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At least 1,135 records · Page 63Linked to original sources
PubMed2000

Persistence of Anopheles arabiensis during the severe dry season conditions in Senegal: an indirect approach using microsatellite loci.

Variation at nine microsatellite loci was investigated to understand how Anopheles arabiensis populations survive the dry season in the sahelian region of Senegal. Low estimates of genetic differentiation (F(ST) = 0.012, R(ST) = 0.009) between two populations, 250 km apart, suggested extensive gene flow across this distance. Despite extreme seasonal fluctuation in abundance with dry season minima in which mosquitoes virtually disappeared, allele frequencies remained stable over time in the village of Barkedji from August 1994 to December 1997 (including four rainy seasons and three dry seasons). The effective population size (Ne) was estimated to be 601 with 95% CI (281, 1592), providing strong evidence against annual bottlenecks. Differences in measures of genetic diversity and linkage disequilibrium between the dry and the rainy seasons were not detected. These results suggest that despite extreme minima in local density, An. arabiensis maintains large permanent deme spread out over large area.

Alleles↗
PubMed2003

Seasonal effect upon excision of acquired melanocytic proliferations.

BACKGROUND: Acquired melanocytic proliferations (AMPs) are excised throughout the year. Questions exist concerning seasonal variation in these excisions. OBJECTIVE: To investigate whether AMPs are removed more often during the spring-summer seasons than in the fall-winter and whether the percentage of benign nevi, dysplastic nevi and melanoma varies according to season. DESIGN: Retrospective analysis of 4794 histologically confirmed biopsies of AMPs was performed. RESULTS: A total of 2802 of the 4794 lesions (58%) were removed during the spring-summer season. These results confirm that seasonal variation in removal of AMPs does occur, and that removal peaks during the warmer months. In addition, the increased numbers of removals were accounted for by increases in benign pigmented lesion removals. CONCLUSIONS: Many etiologic factors can be suggested for increased removal of AMPs during the warmer months. Reasons may include the cosmetic desires of the patient and clothing choices resulting in increased awareness of pigmented lesions. Increases in the number of skin cancer prevention programs offered by dermatologists in the spring also have a large impact on the awareness of the general population and potentially contribute to the seasonal variation.

Arkansas↗
PubMed2002

The effect of season and vaccination for Glässer's disease and post-weaning Colibacillosis in an outdoor pig unit endemically infected with virulent strain of Haemophilus Parasuis serotype 5 and pathogenic Escherichia coli.

UNLABELLED: The objective of this field trial was to determine if vaccination against Haemophilus parasuis serovar 5 (HPS 5) and pathogenic serotypes of Escherichia coli would improve nursery pig performance in an outdoor unit in different seasons. The unit was concurrently infected with HPS 5 and with different serotypes of E. coli. All piglets were born to HPS 5 vaccinated sows. The trial was carried out in four (two summer and two winter) groups. Group 1 (E. coli and HPS vaccinated, summer season) (n = 362): Piglets were vaccinated pre-weaning with inactivated E. coli-VT2e-toxin and post-weaning against HPS 5. Group 2 (non-vaccinated, summer season) (n = 349): Piglets were not vaccinated. Group 3 (E. coli and HPS vaccinated, winter season) (n = 358): The animals were analogously treated as Group 1. Group 4 (non-vaccinated, winter season) (n = 353): Piglets were not vaccinated. The following parameters were evaluated: A: average daily nursery weight gain (ADG), B: nursery mortality, C: feed efficiency (FE). No significant weight differences were detected within the vaccinated and non-vaccinated summer or winter raised groups of weaners. Summer raised weaners were significantly (P<0.05) heavier from day 35 on than winter raised animals. ADG and FE of summer raised pigs were significantly better (weeks 1-3 P<0.05; fourth week post-weaning P<0.01) during the nursery period than that of the winter raised groups. Winter raised vaccinated weaners showed during the last week of nursing significantly (P<0.05) better daily gain and feed efficiency compared with the non-vaccinated winter raised animals. Non-significant ADG and FE differences were detectable between the summer raised vaccinated or non-vaccinated groups of pig. Winter raised non-vaccinated animals suffered significantly (P<0.05) higher nursery mortality (10.63%) compared to the winter raised vaccinated animals. IMPLICATION: In cases of concurrent infections with HPS 5 and with different serotypes of E. coli, especially during winter season, vaccination against both diseases is suggested.

Animal Husbandry↗
PubMed2003

Seasonal effects on the aerobic bacterial and fungal conjunctival flora of normal thoroughbred brood mares in Florida.

OBJECTIVE: To evaluate seasonal effects on the presence or absence of fungal and aerobic bacterial flora of the conjunctival fornix of normal Florida Thoroughbred horses. SAMPLE POPULATION: Both eyes of 100 horses. PROCEDURE: Horses with normal anterior segment ophthalmic examinations from three farms in north central Florida were included. Each animal had the ventral conjunctival fornix of each eye swabbed with sterile culturettes. Samples were taken in October, January, April, and July (1999-2000). Aerobic and fungal cultures were plated. Bacterial cultures were reviewed at 24 and 48 h. Fungal cultures were reviewed weekly for 4 weeks. Logistic regression analysis with season as a factor and age of the horse as a covariate was performed. Statistical significance was set at P < 0.01. RESULTS: Horses ranged from 3 to 24 years of age, with a median age of 9 years. Twenty-four genera of bacteria and 35 genera of fungi were recovered. Corynebacterium sp., Staphylococcus sp., Bacillus sp. and Moraxella sp. were the bacteria most frequently isolated. Mold species, dematiaceous mold species, Chrysosporium sp., Cladosporium sp., and Aspergillus sp. were the most frequently recovered fungi. Season did not have a significant effect on the presence of microorganisms isolated for individual horses adjusted for age. Younger horses had an increased incidence of gram-negative rods and fungal isolates. The number of bacteria and fungi isolated are not uniform across seasons. CONCLUSION: There were no significant differences between the number or type of organisms cultured during the sampling seasons in normal Florida horses. A large range of normal bacterial and fungal flora were isolated from these horses. The number of bacteria and fungi isolated are not uniform across seasons. The likelihood of detecting an organism depends on the horses' age.

Animals↗
PubMed2003

Seasonal variability of QT dispersion in healthy young males.

BACKGROUND: There are few data related to the seasonal influences on the QT dispersion. METHODS: We analyzed the effects of seasons on QT dispersion in a large group of healthy young males. We studied the seasonal variability of QT dispersion in 523 healthy male subjects aged 22 +/- 4 years (ranging from 20 to 26). Four seasonal 12-lead resting electrocardiograms (ECGs) recorded at double amplitude were performed at 25 mm/s at intervals of 3 months. Subsequent ECGs were recorded within 1 hour of the reference winter recording. QT dispersion was defined as the difference between the longest and the shortest mean QT intervals. RESULTS: There was a significant seasonal variation in QT dispersion (P = 0.001), with the largest QT dispersion in winter (71 +/- 18 ms) and the smallest one in spring (43 +/- 19). CONCLUSION: There exists a significant seasonal variation in QT dispersion of healthy subjects and such variability should be taken into consideration in the evaluation process of QT dispersion.

Adult↗
PubMed1983

Seasonal effects on ovarian follicular development in pony mares.

To define ovarian follicular kinetics in the equine ovary during anestrus and the breeding season, the follicular population of pony mares was investigated at mid-anestrus and at the beginning and end of the breeding season. There was a clear effect of season on the exit of reserve (primordial and initiated) follicles since at the beginning of the breeding season we noticed a higher mitotic index for the smaller preantral follicles, leading to an accumulation of small and medium antral follicles. In contrast, the ovaries sampled during anestrus or at the end of the breeding season were very similar; only preovulatory development was lacking in anestrous ovaries. However, atresia was unaffected by season.

Anestrus↗
PubMed2002

Seasonal variation of P-wave dispersion in healthy subjects.

We studied the seasonal variability of P dispersion in 523 healthy male patients, aged 22 +/- 4 years (range, 20-26). Four seasonal 12-lead resting electrocardiograms were recorded at 2 mV/cm standardization and at 50 mm/s paper speed at intervals of three months. Electrocardiograms were recorded between the hours 10 to 12 AM. The difference between the maximum P-wave duration and minimum P-wave duration was calculated and defined as "P dispersion." There was a significant seasonal variation in the maximum P-wave duration (P = .001) and P dispersion (P = .001), with the longest maximum P-wave duration (121 +/- 16 ms) and P dispersion (41 +/- 7 ms) observed in winter and the shortest maximum P-wave duration (106 +/- 15 ms) and P dispersion (24 +/- 8 ms) observed in summer. The minimum P-wave duration did not show any significant seasonal variation. In conclusion, there exists a significant seasonal variation in the maximum P-wave duration and P dispersion in healthy patients. Seasonal variation of P dispersion resulted from the significant variation of maximum P-wave duration.

Adult↗
PubMed2000

The role of brain thyroid hormones in the mechanisms of seasonal changes in mood and behavior.

Many individuals experience seasonal changes in mood and behavior. Various theories have been suggested to explain the mechanisms of these changes. However, the mechanisms of seasonal mood and behavioral changes remain unclear. The author suggests that brain thyroid hormones may play an important role in seasonal changes in mood and behavior. This suggestion is based on the facts that seasonal changes in light and temperature may affect the metabolism of brain thyroid hormones and that small alterations of the brain thyroid economy, independent of peripheral changes in thyroid status, may produce significant behavioral effects. The author further suggests that there may be a fault in the thyroid metabolism in the brain in seasonal affective disorder patients, and that fault cannot be identified by studying the peripheral thyroid hormone metabolism. Seasonal mood and behavioral changes may also be related to the interaction between thyroid hormones and different neurotransmitter systems in the brain.

Affect↗
PubMed2001

Grass pollen immunotherapy: symptomatic improvement correlates with reductions in eosinophils and IL-5 mRNA expression in the nasal mucosa during the pollen season.

BACKGROUND: Tissue eosinophilia and infiltration by T(H)2-type T cells are characteristic features of allergic rhinitis both after allergen challenge and during natural allergen exposure. Specific immunotherapy inhibits allergen-induced nasal eosinophilia. OBJECTIVES: We sought to assess, in the context of a randomized trial, the relationships between symptomatic improvement after immunotherapy and eosinophil numbers and IL-5 expression in the nasal mucosa during the pollen season. METHODS: Nasal biopsy specimens were taken from 37 adults with severe summer hay fever at baseline (out of season) and at peak season after 2 years of treatment with a depot grass pollen extract or placebo. Biopsy specimens were processed for immunohistochemistry by using mAbs against eosinophils (EG2), T cells (CD3), and IL-2 receptor-positive cells (CD25), as well as for in situ hybridization by using a sulfur 35-labeled antisense riboprobe directed against IL-5. RESULTS: Immunotherapy significantly reduced symptoms (49%, P =.01) and medication requirements (80%, P =.007) compared with placebo. There was a 400% increase (P =.004) in eosinophils during the pollen season in placebo-treated patients, which was inhibited in the immunotherapy group (20% increase, P =.04 between groups). Seasonal increases were also observed for CD25(+) cells (P =.002), CD3(+) cells (P =.02), and IL-5 mRNA-expressing cells (P =.03) in the placebo group but not in the immunotherapy group. A significant correlation was observed between eosinophils and IL-5 expression (r = 0.5, P <.05). Both eosinophils (r = 0.6, P <.02) and IL-5 (r = 0.6, P <.02) correlated with symptoms after immunotherapy. CONCLUSION: Improvement in symptoms after grass pollen immunotherapy may result, at least in part, from inhibition of IL-5-dependent tissue eosinophilia during the pollen season.

Biopsy↗
PubMed2003

Age-related seasonal patterns of emergency department visits for acute asthma in an urban environment.

STUDY OBJECTIVE: Asthma morbidity is greater in younger patients. The reasons are not fully understood, although identifying demographic patterns of seasonality may help determine causes and potential prevention. The objective of this study is to determine the relationship between age and seasonal asthma periodicity in patients presenting to the emergency department (ED). METHODS: We conducted a retrospective study of ED visits from 1991 to 2000 in 11 municipal hospitals in New York City, with 911 receiving facilities. There were 673,141 patients who presented to the ED during the study period and had a primary diagnosis of acute asthma. RESULTS: Distinct seasonal patterns were observed, with the highest number of visits occurring in the fall and the fewest in the summer. Seasonal fluctuations of ED visits were highest in children aged 13 years or younger (coefficient of variation [CV] 37.8%; 95% confidence interval [CI] 37.5% to 38.1%), with a peak in CV occurring at approximately age 7 years (CV 43.3%; 95% CI 43.0% to 43.6%). Less variability was noted with increasing age, and the population aged 30 years and older appeared to be the least susceptible to seasonal influences (CV 11.7%; 95% CI 11.3% to 12.1%). Although the total number of asthma visits decreased by more than 30% from 1991 to 2000, the CVs for each year remained within a relatively narrow range of 24.2% to 30.5%. CONCLUSION: In an urban population, seasonal variability of asthma episodes requiring ED visits are closely linked to age, which may be important in understanding the causes of asthma and developing disease-management strategies for the prevention of asthma episodes.

Acute Disease↗
PubMed2003

Determinants of the annual pattern of reproduction in mature male Merino and Suffolk sheep: responses to a nutritional stimulus in the breeding and non-breeding seasons.

This study was designed to test whether an acute improvement in diet would increase gonadotrophin secretion and testicular growth in strongly photoperiod-responsive Suffolk rams and weakly photoperiod-responsive Merino rams in both the breeding (February-March) and the non-breeding (July-August) seasons. Mature rams (n = 5 or 6) of these breeds were fed a maintenance diet (0.9 kg chaff + 100 g lupin grain) or the same diet supplemented with 1.5 kg lupin grain for 42 days in each season. Lupin grain is a rich source of both energy and protein. Testosterone, luteinizing hormone (LH) and follicle stimulating hormone (FSH) were measured in plasma from blood sampled every 20 min for 24 h on Days -1, 12 and 35 relative to the change in feeding. In rams supplemented with lupins, body mass increased in both breeds in both seasons (P < 0.001). Scrotal circumference and LH pulse frequency increased with lupin supplementation in both seasons (P < 0.003) in Merinos, but only during the breeding season (P < 0.003) in Suffolks. Plasma FSH concentrations were affected by diet only during the breeding season, being elevated on Day 12 in lupin-supplemented rams of both breeds (P < 0.05). It was concluded that Merino rams exhibit reproductive responses to improved nutrition irrespective of time of the year, whereas Suffolk rams respond to nutrition only when the hypothalamic reproductive centres are not inhibited by photoperiod. Thus, Suffolks do respond to nutrition, just as Merinos do, but only when photoperiod allows. This difference between breeds appears to be a result of differences in the neuroendocrine pathways that control pulsatile gonadotrophin-releasing hormone secretion.

Animal Nutritional Physiological Phenomena↗
PubMed1994

Testicular and epididymal sperm content in grazing Cashmere bucks: seasonal variation and prediction from measurements in vivo.

Each month, for 15 months, the testes and epididymides were recovered from five Australian cashmere bucks selected at random from a group of mature bucks (initial n = 116) at pasture (location 29 degrees S, 153 degrees E). The extent of seasonal change in testicular and epididymal sperm reserves was determined and indirect methods for predicting these reserves were developed. Paired testicular weight exhibited clear seasonal variation from 137 g in August to 269 g in February. The total elongated spermatid content of the testes, determined by homogenization, showed a very similar seasonal pattern, ranging from 13.8 x 10(9) in September to 36.2 x 10(9) in March. Seasonal changes of similar timing were observed for paired epididymal weight and sperm content. Although changes in total testicular spermatid content were largely the result of change in testicular weight (R2 = 0.72, P < 0.001), the elongated spermatid content of testicular parenchyma (mean, 127 x 10(6) g-1) exhibited significant seasonal variation with elevated values between February and June, suggestive of an increase in the efficiency of spermatogenesis. Daily sperm production, calculated by means of a spermatogenic time divisor for sheep, ranged from 2.76 x 10(9) in September to 7.23 x 10(9) in February. Scrotal circumference, scrotal volume and testicular length x diameter2 were identified as accurate predictors of testicular weight (R2 > or = 0.87) and sperm content (R2 > or = 0.70). The results demonstrate that: (a) cashmere bucks exhibit considerable seasonal variation in spermatogenesis associated primarily with changes in testicular mass but also with changes in the efficiency of spermatogenesis; and (b) indirect measures of testicular size are good predictors of testicular elongated sperm content. When the correct spermatogenic time divisor for goats is determined, such indirect measures may be used to predict daily sperm production.

Animals↗
PubMed2002

Seasonal influences on immunological parameters in HIV-infected homosexual men: searching for the immunomodulating effects of sunlight.

In view of the capacity of ultraviolet radiation (UVR) to induce suppression of various immunological parameters and to enhance the viral replication of HIV, we investigated whether seasonal influences on immunological parameters that are relevant for HIV infection could be identified. As the sunny season is associated with high levels of ambient UVR, a decline of immunological parameters and an increase of the HIV viral load during the summer months might ensue. We analysed the immunological data of the HIV-infected homosexual men who participated in the Amsterdam Cohort Study on HIV infection and AIDS (1984-1996; n = 556). The effect of season on the individual development of various immunological parameters in time was examined by means of a random effects model for repeated measurements. Lower levels in the mean number of CD4+ T cells and the mean CD4+/CD8+ ratio were found during summer and spring, respectively (P = 0.0001/0.0001). For the CD8+ T cells, high mean values were observed both in April and September (P = 0.0001). The highest T-cell reactivity values were found during the summer (P = 0.0001). No effect of season on the viral load was established. The seasonal effect on CD4+ T cells seemed to be more pronounced at a more advanced stage of the HIV infection. It is concluded that the lower CD4+ T-cell counts during summer support the notion that solar UVR may have a suppressive effect on the cellular immunity of HIV-infected persons. However, whether this observation can be attributed to the effect of ambient UVR solely is questionable, as the other immunological parameters follow different seasonal courses and other reports suggest that both internal and environmental factors influence immunological parameters.

Adult↗
PubMed2001

Seasonal population dynamics of Neoechinorhynchus qinghaiensis in the carp, Gymnocypris przewalskii przewalskii, from Qinghai Lake, China.

Studies on the seasonal population dynamics of Neoechinorhynchus qinghaiensis (Acanthocephala: Neoechinorhynchidae) in its fish host Gymnocypris przewalskii przewalskii in the Qinghai Lake, China, were carried out with samples taken in May 1991, August 1992, November 1992 and February 1993. Prevalences were higher than 44% in all seasons. The mean intensity of infection was above 124 worms per fish. The maximum intensity of worms recovered from a single fish was 1402 in the autumn of 1992. Differences in the mean abundance, mean intensity and prevalence are not statistically significant relative to season and this is likely to be related to the stable temperatures recorded at the bottom of Qinghai Lake. Over-dispersed distributions of N. qinghaiensis in the host population, due to heterogeneity and feeding habits, were observed in all seasons. The size composition of both sexes of N. qinghaiensis showed males to be less than 3.5 mm and females between 0.5 and 4.25 mm, with the main recruitment phase in the worm populations occurring in the autumn, extending through winter and spring with the lowest recruitment occurring in the summer. The maturation and copulation of worms were mainly focused in the summer season. The sex ratio of female to male was both high in winter (1.51:1) and spring (1.48:1). The higher proportion of females and the change in the worm sex ratio in winter can be attributed to the reduced longevity of male worms. As immature male worms exhibit a higher proportion of the worm population than females in all seasons, further studies are needed to determine if such a situation compensates for the shorter life span of males.

Acanthocephala↗
PubMed2001

Wuchereria bancrofti in a community with seasonal transmission: stability of microfilaraemia, antigenaemia and filarial-specific antibody concentrations.

The effect of seasonal transmission on microfilaraemia, antigenaemia and filarial-specific antibody levels in individuals infected with Wuchereria bancrofti was investigated in a follow-up study in an endemic community in north-eastern Tanzania. The subjects were 37 adult male residents who were found to be positive for circulating filarial antigen (CFA) at the beginning of the study (26 of whom were also found microfilaraemic with W. bancrofti at this time). Blood samples were collected from each subject in July 1998, January 1999 and July 1999, during the seasons when transmission intensity was high, low and high, respectively. The mean intensities of microfilaraemia and the mean concentrations of CFA were each slightly higher during the low-transmission season than during the two high-transmission seasons but the differences were not statistically significant (P > 0.05). Similarly, the mean levels of filarial-specific IgG1, IgG2, IgG3, IgG4 or IgE did not differ to a statistically significant degree between the three examination times. Microfilaraemias and the levels of CFA and filarial-specific antibodies all therefore appeared to be remarkably stable and largely unaffected by the seasonal variation in transmission. That no variation in the mean IgG4/IgE ratio was observed over the study period may indicate that the level of resistance to W. bancrofti infection in the study subjects was also unaffected by the transmission season.

Adult↗
PubMed1991

Seasonal incidence and diel oviposition periodicity of Haemagogus mosquitoes (Diptera: Culicidae) in Trinidad, W.I. Part III. Haemagogus celeste (Dyar and Nunez Tovar) and Haemagogus leucocelaenus (Dyar and Shannon).

The seasonal incidence and diel oviposition patterns of sylvan Haemagogus celeste and Hg. leucocelaenus in the Pt. Gourde Forest, Trinidad, were monitored weekly for 53 consecutive weeks using conventional ovitraps. During the dry season peak oviposition by Hg. celeste occurred between 10.00 and 12.00 hours, and that by Hg. leucocelaenus between 12.00 and 14.00 hours; during the wet season peak oviposition by both species occurred between 12.00 and 14.00 hours. Diurnal patterns of oviposition were observed for both species during the wet and dry seasons. The numbers of ovipositions and of eggs laid during the wet season were, for both species, significantly higher (P greater than 0.001) than those observed during the dry season.

Animals↗
PubMed1989

Seasonal variation of serum bone GLA protein.

The seasonal variation of serum Bone Gla Protein (BGP) was investigated in 15 normal young individuals (seven women and eight men, aged 27-39 years). Serum BGP exhibited a significant seasonal variation of 23% around the yearly mean (p less than 0.001) with zenith in February and nadir in July. Significant seasonal variations were noted also for serum alkaline phosphatase (p less than 0.01) and serum phosphate (p less than 0.01). Serum calcium, bone mineral content (BMC) and creatinine clearance revealed no significant seasonal variation. The seasonal variation of BGP did not follow the variation in serum total alkaline phosphatase. The seasonal variation of BGP has to be taken into account when using the protein as a marker of bone remodelling activity. The variation was probably caused by changes in the production rate of the protein, since the renal excretion of the protein, as reflected in creatinine clearance, remained unchanged throughout the year.

Adult↗
PubMed2004

An epidemiological study on gender differences in self-reported seasonal changes in mood and behaviour in a general population of northern Sweden.

Gender differences have been reported regarding symptoms, prevalence and heritability of seasonal affective disorders (SAD). We focus on gender aspects in this study of self-reported seasonal changes in mood and behaviour in a general population. The Seasonal Pattern Assessment Questionnaire (SPAQ) was completed by 2620 adults (55.6% women) aged 35-85 years, enrolled in the Betula prospective random cohort study of Umeå, Sweden. October to February turned out to be suitable winter months. SAD was found in 2.2% and sub-syndromal SAD (S-SAD) in 5.7%. Women had about 1.5 times higher prevalences than men, and seasonality problems decreased with age in both genders. Preference for eating least was distributed with a peak in summer, whereas preference for eating most had a major peak in winter (winter eaters) and a minor peak in summer (summer eaters). Significantly more of winter eaters in women, and significantly more of summer eaters in men, felt worst in winter. Seasonal change in weight was considered significantly as a problem by women but not by men. Winter behaviour of sleeping most was considered significantly as a problem by men but not by women. Women reacted significantly to temperature-related changes (negatively to cold/short days and positively to hot/long days), whereas men reacted significantly to sunshine-related changes (negatively to cloudy days and positively to sunny days). Subtle gender differences may thus underlie the pathophysiology of seasonal problems. Studies of an eventual efficacy of treating SAD women with raised ambient temperature, and gender-specific comparisons with other therapies, would be of interest.

Adult↗