Biological parameters of interbreeding subspecies of Meccus phyllosomus (Hemiptera: Reduviidae: Triatominae) in western Mexico.

Understanding the biological parameters of some triatomine subspecies of Meccus phyllosomus (Burmeister) is a crucial first step in estimating the epidemiological importance of this group. Biological parameters related to egg eclosion, egg-to-adult development time, number of blood meals to moult, percentage of females at the end of the cycle, number of laid eggs, and the accumulative mortality for each instar of three M. phyllosomus subspecies [Meccus phyllosomus pallidipennis (Stål), Meccus phyllosomus longipennis (Usinger), and Meccus phyllosomus picturatus (Usinger)] as well as their laboratory hybrids were evaluated and compared. No significant differences (P > 0.05) were recorded among the experimental hybrids (M. p. longipennis × M. p. pallidipennis, M. p. longipennis × M. p. picturatus, M. p. pallidipennis × M. p. picturatus) and reciprocal cohorts. In five of the six studied parameters (egg eclosion, egg-to-adult development time, number of blood meals to moult, number of laid eggs and accumulative mortality), with the exception of the non-significant percentage of females obtained among all the studied cohorts, at least one of the parental cohorts in each set of crosses exhibited better fitness results than by those of their hybrid descendants. The lack of hybrid fitness in our study indicates the maintenance of reproductive isolation of parental genotypes. Moreover, the results lead us to propose that an incipient speciation process by distance is currently developing among the three studied subspecies, increasing the differences between them that modify the transmission efficiency of Trypanosoma cruzi to human beings in Mexico.

Biological characteristics of geographically isolated populations of Meccus mazzottii (Hemiptera: Reduviidae) in southern Mexico.

Chagas disease, caused by Trypanosoma cruzi Chagas, is one of the most epidemiologically important vector-borne zoonoses in Mexico. Among the 32 reported triatomine species from Mexico, Meccus mazzottii (Usinger) (Hemiptera: Reduviidae) is one of the most important vectors of T. cruzi in the southern part of the country. Variability among populations of triatomines has been recorded for several species (Meccus longipennis (Usinger) and Meccus pallidipennis (Stal)) that are closely related to M. mazzottii, showing an apparent influence of local environmental conditions on the biology of each population, which could modify the impact of vector control measurements. Therefore, this study sought to compare the biological features of populations of M. mazzottii from two geographically far apart areas that have similar environmental characteristics and to compare populations from close geographical areas that have different environmental characteristics. The mean longevity, percentages of mortality of nymphs, the total mean number of bloodmeals to molt (considered instar by instar), the mean number of eggs laid by females, and the percentage of hatched eggs were similar between the two localities that are geographically far apart but have similar environmental characteristics. On the other hand, important differences were noticed when a comparison was carried out on the two localities with similar environmental conditions with respect to that locality with different conditions, independent of geographic distance. Most of the studied parameters led us to conclude that the three studied populations are very highly influenced by local environmental conditions. The results of this study indicate the importance of studying the biological characteristics of local populations of triatomines to carry out specific control measurements, instead of using standard ones that could fail if they are not adapted to the target population.

Seroprevalence to Trypanosoma cruzi in rural communities of the state of Querétaro (Mexico): statistical evaluation of tests.

OBJECTIVES: The detection of anti-Trypanosoma cruzi antibodies has become one of the priorities of the clinical establishments in the health sector, due both to the increase in positive cases found in transfusion centres as well as to the appearance of patients with characteristic Chagas cardiopathies that seek emergency treatment in the main hospitals of Querétaro (Mexico). DESIGN AND METHODS: The present study seeks to establish for the first time the infection level of Trypanosoma cruzi, in the rural communities of this state and implement the preventive measures necessary to control and/or eradicate this infection. A transversal study was conducted, examining seriologically 1029 blood samples of the inhabitants of rural areas of the state of Querétaro, to detect anti-Trypanosoma cruzi antibodies. RESULTS: The indirect serological diagnostic tests were indirect hemagglutination, enzymo-immunoenzymatic absorbent, recombinant ELISA, and indirect immunofluorescence. For the diagnostic evaluation of serological tests used, ELISA was considered the control test. CONCLUSIONS: The first conclusion was that the two tests with the greatest serological reactivity were ELISA and recombinant ELISA, followed by IFA and IHA, respectively, with the final percentage of positives being 6.6%, far above the national mean of seroprevalence in Mexico (1.6%). On the other hand, the sensitivity, specificity, VP+, VP-, percentage of concordance and Kappa index of the recombinant ELISA tests, IFA, and IHA were determined against the control ELISA. It was found that ELISA and recombinant ELISA presented a greater sensitivity level, as well as the highest values for the different parameters studied.