Chrysops silacea and C. dimidiata: fly densities and infection rates with Loa loa in the Chaillu mountains, Congo Republic

Noireau, François; Nzoulani, Albert; Sinda, Dominique; Itoua, A.

doi:10.1016/0035-9203(90)90416-c

Cited by 20 publications

(16 citation statements)

References 12 publications

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“…Vector control would be a good alternative method if the density and dispersal of vectors are limited, as suggested by previous studies. For example, the biting density of Chrysops silacea averaged 13/man-day in western Cameroon (Crewe & O'Rourke, 1951) and only 4/ man-hour in the Chaillu mountains of Congo (Noireau et al, 1990b). Our observations on Chrysops dimidiata, as well as C. silacea in southern Cameroon, agree.…”

Section: Introductionsupporting

confidence: 75%

Density and dispersal of the loaiasis vector Chrysops dimidiata in southern Cameroon

Chippaux

Bouchité

Demanou

et al. 2000

Medical Vet Entomology

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By mark-release-recapture experiments, we assessed the density of loaisis vectors, Chrysops dimidiata Wulp plus some Chrysops silacea Austen (Diptera: Tabanidae) and estimated their range of flight in the secondary forest of southern Cameroon. In 1993, the release point was at the centre of the study area and recapture points were at 1,100 m radius. In 1994, releases were on the periphery of the study area and recapture sites were 400-8,000 m from the release points. Results were concordant and showed Chrysops female densities of 785-3,682 flies/ km2. The theoretical flight range was < 6,000 m, with a maximum distance of 4,500 m observed. These results are considered promising for the use of vector control methods against loaiasis.

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Section: Introductionsupporting

confidence: 75%

Density and dispersal of the loaiasis vector Chrysops dimidiata in southern Cameroon

Chippaux

Bouchité

Demanou

et al. 2000

Medical Vet Entomology

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“…Both species were shown to be sensitive to rainfall, but with a dominion of C. silacea over C. dimidiata in the rainy season [23]. The increase in the density of C. silacea but not C. dimidiata might be related to an increase in the rainfall in this area.…”

Section: Discussionmentioning

confidence: 99%

Impact of repeated ivermectin treatments against onchocerciasis on the transmission of loiasis: an entomologic evaluation in central Cameroon

Kouam

Tchatchueng-Mbougua²,

Demanou

et al. 2013

Parasites Vectors

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BackgroundAnnual community-directed treatment with ivermectin (CDTI) have been carried out since 1999 in the Lekie division (central region of Cameroon where most cases of Loa-related post ivermectin severe adverse events were reported) as part of the joined activities of the African Programme for Onchocerciasis Control (APOC) and Mectizan® Donation Program (MDP). As large-scale administration of ivermetine was demonstrated to be an efficient means to control loiasis transmission, it was hypothesized that CDTI would have lowered or halted the transmission of Loa loa in the Lekie division after 13 years of annual drug administration, indicating a possible reduction in the occurrence of Loa-related post-ivermectin severe adverse events.MethodsA 4-month entomologic study was carried out from March to June 2012 in the Lekie division to evaluate the impact of 13 years of CDTI on the transmission of L. loa whose baseline data were recorded in 1999–2000.ResultsThere was a significant reduction in the infection rate for Chrysops silacea and C. dimidiata from 6.8 and 9% in 1999–2000 to 3 and 3.6% in 2012, respectively. The differences in the infective rate (IR) (percentage of flies harboring head L3 larvae), potential infective rate (PIR) (percentage of flies bearing L3 larvae), mean head L3 larvae load (MHL3) (average L3 per infective fly) and mean fly L3 larvae load (MFL3) (average L3 per potentially infective fly) for both C. silacea and C. dimidiata were not significantly different between the two investigation periods. The biting density (BD) was almost three-fold higher in 2012 for C. silacea but not for C. dimidiata. The transmission potential (TP) which is a function of the BD, was higher in the present study than in the baseline investigation for each species.ConclusionThe infection rate remaining high, the high TP and the stability observed in the IR, PIR, MHL3 and MFL3 after 13 years of CDTI suggest that transmission of L. loa is still active. This is an indication that the risk of occurrence of severe adverse events such as fatal encephalopathies is still present, especially for heavily microfilaria-loaded people taken ivermectin for the first time.

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“…In such regions it is probable that most individuals are exposed to infection since the intensity of transmission is high. It was estimated recently that individuals receive 20-24 infective fly bites per year (Noireau et al 1990). In addition, seropositivity is very high, in one hyperendemic zone 95% of the inhabitants had antibodies reacting with L. loa antigens by the age of two years (Goussard et al 1984).…”

Section: Introductionmentioning

confidence: 99%

Antibody‐dependent cell‐mediated immune reactions to Loa loa microfilariae in amicrofilaraemic subjects

Pinder

Leclerc

Everaere

1992

Parasite Immunology

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Antibody-mediated mechanisms that could be important in controlling microfilaraemia in Loa loa infected amicrofilaraemic adults (mf-ve) were studied. These subjects were selected as having a verified ocular passage of an adult L. loa but being amicrofilaraemic and without recent diethylcarbamazine treatment. Sera from 37 mf-ve subjects were compared to 14 sera from heavily (greater than 4000 mf/ml) infected subjects (mf+ve) and 9 sera from Caucasian control subjects for their reactions with L. loa mf (mf). Many mf-ve sera (22/37) were strongly positive in immunofluorescence (IFAT) on living mf. Mf+ve sera were negative, or only weakly positive, and Caucasian sera were negative. Clinical signs were not significantly different between IFAT reactive and non-reactive mf-ve subjects. Approximately half of the IFAT positive, mf-ve sera were also able to agglutinate mf; no other sera were active in this test. Titres ranged from log2 3-6 and in most cases, 9/11, the agglutination reaction was mercaptoethanol-sensitive. Antibody-dependent cellular adherence was studied using mf and leukocytes from uninfected donors. Using cryopreserved mf many heat-inactivated mf-ve sera gave strong reactions with obvious adherence by 4 h and few motile mf remained by 16 h but when fresh mf were employed these reactions were weak. However, addition of complement to many (10/11) mf-ve sera considerably enhanced adherence to fresh mf. The effect of various treatments on the complement source indicated a role for both the classical and alternative pathways. The cells attached to mf were mainly neutrophils (83%) with some eosinophils (15%) and few mononuclear cells (2%). The common occurrence of antibodies able to mediate complement-dependent adherence of polymorphonuclear leukocytes to L. loa mf in the sera of mf-ve subjects may indicate that such a mechanism is important in controlling microfilaraemia in vivo.

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Chrysops silacea and C. dimidiata: fly densities and infection rates with Loa loa in the Chaillu mountains, Congo Republic

Cited by 20 publications

References 12 publications

Density and dispersal of the loaiasis vector Chrysops dimidiata in southern Cameroon

Density and dispersal of the loaiasis vector Chrysops dimidiata in southern Cameroon

Impact of repeated ivermectin treatments against onchocerciasis on the transmission of loiasis: an entomologic evaluation in central Cameroon

Antibody‐dependent cell‐mediated immune reactions to Loa loa microfilariae in amicrofilaraemic subjects

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