A brief history lesson on Loa loa.

A French surgeon at San Domingo in the Caribbean by the name of Mongin, documented the first case report of the parasite Loa loa, which was published in 1707 when Mongin performed an unsuccessful surgery to remove the parasitic worm from a women’s infected eye (Holmes 2013).  Loa loa was considered benign, or unharmful, until the late 1980’s and early 1990’s when more cases were being reported.  Despite more and more cases were reported at this time, the number of cases was still extremely low resulting in a limited understanding of this disease.  To make matters worse, the list of symptoms associated with this infectious nematode seems to be almost never ending (Holmes 2013). 

How does Loa loa get to the eye in the first place?

Close up of an Infected eye Copyright 2011 BMJ Publishing Group LtdAs you can tell by the very graphic images of human eyes infected by Loa loa, once this worm grows into an adult, it can live in subcutaneous tissues such as the eye.  You are probably asking yourself, “But how does it get to places like your eye in the first place?”  Well this is a great question and I would love to answer it for you!

Loa loa Life cylce

 Loa loa is a parasitic species that requires two hosts:  An arthropod host commonly known as the deerfly or the mangofly (both of which are located in the genus Chrysops) and a mammalian host (Tyagi et al. 2011).  Loa loa is transferred to its mammalian host in the form of matured microfilariae, eggs or larva, when the fly host bites a mammal.  Once inside their new host, the microfilariae travel to the subcutaneous tissues in the mammal’s eye and remain there until they reach adulthood.  It may take anywhere from one to four years for these microfilaria to fully mature.  Previously, I mentioned that microfilaria are eggs.  Note that eggs is plural as in more than one! Yes, you read that right, this means that once these eggs mature there are multiple worms living inside their mammalian host!  Loa loa reproduce sexually where an adult male and an adult female worm join together to mate (Roberts and Janovy 2000). They then produce a new generation of microfilariae through mitosis. These microfilariae contain protective sheaths that cover each egg in their first larval stage (Desjardins et al. 2013).  Microfilariae work their way through the mammal’s body by traveling via the lymphatic system and go on to live in a number of different places including blood, lungs, urine, sputum, and even spinal fluid!  When a new fly bites the infected mammal and takes a blood contaminated with microfilariae, it becomes the new arthropod host.  Once ingested, microfilaria lose their protective sheaths and are able to migrate from the stomach or gut of their new host to the thoracic muscles where they undergo three larval developmental stages (Desjardins et al. 2013).  Then they return to the mouth of the fly upon the third developmental stage.  Once the matured microfilariae make their way to the fly’s mouth, they wait for the fly to bite a mammal which will become the new host for young Loa loa.  Thus the cycle repeats itself.

If you would like to learn more about the relationships between Loa loa and its two hosts, we encourage you to check out our INTERACTIONS page!
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