aspects of prevention. Saprolegniasis typically occurs only when water temperatures are less than or equal to 68°F.
Water molds are highly common in aquatic environments like aquariums. High water quality is the first line of defense against outbreaks in an amphibian collection. To achieve this good water quality, owners should obtain a commercial water testing kit from an aquarium store or pet shop and maintain a water quality log that monitors, at the least, temperature, pH, and ammonia levels. Additional tests such as nitrites, nitrates, hardness, and alkalinity may be helpful. Ammonia spikes and temperature drops may lead to outbreaks of saprolegniasis.
Discuss with your veterinarian biological filtration in aquariums and make sure that this system is maintained. Consider adding an ultraviolet (UV) sterilizer to the filtration system that will help with maintaining good water quality.
Ensure that crowding and aggression between tank mates are not contributing to the problem.
Review feeding practices to make sure that malnutrition or feeding too much is not a contributing problem to overloading the filtration system being used.
The prognosis for amphibians with saprolegniasis varies by how long they have had the disease and if it is patchy or more generalized and how rapidly the affected amphibian and the enclosure receives veterinary treatment. Fortunately, the majority of cases have a good prognosis with an early diagnosis and treatment. Prognosis is guarded to poor if deep ulcerations and systemic signs of disease are noted.