Like all filarial organisms, the endemic regions of infections correlate with the areas in which the vector flourishes.In the case of Loa loa, Chrysops fly lives in Africa, especially in the rainforest belt region. In the areas in which a large vector population exists, infection rates are estimated to be over 70 percent. In regions with a minimum number of vectors, less than 10 percent infection rate occurs.
Morphology of Loa loa
The sheathed Loa loa microfilariae usually measures 248 to 300 μm in length. The nuclei fill the organism and are continuous to the tip of the pointing tail. This characteristic helps to distinguish it from the other sheathed microfilariae.
Loa loa worms are usually white in color and have a cylindrical thread- like appearance. The females are relatively large, measuring 38 to 72 mm in length. The adult males are significantly smaller, measuring between 28 and 35 mm in length.
Life Cycle of Loiasis
Human Loa loa infection is caused by the bite of an infected Chrysops fly. Adult worms reside and multiply throughout the subcutaneous tissues. Microfilariae are present in the blood, but only years after the initial infection make diagnosis more difficult.
Clinical symptoms of Loiasis
For loa loa symptoms,after the initial bite, people infected with Loa loa may experience pruritus or itching and localized pain.The development of Calabar swelling at the site of initial discomfort usually follows.This localized subcutaneous edema can occur anywhere in the body and is thought to result from the migration and death of microfilariae.Interestingly, the presence of circulating adult loa loa worms in the subcutaneous tissues usually does not cause discomfort. The adult worms can only be noticed when they migrate under the conjunctiva of the eye(eye worm) or cross under the skin of the nose bridge.
Laboratory Diagnosis of Loa loa
The specimen of choice for Loa loa microfilariae recovery is Giemsa- stained blood. The Knott technique can also be used. These samples provide the best recovery rate when collected during the midday hours, between 10:15 a.m. and 2:15 p.m., because this organism shows diurnal periodicity.The migrating adult worms can be extracted from a variety of body locations, including the eye.Residence in an endemic area and the presence of eosinophilia and Calabar or transient subcutaneous swelling also help in diagnosis.Serological testing is also available.
Treatment of Loiasis
loa loa worm treatment requires a surgical removal of adult Loa loa worms is the treatment of choice. Extracting these worms when trying to cross the eye or the bridge of the nose is the ideal time to remove them. Unfortunately, it is not possible to select the appropriate time to perform such a procedure in advance.
Diethylcarbamazine( DEC) is the medication of choice for the treatment of Loa Loa. Although this anti parasite drug is known to be effective, it should be used with caution. Its use in the treatment of heavily infected patients can lead to serious side effects, including encephalitis.
Prevention and Control of Loiasis
Personal protection measures are essential to stop Loa loa infection spreading.In addition, the destruction of the vector breeding areas, although probably not economically or logistically feasible, would also help to stop the spread of infection.The use of prophylactic DEC, especially for non- natives visiting endemic areas, has also proved effective.