Ildefonso Fernández Salas

MECHANISMS OF INSECTICIDE RESISTANCE IN FIELD POPULATIONS OF AEDES AEGYPTI (L.) FROM QUINTANA ROO, SOUTHERN MEXICO

ABSTRACT Potential insecticide-resistance mechanisms were studied with the use of biochemical assays in Aedes aegypti (L.) collected from 5 municipalities representing the north part of Quintana Roo: Benito Juarez, Cozumel, Isla Mujeres, Lazaro Cardenas, and Solidaridad. The activities of &agr; and &bgr; esterases, mixed-function oxidases (MFO), glutathione-S-transferase (GST), acethylcholinesterase (AChE), and insensitive acethylcholinesterase (iAChE) were assayed in microplates. Three replicates were performed for each enzyme and 60 males and 60 females were analyzed in each population. The New Orleans (NO) susceptible strain of Ae. aegypti was used as a susceptible reference and the threshold criteria for each enzyme were the highest NO absorbance values. In none of the 6 tests were absorbance values correlated in males and females. &agr; esterases were elevated in Benito Juarez, Cozumel females and in Lazaro Cardenas males and females. &bgr; esterases were elevated in Benito Juarez, Cozumel females and in Cozumel and Lazaro Cardenas males. Elevated esterases suggest potential insecticide-resistance mechanisms against organophosphate, carbamate, and some pyrethroid insecticides. Slightly elevated levels of MFOs appeared in Lazaro Cardenas females and in Cozumel, Isla Mujeres, and Solidaridad males. Mechanisms involving iAChE or GST were not apparent.

Quantitative Trait Loci Mapping of Genome Regions Controlling Permethrin Resistance in the Mosquito Aedes aegypti

The mosquito Aedes aegypti is the principal vector of dengue and yellow fever flaviviruses. Permethrin is an insecticide used to suppress Ae. aegypti adult populations but metabolic and target site resistance to pyrethroids has evolved in many locations worldwide. Quantitative trait loci (QTL) controlling permethrin survival in Ae. aegypti were mapped in an F3 advanced intercross line. Parents came from a collection of mosquitoes from Isla Mujeres, México, that had been selected for permethrin resistance for two generations and a reference permethrin-susceptible strain originally from New Orleans. Following a 1-hr permethrin exposure, 439 F3 adult mosquitoes were phenotyped as knockdown resistant, knocked down/recovered, or dead. For QTL mapping, single nucleotide polymorphisms (SNPs) were identified at 22 loci with potential antixenobiotic activity including genes encoding cytochrome P450s (CYP), esterases (EST), or glutathione transferases (GST) and at 12 previously mapped loci. Seven antixenobiotic genes mapped to chromosome I, six to chromosome II, and nine to chromosome III. Two QTL of major effect were detected on chromosome III. One corresponds with a SNP previously associated with permethrin resistance in the para sodium channel gene and the second with the CCEunk7o esterase marker. Additional QTL but of relatively minor effect were also found. These included two sex-linked QTL on chromosome I affecting knockdown and recovery and a QTL affecting survival and recovery. On chromosome II, one QTL affecting survival and a second affecting recovery were detected. The patterns confirm that mutations in the para gene cause target-site insensitivity and are the major source of permethrin resistance but that other genes dispersed throughout the genome contribute to recovery and survival of mosquitoes following permethrin exposure.

Transcription of detoxification genes after permethrin selection in the mosquito Aedes aegypti.

Changes in gene expression before, during and after five generations of permethrin laboratory selection were monitored in six strains of Aedes aegypti: five F2–F3 collections from the Yucatán Peninsula of Mexico and one F2 from Iquitos, Peru. Three biological replicate lines were generated for each strain. The response to selection was measured as changes in the lethal and knockdown permethrin concentrations (LC50, KC50) and in the frequency of the Ile1,016 substitution in the voltage‐gated sodium channel (para) gene. Changes in expression of 290 metabolic detoxification genes were measured using the ‘Aedes Detox’ microarray. Selection simultaneously increased the LC50, KC50 and Ile1,016 frequency. There was an inverse relationship between Ile1,016 frequency and the numbers of differentially transcribed genes. The Iquitos strain lacked the Ile1,016 allele and 51 genes were differentially transcribed after selection as compared with 10–18 genes in the Mexican strains. Very few of the same genes were differentially transcribed among field strains but 10 cytochrome P450 genes were upregulated in more than one strain. Laboratory adaptation to permethrin in Ae. aegypti is genetically complex and largely conditioned by geographic origin and pre‐existing target site insensitivity in the para gene. The lack of uniformity in the genes that responded to artificial selection as well as differences in the direction of their responses challenges the assumption that one or a few genes control permethrin metabolic resistance. Attempts to identify one or a few metabolic genes that are predictably associated with permethrin adaptation may be futile.

Detection of antibodies to West Nile and Saint Louis encephalitis viruses in horses

Señor editor: la fiebre por dengue es la enfermedad viral transmitida por vector más importante a escala mundial,1 y cada vez es más urgente obtener información que nos permita establecer cuáles son las condiciones que preceden a la aparición de una epidemia, en especial aquellas en las que se presentan casos con manifestaciones severas de la enfermedad: fiebre hemorrágica por dengue y síndrome de choque por dengue (FHD y SCD, respectivamente); por tal razón, es importante la aportación de trabajos como el de Espinoza-Gómez F y colaboradores,2 en el cual describen la transmisión de la enfermedad en ausencia aparente de un brote epidémico, basados en la presencia de IgM en muestras de suero de personas asintomáticas. Sin embargo, habría que llevar a cabo trabajos que incluyan la mayor cantidad posible de información, ya que las epidemias son el producto de un conjunto de variables (mosquito vector, clima, estado nutricio, la capacidad virulenta de la cepa viral, movimientos poblacionales, etcétera) que coinciden en tiempo y espacio; de esta forma, el análisis en conjunto de todas estas variables nos permitiría identificar aquellos factores presentes en periodos interepidémicos que están involucrados en la subsiguiente aparición de epidemias. Por ejemplo, en el caso de factores climatológicos se han reportado brotes de dengue asociados con fenómenos como “El Niño”;3 asimismo, se ha observado que el incremento en el número de casos de dengue se asocia con el desplazamiento de la cepa viral predominante por una nueva en una región endémica específica.4,5 Estas cepas nuevas pueden tener características de virulencia distintas, adquiridas mediante diversos mecanismos evolutivos. Estos eventos, así como otros (movimientos poblacionales, por ejemplo) pueden estar sucediendo en periodos interepidémicos. Tomando en cuenta lo anterior, sería interesante poder determinar en el trabajo de Espinoza-Gómez F y colaboradores, qué virus (serotipo/genotipo) estuvo asociado con esta transmisión interepidémica y si es el mismo virus asociado con epidemias anteriores o posteriores; por otra parte, estos datos podrían ser comparados con lo que ocurre en otras regiones endémicas en nuestro país.

Resistance to Permethrin in Aedes aegypti (L.) in Northern Mexico

Abstract. Diagnostic dose (DD) of permethrin was determined in Aedes aegypti (L.), from three states (Coahuila, Sonora, and Tamaulipas) in northern Mexico. After exposing 10 groups of 100 females to the DD obtained and producing 50% mortality, individuals were divided into two categories: survivors and dead. Mosquitoes in each of these categories were dissected to separate the head, thorax, and abdomen. Biochemical tests were done on the head and thorax to determine activity by resistance-related enzymes including: &agr; and &bgr;-esterases, mixed-function oxidases (MFOs), glutathione-S-transferase (GST) and insensitive acetyl cholinesterase (iAChE). Results were compared with those for a susceptible strain of Ae. aegypti from New Orleans. A population from Coahuila showed iAChE as the only enzyme activity that surpassed the threshold established with the susceptible strain, however, this mechanism is not associated with resistance to pyrethroids, but rather with resistance to organophosphate and carbamate insecticides. For the populations from Tamaulipas, none of the mechanisms studied were important in conferring resistance to permethrin. MFOs were present at elevated levels of activity, appearing as the main detoxifying mechanism, in the population from Sonoita, Sonora state.

SEROPREVALENCE OF T. cruzi INFECTION IN BLOOD DONORS AND CHAGAS CARDIOMYOPATHY IN PATIENTS FROM THE COAL MINING REGION OF COAHUILA, MEXICO

Context and Objective: Chagas disease is considered a worldwide emerging disease; it is endemic in Mexico and the state of Coahuila and is considered of little relevance. The objective of this study was to determine the seroprevalence of T. cruzi infection in blood donors and Chagas cardiomyopathy in patients from the coal mining region of Coahuila, Mexico. Design and Setting: Epidemiological, exploratory and prospective study in a general hospital during the period January to June 2011. Methods: We performed laboratory tests ELISA and indirect hemagglutination in three groups of individuals: 1) asymptomatic voluntary blood donors, 2) patients hospitalized in the cardiology department and 3) patients with dilated cardiomyopathy. Results: There were three levels of seroprevalence: 0.31% in asymptomatic individuals, 1.25% in cardiac patients and in patients with dilated cardiomyopathy in 21.14%. Conclusions: In spite of having detected autochthonous cases of Chagas disease, its importance to local public health remains to be established as well as the details of the dynamics of transmission so that the study is still in progress.