Seasonal Variation In Prevalence Research Articles

Digenean parasite communities in flatfishes of the Scotian Shelf and southern Gulf of St. Lawrence

Prevalence of digenean parasites in four major flatfishes of the Scotian Shelf and southern Gulf of St. Lawrence, American plaice (Hippoglossoides platessoides), yellowtail flounder (Limanda ferruginea), witch flounder (Glyptocephalus cynoglossus), and winter flounder (Pseudopleuronectes americanus), is compared between hosts in relation to geographic distribution, season, feeding behavior, and fish length. The 13 parasite species indicate overlap of feeding habits among hosts but also considerable diversity in feeding behavior, supporting the evidence from examination of stomach contents. Prevalence of digeneans in different final hosts varied between geographic areas and may be used to characterize the populations of the comparatively sedentary flatfish populations. Seasonal variation in prevalence was consistent from area to area but differed between parasites, from the expected increase in summer in some, concomitant with increased feeding, to a winter increase in others, probably related to a seasonal change of diet. Fish length had little effect on parasite prevalence in yellowtail flounder and witch flounder but had a notable effect on plaice and winter flounder from the Gulf of St. Lawrence, again apparently related to change of diet.

EFFECTS OF PRESCHOOL SCREENING FOR VISION AND HEARING ON PREVALENCE OF VISION AND HEARING PROBLEMS 6-12 MONTHS LATER

In order to determine whether children screened 6-12 months previously for vision and hearing had fewer vision and hearing problems than a non-screened cohort, a trained nurse-tester examined 763 screened and 743 non-screened kindergarten children matched for age, sex, and socioeconomic status. The screened cohort had significantly fewer vision problems (10%) than the unscreened (15%). The difference for moderately severe problems (visual activity 20/50 or worse) was also significant. 58% more screened than unscreened children were wearing glasses. The screened cohort had more hearing problems (16·8%) than the non-screened group (14%), but the difference was not statistically significant. There was a marked seasonal variation in prevalence of hearing problems, the frequency in November and December being twice that in April, presumably a result of increased frequency of upper respiratory problems in those months. Preschool hearing screening, unlike vision screening, is not associated with improved end results.

Seasonal trends in the prevalence and intensity of spiruroid nematode infections ofRattus r. rattus

Abstract Examination of stomach contents from 191 Rattus r. rattus, trapped over 12 months in an area of bush in the Manawatu district, revealed that 123 (64.4%) of the rats were infected with Physaloptera getula (Physalopteridae) and 39 (20.4%) with Mastophorus muris (Spiruridae). The high prevalence of P. getula did not vary significantly during the year, but there were marked seasonal variations in the numbers of worms per rat, the highest mean counts occurring in autumn and the lowest in late winter and spring. The prevalence of M. muris varied significantly through the year, and was highest in autumn. Mean worm counts per rat appeared to be biphasic, with peaks in spring and autumn; however, since only small numbers of animals were infected, this may not represent what actually occurs. The majority of infections with both nematode species comprised less than 10 worms. Possible reasons for the seasonal variation in prevalence and intensity of infections are discussed. Circumstantial evidence suggests that wetas (Orthoptera: Stenopelmatidae), on which the rats feed, may be an intermediate host of P. getula.

Parasites and Pathological Findings in Enclosed and Free-Ranging Populations of Macropus Rufus (Demarest) (Marsupialia) at Menindee, New South Wales.

A total of 115 Macropus rufus was collected at bimonthly intervals at Menindee, New South Wales, Australia, in 1976 and 1977 and examined for parasites and pathological changes. The animals came from 2 populations, one free-ranging and the other a high-density, enclosed population in Kinchega National Park. No differences in species of helminths present, in prevalence or intensity of infection were noted between the 2 populations. The stomachs were infected with Labiostrongylus longispicularis (prevalence 87.8%), Rugopharynx australis (98.2%), Zoniolaimus spp. (81.6%), Cloacina spp. (71.1%), Papillostrongylus labiatus (47.4%) and Filarinema spp. (92.2%). Hypodontus macropi (93.0%) was the dominant species among the 2 species of cestodes and 3 of nematodes found in the intestine. Progamotaenia festiva (in 74.3%) was found in the bile ducts where it caused mild cholangitis. Only 2 nematode species, F. flagrifer and H. macropi, caused gross and histological lesions. Apart from L. longispicularis none of the helminths showed seasonal variations in prevalence or numbers. Data on worm numbers in relation to host age and on site distribution in the host are presented. The various haematological parameters measured showed no evidence of adverse effects by the parasites, and corticosteroid levels were judged to be within the normal range. The helminth faunas of 9 M. fuliginosus and one M. robustus, grazing sympatrically with M. rufus inside the park are listed. ADDITIONAL ABSTRACT: The parasites reported from 115 red kangaroos (Macropus rufus) in New South Wales in 1976-77 include Tracheomyia macropi (Frogg.), which infected the trachea in 54.5% of the kangaroos [see RAE/B 4, p. 122].

Infant foods as a potential source of diarrhoeal illness in rural West Africa

It is common practice in rural areas of The Gambia to prepare infant foods in quantities which are sufficient to meet the needs of the day rather than one meal. These are then stored at ambient temperatures for periods up to 12 hours for feeding to the child on demand The total viable counts and levels of Bacillus cereus, Clostridium welchii, Staphylococcus aureus and Escherichia coli were determined in 294 infant foods samples from nought to eight hours after preparation. The presence of Salmonella was determined in 10 g samples of food. In the first hour after preparation the proportion of foods dangerously contaminated was high during the rainy season, significantly more so than during the dry season. Foods not consumed fresh were very often hazardous and almost always so after 8 hours. This problem may be a causal factor in weanling diarrhoea which also shows marked seasonal variation in prevalence.

The role of flies in the transmission of eye disease in Egypt.

SummaryTwo species of flies, M. d. vicina and M. sorbens, collected from the faces of Egyptian village children from August, 1955, through June, 1956, were studied for types of internal and external bacterial flora. Enteric bacteria were found in every pool of flies, and organisms associated with respiratory infections, conjunctivitis, and pyogenic infections were frequently isolated. Although seasonal variation in total numbers of bacteria was not observed, organisms of the Micrococcus group were isolated more often than other organisms, and indicated some seasonal variation in prevalence, which was not entirely explainable on the basis of relative fly prevalence. The beta-hemolytic staphylococci and streptococci were isolated most frequently during August, while the nonhemolytic and alpha-hemolytic micrococci were found most often during April, May and June. The corynebacteria were isolated most frequently during May and June.Bacterial types similar to those isolated from flies were obtained from both normal and diseased eyes of Egyptian children. The organisms most commonly isolated from either eyes or flies were the hemolytic micrococci, several of which produced ophthalmia in experimentally infected rabbits.