Impact of repeated annual community directed treatment with ivermectin on loiasis parasitological indicators in Cameroon: Implications for onchocerciasis and lymphatic filariasis elimination in areas co-endemic with Loa loa in Africa

Abstract

BackgroundLoiasis is a filarial infection endemic in the rainforest zone of west and central Africa particularly in Cameroon, Gabon, Republic of Congo, and Democratic Republic of the Congo. Repeated treatments with ivermectin have been delivered using the annual community directed treatment with ivermectin (CDTI) approach for several years to control onchocerciasis in some Loa loa-Onchocerca volvulus co-endemic areas. The impact of CDTI on loiasis parasitological indicators is not known. We, therefore, designed this cross sectional study to explore the effects of several rounds of CDTI on parasitological indicators of loiasis.Methodology/Principal findingsThe study was conducted in the East, Northwest and Southwest 2 CDTI projects of Cameroon. Individuals who consented to participate were interviewed for ivermectin treatment history and enrolled for parasitological screening using thick smears. Ivermectin treatment history was correlated with loiasis prevalence/intensity. A total of 3,684 individuals were recruited from 36 communities of the 3 CDTI projects and 900 individuals from 9 villages in a non-CDTI district. In the East, loiasis prevalence was 29.3% (range = 24.2%–34.6%) in the non-CDTI district but 16.0% (3.3%–26.6%) in the CDTI district with 10 ivermectin rounds (there were no baseline data for the latter). In the Northwest and Southwest 2 districts, reductions from 30.5% to 17.9% (after 9 ivermectin rounds) but from 8.1% to 7.8% (not significantly different after 14 rounds) were registered post CDTI, respectively. Similar trends in infection intensity were observed in all sites. There was a negative relationship between adherence to ivermectin treatment and prevalence/intensity of infection in all sites. None of the children (aged 10–14 years) examined in the East CDTI project harboured high (8,000–30,000 mf/ml) or very high (>30,000 mf/ml) microfilarial loads. Individuals who had taken >5 ivermectin treatments were 2.1 times more likely to present with no microfilaraemia than those with less treatments.ConclusionIn areas where onchocerciasis and loiasis are co-endemic, CDTI reduces the number of, and microfilaraemia in L. loa-infected individuals, and this, in turn, will help to prevent non-neurological and neurological complications post-ivermectin treatment among CDTI adherents.

Collateral impact of community-directed treatment with ivermectin (CDTI) for onchocerciasis on parasitological indicators of Loa loa infection

“…Since L. loa adult worms are lifelong (lifespan estimated up to 15-17 years) [32], repeated treatments with IVM are likely needed to interrupt the transmission of this larial disease, the number of rounds of treatment remaining unknown. The longterm (18 years) implementation of CDTI in the Yabassi Health District likely explain the marked decrease observed in both prevalence and intensity of L. loa infection as was already observed elsewhere in Cameroon [23].…”

“…To date, data on the impact of CDTI on L. loa transmission are unfortunately scanty and those available are controversial. While some exhibited a signi cant decrease in the prevalence and intensity of L. Loa infection both in human and vector populations [22][23], others support ongoing transmission with higher or substantially unchanged entomological indices despite 15 years of annual CDTI [24]. In this context of scarcity and controversy in available data, the present study aimed to assess the long-term collateral impact of CDTI against onchocerciasis on prevalence and intensity of L. loa infection.…”

Validation of Loop Mediated Isothermal Amplification for the Detection of Loa loa Infection in Chrysops sp in Experimental and Natural Field Conditions

“…The study protocol, as a work package attached to the following studies [20,26], received ethical approval from the Cameroon National Ethics Committee. The objective of the study was explained to the trained collectors and informed consent was obtained from all participants.…”

“…More so, accurate detection of the infection rates in vector populations is essential for assessing transmission, deciding when drug treatments may be stopped, and monitoring recrudescence [16]. Several studies have documented reduction of the prevalence and intensity of Loiasis in the human population after treatment with Ivermectin [17][18][19][20];…”

Validation of Loop Mediated Isothermal Amplification for the detection of Loa loa infection in Chrysops spp in experimental and natural field conditions

“…More so, accurate detection of the infection rates in vector populations is essential for assessing transmission, deciding when drug treatments may be stopped, and monitoring recrudescence [12]. Several studies have documented reduction of the prevalence and intensity of loiasis in the human population after treatment with Ivermectin [13][14][15][16]; however, there is little information about the infection rate of the vectors after chemotherapy. In a well organised control program where Ivermectin would deplete micro lariae in the host, Chrysops ies would tend to take up lower numbers of mf in their blood meals.…”