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The distribution of potential West Nile virus vectors, Culex pipiens pipiens and Culex pipiens quinquefasciatus (Diptera: Culicidae), in Mexico City.

Diaz-Badillo A, Bolling BG, Perez-Ramirez G, Moore CG, Martinez-Munoz JP, Padilla-Viveros AA, Camacho-Nuez M, Diaz-Perez A, Beaty BJ, Munoz Mde L - Parasit Vectors (2011)

Bottom Line: Important WNV vectors species, Cx. p. pipiens, Cx. p. quinquefasciatus and Cx. tarsalis, are all present in Mexico City.The presence and abundance of these WNV competent vectors is a cause for concern.Understanding the distribution of these vectors can help improve viral surveillance activities and mosquito control efforts in Mexico City.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Genetics and Molecular Biology, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Madero, México DF, México.

ABSTRACT

Background: Culex spp. mosquitoes are considered to be the most important vectors of West Nile virus (WNV) detected in at least 34 species of mosquitoes in the United States. In North America, Culex pipiens pipiens, Culex pipiens quinquefasciatus, and Culex tarsalis are all competent vectors of WNV, which is considered to be enzootic in the United States and has also been detected in equines and birds in many states of Mexico and in humans in Nuevo Leon. There is potential for WNV to be introduced into Mexico City by various means including infected mosquitoes on airplanes, migrating birds, ground transportation and infected humans. Little is known of the geographic distribution of Culex pipiens complex mosquitoes and hybrids in Mexico City. Culex pipiens pipiens preferentially feed on avian hosts; Culex pipiens quinquefasciatus have historically been considered to prefer mammalian hosts; and hybrids of these two species could theoretically serve as bridge vectors to transmit WNV from avian hosts to humans and other mammalian hosts. In order to address the potential of WNV being introduced into Mexico City, we have determined the identity and spatial distribution of Culex pipiens complex mosquitoes and their hybrids.

Results: Mosquito larvae collected from 103 sites throughout Mexico City during 2004-2005 were identified as Culex, Culiseta or Ochlerotatus by morphological analysis. Within the genus Culex, specimens were further identified as Culex tarsalis or as belonging to the Culex pipiens complex. Members of the Culex pipiens complex were separated by measuring the ratio of the dorsal and ventral arms (DV/D ratio) of the male genitalia and also by using diagnostic primers designed for the Ace.2 gene. Culex pipiens quinquefasciatus was the most abundant form collected.

Conclusions: Important WNV vectors species, Cx. p. pipiens, Cx. p. quinquefasciatus and Cx. tarsalis, are all present in Mexico City. Hybrids of Cx. p. pipiens and Cx. p. quinquefasciatus were also collected and identified. The presence and abundance of these WNV competent vectors is a cause for concern. Understanding the distribution of these vectors can help improve viral surveillance activities and mosquito control efforts in Mexico City.

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PCR amplification of the Ace.2 gene. Larvae collected at various cemeteries in Mexico City were reared to mosquito adults and then identified by PCR amplification of the Ace.2 gene [30]. The Cx. p. pipiens specific band of 610 bp and Cx. p. quinquefasciatus specific band of 274 bp and the expected bands of 610 and 274 bp for hybrids (panel B) are displayed in the agarose gels. *Cx. tarsalis identified by morphological analysis did not produce a PCR amplicon. †Culex spp. mosquitoes that were not identified as pertaining to the Cx. pipiens complex or hybrids by morphological analysis or by the Ace.2 gene assay.
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Figure 4: PCR amplification of the Ace.2 gene. Larvae collected at various cemeteries in Mexico City were reared to mosquito adults and then identified by PCR amplification of the Ace.2 gene [30]. The Cx. p. pipiens specific band of 610 bp and Cx. p. quinquefasciatus specific band of 274 bp and the expected bands of 610 and 274 bp for hybrids (panel B) are displayed in the agarose gels. *Cx. tarsalis identified by morphological analysis did not produce a PCR amplicon. †Culex spp. mosquitoes that were not identified as pertaining to the Cx. pipiens complex or hybrids by morphological analysis or by the Ace.2 gene assay.

Mentions: In order to distinguish the two nominal taxa, the Ace.2 gene was amplified by polymerase chain reaction (PCR) to detect taxa-specific amplicons. The representative results of the Ace.2 PCR assay for mosquitoes collected from cemeteries in Mexico City are shown in Figure 4. The PCR products of 610 and 274 bp were observed for Cx. p. pipiens and Cx. p. quinquefasciatus respectively and both fragments were detected for hybrids (Figure 4-B). The mosquitoes morphologically identified as Cx. tarsalis did not yield any PCR product as expected (Figure 4-A, line 10). The DV/D results were generally concordant with the results from the molecular (Ace.2 gene amplification) results. Out of all mosquitoes analyzed there were only 9 mosquitoes identified as hybrids by DV/D analyses that were identified as Cx. p. quinquefasciatus by molecular analysis in (03-AO) Santa Rosa Axochiac (Table 1). In areas where there may be introgression (Figure 3, faint gray line), individuals with Cx. p. pipiens DV/D ratios were identified as hybrids by molecular analysis and a few with Cx. p. quinquefasciatus DV/D ratios were also identified as hybrids. Interestingly, the most "observable" band correlated best with the morphological analysis. Our molecular analysis revealed that the frequency of members of the Cx. pipiens complex in the collection sites was: Cx. p. quinquefasciatus = 95.5%, Cx. p. pipiens = 14% and hybrids = 10%.


The distribution of potential West Nile virus vectors, Culex pipiens pipiens and Culex pipiens quinquefasciatus (Diptera: Culicidae), in Mexico City.

Diaz-Badillo A, Bolling BG, Perez-Ramirez G, Moore CG, Martinez-Munoz JP, Padilla-Viveros AA, Camacho-Nuez M, Diaz-Perez A, Beaty BJ, Munoz Mde L - Parasit Vectors (2011)

PCR amplification of the Ace.2 gene. Larvae collected at various cemeteries in Mexico City were reared to mosquito adults and then identified by PCR amplification of the Ace.2 gene [30]. The Cx. p. pipiens specific band of 610 bp and Cx. p. quinquefasciatus specific band of 274 bp and the expected bands of 610 and 274 bp for hybrids (panel B) are displayed in the agarose gels. *Cx. tarsalis identified by morphological analysis did not produce a PCR amplicon. †Culex spp. mosquitoes that were not identified as pertaining to the Cx. pipiens complex or hybrids by morphological analysis or by the Ace.2 gene assay.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3117809&req=5

Figure 4: PCR amplification of the Ace.2 gene. Larvae collected at various cemeteries in Mexico City were reared to mosquito adults and then identified by PCR amplification of the Ace.2 gene [30]. The Cx. p. pipiens specific band of 610 bp and Cx. p. quinquefasciatus specific band of 274 bp and the expected bands of 610 and 274 bp for hybrids (panel B) are displayed in the agarose gels. *Cx. tarsalis identified by morphological analysis did not produce a PCR amplicon. †Culex spp. mosquitoes that were not identified as pertaining to the Cx. pipiens complex or hybrids by morphological analysis or by the Ace.2 gene assay.
Mentions: In order to distinguish the two nominal taxa, the Ace.2 gene was amplified by polymerase chain reaction (PCR) to detect taxa-specific amplicons. The representative results of the Ace.2 PCR assay for mosquitoes collected from cemeteries in Mexico City are shown in Figure 4. The PCR products of 610 and 274 bp were observed for Cx. p. pipiens and Cx. p. quinquefasciatus respectively and both fragments were detected for hybrids (Figure 4-B). The mosquitoes morphologically identified as Cx. tarsalis did not yield any PCR product as expected (Figure 4-A, line 10). The DV/D results were generally concordant with the results from the molecular (Ace.2 gene amplification) results. Out of all mosquitoes analyzed there were only 9 mosquitoes identified as hybrids by DV/D analyses that were identified as Cx. p. quinquefasciatus by molecular analysis in (03-AO) Santa Rosa Axochiac (Table 1). In areas where there may be introgression (Figure 3, faint gray line), individuals with Cx. p. pipiens DV/D ratios were identified as hybrids by molecular analysis and a few with Cx. p. quinquefasciatus DV/D ratios were also identified as hybrids. Interestingly, the most "observable" band correlated best with the morphological analysis. Our molecular analysis revealed that the frequency of members of the Cx. pipiens complex in the collection sites was: Cx. p. quinquefasciatus = 95.5%, Cx. p. pipiens = 14% and hybrids = 10%.

Bottom Line: Important WNV vectors species, Cx. p. pipiens, Cx. p. quinquefasciatus and Cx. tarsalis, are all present in Mexico City.The presence and abundance of these WNV competent vectors is a cause for concern.Understanding the distribution of these vectors can help improve viral surveillance activities and mosquito control efforts in Mexico City.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Genetics and Molecular Biology, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Madero, México DF, México.

ABSTRACT

Background: Culex spp. mosquitoes are considered to be the most important vectors of West Nile virus (WNV) detected in at least 34 species of mosquitoes in the United States. In North America, Culex pipiens pipiens, Culex pipiens quinquefasciatus, and Culex tarsalis are all competent vectors of WNV, which is considered to be enzootic in the United States and has also been detected in equines and birds in many states of Mexico and in humans in Nuevo Leon. There is potential for WNV to be introduced into Mexico City by various means including infected mosquitoes on airplanes, migrating birds, ground transportation and infected humans. Little is known of the geographic distribution of Culex pipiens complex mosquitoes and hybrids in Mexico City. Culex pipiens pipiens preferentially feed on avian hosts; Culex pipiens quinquefasciatus have historically been considered to prefer mammalian hosts; and hybrids of these two species could theoretically serve as bridge vectors to transmit WNV from avian hosts to humans and other mammalian hosts. In order to address the potential of WNV being introduced into Mexico City, we have determined the identity and spatial distribution of Culex pipiens complex mosquitoes and their hybrids.

Results: Mosquito larvae collected from 103 sites throughout Mexico City during 2004-2005 were identified as Culex, Culiseta or Ochlerotatus by morphological analysis. Within the genus Culex, specimens were further identified as Culex tarsalis or as belonging to the Culex pipiens complex. Members of the Culex pipiens complex were separated by measuring the ratio of the dorsal and ventral arms (DV/D ratio) of the male genitalia and also by using diagnostic primers designed for the Ace.2 gene. Culex pipiens quinquefasciatus was the most abundant form collected.

Conclusions: Important WNV vectors species, Cx. p. pipiens, Cx. p. quinquefasciatus and Cx. tarsalis, are all present in Mexico City. Hybrids of Cx. p. pipiens and Cx. p. quinquefasciatus were also collected and identified. The presence and abundance of these WNV competent vectors is a cause for concern. Understanding the distribution of these vectors can help improve viral surveillance activities and mosquito control efforts in Mexico City.

Show MeSH
Related in: MedlinePlus