Chagas Disease in Ecuador: Evidence for Disease Transmission in an Indigenous Population in the Amazon Region

Two well-defined synthetic peptides TcD and PEP2 were used in a sero-epidemiological study for the detection of Trypanosoma cruzi infections in an indigenous group in the Amazon region of Ecuador. Of the 18 communities studied along the Río Napo, province of Napo, 15 (83.3%) were found to be positive for T. cruzi infection. Of the 1,011 individuals examined 61 (6.03%) resulted positive. A prevalence of infection of 4.8% was found in children aged 1-5 years. The prevalence of infection increased with age, with adults 50 years or older showing a maximum prevalence of 18.8%. Autochthonous transmission of T. cruzi is present among this isolated indigenous population

Population Biology of Rhodnius domesticus Neiva & Pinto, 1923 (Hemiptera: Reduviidae) under Laboratory Conditions

The entire life cycle of Rhodnius domesticus, fed weekly on mice, was studied under controlled conditions. Aspects related to hatching, life time, mortality, feeding behaviour and fecundity for each stage of the insect life-cycle were evaluated. The hatching rate observed in 100 eggs was 57% and the mean time of hatching was 15.6 days. Forty-six nymphs (80.7%) completed the cycle and the mean time from NI to adult was 93.8 days. The average span in days for each stage was 12.4 for NI, 9.8 for NII, 14.2 for NIII, 16.8 for NIV and 25.0 for NV. The number of bloodmeals in each nymphal stage varied from 1 to 3. The mortality rate was 12.3% for NI, 3.5% for NII and 1.7% for NIII and NV nymphs. The mean number of eggs laid per female in a 9-month period was 333.1. Average adult survival rates were 287.6 +133 and 328 +73 days for males and females respectively.

Systematics and Population Level Analysis of Anopheles darlingi

A new phylogenetic analysis of the Nyssorhynchus subgenus (Danoff-Burg and Conn, unpub. data) using six data sets {morphological (all life stages); scanning electron micrographs of eggs; nuclear ITS2 sequences; mitochondrial COII, ND2 and ND6 sequences} revealed different topologies when each data set was analyzed separately but no heterogeneity between the data sets using the arn test. Consequently, the most accurate estimate of the phylogeny was obtained when all the data were combined. This new phylogeny supports a monophyletic Nyssorhynchus subgenus but both previously recognized sections in the subgenus (Albimanus and Argyritarsis) were demonstrated to be paraphyletic relative to each other and four of the seven clades included species previously placed in both sections. One of these clades includes both Anopheles darlingi and An. albimanus, suggesting that the ability to vector malaria effectively may have originated once in this subgenus. Both a conserved (315 bp) and a variable (425 bp) region of the mitochondrial COI gene from 15 populations of An. darlingi from Belize, Bolivia, Brazil, French Guiana, Peru and Venezuela were used to examine the evolutionary history of this species and to test several analytical assumptions. Results demonstrated (1) parsimony analysis is equally informative compared to distance analysis using NJ; (2) clades or clusters are more strongly supported when these two regions are combined compared to either region separately; (3) evidence (in the form of remnants of older haplotype lineages) for two colonization events; and (4) significant genetic divergence within the population from Peixoto de Azevedo (State of Mato Grosso, Brazil). The oldest lineage includes populations from Peixoto, Boa Vista (State of Roraima) and Dourado (State of São Paulo).

A Study of Cryptosporidium parvum Genotypes and Population Structure

Genetic evidence for the occurrence of two Cryptosporidium parvum subgroups is presented. This evidence is based on restriction fragment length polymorphism analysis of several independent loci. Sequence analysis of the b -tubulin intron revealed additional polymorphism. The stability of the genetic profiles following passage of C. parvum isolates between different hosts was investigated.

Possible hybridization of Brazilian planorbid snails and its importance in population dynamics

This study focuses on the possibility of experimental hybridization among host snail species for Schistosoma mansoni in Brazil, with morphological characterization of the hybrids found. By using albinism as a genetic marker, intraspecific crossbreedings were performed between two strains of each species involved, in addition to interspecific crossbreedings; the only viable crossbreeding was between pigmented Biomphalaria glabrata (Paulista, PE) and albino B. tenagophila (Joinville, SC), with the formation of F1 and F2 generations. All offspring in F1 displayed black eyes and a renal ridge on the mantle, while F2 displayed dissociated morphological traits. With regard to reproduction, F1 was more efficient than F2. The experiment's results suggest post-zygotic reproductive isolation.

Evaluation of Insecticide Resistance and Biochemical Mechanisms in a Population of Culex quinquefasciatus (Diptera: Culicidae) from São Paulo, Brazil

To establish an insecticidal resistance surveillance program, Culex quinquefasciatus mosquitoes from São Paulo, Brazil, were colonized (PIN95 strain) and analyzed for levels of resistance. The PIN95 strain showed low levels of resistance to organophosphates [malathion (3.3-fold), fenitrothion (11.2-fold)] and a carbamate [propoxur (3.0-fold)]. We also observed an increase of 7.4 and 9.9 in a and b esterase activities, respectively, when compared with the reference IAL strain. An alteration in the sensitivity of acetylcholinesterase to insecticide inhibition was also found in the PIN95 mosquitoes. The resistant allele (Ace.1R), however, was found at low frequencies (0.12) and does not play an important role in the described insecticide resistance. One year later, Cx. quinquefasciatus mosquitoes were collected (PIN96 strain) at the same site and compared to the PIN95 strain. The esterase activity patterns observed for the PIN96 strain were similar to those of the PIN95 mosquitoes. However the occurrence of the Ace.1R allele was statistically higher in the PIN96 strain. The results show that esterase-based insecticide resistance was established in the PIN95 Cx. quinquefasciatus population and that an acethylcholinesterase based resistant mechanism has been selected for. A continuous monitoring of this phenomenon is fundamental for rational mosquito control and insecticide application programs.

The population structure of Trypanosoma cruzi: expanded analysis of 54 strains using eight polymorphic CA-repeat microsatellites

Recently we cloned and sequenced the first eight Trypanosoma cruzi polymorphic microsatellite loci and studied 31 clones and strains to obtain valuable information about the population structure of the parasite. We have now studied 23 further strains, increasing from 11 to 31 the number of strains obtained from patients with chronic Chagas disease. This expanded set of 54 strains and clones analyzed with the eight microsatellites markers confirmed the previously observed diploidy, clonal population organization and very high polymorphism of T. cruzi. Moreover, this new study disclosed two new features of the population genetic structure of T. cruzi. The first was the discovery that, similarly to what we had previously shown for strains isolated from insect vectors, mammals and humans with acute disease, isolates from patients in the chronic phase of Chagas disease could also be multiclonal, albeit at a reduced proportion. Second, when we used parsimony to display the genetic relationship among the clonal lineages in an unrooted Wagner network we observed, like before, a good correlation of the tree topography with the classification in three clusters on the basis of single locus analysis of the ribosomal RNA genes. However, a significant new finding was that now the strains belonging to cluster 2 split in two distant sub-clusters. This observation suggests that the evolutionary history of T. cruzi may be more complex than we previously thought.

Population dynamics and feeding behavior of Triatoma brasiliensis and Triatoma pseudomaculata, main vectors of Chagas disease in Northeastern Brazil

Biological parameters of Triatoma brasiliensis and T. pseudomaculata that could influence the epidemiological importance of these insects as vectors of Trypanosoma cruzi were compared. The parameters studied were incubation period, interval between hatching or moulting and first feeding, number of blood meals, development time, mortality, net reproductive rate, instantaneous daily reproductive rate, time-lapse before starting feeding, duration of feeding, blood ingestion capacity, occurrence of defecation and blood ingestion velocity. Most aspects of feeding were similar for the two species, although T. pseudomaculata had a longer life cycle than T. brasiliensis producing one and two generations per year, respectively. The two species had similar instantaneous daily rates of population growth.

Frequency of CCR5 Delta-32 Mutation in Human Immunodeficiency Virus (HIV)-seropositive and HIV-exposed Seronegative Individuals and in General Population of Medellin, Colombia

Repeated exposure to human immunodeficiency virus (HIV) does not always result in seroconversion. Modifications in coreceptors for HIV entrance to target cells are one of the factors that block the infection. We studied the frequency of Delta-32 mutation in ccr5 gene in Medellin, Colombia. Two hundred and eighteen individuals distributed in three different groups were analyzed for Delta-32 mutation in ccr5 gene by polymerase chain reaction (PCR): 29 HIV seropositive (SP), 39 exposed seronegative (ESN) and 150 individuals as a general population sample (GPS). The frequency of the Delta-32 mutant allele was 3.8% for ESN, 2.7% for GPS and 1.7% for SP. Only one homozygous mutant genotype (Delta-32/Delta-32) was found among the ESN (2.6%). The heterozygous genotype (ccr5/Delta-32) was found in eight GPS (5.3%), in one SP (3.4%) and in one ESN (2.6%). The differences in the allelic and genotypic frequencies among the three groups were not statistically significant. A comparison between the expected and the observed genotypic frequencies showed that these frequencies were significantly different for the ESN group, which indirectly suggests a protective effect of the mutant genotype (Delta-32/Delta-32). Since this mutant genotype explained the resistance of infection in only one of our ESN persons, different mechanisms of protection must be playing a more important role in this population.

Sylvatic population of Triatoma infestans from the Bolivian Chaco: from field collection to characterization

A sylvatic Triatoma infestans DM (dark morph) population detected in the Bolivian Chaco was characterized and compared with various domestic ones. The degree of differentiation of DM was clearly within the T. infestans intra-specific level. Nevertheless marked chromatic and morphometric differences as well as differences in antennal pattern, chromosome banding and randomly amplified polymorphic DNA support the hypothesis of a distinct population. Continuous exchange of insects between wild and domestic habitats seems unlikely in the Chaco.

Population genetic analysis of Colombian Trypanosoma cruzi isolates revealed by enzyme electrophoretic profiles

Although Colombia presents an enormous biological diversity, few studies have been conducted on the population genetics of Trypanosoma cruzi. This study was carried out with 23 Colombian stocks of this protozoa analyzed for 13 isoenzymatic loci. The Hardy-Weinberg equilibrium, the genetic diversity and heterogeneity, the genetic relationships and the possible spatial structure of these 23 Colombian stocks of T. cruzi were estimated. The majority of results obtained are in agreement with a clonal population structure. Nevertheless, two aspects expected in a clonal structure were not discovered in the Colombian T. cruzi stocks. There was an absence of given zymodemes over-represented from a geographical point of view and the presumed temporal stabilizing selective phenomena was not observed either in the Colombian stocks sampled several times through the years of the study. Some hypotheses are discussed in order to explain the results found.

Population biology of Allocreadium lobatum Wallin, 1909 (Digenea: Allocreadiidae) in the creek chub, Semotilus atromaculatus, mitchill (Osteichthyes: Cyprinadae), in a Nebraska Creek, USA

Allocreadium lobatum Wallin, 1909 has been reported in cyprinid species of freshwater fish in Canada and in the United States. The population biology of A. lobatum in the host Semotilus atromaculatus Mitchill was studied from May through December 1991, in a USA creek. Overall prevalence (64%) and mean intensity (4.4 ± 0.4) were greater than previously reported while abundance, reported for the first time, was 2.8 ± 0.3. Several trends in A. lobatum population biology as a function of S. atromaculatus length were identified. Mean intensity and abundance of A. lobatum increased with host size and significant differences in prevalence and A. lobatum lengths were found to correlate with host lengths.

Usefulness of microsatellite typing in population genetic studies of Trypanosoma cruzi

Through microsatellite analysis of 53 monoclonal populations of Trypanosoma cruzi, we found a remarkable degree of genetic polymorphism with no single multilocus genotype being observed more than once. The microsatellite profile proved to be stable during 70 generations of the CL Brener clone in culture. The microsatellite profiling presented also high diagnostic sensitivity since DNA amplifications could be achieved with less than 100 fg DNA, corresponding to half parasite total DNA content. Based on these technical attributes the microsatellite assay turns out to be an important tool for direct typing T. cruzi in biological samples. By using this approach we were able to type T. cruzi in feces of artificially infected bugs and in single cells sorted by FACS. The microsatellites have shown to be excellent markers for T. cruzi phylogenetic reconstruction. We used maximum parsimony based on the minimum number of mutational steps to build an unrooted Wagner network, which confirms previous conclusions based on the analysis of the D7 domain of the LSU rDNA gene that T. cruzi is composed by two major groups. We also obtained evidence that strains belonging to rRNA group 2 are subdivided into two genetically distant clusters, and that one of these clusters is more related to rRNA group 1/2. These results suggest different origins for these strains.