27 research outputs found
Hydric stress-dependent effects of Plasmodium falciparum infection on the survival of wild-caught Anopheles gambiae female mosquitoes
Get PDF<p>Abstract</p> <p>Background</p> <p>Whether <it>Plasmodium falciparum</it>, the agent of human malaria responsible for over a million deaths per year, causes fitness costs in its mosquito vectors is a burning question that has not yet been adequately resolved. Understanding the evolutionary forces responsible for the maintenance of susceptibility and refractory alleles in natural mosquito populations is critical for understanding malaria transmission dynamics.</p> <p>Methods</p> <p>In natural mosquito populations, <it>Plasmodium </it>fitness costs may only be expressed in combination with other environmental stress factors hence this hypothesis was tested experimentally. Wild-caught blood-fed <it>Anopheles gambiae </it>s.s. females of the M and S molecular form from an area endemic for malaria in Mali, West Africa, were brought to the laboratory and submitted to a 7-day period of mild hydric stress or kept with water ad-libitum. At the end of this experiment all females were submitted to intense desiccation until death. The survival of all females throughout both stress episodes, as well as their body size and infection status was recorded. The importance of stress, body size and molecular form on infection prevalence and female survival was investigated using Logistic Regression and Proportional-Hazard analysis.</p> <p>Results</p> <p>Females subjected to mild stress exhibited patterns of survival and prevalence of infection compatible with increased parasite-induced mortality compared to non-stressed females. Fitness costs seemed to be linked to ookinetes and early oocyst development but not the presence of sporozoites. In addition, when females were subjected to intense desiccation stress, those carrying oocysts exhibited drastically reduced survival but those carrying sporozoites were unaffected. No significant differences in prevalence of infection and infection-induced mortality were found between the M and S molecular forms of <it>Anopheles gambiae</it>.</p> <p>Conclusions</p> <p>Because these results suggest that infected mosquitoes may incur fitness costs under natural-like conditions, they are particularly relevant to vector control strategies aiming at boosting naturally occurring refractoriness or spreading natural or foreign genes for refractoriness using genetic drive systems in vector populations.</p
Hydric stress-dependent effects of Plasmodium falciparum infection on the survival of wild-caught Anopheles gambiae female mosquitoes
Get PDF<p>Abstract</p> <p>Background</p> <p>Whether <it>Plasmodium falciparum</it>, the agent of human malaria responsible for over a million deaths per year, causes fitness costs in its mosquito vectors is a burning question that has not yet been adequately resolved. Understanding the evolutionary forces responsible for the maintenance of susceptibility and refractory alleles in natural mosquito populations is critical for understanding malaria transmission dynamics.</p> <p>Methods</p> <p>In natural mosquito populations, <it>Plasmodium </it>fitness costs may only be expressed in combination with other environmental stress factors hence this hypothesis was tested experimentally. Wild-caught blood-fed <it>Anopheles gambiae </it>s.s. females of the M and S molecular form from an area endemic for malaria in Mali, West Africa, were brought to the laboratory and submitted to a 7-day period of mild hydric stress or kept with water ad-libitum. At the end of this experiment all females were submitted to intense desiccation until death. The survival of all females throughout both stress episodes, as well as their body size and infection status was recorded. The importance of stress, body size and molecular form on infection prevalence and female survival was investigated using Logistic Regression and Proportional-Hazard analysis.</p> <p>Results</p> <p>Females subjected to mild stress exhibited patterns of survival and prevalence of infection compatible with increased parasite-induced mortality compared to non-stressed females. Fitness costs seemed to be linked to ookinetes and early oocyst development but not the presence of sporozoites. In addition, when females were subjected to intense desiccation stress, those carrying oocysts exhibited drastically reduced survival but those carrying sporozoites were unaffected. No significant differences in prevalence of infection and infection-induced mortality were found between the M and S molecular forms of <it>Anopheles gambiae</it>.</p> <p>Conclusions</p> <p>Because these results suggest that infected mosquitoes may incur fitness costs under natural-like conditions, they are particularly relevant to vector control strategies aiming at boosting naturally occurring refractoriness or spreading natural or foreign genes for refractoriness using genetic drive systems in vector populations.</p
Tick communities of cattle in smallholder rural livestock production systems in sub-Saharan Africa
Get PDFAVAILABILITY OF DATA AND MATERIALS : The datasets generated and/or analysed during the current study are not publicly available due to Contract Research Organization agreements (data will be stored in the archives of Clinglobal, Mauritius), but are available from the corresponding author on reasonable request.CHANGE HISTORY : 12 November 2023. This article has been corrected since original publication.
16 November 2023. A Correction to this paper has been published: https://doi.org/10.1186/s13071-023-06034-2
09 August 2023. A Correction to this paper has been published: https://doi.org/10.1186/s13071-023-05895-xADDITIONAL FILE 1: TABLE S1.
Spatio-temporal variation in tick prevalence in cattle of seven sub-Saharan countries. TABLE S2. Spatio-temporal variation in tick loads in cattle of seven sub-Saharan countries. TABLE S3. and TABLE S4. Distribution of (co-) infestations in cattle individuals.ADDITIONAL FILE 2 : Protocol.BACKGROUND : The majority of the African population lives in rural areas and depends on agriculture for their livelihoods. To increase the productivity and sustainability of their farms, they need access to affordable yield-enhancing inputs of which parasite control is of paramount importance. We therefore determined the status of current tick species with the highest economic impact on cattle by sampling representative numbers of animals in each of seven sub-Saharan countries.
METHODS : Data included tick species’ half-body counts from approximately 120 cattle at each of two districts per country, collected four times in approximately 1 year (to include seasonality). Study sites were chosen in each country to include high cattle density and tick burden.
RESULTS : East Africa (Ethiopia, Uganda and Tanzania) showed overall a higher diversity and prevalence in tick infestations compared to West African countries (Benin, Burkina Faso, Ghana and Nigeria). In East Africa, Amblyomma variegatum (vector of Ehrlichia ruminantium), Rhipicephalus microplus (Babesia bovis, B. bigemina, Anaplasma marginale), R. evertsi evertsi (A. marginale) and R. appendiculatus (Theileria parva) were the most prevalent tick species of economic importance. While the latter species was absent in West Africa, here both A. variegatum and R. microplus occurred in high numbers. Rhipicephalus microplus had spread to Uganda, infesting half of the cattle sampled. Rhipicephalus microplus is known for its invasive behaviour and displacement of other blue tick species, as observed in other East and West African countries. Individual cattle with higher body weights, as well as males, were more likely to be infested. For six tick species, we found reduced infestation levels when hosts were treated with anti-parasiticides.
CONCLUSIONS : These baseline data allow the determination of possible changes in presence and prevalence of ticks in each of the countries targeted, which is of importance in the light of human-caused climate and habitat alterations or anthropogenic activities. As many of the ticks in this study are vectors of important pathogens, but also, as cattle may act as end hosts for ticks of importance to human health, our study will help a wide range of stakeholders to provide recommendations for tick infestation surveillance and prevention.The Bill & Melinda Gates Foundation (BMGF).https://parasitesandvectors.biomedcentral.comhj2024Veterinary Tropical DiseasesSDG-02:Zero Hunge
Tick-borne pathogens and body condition of cattle in smallholder rural livestock production systems in East and West Africa
Get PDFAVAILABILITY OF DATA AND MATERIALS : The datasets generated and/or analysed during the current study are not publicly available due to Contract Research Organization agreements (data will be stored in the archives of Clinglobal, Mauritius), but are available from the corresponding author on reasonable request.ADDITIONAL FILE 1: TABLE S0.
Synthetic positive controls. TABLE S1. Vector-competent ticks for the four tick-borne pathogens covered in the ecological analysis. Table S2. Distribution of (co-)infections in cattle individuals. FIG. S1. Heatmap of TBHPs species-to-species associations (co-infections) based on the HMSC models.ADDITIONAL FILE 2 : Protocol.BACKGROUND : The majority of the African population lives in rural areas where they heavily depend on crop and livestock production for their livelihoods. Given their socio-economic importance, we initiated a standardized multi-country (Benin, Burkina Faso, Ghana, Nigeria, Ethiopia Tanzania and Uganda) surveillance study to assess the current status of important tick-borne haemoparasites (TBHPs) of cattle.
METHODS : We assessed pathogen prevalences (Anaplasma marginale, Anaplasma centrale, Babesia bigemina, Babesia bovis, Ehrlichia ruminantium, and Theileria parva) in the blood of 6447 animals spread over fourteen districts (two districts per country). In addition, we screened for intrinsic (sex, weight, body condition) and extrinsic (husbandry, tick exposure) risk factors as predictors of infections with TBHPs.
RESULTS : There was a large macro-geographic variation observed in A. marginale, B. bigemina, B. bovis and E. ruminantium prevalences. Most correlated with the co-occurrence of their specific sets of vector-competent ticks. Highest numbers of infected cattle were found in Ghana and Benin, and lowest in Burkina Faso. While T. parva was seldomly found (Uganda only: 3.0%), A. marginale was found in each country with a prevalence of at least 40%. Babesia bovis infected individuals had lower body condition scores. Age (as estimated via body weight) was higher in A. marginale infected cattle, but was negatively correlated with B. bigemina and E. ruminantium prevalences. Ehrlichia ruminantium infection was more often found in males, and A. marginale more often in transhumance farming. High levels of co-infection, especially the combination A. marginale × B. bigemina, were observed in all countries, except for Uganda and Burkina Faso. Babesia bigemina was more or less often observed than expected by chance, when cattle were also co-infected with E. ruminantium or A. marginale, respectively.
CONCLUSIONS : Tick-borne pathogens of cattle are ubiquitous in African’s smallholder cattle production systems. Our standardized study will help a wide range of stakeholders to provide recommendations for TBHP surveillance and prevention in cattle, especially for B. bovis which heavily impacts production and continues its spread over the African continent via the invasive Rhipicephalus microplus tick.The Bill & Melinda Gates Foundation.https://parasitesandvectors.biomedcentral.comhj2024Veterinary Tropical DiseasesSDG-02:Zero Hunge
Acaricide resistance status of livestock ticks from East and West Africa and in vivo efficacy of acaricides to control them
Get PDFThrough a collaborative effort across six Sub-Saharan African countries, using recognized international assessment techniques, 23 stocks of three tick species (Rhipicephalus microplus, Rhipicephalus appendiculatus and Amblyomma variegatum) of economic importance for rural small holder farming communities from East and West Africa were collected from cattle, and evaluated in in vitro larval packet tests (LPT). The results demonstrated medium to high resistance to chlorfenvinphos and amitraz across species. Rhipicephalus microplus demonstrated high level alpha-cypermethrin and cypermethrin resistance. Stocks of A. variegatum (West Africa) and R. appendiculatus (Uganda) demonstrated medium level ivermectin resistance.
The four least susceptible stocks (East and West African R. microplus, A. variegatum and R. appendiculatus) were taken into in vivo controlled cattle studies where fipronil was found effective against West and East African R. microplus isolates although persistent efficacy failed to reach 90%. Cymiazole and cypermethrin, and ivermectin based acaricides were partially effective against R. microplus without persistent efficacy. Flumethrin spray-on killed A. variegatum within 72 h for up to 10 days posttreatment, however product application was directly to tick attachment sites, which may be impractical under field conditions. A flumethrin pour-on formulation on goats provided persistent efficacy against A. variegatum for up to one-month. Therapeutic control was achieved against R. appendiculatus through weekly spraying cattle with flumethrin, amitraz or combined cymiazole and cypermethrin. A fipronil pour-on product offered four-week residual control against R. appendiculatus (with slow onset of action).
Few studies have assessed and directly compared acaricidal activity in vitro and in vivo. There was some discordance between efficacy indicated by LPT and in vivo results. This observation calls for more research into accurate and affordable assessment methods for acaricide resistance.
No single active or product was effective against all three tick species, emphasising the need for the development of alternative integrated tick management solutions.The BMGF and a Bill & Melinda Gates Foundation (BMGF) supported project.https://www.elsevier.com/locate/ijpddrhj2024Veterinary Tropical DiseasesSDG-02:Zero HungerSDG-03:Good heatlh and well-bein
Mango anthracnose disease: the current situation and direction for future research
Get PDFMango anthracnose disease (MAD) is a destructive disease of mangoes, with estimated yield losses of up to 100% in unmanaged plantations. Several strains that constitute Colletotrichum complexes are implicated in MAD worldwide. All mangoes grown for commercial purposes are susceptible, and a resistant cultivar for all strains is not presently available on the market. The infection can widely spread before being detected since the disease is invincible until after a protracted latent period. The detection of multiple strains of the pathogen in Mexico, Brazil, and China has prompted a significant increase in research on the disease. Synthetic pesticide application is the primary management technique used to manage the disease. However, newly observed declines in anthracnose susceptibility to many fungicides highlight the need for more environmentally friendly approaches. Recent progress in understanding the host range, molecular and phenotypic characterization, and susceptibility of the disease in several mango cultivars is discussed in this review. It provides updates on the mode of transmission, infection biology and contemporary management strategies. We suggest an integrated and ecologically sound approach to managing MAD
Effects of larval growth condition and water availability on desiccation resistance and its physiological basis in adult Anopheles gambiae sensu stricto
Get PDF<p>Abstract</p> <p>Background</p> <p>Natural populations of the malaria mosquito <it>Anopheles gambiae </it>s.s. are exposed to large seasonal and daily fluctuations in relative humidity and temperature, which makes coping with drought a crucial aspect of their ecology.</p> <p>Methods</p> <p>To better understand natural variation in desiccation resistance in this species, the effects of variation in larval food availability and access to water as an adult on subsequent phenotypic quality and desiccation resistance of adult females of the Mopti chromosomal form were tested experimentally.</p> <p>Results</p> <p>It was found that, under normal conditions, larval food availability and adult access to water had only small direct effects on female wet mass, dry mass, and water, glycogen and body lipid contents corrected for body size. In contrast, when females subsequently faced a strong desiccation challenge, larval food availability and adult access to water had strong carry-over effects on most measured physiological and metabolic parameters, and affected female survival. Glycogen and water content were the most used physiological reserves in relative terms, but their usage significantly depended on female phenotypic quality. Adult access to water significantly influenced the use of water and body lipid reserves, which subsequently affected desiccation resistance.</p> <p>Conclusions</p> <p>These results demonstrate the importance of growth conditions and water availability on adult physiological status and subsequent resistance to desiccation.</p
Environmental stress and the fitness costs of plasmodium falciparum infection in the malaria mosquito anophele gambiae s.s
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Synthesis and Morphology of Flexible Polyurethane Foams Containing Neem Oil and Clove Powder
No full textPolyurethane foams are a versatile class of polymeric materials whose physico-chemical structure and properties can be modified by incorporating additives. This study examined the effect of naturally occurring insect-repelling additives such as neem oil (NO) and clove powder (CP) on the formulation and morphology of flexible polyurethane foam (FPUF) composites. The foams were prepared by the prepolymer method using a box test as applied in the foam industry. The composite material was formulated by varying the isocyanate index (103 and 108) as an excess amount of isocyanate was required to react with the additives. The formulation at 103 was unsuccessful as the foams collapsed immediately after rising. However, at 108, two main categories of foams were successfully prepared: foams containing either NO or CP and the other containing both additives. The effect of these additives on the formulation was examined by monitoring the foam reaction using the cream, tack-free, and rising times. It was observed that the cream, tack-free, and rising times increased with increasing NO/CP content. Conversely, the morphology was studied using scanning electron microscopy (SEM) and optical microscope (OP). The SEM images revealed disruption of the foam network with 1 wt% NO, likewise those containing 1 wt% CP. The cellular network of the foams with simultaneous addition of NO and CP was similar to that of the neat foams and had no broken cell joints and struts due to better dispersion of the additives in the polyurethane matrix. The study indicates that the combined addition of NO and CP modifies the morphology of FPUF, which can influence their physico-mechanical properties
The implication of climate variability on household water management; perception and practices among rural womenfolk in four communities in Ghana
No full textIn most rural communities, women are the sole managers of water supply and sanitation and determine household water management choices and practices. This study investigated the perceptions and household water management practices among womenfolk within rural communities located in the Central Tongu district and the Ada East districts of Ghana. Data collection instruments included household surveys, direct observation and focus group discussions of women within the study communities. The data were analysed using statistical tools embedded in the Statistical Package for the Social Sciences software. Results indicate that socio-demographic factors such as age, education, occupation and cost of water sources shaped household water management decisions. Furthermore, respondents’ perception of climate variability and climate adaptation was low and this, in turn, influenced household water management practices. The paper recommends that capacity building workshops be organized for rural women within the study communities to equip them with the skills to increase their income and in due course, improve their water management choices. Additionally, we suggest the promotion of climate variability and adaptation sensitization workshops of suitable household water management adaptation measures by government and Non-Government Organizations (NGOs) among rural communities
