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At least 469 records · Page 26Linked to original sources
PubMed1998

Investigating potential risk factors for seasonal variation: an example using graphical and spectral analysis methods based on the production of milk components in dairy cattle.

The objective of this study was to illustrate methods for investigating factors associated with seasonality, using milk-component production as an example. Milk-protein and fat percentages showed a seasonal pattern; percentages were lowest during June and July and highest in October and November. Graphical methods were used to compare herd calving patterns to seasonal production patterns and spectral analysis were used to compare seasonal production patterns between farm groups with different management practices. For the comparison of seasonality of production and herd calving patterns, data was obtained from archival records for all cows enrolled in Dairy Herd Improvement (DHI) milk recording in Ontario, Canada from 1990 to 1994. For comparisons of seasonality and management practices, monthly protein and fat percentages were obtained from the Dairy Farmers of Ontario from March 1985 to July 1994. Management information was obtained from responses to questionnaires completed by 364 dairy producers in Ontario. Graphical analyses provided a visualization of the relationship between herd calving patterns and seasonality of production-however, graphical methods alone did not allow statistical inferences to be made. Spectral analyses provided a formal statistical test of the null hypothesis of no association between an independent variable (farm management type) and seasonal production pattern in the data over time, provided that the outcome followed the same seasonal pattern regardless of covariate levels under the null hypothesis.

Animal Husbandry↗
PubMed2000

Factors effecting reproduction in the pig: seasonal effects and restricted feeding of the pregnant gilt and sow.

Recent advances in research on seasonal infertility are discussed with a special focus on implications of the generally recommended restricted post-mating feeding strategy of the early pregnant gilt and sow for the physiology of seasonal infertility. The endocrinological basis of seasonal breeding of the wild and domestic pig is being clarified: as in other seasonal breeders, melatonin is relaying photoperiodic information about season to the pituitary-gonadal axis. Earlier confusion on this matter appears to have been caused by a lack of specificity of the melatonin assays employed. Group housing of the pregnant sow is becoming a common practice and, as an important environmental risk factor for seasonal infertility, may lead to an increase in the incidence of seasonal infertility in the future. After an initial progesterone-mediated beneficial effect on embryonic survival, a restricted post-mating feeding strategy may have a negative effect on maintenance of early pregnancy in the gilt and sow in the summer-autumn period. The endocrinological mechanism of seasonal disruption of pregnancy is yet to be determined. However, it is proposed that LH is reduced in the summer-autumn period and this reduction is amplified by the commonly applied restricted post-mating feeding strategy. These changes in LH secretion, although not as such inducing CL regression, may exert a progesterone-mediated detrimental effect on the capability of embryos to produce adequate embryonic signaling. This may lead to a seasonal disruption of pregnancy and a return to oestrus 25-30 days after mating.

Animals↗
PubMed1998

Seasonal distribution of acute myocardial infarction in the second National Registry of Myocardial Infarction.

OBJECTIVES: This observational study sought to determine whether cases of acute myocardial infarction (AMI) reported to the second National Registry of Myocardial Infarction (NRMI-2) varied by season. BACKGROUND: The existence of circadian variation in the onset of AMI is well established. Examination of this periodicity has led to new insights into pathophysiologic triggers of atherosclerotic plaque rupture. Although a seasonal pattern for mortality from AMI has been previously noted, it remains unclear whether the occurrence of AMI also displays a seasonal rhythmicity. Documentation of such a pattern may foster investigation of new pathophysiologic determinants of plaque rupture and intracoronary thrombosis. METHODS: We analyzed the number of cases of AMI reported to NRMI-2 by season during the period July 1, 1994 to July 31, 1996. Data were normalized so that seasonal occurrence of AMI was reported according to a standard 90-day length. RESULTS: A total of 259,891 cases of AMI were analyzed during the study period. Approximately 53% more cases were reported in winter than during the summer. The same seasonal pattern (decreasing occurrence of reported cases from winter to fall to spring to summer) was seen in men and women, in different age groups and in 9 of 10 geographic areas. In-hospital case fatality rates for AMI also followed a seasonal pattern, with a peak of 9% in winter. CONCLUSION: The present results suggest that there is a seasonal pattern in the occurrence of AMIs reported to NRMI-2 that is characterized by a marked peak of cases in the winter months and a nadir in the summer months. This pattern was seen in all subgroups analyzed as well as in different geographic areas. These findings suggest that the chronobiology of seasonal variation in AMI may be affected by variables independent of climate.

Aged↗
PubMed2002

Seasonal variability in exercise test responses in Ghana.

Exercise-induced bronchospasm (EIB) is widely used in epidemiological studies to investigate the prevalence of asthma. We aimed to determine seasonal variations in the prevalence of EIB in Ghanaian school children from urban-rich (UR), urban-poor (UP), and rural (R) schools. We have previously reported the prevalence of EIB in 9-16-year-old children to be 3.1% in the dry season, with UR children having a significantly higher prevalence of both EIB and atopy compared to UP or R children. In the current study, the prevalence of EIB was assessed in the same 1,095 children in the wet season (5 months following the initial study) using the same methodology. Exercise provocation consisted of free running outdoors for 6 min. In the wet season, 17/1,095 children [mean 1.55%, 95% confidence interval (CI): 0.91-2.47] had a positive response to exercise, compared to our previous report of 34 children (mean 3.1%, 95% CI: 2.15-4.32) with EIB in the dry season (dry vs. wet season, difference 1.55, 95% CI: 0.41-2.69). The proportion of children with a positive response to exercise in the UR school fell from 4.2% (25/599) to 1.3% (8/599) (difference 2.9, 95% CI: 1.2-4.5). In the wet season, there was no difference in the prevalence of EIB among the UR, UP, and R children. Only five of 1,095 subjects (mean 0.5%, 95% CI: 0.15-1.07) demonstrated EIB in both seasons. In conclusion, although exercise challenge remains a useful tool for determining asthma prevalence in epidemiological studies, seasonal variations in the pattern of responses may occur and the results should be interpreted with caution.

Adolescent↗
PubMed1999

Seasonal variations in the diagnosis of childhood cancer in the United States.

Seasonal trends in month of diagnosis have been reported for childhood acute lymphoblastic leukaemia (ALL) and non-Hodgkin's lymphoma (NHL). This seasonal variation has been suggested to represent an underlying viral aetiology for these malignancies. Some studies have shown the highest frequency of diagnoses in the summer months, although this has been inconsistent. Data from the Children's Cancer Group and the Pediatric Oncology Group were analysed for seasonal incidence patterns. A total of 20,949 incident cancer cases diagnosed in the USA from 1 January 1989 through 31 December 1991 were available for analyses. Diagnosis-specific malignancies available for evaluation included ALL, acute myeloid leukaemia (AML), Hodgkin's disease, NHL, rhabdomyosarcoma, neuroblastoma, retinoblastoma, osteosarcoma, Wilms' tumour, retinoblastoma, Ewings' sarcoma, central nervous system (CNS) tumours and hepatoblastoma. Overall, there was no statistically significant seasonal variation in the month of diagnosis for all childhood cancers combined. For diagnosis-specific malignancies, there was a statistically significant seasonal variation for ALL (P = 0.01; peak in summer), rhabdomyosarcoma (P = 0.03; spring/summer) and hepatoblastoma (P = 0.01; summer); there was no seasonal variation in the diagnosis of NHL. When cases were restricted to latitudes greater than 40 degrees ('north'), seasonal patterns were apparent only for ALL and hepatoblastoma. Notably, 33% of hepatoblastoma cases were diagnosed in the summer months. In contrast, for latitudes less than 40 degrees ('south'), only CNS tumours demonstrated a seasonal pattern (P = 0.002; winter). Although these data provide modest support for a summer peak in the diagnosis of childhood ALL, any underlying biological mechanisms that account for these seasonal patterns are likely complex and in need of more definitive studies.

Adolescent↗
PubMed2003

Swiss pilot study of individual seasonal fluctuations of urinary iodine concentration over two years: is age-dependency linked to the major source of dietary iodine?

OBJECTIVE: Because of known significant seasonal fluctuations of iodine concentration in cow's milk (ICM) in Switzerland (winter/summer (w/s) ICM ratio averages 5.6), we looked for seasonal variations and familial aspects in urinary iodine and sodium concentrations (UIC, UNaC). DESIGN: : Prospective sequential cohort investigation. SETTING: University hospital. SUBJECTS: Thirteen children (six girls, seven boys) aged 3-10 y and their parents (n=9) aged 30-47 y. INTERVENTIONS: The volunteers collected 1729 spot urine samples (5.1996-5.1998). UIC data from winter (UIC(w): December-February) and summer seasons (UIC(s): July-September) were compared with UNaC and average milk consumption. Iodine intakes from milk and salt were modelized. RESULTS: Highest seasonal fluctuations of UIC were found in six pre-school children (w/s UIC group average=1.56, significant), followed by seven school children (w/s UIC group average=1.24, N.S.); none existed in adults. UIC/UNaC showed corresponding seasonal fluctuations in children, but not in adults. Winter milk was an important iodine source for children, as proven indirectly by similar seasonal fluctuations of ICM, UIC, UIC/UNaC and an important part within UIC due to milk. CONCLUSIONS: Contribution to UIC from milk intake during winter was high in children (40-50%) and lower in adults (about 20%). Compared with children, dietary habits of adults are more complex and their iodine supply depends mainly on iodized salt and not on milk, so the effect of seasonal ICM variations on UIC is less marked. Because of significant seasonal UIC fluctuations in consumers of fresh milk products in Switzerland, results of future UIC studies conducted during summer and winter seasons should be compared cautiously, especially in young children. Furthermore, consumption of milk is to be promoted, since, besides calcium and vitamins, it is an essential source of iodine. UNaC determination should be included in epidemiologic studies if the dietary source of iodine is questioned.

Adult↗
PubMed1999

Association between seasonal affective disorder and the 5-HT2A promoter polymorphism, -1438G/A.

Genes involved in serotonin metabolism are good candidates for the pathogenesis of seasonal affective disorder (SAD). A functional variant in the serotonin transporter promoter, 5-HTTLPR, has recently been shown to be associated with SAD and seasonality. The purpose of this study was to determine whether -1438G/A, a polymorphism in the 5-HT2A promoter, is associated with SAD and seasonality, and whether it has additive effects with 5-HTTLPR on seasonality. Sixty-seven individuals with SAD and 69 normal volunteers, all screened with the SCID and diagnosed according to DSM-III-R criteria, were genotyped for the -1 438G/A 5-HT2A promoter polymorphism. All had been previously genotyped for 5-HTTLPR and had been assessed for seasonality by the Global Seasonality Scale. There was a significant increase in the frequency of the -1438A variant allele of the 5-HT2A promoter polymorphism in SAD patients (0.47) compared to matched controls (0.36) (P < 0.01). The difference in genotype distribution was also significant (P < 0.05). We found no association between the -1438G/A polymorphism and seasonality scores, and there was no additive effect with 5-HTTLPR on seasonality. In conclusion, we have shown that the -1438G/A 5-HT2A promoter variant is associated with SAD but not with seasonality. We suggest that the association may instead be with the depressive symptoms of SAD. However, these results should be treated with caution until replicated because of the possibility of false-positive findings in case-control association studies.

Adenine↗
PubMed2002

Circadian clock-related polymorphisms in seasonal affective disorder and their relevance to diurnal preference.

Disturbed circadian rhythms have been observed in seasonal affective disorder (SAD). The aim of this study was to further investigate this connection, and to test for potential association between polymorphisms in circadian clock-related genes and SAD, seasonality (seasonal variations in mood and behavior), or diurnal preference (morningness-eveningness tendencies). A total of 159 European SAD patients and 159 matched controls were included in the genetic analysis, and subsets were screened for seasonality (n=177) and diurnal preference (n=92). We found that diurnal preference was associated with both SAD and seasonality, supporting the hypothesis of a link between circadian rhythms and seasonal depression. The complete case-control material was genotyped for polymorphisms in the CLOCK, Period2, Period3, and NPAS2 genes. A significant difference between patients and controls was found for NPAS2 471 Leu/Ser (chi(2)=9.90, Bonferroni corrected P=0.035), indicating a recessive effect of the leucine allele on disease susceptibility (chi(2)=6.61, Bonferroni corrected P=0.050). Period3 647 Val/Gly was associated with self-reported morningness-eveningness scores (n=92, one-way ANOVA: F=4.99, Bonferroni corrected P=0.044), with higher scores found in individuals with at least one glycine allele (t=3.1, Bonferroni corrected P=0.013). A second, population-based sample of individuals selected for high (n=127) or low (n=98) degrees of seasonality, was also genotyped for NPAS2 471 Leu/Ser. There was no significant difference between these seasonality extreme groups, and none of the polymorphisms studied were associated with seasonality in the SAD case-control material (n=177). In conclusion, our results suggest involvement of circadian clock-related polymorphisms both in susceptibility to SAD and diurnal preference.

Analysis of Variance↗
PubMed1999

Secular and seasonal changes in semen quality among young Danish men: a statistical analysis of semen samples from 1927 donor candidates during 1977-1995.

The objective of this study was to investigate whether semen quality has changed during the years 1977-1995 in a group of unselected semen donor candidates, and to determine whether semen quality is subject to seasonal variation, by analysis of time- and season-related changes in semen quality using multiple regression and ANOVA. The study was based on analysis of the first semen sample delivered by 1927 semen donor candidates in Copenhagen during the period 1977-1995, with determination of semen volume, sperm concentration, total sperm count, percentage motile spermatozoa, and a semiquantitative sperm motility score. Multiple linear regression analysis with year, sexual abstinence and season as covariates showed a significant increase in mean sperm concentration from 53.0 x 10(6)/mL in 1977 to 72.7 x 10(6)/mL in 1995 (p < 0.0001) and in mean total sperm count from 166.0 x 10(6) to 227.6 x 10(6) (p < 0.0001). Mean semen volume and percentage motile spermatozoa did not change. Sperm motility deteriorated, as the spermatozoa in 74.2% of the samples were of excellent motility in 1977-1980 compared to only 41.9% in 1993-1995 (chi 2 = 130.0, p < 0.0001). Analysis of variance showed significant variation between seasons regarding sperm concentration (p < 0.0001) and total sperm count (p < 0.0001). Highest sperm counts were found in spring, with a mean concentration (95% C.I.) of 77.6 x 10(6)/mL (71.9-83.7), and lowest in summer, with a mean of 57.5 x 10(6)/mL (50.1-65.4). No other semen parameter varied with season. It is concluded that sperm counts increased, whereas sperm motility decreased, in a group of Danish semen donor candidates, from 1977 to 1995. Due to the retrospective design and the anonymity of the donors, we were unable to control for variation in donor age, and we cannot exclude the possibility that some donor candidates were selected by being accepted as donors by other semen donor services in Copenhagen. With these limitations in mind, we suggest our results should be interpreted cautiously and regarded as a contribution to the ongoing dispute on whether or not there is a continuous decrease in sperm quality. The seasonal variations found in sperm concentration and total sperm count were pronounced and were not attributable to seasonal differences in the length of sexual abstinence. Additionally, the same seasonal pattern was observed in five successive year-intervals. These findings strongly indicate that human testicular function is influenced by season, a phenomenon well known in many lower mammals.

Adult↗
PubMed1996

Sarcoidosis causes abnormal seasonal variation in 1,25-dihydroxy-cholecalciferol.

OBJECTIVES: The spontaneous seasonal variations in the calcium regulating hormones 1,25-dihydroxy-cholecalciferol (1,25-DHCC) and parathyroid hormone (PTH) were investigated in patients with sarcoidosis. DESIGN: Controlled, prospective observational study with measurements in the winter and summer seasons, respectively. SUBJECTS: Twelve patients (age: median 33, range 21-54 years) with biopsy-verified (n = 8) sarcoidosis were included as well as 11 age-matched healthy control subjects. MAIN OUTCOME MEASURES: Serum values of calcium, ionized calcium, phosphate, chloride, bicarbonate, creatinine, albumin, angiotensin-converting enzyme, alkaline phosphatase, 1,25-DHCC, and PTH. Also, 24-h whole body retention of 99mTc methylene-diphosphonate was assessed. RESULTS: The patient group showed an increased level of 1,25-DHCC in the summer season (w:146 +/- 67, s:198 +/- 73 pmol L-1; P < 0.01) in contrast to the opposite finding among controls (w:161 +/- 34, s:144 +/- 43 pmol L-1; P < 0.05). Comparing the individual seasonal changes between the two groups, the difference was marked (P < 0.001). Compared with controls, total serum calcium was elevated in the summer season in the patient group (P < 0.05), in which the same parameter correlated positively with 1,25-DHCC (r = 0.658; P < 0.01). PTH was increased two to three times above the control values throughout the year (patients: w:0.37 +/- 0.13, s:0.24 +/- 0.08 micrograms L-1; controls: w:0.14 +/- 0.09, s:0.10 +/- 0.04 micrograms L-1; P < 0.001); although, the level of this hormone was still found within the reference interval. 24-h whole body bone scintigraphy failed to show any seasonal variation in bone metabolism. In contrast, serum alkaline phosphatase was found to be increased during the summer season compared with the control group (P < 0.001). Angiotensin-converting enzyme showed no seasonal variation. CONCLUSIONS: In sarcoidosis, 1,25-DHCC is abnormally regulated throughout the year, with a significantly higher serum level in the summer season. Uncontrolled production of 1,25-DHCC in sarcoid pulmonary alveolary macrophages is possibly responsible for hypercalcaemic episodes, and this parameter should be used as a marker of disease activity.

Adult↗
PubMed2000

Season of birth is not associated with delayed childhood mortality in Upper River Division, The Gambia.

There is evidence that season of birth may predict adult mortality from infectious diseases in rural Gambia. Using data collected over a five-year period from the rural, eastern region of the Gambia, we examined whether the season of birth influences mortality in childhood. 26 894 births and 3776 deaths among children under the age of five years were recorded in this region during the period 1989-1993. The estimated 1-4 year population was 95 355. In children aged 1-4 years, the mortality rate per 1000 per year was 16.1 (95% CI 14.9, 17.2) for those born in the 'harvest' season (January to June), which was not significantly different from the rate of 17.9 (95% CI 16.7, 19.0) recorded for those born in the 'hungry' season (July to December) (age-stratified Mantel-Haenszel mortality ratio 0. 91, 95% CI 0.83, 1.01; p = 0.08). Nearly all deaths of 1-4 year olds were attributed to infectious diseases, with malaria accounting for over 40%. None of the cause-specific child mortality rates differed significantly according to the season of birth. These data suggest that beyond infancy, when it is easier to separate the effect of season on cause of death from that of the season of birth, there is no marked difference in the rate of death between Gambian children born in the harvest season and those born in the hungry season.

Birth Rate↗
PubMed2002

Seasonal variation in trachoma and bush flies in north-western Australian Aboriginal communities.

BACKGROUND: Among younger age groups trachoma (Chlamydia trachomatis) has been identified as a major cause of morbidity in Australian Aboriginal communities. North-western Australia has two seasons, referred to as the wet and the dry, and until recently most trachoma screening programmes were conducted during the dry season. This study compared the prevalence of trachoma between three Aboriginal communities, two in the west and one in the east Kimberleys with differences in adult bush fly (Musca vetustissima) populations between the wet and dry seasons. METHODS: All preschool and school-aged children in each community were screened for trachoma in February and July 1996 using the World Health Organization method for clinical assessment of trachoma. Flies were trapped fortnightly from September through to May (inclusive) using a wind-orientated fly trap. RESULTS: Two communities in the west Kimberleys had a significantly higher rate of trachoma during the wet season (14-59% in dry season compared with 46-69% in wet season). One community showed no difference but this was probably due to the reduced re-screening rate. Further-more, it was demonstrated that fly populations are so low during the dry season that they were untrappable; however, populations of bush fly significantly increased during the wet season (ranging from 6 to 146 flies per hectare per month). CONCLUSIONS: If bush fly populations are correlated with increased levels of trachoma, then measures aimed at augmenting public health plans for bush fly control may decrease the cross-infection rate. Additionally, based on the results of this study, wet season trachoma screening trips should be considered.

Animals↗
PubMed2001

Grass pollen immunotherapy for seasonal rhinitis and asthma: a randomized, controlled trial.

BACKGROUND: Grass pollen immunotherapy significantly reduces hay fever symptoms and medication requirements. Effects on seasonal asthma are less clear, and concerns over safety persist. OBJECTIVE: The goal of this study was to assess the effects of grass pollen immunotherapy on symptoms, bronchial hyperresponsiveness, and quality of life in seasonal rhinitis and asthma. METHODS: Forty-four patients with severe summer hay fever (of whom 36 reported seasonal chest symptoms and 28 had seasonal bronchial hyperresponsiveness) participated in a randomized, double-blind, placebo-controlled, parallel group study. After symptom monitoring for one summer, participants received injections of a depot grass pollen vaccine (n = 22) or matched placebo injections (n = 22) in a rapid updosing cluster regimen for 4 weeks, followed by monthly injections for 2 years. Outcome measures included hay fever symptoms and medication use, health-related quality of life, and measurements of nonspecific bronchial responsiveness. RESULTS: Significant reductions were observed in the immunotherapy group compared with the placebo group in hay fever symptoms (49%, 15%; P =.01), medication scores (80%, 18%; P =.007), and seasonal chest symptoms (90%, 11%; P <.05). Impairment of overall quality of life (mean score of 7 domains) during the pollen season was less in the immunotherapy group than in the placebo group (median difference [95% CI], 0.8 [0.18-1.5]; P =.02). During the pollen season there was no change in airway methacholine PC(20) (provocation concentration producing a 20% fall in FEV(1)) in the immunotherapy-treated group (P =.5), compared with an almost 3 doubling-dose decrease in the placebo-treated group (P =.01, between-group difference). There were no significant local or systemic side effects during the study. CONCLUSION: Grass pollen immunotherapy improves quality of life in seasonal allergic rhinitis and reduces seasonal asthma symptoms and bronchial hyperresponsiveness.

Adult↗
PubMed2002

Efficacy of combination treatment with anti-IgE plus specific immunotherapy in polysensitized children and adolescents with seasonal allergic rhinitis.

BACKGROUND: Specific immunotherapy (SIT) and treatment with monoclonal anti-IgE antibody have complementary modes of action. OBJECTIVE: The purpose of this study was to determine whether combined therapy could provide better efficacy than either treatment alone. METHODS: We conducted a randomized, double-blinded trial to assess the efficacy and safety of subcutaneously administered anti-IgE (omalizumab) or placebo in children and adolescents with seasonal allergic rhinitis in both a birch pollen season and a grass pollen season (sequential seasons together lasting an average of 84 days). There were 4 treatment arms. Each subject was started on SIT-birch or SIT-grass, and anti-IgE or placebo was started before and maintained during the anticipated pollen seasons (a total of 24 weeks). The primary efficacy variable was symptom load, the sum of daily symptom severity score plus rescue medication use. RESULTS: A total of 221 subjects (intent-to-treat population) aged 6 to 17 years were analyzed for efficacy. Combination therapy reduced symptom load over the 2 pollen seasons by 48% (P <.001) over SIT alone. When analyzed separately by season, the 2 groups receiving unrelated SIT were considered placebo controls. In the grass season, symptom loads were as follows: unrelated (birch) SIT + placebo, 0.89 (reference value); unrelated (birch) SIT + anti-IgE, 0.49 (-45%); SIT-grass + placebo, 0.61 (-32%); SIT-grass + anti-IgE, 0.26 (-71%). CONCLUSION: Anti-IgE therapy conferred a protective effect independent of the type of allergen. Additional clinical benefit was demonstrated in both pollen seasons, whether there was coverage by SIT or not. This combination might prove useful for the treatment of allergic rhinitis, particularly for polysensitized patients.

Adolescent↗
PubMed1997

Seasonal effects on ovarian responsiveness to exogenous gonadotrophins and successful artificial insemination in the snow leopard (Uncia uncia).

Ovaries of the seasonally-breeding snow leopard (Uncia uncia) were examined to determine whether they were responsive to exogenous gonadotrophins throughout the year. The potential of laparoscopic artificial insemination (AI) also was assessed for producing offspring. During the non-breeding, pre-breeding, breeding and post-breeding seasons, females (n = 20) were treated with a standardized, dual-hormone regimen given intramuscularly (600 I.U. of equine chorionic gonadotrophin followed 80-84 h later with 300 I.U. of human chorionic gonadotrophin (hCG)). Laparoscopy was performed 45-50 h after administration of hCG, and all ovarian structures were described. Females with fresh corpora lutea (CL) were inseminated, and anovulatory females were subjected to follicular aspiration to examine oocyte quality. Snow leopards responded to exogenous gonadotrophins throughout the year. Mean number of total ovarian structures (distinct follicles mature in appearance plus CL) did not differ (P > or = 0.05) with season, but the proportion of CL: total ovarian structures was greater (P < 0.01) for the breeding season compared with all other seasons. The proportion of females ovulating was greater (P < 0.05) during the breeding and post-breeding seasons than during the pre-breeding and non-breeding seasons respectively. No Grade-1 quality oocytes were recovered from follicles of anovulatory females. Serum concentrations of oestradiol-17 beta appeared elevated in all females, and neither oestradiol-17 beta concentrations nor progesterone concentrations differed (P > or = 0.05) among seasons. Of 15 females artificially inseminated, the only one that was inseminated in the non-breeding season became pregnant and delivered a single cub. This is the first successful pregnancy resulting from AI in this endangered species.

Animals↗
PubMed1987

Studies on the dynamics of transmission of onchocerciasis in a Sudan-savanna area of North Cameroon II. Seasonal and diurnal changes in the biting densities and in the age-composition of the vector population.

Near the perennial breeding sites in the main water courses the highest monthly biting rates were recorded from June to August (early rainy season) and again from December to February (dry season), but near the rainy season breeding sites in the affluents, or at fly-catching sites, more than 2 km inland from the nearest main river breeding site, the highest rates were recorded between August and December (mid-rainy to early dry season). The variation of the biting rates over the year depended on the waterflow of the main rivers and on the differential dispersal of the flies from the breeding sites during the dry and rainy seasons. At the beginning of the rainy season, when the rivers started flowing, an immigration of non-local flies was observed at the river Mayo Rey near Tcholliré, presumably coming from Simulium breeding sites in the Adamaoua mountains to the South. During three years 77,374 flies were caught by daily catches between 06.00 and 18.30 hours. During the dry season the biting activity of nulliparous and parous flies was highest between 09.00 and 10.00 hours and 16.00 and 17.00 hours, 9% and 22% of the total day-catches respectively. In the rainy season the peak biting rates occurred between 06.00 and 07.00 hours (9%) and again from 16.00 to 17.00 hours (14%). The lowest biting rates were observed between 11.00 and 12.00 hours in both dry and rainy seasons (4% and 3% of the total catch). Nulliparous flies showed higher variations in biting activity than did parous flies, leading to the highest proporation of parous flies during midday.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1993

Seasonal variation of paediatric diseases in The Gambia, west Africa.

In a 3-year prospective study of 9584 consecutive paediatric admissions to the Royal Victoria Hospital in Banjul, The Gambia, we examined the impact of seasonal variations in childhood diseases. The four principal diseases (falciparum malaria, pneumonia, gastro-enteritis and malnutrition) all peaked in September to October following the rainy season. The mortality rate was also higher in the rainy season than in the dry season. Of the 1525 children with cerebral malaria, 83% were admitted during the extended rainy season from July to December. With the emergence of chloroquine-resistant malaria over the 3 years, there was a 27% annual increase in severe anaemia owing to malaria. The median age of malarial anaemia (23 months) was significantly younger than that of cerebral malaria (42 months). Malnutrition peaked immediately following the annual rainy season epidemics of bacterial gastro-enteritis but was not associated with the cool dry season rotavirus outbreaks. Rainy season diarrhoea was also associated with more persistent diarrhoea, an older mean age and a higher mortality. Meningitis was caused by either pneumococcus or Haemophilus influenzae in 64% of cases, of whom 19% were 0-2 months of age. Causes of death in hospital showed good agreement with Gambian community studies. We conclude that analysis of hospital data in a developing country can give accurate information on childhood morbidity and mortality patterns which can be used to set priorities for health care interventions. Seasonal variation is a cardinal feature of paediatric diseases in this part of Africa, and accentuates the vulnerability of children in poor families.

Child↗
PubMed2006

Seasonality in adult asthma admissions, air pollutant levels, and climate: a population-based study.

OBJECTIVE AND BACKGROUND: Most studies of asthma seasonal variations have not examined associations of environmental risk factors and climatic changes associated with seasonality in asthma hospitalizations. This study used population-based data to examine seasonality in asthma admissions and the associated seasonality in levels of air pollutants and climatic factors during a 4-year period in Taiwan. METHODS: A total of 126,671 asthma hospitalizations in Taiwan during 1998-2001 operationalized as monthly admissions per 100,000 population and monthly mean levels of criterion air pollutants and meteorological factors were subjected to Auto-Regressive Integrated Moving Average to test for seasonality and association between asthma admission rates and the pollutant and climatic factor levels. Owing to significant differences in seasonality between pediatric and adult age groups, this study was limited to 99,591 adult asthma cases to examine the seasonality issue as related to the criterion air pollutants and climatic factors using Spearman rank correlations. RESULTS: Seasonal trends showed a hospitalization peak in January through March and a sharp decline beginning in April to a trough in June for both sexes. Seasonal variations in adult asthma admissions were significantly positively correlated with levels of PM10, SO2, CO, NO2, and atmospheric pressure and negatively correlated with temperature and hours of sunshine. CONCLUSIONS: Adult asthma hospitalization propensity is highest in spring and is significantly correlated with air pollution and climate. Air quality control programs and early public warning systems on pollution and atmospheric factors are needed to enable predisposed individuals and their physicians to preempt attacks through primary and secondary preventive measures.

Adolescent↗