Background: In recent times, there has been an increase in the number of Lassa fever cases resulting from the several episodes of Lassa fever epidemics ravaging Nigeria and other West African countries. The presence o...Background: In recent times, there has been an increase in the number of Lassa fever cases resulting from the several episodes of Lassa fever epidemics ravaging Nigeria and other West African countries. The presence of Lassa virus in rodents other than the major reservoir (Mastomys natalensis) has been a public health concern as to the actual burden of the disease. It is therefore of a public health necessity to explore the LASV RNA habouring potential of several species of rodents in endemic as well as non-endemic areas for proper prevention of emergence of outbreaks in non-endemic areas. Objectives: The aim of this study was to detect the presence of LASV RNA in different species of rodents in Ikorodu, Lagos state and Abeokuta, Ogun state. Methods: A total of ninety one (91) rodents were captured from Ikorodu, Lagos State (61 rodents) and Abeokuta, Ogun State (30 rodents), euthanized, bled, and plasma obtained for the detection of LASV RNA by Reverse Transcriptase Polymerase Chain Reaction. Results: A total of 91 rodents consisting of 77 Rattus rattus and 14 Crocidura spp. The S segment of LASV RNA was not in any of the 91 rodents’ plasma samples. Conclusion: The rodents captured within the rural communities of Ikorodu, Lagos State and Abeokuta, Ogun State were found not to habour the LASV RNA. This study is limited by the relatively small sample size. Similar studies should be encouraged both in endemic and non-endemic areas in order to understand the actual burden of Lassa fever as well as put into check future epidemics.展开更多
The spread of Lassa fever infection is increasing in West Africa over the last decade.The impact of this can better be understood when considering the various possible transmission routes.We designed a mathematical mo...The spread of Lassa fever infection is increasing in West Africa over the last decade.The impact of this can better be understood when considering the various possible transmission routes.We designed a mathematical model for the epidemiology of Lassa Fever using a system of nonlinear ordinary differential equations to determine the effect of transmission pathways toward the infection progression in humans and rodents including those usually neglected such as the environmental surface and aerosol routes.We analyzed the model and carried out numerical simulations to determine the impact of each transmission routes.Our results showed that the burden of Lassa fever infection is increased when all the transmission routes are incorporated and most single transmission routes are less harmful,but when in combination with other transmission routes,they increase the Lassa fever burden.It is therefore important to consider multiple transmission routes to better estimate the Lassa fever burden optimally and in turn determine control strategies targeted at the transmission pathways.展开更多
Objective:To investigate which life stage of the parasite has the ability to stimulate release of pro- or anti-inflammatory mediators from macrophages.Methods:The human macrophage/ monocyte cell line THP-1,the mouse m...Objective:To investigate which life stage of the parasite has the ability to stimulate release of pro- or anti-inflammatory mediators from macrophages.Methods:The human macrophage/ monocyte cell line THP-1,the mouse macrophage cell line RAW 264.7 and naive peritoneal macrophages（PM） from the rodent host Mastomys coucha（M.coucha） were incubated at 37℃in 5%CO<sub>2</sub> atmosphere with extracts of microfilariae（Mf）,third stage infective larvae（L<sub>3</sub>） and adult worms（Ad） of Brugia malayi.After 48 hr post exposure,IL-1β,IL-6,TNF-α,IL-10 and nitric oxide（NO） in cell-free supernatants were estimated.Results:Extracts of all the life stages of the parasite were capable of stimulating pro-（IL-1β,IL-6 and TNF-α） and anti-inflammatory （IL-10） cytokines in both the cell lines and peritoneal macrophages of M.coucha.Mf was the strongest stimulator of pro-inflammatory cytokines followed by L<sub>3</sub> and Ad;however,Ad was a strong stimulator of IL-10 release.Mf was found to have potential to modulate LPS-induced NO release in RAW cells.Ad-induced NO release was concentration dependent with maximum at 20μg/mL in both RAW and PMs.Conclusions:The results show that parasites at all life stages were capable of stimulating pro-（IL-1β,IL-6 and TNF-α） and anti-inflammatory（IL-10） cytokines and NO release from macrophages of susceptible host M.coucha,human and mouse macrophage cell lines.Mf can suppress the LPS-induced NO release in RAW cells.The findings also show that the two cell lines may provide a convenient in vitro system for assaying parasite-induced inflammatory mediator release.展开更多
Survival and maturation rates of female Mastomys natalensis were analysed based on a ten-year monthlycapture-recapture data set. We investigated whether direct and delayed density dependent and independent (rainfall)v...Survival and maturation rates of female Mastomys natalensis were analysed based on a ten-year monthlycapture-recapture data set. We investigated whether direct and delayed density dependent and independent (rainfall)variables accounted for the considerable variation in demographic traits. It was estimated that seasonal and annualcovariates accounted for respectively 29 and 26% of the total variation in maturation rates and respectively 17 and11% of the variation in survival rates. Explaining the between-year differences in maturation rates with annual pastrainfall or density did not improve the model fit. On the other hand we showed that maturation rates were correlatednegatively with density the previous month and positively to cumulative rainfall over the past three months.Survival estimates of both adults and subadults varied seasonally, with higher estimates during the increase phase(dry season). The subadults were characterised by a very high survival rate (> 0.95) during this phase. In thedecrease phase only minor differences were found between survival rates of subadults and adults. We found that39% of the between-year variation in survival can be explained by accumulated rainfall over the past year.展开更多
Exploration and activity are often described as trade-offs between the fitness benefits of gathering information and resources, and the potential costs of increasing exposure to predators and para- sites. More explora...Exploration and activity are often described as trade-offs between the fitness benefits of gathering information and resources, and the potential costs of increasing exposure to predators and para- sites. More exploratory individuals are predicted to have higher rates of parasitism, but this relationship has rarely been examined for virus infections in wild populations. Here, we used the multimammate mouse Mastomys natalensis to investigate the relationship between exploration, activity, and infection with Morogoro virus （MORV）. We characterized individual exploratory behav- ior （open field and novel object tests） and activity （trap diversity）, and quantified the relationship between these traits and infection status using linear regression. We found that M. natalensis expresses consistent individual differences, or personality types, in exploratory behavior （repeat- ability of 0.30, 95% CI： 0.21-0.36）. In addition, we found a significant contrasting effect of age on ex- ploration and activity where juveniles display higher exploration levels than adults, but lower field- activity. There was however no statistical evidence for a behavioral syndrome between these 2 traits. Contrary to our expectations, we found no correlation between MORV infection status and exploratory behavior or activity, which suggests that these behaviors may not increase exposure probability to MORV infection. This would further imply that variation in viral infection between individuals is not affected by between-individual variation in exploration and activity.展开更多
Studies of populations of the multimammate rat Mastomys natalensis in Morogoro, Tanzania, show that soil textureappears to influence the population abundance and distribution of these rats in agricultural fields. The ...Studies of populations of the multimammate rat Mastomys natalensis in Morogoro, Tanzania, show that soil textureappears to influence the population abundance and distribution of these rats in agricultural fields. The lowest rodentpopulation abundance was found on sandy clay soils (F(2, 5) = 8.42;P = 0.025). The population abundances of M.natalensis on sandy clay loam and sandy loam soils did not differ significantly (P ≤ 0.05), possibly because thesesoils have a very similar texture. The results of this study suggest that M. natalensis prefers loam-textured soilswith a high percentage of sand, which are probably better than clay soils for burrowing and nesting, particularly inthe rainy season. The lower preference for clay soils is probably related to the poor aeration in these soils and thewaterlogging that occurs during the wet season.展开更多
Consistent among individual variation in behavior,or animal personality,is present in a wide variety of species.This behavioral variation is maintained by both genetic and environmental factors.Parental effects are a ...Consistent among individual variation in behavior,or animal personality,is present in a wide variety of species.This behavioral variation is maintained by both genetic and environmental factors.Parental effects are a special case of environmental variation and are expected to evolve in populations experiencing large fluctuations in their environment.They represent a non-genetic pathway by which parents can transmit information to their offspring,by modulating their personality.While it is expected that parental effects contribute to the observed personality variation,this has rarely been studied in wild populations.We used the multimammate mouse Mastomys natalensis as a model system to investigate the potential effects of maternal personality on offspring behavior.We did this by repeatedly recording the behavior of individually housed juveniles which were born and raised in the lab from wild caught females.A linear correlation,between mother and offspring in behavior,would be expected when the personality is only affected by additive genetic variation,while a more complex relationship would suggests the presence of maternal effects.We found that the personality of the mother predicted the behavior of their offspring in a non-linear pattern.Exploration behavior of mother and offspring was positively correlated,but only for slow and average exploring mothers,while this correlation became negative for fast exploring mothers.This may suggests that early maternal effects could affect personality in juvenile M.natalensis,potentially due to density-dependent and negative frequency-dependent mechanisms,and therefore contribute to the maintenance of personality variation.展开更多
The multimammate rat,Mastomys natalensis Smith 1834,is a dominant species in agro-ecosystems in Sub-Saharan Africa,but adapts quickly to changes in non-agricultural landscape,particularly woodlands and forests.In this...The multimammate rat,Mastomys natalensis Smith 1834,is a dominant species in agro-ecosystems in Sub-Saharan Africa,but adapts quickly to changes in non-agricultural landscape,particularly woodlands and forests.In this study we report on reproduction and population dynamics of M.natalensis in deforested high elevation localities in the Usambara Mountains,north-east Tanzania.We conducted Capture-Mark-Recapture studies in 2002-2004,and established that reproduction of M.natalensis takes place in the extended wet season between February and June,and the population density peaks in June-August.Reproduction cease in July to January and population density drops from July onwards.Reproduction and population density fluctuations are linked to the duration and amount of rainfall.In years when rainfall was below average and the wet season was short,the population density was significantly lower(below 10 animals/ha and 60 animals/ha in 2003 and 2004 respectively,compared to>100 animals/ha in 2002 when rainfall was above the seasonal average)(Fdf 2,13=9.092,p<0.01 for in between years variations and Fdf_(12,15)=5.389,p<0.01 for effect of cumulative annual rainfall on population density).These densities were much lower than in the lowland savannah habitats in central and southwest Tanzania.A comparison between the farmland/fallow mosaic fields and agro-forestry areas showed higher population densities in the former,which have similarities to the preferred habitats in the lowland savannahs.The increasing abundance of M.natalensis in the Usambara could have some consequences:M.natalensis is major pest and is involved in the plague cycle in the western Usambara Mountains.Mastomys natalensis is also a strong competitor and the impact on endemic rodent species,e.g.Lophuromys flavopunctatus and Praomys delectorum is unknown.展开更多
文摘Background: In recent times, there has been an increase in the number of Lassa fever cases resulting from the several episodes of Lassa fever epidemics ravaging Nigeria and other West African countries. The presence of Lassa virus in rodents other than the major reservoir (Mastomys natalensis) has been a public health concern as to the actual burden of the disease. It is therefore of a public health necessity to explore the LASV RNA habouring potential of several species of rodents in endemic as well as non-endemic areas for proper prevention of emergence of outbreaks in non-endemic areas. Objectives: The aim of this study was to detect the presence of LASV RNA in different species of rodents in Ikorodu, Lagos state and Abeokuta, Ogun state. Methods: A total of ninety one (91) rodents were captured from Ikorodu, Lagos State (61 rodents) and Abeokuta, Ogun State (30 rodents), euthanized, bled, and plasma obtained for the detection of LASV RNA by Reverse Transcriptase Polymerase Chain Reaction. Results: A total of 91 rodents consisting of 77 Rattus rattus and 14 Crocidura spp. The S segment of LASV RNA was not in any of the 91 rodents’ plasma samples. Conclusion: The rodents captured within the rural communities of Ikorodu, Lagos State and Abeokuta, Ogun State were found not to habour the LASV RNA. This study is limited by the relatively small sample size. Similar studies should be encouraged both in endemic and non-endemic areas in order to understand the actual burden of Lassa fever as well as put into check future epidemics.
文摘The spread of Lassa fever infection is increasing in West Africa over the last decade.The impact of this can better be understood when considering the various possible transmission routes.We designed a mathematical model for the epidemiology of Lassa Fever using a system of nonlinear ordinary differential equations to determine the effect of transmission pathways toward the infection progression in humans and rodents including those usually neglected such as the environmental surface and aerosol routes.We analyzed the model and carried out numerical simulations to determine the impact of each transmission routes.Our results showed that the burden of Lassa fever infection is increased when all the transmission routes are incorporated and most single transmission routes are less harmful,but when in combination with other transmission routes,they increase the Lassa fever burden.It is therefore important to consider multiple transmission routes to better estimate the Lassa fever burden optimally and in turn determine control strategies targeted at the transmission pathways.
基金supported by a grant Indian Council of Medical Research, New Delhi and SP/SO/B-46/2000 from the Department of Science and Technology,New DelhiUGC Senior Research Fellowship support to SKV
文摘Objective:To investigate which life stage of the parasite has the ability to stimulate release of pro- or anti-inflammatory mediators from macrophages.Methods:The human macrophage/ monocyte cell line THP-1,the mouse macrophage cell line RAW 264.7 and naive peritoneal macrophages（PM） from the rodent host Mastomys coucha（M.coucha） were incubated at 37℃in 5%CO<sub>2</sub> atmosphere with extracts of microfilariae（Mf）,third stage infective larvae（L<sub>3</sub>） and adult worms（Ad） of Brugia malayi.After 48 hr post exposure,IL-1β,IL-6,TNF-α,IL-10 and nitric oxide（NO） in cell-free supernatants were estimated.Results:Extracts of all the life stages of the parasite were capable of stimulating pro-（IL-1β,IL-6 and TNF-α） and anti-inflammatory （IL-10） cytokines in both the cell lines and peritoneal macrophages of M.coucha.Mf was the strongest stimulator of pro-inflammatory cytokines followed by L<sub>3</sub> and Ad;however,Ad was a strong stimulator of IL-10 release.Mf was found to have potential to modulate LPS-induced NO release in RAW cells.Ad-induced NO release was concentration dependent with maximum at 20μg/mL in both RAW and PMs.Conclusions:The results show that parasites at all life stages were capable of stimulating pro-（IL-1β,IL-6 and TNF-α） and anti-inflammatory（IL-10） cytokines and NO release from macrophages of susceptible host M.coucha,human and mouse macrophage cell lines.Mf can suppress the LPS-induced NO release in RAW cells.The findings also show that the two cell lines may provide a convenient in vitro system for assaying parasite-induced inflammatory mediator release.
文摘Survival and maturation rates of female Mastomys natalensis were analysed based on a ten-year monthlycapture-recapture data set. We investigated whether direct and delayed density dependent and independent (rainfall)variables accounted for the considerable variation in demographic traits. It was estimated that seasonal and annualcovariates accounted for respectively 29 and 26% of the total variation in maturation rates and respectively 17 and11% of the variation in survival rates. Explaining the between-year differences in maturation rates with annual pastrainfall or density did not improve the model fit. On the other hand we showed that maturation rates were correlatednegatively with density the previous month and positively to cumulative rainfall over the past three months.Survival estimates of both adults and subadults varied seasonally, with higher estimates during the increase phase(dry season). The subadults were characterised by a very high survival rate (> 0.95) during this phase. In thedecrease phase only minor differences were found between survival rates of subadults and adults. We found that39% of the between-year variation in survival can be explained by accumulated rainfall over the past year.
文摘Exploration and activity are often described as trade-offs between the fitness benefits of gathering information and resources, and the potential costs of increasing exposure to predators and para- sites. More exploratory individuals are predicted to have higher rates of parasitism, but this relationship has rarely been examined for virus infections in wild populations. Here, we used the multimammate mouse Mastomys natalensis to investigate the relationship between exploration, activity, and infection with Morogoro virus （MORV）. We characterized individual exploratory behav- ior （open field and novel object tests） and activity （trap diversity）, and quantified the relationship between these traits and infection status using linear regression. We found that M. natalensis expresses consistent individual differences, or personality types, in exploratory behavior （repeat- ability of 0.30, 95% CI： 0.21-0.36）. In addition, we found a significant contrasting effect of age on ex- ploration and activity where juveniles display higher exploration levels than adults, but lower field- activity. There was however no statistical evidence for a behavioral syndrome between these 2 traits. Contrary to our expectations, we found no correlation between MORV infection status and exploratory behavior or activity, which suggests that these behaviors may not increase exposure probability to MORV infection. This would further imply that variation in viral infection between individuals is not affected by between-individual variation in exploration and activity.
文摘Studies of populations of the multimammate rat Mastomys natalensis in Morogoro, Tanzania, show that soil textureappears to influence the population abundance and distribution of these rats in agricultural fields. The lowest rodentpopulation abundance was found on sandy clay soils (F(2, 5) = 8.42;P = 0.025). The population abundances of M.natalensis on sandy clay loam and sandy loam soils did not differ significantly (P ≤ 0.05), possibly because thesesoils have a very similar texture. The results of this study suggest that M. natalensis prefers loam-textured soilswith a high percentage of sand, which are probably better than clay soils for burrowing and nesting, particularly inthe rainy season. The lower preference for clay soils is probably related to the poor aeration in these soils and thewaterlogging that occurs during the wet season.
基金B.V.B.was funded by the Ph.D.fellowship from the Research Foundation Flanders(FWO)(grant ID:11A0817N).
文摘Consistent among individual variation in behavior,or animal personality,is present in a wide variety of species.This behavioral variation is maintained by both genetic and environmental factors.Parental effects are a special case of environmental variation and are expected to evolve in populations experiencing large fluctuations in their environment.They represent a non-genetic pathway by which parents can transmit information to their offspring,by modulating their personality.While it is expected that parental effects contribute to the observed personality variation,this has rarely been studied in wild populations.We used the multimammate mouse Mastomys natalensis as a model system to investigate the potential effects of maternal personality on offspring behavior.We did this by repeatedly recording the behavior of individually housed juveniles which were born and raised in the lab from wild caught females.A linear correlation,between mother and offspring in behavior,would be expected when the personality is only affected by additive genetic variation,while a more complex relationship would suggests the presence of maternal effects.We found that the personality of the mother predicted the behavior of their offspring in a non-linear pattern.Exploration behavior of mother and offspring was positively correlated,but only for slow and average exploring mothers,while this correlation became negative for fast exploring mothers.This may suggests that early maternal effects could affect personality in juvenile M.natalensis,potentially due to density-dependent and negative frequency-dependent mechanisms,and therefore contribute to the maintenance of personality variation.
文摘The multimammate rat,Mastomys natalensis Smith 1834,is a dominant species in agro-ecosystems in Sub-Saharan Africa,but adapts quickly to changes in non-agricultural landscape,particularly woodlands and forests.In this study we report on reproduction and population dynamics of M.natalensis in deforested high elevation localities in the Usambara Mountains,north-east Tanzania.We conducted Capture-Mark-Recapture studies in 2002-2004,and established that reproduction of M.natalensis takes place in the extended wet season between February and June,and the population density peaks in June-August.Reproduction cease in July to January and population density drops from July onwards.Reproduction and population density fluctuations are linked to the duration and amount of rainfall.In years when rainfall was below average and the wet season was short,the population density was significantly lower(below 10 animals/ha and 60 animals/ha in 2003 and 2004 respectively,compared to>100 animals/ha in 2002 when rainfall was above the seasonal average)(Fdf 2,13=9.092,p<0.01 for in between years variations and Fdf_(12,15)=5.389,p<0.01 for effect of cumulative annual rainfall on population density).These densities were much lower than in the lowland savannah habitats in central and southwest Tanzania.A comparison between the farmland/fallow mosaic fields and agro-forestry areas showed higher population densities in the former,which have similarities to the preferred habitats in the lowland savannahs.The increasing abundance of M.natalensis in the Usambara could have some consequences:M.natalensis is major pest and is involved in the plague cycle in the western Usambara Mountains.Mastomys natalensis is also a strong competitor and the impact on endemic rodent species,e.g.Lophuromys flavopunctatus and Praomys delectorum is unknown.
