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Loiasis is a tropical infection caused by the microfilarial nematode Loa loa. Increased numbers of cases of loiasis have been diagnosed outside of the endemic areas in Western and Central Africa because of widespread international travel. The author presents three cases of loiasis discovered at Howard University followed by a review of the literature.
An adult worm was isolated from the left upper eyelid of a man, eight years after he had left an area in which L loa is endemic. We described his case in order to draw attention to some differences between reported features of the disease in areas in which the worm is endemic and in areas in which it is not.
Human filariasis and its vectors are little known in Ethiopia. Wuchereia bancrofti is confined to the western lowlands and cannot be the aetiological agent of elephantiasis in the highlands. Onchocerca volvulus is widespread in the south-western highlands. Loa loa and Dipetalonema perstans are reported here for the first time and appear to be uncommon. Studies were conducted in 1973, mostly near Jimma in Kaffa Province, on potential vectors of all but the first of these parasites. Among Simuliidae, the only blackflies of apparent medical importance were S. woodi ethiopiense and a possibly new member of the S. damnosum complex. The former is less seasonal and much less numerous than the latter, but may be more widespread and important along smaller and higher streams. Onchocerca larvae were recovered from "damnosum", but not from the small number (46) of ethiopiense examined. In August, at the height of the rainy season, the biting-rate of ethiopiense at 1,710 m altitude on the Gilgil Ghibe river reached 9.5/man-hour at 10-1100 hours and about 12/man-hour at 14-1600 hours. At the same time and place, the attack of "damnosum" reached a midday climax of about 1,800/man-hour; this peak could be delayed or suppressed by rain. Another possibly anthropophilic blackfly, S. dentulosum, tended to become most common in December afer the rainy season had passed, but proved incompetent to bite man successfully. The only feasible loiasis vector found in Ethiopia was Chrysops streptobalius; however, this tabanid was not closely associated with man. Up to 34/man-day were caught in watermeadows by the Gojeb river (altitude 1,160 m) in October. Man-biting species of Ceratopogonidae in various parts of Ethiopia were Culicoides fulvithorax, C. grahamii, C. kingi and C. milnei. The first two of these were anthropophilic in lowlands, but apparently not so in highlands. C. milnei was extremely abundant biting man highlands. C. milnei was extremely abundant biting man and domestic animals both indoors and outdg cycle was irregular, usually displaying a succession of ill-define nocturnal peaks; sometimes it attacked in daylight. Up to 35,000 C. milnei per trap-night were caught in light traps. Most of the females entering light traps in a stable were already engorged with blood. It seemed very likely that C. milnei would prove to be of veterinary importance. No firm indication was obtained as to what may transmit D. perstans in Ethiopia.
Serum samples from persons who lived in areas where onchocerciasis occurred or who had filariasis were examined with the complement fixation test and the indirect hemagglutination test for the presence of antibodies against crude extracts from Dirofilaria immitis, Onchocerca volvulus, Dipetalonema viteae, and Ascaris suum. The results could be interpreted as follows: 1. The indirect hemagglutination test was more sensitive than the complement fixation test for the demonstration of antibodies in sera from European and indigenous inhabitants of endemic areas. 2. There were no differences between the responses to the four crude worm extracts among the groups of 21 patients with Loa loa, 12 patients with Onchocerca volvulus, 11 patients with Dipetalonema perstans, and 22 patients with clinical filariasis in whom no microfilaria had been found. It was concluded that the examination with crude extracts cannot give any information about the antigens that had caused the stimulation of antibodies.
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Circulating absolute eosinophil levels were studied over a 24 hour period in a series of 10 patients with presumed parasitological disease. Seven of these ten had the distinct nocturnal increase and a percentage swing paralleling that found in normal subjects. Three patients had a reversed pattern. The latter were thought to have one or other form of filariasis. Two patients with loasis and a "physiological response" had suppression as anticipated to exogenous steroid. It is concluded that steroid administration will not separate parasitic from other causes of eosinophilia.
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Four species of primates, baboon (Papio anubis), patas monkeys (Erythrocebus patas), green monkey (Cercopithecus aethiops) and chimpanzee (Pan troglodytes) were inoculated with third-stage larvae of a human strain of Loa loa from Cameroon, West African. The baboon and patas monkeys developed patent infections after 135 to 148 days; the green monkeys and chimpanzee did not. In each animal which became patent, microfilaremia rose rapidly to high levels. In the baboon, but not in the patas monkeys, there was a suppression of microfilaremia during the 4th month of patency. After splenectomy, microfilariae reappeared in the peripheral blood in large numbers. In both baboon and patas monkeys, the microfilariae of Loa loa maintain the diurnal periodicity so characteristic of their behavior in man.
Chrysops atlanticus, an American species of deerfly collected along the Mississippi Gulf Coast, will support the development of the microfilaria of human Loa loa to the infective stage. Development takes place in the fat body of the fly and requires 9 to 10 days of development and pattern of morphogenesis of the parasite in C. atlanticus is virtually identical to that described in natural African vectors. Chrysops atlanticus will support the development of large numbers of L. loa to the infective stage without apparent ill effects. Two uninfected patas nonkeys each were given 75 third-stage larvae obtained from experimentally infected C. atlanticus. Both animals developed patent infections in approximately 5 months, clearly demonstrating that the entire life cycle of Loa loa can be maintained in the laboratory outside endemic areas.
Loa loa, also known as the African eye worm, is a common parasite in the central part of West Africa. As Chrysops silacea and C. dimidiata, the only important vectors of loaiasis, are found exclusively in the tropical rain forests of West Africa, the parasite's transmission is confined to this region. References by early writers to the extraction of Loa loa from the eye of a man on the Island of Ormus (today known as Hormuz or Hormus) in the Persian Gulf apparently were based on a misinterpretation of an illustration by de Bry (1595) of the blinding of a royal relative.
Loaiasis was seen in an African student in Indiana, who had non-specific complaints, leukocyte count of 8,400/mm3, a 47% eosinophilia, and a high Loa loa microfilaremia. Successful treatment with diethylcarbamazine (Hetrazan) produced no allergic manifestations and no reactions to the adult parasites were evident.
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A report about a case of loa-loa filariasis whereby after removal of a female worm out of the subconjunctival space no microfilariae but a schisslike edema of the attacked eye's retina was found. In this connection the author gave some observations on the particularies of loa-loa filariasis.