Written by Andrew Smart, Conservation and Science Manager
It’s not easy working with amphibians and controlling the desire to pick them up and look at them. …from our childhood, the excitement of catching a frog, rescuing a toad or catching a newt in a pond are feelings we carry with us into adulthood. Amphibians are wonderful animals, we want to look at them, observe them and hold them in our hands. But what happens when we do that?
What does it mean for the animals and why do we need to pause and remind ourselves the best thing to do is not handle amphibians at all?
The Amphibian and Reptile groups of Great Britain advice note 4 (ARG, 2017) suggests that amphibian workers should:
- Handle [animals] with powder free disposable vinyl gloves which are rinsed in pond water before contact with animals.
- A single set of gloves can be used when working at any site but should be disposed of between sites.
- Equipment, including footwear, nets, traps etc should also be disinfected between sites.
The Herpetofauna Workers Manual (revised 2003) : suggests that:
- handling is kept to an absolute minimum because of the impact of the warmth of the human hand on the animal
- if necessary, “good practice [is] to wet hands with pond water before handling amphibians”.
The risk of transmission of disease such as ranavirus or chytridiomycosis (chytrid fungus) caused by Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans (Bsal) between sites remains high as spores can survive on equipment, footwear or vegetation. Chytrid causes death by disrupting the uptake of salts through the skin, disrupting amphibian metabolism and ultimately stopping their hearts from beating (ARC, 2024). The ‘perceived wisdom’ is that handling with dry hands can damage the mucus layer, hence the need to wet either hands or gloves prior to handling an amphibian.
Varga et al (2019) highlighted the value of amphibian skin as an ‘innate immune organ’ acting as the first line of defence against pathogens in an aquatic environment. Amphibians have a glandular network beneath their skin that produces antimicrobial and toxic chemicals which help protect the animal against pathogens and predators. Mucosal glands produce a mucus layer which protects the skins, maintaining elasticity, permeability and moisture on the skin surface (Varag et al, 2010). Along with acting as a physical barrier between amphibians and their environment, the mucus layer is a matrix containing bacteria and antimicrobial, antibacterial, antiviral, antifungal or anti-parasite secretions from the animal itself. In many species the mucus also contains alkaloids, secreted as a defence against predation. Damage to this mucus layer can have an impact on animals; handling can remove the mucus layer and some chemical pollutants, such as pesticides, can damage skin mucus having a sub-lethal effect on amphibians in both larval and adult forms.
A recent review by Woodhams et al (2023) considered the ‘adaptive microbiome hypothesis’ arguing that amphibians, like other vertebrates (including humans) have large numbers of bacteria on their skin. Previously, Rollins-Smith (2009) found beneficial bacteria within the skin mucus of amphibians produce antifungal compounds which inhibit the growth of Bd and suggested that bio-augmentation could be a future possibility to protect highly endangered species. Woodham’s (2023) review found evidence that while Bd was increasingly virulent as it passed through Central America; in Panama, amphibian ‘mucosal skin defences’ were higher after the disease appeared, indicating a possible response by amphibian populations as their microbial community evolved to combat Bd. The hypothesis proposed suggests that on recovery from an initial infection, the microbial community can better combat subsequent exposures. This could also explain why some amphibians can operate as carriers of Bd and Bsal fungus while others suffer significant mortality on exposure.
In 2010 Phillott et al highlighted the need to minimise exposure of amphibians to pathogens during any form of field study, emphasising the need for strict bio-security and hygiene when moving between sites, including:
- disinfecting footwear using sodium hypochlorite
- disinfecting equipment such as scales, callipers or containers
Phillott et al (2010) also discussed the damage that can result from handling amphibians and identified a number of papers that found stressed animals had a greater risk of infection. Apart from the impact on their skin, handling amphibians can cause the stress, and repeated handling has been shown to impact their behaviour. Bliley and Woodley (2012) studied the impact of repeated handling in a species of salamander and found that repeated handling reduced feeding behaviour in females and activity in both males and females. They argued that stressed animals may even avoid reproduction and divert energy into immediate survival.
Phillott et al (2010) argued the direct transfer of microbes and spores between animals can be reduced by using single-use gloves. Importantly, they highlighted previous work that found some tadpoles suffer lethal and sublethal effects when exposed to latex (Gutleb at al 2001) and nitrile and to a lesser extent vinyl so larvae should only be handled with gloves that have been proven safe for that species or with hands wetted by water from the source pond. They argued that when gloves are not available, hand washing with 70% ethanol allowing the hands to air dry between handling is an alternative. If this is not possible in the field, ‘hand washing in the water body to which the amphibian is naturally exposed’ is the best alternative (Phillott 2010).
There seems to be some variation in the impact of gloves; Mendez et al (2008) found that water washed from nitryl gloves killed Bd spores on contact while latex and polyethylene gloves had no effect. It is important to note the effect of vinyl gloves varied with brands and batches. Human skin also demonstrated a fungicidal effect on Bd, possibly due to the presence of antifungal peptides on the skin surface. They recommended that to minimise the risk of transfer of disease between individuals single use disposable gloves were the best option followed by bare hands as a preferable alternative to continual use of the same pair of gloves (Mendez 2008).
A more recent study (Thomas et al, 2020) in evaluating the impact of nitrile and vinyl gloves on Bd and Bsal found glove ‘rinsewater’ led to a reduction in Bd and Bsal spore production compared to water alone. They recommended:
- the single use of nitrile gloves should be advocated to handle amphibians.
- at a minimum gloves should be changed between each population
- the repeated use of the same pair of gloves should be preferred above handling animals bare handed
So we know the value of the mucus layer on the skin of an amphibians and we understand the risk of damaging that skin, disrupting the animal’s immune defences. We are also aware of the risk of disease transmission from animal to animal if we handle multiple animals in the field. There remains a dilemma as to which advice to follow; the 2017 guidance aligns with the most recent experimental work but how does a toad patroller change their gloves between each animal and still manage to collect the animals before they reach the road verge?
We have to agree a sensible approach; animals in the same population share the risk of disease transfer within their aquatic environment and so the existing 2017 ARG Advice Note 4 appears to remain the most sensible approach to handling animals. However, on some occasions, if necessary, a hand dipped in the source water-body may do less damage than not moving the animal.
Ideally, we should do our best to restrain our excitement and look rather than touch!
References:
ARC [online] accessed 2024 Chytrid fungus | Amphibian and Reptile Conservation (arc-trust.org)
ARG (2017) [online] accessed 2024 4. Advice note 4 (revised) – Amphibian Disease Precautions, A Guide for UK Fieldworkers.pdf – Amphibian and Reptile Groups of the UK (arguk.org)
Bliley, J.M. and Woodley, S.K., 2012. The effects of repeated handling and corticosterone treatment on behavior in an amphibian (Ocoee salamander: Desmognathus ocoee). Physiology & behavior, 105(5), pp.1132-1139.
Gent, T. and Gibson, S. eds., 2003. Herpetofauna workers’ manual (rveisd reptint) . Peterborough: Joint Nature Conservation Committee. Herpetofauna Workers’ Manual (revised reprint) | JNCC Resource Hub
Gutleb, A.C., Bronkhorst, M., van den Berg, J.H. and Murk, A.J., 2001. Latex laboratory-gloves: an unexpected pitfall in amphibian toxicity assays with tadpoles. Environmental toxicology and pharmacology, 10(3), pp.119-121.
Mendez, D., Webb, R., Berger, L. and Speare, R., 2008. Survival of the amphibian chytrid fungus Batrachochytrium dendrobatidis on bare hands and gloves: hygiene implications for amphibian handling. Diseases of aquatic organisms, 82(2), pp.97-104.
Phillott, A.D., Speare, R., Hines, H.B., Skerratt, L.F., Meyer, E., McDonald, K.R., Cashins, S.D., Mendez, D. and Berger, L., 2010. Minimising exposure of amphibians to pathogens during field studies. Diseases of aquatic organisms, 92(2-3), pp.175-185.
Rollins-Smith, L.A., 2009. The role of amphibian antimicrobial peptides in protection of amphibians from pathogens linked to global amphibian declines. Biochimica et Biophysica Acta (BBA)-Biomembranes, 1788(8), pp.1593-1599.
Thomas, V., Van Rooij, P., Meerpoel, C., Stegen, G., Wauters, J., Vanhaecke, L., Martel, A. and Pasmans, F., 2020. Instant killing of pathogenic chytrid fungi by disposable nitrile gloves prevents disease transmission between amphibians. Plos one, 15(10), p.e0241048.
Varga, J.F., Bui-Marinos, M.P. and Katzenback, B.A., 2019. Frog skin innate immune defences: sensing and surviving pathogens. Frontiers in immunology, 9, p.433806.
Woodhams, D.C., McCartney, J., Walke, J.B. and Whetstone, R., 2023. The adaptive microbiome hypothesis and immune interactions in amphibian mucus. Developmental & Comparative Immunology, 145, p.104690.