The sudden appearance of chytridiomycosis, the cause of amphibian deaths and population declines in several continents, suggests that its etiologic agent, the amphibian chytrid Batrachochytrium dendrobatidis, was introduced into the affected regions. However, the origin of this virulent pathogen is unknown. A survey was conducted of 697 archived specimens of 3 species of Xenopus collected from 1879 to 1999 in southern Africa in which the histologic features of the interdigital webbing were analyzed. The earliest case of chytridiomycosis found was in a Xenopus laevis frog in 1938, and overall prevalence was 2.7%. The prevalence showed no significant differences between species, regions, season, or time period. Chytridiomycosis was a stable endemic infection in southern Africa for 23 years before any positive specimen was found outside Africa. We propose that Africa is the origin of the amphibian chytrid and that the international trade in X. laevis that began in the mid-1930s was the means of dissemination. (+info)
The ants of North and Central America: the genus Mycocepurus (Hymenoptera: Formicidae).
(50/268)
We provide a review of the North American ants (north of Colombia) of the ant genus Mycocepurus, including keys to the workers and females, illustrations and distribution maps. The distribution of M. tardus is extended to Nicaragua and Costa Rica. The female of M. curvispinosus is described. (+info)
Initial acculturation and HIV risk among new Hispanic immigrants.
(51/268)
PURPOSE: Research on the initial stage of acculturation of new immigrants is crucial for identifying AIDS prevention policies and priorities for this vulnerable population. METHODS: This study employed an exploratory approach and qualitative data collection methods to identify and describe social and behavioral factors influencing risk for HIV infection among recent Hispanic immigrants (<3 years in the United States). Immigrants from Guatemala, El Salvador, Honduras, the Dominican Republic and Mexico were interviewed in urban, suburban and semirural settings in the New York Metropolitan Area. Data were collected through ethnographic fieldwork, in-depth interviews (N=51), focus groups (N=11; total number of participants=86) and individual interviews with health and social service providers (N=26). RESULTS: Initial stages of acculturation for immigrants reflect both retention and change in attitudes and behaviors involving their mental health, gender role norms, social and sexual behavior, and alcohol and other drug use. Current living environments may introduce conditions affecting HIV risk and prevention, while sustained connections to countries of origin may support retention of attitudes and behaviors with positive and negative risk implications. CONCLUSIONS: Specific epidemiological, environmental, economic, social and psychosocial factors are identified that provide the context for risk and prevention. The challenges and opportunities faced by these new communities must be distinguished from those of more acculturated immigrant populations if culturally appropriate interventions are to be developed. (+info)
Domestication of a Mesoamerican cultivated fruit tree, Spondias purpurea.
(52/268)
Contemporary patterns of genetic variation in crops reflect historical processes associated with domestication, such as the geographic origin(s) of cultivated populations. Although significant progress has been made in identifying several global centers of domestication, few studies have addressed the issue of multiple origins of cultivated plant populations from different geographic regions within a domestication center. This study investigates the domestication history of jocote (Spondias purpurea), a Mesoamerican cultivated fruit tree. Sequences of the chloroplast spacer trnG-trnS were obtained for cultivated and wild S. purpurea trees, two sympatric taxa (Spondias mombin var. mombin and Spondias radlkoferi), and two outgroups (S. mombin var. globosa and Spondias testudinus). A phylogeographic approach was used and statistically significant associations of clades and geographical location were tested with a nested clade analysis. The sequences confirm that wild populations of S. purpurea are the likely progenitors of cultivated jocote trees. This study provides phylogeographic evidence of multiple domestications of this Mesoamerican cultivated fruit tree. Haplotypes detected in S. purpurea trees form two clusters, each of which includes alleles recovered in both cultivated and wild populations from distinct geographic regions. Cultivated S. purpurea populations have fewer unique trnG-trnS alleles than wild populations; however, five haplotypes were absent in the wild. The presence of unique alleles in cultivation may reflect contemporary extinction of the tropical dry forests of Mesoamerica. These data indicate that some agricultural habitats may be functioning as reservoirs of genetic variation in S. purpurea. (+info)
Recombination hotspots and population structure in Plasmodium falciparum.
(53/268)
Understanding the influences of population structure, selection, and recombination on polymorphism and linkage disequilibrium (LD) is integral to mapping genes contributing to drug resistance or virulence in Plasmodium falciparum. The parasite's short generation time, coupled with a high cross-over rate, can cause rapid LD break-down. However, observations of low genetic variation have led to suggestions of effective clonality: selfing, population admixture, and selection may preserve LD in populations. Indeed, extensive LD surrounding drug-resistant genes has been observed, indicating that recombination and selection play important roles in shaping recent parasite genome evolution. These studies, however, provide only limited information about haplotype variation at local scales. Here we describe the first (to our knowledge) chromosome-wide SNP haplotype and population recombination maps for a global collection of malaria parasites, including the 3D7 isolate, whose genome has been sequenced previously. The parasites are clustered according to continental origin, but alternative groupings were obtained using SNPs at 37 putative transporter genes that are potentially under selection. Geographic isolation and highly variable multiple infection rates are the major factors affecting haplotype structure. Variation in effective recombination rates is high, both among populations and along the chromosome, with recombination hotspots conserved among populations at chromosome ends. This study supports the feasibility of genome-wide association studies in some parasite populations. (+info)
Validation of a rapid and reliable test for diagnosis of chagas' disease by detection of Trypanosoma cruzi-specific antibodies in blood of donors and patients in Central America.
(54/268)
In this study we compared the performance of the Chagas Stat-Pak rapid immunochromatographic test with a standard enzyme-linked immunosorbent assay (ELISA) in the serodiagnosis of Chagas' disease in Central America. Out of 3,400 blood donor samples, 156 (4.6%) were positive in both assays. Three sera out of 2,084 samples from reference laboratories were negative with the rapid test but positive with the ELISA (99.8% agreement). Agreement of 100% between the two tests was observed with 339 additional sera from patients with cardiopathies and 175 sera from potential blood donors in emergency surgical cases occurring on weekends or at night. In conclusion, Chagas Stat-Pak showed 99.6% and 99.9% sensitivity and specificity, respectively, when assayed with 5,998 serum samples. It is a sensitive and specific alternative to the ELISA, as required in medical emergencies and blood screenings in Central America. (+info)
Epidemiology of neurocysticercosis in Houston, Texas.
(55/268)
We identified 114 patients with neurocysticercosis admitted to Ben Taub General Hospital in Houston, Texas between January 1994 and June 1997. Most of these patients were born in Mexico (78%) or Central America (16%), but 6% were born in the United States. Review of neurology clinic records identified 54 patients diagnosed with neurocysticercosis, representing 2% of all neurology clinic patients and 16% of all Hispanics diagnosed with seizures. Forty-one patients were interviewed and all reported significant risk factors for infection, including ingestion of undercooked pork, pig husbandry, immigration from and frequent travel to villages in disease-endemic areas, or personal/family history of taeniasis. Among Mexican immigrants, most were born in rural areas in Central (31%) or north central Mexico (38%). Significantly fewer of the patients were from the border states (15%). The median period from immigration to diagnosis was 58 months, but it was 28 months for the 13 patients who had not left the United States after immigration. Although neurocysticercosis is being diagnosed with increasing frequency in the United States, acquisition of infection is still strongly associated with pig husbandry in rural Latin America, with little evidence of local transmission. Even among urban immigrants to the United States and United States-born cases, there is close ongoing contact with disease-endemic villages. (+info)
Montane speciation patterns in Ithomiola butterflies (Lepidoptera: Riodinidae): are they consistently moving up in the world?
(56/268)
Tropical lowland areas have often been seen as the centres of terrestrial species proliferation, but recent evidence suggests that young species may be more frequent in montane areas. Several montane speciation modes have been proposed, but their relative frequencies and predominant evolutionary sequence remain unclear because so few biogeographic and phylogenetic studies have tested such questions. I use morphological data to generate a phylogenetic hypothesis for all 11 species of the riodinid butterfly genus Ithomiola (Riodininae: Mesosemiini: Napaeina). These species are shown here to be all strictly geographically and elevationally allo- or parapatrically distributed with respect to their closest relatives in lowland and montane regions throughout the Neotropics. The overwhelming pattern in Ithomiola is of repeated upward parapatric speciation across an elevational gradient, and the genus appears to provide the clearest example to date of vertical montane speciation. All of the young derived species are montane and all of the old basal species are confined to the lowlands, supporting the hypothesis of montane regions largely as 'species pumps' and lowland regions as 'museums'. Possible reasons for the post-speciation maintenance of parapatric ranges in Ithomiola are discussed. (+info)