Morphology   

Morphology of Adult Loa loa worms

The morphology of adult Loa loa male and females is very different from one another.  What is unique about the different sexes of these worms is that the males are significantly smaller than females and grow at much faster rates (Eberhard and Orihel 1981).  Adult male worms range from about 2 cm to 3.5 cm in length while female worms range from about 2 cm to 7 cm in length (Roberts and Janovy 2000).  The diameter of both male and female worms is about 0.035 cm to 0.045 cm, males measuring closer to 0.035 cm and females closer to 0.045 cm (Roberts and Janovy 2000).  A few centimeters may not seem very large at first, but when you compare this worm to the human eye which is about 2.5 cm in diameter you can really begin to understand just how large these worms are in comparison to the eyeballs and other tissues that they call home.

Morphology of Microfilariae

Microfilariae are extremely small ranging from 250-300 μm long by 6-8 μm in diameter.  These young worms develop through three larval stages during their life as microfilariae.  During their first larval stage, microfilariae eggs are protected by sheath coverings.  They shed these sheath coverings when they are transferred from the body fluid of their mammalian host to the mouth of their arthropod host and travel to the fly's mid-gut where they develop into their second larval stage (Eberhard and Orihel 1981).  In the third stage, microfilariae migrate back up to the mouth of the fly where they wait to be transferred to their mammalian host (Eberhard and Orihel 1981).

How does Loa loa move about its hosts?

Loa loa does the most of its traveling while in the form of microfilaria and involves the use of two hosts: a Chrysops fly and a mammal.  If you are interested in learning more about these hosts, check out the life cycle of Loa loa on our REPRODUCTION page or take a look at how Loa loa interacts with its hosts on our INTERACTIONS page! 

When a Chrysops fly bites an infected mammal, microfilariae is transferred through the mammal’s blood to the fly.  Once the infected fly feeds on a new mammal, the third stage microfilariae larva is transferred into the mammal’s blood stream. It uses the circulatory system to migrate to the subcutaneous tissue of the mammal’s body, most notably the eye (Roberts and Janovy 2000).  Adult Loa loa will grow and develop in the subcutaneous tissues and usually remain there the rest of their lives which can be up to 17 years!  A small percentage of worms migrate from subcutaneous tissues to other organs in the body through lymphatic system (Roberts and Janovy 2000).  When adult Loa loa mate and produce new microfilariae, these new eggs "hop aboard" the blood stream and either remain there or travel to other bodily fluids such as spinal fluid, or urine, where they await the bite of a Chrysops fly (Roberts and Janovy 2000). Studies have shown that microfilariae express diurnal periodicity.  Well you may be asking, “What in the world is diurnal periodicity?”  This is just a fancy biological term which means that microfilaria live in the blood stream primarily during the day, while very few live there during night (Tyagi et al. 2011).

Other interesting adaptations of Loa loa

A unique characteristic Loa loa express that differs from others in their family is that their body nuclei are located in the tip of the tail and are clumped together in a row with minimal spacing between them.  It has also been found that Loa loa do not have an immune system that is specific to their species. In fact, they really do not have their own immune system at all.  Research has found that Loa loa has actually adapted in a way that their immune systems mimic that of their hosts (Desjardins et al. 2013).

If you would like to learn more about the reproduction of Loa loa check out our REPRODUCTION page! 
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