Animal and worker exposure to dust and biological particles in animal care houses

An aerobiological study was performed to evaluate the potential exposure of animals and workers to dust constituents generated during routine animal house work. Different rooms of air conditioned (A, control) and passively ventilated (B, non-air conditioned) animal facilities were sampled, in order to evaluate total airborne culturable fungi and bacteria, fungal spore concentrations and particle levels. Airborne room particles were analyzed gravimetrically and for endotoxin content. All parameters, except for culturable fungi, were higher in facility B and statistically significant, with respect to those from the control facility A. Median values for airborne particle concentration, endotoxin and fungal spores in facility B were: 115 µg m^–3, 25 EU m^–3, and 2173 spores m^–3, respectively. Median values for facility A were: 66 µg m^–3, 9 EU m^–3, and 248 fungal spores m^–3. Broncheoalveolar lavage from rats kept in the rat room of B, presented median concentrations of total cells and lactate dehydrogenase, higher than those found in the control facility (4.4 × 10⁵ vs. 1.1 × 10⁵ and 2.7 UmL^-1 vs. 0.39 UmL^–1, respectively). Values of total and biological particles of both facilities, as well as the time spent in different rooms, showed that worker exposure was higher during cage washing. It was especially high in the passively ventilated facility (airborne particles 686 µg m^–3 3.5 h^–1 vs. 976 µg m^–3 3.5 h^–1, endotoxin 70 EU m^–3 3.5 h^–1 vs. 108 EU m^–3 3.5 h^–1). The type of basidiospores and ascospores found, as well as the significant correlation between particle levels and endotoxin contents suggests that wood chip bedding disturbance during cage washing is an important source for airborne biological particles. The changes in broncheoalveolar lavage components found in rats from these facilities and previously reported changes in pro-inflammatory cellular responses found in workers, indicate that these relatively low levels of exposure are enough to induce a biological response. Studies considering the composition of mixed organic dusts, would be needed to reevaluate current occupational standards.     

Aerosols of Mycoplasmas, L Forms, and Bacteria: Comparison of Particle Size, Viability, and Lethality of Ultraviolet Radiation

Aerosols of microorganisms were tested for particle size by use of an Andersen sampler. Mycoplasma aerosols had an average count median diameter (CMD) of 2.1 ± 0.5 μ. Staphylococcus aureus L forms gave an average CMD of 4.6 ± 1.7 μ; the diphtheroid L form, a CMD of 3.4 ± 0.3 μ. Escherichia coli had a CMD of 5.4 ± 2.5 μ; Neisseria sicca, 3.3 ± 0.5 μ; N. meningitidis, 3.4 ± 0.2 μ. S. aureus ATCC 6538, the parent strain of the L form, yielded a CMD of 3.9 ± 1.2 μ. Candida albicans gave an average CMD of 5.9 ± 1.4 μ. All organisms tested survived aerosolizing and could be recovered in viable form for at least 1 hr. Ultraviolet radiation at 2,537 A destroyed the bacteria and mycoplasmas instantaneously, and destroyed 87% of the L forms of S. aureus, 69% of the diphtheroid L form, and 98% of the C. albicans cells. After irradiation, viable particles of the L form and C. albicans aerosols were consistently larger, indicating that clumping led to survival. Submicron size particles were found in aerosols of all species tested except C. albicans.     

The amount and value of work time of community medicine distributors in community case management of malaria among children under five years in the Ejisu-Juaben District of Ghana

ABSTRACT: BACKGROUND: The contribution of community medicine distributors (CMD) to prompt health service delivery in areas described as "hard-to-reach" is important but the value of their work time remains unknown and thus makes it difficult to design appropriate regular financial incentives to motivate them. This makes CMDs feel their efforts are not recognized. An attempt to estimate the value of 54 CMDs work time involved in community case management of malaria (CCMm) in a rural district in Ghana is presented. METHODS: Time spent by CMDs on CCMm activities were recorded for a period of 12 months to determine the work-time value. Cost analysis was performed in Microsoft Excel with data from CMD records and at 2007 market price in Ghana. RESULTS: A CMD spent 4.8 hours, [95% CI: 3.9; 5.3] on all CCMm-related activities per day. The time value of CMD work ranged from GHc 2.04 (US$ 2.24) to GHc 4.1 [US$ 4.6] per week and GHc 19.2 - 86.4 (US$ 21.10-94.95) per month. The gross wage outside CCMm as reported by CMD was GHc 58.4 [US$ 64.69] and value of foregone income of GHc 86.40 (US$94.95) per month, about 14-times higher than the monthly incentives of GHc 6.0 given by the CCMm programme. CONCLUSION: The value of work time and the foregone income of CMDs in CCMm are high and yet there are no regular and sustainable incentives provided for them. The results are significant to policy in designing incentives to motivate CMDs in large-scale implementation of CCMm.     

Size and UV Germicidal Irradiation Susceptibility of Serratia marcescens when Aerosolized from Different Suspending Media

Experimental systems have been built in laboratories worldwide to investigate the influence of various environmental parameters on the efficacy of UV germicidal irradiation (UVGI) for deactivating airborne microorganisms. It is generally recognized that data from different laboratories might vary significantly due to differences in systems and experimental conditions. In this study we looked at the effect of the composition of the suspending medium on the size and UVGI susceptibility of Serratia marcescens in an experimental system built in our laboratory. S. marcescens was suspended in (i) distilled water, (ii) phosphate buffer, (iii) 10% fetal calf serum, (iv) phosphate-buffered saline (saline, 0.8% sodium chloride), and (v) synthetic saliva (phosphate-buffered saline with 10% fetal calf serum). At low humidity (36%), S. marcescens suspended in water-only medium was the most susceptible to UVGI, followed by those in serum-only medium. The count median diameters (CMDs) for culturable particles from water-only and serum-only media were 0.88 and 0.95 μm, respectively, with the measurements based on their aerodynamic behavior. The bacteria suspended in phosphate buffer, synthetic saliva, and phosphate-buffered saline had similar UVGI susceptibility and CMD at 1.0, 1.4, and 1.5 μm, respectively. At high humidity (68%) the CMD of the particles increased by 6 to 16%, and at the same time UVGI susceptibility decreased, with the magnitude of decrease related to the type of suspending medium. In conclusion, the choice of suspending medium influenced both size and UVGI susceptibility of S. marcescens. These data are valuable for making comparisons and deciding on the use of an appropriate medium for various applications.     

Dispersal of fungal spores from three types of air handling system duct material

Exposure to airborne microorganisms in indoor environments may result in infectious disease or elicit an allergic or irritant response. Air handling system components contaminated by fungi have been implicated in the dispersal of spores into the indoor environment, thereby serving as a route of exposure to occupants. This study was conducted to provide quantitative data on the dispersal of spores from fungal colonies growing on three types of duct material. Galvanized metal, rigid fibrous glass ductboard, and fiberglass duct liner were soiled and contaminated with a known concentration of Penicillium chrysogenum spores. The duct materials were incubated in humidity chambers to provide a matrix of growing, sporulating fungal colonies at a contamination level of 109 colony forming units (CFU) per duct section, consistent for all materials. For each experiment a contaminated duct section was inserted into the air handling system of an experimental room, and the air handling system was operated for three 5-minute cycles with an air flow of 4.2 m3 min–1. The duct air velocity was approximately 2.8 m sec–1. The airborne concentration of culturable P. chrysogenum spores (CFU m–3), total P. chrysogenum spores (spores m–3), and total P. chrysogenum-sized particles (particles m–3) were measured in the room using Andersen single-stage impactor samplers, Burkard slide impactor samplers, and an aerodynamic particle sizer, respectively. The highest airborne concentrations (104 CFU m–3; 105 spores m–3; 104 particles m–3) were measured during the first operating cycle of the air handling system for all duct materials with decreasing airborne concentrations measured during the second and third cycles. There was no significant difference in spore dispersal from the three contaminated duct materials. These data demonstrate the potential exposure for building occupants to high concentrations of spores dispersed from fungal colonies on air handling system duct materials during normal operation of the system.     

Size and UV germicidal irradiation susceptibility of Serratia marcescens when aerosolized from different suspending media

Experimental systems have been built in laboratories worldwide to investigate the influence of various environmental parameters on the efficacy of UV germicidal irradiation (UVGI) for deactivating airborne microorganisms. It is generally recognized that data from different laboratories might vary significantly due to differences in systems and experimental conditions. In this study we looked at the effect of the composition of the suspending medium on the size and UVGI susceptibility of Serratia marcescens in an experimental system built in our laboratory. S. marcescens was suspended in (i) distilled water, (ii) phosphate buffer, (iii) 10% fetal calf serum, (iv) phosphate-buffered saline (saline, 0.8% sodium chloride), and (v) synthetic saliva (phosphate-buffered saline with 10% fetal calf serum). At low humidity (36%), S. marcescens suspended in water-only medium was the most susceptible to UVGI, followed by those in serum-only medium. The count median diameters (CMDs) for culturable particles from water-only and serum-only media were 0.88 and 0.95 micro m, respectively, with the measurements based on their aerodynamic behavior. The bacteria suspended in phosphate buffer, synthetic saliva, and phosphate-buffered saline had similar UVGI susceptibility and CMD at 1.0, 1.4, and 1.5 micro m, respectively. At high humidity (68%) the CMD of the particles increased by 6 to 16%, and at the same time UVGI susceptibility decreased, with the magnitude of decrease related to the type of suspending medium. In conclusion, the choice of suspending medium influenced both size and UVGI susceptibility of S. marcescens. These data are valuable for making comparisons and deciding on the use of an appropriate medium for various applications.     

Fungal spore concentrations in the air at Tiruchirapalli (India) 1987–1988

Summary Using an aeroscope, airborne fungal spores were sampled for two years, 1987–1988 at Tiruchirapalli, Tamil Nadu, India. The aerospora components, their seasonal and annual variations in incidence in the air are discussed and a spore calendar for Tiruchirapalli is presented.     

Ultrastructure and functional characteristics of the optic nerve of Rana temporaria L. in the norm and during degeneration

Results of electron microscopy and electrophysiological studies of the frog optic nerve are presented. The nerve contains 96% unmyelinated (about 210,000) and 4% myelinated (8700–14,800) fibers. The peripheral zone of the nerve (20–30 µm) has relatively few myelinated fibers, whereas in other zones these fibers are distributed uniformly (counting area 300–400 µm²). The curve of the distribution of the diameters of myelinated fibers has a number of peaks: a main peak at 1 µm and additional peaks at 0.6 and 1.6 µm (the latter is more prominent). Individual fibers have a diameter of 0.4–3.9 µm. The diameter of the unmyelinated fibers are 0.1–0.4 µm; 64% of these fibers have a diameter of 0.2 µm. Most fibers at a temperature of 18–20° conduct at 0.3–0.4 m/sec and a few (myelinated with a diameter of 1.0–1.6 µm) at 3 and 6 m/sec. After enucleation the myelinated fibers degenerate at first and are phagocytized by neuroglia; the ultrastructure and function of the unmyelinated fibers at 18–20° remain unchanged up to 100 days postoperation.A. N. Severtsov Institute of Evolutionary Animal Morphology and Ecology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 2, No. 6, pp. 627–635, November–December, 1970.     

Mass loss and qualitative change in stream-incubated fine particulate organic matter derived from leaves differing in rate of processing

The initial quantitative breakdown of fine particulate organic matter (FPOM) was investigated by measuring the loss (over 73 days) of substrate mass of particles of known size ranges (53–125 µm, 125–250 µm, 250–500 µm, 500 µm-1 mm) and derived from known organic sources (Alnus rubra, Acer macrophyllum, Polystichum munitum). Qualitative examinations (organic content, C : N ratio) also were made. Particles ranging from 500 µm to 1 mm in diameter differed greatly from particles in other size ranges, and results of studies with these particles closely resembled results of coarse particulate (CPOM) leaf pack studies. Despite variation, alder particles generally exhibited the greatest mass loss, those of sword-fern, the least, and mass loss of bigleaf maple particles was intermediate. Organic contents of all particle substrates decreased over time. In general, the C : N ratios of alder particles increased, those of bigleaf maple decreased, and those of sword-fern exhibited little change. All particle substrates were incubated in the field in vials, which allowed for influx of natural detritus of unknown source and period of residence. Given the overall abundance and prevalence of the FPOM resource in lotic systems, standardization of a procedure such as that used in this investigation would be useful in extending understanding of stream system processes, including detrital processing and decomposition.     

Trophic structure and productivity of the lagoonal communities of Tikehau atoll (Tuamotu Archipelago,French Polynesia)

Carbon standing stocks and fluxes were studied in the lagoon of Tikehau atoll (Tuamotu archipelago, French Polynesia), from 1983 to 1988.The average POC concentration (0.7–2000 µm) was 203 mg C m^–3. The suspended living carbon (31.6 mg C m^–3) was made up of bacteria (53%), phytoplankton < 5 µm (14.2%), phytoplankton > 5 µm (14.2%), nanozooplankton 5–35 µm (5.7%), microzooplankton 35–200 µm (4.7%) and mesozooplankton 200–2000 µm (7.9%). The microphytobenthos biomass was 480 mg C m^–2.Suspended detritus (84.4% of the total POC) did not originate from the reef flat but from lagoonal primary productions. Their sedimentation exceeded phytobenthos production.It was estimated that 50% of bacterial biomass was adsorbed on particles. the bacterial biomass dominance was explained by the utilisation of 1) DOC excreted by phytoplankton (44–175 mg C m^–2 day ^–1) and zooplankton (50 mg Cm^–2 day^–1)2) organic compounds produced by solar-induced photochemical reactions 3) coral mucus.50% of the phytoplankton biomass belongs to the < 5 µm fraction. This production (440 mg C m^–2 day^–1) exceeded phytobenthos production (250 mg C m^–2 day^–1) when the whole lagoon was considered.The zooplankton > 35 µm ingested 315 mg C m^–2 day^–1, made up of phytoplankton, nanozooplankton and detritus. Its production was 132 mg C m^–2 day^–1.     

Common Mental Disorder Symptoms among Patients with Malaria Attending Primary Care in Ethiopia: A Cross-Sectional Survey

Background

Common Mental Disorders (CMDs) are frequent among patients attending primary care. In Africa, CMDs are often misdiagnosed as physical illnesses because many of the patients complain of somatic symptoms of mental distress. We explored whether there was difference in the levels of CMD symptoms between patients with thick film confirmed and clinical cases of malaria with negative thick film in primary care.

Methods

A cross-sectional comparative study was conducted on 300 adults with a clinical diagnosis of malaria in primary care centres in Jimma, Ethiopia. Patients were recruited consecutively until 100 cases of ‘malaria’ with a negative thick film and 200 cases of malaria with a positive thick film consented to participate. The 20-item Self-Reporting Questionnaire (SRQ-20) was used to measure CMD. The non-parametric Wilcoxon rank-sum test was used to explore the association between thick film result and CMD.

Results

Participants had a mean age of 28.2 (S.D = 10.9) years and the majority (57.3%) were women. The prevalence of high CMD symptoms (six or more symptoms on the SRQ-20) was 24.5%. Suicidal ideation was reported by 13.8% of the participants. CMD symptoms were significantly higher in patients who had taken medication prior to visiting the primary care (p = 0.012) and in those whose symptoms had been present for seven days or more (p = 0.041). There was no statistically significant association between level of CMD symptoms and having a negative thick film result (OR 0.98; 95%CI 0.92, 1.04) or objective presence of fever (OR 1.04; 95%CI 0.93, 1.15).

Conclusions

CMD symptoms among cases of malaria did not appear to be associated with a negative thick film result. The high levels of CMD symptoms, including suicidal ideation, calls for further studies to investigate the persistence and progression of these symptoms following resolution of the acute malarial episode.     

Phosphorus sedimentation in seasonal anoxic Lake Scharmützel, NE Germany

The seasonal course of phosphorus (P) fractions of sinking particulate matter has been studied at the deepest location of dimictic eutrophic Lake Scharmützel (29.5 m) by paired sediment traps at 9 and 27 m water depth from May 1996 to December 1997. Relatively large depositional fluxes and considerably variable P fluxes, mainly carried by allochthonous particles, diatoms in spring, and iron during overturns transport almost 60% of the average water column P pool to the sediment surface. The contribution of resuspension and sediment focusing (24–34%) is relatively small. A sequential chemical P extraction of the matter entrapped revealed that ,loosely adsorbed` P contributed to 5–14%, organic bound P to 55–68%, and Ca-associated P to 3–6% of the annual P flux, depending on season and depth. The redox-sensitive (iron bound) P ranged from only 12% of the annual P flux during anoxic sulfidic conditions to 28% during oxic conditions. On an annual basis, 16–18% of sedimenting P was recycled within the water column, and 71–75% of total primary P flux was recycled at the sediment surface. Ultimately, 10–23% of P became incorporated into recent sediments indicating the long residence time for P and a high internal resupply of P for primary production.     

Particle size dependent feeding by the rotifer Brachionus plicatilis

Size selective feeding by Brachionus plicatilis was investigated with algae and bacteria (0.3–3.5 µm) and mono-disperse latex beads (0.3–3.0 µm) in short term feeding experiments. B. plicatilis demonstrated maximum clearance rate of particles with diameter 2µm, but particles with diameter down to 0.3 µm were also ingested. The clearance rate of bacteria was 15–55% of that obtained for optimal sized particles (2 µm), and was related to particle size. The relative reduction in retention of particles with diameter < 2 µm was more pronounced for latex beads than for natural food particles, suggesting other mechanisms than size to be important for the particle retention by the rotifer. This is emphasized by the fact that the clearance rates were much lower for latex beads than for natural food particles of comparable size. Efficient retention of bacteria was observed for rotifers in poor physiological condition, i.e. rotifers with low maximum clearance rate. This may reflect a strategy to optimize energy utilization by reducing locomotion costs and increasing energy intake.The results indicate that B. plicatilis has a low to medium ability to feed on bacteria. In natural ecosystems, its importance as a bacterial grazer is of limited importance. At high population densities, such as in live feed cultures, the rotifer may, however, efficiently remove bacteria from the culture.     

Characteristics of plankton communities in Chinese integrated fish ponds: effects of excessive grazing by planktivorous carps on plankton communities

Biomass and production of plankton communities were investigated in two Chinese integrated fish culture ponds in August, Dianshanhu Pond (with high density of planktivorous carp) and Pingwang Pond (with low density of planktivorous carp). The plankton communities were composed of rotifers, protozoans, phytoplankton (<40 µm) and bacteria. The large phytoplankton (>40 µm), cladocerans and copepods were rare because of grazing pressure by the carp. The density or biomass of bacteria (1.93 × 10⁷ and 2.20 × 10⁷ cells ml^–1 on average in Dianshanhu and Pingwang Ponds, respectively), picophytoplankton (24.6 and 18.5 mg m^–3 Chla on average) and rotifers (5372 and 20733 ind. 1^–1 on average) exceeded the maximum values reported for natural waters.The average [³H]thymidine uptake rates were 694 and 904 pmoles 1^–1 h^–1 (13.4 and 20.6 µgC 1^–1) and the bacterial production by the >2 µm fraction amounted 21–28% of total [³H] thymidine uptake rate in both ponds. The mean chlorophylla concentrations were 59.1 and 183 mg m^–3 in Dianshanhu and Pingwang Ponds, respectively. 82.4% and 65.3% of the total Chla was contributed by the <10 µm nano- and picophytoplankton in each pond, respectively. In particular, the picophytoplankton contribution amounted 41.2% of thtal Chla in Dianshanhu Pond. Primary production was 2.5 and 3.4 gC m^–2 d^–1 in each pond, respectively, and >50% of production was contributed by picophytoplankton. The mean biomasses of protozoa were 168 µg 1^–1 and 445 µg 1^–1 and those of rotifers were 763 µg 1^–1 and 1186 µg 1^–1 in Dianshanhu and Pingwang Ponds, respectively. The ecological efficiencies expressed in terms of the ratios of primary production to zooplankton production were 0.22 and 0.31, for the two ponds.     

Coccidian parasites (Apicomplexa: Eimeriidae) of the endemic Florida snake Tantilla relicta Telford (Serpentes: Colubridae)

The endemic Florida snake Tantilla relicta Telford is parasitised by six species of coccidia. Caryospora tantillae n. sp. has nearly spherical oöcysts, 19.6 × 18.9 µm (16–22 × 16–21), with no polar body, and an oöcyst length/width ratio (shape index, SI) of 1.04 (1.00–1.11). Ovoidal sporocysts are 15.1 × 11.6 µm (12–17 × 10–13), with an SI of 1.30 (1.1–1.6), a single prominent Stieda body and a sporocyst residuum. Sporozoites are 14 × 2.5 µm. Caryospora relictae n. sp. also has nearly spherical oöcysts, 18.5 × 17.6 µm (16–22 × 15–20), but is distinguished by having a distinct polar body and a substieda body in sporocysts. The oöcyst SI is 1.05 (1.0–1.2). Sporocysts are ovoidal, 14.8 × 11.4 µm (12–17 × 10–16), with an SI of 1.29 (1.1–1.5) and a sporocyst residuum. Sporozoites are 10–14 × 2–2.5 µm. Isospora cf. wilsoni has ovoidal to spherical oöcysts without a micropyle, measure 17.4 × 17.1 µm (15–19 × 15–19), and have an SI of 1.02 (1.00–1.07). Oöcysts have no polar granule or oöcyst residuum. Sporocysts are ovoidal, 11.4 × 8.2 µm (9–14 × 7–10), with an SI of 1.39 (1.18–1.62). Both a Stieda body and sporocyst residuum are present, but a substieda body, characteristic of I. wilsoni as described, was not observed. Sporozoites are 7–8 × 2.5–3 µm. An Eimeria sp., of which the sample was too small to justify taxonomic designation, has nearly spherical oöcysts without micropyle, a size of 22.5 × 20.9 µm (22–23 × 20–22), an SI of 1.08 (1.00–1.12) and no polar granule. Sporocysts measure 12.5 × 8.9 µm (11–14 × 7–11) and have an SI of 1.44 (1.18–1.87), a sporocyst residuum and no Stieda body. Sporozoites are 13 × 5 µm. Eimeria amphorae n. sp. has ovoidal to spherical oöcysts without a micropyle, a size of 24.8 × 22.3 µm (23–27 × 20–26), an SI of 1.12 (1.02–1.25) and no polar granule or oöcyst residuum. Sporocysts are elongate, 18.4 X 8.0 µm (17-22 × 6-9.5), with an SI 2.33 (1.79–3.00) and no discernible Stieda body or sporocyst residuum. Sporocyst shape differs by orientation, rectangular to amphora-like, tapering abruptly to a blunt point; sporozoites large, 15.5 × 4.2 µm. A biliary parasite, Eimeria pleistocenensis n. sp., has ovoidal to elongate oöcysts, without micropyle, with a size of 27.8 × 19.4 µm (23–32 × 14–23), with an SI of 1.44 (1.17–1.82) and an oöcyst residuum but no polar granule. Sporocysts ovoidal, 10.7 × 8.6 (9–13 × 8–10), with an SI of 1.24 (1.05–1.37), a sporocyst residuum, but without Stieda body; sporozoites 8.8 × 2.7 µm. Similar oöcysts from other Tantilla relicta populations, T. relicta neilli in north Florida T. relicta pamlica in southeastern Florida and T. relicta relicta in south-central Florida, have dimensions that lie within the range of variation in the type population and identically shaped sporocysts that suggest conspecificity with E. pleistocenensis, and presence of the species in the precursor to Tantilla relicta prior to the second interglacial period.     

Quantity and quality of seston in an impounded and a free-flowing river in Virginia,U.S.A.

Seston in the impounded North Anna River (NAR) was analyzed and compared to that in the free-flowing South Anna River (SAR) in Virginia, U.S.A. A wet filtration technique was used to separate seston into five size classes. The overall quantity of organic seston was much lower in the NAR than in the SAR. The seston in the NAR was composed of more living organisms, in particular zooplankters in the medium large (234–864 µm) and small (105–234 µm) size classes and diatoms and other algae in the fine (43–105 µm) and very fine (25–43 µm) size classes. The percentage of zooplankton declined sharply before reaching the downstream study site (32 km). The seston in the NAR tended to consist of slightly larger particles, but 80–85% of the seston in both rivers was in the ultrafine (0.45–25 µm) size class, which was almost entirely composed of detritus. One indication of seston food quality, the organic/inorganic ratio, was considerably higher for the medium large and small size classes in the NAR immediately below the dam and for the fine and very fine size classes farther downstream. Another indication of food quality, the usable caloric content, showed that the seston in the NAR contained considerably less total assimilable energy as far as 32 km downstream from the dam, but that the medium large and small size classes were rich in assimilable energy immediately below the dam because of zooplankton released from the reservoir. Thus, the overall quantity and quality of seston was lower in the NAR, but the quality of the seston, for at least a short distance below the dam, was higher in a well-defined size range that can be effectively utilized by certain filter feeders.     

A laboratory study of feeding and assimilation in Euchlanis dilatata lucksiana

Feeding of Euchlanis dilatata lucksiana, a brachionid rotifer isolated from the Loosdrecht Lakes (The Netherlands), was examined in the laboratory using ¹⁴C-labelled food. The gut-filling time at a food concentration of 9.6 µg C ml^–1 was about 15 minutes. Animals which were fed on 3 size fractions of the lake seston (< 7 µm, 7–15 µm, and 15–33 µm) showed a clear preference (Jacobs' selectivity index) for the largest size fraction. This fraction was composed predominantly of filamentous cyanobacteria. For animals weighing 0.37–0.49 µm C ind.^–1 the daily ration (daily food consumption per unit body weight × 100) ranged from 50 to 100% at food levels of 2 mg C l^–1 and below, but increased to 150–250% at food concentrations of 5 mg C l^–1 and above. The assimilation efficiency was 100% up to 5 mg C l^–1 of food, but decreased to about 80% at higher food levels.     

Growth and age structure of the swan mussel Anodonta cygnea (L.) at different depths in lake Mattsee (Salzburg, Austria)

Unionid clams were collected at 1–2 m, 3–4 m and 6–7 m depth in lake Mattsee, a moderately mesotrophic lake, to investigate the effect of depth on clam growth and age structure. No significant differences in age structure of Anodonta cygnea were found (p=0.65). Three and ten years old clams were present at all depths, but in different percentages. Whereas at 1–2 m 13.3% of the collected clams were <4 years old, this percentage was 4.4% at 6–7 m and 7.1% at 3–4 m. A greater percentage (6.7%) of older mussels (9, 10 years) were collected at 6–7 m than at 1–2 m (2.2%). Growth declined with depth. Total length at a given age of clams at 1–2 m and 3–4 m did not differ (p=0.54), whereas differences were significant between clams at 1–2 m and 6–7 m (p<0.05) as well as between 3–4 m and 6–7 m (p<0.05). The Growth constant k was highest at 1–2 m depth.     

Growth of water hyacinth (Eichhornia crassipes (Mart.) Solms) in the middle Paraná River (Argentina)

The productivity of water hyacinth in the middle Paraná River was measured at three initial biomass levels by means of periodic harvesting of plants contained in 2 m² floating baskets. The measuring period extended between August 1981 and July 1982. Initial biomass densities were 2, 5 and 10 kg (fw) m^–2.Compared with inner island ponds, flowing waters connected to the main river showed better conditions for water hyacinth growth. The duration of the growth period was some 30% longer than in island ponds, probably due to the relatively warmer river waters. Productivity ranged between 108 and 164 g (fw) m ^–2 d^–1 (annual average) for the lower and higher initial biomass values, respectively.     

Genetic epidemiology of congenital muscular dystrophy in a sample from north-east Italy

Congenital muscular dystrophy (CMD) is a heterogenous disease with autosomic recessive transmission. In an epidemiological study in four provinces of Veneto (region of 2586830 inhabitants in north-east Italy), the recorded incidence rate for the period 1979–1993 was 4.65 x 10^–5; the prevalence rate in the year 1993 was 6.8 × 10^–6. The incidence and the prevalence rates that we have obtained during the course of our investigation represent the first estimates for CMD in Europe and show that this myopathy is among the most frequent neuromuscular diseases with autosomic recessive transmission.