Community-serving research addressing climate change impacts on vector-borne diseases

The impacts of climate change on vector-borne diseases are uneven across human populations. This pattern reflects the effect of changing environments on the biology of transmission, which is also modulated by social and other inequities. These disparities are also linked to research outcomes that could be translated into tools for transmission reduction, but are not necessarily actionable in the communities where transmission occurs. The transmission of vector-borne diseases could be averted by developing research that is both hypothesis-driven and community-serving for populations affected by climate change, where local communities interact as equal partners with scientists, developing and implementing research projects with the aim of improving community health. In this Personal View, we share five principles that have guided our research practice to serve the needs of communities affected by vector-borne diseases.

First report of imported canine visceral leishmaniasis cases in Panama, Central America: Public health implications

According to the last leishmaniasis report from the Pan American Health Organization (2021) so far Panama is considered free of visceral leishmaniasis (VL). Although the presence of potential vectors and reservoirs involved in the VL transmission cycle have been described in some rural regions of the country, no cases have been reported in humans and domestic or wild animals. Dogs play an important role in the urban transmission of VL; therefore, it is important to detect possible cases of canine visceral leishmaniasis (CVL) in the country. In this sense,this study reports for the first time the Leishmania (Leishmania) infantum infection in imported dogs in Panama. Eleven dogs with clinical suspicion of CVL were evaluated by parasitological (bone marrow aspirate smear), serological (indirect immunofluorescence and/or reference immunochromatographic rapid test) and molecular tests (conventional PCR). The dogs included in this study were analyzed during the period from 2013 to 2020. All dogs presented clinical manifestations compatible with CVL. The samples were initially evaluated by smears and/or rapid serological tests by private practice veterinarians, and later confirmed by serological and/or molecular tests at the national reference laboratory for Leishmania diagnosis. The diagnosis was confirmed in 5/11 dogs by serological, parasitological and/or conventionals PCR targeting kDNA minicircle and Hsp70 gene. Leishmania (L.) infantum species was identified in 3/5 dogs by PCR-RFLP and by sequencing Hsp70-PCR products. This study evidenced the need to increase awareness of private practitioners as well as public health veterinarians on visceral leishmaniasis (VL), and to consider this parasitosis in the differential diagnosis of dogs with clinical and epidemiological characteristics compatible with the disease.

Genetic Diversity of Trypanosoma cruzi in Panama Inferred by Multi-locus Sequence Typing of Mitochondrial Genes

The objective of this study was to provide information on Trypanosoma cruzi genetic diversity among isolates obtained from different biological sources circulating in endemic areas of Panama. Initial discrete typing units (DTUs) assignment was performed evaluating three single locus molecular markers (mini-exon, heat shock protein 60 and glucose-6-phosphate isomerase genes). Further diversity within TcI lineages was explored using a multi-locus sequence typing approach with six maxicircle genes. Haplotype network analysis and evolutionary divergency estimations were conducted to investigate the genetic relatedness between Panamanian TcI isolates and isolates from different endemic regions in the Americas. Our molecular approach validated that TcI is the predominant DTU circulating in Panama across different hosts and vector species, but also confirmed the presence of TcIII and TcVI circulating in the country. The phylogenetic tree topography for most Panamanian TcI isolates displayed a high level of genetic homogeneity between them. The haplotype network analysis inferred a higher genetic diversity within Panamanian TcI isolates, displaying eight different haplotypes circulating in endemic regions of the country, and revealed geographical structuring among TcI from different endemic regions in the Americas. This study adds novelty on the genetic diversity of T. cruzi circulating in Panama and complements regional phylogeographic studies regarding intra-TcI variations.

Long-term transmission patterns and public health policies leading to malaria elimination in Panamá

Background

The present study provides a countrywide perspective of the malaria situation in Panamá over a long-term framework, with the purpose of identifying historical malaria resurgence events and their potential causes.

Methods

A descriptive-ecological study was conducted by analysing demographic and epidemiological annual malaria time series data in Panamá (1884–2019) using several data sources. Malaria intensity indicators were calculated during the study period. The effects of El Niño Southern Oscillation on malaria transmission were also analysed using a retrospective analysis of malaria cases between 1957 and 2019.

Results

Several factors were identified responsible for malaria resurgence in Panamá, mostly related with Malaria Control Programme weakening. During the past 20 years (2000–2019) malaria has progressively increased in prevalence within indigenous settlements, with a predominance of male cases and a high proportion (15% of total cases) in children less than 5 years old. During this period, a significant and increasing proportion of the Plasmodium falciparum cases were imported. Retrospective analysis (1957–2019) evidenced that ENSO had a significant impact on malaria transmission dynamics in Panamá.

Conclusions

Data analysis confirmed that although authorities have been successful in focalizing malaria transmission in the country, there are still neglected issues to be solved and important intercultural barriers that need to be addressed in order to achieve elimination of the disease by 2022. This information will be useful for targeting strategies by the National Malaria Elimination Programme.

Population genetics of two chromatic morphs of the Chagas disease vector Rhodnius pallescens Barber, 1932 in Panamá

Rhodnius pallescens is the principal vector of Chagas disease in Panama. Recently a dark chromatic morph has been discovered in the highlands of Veraguas Province. Limited genetic studies have been conducted with regards to the population structure and dispersal potential of Triatominae vectors, particularly in R. pallescens. Next generation sequencing methods such as RADseq and complete mitochondrial DNA (mtDNA) genome sequencing have great potential for examining vector biology across space and time. Here we utilize a RADseq method (3RAD), along with complete mtDNA sequencing, to examine the population structure of the two chromatic morpho types of R. pallescens in Panama. We sequenced 105 R. pallescens samples from five localities in Panama. We generated a 2216 SNP dataset and 6 complete mtDNA genomes. RADseq showed significant differentiation among the five localities (F_CT = 0.695; P = .004), but most of this was between localities with the dark vs. light chromatic morphs (Veraguas vs. Panama Oeste). The mtDNA genomes showed a 97-98% similarity between dark and light chromatic morphs across all genes and a 502 bp insert in light morphs. Thus, both the RADseq and mtDNA data showed highly differentiated clades with essentially no gene flow between the dark and light chromatic morphs from Veraguas and central Panama respectively. We discuss the growing evidence showing clear distinctions between these two morpho types with the possibility that these are separate species, an area of research that requires further investigation. Finally, we discuss the cost-effectiveness of 3RAD which is a third of the cost compared to other RADseq methods used recently in Chagas disease vector research.

Regional biogeography of microbiota composition in the Chagas disease vector Rhodnius pallescens

Background

Triatomine bugs are vectors of the protozoan parasite Trypanosoma cruzi, which causes Chagas disease. Rhodnius pallescens is a major vector of Chagas disease in Panama. Understanding the microbial ecology of disease vectors is important in the development of vector management strategies that target vector survival and fitness. In this study we examined the whole-body microbial composition of R. pallescens from three locations in Panama.

Methods

We collected 89 R. pallescens specimens using Noireau traps in Attalea butyracea palms. We then extracted total DNA from whole-bodies of specimens and amplified bacterial microbiota using 16S rRNA metabarcoding PCR. The 16S libraries were sequenced on an Illumina MiSeq and analyzed using QIIME2 software.

Results

We found Proteobacteria, Actinobacteria, Bacteroidetes and Firmicutes to be the most abundant bacterial phyla across all samples. Geographical location showed the largest difference in microbial composition with northern Veraguas Province having the most diversity and Panama Oeste Province localities being most similar to each other. Wolbachia was detected in high abundance (48–72%) at Panama Oeste area localities with a complete absence of detection in Veraguas Province. No significant differences in microbial composition were detected between triatomine age class, primary blood meal source, or T. cruzi infection status.

Conclusions

We found biogeographical regions differ in microbial composition among R. pallescens populations in Panama. While overall the microbiota has bacterial taxa consistent with previous studies in triatomine microbial ecology, locality differences are an important observation for future studies. Geographical heterogeneity in microbiomes of vectors is an important consideration for future developments that leverage microbiomes for disease control.

Blood Meal Source Characterization Using Illumina Sequencing in the Chagas Disease Vector Rhodnius pallescens (Hemiptera: Reduviidae) in Panamá

Accurate blood meal identification is critical to understand hematophagous vector-host relationships. This study describes a customizable Next-Generation Sequencing (NGS) approach to identify blood meals from Rhodnius pallescens (Hemiptera: Reduviidae) triatomines using multiple barcoded primers and existing software to pick operational taxonomic units and match sequences for blood meal identification. We precisely identified all positive control samples using this method and further examined 74 wild-caught R. pallescens samples. With this novel blood meal identification method, we detected 13 vertebrate species in the blood meals, as well as single and multiple blood meals in individual bugs. Our results demonstrate the reliability and descriptive uses of our method.

Calmodulin Polymerase Chain Reaction-Restriction Fragment Length Polymorphism for Leishmania Identification and Typing

A precise identification of Leishmania species involved in human infections has epidemiological and clinical importance. Herein, we describe a preliminary validation of a restriction fragment length polymorphism assay, based on the calmodulin intergenic spacer region, as a tool for detecting and typing Leishmania species. After calmodulin amplification, the enzyme HaeIII yielded a clear distinction between reference strains of Leishmania mexicana, Leishmania amazonensis, Leishmania infantum, Leishmania lainsoni, and the rest of the Viannia reference species analyzed. The closely related Viannia species: Leishmania braziliensis, Leishmania panamensis, and Leishmania guyanensis, are separated in a subsequent digestion step with different restriction enzymes. We have developed a more accessible molecular protocol for Leishmania identification/typing based on the exploitation of part of the calmodulin gene. This methodology has the potential to become an additional tool for Leishmania species characterization and taxonomy.

Clonal outbreak of Plasmodium falciparum infection in eastern Panama

Identifying the source of resurgent parasites is paramount to a strategic, successful intervention for malaria elimination. Although the malaria incidence in Panama is low, a recent outbreak resulted in a 6-fold increase in reported cases. We hypothesized that parasites sampled from this epidemic might be related and exhibit a clonal population structure. We tested the genetic relatedness of parasites, using informative single-nucleotide polymorphisms and drug resistance loci. We found that parasites were clustered into 3 clonal subpopulations and were related to parasites from Colombia. Two clusters of Panamanian parasites shared identical drug resistance haplotypes, and all clusters shared a chloroquine-resistance genotype matching the pfcrt haplotype of Colombian origin. Our findings suggest these resurgent parasite populations are highly clonal and that the high clonality likely resulted from epidemic expansion of imported or vestigial cases. Malaria outbreak investigations that use genetic tools can illuminate potential sources of epidemic malaria and guide strategies to prevent further resurgence in areas where malaria has been eliminated.

Flight behavior and performance of Rhodnius pallescens (Hemiptera: Reduviidae) on a tethered flight mill

ABSTRACT Flight dispersal of the triatomine bug species Rhodnius pallescens Barber, the principal vector of Chagas disease in Panama, is an important mechanism for spreading Trypanosoma cruzi, causative agent of Chagas disease. This study measures R. pallescens flight performance using a tethered flight mill both when uninfected, and when infected with T. cruzi or Trypanosoma rangeli. Forty-four out of the 48 (91.7%) insects initiated flight across all treatments, and trypanosome infection did not significantly impact flight initiation. Insects from all treatments flew a cumulative distance ranging from 0.5 to 5 km before fatiguing. The median cumulative distance flown before insect fatigue was higher in T. cruzi- and T. rangeli-infected insects than in control insects; however, this difference was not statistically significant. There was a positive relationship between parasite load ingested and time until flight initiation in T. rangeli-infected bugs, and T. rangeli- and T. cruzi-infected females flew significantly faster than males at different time points. These novel findings allow for a better understanding of R. pallescens dispersal ability and peridomestic management strategies for the prevention of Chagas disease in Panama.

Enteric parasites and enteroaggregative Escherichia coli in children from Cañazas County, Veraguas Province, Panama

This study was designed to examine the height-for-age z-scores (HAZ), and the prevalence of intestinal inflammation, gastrointestinal infections with parasites, and enteroaggregative Escherichia coli (EAEC) in rural Panamanian children. Stool microscopy and polymerase chain reaction (PCR) testing for EAEC detected Giardia lamblia (32%, 32 of 100) and EAEC (13%, 11 of 87) in the study participants, respectively. Anthropometric analyses showed that those children who were > 12 months of age had lower HAZ scores (mean of -1.449) than the reference population. As a group, the children in the study 1 to 5 years of age did not show recovery from the previously mentioned decline in terms of their HAZ. The HAZ means of the children infected with G. lamblia, EAEC, and Ascaris lumbricoides were -1.49, -1.67, and -2.11, respectively. Furthermore, the study participants with A. lumbricoides and EAEC infections in the presence of lactoferrin showed another decrease of 0.19 and 0.13, respectively, in their HAZ means.

Genetic, cytogenetic and morphological trends in the evolution of the Rhodnius (Triatominae: Rhodniini) trans-Andean group

The Rhodnius Pacific group is composed of three species: Rhodnius pallescens, R. colombiensis and R. ecuadoriensis, which are considered important vectors of trypanosomes (Trypanosoma cruzi and T. rangeli) infecting humans. This group is considered as a recent trans-Andean lineage derived from the widespread distributed sister taxa R. pictipes during the later uplift of northern Andes mountain range. The widest spread species R. pallescens may be a complex of two divergent lineages with different chromosomal attributes and a particular biogeographical distribution across Central America and Colombia with several southern populations in Colombia occupying the same sylvatic habitat as its sister species R. colombiensis. Although the taxonomy of Rhodnius Pacific group has been well studied, the unresolved phylogenetic and systematic issues are the target of this paper. Here we explore the molecular phylogeography of this species group analyzing two mitochondrial (ND4 and cyt b) and one nuclear (D2 region of ribosomal 28S gene) gene sequences. The molecular analyses suggest an early divergence of the species R. ecuadoriensis and R. colombiensis, followed by a recent expansion of R. pallescens lineages. The phylogenetic relationship between sympatric R. pallescens Colombian lineage and R. colombiensis was further explored using wing morphometry, DNA genome size measurements, and by analyzing chromosomal behavior of hybrids progeny obtained from experimental crosses. Our results suggest that the diversification of the two R. pallescens lineages was mainly influenced by biogeographical events such as (i) the emergence of the Panama Isthmus, while the origin and divergence of R. colombiensis was associated with (ii) the development of particular genetic and chromosomal features that act as isolation mechanisms from its sister species R. pallescens (Colombian lineage). These findings provide new insights into the evolution of the Rhodnius Pacific group and the underlying biological processes that occurred during its divergence.

The calmodulin intergenic spacer as molecular target for characterization of Leishmania species

Background

Human leishmaniasis is a neglected disease caused by parasites of the genus Leishmania. Clinical aspects of this disease can vary significantly, reflecting the wide range of parasites in the genus Leishmania. Knowing accurately the Leishmania species infecting humans is important for clinical case management and evaluation of epidemiological risk. Calmodulin is an essential gene in trypanosomatids that modulates the calcium metabolism in various cellular activities. Despite its strong conservation in trypanosomatids, it has been recently observed that its untranslated regions (UTR) diverge among species.

Methods

In this study we analyzed the sequences and the absolute dinucleotide frequency of the intergenic spacer of the calmodulin gene (containing both, 3′ and 5′UTR) in nine reference Leishmania species and ten clinical isolates obtained from patients with cutaneous leishmaniasis.

Results

We show that the short calmodulin intergenic spacers exhibit features that make them interesting for applications in molecular characterization and phylogenetic studies of Leishmania. Dendrograms based on sequence alignments and on the dinucleotide frequency indicate that this particular region of calmodulin gene might be useful for species typing between the Leishmania and Viannia subgenera.

Conclusions

Mutations and composition of the calmodulin intergenic spacer from Leishmania species might have taxonomic value as parameters to define if an isolate is identical to a certain species or belongs to one of the two current subgenera.

Leishmaniasis sand fly vector density reduction is less marked in destitute housing after insecticide thermal fogging

BACKGROUND

Insecticide thermal fogging (ITF) is a tool to control vector borne diseases. Insecticide application success for vector control has been associated with housing materials and architecture. Vector abundance is correlated with weather changes. Nevertheless, housing quality and weather impacts on vector abundance have been unaccounted for in most New World insecticide control trials for leishmaniasis vectors.

METHODS

We conducted a 15 month insecticide control trial that included two deltamethrin [6 mg a.i.m-2] based ITF interventions in 12 of 24 monitored houses at Trinidad de Las Minas, a hyperendemic cutaneous leishmaniasis transmission village in western Panamá. During the study we followed sand fly (SF) abundance, keeping track of rainfall and quantified housing quality using an index based on architecture and construction materials.

RESULTS

We found a 50 to 80% reduction in SF density in the fogged houses when compared with control houses, while controlling for seasonal changes in SF abundance associated with rainfall. We found heterogeneities in the reductions, as abundance changed according to SF species: Lutzomyia gomezi, Lu. panamensis, Lu. dysponeta and Lu. triramula reduced in density between 40% and 90% after ITF. In contrast, Lu. trapidoi density increased 5% after ITF. Differences in the impact of ITF were associated with housing quality, the most destitute houses, i.e., those with features that ease insect entrance, had a disproportionally larger SF abundance, in some cases with increased domiciliary SF density following the ITF.

CONCLUSION

Our results suggest the potential of insecticide application to control SF density and leishmaniasis transmission could depend on housing quality beyond insecticide efficiency.

Clinical cutaneous leishmaniasis rates are associated with household Lutzomyia gomezi, Lu. Panamensis, and Lu. trapidoi abundance in Trinidad de Las Minas, western Panama

American cutaneous leishmaniasis (ACL) transmission patterns have been increasingly associated with domestic and peridomestic environments. Here, we present results from an epidemiological survey of 94 people from 24 households in Trinidad de Las Minas, western Panama. We studied the role of sand fly abundance, housing quality, peridomicile landscape matrix, and vegetation structure on shaping household clinical ACL rate patterns at Trinidad de Las Minas. We found that sand fly abundance was significantly associated with household clinical ACL rates, with a 6% rate increase for each additional Lutzomyia gomezi sand fly found inside a domicile.

Changes in phlebotomine sand fly species composition following insecticide thermal fogging in a rural setting of Western panamá

American Cutaneous Leishmaniasis, ACL, is a zoonotic disease with a large richness of co-occurring vector species in transmission foci. Here, we describe changes in patterns of phlebotomine sand fly (Diptera: Psychodidae: Phlebotominae) species composition at the village of Trinidad de Las Minas, Capira, Panamá, a hyperendemic focus of ACL transmission, subjected to a vector control intervention with insecticide thermal fogging (ITF). Our study setting consisted of 24 houses, 12 subjected to two rounds of ITF and 12 kept as control. During 15 months (April 2010- June 2011) we monitored sand fly species composition and abundance with modified HP light traps inside (domicile) and outside (peridomicile) the studied houses. From 5628 sand flies collected, we were able to identify 5617 of the samples into 24 species, a number of species close to 25±1.6, the estimate from the Chao2 Index. The most abundant species were Lutzomya trapidoi (20%), Lu. gomezi (20%) and Lu. triramula (20%). Cluster analyses showed that most of the 24 houses had high similarity in relative abundance patterns of the six most common species, with only few peripheral houses not following the main cluster pattern. We also found that species richness was decreased to 22 species in the fogged houses, of which only 19 were found in the domiciliary environment. Changes in species richness were especially notorious at the end of the wet season. Our results suggest that species richness can decrease following ITF in domiciliary environments, primarily affecting the less common species.

Evaluation of PCR for cutaneous leishmaniasis diagnosis and species identification using filter paper samples in Panama, Central America

Cutaneous leishmaniasis (CL) is a major vectorborne disease in Panama. In this study, the diagnostic performance and usefulness of two DNA extraction procedures from skin scraping samples collected on FTA filter paper for subsequent PCR diagnosis of CL was evaluated. A positive CL laboratory diagnosis was based on a positive parasitological test (Giemsa-stained smears or in vitro culture) and/or positive PCR test performed from skin scrapings collected in TE buffer (PCR-TE). Of 100 patients with skin lesions suggestive of CL, 82 (82%) were confirmed as CL positive. The sensitivity was calculated for each of the PCR approaches from samples collected on filter paper. The highest sensitivity was achieved by PCR-FTA processed by Chelex 100 (PCR-Chelex) (0.94). PCR-FTA extracted using the FTA purification reagent presented a lower sensitivity (0.60). Good concordance between routine PCR-TE and PCR-Chelex was observed (percent agreement=0.88, κ index=0.65). In conclusion, use of FTA filter paper for skin scraping collection combined with PCR is a reliable and convenient method for CL diagnosis in Panama, with comparable performance to the routine PCR method and with improved sensitivity compared with those of conventional parasitological methods.

A new endemic focus of Chagas disease in the northern region of Veraguas Province, Western Half Panama, Central America

BACKGROUND

Chagas disease was originally reported in Panama in 1931. Currently, the best knowledge of this zoonosis is restricted to studies done in historically endemic regions. However, little is known about the distribution and epidemiology of Chagas disease in other rural areas of the country.

METHODS AND FINDINGS

A cross-sectional descriptive study was carried out between May 2005 - July 2008 in four rural communities of the Santa Fe District, Veraguas Province. The study included an entomologic search to collect triatomines, bloodmeal type identification and infection rate with trypanosomes in collected vectors using a dot- blot and PCR analysis, genotyping of circulating Trypanosoma cruzi (mini-exon gene PCR analysis) and the detection of chagasic antibodies among inhabitants. The vector Rhodnius pallescens was more frequently found in La Culaca and El Pantano communities (788 specimens), where it was a sporadic household visitor. These triatomines presented darker coloration and larger sizescompared with typical specimens collected in Central Panama. Triatoma dimidiata was more common in Sabaneta de El Macho (162 specimens). In one small sub-region (El Macho), 60% of the houses were colonized by this vector. Of the examined R. pallescens, 54.7.0% (88/161) had fed on Didelphis marsupialis, and 24.6% (34/138) of T. dimidiata specimens collected inside houses were positive for human blood. R. pallescens presented an infection index with T. cruzi of 17.7% (24/136), with T. rangeli of 12.5% (17/136) and 50.7% (69/136) were mixed infections. In 117 T. dimidiata domestic specimens the infection index with T. cruzi was 21.4%. Lineage I of T. cruzi was confirmed circulating in these vectors. A T. cruzi infection seroprevalence of 2.3% (24/1,056) was found in this population.

CONCLUSIONS

This is the first report of Chagas disease endemicity in Santa Fe District, and it should be considered a neglected public health problem in this area of Panama.

Prospects for malaria elimination in non-Amazonian regions of Latin America

Latin America contributes 1-1.2 million clinical malaria cases to the global malaria burden of about 300 million per year. In 21 malaria endemic countries, the population at risk in this region represents less than 10% of the total population exposed worldwide. Factors such as rapid deforestation, inadequate agricultural practices, climate change, political instability, and both increasing parasite drug resistance and vector resistance to insecticides contribute to malaria transmission. Recently, several malaria endemic countries have experienced a significant reduction in numbers of malaria cases. This is most likely due to actions taken by National Malaria Control Programs (NMCP) with the support from international funding agencies. We describe here the research strategies and activities to be undertaken by the Centro Latino Americano de Investigación en Malaria (CLAIM), a new research center established for the non-Amazonian region of Latin America by the National Institute of Allergy and Infectious Diseases (NIAID). Throughout a network of countries in the region, initially including Colombia, Guatemala, Panama, and Peru, CLAIM will address major gaps in our understanding of changing malaria epidemiology, vector biology and control, and clinical malaria mainly due to Plasmodium vivax. In close partnership with NMCPs, CLAIM seeks to conduct research on how and why malaria is decreasing in many countries of the region as a basis for developing and implementing new strategies that will accelerate malaria elimination.

Lack of association between IL-6-174G/C gene polymorphism and Chagas disease

The aim of this study was to investigate the role of the IL-6-174G/C gene polymorphism in susceptibility/resistance to Trypanosoma cruzi infection in two independent cohorts from Colombia and Peru. We determined the IL-6-174G/C genotypes in a sample of 399 seronegative individuals and 317 serologically positive patients from Colombia and Peru. All individuals are from regions where T. cruzi infection is endemic. No statistically significant differences in the frequency of IL-6-174G/C gene polymorphism between chagasic patients and controls or between asymptomatic and individuals with cardiomyopathy were observed. Our results do not support an evidence for a major role contribution of this IL-6 gene polymorphism in the susceptibility to or clinical manifestations of Chagas disease in these studied cohorts.

Molecular epidemiology of American tegumentary leishmaniasis in Panama

American tegumentary leishmaniasis is an increasing public health problem in Panama. This study describes the clinical characteristics and the molecular epidemiology of leishmaniasis in Panama over a 5-year period (2004-2008). Additionally, we applied a polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP)-based assay to identify Leishmania species in clinical isolates, skin scrapings, and sandflies specimens. Whereas 60.3% of cases were detected with conventional parasitologic techniques (smear or in vitro culture), the PCR detected 72% positive patients. Our clinical-epidemiologic data corroborate the high incidence of L. (Viannia) panamensis and provide evidence of peridomestic and/or domestic transmission. Mucosal involvement was observed in 4.2% of the patients. The overall natural infection rate with Leishmania in 103 pools of sandflies was 0.46%. Lutzomyia gomezi and Lutzomya panamensis were the prevalent species incriminated as vectors at the capture sites in central Panama. This study contributes to a better knowledge of the current epidemiology of tegumentary leishmaniasis in Panama.

Revising antimalarial drug policy in Central America: experience in Panama

Panama is the first country in the Central American region that has officially discarded chloroquine as a first-line drug to treat Plasmodium falciparum cases. Here we describe the clinical and molecular findings from autochthonous P. falciparum fatal cases, and the epidemiological situation that led to a change in the national antimalarial drug policy. Our results illustrate the potential pathogenicity of the strain of P. falciparum circulating in the country and provide molecular evidence of parasite resistance to chloroquine and antifolate drugs. The public health threats of these findings for the Central American region are discussed.

Prevalence of Plasmodium falciparum mutations associated with antimalarial drug resistance during an epidemic in Kuna Yala, Panama, Central America

A molecular epidemiology study was conducted to determine the distribution of antimalarial drug resistance alleles among field isolates of Plasmodium falciparum. Samples were obtained during an epidemic affecting Kuna Amerindians in Panama. A high prevalence of mutations associated with chloroquine, pyrimethamine, and sulfadoxine was observed. Genotype analysis of msp2 revealed a low genetic diversity of P. falciparum parasites circulating in the studied area. The public health implications of these findings for the Central American region are discussed.

No evidence for association of the inducible nitric oxide synthase promoter polymorphism with Trypanosoma cruzi infection

The purpose of the present study was to address the possible contribution of the (CCTTT)n microsatellite polymorphism in the NOS2 promoter region to the susceptibility to chronic Trypanosoma cruzi infection and to Chagas' disease related cardiomyopathy. We determined the (CCTTT)n genotypes in a sample of 76 serologically positive chagasic individuals and in 78 healthy controls. No statistically significant differences were observed between total chagasic patients and healthy controls with regard to frequency of the (CCTTT)n microsatellite repeat of any given length. Likewise, we found no differences in the distribution of the (CCTTT)n microsatellite repeats between seropositives without manifestations of the disease and those with chagasic cardiomyopathy. Our data suggest that the NOS2 promoter pentanucleotide microsatellite polymorphisms analyzed do not play a major role in the pathogenesis of chronic T. cruzi infection in this Peruvian sample.

Chemokine receptor CCR5 polymorphisms and Chagas' disease cardiomyopathy

In this study we investigated the possible role of two CCR5 gene polymorphisms, CCR5Delta32 deletion and CCR5 59029 A-->G promoter point mutation, in determining the susceptibility to Trypanosoma cruzi infection as well as in the development of chagasic heart disease. These CCR5 polymorphisms were assessed in 85 seropositive (asymptomatic, n=53; cardiomyopathic, n=32) and 87 seronegative individuals. The extremely low frequency (0.009) of the CCR5Delta32 allele in our population did not allow us to analyse its possible influence on T. cruzi infection. We found no differences in the distribution of CCR5 59029 promoter genotype or phenotype frequencies between total chagasic patients and controls. However, we observed that the CCR5 59029-A/G genotype was significantly increased in asymptomatic with respect to cardiomyopathic patients (P=0.02; OR=0.33, 95% CI 0.10-0.94). In addition, the presence of the CCR5 59029-G allele was also increased in asymptomatics when compared with cardiomyopathics (P=0.02; OR=0.35, 95% CI 0.12-0.96). Our data suggest that the CCR5 59029 promoter polymorphism may be involved in a differential susceptibility to chagasic cardiomyopathy.

Lack of association between NRAMP1 gene polymorphisms and Trypanosoma cruzi infection

Genetic analysis in mice and humans have established the key role of the human natural resistance-associated macrophage protein 1 (NRAMP1) in resistance to intracellular infections. In the present study we investigated whether four NRAMP1 polymorphisms (5'(GT)n, -236 C-->T, D543N, and 3'UTR deletion) were important in determining the susceptibility to Trypanosoma cruzi infections as well as in the development of chagasic cardiac disease. Genotyping for these variants was assessed in 83 seropositive (asymptomatic, n=51, cardiomyopathic, n=32) and 85 seronegative individuals from a Peruvian population where T. cruzi is endemic. No statistically significant differences either between patients and controls or between asymptomatic and cardiomyopathic individuals were observed with respect to NRAMP1 variants. Our data suggest that the NRAMP1 genetic polymorphism analysed do not play a major role in the pathogenesis of T. cruzi infection in this Peruvian sample.

HLA class I and class II allele distribution in the Peruvian population

The distribution of HLA-A, -B, -C, -DRB1 and -DQB1 alleles in the Peruvian population was studied and compared with those of other populations in order to provide further information about their anthropological origin. Our data are consistent with the Mestizo character of this population. In terms of genetic distance Peruvians are closest to Bolivians, which is in agreement with the geographical location and the cultural and anthropological background of the two human groups. Several HLA-B alleles originally described in genetically isolated Amerindian tribes are also present in the sample studied here. This fact and the reported finding of these alleles in several Amerindian groups suggests that they were present in the first wave of humans that populated South America (Paleoindians) before they split to give rise to the different South American tribes.