View source for Loa loa

{{Taxobox

| image = L_loa_whole_HBa.jpg
| image_width = 240px
| image_caption = ''Loa loa'' [[microfilaria]] in [[thin blood smear]]<br/>([[Giemsa stain]])
| regnum = [[Animal]]ia
| phylum = [[Nematode|Nematoda]]
| classis = Chromadorea
| ordo = [[Spirurida]]
| superfamilia = [[Filarioidea]]
| familia = [[Onchocercidae]]
| genus = ''[[Loa (roundworm)|Loa]]''
| species = '''''L. loa'''''
| binomial = ''Loa loa''
| binomial_authority = (Cobbold, 1864){{Verify source|date=July 2010}}<!-- "Guyot, 1778" or with parentheses? -->
| synonyms =
''Filaria loa'' <small>Cobbold, 1864</small>
}}
__NOTOC__
{{Loa loa filariasis}}
{{About0|Filariasis}}
{{CMG}}

==Overview==
'''''Loa loa''''' is the [[filaria]]l [[nematode]] (roundworm) [[species]] that causes [[Loa loa filariasis]]. It is commonly known as the '''"eye worm"'''. Its geographic distribution includes Africa and India.<ref name="FoP">Schmidt, Gerald et al.  "Foundations of Parasitology".  7th ed.  McGraw Hill, New York, NY, 2005.</ref>

''L. loa'' is one of three parasitic filarial nematodes that cause [[Subcutaneous tissue|subcutaneous]] [[filariasis]] in humans.  The two other filarial nematodes are ''[[Mansonella streptocerca]] and [[Onchocerca volvulus]]'' (causes [[river blindness]]).

Maturing [[larva]]e and adults of the "eye worm" occupy the subcutaneous layer of the skin &ndash; the fat layer &ndash; of humans, causing disease. The young larvae develop in [[horseflies]] of the [[genus]] ''[[Chrysops]]'' (deer flies, yellow flies), including the species ''[[Chrysops dimidiata|C. dimidiata]]'' and ''[[Chrysops silacea|C. silacea]]'', which infect humans by biting them.

== Biology ==

===Morphology===

Loa loa worms have a simple body including a head, body, and tail.   Males range from 20mm to 34mm long and 350μm to 430μm wide.  Females range from 20mm to 70mm long and are about 425μm wide.<ref name="FoP"/>

===Life cycle===

Three species involved in the life cycle include the parasite ''Loa loa'', the fly vector, and the human host:<ref>[http://www.dpd.cdc.gov/dpdx/HTML/Filariasis.htm "Filariasis".] Parasites and Health. Center for Disease Control.</ref>

* A vector fly bites an infected human host and ingests microfilariae.
* Microfilariae move to the fat body of the insect host.
* Microfilariae develop into first stage larvae, second stage, then third stage larvae.
* Third stage larvae (infective) travel to the proboscis of fly.
* An infected vector fly bites an uninfected human host and the third stage larvae penetrates the skin and enters human subcutaneous tissue.
* Larvae mature into adults, who produce microfilariae that have been found in spinal fluid, urine, peripheral blood, and lungs.

== Disease ==
{{main|Loa loa filariasis}}

===Pathogenesis===

Loa loa parasites infect human hosts by travelling from the entry site through subcutaneous tissues and causing inflammation in the skin wherever they travel.  If a parasite stops in one place for a short period of time, the human host will suffer from local inflammation known as Calabar swellings.  These are localized, tense, inflammatory pruritic subcutaneous edema seen in joints of extremities, lasting for 1–3 days. They represent areas of angioedema resulting from a host response to allergens released by the maturating worm and its metabolic products.<ref name="Rivière, E. 2012">Rivière, E., Kerautret, J., Combillet, F., & Malvy, D. (2012). African Eye Worm. Journal Of Global Infectious Diseases, 4(2), 135-136. doi:10.4103/0974-777X.96782</ref> Calabar swellings often occur in the wrist and ankle joints but disappear as soon as the parasite begins to move again.  Parasites can also travel through and infect the eye, causing the swelling of the eye.  Common symptoms include itching, joint pain, fatigue, and death.<ref name="FoP"/>

===Diagnosis and treatment===

The main methods of diagnosis include the presence of microfilariae in the blood, the presence of a worm in the eye, and the presence of skin swellings.  Surgical removal of the worm can easily be performed.  The common treatment for the disease is the use of the drug [[Ivermectin]].<ref name="FoP"/>

Ivermectin has become the most common antiparasitic agent used worldwide but can lead to residual microfilarial load when given in the management of loiasis. High microfilarial loads should be decreased by a course of ivermectin, a prolonged administration of albendazole, or cytapheresis sessions to prevent occurrence of serious adverse events, including fatal encephalopathy induced by dying microfilariae. Cytapheresis is helpful in decreasing very high microfilarial loads up to 75%. Diethylcarbamazine kills both microfilariae and adult worms but has more severe side effects and can be fatal.

==References==
{{Reflist|2}}
* [http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Info&id=7209&lvl=3&lin=f&keep=1&srchmode=1&unlock Taxonomy Browser: Loa Loa.] National Center for Biotechnology Information (NCBI).

{{Helminthiases}}