Efficiency of two larval diets for mass-rearing of the mosquito Aedes aegypti.

Aedes aegypti is a major vector of arboviruses that may be controlled on an area-wide basis using the sterile insect technique (SIT). Larval diet is a major factor in mass-rearing for SIT programs. We compared dietary effects on immature development and adult fitness-related characteristics for an International Atomic Energy Agency (IAEA) diet, developed for rearing Ae. albopictus, and a standardized laboratory rodent diet (LRD), under a 14:10 h (light:dark) photoperiod ("light" treatment) or continuous darkness during larval rearing. Larval development was generally fastest in the IAEA diet, likely reflecting the high protein and lipid content of this diet. The proportion of larvae that survived to pupation or to adult emergence did not differ significantly between diets or light treatments. Insects from the LRD-dark treatment produced the highest proportion of male pupae (93% at 24 h after the beginning of pupation) whereas adult sex ratio from the IAEA diet tended to be more male-biased than that of the LRD diet. Adult longevity did not differ significantly with larval diet or light conditions, irrespective of sex. In other aspects the LRD diet generally performed best. Adult males from the LRD diet were significantly larger than those from the IAEA diet, irrespective of light treatment. Females from the LRD diet had ~25% higher fecundity and ~8% higher egg fertility compared to those from the IAEA diet. Adult flight ability did not differ between larval diets, and males had a similar number of copulations with wild females, irrespective of larval diet. The LRD diet had lower protein and fat content but a higher carbohydrate and energetic content than the IAEA diet. We conclude that the LRD diet is a low-cost standardized diet that is likely to be suitable for mass-rearing of Ae. aegypti for area-wide SIT-based vector control.

Inflammatory biomarkers, disease activity index, and self-reported disability may be predictors of chronic arthritis after chikungunya infection: brief report.

The chikungunya virus (ChikV) is a reemerging mosquito-borne pathogen that causes disabling chronic arthritis. The relationship between clinical evolution and inflammatory biomarkers in patients with ChikV-induced arthritis has not been fully described. We performed a prospective case series to evaluate the association among joint involvement, self-reported disability, and inflammatory biomarkers. Patients with ChikV infection were followed for 1 year. Joint involvement and self-reported disability were evaluated with disease activity index 28 (DAS-28) and World Health Organization Disablement Assessment Schedule II (WHODAS-II). Interleukin-6 (IL-6), C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and rheumatoid factor (RF) were used as biomarkers. Ten patients with mean age 48 ±15.04 years were included. Symptoms at diagnosis were fever, arthralgias, myalgias, rash, arthritis, nausea, vomiting, and back pain. Polyarticular involvement was present in seven cases. At diagnosis, measures were as follows: DAS-28, 5.08±1.11; WHODAS-II score, 72.3±10.3 %; CRP, 5.09±7.23 mg/dL; ESR, 33.5±17.5 mm/h; RF, 64±21.7 IU/mL; and IL-6, 17.6±10.3 pg/mL. Six patients developed subacute and chronic symptoms. During follow-up, DAS-28 index, WHODAS-II score, ESR, and IL-6 were statistically different in patients with subacute and chronic symptoms compared to those who resolved in the acute phase (p < 0.05). DAS-28 index, WHODAS-II score, and IL-6 were related to chronicity of articular symptoms and could be used as predictors of ChikV-induced arthritis.

Characterization of the dengue outbreak in Nuevo Leon state, Mexico, 2010.

We studied serotypes circulating dengue virus (DENV) cases, entomological Breteau index, rain-fall index and epidemiology of groups affected during the 2010 outbreak in Nuevo Leon, Mexico. From 2,271 positive cases, 94% were dengue classic and 6% dengue hemorrhagic fever; DENV1 was mainly isolated (99%) (Central-American lineage of American-African-genotype). We found correlation between two environmental phenomena (Increment of rainfall and vector-indexes) (p ≤ 0.05) with epidemiological, clinical and risk of DENV-1 ongoing transmission.

Detection of West Nile virus-specific antibodies and nucleic acid in horses and mosquitoes, respectively, in Nuevo Leon State, northern Mexico, 2006-2007.

In the last 5 years, there has been only one reported human case of West Nile virus (WNV) disease in northern Mexico. To determine if the virus was still circulating in this region, equine and entomological surveillance for WNV was conducted in the state of Nuevo Leon in northern Mexico in 2006 and 2007. A total of 203 horses were serologically assayed for antibodies to WNV using an epitope-blocking enzyme-linked immunosorbent assay (bELISA). Seroprevalences for WNV in horses sampled in 2006 and 2007 were 26% and 45%, respectively. Mosquito collections in 2007 produced 7365 specimens representing 15 species. Culex mosquitoes were screened for WNV RNA and other genera (Mansonia, Anopheles, Aedes, Psorophora and Uranotaenia) were screened for flaviviruses using reverse-transcription (RT)-PCR. Two pools consisting of Culex spp. mosquitoes contained WNV RNA. Molecular species identification revealed that neither pool included Culex quinquefasciatus (Say) (Diptera:Culicidae) complex mosquitoes. No evidence of flaviviruses was found in the other mosquito genera examined. These data provide evidence that WNV is currently circulating in northern Mexico and that non-Cx. quinquefasciatus spp. mosquitoes may be participating in the WNV transmission cycle in this region.

A mutation in the voltage-gated sodium channel gene associated with pyrethroid resistance in Latin American Aedes aegypti.

Pyrethroids are commonly used as mosquito adulticides and evolution of resistance to these compounds is a major threat to public health. 'Knockdown resistance' to pyrethroids (kdr) is frequently caused by nonsynonymous mutations in the voltage-gated sodium channel transmembrane protein (para) that reduce pyrethroid binding. Early detection of kdr is critical to the development of resistance management strategies in mosquitoes including Aedes aegypti, the most prevalent vector of dengue and yellow fever viruses. Brengues et al. described seven novel mutations in hydrophobic segment 6 of domain II of para in Ae. aegypti. Assays on larvae from strains bearing these mutations indicated reduced nerve sensitivity to permethrin inhibition. Two of these occurred in codons Iso1011 and Val1016 in exons 20 and 21 respectively. A transition in the third position of Iso1011 encoded a Met1011 replacement and a transversion in the second position of Val1016 encoded a Gly1016 replacement. We have screened this same region in 1318 mosquitoes in 32 additional strains; 30 from throughout Latin America. While the Gly1016 allele was never detected in Latin America, we found two new mutations in these same codons. A transition in the first position of codon 1011 encodes a Val replacement while a transition in the first position of codon 1016 encodes an Iso replacement. We developed PCR assays for these four mutations that can be read either on an agarose gel or as a melting curve. Selection experiments, one with deltamethrin on a field strain from Santiago de Cuba and another with permethrin on a strain from Isla Mujeres, Mexico rapidly increased the frequency of the Iso1016 allele. Bioassays of F(3) offspring arising from permethrin susceptible Val1016 homozygous parents and permethrin resistant Iso1016 homozygous parents show that Iso1016 segregates as a recessive allele in conferring kdr. Analysis of segregation between alleles at the 1011 and 1016 codons in the F(3) showed a high rate of recombination even though the two codons are only separated by a ~250 bp intron. The tools and information presented provide a means for early detection and characterization of kdr that is critical to the development of strategies for resistance management.

Sublethal iridovirus disease of the mosquito Aedes aegypti is due to viral replication not cytotoxicity.

Invertebrate iridescent viruses (Iridoviridae) possess a highly cytotoxic protein. In mosquitoes (Diptera: Culicidae), invertebrate iridescent virus 6 (IIV-6) usually causes covert (inapparent) infection that reduces fitness. To determine whether sublethal effects of IIV-6 are principally due to cytotoxicity of the viral inoculum (which inhibits macromolecular synthesis in the host), or caused by replication of the virus larvae of the mosquito Aedes aegypti (L) were exposed to untreated IIV-6 virus that had previously been deactivated by heat or ultraviolet light. Control larvae were not exposed to virus. Larval development time was shortest in control larvae and extended in larvae exposed to untreated virus. Covertly infected mosquitoes laid significantly fewer eggs, produced between 20 and 35% fewer progeny and had reduced longevity compared to other treatments. Wing length was shortest in mosquitoes exposed to heat-deactivated virus. Multivariate analysis of the same data identified fecundity and progeny production as the most influential variables in defining differences among treatments. Overall, viral infection resulted in a 34% decrease in the net reproductive rate (R0) of covertly infected mosquitoes, vs. only 5-17% decrease of R0 following treatments with deactivated virus, compared to controls. Sublethal effects of IIV-6 in Ae. aegypti appear to be mainly due to virus replication, rather than cytotoxic effects of the viral inoculum.

The use of sticky ovitraps to estimate dispersal of Aedes aegypti in northeastern Mexico.

A newly designed sticky ovitrap was used to determine the dispersal flight of the dengue vector Aedes aegypti in northeastern Mexico. Unfed marked females were released in the field where 100 sticky ovitraps had been positioned within a circular area 300 m in diameter. Success of this method was represented by a 7.7% (31 of 401) recapture rate during a 19-day sampling period. The maximum dispersal distance was 120 m with a mean of 30.5 m +/- 4.5 SD. Drastic hot and dry climatic conditions at the study site may have restricted mosquito dispersal. As expected, mostly gravid female mosquitoes were captured in the ovitraps. The method of sticky ovitraps proved to be useful and inexpensive for Ae. aegypti dispersal studies in Latin American countries. In addition to the marked mosquito populations, unmarked Ae. aegypti, Culex sp., roaches, and even small vertebrates such as lizards and sparrows were found glued to the sticky ovitraps. Based on these studies, the use of sticky ovitraps is recommended for Ae. aegypti dispersal studies, specially for dengue control programs in developing countries.

Genetic isolation by distance among Aedes aegypti populations along the northeastern coast of Mexico.

A population genetic analysis of gene flow was conducted among 10 Aedes aegypti collections from seven cities along the northeastern coast of Mexico. Four collections were made from Monterrey to examine local patterns of gene flow. Markers included 60 random amplified polymorphic DNA (RAPD) loci amplified by the polymerase chain reaction and single strand conformation polymorphism analysis of variation in a 387-basepair region of the NADH dehydrogenase subunit 4 from the mitochondrial DNA (mtDNA). Seven mitochondrial haplotypes were detected and phylogenetic analysis identified two well-supported clades. Regression analysis of geographic distances and pairwise FST estimated from RAPD markers indicated that populations are isolated by distance and that free gene flow occurs among collections within 90-250 km. Isolation by distance was not detected using mtDNA haplotypes. The Nuevo Laredo collection had unique RAPD and mtDNA haplotype frequencies and reduced heterozygosity suggesting that few mosquitoes established this population.

Field evaluation of Mesocyclops longisetus (Copepoda: Cyclopoidea) for the control of larval Aedes aegypti (Diptera Culicidae) in northeastern Mexico.

Field trials of the predacious copepod Mesocyclops longisetus Thiubaud were conducted in northeastern Mexico to determine the effectiveness of this species to control larval Aedes aegypti (L.) populations and to survive and reproduce in nature. Groups of 200, 50, and 50 ovigerous M. longisetus females were inoculated into 200-liter metal drums, discarded tires, and cemetery flower vases, respectively, which are 3 of the more important Aedes breeding sites in this area. Larvae were sampled at 15-d intervals, and total surviving cyclops were collected at the end of the study, 120 d later. Community participation was solicited through a simple training program on copepod rescue before drum cleaning and facilitated by the addition of a drum marker to remind residents of copepod presence. Results showed good cooperation and after 4 mo all peridomestic drums, still supported variable numbers of cyclopoids. Average of larvae reduction was 37.5% for drums, 67.5% for flower vases, and 40.9% for tires. This study shows difficulties of using cyclopoids for tires and vases in areas where prolonged dry seasons desiccated these habitats and reduced copepod survival.

Abundance and parity rate of Lutzomyia cruciata (Diptera:Psychodidae) in an endemic focus of localized cutaneous leishmaniasis in southern Mexico.

Human bait catches were carried out from 5 through 27 March 1994 in an endemic focus of cutaneous leishmaniasis in the state of Campeche, Mexico. Females of Lutzomyia cruciata (Coquillet) were dissected and 67% were parous. The number of total and parous females collected per day was analyzed by time series, but neither the gonotrophic cycle length nor survivorship could be estimated. However, a survival rate per oviposition cycle of 0.68 was estimated from the least square regression of parous on total females. Additional evidence for L. cruciata as a vector of human leishmaniasis is discussed.

Population dynamics and biting rhythm of the anthropophilic sandfly Lutzomyia cruciata (Diptera: Psychodidae) in Southeast, Mexico.

Sandflies attracted by human bait were caught in an endemic focus of localized cutaneous leishmaniasis in the state of Campeche, Mexico. Catches were carried out monthly from February 1994 to January 1995 between 18:00 and 22:00 h. Lutzomyia cruciata was the only species caught. The highest population peak of Lu. cruciata was found in March with lesser peaks in February, December 1994, and January 1995. Maximum biting rate of Lu. cruciata was found between 18:00 and 19:00 h. The host-seeking females of Lu. cruciata were directly related to levels of humidity between 88 and 100%. Low and high temperature had a negative effect upon Lu. cruciata activity. The possible role of Lu. cruciata as vector of leishmaniasis in the state of Campeche, Mexico is discussed.

Biochemical systematics and population genetic structure of Anopheles pseudopunctipennis, vector of malaria in Central and South America.

An electrophoretic survey of 42 populations of Anopheles pseudopunctipennis collected throughout its known geographic distribution was performed to clarify the taxonomic status of this important malaria vector species. The results indicated strong differences in the allele frequencies of three enzyme loci (glycerol dehydrogenase, 6-phosphogluconate dehydrogenase, and phosphoglucomutase) of the 33 loci analyzed. No fixed electromorphic differences separate the populations of An. pseudopunctipennis. The populations of An. pseudopunctipennis showed little genetic divergence, with Nei distances ranging from 0 to 0.079. A comparison of An. pseudopunctipennis data with either one of three other Anopheles species showed a high genetic distance of 0.335 with a closely related species, An. franciscanus; 0.997 with An. crucians, and 2.355 with An. (Nyssorhynchus) albimanus. Geographic populations of An. pseudopunctipennis were classified into three clusters; one cluster included populations collected in North America (United States and Mexico) and Guatemala, one cluster included populations from Belize and South America (Colombia, Ecuador, Peru, Chile, and Argentina); and one cluster was represented by populations from the Island of Grenada (type-locality of An. pseudopunctipennis). Based on our isozyme analyses, we defined these clusters as three geographic populations of An. pseudopunctipennis. Of the two mainland populations, one extends from the southern United States south through Mexico and Guatemala, and the other extends north from southern South America through Central America to Belize. These two geographic populations converge in southern Mexico and northern Central America. One part of the convergence zone was identified in the area of eastern Guatemala and southern Belize.

[The role of the Aedes aegypti vector in the epidemiology of dengue in Mexico]. / El papel del vector Aedes aegypti en la epidemiología del dengue en México.

The role of Aedes aegypti (Lineo) in the epidemiology of dengue fever in Mexico is herein discussed based on the vectorial capacity model. Comments on the advantages and disadvantages of each model component at the time of field determinations are also presented. Emphasis is made on the impact of sampling and method bias on the results of vectorial capacity studies. The paper also addresses the need to increase vector biology knowledge as an input for epidemiological work to explain and predict dengue fever outbreaks. Comments on potential entomological variables not considered by the quantitative model are included. Finally, we elaborate on the introduction of Aedes albopictus (Skuse) in Mexico as a new risk factor and on its implications for the understanding of dengue fever transmission in Mexico.

Bionomics of larval populations of Anopheles pseudopunctipennis in the Tapachula foothills area, southern Mexico.

The population dynamics of Anopheles pseudopunctipennis larvae were studied in a foothill region near Tapachula, Mexico. Systematic surveillance of wet-season and dry-season habitats was conducted during 1990 and 1991. Sampling along transects of the Coatan River was employed to quantify habitat availability and population densities of larvae during the dry season. During the wet season, larvae were most abundant in temporary habitats, such as seepage springs, rain pools, and pools in stream and river margins. The temporary habitats disappeared during the dry season, which occurred concurrent with increasing densities of larvae in dry-season habitats within transects along the Coatan River. The great abundance of the dry-season riverine habitats, viz., small pools with filamentous algae, resulted in peak densities of host-seeking adult populations in villages associated with the river. During both seasons, there were significant associations between the presence and abundance of larvae and habitats containing filamentous algae, and secondarily with selected aquatic and semiaquatic plants. There was a significant correlation between mean numbers of larvae per habitat and mean numbers of breeding sites in the transects. Overall, An. pseudopunctipennis larvae were very abundant during the dry season and relatively uncommon during the wet season.

Bionomics of adult Anopheles pseudopunctipennis (Diptera: Culicidae) in the Tapachula foothills area of southern Mexico.

Field studies on the bionomics of adult Anopheles pseudopunctipennis Theobald were conducted to assess its relative importance as a primary vector of vivax malaria in southern Mexico. In four malaria endemic villages in a foothill region near Tapachula, Mexico, population densities of A. pseudopunctipennis increased during the dry seasons of 1990 and 1991. The pattern of nocturnal host-seeking activity indoors was unimodal with a late night peak at 0100 hours enhancing its vectorial significance, because it occurred when most residents were asleep and fully exposed to the anophelines. Comparisons of trapping methods showed that a horse-baited trap was more effective than human landing catches or UV light traps. Pit shelters, on the other hand, were more effective than indoor and natural shelter resting collections. Results of enzyme-linked immunosorbent assays performed on wild-caught A. pseudopunctipennis specimens documented the presence of natural infections with the VK210 and new VK247 circumsporozoite polymorphs of P. vivax. These findings verify the importance of A. pseudopunctipennis as a major vector of vivax malaria at higher elevations and extend the geographical range of the VK247 P. vivax polymorph in Mexico.

Gonotrophic cycle and survivorship of Anopheles pseudopunctipennis (Diptera: Culicidae) in the Tapachula foothills of southern Mexico.

Mark-release-recapture experiments were conducted to determine the length of the gonotrophic cycle and survivorship of Anopheles pseudopunctipennis Theobald in the Tapachula foothills of southern Mexico. Separate trials with wild-caught females were conducted in the early and late dry season to examine intraseasonal differences. The gonotrophic cycle of insectary-reared, nulliparous females was estimated during the late dry season. A total of 5.4-5.7% of marked females was recaptured. A 3-d gonotrophic cycle was characteristic of wild-caught females, whereas a 4-d gonotrophic cycle was characteristic for insectary-reared females. Engorged, wild-caught females completed oogenesis in approximately 60 h under field conditions. Blood digestion in 23.5% of 2,221 and 21.9% of 1,195 engorged, wild-caught females held in the insectary was not accompanied by egg development. Dissections of these females showed that nearly 85% were nulliparous and presumably pregravid. These statistics plus other field data were used to determine that 60% of all nulliparous entered a pregravid condition. The body size and wing length of gravids was significantly larger than pregravids. Daily survival estimates of 0.875 and 0.884 were calculated for field-collected females during the early and late dry season, respectively.

Host selection patterns of Anopheles pseudopunctipennis under insecticide spraying situations in southern Mexico.

Studies of host selection patterns of Anopheles pseudopunctipennis were conducted in villages in foothills near Tapachula, Mexico. Based on 2 years of collections, 53.8 and 86.1% of all engorged females resting inside houses were found to contain human blood. Estimates of weighted and unweighted human blood indices, including data from outdoor resting collections, varied from 29.5 to 54.7%. Humans and dogs were the more common blood sources for all An. pseudopunctipennis mosquitoes, accounting for 96% of blood meals tested. Results of analyses of host preference through estimates of forage ratios (FRs) indicated that the large numbers of blood meals from humans and dogs were more reflective of host availability than host preference. An FR of less than 1 indicated that, in terms of host availability, proportionately fewer An. pseudopunctipennis females fed on humans than other large animal hosts. In contrast, FRs of 15-20 and 5-7 revealed strong selective biases for horses and pigs as sources of blood meals, respectively. The proportion of outdoor-resting, blood-engorged females containing human blood declined markedly after houses were sprayed with DDT. This response to house spraying is attributed to an excito-repellency effect of DDT.