“Bumblefoot” in penguins probably sounds like the cutest disease you could suffer from. Just the word “bumble” makes a person think of some confused little bee which keeps bumping into a window or getting blown off course by the tiniest gust of wind. Unfortunately, the condition is a little more gruesome than the name suggests, so prepare yourselves, because it’s going to get grisly.

Penguins are one of the most popular avian species to be kept in captivity worldwide. Whether you agree or disagree with captive collections, the benefit of these colonies is that we can learn more about the species – their lifecycles, their biology and ultimately how they are impacted by global changes. But by keeping animals in captivity we begin to see an array of new hurdles to overcome; collectively known as “husbandry induced diseases,” and this is where bumblefoot comes into play. Penguins are relatively simple animals to keep due to their small size, basic dietary needs, and they’re easily entertained, spending hours chasing the reflections from a glitter ball. However, they’re not well adapted for the sedentary lifestyle of captivity. 

What is bumblefoot in penguins?

Bumblefoot, or ulcerative pododermatitis refers to the inflammation of the footpad which can be fatal if left untreated. While the primary, blister-like lesions on the base of the foot are not seriously detrimental to overall health, they render the animal susceptible to secondary infection, leading to chronic lameness or septicaemia (Tolpinrud et al., 2017). Warning signs of bumblefoot include limping, lopsided posture to avoid putting pressure on the infected foot and lying down for extended periods of time.  The condition has been identified in a variety of species including rodents, raptors and in rare cases humans (Stransky et al., 2016); each exhibiting the hot, painful lesions on the sole of the foot. However heavy bodied birds which spend more time on foot than in flight appear the most affected taxa.

Bumblefoot lesions on the foot of a captive penguin. Image by Louise Chiverton

So, what’s causing bumblefoot? If you think about blisters on a human foot, it’s usually due to friction between the shoe and heel and you’ve probably been walking for a long time (or maybe you’ve just got really sweaty feet!). These factors are similar to those affecting captive penguins; moist substrate, overuse of the foot pad through increased weight bearing, and reduced activity levels in a captive environment all seem to increase the likelihood of bumblefoot.

Inactivity in captive penguins may lead to increases in bumblefoot

In the wild, Humboldt penguins have been found foraging up to 72km from their rocky nesting beaches in South America (Culik et al. 1998, Chiu et al. 2011) yet in captivity will spend most of their time standing and waiting for food to be brought to them.  Even though zoos meet animal welfare legislation by providing the correct diet and environment for the penguins, in captivity our flightless friends become less inclined to swim unless they are actually fed in the water. Considering their wild cousins spend most of their lives in the ocean, the increased time spent waddling on land is considered just one of the factors to increase bumblefoot onset in these tuxedo wearing birds.

Weird weight distribution of penguins

Bumblefoot is a prevalent condition in non-aquatic species too, with a wide range of research conducted on raptors and the way they spread their weight. The foot of a bird of prey has evolved to stand on a flat surface (think of the wide branches and cliff faces you see in documentaries), but most captive display raptors are tethered to perches, causing them to put pressure directly on their “heel” rather than spreading their weight across the whole foot. Whilst penguins do not even try to stand on perches, their increased time on land has led to some unusual postures. Even before suffering with bumblefoot, captive penguins have been spotted resting back on their heels and raising their toes skywards, as if to take the weight off their toes. This seems to cause a more severe lesion on the main foot pad.

Substrate in zoo enclosures may lead to bumblefoot

Wet, hard surfaces? Standing still? The factors leading to bumblefoot in just one photo. Photo by Louise Chiverton

Penguins of all species take to solid ground for two key reasons: breeding and moulting, with some species estimated to spend 75% of their lives at sea (BAS, 2015). Yet in captivity, penguins are found to choose standing over swimming, particularly on flat, unnatural substrates such as concrete or render. In studies on farmed poultry, wet mulchy substrate was linked to higher rates of bumblefoot and when research was undertaken on captive penguins, similar links were made; penguins with wet feet standing on wet substrates had worse feet. Makes perfect sense when you think about it – our own skin cuts easier when wet and infections have easy access to the blood stream. And for penguins, secondary infections can be fatal.

Where do we go from here?

The research all points towards these three factors as the leading causes of bumblefoot. But now, work needs to be done to relieve the pressure off the feet off penguins – both in captivity and in the wild. That’s right, even wild penguins have been spotted with the classic symptoms of bumblefoot and that might be through human influence too. Remember climate change? Well the thought process is that as the ice sheets recede and sea levels start to rise, wild penguins may well be spending more time standing on damp, harsher substrates… just like those in captivity. Whilst further studies need to be completed to properly understand the impact on wild populations, what can be said for certain is that zoo collections must evaluate their enclosure design to reduce bumblefoot onset in the future.

Did you know any of this about penguin health and disease? Let us know what you learned. Also, we more that appreciate any support you can provide so we can continue to provide this type of information to you.

Check out some of our other blogs, too, about penguins:

• Zookeepers Help Penguin Conservation
• The choice of non-breeding penguins: To fast or not to fast?

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References:

1. BAS (2015). Penguins – British Antarctic Survey. [online] Available at: https://www.bas.ac.uk/about/antarctica/wildlife/penguins/ [Accessed 26 Jul. 2019].
2. Chiu, A.; Cárdenas, S.; Cardeña, M.; Bussalleu, A.; Guerrero, P.; Sandoval, F.; Tremblay, Y., 2011, The route of the Penguin : Use of marine habitat and pattern of attention to the nest by the Penguin of Humboldt ( Spheniscus humboldti ) in Punta San Juan , Peru.  Boletín Informativo UNOP 6: 21-27.
3. Culik, B., Luna-Jorquera, G., Oyarzo, H. and Correa, H. (1998), Humboldt penguins monitored via VHF telemetry, Marine Ecology Progress Series, 162, pp.279-286.
4. Stransky, O., Blum, R., Brown, W., Kruse, D. and Stone, P. (2016). Bumble Foot: A Rare Presentation of a Fusobacterium varium Infection of the Heel Pad in a Healthy Female, The Journal of Foot and Ankle Surgery, 55(5), pp.1087-1090.
5. Tolpinrud, A., O’Brien, M. F., Justice, W.S.M., Barrows, M., Steele, O. D. M., Gent, S., Meredith, A. ,(2017) Infrared Thermography as a Diagnostic Tool for Pododermatitis in Captive Greater Flamingos (Phoenicopterus roseus), Journal of Zoo and Aquarium Research, 5(1), pp. 48-55.