Suchergebnisse

Context.
In many parts of the world, brown rats have colonised sewer systems and the rat populations in sewers are often thought to be a source of problems with rats on the surface. The management of sewer rat populations is usually performed with little, if any, knowledge of the dynamics and behaviour of these populations.


Aims.
The study aimed to uncover the population dynamics, movements and distribution of rats in populations living in sewers.


Methods.
We studied rats in a capture–mark–recapture study in two adjacent but separate sewer systems in suburban Copenhagen, Denmark, covering a surface area of 30 Ha. Multiple-capture live traps were placed in manholes in public sewers; animals were marked individually and data were collected every fourth week for a period of almost 3 years.


Key results.
In total, 332 individual rats were trapped. Approximately one-third were only caught once, half of these were juveniles. The median time an individual was present in the sewers was 4 months with maxima up to 22 months. Abundance ranged from 2 to 44 animals per sewer system and the dynamics showed no regular fluctuations. Rats were distributed throughout the study area, regardless of sewer dimensions. Juvenile rats were captured more in the smaller and drier sewer sections. Activity areas of rats of both sexes overlapped partially, and observations of bite wounds were rare, suggesting a high degree of tolerance. The average maximal distance covered by rats was ~200 m for both sexes. Day-to-day movements took place over shorter distances. There were no movements of rats between sewer systems and no sewer rats were observed to be active on the surface. The rat populations seemed to be substructured in smaller groups.


Conclusions.
Sewer rat populations vary irregularly in abundance. Pipe dimensions are not important for the presence of rats but breeding seems concentrated in smaller and drier pipes. Most individuals are resident and live in small groups that are active in a limited area only, but still there is a fair group of dispersing rats.


Implications.
Sewer rat management should be spread out spatially in a sewer system since most rats move over short areas only. Recolonisation by dispersing rats must be taken into account if sewer systems are connected. It is likely that targeting smaller and drier pipes will affect reproductive success.

Context
Toe clipping is a widely used method for permanent marking of small mammals, but its effects are not well known, despite the ethical and scientific implications. Most studies do not find any clear effects, but there is some indication that toe clipping can affect survival in specific cases. Although effects on survival are arguably the most important, more subtle effects are also plausible, yet very few studies have included body condition and none has investigated effects on mobility.

Aims
We analysed the effects of toe clipping on free-living Mastomys natalensis, a common, morphologically and behaviourally intermediate small rodent.

Methods
Using a 17-year capture–mark–recapture dataset, we compared movement, body weight and survival between newly and previously clipped animals, and tested whether any of these parameters correlated with the number of clipped toes.

Key results
No evidence for a correlation between total number of clips and any of the variables was found. Newly clipped animals had a slightly smaller weight change and larger travel distance than did those that were already clipped, and we show that this is most likely due to stress caused by being captured, clipped and handled for the first time rather than to the actual clipping.

Conclusions
The combination of trapping, handling and marking has a detectable effect on multimammate mice; however, there is no evidence for a clear effect of toe clipping.

Implications
Our study suggests a re-evaluation of ethical guidelines on small-mammal experiments, so as to reach a rational, fact-based decision on which marking method to use.

Context
Reproduction and survival are two of the most important demographic factors that play a major role in changing population abundances of pest species over time and space, solid understanding of which is a useful input to forecast future population changes for proactive management.

Aims
We investigated the effects of rainfall, crop-development stage and density of stone bunds on reproductive patterns, and the effects of stone-bund density and sex on survival probabilities of two widespread rodent species (Mastomys awashensis and Arvicanthis dembeensis) in Ethiopian highlands.

Methods
Rodent population dynamics were monitored from April 2007 to February 2011, using capture–mark–recapture (CMR) technique in four 60 × 60 m permanent square grids for four consecutive cropping seasons. Two of the grids represented fields with low stone-bund density (LSBD, ~15 m apart) and the other two represented fields with high stone-bund density (HSBD, ~10 m apart).

Key results
Reproduction was seasonal, commencing during the wet season following the rain and continuing through the early dry season. We found an increase in the abundance of reproductively active female individuals of both species towards the milky and fruiting crop stages and around harvest period. We found no strong difference in survival probability between the two rodent species with variation in stone-bund density and sex.

Conclusion
Stone bunds play a minor role in the reproduction and survival of the rodent species at the observed abundances.

Implications
In terms of pest management, the high local survival rates estimated for both rodent species matter more than survival differences owing to variations in stone-bund density and sex.

Background: Parasite evolution is hypothesized to select for levels of parasite virulence that maximise transmission success. When host population densities fluctuate, low levels of virulence with limited impact on the host are expected, as this should increase the likelihood of surviving periods of low host density. We examined the effects of Morogoro arenavirus on the survival and recapture probability of multimammate mice (Mastomys natalensis) using a seven-year capture-mark-recapture time series. Mastomys natalensis is the natural host of Morogoro virus and is known for its strong seasonal density fluctuations. Results: Antibody presence was negatively correlated with survival probability (effect size: 5-8% per month depending on season) but positively with recapture probability (effect size: 8%). Conclusions: The small negative correlation between host survival probability and antibody presence suggests that either the virus has a negative effect on host condition, or that hosts with lower survival probability are more likely to obtain Morogoro virus infection, for example due to particular behavioural or immunological traits. The latter hypothesis is supported by the positive correlation between antibody status and recapture probability which suggests that risky behaviour might increase the probability of becoming infected. ; University of Antwerp [GOA BOF FFB3567]; Antwerp study centre for disease (ASCID) [GOA BOF FFB3567]; INCO-DEV grant [ICA4-CT2002-10050]; German Research Foundation (Focus Programs from Deutsche Forschungsgemeinschaft) [GU 883/3-1, GU 883/3-2]; European Union's Horizon research and innovation programme under the Marie Sklodowska-Curie grant [707840] ; This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.

Background. Malaria "hotspots" have been proposed as potential intervention units for targeted malaria elimination. Little is known about hotspot formation and stability in settings outside sub-Saharan Africa. Methods. Clustering of Plasmodium infections at the household and hotspot level was assessed over 2 years in 3 villages in eastern Cambodia. Social and spatial autocorrelation statistics were calculated to assess clustering of malaria risk, and logistic regression was used to assess the effect of living in a malaria hotspot compared to living in a malaria-positive household in the first year of the study on risk of malaria infection in the second year. Results. The crude prevalence of Plasmodium infection was 8.4% in 2016 and 3.6% in 2017. Living in a hotspot in 2016 did not predict Plasmodium risk at the individual or household level in 2017 overall, but living in a Plasmodium-positive household in 2016 strongly predicted living in a Plasmodium-positive household in 2017 (Risk Ratio, 5.00 [95% confidence interval, 2.09-11.96], P < .0001). There was no consistent evidence that malaria risk clustered in groups of socially connected individuals from different households. Conclusions. Malaria risk clustered more clearly in households than in hotspots over 2 years. Household-based strategies should be prioritized in malaria elimination programs in this region. ; This work was supported by the Department of Economy, Science and Innovation of the Flemish government. M.B.T. was supported by a 2014 Erasmus Mundus Joint Doctorate Fellowship (specific grant agreement 2014-0681), and by a Les Amis des Instituts Pasteur a Bruxelles 2017 research fellowship.