Balloon Syndrome and Contagious Cancers: 5 Bizarre Animal Ailments

Animals are just as vulnerable to illness as humans, but sometimes the ailments affecting them seem utterly bizarre. Let's take a look at...

• Hedgehog Balloon Syndrome
• Chronic Wasting Disease (or Zombie Deer Disease)
• Saiga Antelope Mass Mortality
• Tasmanian Devil Contagious Cancers
• Parasitoid Wasps, Caterpillars and Domesticated Viruses

Hedgehog Balloon Syndrome

Hedgehogs are fairly small, spiked creatures native to Europe, Asia and Africa - and to be honest, they look a little bit like a sea-urchin grew a short snout and ventured onto land. If threatened, they curl up to present a ball of short spikes to any potential predator - but the anatomy required for this feat makes them the sole victims of a unique condition called "balloon syndrome."

Because their skin needs to be fairly loose to allow them to curl up tightly, there's room for gas to become trapped in the gap. If the hedgehog gets injured, air can get under the skin and become trapped when the creature heals... as can gas produced by bacteria in an infected wound.

Hedgehogs suffering from this condition can balloon up, with some reaching twice their normal size. It is treatable however - vets typically administer a course of antibiotics and puncture the skin with a needle to let the creature deflate!

Chronic Wasting Disease (or Zombie Deer Disease)

Have you heard of mad cow disease? The earliest known cases of bovine spongiform encephalitis (Creutzfeldt-Jakob disease in humans) appeared in the UK, resulting in mass livestock culls and a years-long export ban on British beef. Thanks to changes in farming and livestock preparation, BSE has almost been eradicated throughout the world... but a new version may be about to raise its ugly horned head, and this time it's carried by deer.

Known as chronic wasting disease (or the more theatrical "zombie deer disease") this condition is caused by infectious prions just like BSE. Harmless or helpful prion proteins occur in many animals - but if these prions are produced "misfolded" they act more like a virus, forcing other prions to assume their misfolded shape.

Contact with misfolded prions can damage normal cells, or they can clump up and disrupt the brain. Even worse, the prions can infect other animals if tainted meat is consumed - or even if there's contact with body fluids.

Researchers in the USA and Canada are currently trying to evaluate CWD in the native population of deer, reindeer, elk and moose. As of 2026 the condition has been reported in 36 states, reducing infected animals to stumbling, drooling and listless "zombies."

What we don't know yet is whether CWD can make the jump to humans like BSE did. Research so far has been inconclusive, with some studies suggesting it could and others that it couldn't. More worrying is the fact that a pair of hunters who regularly ate deer in an area with CWD died in 2022... of CJD. That's concerning given how rare CJD is, suggesting that the prions may indeed be capable of contaminating us!

Saiga Antelope Mass Mortality

Saiga antelope are critically endangered - and after reading about their medical history over the past few decades, you'll see why.

Over a few weeks in 2015, around 200,000 saiga browsing the grass of Kazakhstan keeled over and died from hemorrhagic septicemia caused by Pasteurella multocida bacteria. What makes this incredibly strange is that the bacteria were already living harmlessly on the tonsils of the animals - so what turned them into a biological time-nuke?

Well, it seems that a number of individually harmless events turned the bacteria terminal. 2015 was unusually humid and warm - and at the time of the die-off, the herds were in the process of calving (which takes a lot of energy out of the animals.)

The antelope were likely the victims of an opportunistic infection, with the heat and humidity allowing the bacteria to flourish and overwhelm their weakened immune systems. The species actually has a history of mass die-offs, with two previous events occurring in 1980s (and also another event earlier in 2015!)

Tasmanian Devil Contagious Cancers

Did you know that some types of cancer are contagious? Given that almost all cancers arise from mutations in the cells of their host (and die alongside them) this may seem a little crazy, but "devil facial tumor disease" has pushed Tasmanian devils to the brink of extinction.

So how can these tumors spread? Well, the cancer has two advantages that allow it to jump hosts. For one thing, the cancer seems to be pretty stealthy and devil immune systems struggle to identify it as an intruder... which means that it doesn't face much resistance. The other thing is that Tasmanian devils have very poor genetic diversity - or to put it another way, it's like they're all fairly closely related. Just like relatives are good candidates for organ transplants, the cancer cells from one devil can thrive in another.

With those hurdles passed, the only barrier to the cancer is how it can actually spread between the devils - and the answer is aggressive physical contact. The devils frequently bite each other on the face or neck... and any cancerous cells that get introduced into a wound can take root, colonizing a new host.

It probably goes without saying that transmissible cancers are an incredibly rare thing (or at least, they seem to be) but there are two other known types; bivalve transmissible neoplasias (in mollusks) and canine transmissible venereal tumor (in dogs and other canids.)

Parasitoid Wasps, Caterpillars and Domesticated Viruses

Now let's take a look at something that outdoes most sci-fi body-horror. Parasitoid wasps inject their eggs into the bodies of caterpillars (or other creatures depending on the species) where the larvae will hatch and devour them from within. Of course, the immune systems of the hosts will fight back, so the wasps often rely on complex venoms or biological mimicry to suppress or evade attempts to destroy the eggs... but some parasitoid wasps use domesticated viruses instead.

The viruses seem to have become a part of these wasps - their DNA holds templates for viral components, which are assembled by female wasps in an organ known as the calyx. The wasp injects the virus alongside an egg to suppress the victim's immune system, allowing the larvae to eat without interruption.

The virus may be even more sinister than it appears. Plants normally respond to caterpillars grazing on them by releasing toxins (or in some cases, attempting to attract predators) but researchers found that caterpillars infected by a polydnavirus had less glucose oxidase in their saliva. Why does this matter? Well, plants can sense the presence of glucose oxidase and use it as an indicator that they need to defend themselves - less glucose oxidase means less defenses and a better chance of the caterpillar surviving and eating well... at least, until the wasp gobbles up its innards!

Thanks for reading - perhaps you'd also like...

• Grim Hybrids and Mummified Scarabs: Explore 6 Strange Sets of Animal Remains
• Drama, Sprays and Crawling Back Out: 3 Weird Ways Animals Avoid Being Lunch
• Toxic Turtles and a Man-Killing Frog: 5 Damp and Deadly Natural Poisoners

Sources and Further Info:

• Hedgehog 'blown up like beach ball' has balloon syndrome
• Does 'zombie deer disease' pose risks for humans?
• Scientists uncover secret of mass mortality event in remote steppe grassland of Central Asia - Sudden death of 200,000 critically endangered saiga antelopes was caused by unusual environmental conditions
• About Devil Facial Tumour Disease
• CAES researchers study how parasitic wasps use ancient viruses to ensure survival
• Virus inhibits immune response of caterpillars and plants