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Population genetics of two key mosquito vectors of Rift Valley Fever virus reveals new insights into the changing disease outbreak patterns in Kenya.

Tchouassi DP, Bastos AD, Sole CL, Diallo M, Lutomiah J, Mutisya J, Mulwa F, Borgemeister C, Sang R, Torto B - PLoS Negl Trop Dis (2014)

Bottom Line: Our data strongly suggest that unlike Ae. mcintoshi, Ae. ochraceus appears to be a relatively recent, single 'introduction' into Kenya.These results, together with increasing isolations from this vector, indicate that Ae. ochraceus will likely be of greater epidemiological importance in future RVF outbreaks in Kenya.Furthermore, the overall vector complexity calls into question the feasibility of mosquito population control approaches reliant on genetic modification.

View Article: PubMed Central - PubMed

Affiliation: International Centre of Insect Physiology and Ecology (ICIPE), Nairobi, Kenya; Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa.

ABSTRACT
Rift Valley fever (RVF) outbreaks in Kenya have increased in frequency and range to include northeastern Kenya where viruses are increasingly being isolated from known (Aedes mcintoshi) and newly-associated (Ae. ochraceus) vectors. The factors contributing to these changing outbreak patterns are unclear and the population genetic structure of key vectors and/or specific virus-vector associations, in particular, are under-studied. By conducting mitochondrial and nuclear DNA analyses on >220 Kenyan specimens of Ae. mcintoshi and Ae. ochraceus, we uncovered high levels of vector complexity which may partly explain the disease outbreak pattern. Results indicate that Ae. mcintoshi consists of a species complex with one of the member species being unique to the newly-established RVF outbreak-prone northeastern region of Kenya, whereas Ae. ochraceus is a homogeneous population that appears to be undergoing expansion. Characterization of specimens from a RVF-prone site in Senegal, where Ae. ochraceus is a primary vector, revealed direct genetic links between the two Ae. ochraceus populations from both countries. Our data strongly suggest that unlike Ae. mcintoshi, Ae. ochraceus appears to be a relatively recent, single 'introduction' into Kenya. These results, together with increasing isolations from this vector, indicate that Ae. ochraceus will likely be of greater epidemiological importance in future RVF outbreaks in Kenya. Furthermore, the overall vector complexity calls into question the feasibility of mosquito population control approaches reliant on genetic modification.

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Related in: MedlinePlus

Chronogram of divergence times for Ae. mcintoshi and Ae. ochraceus from Kenya and Senegal represented on a maximum likelihood tree obtained from the analysis of the mtDNA dataset.Node positions indicate mean estimated divergence times and numbers on nodes the BS values. Taxon abbreviations follow those provided in Table 2 with arbitrary numbers indicating specific sequence samples.
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pntd-0003364-g003: Chronogram of divergence times for Ae. mcintoshi and Ae. ochraceus from Kenya and Senegal represented on a maximum likelihood tree obtained from the analysis of the mtDNA dataset.Node positions indicate mean estimated divergence times and numbers on nodes the BS values. Taxon abbreviations follow those provided in Table 2 with arbitrary numbers indicating specific sequence samples.

Mentions: We compared the divergence times of both species for samples from Kenya and Senegal (using the COI dataset of Ae. ochraceus and 22 Ae. mcintoshi sequences representative of the four clades obtained in the phylogenetic analysis including Ae. aegypti from the GenBank as outgroup). We estimated that the split of Ae. ochraceus and Ae. mcintoshi sister taxa could have occurred about 4.5 million years ago (MYA) during the Pliocene (Fig. 3). Our dating puts the age of the Ae. mchintoshi complex at approximately 2.7 million years (late Pliocene), the age of clade IV at around 0.608 MYA and the time to coalescence of the Kenyan sister taxa (clades I and II) at around 1.327 MYA (Pleistocene). Our analysis estimates the time to coalescence for Ae. ochraceus at approximately 0.617 MYA, similar to dates estimated for clades IV and I of Ae. mcintoshi. Based on these results it appears that at around 600,000 years ago, there was a major radiation/diversification as the three best-represented lineages (viz. Ae. ochraceus, and Ae. mcintoshi clades I and IV) all were estimated to have arisen around the same time. The divergence pattern of Ae. ochraceus suggests the possibility of a single introduction from Senegal and then a rapid radiation in Kenya (Fig. 3).


Population genetics of two key mosquito vectors of Rift Valley Fever virus reveals new insights into the changing disease outbreak patterns in Kenya.

Tchouassi DP, Bastos AD, Sole CL, Diallo M, Lutomiah J, Mutisya J, Mulwa F, Borgemeister C, Sang R, Torto B - PLoS Negl Trop Dis (2014)

Chronogram of divergence times for Ae. mcintoshi and Ae. ochraceus from Kenya and Senegal represented on a maximum likelihood tree obtained from the analysis of the mtDNA dataset.Node positions indicate mean estimated divergence times and numbers on nodes the BS values. Taxon abbreviations follow those provided in Table 2 with arbitrary numbers indicating specific sequence samples.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4256213&req=5

pntd-0003364-g003: Chronogram of divergence times for Ae. mcintoshi and Ae. ochraceus from Kenya and Senegal represented on a maximum likelihood tree obtained from the analysis of the mtDNA dataset.Node positions indicate mean estimated divergence times and numbers on nodes the BS values. Taxon abbreviations follow those provided in Table 2 with arbitrary numbers indicating specific sequence samples.
Mentions: We compared the divergence times of both species for samples from Kenya and Senegal (using the COI dataset of Ae. ochraceus and 22 Ae. mcintoshi sequences representative of the four clades obtained in the phylogenetic analysis including Ae. aegypti from the GenBank as outgroup). We estimated that the split of Ae. ochraceus and Ae. mcintoshi sister taxa could have occurred about 4.5 million years ago (MYA) during the Pliocene (Fig. 3). Our dating puts the age of the Ae. mchintoshi complex at approximately 2.7 million years (late Pliocene), the age of clade IV at around 0.608 MYA and the time to coalescence of the Kenyan sister taxa (clades I and II) at around 1.327 MYA (Pleistocene). Our analysis estimates the time to coalescence for Ae. ochraceus at approximately 0.617 MYA, similar to dates estimated for clades IV and I of Ae. mcintoshi. Based on these results it appears that at around 600,000 years ago, there was a major radiation/diversification as the three best-represented lineages (viz. Ae. ochraceus, and Ae. mcintoshi clades I and IV) all were estimated to have arisen around the same time. The divergence pattern of Ae. ochraceus suggests the possibility of a single introduction from Senegal and then a rapid radiation in Kenya (Fig. 3).

Bottom Line: Our data strongly suggest that unlike Ae. mcintoshi, Ae. ochraceus appears to be a relatively recent, single 'introduction' into Kenya.These results, together with increasing isolations from this vector, indicate that Ae. ochraceus will likely be of greater epidemiological importance in future RVF outbreaks in Kenya.Furthermore, the overall vector complexity calls into question the feasibility of mosquito population control approaches reliant on genetic modification.

View Article: PubMed Central - PubMed

Affiliation: International Centre of Insect Physiology and Ecology (ICIPE), Nairobi, Kenya; Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa.

ABSTRACT
Rift Valley fever (RVF) outbreaks in Kenya have increased in frequency and range to include northeastern Kenya where viruses are increasingly being isolated from known (Aedes mcintoshi) and newly-associated (Ae. ochraceus) vectors. The factors contributing to these changing outbreak patterns are unclear and the population genetic structure of key vectors and/or specific virus-vector associations, in particular, are under-studied. By conducting mitochondrial and nuclear DNA analyses on >220 Kenyan specimens of Ae. mcintoshi and Ae. ochraceus, we uncovered high levels of vector complexity which may partly explain the disease outbreak pattern. Results indicate that Ae. mcintoshi consists of a species complex with one of the member species being unique to the newly-established RVF outbreak-prone northeastern region of Kenya, whereas Ae. ochraceus is a homogeneous population that appears to be undergoing expansion. Characterization of specimens from a RVF-prone site in Senegal, where Ae. ochraceus is a primary vector, revealed direct genetic links between the two Ae. ochraceus populations from both countries. Our data strongly suggest that unlike Ae. mcintoshi, Ae. ochraceus appears to be a relatively recent, single 'introduction' into Kenya. These results, together with increasing isolations from this vector, indicate that Ae. ochraceus will likely be of greater epidemiological importance in future RVF outbreaks in Kenya. Furthermore, the overall vector complexity calls into question the feasibility of mosquito population control approaches reliant on genetic modification.

Show MeSH
Related in: MedlinePlus