Amphibian chytrid (Batrachochytrium dendrobatidis)
Chytridiomycosis is a skin disease caused by a microscopic fungus, Batrachochytrium dendrobatidis (often abbreviated as "Bd"). This aquatic fungus attacks the outer layer of skin in amphibians, a vital organ for them because they breathe an...
What is it?
Chytridiomycosis is a skin disease caused by a microscopic fungus, Batrachochytrium dendrobatidis (often abbreviated as "Bd"). This aquatic fungus attacks the outer layer of skin in amphibians, a vital organ for them because they breathe and drink partly through their skin. In the North African green frog (Pelophylax saharicus), a species found in Tunisian water bodies, this infection can go unnoticed in some tolerant individuals but cause serious or even fatal disease in others, especially under stress or unfavorable environmental conditions. It is considered by world animal health organizations as one of the major causes of amphibian population decline worldwide.
Key point
A disease with major impact on amphibian populations worldwide, capable of causing mass mortality during epidemic episodes; any suspicion in a breeding facility or natural body of water deserves particular attention.
Commonly observed signs
These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.
Related signs — each one links to its page:
Signs are often subtle and non-specific, which makes diagnosis difficult without veterinary examination. Changes in skin color or abnormal thickening of the skin may be observed, along with shedding (skin peeling in small pieces), diffuse redness, especially on the belly and legs. Affected animals often become lethargic, remain still in an unusual way, lose appetite, and adopt an abnormal posture with hind legs spread out. Jerky movements, loss of the ability to jump properly, or spasms may appear in advanced cases. Death can occur rapidly once severe symptoms develop, linked to a serious mineral and fluid imbalance caused by skin damage.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
The disease is caused by a single-celled aquatic fungus, Batrachochytrium dendrobatidis, which produces mobile spores capable of swimming in water to find a new host. Once on the skin of an amphibian, the fungus develops in the surface cells and disrupts their normal function, particularly the exchange of water and essential minerals vital for the animal's survival.
Cool to moderate temperatures favour fungal development, whereas higher heat tends to limit its growth. High animal density in the same body of water or terrarium increases transmission risk. Stress from transport, captivity, poor water quality, or cohabitation with other amphibian species that carry the fungus without showing symptoms is also an aggravating factor. Young individuals and animals already weakened appear more vulnerable to severe forms.
Transmission
Transmission occurs mainly through direct contact between amphibians in water, or indirectly through contaminated water, mud, or wet equipment (nets, boots, aquariums) that has been in contact with infected animals or water. The fungal spores can survive for some time in the aquatic environment, which facilitates spread between water bodies if the equipment is not disinfected.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
Definitive diagnosis can only be made in the laboratory through non-invasive skin sampling (swab) analysed using molecular biology techniques (PCR) that detect the fungus's DNA. The veterinarian can also perform microscopic examination of skin scrapings. Clinical examination alone cannot confirm the disease, as the signs are common to other skin conditions in amphibians.
Treatment
Treatment, when indicated and carried out under the supervision of a veterinarian specialised in exotic animals, may combine antifungal baths and adjustment of the environmental temperature, the latter being unfavourable to the fungus when raised within the limits tolerated by the species. General support (rehydration, correction of imbalances) is often necessary in the most weakened animals. No self-treatment should be attempted without professional advice, as the choice and duration of antifungal therapy must be tailored by a veterinarian.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Prevention relies mainly on hygiene and biosecurity: systematically disinfect equipment (nets, containers, boots) between different bodies of water or animal populations, avoid introducing new amphibians without prior quarantine, and never release a captive amphibian into the wild. For amphibians kept in captivity, it is recommended to maintain good water quality, a temperature appropriate to the species, and reasonable animal density. Any new acquisition should ideally be examined by a veterinarian experienced in exotic animals before any contact with other animals.
Possible complications
Without treatment, infection can lead to failure of skin function, severe imbalance of mineral salts and hydration, potentially resulting in cardiac arrest and death. At population level, the disease can cause significant declines or even local extinctions in certain susceptible amphibian species.
When to see a veterinarian
Visible changes in skin appearance (color, texture, flaking)
An amphibian that is unusually sluggish and not responding normally to stimulation
Prolonged loss of appetite in a captive amphibian
Abnormal posture with rear legs splayed out or difficulty moving
Unexplained deaths in a group of amphibians kept together
Prognosis
The outlook is highly variable. Some individuals, especially healthy adults, can harbor the fungus without showing any signs of disease. However, once severe clinical signs develop, the course of the illness can be rapid and the prognosis becomes guarded to poor without prompt veterinary intervention.
Frequently asked questions
Can chytrid fungus be transmitted to humans or other domestic animals?
No, this fungus is specific to amphibians. It poses no known risk to humans, dogs, cats, or livestock.
Can a wild North African green frog be a carrier without being sick?
Yes, certain individuals and certain populations tolerate the fungus without developing visible symptoms, while potentially being able to transmit it to other, more susceptible amphibians.
Should equipment be disinfected after an outing in a humid natural environment?
It is strongly recommended, especially if equipment (boots, nets) has been used at several different water bodies, in order to limit the spread of the fungus between amphibian populations.
Can one release an amphibian from captivity into the wild after apparent recovery?
This practice is generally discouraged because even an animal that appears to be cured can remain a carrier of the fungus and contaminate local wild populations.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
EFSA — Autorité européenne de sécurité des aliments
Content reviewed by the TunisieVet editorial team · Updated 28 August 2026
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