Different distribution of malaria parasite in left and right extremities of vertebrate hosts translates into differences in parasite transmission

International audienceMalaria, a vector-borne disease caused by Plasmodium spp., remains a major global cause of mortality. Optimization of disease control strategies requires a thorough understanding of the processes underlying parasite transmission. While the number of transmissible stages (gametocytes) of Plasmodium in blood is frequently used as an indicator of host-to-mosquito transmission potential, this relationship is not always clear. Significant effort has been made in developing molecular tools that improve gametocyte density estimation and therefore prediction of mosquito infection rates. However a significant level of uncertainty around estimates remains. The weakness in the relationship between gametocyte burden, measured from a blood sample, and the mosquito infection rate could be explained by a non-homogeneous distribution of gametocytes in the bloodstream. The estimated gametocyte density would then only be a single snapshot that does not reflect the host infectivity. This aspect of Plasmodium infection, however, remains largely neglected. In both humans and birds, we found here that the gametocyte densities differed depending on which side of the body the sample was taken, suggesting that gametocytes are not homogeneously distributed within the vertebrate host. We observed a fluctuating asymmetry, in other words, the extremity of the body with the highest density of parasites is not always the same from one individual to another. An estimation of gametocyte density from only one blood sample, as is commonly measured, could, therefore, over-or underestimated the infectivity of gametocyte carriers. This might have important consequences on the epidemiology of the disease since we show that this variation influences host-to-mosquito transmission. Vectors fed on the least infected body part had a lower parasite burden than those fed on the most infected part. The heterogeneous distribution of gametocytes in bloodstream should be considered to improve diagnosis and test new malaria control strategies

Comparative evaluation of automated KingFisher Flex Purification System 96 (ThermoFisher Scientific) and manual QIAamp Viral RNA Mini Kit (Qiagen) extraction methods for SARS-CoV-2

Background: The extraction step of the viral material of the severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) influences the quality of reverse transcriptase-polymerase chain reaction (RT-PCR) results in diagnosis of coronavirus disease 2019 (COVID-19). The purpose of this cross-sectional study was to evaluate the diagnostic performance of the automated extraction system "KingFisher Flex Purification System 96 (ThermoFisher)" compared to the manual method with the "QIAamp Viral RNA Mini Kit (Qiagen)". Methodology: From October to December 2020, comparative diagnostic evaluation of two methods of SARSCoV-2 RNA extraction methods was conducted on 159 fresh and 120 frozen nasopharyngeal and oropharyngeal specimens collected from travellers and suspected cases or contacts of COVID-19 patients in Burkina Faso. The FastPlexTM Triplex 1-Step COVID 19 Detection Kit (RT-PCR, RNA extraction free) (Precigenome LLC) was used to amplify on the same PCR plate, RNA extracts from manual QIAamp Viral RNA Mini Kit and automated KingFisher Flex Purification System 96 (ThermoFisher) using the QuantStudio5 thermal cycler (Applied Biosystems). Analysis of the diagnostic performance of the SARS-CoV-2 RT-PCR assay following RNA extraction by the two methods was done using an online OpenEpi software. Results: For fresh samples, the study found a slightly higher RT-PCR positivity rate following manual extraction (12.6%) than automated extraction (9.4%). For frozen samples, the positivity rate was far higher for manual (38.33%) than automated extraction method (20.83%). The results show that the performance of the automated extraction was inferior when compared to the manual extraction for both fresh samples (sensitivity 35%, specificity 94.2%) and frozen samples (sensitivity 43.5%, specificity 93.2%). However, using McNemar Chi-square with Yates correction, there was no significant difference in positivity rate of RT-PCR (x2=0.76, p=0.38) between the two extraction methods for the fresh samples, but there was a significant difference (x2=12.9, p= 0.0003) in the extraction of the frozen samples. Conclusion: The results of this study showed that KingFisher Flex Purification System 96 (ThermoFisher) automatic extraction method was less sensitive and specific than QIAamp Viral RNA Mini Kit (Qiagen) manual extraction method. This information can serve as guide to laboratories in the choice of RNA extraction methods to use for RT-PCR detection of SARS-CoV-2

Trends in Insecticide Resistance in Natural Populations of Malaria Vectors in Burkina Faso, West Africa: 10 Years’ Surveys

International audienc

Neemazal ® as a possible alternative control tool for malaria and African trypanosomiasis?

Background: Research efforts to identify possible alternative control tools for malaria and African trypanosomiasis are needed. One promising approach relies on the use of traditional plant remedies with insecticidal activities. Methods: In this study, we assessed the effect of blood treated with different doses of NeemAzal ® (NA, neem seed extract) on mosquitoes (Anopheles coluzzii) and tsetse flies (Glossina palpalis gambiensis) (i) avidity to feed on the treated blood, (ii) longevity, and (iii) behavioural responses to human and calf odours in dual-choice tests. We also gauged NeemAzal ® toxicity in mice. Results: In An. coluzzii, the ingestion of NA in bloodmeals offered by membrane feeding resulted in (i) primary antifeedancy; (ii) decreased longevity; and (iii) reduced response to host odours. In G. palpalis gambiensis, NA caused (i) a knock-down effect; (ii) decreased or increased longevity depending on the dose; and (iii) reduced response to host stimuli. In both cases, NA did not affect the anthropophilic rate of activated insects. Overall, the most significant effects were observed with NA treated bloodmeals at a dose of 2000 μg/ml for mosquitoes and 50 μg/ml for tsetse flies. Although no mortality in mice was observed after 14 days of follow-up at oral doses of 3.8, 5.6, 8.4 and 12.7 g/kg, behavioural alterations were noticed at doses above 8 g/kg. Conclusion: This study revealed promising activity of NA on A. coluzzii and G. palpalis gambiensis but additional research is needed to assess field efficacy of neem products to be possibly integrated in vector control programmes

Diversity of phytopathogenic polypores and their interaction with host plants in three biotopes in western Burkina Faso

In order to provide data on polypore identification and their taxonomy, survey studies were undertaken in tree biotope of polypore occurrence. The main objective of this study was to provide a scientific database on the diversity of phytopathogenic polypore and interactions with the host plants in their biotope. Transects of 1 km length covering a width of 50 m were selected at each site. Basidiomes were collected along the transects from roots, trunks and/or branches of forest species Sixty-three species of polypore were identified on twenty-three species of host plants belonging to eleven families. The families most prone to polypore infection were Fabaceae, Apocynaceae, Combretaceae, Anacardiaceae and Caesalpiniaceae. These phytopathogenic polypore were annual to perennial. They grow on roots, trunks and branches of trees and shrubs causing crown and root rots, and trunk cankers on the host plants. The genus Phellinus was the most represented in the agrosystems and in the classified forest of Kou. Similarly, the terricolous species represented by the genera Ganoderma, Amauroderma and Laetiporus were found mainly in the classified forest of Niangoloko and gallery forests of Dan.  &nbsp

Effects of Maruca vitrata multi-nucleopolyhedrovirus and neem oil, Azadirachta indica Juss on the eggs of the cowpea pod borer, Maruca vitrata Fabricius (Lepidoptera: Crambidae)

Cowpea, Vigna unguiculata (L.) Walp., is the most cultivated and consumed legume in West Africa and is typically attacked by several insect pests, including Maruca vitrata, leading to reduced yields. This study assessed under laboratory conditions the efficacy of neem oil and M. vitrata multi-nucleopolyhedrovirus (MaviMNPV) against M. vitrata eggs as alternatives to second generation pesticides. Hatching and mortality rates after biopesticide application of neem oil, MaviMNPV, and the two in combination reduced the egg viability by 89%, 84% and 91%, respectively. Moreover, the combination of MaviMNPV and neem oil induced 100% mortality among the hatched larvae, compared to 60% and 100% alone, respectively. Implications for using these biopesticides are discussed within an integrated pest management (IPM) context

The legume pod borer, Maruca vitrata Fabricius (Lepidoptera: Crambidae), an important insect pest of cowpea: a review emphasizing West Africa

The legume pod borer Maruca vitrata Fabricius (Lepidoptera: Crambidae) is a pantropical insect pest of legumes. In West Africa M. vitrata is the most devastating insect pest of cowpea, a food crop providing much-needed, inexpensive protein to farmers and consumers. Various approaches to controlling this pest have been tried, including cultural management, host plant resistance and use of synthetic and botanical pesticides, all with limited success. In this review we present information on the distribution, morphology, molecular characteristics, behavior and host plants of M. vitrata. We give especial attention to innovative management tactics being developed for West Africa, including genetically engineered Bt cowpea, new biopesticides and use of exotic parasitoids. We discuss research needs for enhancing integrated pest management (IPM) for M. vitrata in Africa

West African Anopheles Gambiae Mosquitoes Harbor a Taxonomically Diverse Virome Including New Insect-Specific Flaviviruses, Mononegaviruses, and Totiviruses

Anopheles gambiae are a major vector of malaria in sub-Saharan Africa. Viruses that naturally infect these mosquitoes may impact their physiology and ability to transmit pathogens. We therefore used metagenomics sequencing to search for viruses in adult Anopheles mosquitoes collected from Liberia, Senegal, and Burkina Faso. We identified a number of virus and virus-like sequences from mosquito midgut contents, including 14 coding-complete genome segments and 26 partial sequences. The coding-complete sequences define new viruses in the order Mononegavirales, and the families Flaviviridae, and Totiviridae. The identification of a flavivirus infecting Anopheles mosquitoes broadens our understanding of the evolution and host range of this virus family. This study increases our understanding of virus diversity in general, begins to define the virome of a medically important vector in its natural setting, and lays groundwork for future studies examining the potential impact of these viruses on anopheles biology and disease transmission

Magnitude and associated factors of latent tuberculosis infection due to Mycobacterium tuberculosis complex among high-risk groups in urban Bobo-Dioulasso, Burkina Faso

Objectives: To determine the prevalence and risk factors for latent tuberculosis infection (LTBI) among three high-risk groups - household contacts of TB index cases, healthcare workers and slaughterhouse workers - in Bobo-Dioulasso, Burkina Faso. Methods: Participants were recruited to this cross-sectional study from March to July 2020 after giving informed consent. Sociodemographic, clinical and biological data were collected using a structured questionnaire. The QuantiFERON-TB Gold Plus test (QFT-Plus) and the tuberculin skin test (TST) were used for detection of LTBI. Bivariate and multivariate logistic regression analyses were performed to identify risk factors for LTBI. Results: The prevalence of LTBI among 101 participants (age range 15-68 years) was 67.33% [95% confidence interval (CI) 57.27-76.33] and 84.16% (95% CI 75.55-90.66) based on QFT-Plus and TST results, respectively. Compared with healthcare workers and household contacts of TB index cases, the prevalence of LTBI among slaughterhouse workers was significantly higher for both QTF-Plus (96.8%; P /=15 years of exposure (AOR 5.617, 95% CI 1.202-32.198), having an animal at home (AOR 2.735, 95% CI 1.102-6.789) and protozoal infection (AOR 2.591, 95% CI 1.034-6.491) were significantly associated with LTBI on the QFT-Plus assay. Conclusion: The prevalence of LTBI was high in all three groups, particularly slaughterhouse workers. The risk factors identified could form the basis of targeted intervention

Do bednets including piperonyl butoxide offer additional protection against populations of Anopheles gambiae s.l. that are highly resistant to pyrethroids? An experimental hut evaluation in Burkina Fasov

Malaria control is dependent on the use of longlasting insecticidal nets (LLINs) containing pyrethroids. A new generation of LLINs containing both pyrethroids and the synergist piperonyl butoxide (PBO) has been developed in response to increasing pyrethroid resistance in African malaria vectors, but questions remain about the performance of these nets in areas where levels of pyrethroid resistance are very high. This study was conducted in two settings in southwest Burkina Faso, Vallée du Kou 5 and Tengrela, where Anopheles gambiae s.l. (Diptera: Culicidae) mortality rates in World Health Organization (WHO) discriminating dose assays were < 14% for permethrin and < 33% for deltamethrin. When mosquitoes were pre-exposed to PBO in WHO tube assays, mortality rates increased substantially but full susceptibility was not restored. Molecular characterization revealed high levels of kdr alleles and elevated levels of P450s previously implicated in pyrethroid resistance. In cone bioassays and experimental huts, PBO LLINs outperformed the pyrethroid-only equivalents from the same manufacturers. Blood feeding rates were 1.6-2.2-fold lower and mortality rates were 1.69-1.78-fold greater in huts with PBO LLINs vs. non-PBO LLINs. This study indicates that PBO LLINs provide greater personal and community-level protection than standard LLINs against highly pyrethroid-resistant mosquito populations