A man who dismissed a small bump on his eyelid was shocked to learn that it was actually caused by a rare parasite never before contracted in the US.
Virtually all Americans have experienced a stubborn stye on the eyelid at least once during their lifetimes, which normally resolves within a week with some help from warm compresses.
In cases where the bump lingers, doctors say it may be a cyst and may ask patients to wait a month before they drain it of fluid in an appointment.
But in a stunning new case, researchers found that one eyelid bump was caused by a mosquito-borne worm that infested the skin – in an infection never before seen in the US.
In the Centers for Disease Control and Prevention (CDC) report, researchers revealed how the unidentified man went to a hospital in southern California after having the bump on his lower left eyelid for five months.
It measured 0.3 inches (eight millimeters) across and had leaked fluid when it first appeared, before settling. After scans, doctors removed it during surgery.
Initially, they suspected it was a cyst – medically termed a chalazion. However, after it was removed and analyzed under a microscope, they found it was crawling with worms.
The man, 74, had no idea he had the worms, but reported that the bump, on his lower left eyelid, had appeared after he was bitten by an unidentified insect.
An unidentified man went to a hospital in southern California after having a bump on his lower left eyelid for five months (stock image)
The above red circle shows the parasite in an MRI image of the patient’s head
He said he also suffered from pain and swelling when the bite happened, but that this subsided shortly after.
The report stated the worm was a nematode, or long parasitic roundworm, called Dirofilaria repens, which is typically found infesting the skin of dogs and cats. In rare cases, it can also infect humans. Generally, it is found in the skin, but it has also been detected in the eye.
Pets are infected with the roundworm via mosquito bites, where the worm migrates from the skin into the bloodstream where it reproduces. Young worms are then taken up by mosquitoes, which transfer them to new hosts.
In rare cases, the parasite can also infect humans via mosquito bites.
The parasite is endemic in Europe, but has not previously been recorded infecting people who have not left the US.
In the latest case, the patient reported no recent travel, suggesting that they were infected in southern California.
Most patients with the parasite have no symptoms, the CDC says. Warning signs include swelling or inflammation in the skin and a bump that does not resolve on its own.
In serious cases, patients may also cough up blood, and suffer from chest pain, fever and breathing problems.
Doctors can easily treat the infection using surgery to remove the bump or anti-roundworm drugs. In cases where it infects the eye, they warn that it can lead to vision loss.
The above shows the lifecycle of Dirofilariasis roundworms
Dr Usiwoma Abugo, an ophthalmologist and clinical spokesperson for the American Academy of Ophthalmology, said: ‘The recent finding of a nematode in a patient’s eyelid is concerning, but it is important to note that it is a new and uncommon finding.
‘The public should be mindful of this if they have a bump that is typically common that does not resolve after months of routine intervention.’
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She added: ‘This patient may also have a significant history of being bitten prior to the formation of the bump.
‘The inflammation is not always limited to the eyelid, it can extend to other structures around or on the eye itself.
‘If this is you, be sure to reach out to your ophthalmologist to evaluate the inflammation more closely.’
The researchers noted in the paper that the increasing mosquito population in the state may have raised the risk of an infection.
The patient did not suffer any vision loss and recovered six months after his surgery.
Previous surveys have not detected the roundworm in the US, but it has been detected in South America in recent years.
In the US, the mosquito-borne worm infections have been recorded in humans in every state, but these have all been caused by a different species.
In the US, Dirofilaria immitis, which can infect humans, causes heartworms in dogs, and Dirofilaria tenuis can infect raccoons.
Experts say that infections with the worm can be avoided primarily by preventing mosquito bites and leaving as little skin exposed as possible.
Anyone who suspects an infection with the worm is urged to contact their health provider.
