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M H Rodríguez

Publications and source records attributed to M H Rodríguez.

36 records · Page 2Linked to original sources
PubMed1996

Genetic differences among Anopheles vestitipennis subpopulations collected using different methods in Chiapas state, southern México.

Biting activity and population genetic studies of the malaria vector Anopheles vestitipennis were conducted in southern México. Three subpopulations were collected from 2 villages; 2 subpopulations were from the same village, one on human bait and one with an animal-baited trap; the third was collected from a cattle corral in the 2nd village (280 km away SSE). The anthropophilic subpopulation had steady activity with 61% of bites occurring before midnight, significantly different from those of the 2 zoophilic subpopulations, which had 78-82% of bites before midnight and 2 biting peaks, one at 1900-2100 h and the other at 0400-0500 h. Isozyme analysis (13 enzymes) of these subpopulations indicated that differences between the 2 sympatric subpopulations (D = 0.07), collected using 2 different methods, were greater than that between the 2 allopatric ones (D = 0.03). These studies suggest the existence of 2 genetically different subpopulations of An. vestitipennis with specific host preferences.

Alleles↗
PubMed1995

Control of Anopheles albimanus mosquitos in southern Mexico by spraying their preferred indoor resting sites.

The traditional indoor spraying technique to control Anopheles albimanus mosquitos was compared with a selective method that targets their preferred resting sites in coastal villages of southern Mexico. We also determined whether mosquitos changed their preferred resting sites following insecticide applications. In the selective spraying approach, two 1-m wide horizontal swaths of bendiocarb insecticide were applied 0.75-1.75 m from the base of the walls and at 1-m upwards from the base of the inner roof at a target dose of 0.4 g/m2. A 2-year follow-up (1988-90), which included four insecticide treatments, showed that the selective spraying was as effective as full spraying for controlling A. albimanus. Also the mosquitos preferred resting sites that were not modified by the insecticide applications. Finally, the use of this techniques required 46% less time and cost 67% less than conventional spraying.

Animals↗
PubMed1995

In vitro growth of Vibrio cholerae in cholera stool fluid leads to differential expression of virulence factors.

We report on the physiological response of Vibrio cholerae upon growth on bacteria-free intestinal fluids prepared from feces of individuals in the acute phase of cholera. Sterilized stool fluids supported growth of V. cholerae to reach 0.3-0.4 O.D. units (600 nm) at 37 degrees C. Scanning electron microscopy showed vibrios to be slender and elongated as compared to bacteria in synthetic media. Growth in stool fluid apparently induced expression of several immunoreactive proteins using cholera convalescent sera. Supernatants of fluid-grown vibrios had undetectable cholera toxin (CT) concentrations. Soluble hemagglutinins and soluble proteases were much less reduced when compared to cultures in Syncase or AKI media while cell-associated mannose-sensitive hemagglutinin (MSHA) was expressed at good levels. Lack of production of CT in fluid devoid of tissue may be due to absence of stimulating elements in intact intestine. Alternatively, culturing V. cholerae in stool fluid might resemble a late proliferation stage where downregulation of toxin might occur. Irrespectively, concomitant production of other virulence factors represents a phenomenon of differential regulation by fluid. Efforts are now underway to determine if this response depends upon factors in stool fluid acting through known genetic regulatory cascades or other. Attempts are also geared to identify fluid-induced proteins and their genes.

Biological Factors↗
PubMed1994

Susceptibility of three laboratory strains of Anopheles albimanus (Diptera: Culicidae) to coindigenous Plasmodium vivax in southern Mexico.

Three morphologically different pupal phenotypes (green, striped, brown) were selected from a parent strain of Anopheles albimanus Wiedemann collected from the Suchiate region in the state of Chiapas, Mexico. Significant differences in susceptibility to coindigenous Plasmodium vivax Grassi & Feletti were observed when striped was compared with the parent colony as well as with brown and with green phenotypes. Differences in susceptibility were not significant between the other phenotypes and the parent colony.

Animals↗
PubMed1994

Attempted isolation of the gene encoding the 21 Kd Plasmodium berghei ookinete transmission blocking antigen from Plasmodium yoelli and Plasmodium vivax.

The 21kD ookinete antigen of Plasmodium berghei (Pbs 21) has been shown to elicit an effective and long lasting transmission blocking immune response in mice. Having cloned and sequenced this antigen (Paton et al. 1993) the sequence was compared to the genes of the same family previously identified in P. falciparum, P. gallinaceum (Kaslow et al. 1989) and P. reichenowi (Lal et al. 1990). Four conserved areas were identified in this comparison, to which degenerate oligonucleotides were designed. PCR amplification and screening of genomic libraries was then carried out using these oligonucleotides. The P. yoelii gene was successfully cloned and a number of novel P. vivax genes identified but the P. vivax homologue of Pbs21 remains elusive.

Animals↗
PubMed1994

Intradomicillary pre- and postfeeding behavior of Anopheles pseudopunctipennis of southern Mexico: implications for malaria control.

The intradomicillary pre- and postfeed resting behavior of Anopheles pseudopunctipennis was studied in an experimental house in southern Mexico. During resting periods (both pre-/postfeed) mosquitos had greater contact (landings) with the inner roof than with the walls and other surfaces. A comparison of mean landing frequency and overall resting time (pre-/postfeed) showed that a greater periodic and prolonged contact occurred prefeed, probably as a result of disturbed activity associated with host movements. Pre-/postfeed resting patterns on walls were limited to a 0.6-0.5-m-wide band, nearly 1 m from the floor, and to a narrower band on the roof, 0.3-0.2 m wide, approximately 2.3 m from the floor, respectively. We calculated that with a band width of 0.8 m on the walls and another band 0.8 m wide on the roof, 87.2% of the mosquitoes had at least one contact with either the wall, the roof, or with both surfaces, along with an overall mean resting time (pre-/postfeed) of 8.1 min/landing. These findings suggest that a high potential for control can be achieved by spraying preferred wall and roof resting sites in this region where the intradomicillary application of residual insecticide is the primary malaria control measure.

Animals↗
PubMed1994

Peri-/intradomicillary behavior in relation to host-seeking of Anopheles pseudopunctipennis in southern Mexico.

Peri-/intradomicillary resting and host-seeking behavior of Anopheles pseudopunctipennis was studied in an experimental house (surrounded by a curtain-net) that had not been sprayed with insecticide. Peak mosquito densities were recorded resting on vegetation 1 h earlier (1900-2000 h) than on the curtain-net, suggesting that a proportion of females prefer resting on adjacent vegetation prior to moving indoors. Between 2000 and 2100 h there was a marked decrease in numbers of mosquitoes resting on the exterior of the curtain-net. In separate experiments without the net, a single peak in numbers of mosquitoes resting on interior surfaces and/or biting human bait occurred between 2000 and 2100 h. Unfed mosquitoes had higher numbers of contacts with wall surfaces than with the roof. Moreover, a higher proportion of mosquitoes collected on human bait had > or = 1 dilatation(s), and higher parity rates than those resting on walls. Higher proportions of parous mosquitoes more frequently fed from 1800 to 2100 h, whereas higher proportions of nulliparous mosquitoes fed during morning hours. Nearly 25% of all mosquitoes exited 1 h following their release inside the house, whereas nearly 7% remained indoors for > 9 h. Overall results demonstrated that the behavior of An. pseudopunctipennis females depends on outdoor/indoor stimuli, being multivariable in nature. This includes contacts with a variety of biological (i.e., vegetation, human) and inert surfaces, which in part appears to be controlled by age structure.

Animals↗
PubMed1993

Anopheles albimanus (Diptera: Culicidae) host selection patterns in three ecological areas of the coastal plains of Chiapas, southern Mexico.

The host-feeding patterns of Anopheles albimanus Wiedemann were described and the effect of host availability on these patterns was assessed in three different ecological areas of coastal Chiapas, Mexico. Resting mosquitoes were collected indoors and outdoors during rainy seasons. A 20% sample of blood-fed mosquitoes was tested to determine the source of the blood meal using an ELISA. The unweighted human blood index (HBI) of An. albimanus in the three areas ranged from 0.11 to 0.21. This mosquito species fed more frequently on bovines than on any other host, but the forage ratio indicated that there was also a high preference for equines. Some females tended to rest or complete their gonotrophic cycle indoors after feeding on animals, but females also fed on man and rested outdoors. Host availability and ecological conditions appeared to be responsible for differences observed in the HBI among areas.

Animals↗
PubMed1993

Indoor low-volume insecticide spray for the control of Anopheles albimanus in southern Mexico. Village-scale trials of bendiocarb, deltamethrin and cyfluthrin.

A comparative insecticide village-scale trial was carried out to determine the efficacy of low-volume (LV) indoor spray of bendiocarb, deltamethrin and cyfluthrin for the control of Anopheles albimanus in a coastal plain of southern Mexico. Low-volume spray was conducted with knapsack mist-blowers, giving an average discharge rate of 215 ml/min, which deposited droplets of 50-100 microns. Using this technique, 25 houses were treated/sprayman/day as compared with 8 houses/sprayman/day using conventional hand compression pumps. Indicators of LV mortality showed a residual activity of 10 wk as compared with 13 wk of activity for wettable powder (WP) (bendiocarb). When comparing expenditures, LV spray costs were 43% less when using bendiocarb, 83% less with deltamethrin and 74% less with cyfluthrin with respect to the conventional WP spray of the same insecticides. Low-volume spray time was reduced by one-third, with respect to WP. Malaria incidence was reduced by 53 and 56%, respectively, in the bendiocarb LV and deltamethrin LV treated villages as compared with the untreated village.

Animals↗
PubMed1993

Dynamics of population densities and vegetation associations of Anopheles albimanus larvae in a coastal area of southern Chiapas, Mexico.

Spatial and seasonal variations on Anopheles albimanus larval densities and their plant associations were investigated in larval habitats in southern Mexico between April 1989 and May 1990. Thirty-four plant groups were dominant in larval habitats. Dense larval populations were associated with 3 genera of plants, Cynodon, Echinocloa and Fimbristylis and no larvae were found in habitats with Salvinia and Rhizophora. Low significant positive or negative associations were documented with the other 12 plant genera. Larval habitats were classified according to the morphology of their dominant plants. Higher larval densities were observed in the groups characterized by relatively short emergent vegetation. The distribution of habitat-types within 5 identified vegetation units showed a significantly dependent relationship. For the entire study period, highest larval densities were detected in flooded pasture/grassland vegetation units. For all vegetation units, higher larval densities were found when the dominant plant type covered between 25-50% of the breeding site. The integration of data from habitat-types into vegetation units did not result in loss of information.

Animals↗
PubMed1991

Age structure and abundance levels in the entomological evaluation of an insecticide used in the control of Anopheles albimanus in southern Mexico.

Applications of bendiocarb produced a high insecticidal residual effect lasting up to 3 months on the most common indoor house surfaces. No significant decreases in mosquito man-biting rate levels were observed between treated and untreated villages. It was shown that almost equal proportions of intra- and peridomicillary mosquitoes came into contact with the insecticide, indicating that mosquitoes commonly enter houses, rest on treated surfaces and return to bite both indoors and outdoors. Although the insecticide was found to have a significant effect on the percentage parity (interpreted as abundance of older individuals) of intra- and peridomicillary Anopheles albimanus mosquitoes, parity recovered and continued a normal cyclic pattern that appeared to be dependent on relative abundance. The proximity of a treated village to an untreated village (1.2 km) can affect the age structure of mosquito populations through shared common resting and breeding sites.

Age Factors↗
PubMed1990

Effect of indoor residual spraying of DDT and bendiocarb on the feeding patterns of Anopheles pseudopunctipennis in Mexico.

Intense and persistent use of DDT for malaria control has increased resistance and induced exophilic behavior of Anopheles pseudopunctipennis. An evaluation of bendiocarb and DDT to control this species in Sinaloa, Mexico, showed that, in spite of DDT-resistance, both insecticides produced similar effects. Feeding patterns were analyzed to explain these results. Resting mosquitoes were collected over the dry and wet seasons. Anophelines were tested in an ELISA to determine the source of the meals. The human blood index (HBI) ranged from 3.3 to 6.8% in DDT- and from 12.7 to 26.9% in bendiocarb-sprayed houses. Irritability and repellency in DDT-sprayed houses could explain the reduced HBI. In contrast, bendiocarb produced higher mortality. These effects could have affected different components of the vectorial capacity and similarly reduced malaria.

Animals↗
PubMed1990

Small scale field trials of Bacillus sphaericus (strain 2362) against anopheline and culicine mosquito larvae in southern Mexico.

Experimental breeding sites simulating natural conditions were used to evaluate the efficacy of 2 formulations of Bacillus sphaericus (strain 2362) against Anopheles albimanus and culicine (mostly Culex coronator and Cx. quinquefasciatus) mosquito larvae of southern Mexico. Three doses of each formulation were used in a first field trial: 2, 3 and 4 g/m2 (granular) or 2, 3 and 4 ml/m2 (liquid); and in a second field trial: 0.125, 0.24 and 0.5 g/m2 (granular) or 0.125, 0.25 and 0.5 ml/m2 (liquid). The optimum concentrations of each formulation for effective control of larval populations over periods of 3-4 months were 0.125 ml/m2 of liquid product for Culex spp. and 2 g/m2 of granular product for An. albimanus (ca. 70% mean reduction).

Animals↗
PubMedDate not supplied

Anopheles vestitipennis, the probable vector of Plasmodium vivax in the Lacandon forest of Chiapas, México.

Baseline studies to evaluate the role of different anopheline mosquitoes as probable vectors of malaria in the Lacandon rainforest region in Chiapas (México) were carried out in 3 rural villages between June and November 1988. Anopheles vestitipennis was the most abundant species in all the villages, followed by An. albimanus, An. punctimacula and An. darlingi. Human bait collections showed that An. vestitipennis and An. albimanus tended to bite man either indoors or outdoors, while An. punctimacula preferred to bite outdoors. Monthly man-biting rates of An. vestitipennis tended to follow the rainfall pattern. Plasmodium vivax was detected in An. vestitipennis only, with an estimated overall infection rate of 4.67 per 1000 mosquitoes (range 0-54.42, of 3500 mosquitoes assayed). This is the first incrimination of An. vestitipennis as a probable vector of P. vivax in México.

Animals↗
PubMedDate not supplied

An enzyme-linked immunosorbent assay using detergent-soluble Plasmodium vivax antigen for seroepidemiological surveys.

An enzyme-linked immunosorbent assay (ELISA) to detect antibodies to Plasmodium vivax parasites in human sera was developed using P. vivax-infected erythrocytes from local malarious patients in southern Mexico. Infected cells were concentrated using a discontinuous Percoll gradient and detergent-soluble antigens obtained using Triton X100. The use of detergent and the addition of protease inhibitors to the antigen preparation ensured high sensitivity and reproducibility of the assay. No cross reactions were observed in sera immune to other protozoan, helmintic and bacterial infections, although some cross reactivity was seen in P. falciparum immune sera. A strong correlation between antibody titre values obtained by the ELISA and those obtained using an IFAT was observed. In a small field trial, carried out in a village where malaria transmission occurs, both ELISA and IFAT produced similar seroepidemiological profiles with regard to frequency of positive antibody titres and their distribution among the different age groups of the population.

Adolescent↗
PubMedDate not supplied

[Effectiveness of a carbamate insecticide as a household low-volume spray for malaria control].

A comparative regional-scale evaluation of the epidemiological impact of low volume (LV) spray of bendiocarb and the conventional spray of DDT against malaria in an endemic area of northern Chiapas was carried out. Three Anopheline species were found: Anopheles pseudopunctipennis, An. albinanus and An. argyritarsis. The most prevalent was An. pseudopunctipennis, a species we suspect may be involved in the transmission of most malaria cases. This species showed high levels of resistance to DDT. However, this insecticide had a long residual effect in wall bioassays, with mortalities > or = 95 per cent for up to 21 weeks in wood, sticks and plaster. Susceptibility to bendiocarb was total, and mortality to LV bendiocarb was > or = 75 per cent for up to 16 weeks in wood, sticks and straw. Very low numbers of mosquitoes were found throughout the evaluation, although malaria transmission continued in control villages (sprayed with DDT), as well as treated villages (sprayed with LV bendiocarb). No plasmodium infected mosquitoes were found, perhaps due to a very small sample size. The LV spray methodology was found to be 1.7 times more effective than conventional spraying in reducing malaria incidence. A net reduction of 1.6 times in insecticide application time was also found, which would allow spraying at the right time, especially when urgent control measures have to be applied, such as in malaria outbreaks. Finally, the new methodology costs 2.2 times more than the conventional ddt spraying, but if the potential of using spray workers in other activities is considered, costs would be comparable to those of DDT spraying.

Aerosols↗