Survival of parasite eggs upon storage in sludge.

Destruction rates of parasite eggs in stored sludge were examined to help understand the fate of these agents of enteric diseases in sludge lagoons. Eggs from the roundworms, Ascaris spp., Toxocara spp., Trichuris spp., and the tapeworm, Hymenolepis spp., were treated with domestic sludges by aerobic or anaerobic processes. Sludge samples seeded with eggs were stored at 4 or 25 degrees C or in a container inserted into the ground to simulate lagoon conditions. The number of eggs recovered from the samples decreased with storage time. The viability and infectivity of eggs recovered were related to the storage temperature; i.e., the eggs stored at 4 degrees C remained viable longer than those stored at 25 degrees C. After 25 months at 4 degrees C, the Toxocara eggs and some Ascaris eggs remained both viable and infective, whereas most of these eggs stored at 25 degrees C were rendered nonviable after 10 to 16 months of storage in sludge. Although storage temperature was found to be the most important factor affecting the destruction and viability of these eggs, other factors, such as the type of sludge digestion, whether or not the eggs were digested along with the sludge or added later, storage in the soil versus sludge, pH, and egg species also exhibited some minor effects. These controlled laboratory studies suggest that lagooning of sludge can be an effective method for the elimination of parasite eggs, particularly in warmer geographical locations.     

Survival rates of parasite eggs in sludge during aerobic and anaerobic digestion.

The effects of mesothermic anaerobic or aerobic sludge digestion on survival of eggs from the roundworms Ascaris suum, toxocara canis, Trichuris vulpis, and Trichuris suis and from the rat tapeworm Hymenolepis diminuta were studied. Destruction of eggs throughout a 15-day treatment period, as well as their viabilities after reisolation, was analyzed. The laboratory model digesters used in this study were maintained at a 15-day retention schedule, partially simulating a continuously operating system. Ascaris eggs were destroyed in the anaerobic (23%) or aerobic (38%) digesters, and 11% Trichuris eggs were destroyed in the aerobic digesters. Trichuris eggs in anaerobic digesters and Toxocara eggs in either anaerobic or aerobic digesters were not destroyed. Destruction of eggs in digesters was correlated with the state of the eggs before subjection to the treatment processes; i.e., some Ascaris and Trichuris eggs were already embryonated in host intestinal contents or feces and hence past their most resistant stage. The viabilities of Ascaris and Toxocara eggs that survived the digestion processes were greater in anaerobically treated than in aerobically treated material. Eggs from Hymenolepis were nonviable before use in the experiments. However, they were more effectively destroyed in aerobic digesters than in anaerobic digesters.     

Survival of indigenous enteric viruses during storage of waste water sludge samples

The stability of indigenous enteric viruses in samples of settled primary and mixed-liquor activated sludges was studied at 2, 23, and -70 degrees C. Changes of virus titer which occurred in these samples were followed during an 84-day observation period, with rates of change then calculated by least-squares regression. Virus survival was found to be statistically dependent (p less than or equal to 0.05) upon storage temperature but not sludge solids content. Based upon the observed rates of inactivation, the average times which would be required for a 90% decrease in virus titer are 26 days at 23 degrees C, 180 days at 2 degrees C, and 163 days at -70 degrees C. As a group, the rates of virus inactivation observed at 2 degrees C were statistically different (p less than or equal to 0.05) from those observed at 23 degrees C, but not different from those observed at -70 degrees C. The three study temperatures were selected to approximate holding of samples in an air-conditioned room, on wet ice (H2O), and on dry ice (CO2).     

Parasitism of Meloidogyne eggs by a new fungal parasite

Dactylella oviparasitica, a fungus isolated from Meloidogyne egg masses, was shown to parasitize eggs on agar and in soil, when inoculated as either myceliunt or conidia. The fungus also grew saprophytically on eggs killed ,with methyl bromide or heat. The amount of parasitism in the laboratory suggested that the fungus may be a useful biological control agent against Meloidogyne.     

Experimental shift in hosts' acceptance threshold of inaccurate-mimic brood parasite eggs

Hosts are expected to evolve resistance strategies that efficiently detect and resist exposure to virulent parasites and pathogens. When recognition is not error-proof, the acceptance threshold used by hosts to recognize parasites should be context dependent and become more restrictive with increasing predictability of parasitism. Here, we demonstrate that decisions of great reed warblers Acrocephalus arundinaceus to reject parasitism by the common cuckoo Cuculus canorus vary adaptively within a single egg-laying bout. Hosts typically accept one of their own eggs with experimentally added spots and the background colour left visible. In contrast, hosts reject such spotted eggs when individuals had been previously exposed to and rejected one of their own eggs whose background colour had been entirely masked. These results support patterns of adaptive modulation of antiparasitic strategies through shifts in the acceptance threshold of hosts and suggest a critical role for experience in the discrimination decisions between inaccurate-mimic parasite eggs and hosts' own eggs.     

Free calcium wave upon activation in Xenopus eggs

Eggs of Xenopus laevis were preloaded with aequorin and the spatial and temporal pattern of free calcium release in the egg cortex on artificial activation was determined by the aequorin luminescence emitted from the thin cortical layer of naturally opaque eggs. The aequorin luminescence was detected with a photonic microscope system consisting of a light microscope and a two-dimensional photon-counting system with an image processor. A free calcium increase was initiated around the point of prick activation. The state of increased Ca2+ propagated in the cortical cytoplasm of the egg as a wave with a velocity of about 8 micron/sec at 22 degrees C. This wave reached the antipode by 5 to 6 min of prick activation. The spatial pattern of the Ca2+ wave was similar to that of changes in brightness of the egg surface on activation, termed the "activation wave" by K. Hara and P. Tydeman (1979, Wilhelm Roux's Arch. Dev. Biol. 186, 91-94). To examine the temporal correlation between the Ca2+ wave and the activation wave, images of aequorin luminescence and those of the egg cortex taken by incident light illumination were recorded alternately in the same egg. The zone of free calcium increase corresponded to the light (relaxation) zone of the activation wave, where exocytosis of cortical granules and elongation of microvilli were taking place.     

Long-term storage of eggs of Simulium ornatum

A method for the storage of non-diapausing eggs of Simulium ornatum Meigen has been developed. High survival rates for 5-6 months depend on the age of eggs when placed at reduced temperature. A period of precooling or conditioning is required for 28 days before storage of the eggs at 1 degree C with lowering of oxygen partial pressure. Induced quiescence does not appear to affect development from egg to adult.     

Brood parasite eggs enhance egg survivorship in a multiply parasitized host

Despite the costs to avian parents of rearing brood parasitic offspring, many species do not reject foreign eggs from their nests. We show that where multiple parasitism occurs, rejection itself can be costly, by increasing the risk of host egg loss during subsequent parasite attacks. Chalk-browed mockingbirds (Mimus saturninus) are heavily parasitized by shiny cowbirds (Molothrus bonariensis), which also puncture eggs in host nests. Mockingbirds struggle to prevent cowbirds puncturing and laying, but seldom remove cowbird eggs once laid. We filmed cowbird visits to nests with manipulated clutch compositions and found that mockingbird eggs were more likely to escape puncture the more cowbird eggs accompanied them in the clutch. A Monte Carlo simulation of this 'dilution effect', comparing virtual hosts that systematically either reject or accept parasite eggs, shows that acceptors enjoy higher egg survivorship than rejecters in host populations where multiple parasitism occurs. For mockingbirds or other hosts in which host nestlings fare well in parasitized broods, this benefit might be sufficient to offset the fitness cost of rearing parasite chicks, making egg acceptance evolutionarily stable. Thus, counterintuitively, high intensities of parasitism might decrease or even reverse selection pressure for host defence via egg rejection.     

Detection of parasite eggs from archaeological excavations in the Republic of Korea

Excavations at two sites dating from 2000 BC-1900 AD in southeastern areas of the Republic of Korea, revealed the remains of several structures. Examination of the contents suspected privies revealed the presence of eggs from 5 kinds of parasite: Ascaris, Trichuris, Clonorchis, and two species of unknown trematodes. Clonorchis sinensis eggs were found in a soil dating from around AD 668-935. This is the first record of C. sinensis eggs in archaeological materials in the Republic of Korea.     

Survival of maternal mRNA in anucleate and unfertilized mouse eggs

Unfertilized mouse eggs were parthenogenetically activated in vitro and then bisected. Anucleate fragments were aged in vitro, and their protein synthesis was analyzed by two-dimensional polyacrylamide gel electrophoresis. Proteins were compared with those which were synthesized by aging unfertilized eggs and those which were translated in vitro from mRNA extracted from the unfertilized eggs. Normally cleaving parthenogenetic eggs served as controls. Cytoplasts and unfertilized eggs synthesized considerable quantities of protein after 2 days in culture. The protein patterns of cytoplasts and unfertilized eggs shifted in this time mainly within a group of proteins with a molecular mass of about 35 kDa. This shift was also seen in controls between day 1 and 2 but was delayed in unfertilized eggs. There was no clear appearance of new proteins in aging cytoplasts, which might have indicated a selective activation of maternal mRNA at a certain time after the activation stimulus, nor was such a change apparent in unfertilized eggs. The survival of maternal allozymes of glucose phosphate isomerase was tested in cytoplasts derived from fertilized eggs. The allozymes remained active during 4 days of aging and did not change their quantitative correlation.     

Dissodinium pseudolunula (Dinophyta), a parasite on copepod eggs

Direct observation as well as culture experiments revealed Dissodinium pseudolunula as an ectoparasite on eggs of the marine planktonic copepod Temora longicornis. The vegetative life cycle, especially the parasitic phase, which involves phagocytosis, is reported for the first time. The species resembles D. pseudocalani, which is also parasitic upon copepod eggs. The taxonomic position and the survival of D. pseudolunula during the absence of the host in the winter is discussed.     

Egg removal by cuckoos forces hosts to accept parasite eggs

Many avian brood parasites remove one or more host eggs before laying their own eggs in the host nest. Various hypotheses have been proposed to explain the adaptive significance of this behaviour, but none of them provides an adequate explanation. Here we provide a new hypothesis for explaining why a parasite removes host eggs before laying its own. In this study, we attempted to answer this question by constructing a mathematical model that focused on the changes in host decision making according to reduced clutch size as a consequence of egg removal by parasites. We assume that a host selects one of the following two options to maximise the number of its own chicks: trying to eject a suspicious egg from the nest (trying‐to‐eject) or acceptance without trying to eject the egg (acceptance). The option selected depends on the number of eggs in the nest. Our model provides a new explanation for egg removal behaviour by showing that the host should select trying‐to‐eject if there is a large number of eggs in the nest but acceptance with a small number of eggs. This is because the relative payoff for a host that selects trying‐to‐eject decreases with the number of eggs in the nest. Therefore, parasites benefit by removing the host egg because this behaviour reduces the number of eggs in the nest, thereby increasing the probability of their own eggs being accepted. Thus, hosts have evolved egg ejection to combat brood parasites, but it may also have facilitated the evolution of egg removal by parasites. This hypothesis may also apply to brood parasitic species that do not eject host chicks. In addition, this hypothesis may explain other parasitic behaviours, such as egg damaging and egg puncturing, which lead to reductions in the host clutch size.     

Solubility changes of proteins in sea urchin eggs upon fertilization

The results presented in this paper give evidence of changes in solubility occurring in a protein fraction of the eggs of Arbacia lixula upon fertilization. The electrophoretic analysis indicates that it is only one part of one of the components of the KCl fraction that undergoes the change. However, under some experimental conditions (freezing and thawing of the KCl fraction or extraction of the whole eggs with water at room temperature) a larger portion of the KCl fraction, namely the whole group of components a and b, may be involved and undergoes coagulation. Therefore assuming that the results obtained on the extracts of frozen-dried fertilized eggs do reflect what actually occurs under natural conditions, we must also assume the existence of mechanisms controlling the extent of this change in the living eggs. The fact that in many cases one part or the whole of the sensitive fraction has been found to undergo an increase in solubility may suggest that the process of coagulation discovered by Mirsky is a two-step process. In the first step the sensitive fraction undergoes a change that makes it more soluble and then, when certain conditions are fulfilled, coagulation occurs. An alternative explanation could also be that the coagulated or coagulating fraction is attacked by the proteolytic enzyme that, as shown by Lundblad (1949, 1950), is activated on fertilization. This, however, seems to be less probable, as extraction was always carried out at 0° C. and in as short a time as possible. However, further experiments are needed to decide whether the coagulation of the sensitive fraction is an actual occurrence under natural conditions. The results obtained with the eggs of Arbacia punctulata may cast some doubt on this assumption.     

Survival of Trichinella spiralis larvae in sewage sludge anaerobic digesters

The survival of some bacteria, viruses, protozoans, and helminths through the sewage digestion process has been a question of considerable concern among researchers throughout the world. Among the most resistant organisms are some of the pathogenic roundworms and tapeworms. Encysted larvae of Trichinella spiralis are sometimes present in animal tissues discarded as waste from slaughterhouses, restaurants or other sources. In experimental anaerobic sewage digesters, encysted larvae of T. spiralis, in rat muscle, were able to survive a maximum of 96 hr in a "batch" digester. In a digester "fed" daily with small numbers of encysted larvae, "draw-off" remained infective for white rats throughout a 16-day experimental period. Potentially infective material could be present when there is continuous "draw-off" from the anaerobic digesters.