Clinical, paraclinical and genetic aspects of autosomal recessive cerebellar ataxias (ARCA) in Mali

Introduction

Autosomal recessive cerebellar ataxias (ARCA) are a group of rare and heterogynous neurodegenerative diseases mainly characterized by unbalance and walking difficulty and movement incoordination.

Objectives

To clinically and paraclinically characterize ARCA in the department of Neurology at the Teaching Hospital of Point G and identify the underlying genetic defect.

Patients and method

We have conducted a longitudinal and prospective study from January 2018 to December 2020. Patients with ARCA phenotype seen in the Department of Neurology at the Teaching Hospital of Point "G" were enrolled.

Results

We have enrolled 7 families totaling 13 patients after giving an informed verbal and written consent. The sex ratio was 2.2 in favor of males, Kayes region and Fulani ethnic group were respectively the most represented region and ethnic group.Walking difficulty represented the major symptom followed by loss of vibration and joint sense, nystagmus, dysarthria and skeletal deformities. Alpha-foetoprotein level was high in one patient. Genetic testing confirmed Friedreich ataxia in one family and was not conclusive in 4 families.

Conclusion

This study showed that ARCA are not uncommon in Mali and genetic testing is crucial to confirm the diagnosis.

Multiple Resistance Mechanisms to Pyrethroids Insecticides in Anopheles gambiae sensu lato Population From Mali, West Africa

Background

Insecticide-based vector control is responsible for reducing malaria mortality and morbidity. Its success depends on a better knowledge of the vector, its distribution, and resistance status to the insecticides used. In this paper, we assessed Anopheles gambiae sensu lato (A gambiae s.l.) population resistance to pyrethroids in different ecological settings.

Methods

The World Health Organization standard bioassay test was used to assess F₀A gambiae s.l. susceptibility to pyrethroids. Biochemical Synergist assays were conducted with piperonyl butoxide (PBO), S,S,S-tributyl phosphotritioate, and diethyl maleate. L1014F, L1014S, and N1575Y knockdown resistance (kdr) mutations were investigated using TaqMan genotyping.

Results

Anopheles gambiae sensu lato was composed of Anopheles arabienisis, Anopheles coluzzii, and A gambiae in all study sites. Anopheles gambiae sensu lato showed a strong phenotypic resistance to deltamethrin and permethrin in all sites (13% to 41% mortality). In many sites, pre-exposure to synergists partially improved the mortality rate suggesting the presence of detoxifying enzymes. The 3 kdr (L1014F, L1014S, and N1575Y) mutations were found, with a predominance of L1014F, in all species.

Conclusions

Multiple resistance mechanisms to pyrethroids were observed in A gambiae s.l. in Mali. The PBO provided a better partial restoration of susceptibility to pyrethroids, suggesting that the efficacy of long-lasting insecticidal nets may be improved with PBO.

Performance of pirimiphos-methyl based Indoor Residual Spraying on entomological parameters of malaria transmission in the pyrethroid resistance region of Koulikoro, Mali

Malaria vector control in Mali relies heavily on the use of long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) in selected districts. As part of strengthening vector control strategies in Koulikoro district, the National Malaria Control Programme (NMCP) through the support from the US President's Malaria Initiative (PMI) has strategically driven the implementation of IRS, with the LLINs coverage also rising from 93.3% and 98.2%. Due to the increased reports of vector resistance to both pyrethroid and carbamates, there was a campaign for the use of pirimiphos-methyl, an organophosphate at Koulikoro between 2015 and 2016. In this study, the effect of IRS on malaria transmission was assessed, by comparing some key entomological indices between Koulikoro, where IRS was implemented and its neighboring district, Banamba that has never received IRS as vector control intervention. The study was conducted in two villages of each district (Koulikoro and Banamba). Pyrethrum spray catches and entry window trapping were used to collect mosquitoes on a monthly basis. WHO tube tests were carried out to assess mosquito susceptibility to insecticides. Mosquitoes were identified to species level by PCR and their infection to P. falciparum was detected by Enzyme Linked-Immuno-Sorbent Assay (ELISA). Of the 527 specimens identified, An. coluzzii was the most frequent species (95%) followed by An. gambiae (4%) and An. arabiensis (1%). Its density was rainfall dependent in the no-IRS area, and almost independent in the IRS area. The infection rate (IR) in the no-IRS area was 0.96%, while it was null in the IRS area. In the no-IRS area, the entomological inoculation rate (EIR) was 0.21 infective bites /person month with a peak in September. High resistance to pyrethroids and carbamates and susceptibility to organophosphates was observed at all sites. The introduction of pirimiphos-methyl based IRS for vector control resulted in a significant decrease in malaria transmission. An. gambiae s.l., the main malaria vector in the area, was resistant to pyrethroids and carbamates but remained susceptible to the organophosphate pirimiphos-methyl.

Acetylcholinesterase (ace-1R) target site mutation G119S and resistance to carbamates in Anopheles gambiae (sensu lato) populations from Mali

BACKGROUND

The long-lasting insecticidal nets (LLINs) and indoor residual spraying of insecticide (IRS) are major malaria vector control strategies in Mali. The success of control strategies depends on a better understanding of the status of malaria vectors with respect to the insecticides used. In this study we evaluate the level of resistance of Anopheles gambiae (sensu lato) to bendiocarb and the molecular mechanism that underlies it.

METHODS

Larvae of An. gambiae (s.l.) were collected from breeding habitats encountered in the three study sites and bioassayed with bendiocarb. The ace-1 target site substitution G119S was genotyped using a TaqMan assay.

RESULTS

The three species of the An. gambiae complex in Mali, i.e. An. arabiensis, An. coluzzii and An. gambiae (s.s.) were found in sympatry in the three surveyed localities with different frequencies. We observed a resistance and suspicious resistance of the three species to bendiocarb with a mortality rate ranging from 37% to 86%. The allelic frequency of the G119S mutation was higher in An. gambiae (s.s.) compared to the other two species; 42.86%, 25.61% and 16.67% respectively in Dangassa, Koula, and Karadié. The allelic frequency of G119S in An. coluzzii ranged from 4.5% to 8.33% and from 1.43% to 21.15% for An. arabiensis. After exposure to bendiocarb, the G119S mutation was found only in survivors. The survival of Anopheles gambiae (s.l) populations from the three surveyed localities was associated with the presence of the mutation.

CONCLUSIONS

The study highlights the implication of G119S mutation in bendiocarb resistance in An. gambiae (s.s.), An. arabiensis and An. coluzzii populations from the three surveyed localities.

[Susceptibility status of Anopheles gambiae sensu lato to insecticides commonly used for malaria control in Mali]

The objective of this work was to monitor the susceptibility of malaria vectors to insecticides in nine sentinel sites of the National Malaria Control Program in Mali. The study was performed during the rainy seasons of 2010 and 2011. WHO bioassays were conducted using F0 and/or F1 from wild collected females. The insecticides used were lambda-cyhalothrin 0.05%, DDT 4%, permethrin 0.75%, deltamethrin 0.05%, bendiocarb 0.1% and fenitrothion 1.0%. Results showed suspicion of resistance to pyrethroids and organochlorine in An. gambiae s.l. at almost all the sites except Yanfolila where the vector was susceptible to lambda-cyhalothrin (98.0%) [CI 95%, 98-99.8] and to DDT (100%). An. gambiae s.l. was susceptible to bendiocarb in five of the sites (Gao, Bougouni, Djenné, Yanfolila, Tombouctou) while there was a suspicion of resistance at the other sites (Kati, Niono, Bandiagara, Kita). Fenitrothion remains efficient except in the rice area of Niono, where there was a suspicion of resistance with a mortality rate of 92% [IC 95% 88.3-94.8]. Thus, it could be used as an alternative insecticide for IRS in Mali. These results show resistance to pyrethroids, the main insecticide family used in public health (and to some extent in agriculture). This could compromise the malaria vector control efforts in Mali where pyrethroids are used for both in bed nets and in IRS.

SNP genotyping defines complex gene-flow boundaries among African malaria vector mosquitoes

Mosquitoes in the Anopheles gambiae complex show rapid ecological and behavioral diversification, traits that promote malaria transmission and complicate vector control efforts. A high-density, genome-wide mosquito SNP-genotyping array allowed mapping of genomic differentiation between populations and species that exhibit varying levels of reproductive isolation. Regions near centromeres or within polymorphic inversions exhibited the greatest genetic divergence, but divergence was also observed elsewhere in the genomes. Signals of natural selection within populations were overrepresented among genomic regions that are differentiated between populations, implying that differentiation is often driven by population-specific selective events. Complex genomic differentiation among speciating vector mosquito populations implies that tools for genome-wide monitoring of population structure will prove useful for the advancement of malaria eradication.

Evidence for subdivision within the M molecular form of Anopheles gambiae

The principal vector of malaria in sub-Saharan Africa, Anopheles gambiae is subdivided into two molecular forms M and S. Additionally, several chromosomal forms, characterized by the presence of various inversion polymorphisms, have been described. The molecular forms M and S each contain several chromosomal forms, including the Savanna, Mopti and Forest forms. The M and S molecular forms are now considered to be the reproductive units within A. gambiae and it has recently been argued that a low recombination rate in the centromeric region of the X chromosome has facilitated isolation between these forms. The status of the chromosomal forms remains unclear however. Therefore, we studied genetic differentiation between Savanna S, Forest S, Forest M and Mopti M populations using microsatellites. Genetic differentiation between Savanna S and Forest S populations is very low (F(ST) = 0.0053 +/- 0.0049), even across large distances. In comparison, the Mopti M and Forest M populations show a relatively high degree of genetic differentiation (F(ST) = 0.0406 +/- 0.0054) indicating that the M molecular form may not be a single entity, but could be subdivided into at least two distinct chromosomal forms. Previously it was proposed that inversions have played a role in the origin of species within the A. gambiae complex. We argue that a possible subdivision within the M molecular form could be understood through this process, with the acquisition of inversions leading to the expansion of the M molecular form into new habitat, dividing it into two distinct chromosomal forms.

Reproductive output of female Anopheles gambiae (Diptera: Culicidae): comparison of molecular forms

Knowledge of ecological differences between the molecular forms of Anopheles gambiae Giles (Diptera: Culicidae) might lead to understanding of their unique contribution to disease transmission, to better vector control, and to identification of the forces that have separated them. We compared female fecundity measured as egg batch size in relation to body size between the molecular forms in Mali and contrasted them with their sibling species, Anopheles arabiensis Patton. To determine whether eggs of different egg batches are of similar "quality," we compared the total protein content of first-stage larvae (L1s), collected < 2 h after hatching in deionized water. Egg batch size significantly varied between An. gambiae and An. arabiensis and between the molecular forms of An. gambiae (mean batch size was 186.3, 182.5, and 162.0 eggs in An. arabiensis and the M and the S molecular form of An. gambiae, respectively). After accommodating female body size, however, the difference in batch size was not significant. In the S molecular form, egg protein content was not correlated with egg batch size (r = -0.08, P > 0.7) nor with female body size (r = -0.18, P > 0.4), suggesting that females with more resources invest in more eggs rather than in higher quality eggs. The mean total protein in eggs of the M form (0.407 microg per L1) was 6% higher than that of the S form (0.384 microg per L1), indicating that the M form invests a greater portion of her resources into current (rather than future) reproduction. A greater investment per offspring coupled with larger egg batch size may reflect an adaptation of the M form to low productivity larval sites as independent evidence suggests.

[Presence and risk of transmission of Wuchereria bancrofti is a reality in rural Mali: the case of the town of Bariambani in the Cirle of Kati]

Previous studies on lymphatic filariasis in Mali showed high infection rate in rural area. This study was aimed to find Wuchereria bancrofti microfilaria in human peripheral blood and larvae in vectors. For that purpose we carried out an entomological, clinical and parasitological study in Banambani a village located at 25 km from Bamako the capital city. The parasitological and clinical study was a single cross sectional study including night blood thick smear and physical examination. The entomological study was longitudinal with three annual surveys at the beginning, the middle and the end of the rainy season with parasite detection on vector by PCR. The infection rates by night thick smear was 1.5% of the study sample. The transmission was assured by Anopheles gambiae s.l and Anopheles funestus. Wuchereria bancrofti larvae have been detected on 0.5% of the vectors. The higher entomological inoculation rate (EIR) for An. gambiae s.l has been observed in August (4.03 infective bites per man per night) and in October for An. funestus (1.9 infective bites per man per night). Lymphatic filariasis is present in Malian rural area and transmission still occurring.

Gene flow among populations of the malaria vector, Anopheles gambiae, in Mali, West Africa

The population structure of the Anopheles gambiae complex is unusual, with several sibling species often occupying a single area and, in one of these species, An. gambiae sensu stricto, as many as three "chromosomal forms" occurring together. The chromosomal forms are thought to be intermediate between populations and species, distinguishable by patterns of chromosome gene arrangements. The extent of reproductive isolation among these forms has been debated. To better characterize this structure we measured effective population size, N(e), and migration rates, m, or their product by both direct and indirect means. Gene flow among villages within each chromosomal form was found to be large (N(e)m > 40), was intermediate between chromosomal forms (N(e)m approximately 3-30), and was low between species (N(e)m approximately 0.17-1.3). A recently developed means for distinguishing among certain of the forms using PCR indicated rates of gene flow consistent with those observed using the other genetic markers.

The distribution and inversion polymorphism of chromosomally recognized taxa of the Anopheles gambiae complex in Mali, West Africa

Data from polytene chromosome studies on the Anopheles gambiae complex in Mali were reviewed. The banding pattern was successfully scored in 17,705 specimens from 76 sampling sites representing the main ecological strata of the country. Two members of the complex, namely An. arabiensis and An. gambiae, were found widespread and frequently sympatric, with the latter prevalent in most localities. Population genetic analysis of the inversion polymorphisms indicated the existence of panmictic conditions for An. arabiensis only, whereas the parallel study of An. gambiae supported its splitting into at least three reproductive units, characterized by different 2R chromosome arrangements, designated Bamako, Mopti and Savanna. The chromosomal evidence was consistent with the hypothesis of complete reproductive isolation between Bamako and Mopti. Partial isolation between these two taxa and Savanna was suggested by the scoring of hypothetical hybrid 2R heterokaryotypes in various samples, but the actual hybrid origin of these specimens was not confirmed. Different patterns of geographical and seasonal distribution were shown as follows. An. arabiensis prevails in arid savannas (Sahel and Northern Sudan savanna) out of the flooded or irrigated zones; it is able to withstand the most arid conditions of Saharan localities and its breeding might extend throughout the dry season. An. gambiae Savanna and Bamako prevail in relatively humid savannas (Southern Sudan savanna) and their breeding generally occurs only during the rainy season. The Savanna taxon was almost absent in flooded or irrigated zones and in riverine localities; the Bamako taxon is distributed along the upper river Niger and its tributaries. An. gambiae Mopti extends its range in all ecological zones present in Mali including the Sahel and predesertic areas, showing high relative frequencies up to absolute dominance in flooded or irrigated areas; its breeding is highly successful also during the dry season. Rainfall at the sampling sites was found to correlate positively with the frequency of Savanna and negatively with the frequency of Mopti. The remarkable ecological flexibility of the latter was found associated with wide seasonal and geographical variations in its 2R inversion polymorphism bc/u. Higher frequencies of the bc arrangement were recorded both in the Southern localities during the dry season and in the Northern more arid localities during the rainy season. The absence or scarcity of An. arabiensis and An. gambiae Savanna in most flooded or irrigated zones suggests their competitive exclusion by An. gambiae Mopti.

[Malaria transmission in the rural zone of Niakhar, Senegal]

The anopheline bioecology and the malaria transmission were studied from January to December 1995 in three villages of the sahelian rural area of Niakhar, Senegal. This area of 29000 inhabitants, has been for several decades, a regional observatory for population and health. The three methods used for collecting mosquitoes were the collection at larval stages, the all night human biting collection, and the pyrethrum spray catch in houses during afternoons. The anophelines collected were, by numerical importance: Anopheles arabiensis, An. rufipes, An. gambiae, An. pharoensis, An. funestus and An. coustani. In the An. gambiae complex, An. arabiensis represented 97% of man biting females and 98% of half gravid resting females (difference not significant); the other reminding species of this complex was always An. gambiae. These two species belonging to the An. gambiae complex were responsible for the totality of the transmission. The anthropophilic index, obtained from half gravid indoor resting An. gambiae s.l., was 83%. The annual biting rate of An. gambiae s.l. varied from 512 to 1558 bites per man per night, depending on the villages. Vectors were observed all year long but their densities were low during the dry season. Vector population presented a notable increase due to the rains, with a maximum of about 10 bites per man per night in September or at the beginning of October; during September the biting rate represented 48% of the annual biting rate. The sporozoitic index of An. gambiae s.l., obtained by ELISA revealing the circumsporozoite protein, was 1.6% for human biting females and 1.8% for half-gravid resting females (difference not significant). Plasmodium falciparum was the only plasmodial species observed among infected anophelines. The annual transmission in the vo villages representative of the Niakhar area were 9 and 12 bites of infected anophelines per man, occurring mainly from August to October. In the third village, not representative of the area regarding permanent breeding places, the transmission was 26 bites of infected anopheline per man per year. These results were discussed in the Senegambian and sahelian contexts.

Mark-release-recapture experiments with Anopheles gambiae s.l. in Banambani Village, Mali, to determine population size and structure

Mark-release-recapture experiments with Anopheles gambiae s.l. were performed during the wet seasons of 1993 and 1994 in Banambani, Mali. All recaptured mosquitoes were identified to species by PCR analysis and, when possible, by chromosomal analysis to chromosomal form. Two species of the An. gambiae complex were present: An. gambiae s.s. and An. arabiensis; their ratio differed greatly from one year to the next. Three chromosomal forms of An. gambiae s.s. were found--Bamako, Savanna and Mopti. The drier 1993 was characterized by a high frequency of An. arabiensis and of the Mopti chromosomal forms of An. gambiae s.s. These trends were consistent with large-scale geographical patterns of abundance along a precipitation gradient. We observed no difference in dispersal between the two species, nor among the chromosomal forms of An. gambiae s.s. Therefore, in this situation at least, it is reasonable to group such data on the An. gambiae complex as a whole for analysis. Population size of An. gambiae s.l. females in the village was estimated to be 9000-11,000 in 1993 and 28,000 in 1994. The corresponding numbers were somewhat higher when independently-derived values of daily survival were used. These were consistent with estimates of effective population size obtained from patterns of gene frequency change.

Ecological genetic studies in the chromosomal form Mopti of Anopheles gambiae s.str. in Mali, west Africa

Among the sibling species of the Afrotropical Anopheles gambiae complex, the nominal taxon (An. gambiae s.str.) is the major malaria vector. Its bionomics suggest a man-dependent speciation process which involves, in West Africa, various incipient species chromosomally recognized by different combinations of 2R paracentric inversions. One of the most recent evolutionary steps of such a speciation process appears to be the chromosomal form Mopti, which is associated with dry season irrigation in arid zones, and is characterized by a remarkable ecological flexibility related to three 2R alternative arrangements, namely bc, u and +, whose expected karyotypes are found in Hardy-Weinberg equilibrium. The study of this chromosomal polymorphism in samples from a 16-locality transect in Mali shows wide variations and highly significant correlation with both temporal and spatial climatic differences. Mosquitoes homokaryotypic for 2Rbc are the actual dry season and arid areas breeders. The regular rise of 2Rbc frequency, up to fixation, during each dry season, corresponds to the South-North clinal increase of the same arrangement along the transect, from about 30% in the humid savanna to near fixation in the South-Saharan zone. This coherent ecological genetics case provides full support to the hypothesis of the adaptive nature of paracentric inversions. Moreover, the very peculiar system of combinations of contiguous 2R inversions, utilized by Mopti as well as by other chromosomal forms of An. gambiae, suggests a process of polygenic reorganization based on linkage disequilibria and involving the inversions as driving selection units.