Studies of Anopheles gambiae s.l (Diptera: Culicidae) exhibiting different vectorial capacities in lymphatic filariasis transmission in the Gomoa district, Ghana

<p>Abstract</p> <p>Background</p> <p>Two lymphatic filariasis endemic communities Mampong and Hwida in Ghana have been regularly monitored for impact on transmission after annual mass drug administration (MDA) with albendazole and ivermectin. After six MDAs even though the ABR for Mampong was 55883/person/year and that of Hwida was 2494/person/year, they both had ATPs of 15.21 infective larvae/person/year. Interestingly the human microfilaraemia levels had reduced significantly from 14% to 0% at Mampong and 12% to 3% at Hwida. In an attempt to understand this anomaly, we collected mosquitoes over a 5-month period using human landing catches to determine the species composition, the number of cibarial teeth, the lengths and widths of the cibarium and the cibarial dome of the vector populations.</p> <p>Results</p> <p>Out of 2553 mosquitoes caught at Mampong, 42.6% were <it>An. gambiae </it>s.l. All 280 identified further by PCR were <it>An. gambiae </it>s.s (275 M and 5 S molecular forms). At Hwida, 112 mosquitoes were obtained; 67 (59.8%) were <it>An. gambiae </it>s.l, comprised of 40 (59.7%) <it>An. melas</it>, 24 (35.8%) <it>An. gambiae </it>s.s (17 and 5 M and S molecular forms respectively) and 3 (4.5%) unidentified. The mean number of teeth for <it>An. melas </it>was 14.1 (median = 14, range = 12-15), <it>An. gambiae </it>s.s., 15.7 (median = 15, range = 13-19) M form 15.5 (median = 15 range = 13-19) and S form 16 (median = 16, range 15-17). The observed differences in teeth numbers were significantly different between <it>An. melas </it>and <it>An. gambiae </it>s.s (p = 0.004), and the M form (p = 0.032) and the S form (p = 0.002).</p> <p>Conclusions</p> <p>In this study, <it>An. gambiae </it>s.s was the main vector at Mampong and was found to possess significantly more cibarial teeth than <it>An. melas</it>, the principal vector at Hwida. We postulate that the different impact observed after 6 MDAs may be due to <it>An. gambiae </it>s.s exhibiting 'facilitation' at Mampong and at Hwida <it>An. melas </it>the main vector exhibits 'limitation'. Thus it may be necessary to compliment MDA with vector control to achieve interruption of transmission in areas where <it>An. melas </it>may exhibit limitation.</p

Wolbachia-Based Dengue Virus Inhibition Is Not Tissue-Specific in Aedes aegypti.

BACKGROUND:Dengue fever, caused by the dengue virus (DENV), is now the most common arbovirus transmitted disease globally. One novel approach to control DENV is to use the endosymbiotic bacterium, Wolbachia pipientis, to limit DENV replication inside the primary mosquito vector, Aedes aegypti. Wolbachia that is naturally present in a range of insects reduces the capacity for viruses, bacteria, parasites and fungi to replicate inside insects. Wolbachia's mode of action is not well understood but may involve components of immune activation or competition with pathogens for limited host resources. The strength of Wolbachia-based anti DENV effects appear to correlate with bacterial density in the whole insect and in cell culture. Here we aimed to determine whether particular tissues, especially those with high Wolbachia densities or immune activity, play a greater role in mediating the anti DENV effect. METHODOLOGY/FINDINGS:Ae. aegypti mosquito lines with and without Wolbachia (Wildtype) were orally fed DENV 3 and their viral loads subsequently measured over two time points post infection in the midgut, head, salivary glands, Malpighian tubules, fat body and carcass. We did not find correlations between Wolbachia densities and DENV loads in any tissue, nor with DENV loads in salivary glands, the endpoint of infection. This is in contrast with strong positive correlations between DENV loads in a range of tissues and salivary gland loads for Wildtype mosquitoes. Lastly, there was no evidence of a heightened role for tissues with known immune function including the fat body and the Malpighian tubules in Wolbachia's limitation of DENV. CONCLUSION/SIGNIFICANCE:We conclude that the efficacy of DENV blocking in Wolbachia infected mosquitoes is not reliant on any particular tissue. This work therefore suggests that the mechanism of Wolbachia-based antiviral effects is either systemic or acts locally via processes that are fundamental to diverse cell types. We further conclude that the relationship between DENV blocking and Wolbachia density is not linear in mosquito tissues

Effect of repeat human blood feeding on Wolbachia density and dengue virus infection in Aedes aegypti

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Interactions between Wolbachia and the Mosquito Vector of Dengue Virus Aedes aegypti

Dengue fever is a severely debilitating disease caused by the dengue virus (DENV) and transmitted by <i>Aedes aegypti</i> mosquitoes. There is no specific treatment for the disease and the current vaccine does not give complete protection against DENV. A novel control approach involves the use of the maternally transmitted endosymbiotic bacterium <i>Wolbachia</i> as a bio-control agent. <i>Wolbachia</i> is present in 40% of insects but not <i>Ae. aegypti</i>. However <i>Wolbachia </i>has been artificially introduced into <i>Ae. aegypti</i> where it forms stably inherited infections. <i>Wolbachia</i> is able to manipulate female reproduction leading to inviable eggs when an infected male mates with an uninfected female or females with a different strain of <i>Wolbachia</i>. This characteristic, known as cytoplasmic incompatibility enables <i>Wolbachia</i> infection to spread through wild populations. <i>Wolbachia</i> also has the ability to limit the replication of co-infecting pathogens in mosquitoes. <i>Wolbachia</i> infected mosquitoes are currently being released into the field to trial whether they will interrupt DENV transmission to humans. <br> <br> The mechanistic basis of <i>Wolbachia</i>-DENV blocking is not well understood. There is evidence that <i>Wolbachia</i> activates the host’s immune response thereby making it able to resist subsequent DENV infection in a process known as ‘immune priming’. Competition between <i>Wolbachia</i> and the virus for limited host resources has also been linked with <i>Wolbachia</i>-DENV blocking. Immune priming and resource competition, however, do not fully explain <i>Wolbachia</i>-DENV inhibition. The strength of blocking appears to correlate with <i>Wolbachia</i> density, with highly infected mosquitoes and cell lines exhibiting almost complete DENV inhibition. <br> <br> This thesis therefore focussed on understanding the effect <i>Wolbachia</i> density has on DENV blocking in various mosquito tissues by increasing nutritional resources through feeding <i>Ae. aegypti</i> mosquitoes multiple human blood meals. We found that multiple blood meals do not increase <i>Wolbachia</i> density or DENV blocking, indicating that the <i>Wolbachia</i>-mediated DENV inhibition should be stable throughout the lifespan of <i>Ae. aegypti</i>. This thesis also investigated whether particular mosquito tissues were important for DENV blocking by virtue of their <i>Wolbachia</i> density or functional roles in infection and immunity. We found that no particular tissue type was important for <i>Wolbachia</i>-DENV blocking, suggesting that the mechanisms underpinning blocking should be systemic or fundamental to diverse cell types. <br> <br> Mosquitoes are naturally infected with viruses, including flaviruses known as insect-specific flaviviruses (ISF). Although ISF are incapable of infecting vertebrates they may alter susceptibility of mosquitoes to medically important flaviviruses. The effect <i>Wolbachia</i> has on ISF is currently unknown. This thesis therefore examined whether the anti-virus effect demonstrated for flaviviruses including DENV is observed for ISF. Surprisingly, <i>Wolbachia</i> enhanced ISF infection rates and loads indicating that <i>Wolbachia</i>-mediated anti-virus effect is not universal to all flaviviruses. Further study is therefore required of <i>Wolbachia</i>-ISF interactions and the effect this has on arboviruses such as DENV. <br> <br> This thesis has clearly demonstrated that feeding mosquitoes repeatedly on human blood does not influence <i>Wolbachia</i>-DENV inhibition and that blocking is not dependent on a particular tissue type further adding to the emerging understanding of <i>Wolbachia</i>-DENV interactions. In addition it has demonstrated that the anti-virus effect of <i>Wolbachia</i> is not common to all flaviviruses

Effect of repeat human blood feeding on Wolbachia density and dengue virus infection in Aedes aegypti

BACKGROUND: The introduction of the endosymbiotic bacterium, Wolbachia into Aedes aegypti populations is a novel approach to reduce disease transmission. The presence of Wolbachia limits the ability of the mosquito to transmit dengue virus (DENV) and the strength of this effect appears to correlate with Wolbachia densities in the mosquito. There is also some evidence that Wolbachia densities may increase following the consumption of a bloodmeal. Here we have examined whether multiple blood feeds lead to increases in density or associated changes in Wolbachia-mediated blocking of DENV. METHODS: The Wolbachia infected Aedes aegypti mosquito line was used for the study. There were three treatment groups; a non-blood fed control, a second group fed once and a third group fed twice on human blood. All groups were orally infected with DENV-2 and then their midguts and salivary glands were dissected 10–11 days post infection. RNA/DNA was simultaneously extracted from each tissue and subsequently used for DENV RNA copies and Wolbachia density quantification, respectively. RESULTS: We found variation between replicate vector competence experiments and no clear evidence that Wolbachia numbers increased in either the salivary glands or remainder of the body with feeding and hence saw no corresponding improvements in DENV blocking. CONCLUSIONS: Aedes aegypti are “sip” feeders returning often to obtain bloodmeals and hence it is important to assess whether repeat blood feeding improved the efficacy of Wolbachia-based DENV blocking. Our work suggests in the laboratory context when Wolbachia densities are high that repeat feeding does not improve blocking and hence this ability should likely be stable with respect to feeding cycle in the field

Effect of repeat human blood feeding on Wolbachia density and dengue virus infection in Aedes aegypti

BACKGROUND: The introduction of the endosymbiotic bacterium, Wolbachia into Aedes aegypti populations is a novel approach to reduce disease transmission. The presence of Wolbachia limits the ability of the mosquito to transmit dengue virus (DENV) and the strength of this effect appears to correlate with Wolbachia densities in the mosquito. There is also some evidence that Wolbachia densities may increase following the consumption of a bloodmeal. Here we have examined whether multiple blood feeds lead to increases in density or associated changes in Wolbachia-mediated blocking of DENV. METHODS: The Wolbachia infected Aedes aegypti mosquito line was used for the study. There were three treatment groups; a non-blood fed control, a second group fed once and a third group fed twice on human blood. All groups were orally infected with DENV-2 and then their midguts and salivary glands were dissected 10–11 days post infection. RNA/DNA was simultaneously extracted from each tissue and subsequently used for DENV RNA copies and Wolbachia density quantification, respectively. RESULTS: We found variation between replicate vector competence experiments and no clear evidence that Wolbachia numbers increased in either the salivary glands or remainder of the body with feeding and hence saw no corresponding improvements in DENV blocking. CONCLUSIONS: Aedes aegypti are “sip” feeders returning often to obtain bloodmeals and hence it is important to assess whether repeat blood feeding improved the efficacy of Wolbachia-based DENV blocking. Our work suggests in the laboratory context when Wolbachia densities are high that repeat feeding does not improve blocking and hence this ability should likely be stable with respect to feeding cycle in the field

Daisy, printemps 69 : roman / Arnaud Guillon

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