Loa

LOA (Loa), generic name for roundworms (nematodes) of the suborder Filariata, 30 SI family Filariidae and subfamily Loanae. The genus Loa Stiles (1905) is characterized by the following features: the mouth is devoid of lips, there are two lateral and four submedian papillae on the head. The cuticle is thick, unstriated, provided with warty outgrowths, except for the anterior end of the male and female and the posterior end of the female. The male has no alae, the spicules are unequal. On the tail of the female there is a pair of papillae near the apex. The vulva is behind the esophagus. Adult worms inhabit the subcutaneous tissue, microfilariae are in the blood. In humans, two species parasitize - L. loa and L. extraocularis. a) Loa loa (Guyot; 1778). Synonyms: Filaria oculi Gervais et van Beneden, 1859; Dracunculus oculi Diebing, 1860; Dracunculus loa Cobbold, 1814; Filaria subconjunctivalis Guyon, 1864; Filaria diurna Manson, 1891; Filaria bourgi Brumpt, 1903. - Brief description. Male - 22-34 mm in length with a width of 0.3-0.43 mm. The length of the large spicule is 0.123-0.190 mm; in its posterior part the spicule appears to be broken and ends with a split apex. The small spicule is 0.088-0.115 mm. It consists of a tubular section with a proximal process; its distal end is rounded; club-shaped stalked papillae are distributed unevenly and asymmetrically. The cloaca is 0.08 mm from the posterior end. Female - 50-63 mm in length with a width of 0.5 mm. Anus is 0.17-0.265 mm from the posterior end. The vulva is 2.0-2.5 mm from the anterior end. Microfilaria, so-called Microfilaria diurna (larvae appear in the peripheral blood only during the day, unlike Wuchereria Bancrofti, whose larvae M. nocturna can be found in the peripheral blood only at night), according to Manson - 0.25-0.30 mm in length with a width of 0.0047-0.008 mm. The definitive host is only humans. Localization: subcutaneous tissue, rarely - serous membranes, in particular the pericardium. Often L. wanders and penetrates under the conjunctiva of the eye [see separate table (pp. 175-176), figures 1 and 2]. Intermediate hosts and vectors of the parasite - deer flies: Chrysops dimidiatus and Chrysops silaceus. The development of larvae from ingested microfilariae occurs mainly in the muscles and in the fat body of the posterior part of the abdomen of the deer fly. The developed larva reaches about 2 mm in length and 0.025 mm in thickness. The penetration of larvae into the human body during the bite of a deer fly occurs in such a way that the larva breaks the thin cuticle between the terminal lobes of the lower lip of the deer fly, gets on the human skin, and actively bores through it. - Geographical distribution: West Africa, India, South America. - Pathogenesis. Inhabiting the subcutaneous tissue, L. loa can occur in various parts of the human body. Wandering through the subcutaneous tissue, loa can cause unpleasant subjective sensations in the form of itching and sometimes pain, which patients most often qualify as 'rheumatic'. Wandering edemas on the body are often noted. Sometimes inflammatory processes in the subcutaneous tissue occur on the basis of loaosis. When located in the area of the eyes, the parasite can cause itching, tearing, swelling of the eyelids, conjunctivitis and inflammation of the lacrimal sacs. Diagnosis is made both according to clinical signs and palpation of the worm under the skin, and by detecting microfilariae in the blood. b) Loa extraocularis Skrjabin; 1917. Syn. Filaria extraocularis. This nematode was described by Skrjabin and is known only from one specimen of an immature female. The parasite was obtained by surgeon Vladychensky in Krasnodar from a peasant woman from a swelling in the area of the inner angle of the eye between the wall of the orbit and the eyeball. - Brief description: length 148 mm and width 0.612 mm. The cuticle is covered with fine transverse striations. The esophagus is 0.935 mm in length, the nerve ring is 0.273 mm from the anterior end, and the vulva is located 2.4 mm from the head. In the patient, the eye gradually became difficult to open due to increasing swelling; the swelling reached the size of a pea, interfered with vision, but was painless. When the swelling was incised, a thin worm emerged from it, making energetic movements. The parasite was surrounded by a dense fibrous capsule. The wound healed per primam, the patient was discharged healthy. There were no parasites in the blood, eosinophilia 4.4%, otherwise normal.