Increased frequency of Th2-type cytokine-producing T cells in microfilaremic loiasis. (1/40)

The frequency of cytokine-producing peripheral blood mononuclear cells was assessed in 28 subjects with microfilaremic loiasis and in 14 amicrofilaremic individuals. In addition, a subgroup of seven microfilaremic individuals coinfected with Plasmodium malariae was evaluated. By using flow cytometry for the intracellular detection of cytokines, a more pronounced T helper (Th)2 cell-type response with the expansion of interleukin (IL)-4, IL-10, and IL-13 expressing CD4+ cells in the microfilaremic compared with the amicrofilaremic group was noted. Expression of IL-5 was equivalent in both groups as was the frequency of Th2-type cytokines expressing CD8+ cells and of Th1-type cytokines (interferon [IFN]-gamma, IL-2, IFN-gamma/IL-2) producing CD4+ and CD8+ cells. Th0-type cytokine-expressing cells, represented by IL-4/IFN-gamma, IL-10/IFN-gamma, and IL-13/IFN-gamma, were equally distributed within groups. Coinfection of P. malariae did not significantly alter the cytokine expression compared with microfilaremic individuals without P. malariae infections. By identifying a large panel of cytokine-producing T cell subpopulations, a Th2-driven immune response in microfilaremic Loa loa patients was noted.  (+info)

Genetic epidemiology of host predisposition microfilaraemia in human loiasis. (2/40)

Evidence is accumulating from experimental and human studies that genetic factors are involved both in the control of infectious diseases and in the regulation of infection levels and clinical presentation. So far few studies have investigated the role of these genetic factors in human infection by the filarial parasite Loa loa. We present a segregation analysis on 74 nuclear families who live in the tropical rainforest of southern Cameroun and are exposed to homogeneous loiasis transmission. The results indicate that there is a genetic predisposition to be microfilaraemic and that predisposed subjects might be genetically unable to mount an efficient immune response against loiasis antigens. This individual susceptibility could explain at least in part why the prevalence of infection (microfilaraemic individuals) does not usually exceed 30% of the exposed population in hyperendemic regions. Further genetic studies, based on linkage analysis using both familial information and genetic markers, will help to identify the nature of the genetic factors predisposing to microfilaraemia.  (+info)

Use of polymerase chain reaction for accurate follow-up of Loa loa experimental infection in Mandrillus sphinx. (3/40)

Mandrills (Mandrillus sphinx) experimentally infected with human Loa loa usually remain microfilaremic for a long period of time. Nevertheless some control their microfilaremia while still harboring adults worms, and therefore become occult-infected. A nested polymerase chain reaction (PCR) assay, targeted on the repeat 3 region of the gene coding for the L. loa 15-kD protein (15r3-PCR), has been evaluated in mandrills infected with third-stage larvae (L3) of L. loa. The results of this assay were negative during the prepatency period (4 months after inoculation), but became positive when microfilariae appeared in the blood, and remained positive in all mandrills, even in those that became amicrofilaremic. These results show that the positivity of the 15r3-PCR assay is linked to the appearance of microfilariae in peripheral blood and demonstrated that L. loa-specific DNA can be detected in blood from occult-infected mandrills.  (+info)

Chrysops silacea biting densities and transmission potential in an endemic area of human loiasis in south-west Cameroon. (4/40)

We studied the biting densities of Chrysops silacea and the transmission of loiasis over 1 year in a regenerated forest in the south-west province of Cameroon. A total of 3015 flies caught near a wood fire at ground level during rainy and dry seasons were identified morphologically and 1975 caught during the rainy season were dissected to determine their physiological age and infection rate. The prevalence of microfilaraemia in the human population in the study area was determined using the thick blood smear method. Chrysops silacea was the only species caught. The daily and seasonal biting cycle of C. silacea showed two peaks of activities, 9-11 a.m. and 2-4 p.m. The biting cycles of parous and nulliparous flies showed the same trends, but the density of nulliparous flies biting at all time of the day was 2-3 times higher. Chrysops silacea biting density was high during the rainy season (9.06 +/- 6.88 flies/man/h) and lowest during the dry season (0.44 +/- 0.75 flies/man/h). An infection rate of 1.72% and a monthly morning and afternoon transmission potentials of 120769.11 and 139016.64 infective head L3/man were observed, respectively, in the rainy season. Even though few Chrysops carried Loa loa infective larvae (0.7%), their parasite load was high, giving a high level of transmission of L. loa in the area. A total of 20.37% of the people examined for blood microfilariae were positive. These results suggest that the study area is an active focus of loiasis transmission.  (+info)

Expression of filarial-specific IgG subclasses under different transmission intensities in a region endemic for loiasis. (5/40)

Specific IgG subclasses were investigated in two villages (Okoumbi and Ndjokaye) in southeast Gabon with different Loa loa transmission intensities of approximately 9,000 and 1,300 infective larvae (L3) per person per year, respectively. IgG subclasses were measured by an enzyme-linked immunosorbent assay (ELISA) using extracts of L. loa L3, microfilariae (MF), or adult worms. Levels of L3-specific IgG3 were significantly higher in the village with low transmission (Ndjokaye) (P = 0.006). In contrast, MF-specific IgG2 was significantly higher in Okoumbi than in Ndjokaye (P = 0.0009). In the high-transmission village (Okoumbi), levels of both MF- and adult-specific IgG4 were significantly increased in MF carriers compared with amicrofilaremic subjects (P = 0.0015 and P = 0.003, respectively), while levels of L3- and MF-specific IgG1 were significantly higher in amicrofilaremic individuals compared with MF carriers (P = 0.04 and P = 0.03, respectively). Furthermore, among microfilaremic individuals, the level of the specific IgG1 subclass was much lower in Okoumbi than in Ndjokaye (P = 0.036). These results suggest that the expression of antigen-specific IgG3 and IgG2 is more likely to vary with transmission intensity, whereas antigen-specific IgG4 and IgG1 varies with adult worm and MF burden.  (+info)

Rapid assessment method for prevalence and intensity of Loa loa infection. (6/40)

OBJECTIVE: To assess the validity of observations on eye worm and Calabar swellings for the rapid assessment of the prevalence and intensity of loiasis at the community level. METHOD: A total of 12895 individuals over the age of 15 years living in 102 communities in Cameroon and Nigeria took part in the study. A standardized questionnaire was administered to participants from whom finger-prick blood samples were collected and examined for Loa loa microfilariae. Rapid assessments of the prevalence and intensity of loiasis were made on the basis of a history of eye worm or Calabar swellings. FINDINGS: There was a strong correlation between the indices of the rapid assessment procedures and the parasitological indices of L. loa endemicity. The rapid assessment indices were effective in diagnosing high-risk communities (sensitivity 94-100%; specificity 66-92%). The highest sensitivity (100%) and specificity (92%) were obtained with a rapid assessment procedure based on a history of eye worm lasting 1-7 days together with confirmation by the guided recognition of a photograph of adult L. loa in the eye. CONCLUSION: Rapid assessment of the prevalence and intensity of loiasis at the community level can be achieved using a procedure based on the history of eye worm lasting 1-7 days together with confirmation by the guided recognition of a photograph of an adult L. loa in the eye.  (+info)

Serum immunoglobulin G4 antibodies to the recombinant antigen, Ll-SXP-1, are highly specific for Loa loa infection. (7/40)

The clinical manifestations and geographic distribution of loiasis overlap with those of other human filarial parasites, presenting challenges in the specific diagnosis of loiasis that may lead to delays in appropriate therapy. A recombinant antigen (Ll-SXP-1), preferentially recognized by serum samples from experimentally infected rhesus monkeys, was identified from a Loa loa L3 cDNA library. IgG4 antibody reactivity to purified Ll-SXP-1 was assessed by means of ELISA, using serum samples from patients with loiasis, lymphatic filariasis, onchocerciasis, mansonellosis, or other helminthiases and healthy control subjects. The assay was 56% sensitive and 98% specific for loiasis. Antibody reactivity was detectable before microfilaremia in experimentally infected rhesus monkeys and declined (but did not disappear) after diethylcarbamazine therapy in infected patients. IgG4 antibodies to recombinant Ll-SXP-1 are a highly specific marker of L. loa infection and may be useful for the diagnostic evaluation of persons with filariasis of unclear etiology.  (+info)

Human loiasis in a Cameroonian village: a double-blind, placebo-controlled, crossover clinical trial of a three-day albendazole regimen. (8/40)

Because of the life-threatening, post-treatment reactions that have occurred in patients with loiasis treated with ivermectin, evaluation of a short-course albendazole regimen was undertaken in a Loa-endemic region of Cameroon. In a placebo-controlled, double-blinded, crossover study, 99 subjects with microfilaremia (100-3,3837/mL) were assigned to receive albendazole (400 mg; n = 48) or placebo (n = 51) for three days and were followed for 180 days; at day 180, the groups were crossed over and followed for an additional six months. In those initially receiving albendazole (ALB/PLAC), microfilarial levels decreased significantly by day 90 (P < 0.043), but returned to baseline by day 180. In those receiving albendazole at day 180 (PLAC/ALB), microfilarial levels also decreased following albendazole (P = 0.005). Blood eosinophil and antifilarial IgG levels did not change significantly for either group, although antifilarial IgG4 levels did in the ALB/PLAC group at day 180. Most subjects continued to have elevations in microfilaremia, suggesting that more intensive regimens of albendazole will be necessary to reduce Loa microfilaremia to levels safe enough to allow for ivermectin use.  (+info)