First Vienna Passion Parasitology Club writes:

Dear Twip team, 

thank you for another wonderful TWIP episode. Please see our case guess below.

Happy holidays! 

Michelle & Alex


Dear Calabar-rators,

As always, we are writing to you from a very sunny but cold Boston and from rainy Vienna. Last week it snowed in Vienna and everything is now looking even more beautiful than it usually does. 

Our patient is a 46 year old male without significant past medical history, except for episodic swellings of the right upper extremity for the last 5-10 years. A few years ago he also started noticing an irritating sensation under his right eyelid. He works as a vet and epidemiologist and reports extensive travel history to Africa with animal contact with bats, rodents and birds. 

When first hearing about the patient’s symptoms, a few thoughts come to mind. The prickling sensation could be caused by an infection with onchocerciasis (river blindness) or acanthamoeba keratitis, but combined with the traveling swellings it starts to sound a lot like loiasis. 

Loiasis, also called the African eye worm, is a filarial disease transmitted by the flies Chrysops silacea and Chrysops dimidiata. These flies bite the host to take a blood meal and lay third-stage larva onto the skin, which then enter the skin through the bite wound. The larvae then grow up into adult worms, this process takes up to 5 months. Adult worms later produce microfilariae, which start to penetrate into various tissues and organs and can reside there for many years.

The swellings encountered in loa loa patients are actually angioedema. They occur episodically and are called calabar swellings. Originally, they were named by a Scottish physician who observed these swellings in a woman who had returned home after living in Calabar, modern-day Nigeria, for several years.The swellings are non-tender and can feel itchy.

Other symptoms caused by the disease include itchiness all over the body, hives, muscle pains, joint pains, and tiredness. Additionally, adult worms may be seen moving under the skin. More severe but very rare symptoms include kidney damage, lung edema and lung infection, etc. 

Diagnosis can be usually made by microbiological identification of the worm taken from the eye, by identifying microfilariae in a blood smear or by serological testing. Blood should be drawn around midday, as the concentration of microfilariae is highest at this time; for returning travelers, the timing of the blood draw should be adjusted to the time zone they recently came from, as this only starts to adjust after about two weeks.

Treatment can include surgery to remove single worms found in or around the eye; however, this treatment aims only to relieve the anxiety of the patient. To achieve cure, treatment with diethylcarbamazine (DEC) is most effective, as it targets both microfilariae and adult worms; however, with higher circulating levels of microfilariae, adverse reactions like urticaria, swellings and encephalopathy become more common. While apheresis can be used to decrease microfilaria levels, prolonged administration of albendazole to kill adult worms and thereby reduce microfilaria levels has become more common.

It is not uncommon for patients to require several courses of DEC before achieving complete cure; however, these data come from endemic areas, where continuous exposure is likely, and returning travelers may have higher cure rates. Before DEC treatment, onchocerciasis should be excluded or pretreatment with ivermectin administered well in advance in order to avoid the dreaded Mazotti reaction, an inflammation of skin and eyes.  

There is no vaccine for prevention of loiasis. Exposure prophylaxis is recommended for all travelers and permanent residents of endemic areas, which are largely contained within high-endemicity areas for malaria-transmission. There are no mass drug administration campaigns aimed at reducing the burden of loiasis. Long-term travelers can take DEC chemoprophylaxis to reduce symptoms.

Thank you for this great case. All the best, 

Michelle and Alexander from the First Vienna Parasitology Passion Club

Michelle Naegeli, MD

Postdoctoral Research Fellow

Department of Pathology 

Beth Israel Deaconess Medical Center | Harvard Medical School 

Center for Life Sciences | 3 Blackfan Circle | Boston, MA 02115

Agnese writes:

Dear Professors,

Thank you for another amazing case!

I think, from the hint of the eye, that we are talking about Loa loa! It would match the intermittent, long-standing swelling, the worm crossing the eye and the travel anamnesis.

He said he have also traveled to South East Asia, so maybe Gnathostomiasis should be also in the differential, but he stayed in the endemic area for a short time and the excursion of the worm to the eye is less typical.

Hope you are still drawing names for the book! 

Thank you for your amazing podcast,


Eyal writes:

Dear Vincent and the sages of the microscopic eukaryotes. 

Greetings from Sydney and the land down under (Where women glow and men plunder? Man at work reference…).

Where summer has truly arrived. It is now 30c and hot with over 40c expected for tomorrow. 

I apologize for not submitting my guesses in time for the last few episodes. I’ve been preoccupied with everything happening in the world lately, however I am still listening to all the TWiX religiously 🙂

I have been utterly wrong in my last few guesses. Hopefully I can do better this time.

As for the 46-year-old male with extensive travels to Central and West Africa. Who had recurring swelling in his extremities and maybe recently some movement under the eyelid.

First, I tried to look at worm parasites in Liberia, Ghana, Democratic Republic of Congo (DRC), Uganda, and Rwanda that cause swelling and came up with the following list:

Wuchereria bancrofti – causes lymphatic filariasis, or elephantiasis

Loa loa – cause localized swelling, known as Calabar swellings, in the extremities and migrates to the eye.

Onchocerca volvulus – causes river blindness.

Since there was no mention of a fast flowing river and the swelling symptoms resolve within days and the mention of a movement under the eye. My guess would be Loa loa.

As always it is such a pleasure to listen and learn from all of you.

Thank you so much.


Rafid writes:

Hello TWIP team,

Greetings from rural Quebec. With the arrival of winter the hospital where I work has been very busy with patients presenting with respiratory illnesses and their complications so I have not too much time to analyze this case. My best quick guess for a patient who has travelled to central Africa and now has seen something cross his eye and has  transient swellings of his extremities which sound like Calabar swellings is the filarial loa loa disease. This parasite is transmitted by the deer fly. This horrible insect is ubiquitous in rural Quebec in the hot summer months. I can’t leave my house or take a walk in the woods, let alone go for a run without being attacked by these nasty creatures that take a painful bite out of you. They are DEET resistant, very rapid and very difficult to kill. Even when you smack them they only get winded and get up and fly away a few moments later. Theses bugs don’t like the city however and even if I run on a country road that is paved they leave me alone, therefore I assume that our patient got infected because his work took him deep into the bush. Luckily it is -10 Celsius today so I can go for a run without being attacked by these monsters.

Thank you again for your time and thank you Vincent as I got an email yesterday saying that the parasitology book that you guys gifted me is on the way. Can’t wait to see it.



Felix writes:

Dear hosts,

greetings from snowy south Germany. My guess for the case of migrating joint swelling and eye irritation is Loa loa. I am a little bit unsure why the lab work is unremarkable and there is no eosinophilia but I guess in chronically infected patients it may be the case.

Now we need to find microfilariae in the blood or catch the worm red-handed in the eye.

For treatment DEC is recommended after ruling out risk factors for encephalopathy.

I would love to know how you proceed if there is heavy infection or risk factors.

Other parasitic differentials could be gnathostomiasis or mansolelliasis.

Until next time.


Håkon writes:

Hello cast and crew of TWIP- greetings from balmy albeit wet Athens GA. It’s funny that your case involved a little white worm peeking out of an eye as just this last week a friend of mine reached out asking about a similar problem in his dog, which I have attached a photo of below. While I am certain our veterinary epidemiologist probably didn’t get onchocerca lupi from a southern US state like this dog did, his case did make me wonder about the myriad different filarial worms he could have acquired. Depending on the size of the nematode extracted from his eye and the morphology, (could also look at the microfilaria in the blood) it could be Loa Loa, O. volvulus, Wucheraria bancrofti or Brugia malayi. Originally I had thelazia on the list as well but given his skin issues and swelling a filarial worm from his travels through Africa or Southeast Asia seems most reasonable. Final guess- Onchocerca volvulus. Treatment would be DEC and Ivermectin but depending on the size of the nematode burden it might be prudent to consult a specialist to avoid a Mazzotti reaction.

All the best,


Anthony writes:

Appears to be some sort of larvae migrans

Loa Loa, Gnathostoma and Dirofilaria repens are all possible

– Anthony