Similar non-random processes maintain diversity in two tropical rainforests.
(9/1413)
Quadrat-based analysis of two rainforest plots of area 50 ha, one in Panama (Barro Colorado Island, BCI) and the other in Malaysia (Pasoh), shows that in both plots recruitment is in general negatively correlated with both numbers and biomass of adult trees of the same species in the same quadrat. At BCI, this effect is not significantly influenced by treefall gaps. In both plots, recruitment of individual species is negatively correlated with the numbers of trees of all species in the quadrats, but not with overall biomass. These observations suggest, but do not prove, widespread frequency-dependent effects produced by pathogens and seed-predators that act most effectively in quadrats crowded with trees. Within-species correlations of mortality with numbers or biomass are not found in either plot, indicating that most frequency-dependent mortality takes place before the trees reach 1 cm in diameter. Stochastic effects caused by BCI's more rapid tree turnover may contribute to a larger variance in diversity from quadrat to quadrat at BCI, although they are not sufficient to explain why BCI has fewer than half as many tree species as Pasoh. Finally, in both plots quadrats with low diversity show a significant increase in diversity over time, and this increase is stronger at BCI. This process, like the frequency-dependence, will tend to maintain diversity over time. In general, these non-random forces that should lead to the maintenance of diversity are slightly stronger at BCI, even though the BCI plot is less diverse than the Pasoh plot. (+info)
Leptospiral infection among primitive tribes of Andaman and Nicobar Islands.
(10/1413)
The Andaman islands were known to be endemic for leptospirosis during the early part of the century. Later, for about six decades no information about the status of the disease in these islands was available. In the late 1980s leptospirosis reappeared among the settler population and several outbreaks have been reported with high case fatality rates. Besides settlers, these islands are the home of six primitive tribes of which two are still hostile. These tribes have ample exposure to environment conducive for transmission of leptospirosis. Since no information about the level of endemicity of the disease among the tribes is available, a seroprevalence study was carried out among all the accessible tribes of the islands. A total of 1557 serum samples from four of the tribes were collected and examined for presence of antileptospiral antibodies using Microscopic Agglutination Test (MAT) employing 10 serogroups as antigens. An overall seropositivity rate of 191% was observed with the highest rate of 53.5% among the Shompens. The seropositivity rates in the other tribes were 16.4% among Nicobarese, 222% among the Onges and 14.8% among the Great Andamanese. All of the tribes except the Onges showed a similar pattern of change in the seroprevalence rates with age. The prevalence rates were rising from low values among children to reach a peak in those aged 2140 years and then declined. Among Onges the seroprevalence rates continued to rise beyond 40 years. In all the tribes, seroprevalence rates were found to be significantly higher among the males. The commonest serogroups encountered were Australis followed by Grippotyphosa, Icterohaemorrhagiae, Pomona and Canicola. (+info)
Relationship between aneurysmal subarachnoid hemorrhage and climatic conditions in the subtropical region, Amami-Oshima, in Japan.
(11/1413)
Epidemiological studies of the relationship between climate and the onset of aneurysmal subarachnoid hemorrhage (SAH) have been reported in the temperate and subarctic latitudes. However, the relationship between the incidence of aneurysmal SAH and the climatic variations in the subtropical region remains uncertain. Epidemiological analysis requires study of an extremely isolated area. This study analyzed the relationship between the onset of aneurysmal SAH and climatic conditions in the isolated subtropical island of Amami-Oshima in Japan. During an 11-year period from 1986 to 1996, 210 patients with a primary diagnosis of aneurysmal SAH were identified by computed tomography and angiography. The mean annual age-adjusted incidence of aneurysmal SAH was 15.5 per 100,000 population (10.4 for males and 20.6 for females). No significant seasonal variations in the incidence of aneurysmal SAH and admission clustering were observed in males (p > 0.05) or females (p > 0.05). Furthermore, temperature, atmospheric pressure, and relative humidity were not significantly correlated with the monthly incidence of aneurysmal SAH. However, the occurrence of aneurysmal SAH tended to be higher in both females and the elderly during the winter and spring seasons and not during other seasons. This study indicates that seasonal and climatic conditions do not strongly contribute to the incidence of aneurysmal SAH in subtropical regions. However, elderly people are affected more by climatic conditions than young people. (+info)
Association of seasonal reproductive patterns with changing food availability in an equatorial carnivore, the spotted hyaena (Crocuta crocuta).
(12/1413)
Reproductive seasonality was examined in an equatorial population of free-living spotted hyaenas (Crocuta crocuta) in Kenya. The study population was observed continuously for 10 years, during which time the dates of all births, conceptions, weanings, and cub deaths were recorded. Local prey abundance was estimated two to four times per month, and rainfall was recorded daily throughout the study period. Births occurred during every month of the year, but a distinct trough in births occurred from February to May. This trough occurred approximately one gestation period after the phase of the annual cycle during which prey animals were least abundant in the home range of the hyaenas, and conceptions occurred most frequently when food abundance was greatest. Neither rainfall nor cub mortality were correlated with births or conceptions. Thus, although spotted hyaenas are capable of breeding throughout the year, they exhibit a moderate degree of seasonality that most likely reflects responses to seasonal variation in energy availability. (+info)
Temporal and spatial patterns of malaria reinfection in northeastern Venezuela.
(13/1413)
We stratified the risk of malaria transmission (Plasmodium vivax) in 35 villages along a coastal range in northeastern Venezuela (51 km2) where the main vector is the mosquito Anopheles aquasalis. After 20 years without local malaria transmission, reinfection of the entire area occurred from May to December 1985 by local (continuous) and jump (discontinuous) dispersal. Epidemiologic, environmental, and vector variables were investigated with the aid of a Geographic Information System. Risk factors for malaria transmission were human population density, proximity to pre-adult mosquito habitats (< 500 m), and the number of pre-adult habitats nearby. Most inhabitants, immature mosquito habitats, and malaria cases were located at low elevations and on gentle slopes. High prevalence of malaria during the dry seasons was associated with the presence of permanent bodies of water containing An. aquasalis. Occurrence of a La Nina event in 1988 (wet and cool phase of the El Nino Southern Oscillation) triggered malaria transmission to unusually high levels, consolidating infection in the area, and rendering traditional control efforts useless. We recommend tracking malaria persistence per village and associated risk factors as methods to reduce the cost of malaria control programs. (+info)
Dengue seroconversion among Israeli travelers to tropical countries.
(14/1413)
We tested for dengue seroconversion among 104 Israeli young adults who traveled to tropical countries for at least 3 months. Seven (6. 7%) seroconverted during travel; four (3.8%) had immunoglobulin (Ig) M antibodies; one was symptomatic with borderline IgM and a rise in IgG; two others (1.9%) had a rise in IgG titers, without detectable IgM. All four IgM-positive patients had traveled to Southeast Asia. (+info)
An evaluation of mattress encasings and high efficiency particulate filters on asthma control in the tropics.
(15/1413)
The effect of two allergen avoidance modalities, Allergy Control Covers (ACC) and High Efficiency Particulate Filters (HEPA) on asthma control in children were evaluated. This was an open study involving 24 dust mite sensitive asthmatic children. Following a 4 week run-in period, the subjects were randomly allocated to use mattresses fitted with ACC (n = 6), HEPA filters in their bedrooms (n = 12) or act as controls (n = 6) for a study duration of 4 months. Measurements of the major Dermatophagoides spp. mite allergens, Der p 1 and Der f 1, levels in dust samples obtained from mattresses were made at baseline, 1, 2 and 4 months post implementation. Daily symptom scores including morning and evening peak flow readings, and monthly spirometry and exercise bronchoprovocation tests were carried out Our results showed that dust mite allergen levels in mattresses fell at 1 and 2 months post implementation in the ACC group (p<0.05). In contrast, no decrease in allergen levels was seen in the HEPA and control group. At the end of the 16 weeks, only the ACC group showed improvement in FEV1 and reduction in diurnal peak expiratory flow rate (p<0.05). Improvement in mean symptom scores was also observed for both the ACC and HEPA groups, but not the control groups (p<0.05). Although the numbers in this study were small, the results Indicate that the effectiveness on mite exposure barrier covers was short-lived, and the improvement in asthma control though documented was not obvious. (+info)
An Advisory Committee Statement (ACS). Committee to Advise on Tropical Medicine and Travel (CATMAT). Statement on meningococcal vaccination for travellers.
(16/1413)
The Committee to Advise on Tropical Medicine and Travel (CATMAT) provides Health Canada with ongoing and timely medical, scientific, and public-health advice relating to tropical infectious disease and health risks associated with international travel. Health Canada acknowledges that the advice and recommendations set out in this statement are based upon the best current available scientific knowledge and medical practices, and is disseminating this document for information purposes to both travellers and the medical community caring for travellers. Persons administering or using drugs, vaccines, or other products should also be aware of the contents of the product monograph(s) or other similarly approved standards or instructions for use. Recommendations for use and other information set out herein may differ from that set out in the product monograph(s) or other similarly approved standards or instructions for use by the licensed manufacturer(s). Manufacturers have sought approval and provided evidence as to the safety and efficacy of their products only when used in accordance with the product monographs or other similarly approved standards or instructions for use. (+info)