Tick paralysis in humans

paralysis tick

Tick paralysis in humans is rare so even when veterinarian Dr Olivia Pozzan developed all the telltale signs, getting a diagnosis took some time. Deepa Gopinath reports

When Dr Olivia Pozzan woke up with an agonisingly painful right ear, she assumed it was a lingering effect of the sinusitis that she had been suffering for some time. That right ear had always given Dr Pozzan trouble. She’d had several surgical operations on it as a teenager to address a non-cancerous middle-ear growth called a cholesteatoma. The ordeal had left her completely deaf in that ear, and prone to a build-up of wax which needed to be removed regularly by an ENT specialist.

paralysis tick
The engorged tick in Dr Pozzan’s ear canal

Mystery symptoms

So, in late 2018 when the Sunshine Coast-based veterinarian felt the throbbing in her ear, she gulped down a dose of anti-inflammatory pain relief and just got on with it. But eight days later, the right side of her face drooped, she couldn’t move her muscles, and suddenly the world seemed to be spinning. Nausea and violent vomiting took hold, and even walking without stumbling was a challenge. An avid traveller and hiker, Dr Pozzan knew this was much more than just severe sinusitis. 

In the hospital, Dr Pozzan received a battery of tests while she tried to focus her eyes and clear the brain fog that had set in. Neurological exams, MRI, CT scans, blood tests and otoscopic examinations by six different doctors all failed to nail a definitive diagnosis. The emerging tentative diagnosis was Ramsay Hunt syndrome, a complication of the viral disease shingles, which leads to facial nerve paralysis.

paralysis tick
The facial paralysis resulting from the tick’s toxins

It was the seventh doctor, an ENT specialist, who finally cleared the right ear of wax and looked again. What he saw was a familiar sight to many Australian veterinarians while treating their animal patients: a fully engorged paralysis tick. The tick, which normally causes paralysis in domestic animals, had lodged in Dr Pozzan’s right ear canal, its movements inaudible due to her deafness in that ear. In its protected position, the parasite had attached itself and begun to feed, injecting a neurotoxin over 12 days at doses which likely would have killed a dog or cat.

The paralysis tick

Jan Slapeta, Professor of Veterinary Parasitology at the University of Sydney and deputy editor of the International Journal for Parasitology understands the dangers of tick paralysis. As she explains, “The paralysis tick (Ixodes holocyclus) attaches to the host with specialised mouth parts that pierce and anchor the tick to the host. The tick then starts to alternate between blood sucking and spitting saliva into the host. The tick will take at least a week to fully engorge and only then will fall off. It is only on day three that the tick starts to produce the ‘special’ saliva that contains the mix of toxins. The toxin affects the host’s nervous system and will, if a sufficient amount of it is present in the body, lead to muscle weakness, difficulty speaking, and eventual paralysis of the respiratory system.”

“The paralysis tick (Ixodes holocyclus) attaches to the host with specialised mouth parts that pierce and anchor the tick to the host.”

Jan Slapeta, Professor of Veterinary Parasitology, University of Sydney

This mechanism certainly explained Dr Pozzan’s symptoms, particularly with respect to where the tick was located. The paralysis tick was, astoundingly, engorged to over one centimetre in length when it was removed from Dr Pozzan’s ear canal. 

paralysis tick
Dr Pozzan today

The Australian paralysis tick is found on the east coast of Australia due to its requirement for both heat and high relative humidity to thrive. Professor Slapeta says that while ticks do often attach to humans in endemic regions, they only rarely cause paralysis in people—unlike in our companion animals. “Many people living close to the bush and spending time in the bush will experience tick attachment. Kids playing outdoors in the shrubs and long grass are perfect targets. Ticks don’t have any special region they like to attach to on humans but tend to be found in places where they are least likely to be brushed off such as the scalp and behind the ears. My advice is to never underestimate a child’s complaint about itchiness around the scalp, around the ear or the armpit.” 

Treating tick paralysis in humans

The administration of tick anti-toxin serum is an important component of the treatment protocol for tick paralysis in dogs and cats. In humans, the high risk of anaphylactic reaction to anti-toxin serum precludes its use. Instead, affected humans are treated with careful supportive care as determined by the symptoms. 

Dr Pozzan, who has removed many engorged paralysis ticks from her patients over three decades in veterinary practice, had already performed a tick search of her own scalp while doctors around her discussed diagnoses more common to humans. When the neurotoxin-injecting parasite was found after numerous otoscopic examinations, the RSPCA veterinarian watched as the squirming creature was killed with an injection of phenol, then carefully removed from her ear canal. It was a dubious pleasure to behold, and one that would lead to her full recovery six weeks later.

“It was the grossest, ugliest, and yet most welcome sights I have ever seen,” Dr Pozzan says, her smile no longer lopsided.


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