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We introduce a system of differential equations to assess the impact of (self-)quarantine of symptomatic infectious individuals on disease dynamics. To this end we depart from using the classic bilinear infection process, but rema...
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We introduce a system of differential equations to assess the impact of (self-)quarantine of symptomatic infectious individuals on disease dynamics. To this end we depart from using the classic bilinear infection process, but remain within the framework of the mass-action assumption. From the mathematical point of view, the model we propose is interesting due to the lack of continuous differentiability at disease-free steady states, which implies that the basic reproductive number cannot be computed following established mathematical approaches for certain parameter values. However, we parametrise our mathematical model using published values from the COVID-19 literature, and analyse the model simulations. We also contrast model simulations against publicly available COVID-19 test data, focusing on the first wave of the pandemic during March–July 2020 in the UK. Our simulations indicate that actual peak case numbers might have been as much as 200 times higher than the reported positive test cases during the first wave in the UK. We find that very strong adherence to self-quarantine rules yields (only) a reduction of 22% of peak numbers and delays the onset of the peak by approximately 30–35 days. However, during the early phase of the outbreak, the impact of (self)-quarantine is much more significant. We also take into account the effect of a national lockdown in a simplistic way by reducing the effective susceptible population size. We find that, in case of a 90% reduction of the effective susceptible population size, strong adherence to self-quarantine still only yields a 25% reduction of peak infectious numbers when compared to low adherence. This is due to the significant number of asymptomatic infectious individuals in the population.
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Few aquatic animal diseases have been modelled sufficiently thoroughly to enable a credible risk assessment to be carried out - and few aquaculture management models can reliably ensure that satisfactory health status is maintaine...
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Few aquatic animal diseases have been modelled sufficiently thoroughly to enable a credible risk assessment to be carried out - and few aquaculture management models can reliably ensure that satisfactory health status is maintained in farmed fish or shellfish stocks. However, a century of experience has told us a story of diseases on the move and about the ways they travel.
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Devil facial tumour disease (DFTD), is an emerging infectious cancer thought to be spread by biting. It is causing ongoing, severe population decline of the Tasmanian devil (Sarcophilus harrisii), the largest surviving marsupial c...
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Devil facial tumour disease (DFTD), is an emerging infectious cancer thought to be spread by biting. It is causing ongoing, severe population decline of the Tasmanian devil (Sarcophilus harrisii), the largest surviving marsupial carnivore and there are concerns that DFTD may lead to extinction of the devil. Whether extinction is likely depends on contact rates and their relationship to host density. We investigated contact rates using two different datasets. The first consisted of field observations of contact and biting behaviour around prey carcasses and, the second was a 3-year longitudinal series of injuries in a marked devil population. During feeding interactions at carcasses, contact rates were significantly positively associated with population density and subadults delivered more bites than adult males and females. Injuries from the marked devil population did not differ between adult males and females. In two of the three years, penetrating biting (resulting in injury) increased markedly during the mating season and was more frequent in adults than in subadults. Among injured devils with wounds penetrating the dermal layer, adults were more frequently bitten in the head (the location of primary tumours) in the mating season than in other seasons, and had more head bites than subadults. Our results suggest that the mating season may be the key period for disease transmission. If most penetrating bites occur during mating interactions, DFTD transmission is likely to be frequency dependent, which means that there would be no threshold host density for disease persistence, and disease-induced extinction is possible.
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The question of whether SARS-CoV-
2
is mainly transmitted by droplets or aerosols
has been highly controversial. We sought to explain this controversy through a historical analysis of transmission research in other diseases. Fo...
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The question of whether SARS-CoV-
2
is mainly transmitted by droplets or aerosols
has been highly controversial. We sought to explain this controversy through a historical analysis of transmission research in other diseases. For most of human
history, the dominant paradigm was that many diseases were carried by the air, often
over long distances and in a phantasmagorical way. This miasmatic paradigm was challenged
in the mid to late 19th century with the rise of germ theory, and as diseases
such as cholera, puerperal fever, and malaria were found to actually transmit in other
ways. Motivated by his views on the importance of contact/droplet infection, and the
resistance he encountered from the remaining influence of miasma theory, prominent
public health official Charles Chapin in 1910 helped initiate a successful paradigm
shift, deeming airborne transmission most unlikely. This new paradigm became dominant.
However, the lack of understanding of aerosols led to systematic errors in the
interpretation of research evidence on transmission pathways. For the next five decades,
airborne transmission was considered of negligible or minor importance for all
major respiratory diseases, until a demonstration of airborne transmission of tuberculosis
(which had been mistakenly thought to be transmitted by droplets) in 1962. The
contact/droplet paradigm remained dominant, and only a few diseases were widely
accepted as airborne before COVID-19:
those that were clearly transmitted to people
not in the same room. The acceleration of interdisciplinary research inspired by the
COVID-19
pandemic has shown that airborne transmission is a major mode of transmission
for this disease, and is likely to be significant for many respiratory infectious
diseases.
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Social network theory has made major contributions to our understanding of human social organisation but has found relatively little application in the field of animal behaviour. In this review, we identify several broad research ...
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Social network theory has made major contributions to our understanding of human social organisation but has found relatively little application in the field of animal behaviour. In this review, we identify several broad research areas where the networks approach could greatly enhance our understanding of social patterns and processes in animals. The network theory provides a quantitative framework that can be used to characterise social structure both at the level of the individual and the population. These novel quantitative variables may provide a new tool in addressing key questions in behavioural ecology particularly in relation to the evolution of social organisation and the impact of social structure on evolutionary processes. For example, network measures could be used to compare social networks of different species or populations making full use of the comparative approach. However, the networks approach can in principle go beyond identifying structural patterns and also can help with the understanding of processes within animal populations such as disease transmission and information transfer. Finally, understanding the pattern of interactions in the network (i.e. who is connected to whom) can also shed some light on the evolution of behavioural strategies.
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Turbellarian black spot disease is described in a bluespine unicornfish Naso unicornis (Perciformes, Acanthuridae) collected from the wild off Noumea, New Caledonia, South Pacific. Each cyst contained a whitish worm, 2 to 4 mm in ...
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Turbellarian black spot disease is described in a bluespine unicornfish Naso unicornis (Perciformes, Acanthuridae) collected from the wild off Noumea, New Caledonia, South Pacific. Each cyst contained a whitish worm, 2 to 4 mm in length, which was able to swim freely in seawater. Cyst walls consisted of fibrous tissue with a scattering of melanocytes. Worms had 2 eyespots at the anterior end, a pharynx at the posterior end and a largely undeveloped reproductive system. They were identified as Piscinquilinus sp, (= Ichthyophaga sp.), a genostomatid turbellarian. The disease spread within 2 wk from a single infected fish to 3 other unicornfish in the same tank, in spite of copper sulphate and diluted seawater treatment; however, other fish from several families kept in the same tank were not infected, suggesting specificity of these parasites. Praziquantel injections into the infected fish eliminated the infection. Other cases of turbellarian infections are reported from 7 fish species off New Caledonia; prevalence is very low (0.3%).
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摘要 :
Turbellarian black spot disease is described in a bluespine unicornfish Naso unicornis (Perciformes, Acanthuridae) collected from the wild off Noumea, New Caledonia, South Pacific. Each cyst contained a whitish worm, 2 to 4 mm in ...
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Turbellarian black spot disease is described in a bluespine unicornfish Naso unicornis (Perciformes, Acanthuridae) collected from the wild off Noumea, New Caledonia, South Pacific. Each cyst contained a whitish worm, 2 to 4 mm in length, which was able to swim freely in seawater. Cyst walls consisted of fibrous tissue with a scattering of melanocytes. Worms had 2 eyespots at the anterior end, a pharynx at the posterior end and a largely undeveloped reproductive system. They were identified as Piscinquilinus sp, (= Ichthyophaga sp.), a genostomatid turbellarian. The disease spread within 2 wk from a single infected fish to 3 other unicornfish in the same tank, in spite of copper sulphate and diluted seawater treatment; however, other fish from several families kept in the same tank were not infected, suggesting specificity of these parasites. Praziquantel injections into the infected fish eliminated the infection. Other cases of turbellarian infections are reported from 7 fish species off New Caledonia; prevalence is very low (0.3%).
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Baylisascaris procyonis is a common parasitic nematode of the raccoon Procyon lotor. In intermediate or accidental hosts, including humans, B. procyonis can cause severe disease and mortality, and the parasite is increasingly view...
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Baylisascaris procyonis is a common parasitic nematode of the raccoon Procyon lotor. In intermediate or accidental hosts, including humans, B. procyonis can cause severe disease and mortality, and the parasite is increasingly viewed as an important wildlife conservation and public health concern. The prevalence of B. procyonis was assessed over a 4-year period in a population of raccoons in a forested region of lower New York. Prevalence ranged from 0% (undetected) to 21%, which was relatively low compared to values reported in other studies from the north-east. During year three of the study, a subset of the raccoon population was experimentally manipulated through altered resource distribution to enhance the contact of individuals. Within the manipulated subpopulation, prevalence of B. procyonis increased to 54% which was significantly greater than prevalence in the same subpopulation before perturbation or than prevalence among raccoons that were not subject to increased intraspecific contact. These observations suggest that altered resource distributions that directly influence raccoon behaviour may indirectly play a role in the ecology of B. procyonis.
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Grapevine leafroll associated virus-3 (GLRaV-3) and Grapevine leafroll associated virus-5 (GLRaV-5), two members of the genus Ampelovirus associated with grapevine leafroll disease, were transmitted by the mealybug Planococcus fic...
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Grapevine leafroll associated virus-3 (GLRaV-3) and Grapevine leafroll associated virus-5 (GLRaV-5), two members of the genus Ampelovirus associated with grapevine leafroll disease, were transmitted by the mealybug Planococcus ficus and the soft scale insect Ceroplastes rusci from infected to healthy vines under experimental conditions. The efficiencies of transmission of GLRaV-3 and GLRaV-5 by P. ficus were 23.3 and 8.3%, respectively, and by C. rusci were 3.3 and 1.7%, respectively. Juvenile instars of P. ficus were more efficient in transmission of the viruses than adult females. This is the first report of the ability of C. rusci to transmit these viruses to grapevines.
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Pathogen transmission can involve direct and/or indirect pathways. Using theoretical models, in this study we ask, "do directly and indirectly transmitted pathogens yield different population-level epidemiological dynamics" and "c...
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Pathogen transmission can involve direct and/or indirect pathways. Using theoretical models, in this study we ask, "do directly and indirectly transmitted pathogens yield different population-level epidemiological dynamics" and "can the transmission pathway be inferred from population-level epidemiological data" Our approach involves comparing the continuous-time dynamics of a class of compartmental epidemiological models with direct versus environmentally mediated indirect transmission pathways. Combing analytical theory and numerical simulations we show that models with direct and indirect transmission can produce quantitatively similar time series when the pathogen cannot reproduce in the environment, particularly when the environmental pathogen dynamics are fast. We apply these results to a previous study on chronic wasting disease and show that identifying the transmission pathway is more difficult than previously acknowledged. Our analysis and simulations also yield conditions under which numerical differences can potentially identify the transmission route in oscillating endemic systems and systems where the environmental pathogen dynamics are not fast. This work begins to identify how differences in the transmission pathway can result in quantitatively different epidemiological dynamics and how those differences can be used to identify the transmission pathway from population level time series.
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