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LOIASIS

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Loiasis is a nematode disease vectored to humans by flies of the family Tabanidae. Occurance of the disease is primarily in forested areas of Nigeria, Ghana, Angola, Sudan, Uganda, Guinea, Congo and the Cameroons. The microfilariae are diurnally periodic and migrate to different parts the body at different times of the day and night. When they are situated just below the skin they can be transferred to tabanid flies that bite during the daytime. Service listed the principal vectors as Chrysops silaceus, C. dimidiatus, C. distinctipennis and C. longicornis.

 

Following a blood meal some of the ingested microfilariae that manage to survive digestion penetrate the intestinal wall and migrate to the abdomen or thorax and head (Service 2008). After two molts they develop into a 3rd stage larva, which is only 2 mm. in length. These move to the thorax and head and after 7-15 days amass in the fly's proboscis. When a vector feeds on humans as many as 200 stage-3 larvae can be left on the skin. Service (2008) noted that most of these die, but some pass through the wounds made by the biting fly or even through skin abrasions. They migrate to connective tissue where they mature in about three months. Several months later the microfilariae can be found in the peripheral blood.

 

Reservoir hosts may involve forest simians that are bitten by Chrysops centurionis and C. langi that are active at twilight or nighttime. However, transmission to humans is uncertain.

 

CONTROL

 

The Tabanidae are extremely difficult to control, especially in areas where aquatic habitats cannot be practically reduced, such as swamps and lakes. Nevertheless, . Control measures have involved draining swampland where the flies breed. Insecticidal control is also plagued by the development of resistance and difficulties in locating principal breeding areas. Service (2008) noted that some control could be achieved with attractant traps for adults and the use of repellents.

 

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Key References: <medvet.ref.htm> <Hexapoda>

 

Anderson, J. F. 1985. The control of horse flies and deer flies (Diptera: Tabanidae). Myia 3: 547-98.

Anthony, D. W. 1962. Tabanids as disease vectors. IN: Biological Transmission of Disease Agents. Academic Press, NY. p. 93-107.

Braga da Rosa; Gustavo A. 2006. Predation of hill topping horse-flies (Tabanidae) by birds in Brazil. Ornitologia Neotropical. 17:

619622.

Cheke, R. A., J. Mas & J. F. Chainey. 2003. Potential vectors of Ioiasis and other tabanids on the island of Bioko, Equatorial

Guinea. Med. Vet. Ent. 17: 221-3.

Chippaux, J. P., B. Bouchite, M. Demanov, I. Morlais & G. LeGoff. 2000. Density and dispersal of the Loiasis vector Chrysops dimidiata in southern Cameroon. Med. & Vet. Ent. 14: 339-44.

Eaton, Eric R.; Kaufman, Kenn (2007). "Deer flies and horse flies". Kaufman Field Guide to Insects of North America. Hillstar

Editions. p. 284.

Egri, A.; Blaho, M.; Kriska, G.; Farkas, R.; Gyurkovszky, M.; Akesson, S.; Horvath, G. 2012. "Polarotactic tabanids find striped

patterns with brightness and/or polarization modulation least attractive: An advantage of zebra stripes". Journal of

Experimental Biology. 215 (5): 736.

Foil, L. D. 1989. Tabanids as vectors of disease agents. Parasitology Today 5: 88-95.

Legner, E. F. 1995. Biological control of Diptera of medical and veterinary importance. J. Vector Ecology 20(1): 59_120.

Legner, E. F. 2000. Biological control of aquatic Diptera. p. 847_870. Contributions to a Manual of Palaearctic Diptera, Vol. 1,

Science Herald, Budapest. 978 p.

Matheson, R. 1950. Medical Entomology. Comstock Publ. Co, Inc. 610 p.

Middlekauff, Woodrow Wilson; Lane, Robert S. 1980. Adult & Immature Tabanidae (Diptera) of California. University of California

Press. pp. 12.

Noireau, F., A. Nzoulani, D. Sinda & A. Itoua. 1990. Transmission indices of Loa loa in the Chaillu Mountains, Congo. Amer. J

Trop. Med. 43: 382-8.

Padgett, J.J.; Jacobsen, K.H. (2008). "Loiasis: African eye worm". Transactions of the Royal Society of Tropical Medicine and

Hygiene. 102 (10): 9839.

Quercia, O.; Emiliani, F.; Foschi, F.G.; Stefanini, G.F. The wasp-horsefly syncrome. European Annals of Allergy and Clinical Immunology

40 (3): 6163

Service, M. 2008. Medical Entomology For Students. Cambridge Univ. Press. 289 p

Legner, E. F. 1995. Biological control of Diptera of medical and veterinary importance. J. Vector Ecology 20(1): 59-120.

Legner, E. F. 2000. Biological control of aquatic Diptera. p. 847-870. Contributions to a Manual of Palaearctic Diptera,

Vol. 1, Science Herald, Budapest. 978 p.

Thomson, M. C., V. Obsomer & J. Kamgno et al. 2004. Mapping the distribution of Loa loa in Cameroon in support of the African

Programme for Onchocerciasis Control. Filaria J. 3: 7.

Wilkerson, R.C.; Butler, J.F.; Pechuman, L.L. (1985). "Swarming, hovering & mating behavior of male horse flies & deer flies

(Diptera: Tabanidae)". Myia. 3: 515546.