PubMed Health⌕ Search

Biomedical subjects

H Leirs

Publications and source records attributed to H Leirs.

17 recordsLinked to original sources
PubMed2006

Plague metapopulation dynamics in a natural reservoir: the burrow system as the unit of study.

The ecology of plague (Yersinia pestis infection) in its ancient foci in Central Asia remains poorly understood. We present field data from two sites in Kazakhstan where the great gerbil (Rhombomys opimus) is the major natural host. Family groups inhabit and defend burrow systems spaced throughout the landscape, such that the host population may be considered a metapopulation, with each occupied burrow system a subpopulation. We examine plague transmission within and between family groups and its effect on survival. Transmission of plague occurred disproportionately within family groups although not all gerbils became infected once plague entered a burrow system. There were no spatial patterns to suggest that family groups in close proximity to infected burrow systems were more at risk of infection than those far away. At one site, infection increased the chances of burrow-system extinction. Overall, it is useful to consider the burrow system as the unit of study within a much larger metapopulation.

Animals↗
PubMed2006

Demographic and spatio-temporal variation in human plague at a persistent focus in Tanzania.

Human plague in the Western Usambara Mountains in Tanzania has been a public health problem since the first outbreak in 1980. The wildlife reservoir is unknown and eradication measures that have proved effective elsewhere in Tanzania appear to fail in this region. We use census data from 2002 and hospital records kept since 1986 to describe the temporal, spatial and demographic variation in human plague. A seasonal peak in cases occurs from December to February with the numbers of cases during this peak varying between 0 and 1150. Variation in incidence, calculated for each village as the mean number of cases per thousand inhabitants per year, indicates that human plague is concentrated around a group of three neighbouring, relatively isolated, high-altitude villages; Nywelo, Madala and Gologolo. However, there was no evidence that these villages were acting as a source of infection for the remainder of the focus. The likelihood of becoming infected with plague is highest between the ages of 5 and 19 and lowest for adult men. This was most clear in the ward encompassing the three high-incidence villages where the risk of plague among children aged 10-14 was 2.2 times higher than for adults aged 30-34, and among adults aged 30-34, the risk was 2.4 times higher for women than men.

Adolescent↗
PubMed2006

A model of Leptospirosis infection in an African rodent to determine risk to humans: seasonal fluctuations and the impact of rodent control.

Human leptospirosis (Leptospira spp. infection) is a worldwide public health problem that is of greatest concern for humid tropical and subtropical regions. The magnitude of the problem in these areas is larger because of the climatic and environmental conditions the bacterium face outside their hosts but also because of the frequency of contacts between people and sources of infection. Rodents are thought to play the most important role in the transmission of human leptospirosis. We here model the dynamics of infection in an African rodent (Mastomys natalensis) that is thought to be the principal source of infection in parts of Tanzania. Our model, representing the climatic conditions in central Tanzania, suggests a strong seasonality in the force of infection on humans with a peak in the abundance of infectious mice between January and April in agricultural environments. In urban areas the dynamics are predicted to be more stable and the period of high numbers of infectious animals runs from February to July. Our results indicate that removal of animals by trapping rather than reducing the suitability of the environment for rodents will have the greater impact on reducing human cases of leptospirosis.

Animals↗
PubMed2006

Implications of increased susceptibility to predation for managing the sylvatic cycle of Echinococcus multilocularis.

The ability to increase the chances that infectious prey are taken by predators is an observed feature of many parasites that rely on one or more predator-prey relationships to complete their life-cycle. In the sylvatic life-cycle of Echinococcus multilocularis - the causative agent of human alveolar echinococcosis-- foxes are the final host, with voles acting as intermediate hosts. Here we review the evidence that E. multilocularis causes increased susceptibility to predation and present a general mathematical model for the sylvatic life-cycle. The ability to increase susceptibility to predation in the intermediate host reduces the sensitivity of the parasite population to adverse conditions. For example, there is no critical density of foxes below which the parasite is expected to die out, even if the effect of the parasite on infected prey is very small. We suggest that increased susceptibility to predation is a plausible explanation for the observed resilience of E. multilocularis during and following field trials of praziquantel baiting.

Animals↗
PubMed2005

Fluctuating rodent populations and risk to humans from rodent-borne zoonoses.

The fluctuations in abundance of a wildlife reservoir are an attractive explanation for temporal variation in primary human cases of a zoonosis. This is because high abundance may lead to more contact between humans and animals, but also to outbreaks of disease within the reservoir population. We propose a mathematical framework that sets out the consequences of correlation between reservoir abundance and reservoir prevalence for how numbers of human cases are related to reservoir abundance. The fluctuations of rodent populations are well studied and often dramatic. A review of field studies of rodent reservoirs for plague, hantaviruses, and other zoonoses shows that, at a seasonal time scale, a positive correlation between host abundance and host prevalence is rarely observed. More commonly, there is an inverse relationship or negative correlation such that a seasonal increase in rodent abundance is not accompanied by a corresponding increase in the abundance of infectious animals. Seasonal changes in rodent abundance are hence unlikely to fully explain seasonal variation in primary human cases. The few longer field studies (>5 years) show a positive but delayed relationship between reservoir abundance and reservoir prevalence.

Animals↗
PubMed2001

Palatability and toxicity of fipronil as a systemic insecticide in a bromadiolone rodenticide bait for rat and flea control.

Vector control in plague-infested areas requires a simultaneous killing of rodents and their fleas. We investigated the efficacy of a combination of a systemic insecticide, fipronil, in a rodenticide bait formulation under laboratory conditions. Four different concentrations of fipronil (0.05%, 0.005%, 0.0005% with acetone as a solvent, and 0.05% with propylene glycol as a solvent) and two controls (solvents only) were combined with the rodenticide bait (crushed organically grown wheat with 0.005% bromadiolone). Each concentration was offered together with an untreated non-poisonous challenge bait to 10 singly caged Rattus rattus L., each with 100 rat fleas Xenopsylla cheopis Rothschild (Siphonaptera: Pulicidae) in the nest. Treated bait consumption was relatively low and an unsatisfactory rat mortality of around 50% only was obtained in all tests. The palatability of the bait, however, was not affected by the fipronil concentration. Even at the lowest fipronil concentration, average flea mortality was still above 95%, and doses of more than I mg fipronil per kg rat body weight gave a nearly complete kill of fleas. Fipronil can be highly effective as a systemic insecticide to for flea control, provided that a more attractive bait base for roof rats is used.

4-Hydroxycoumarins↗
PubMed2000

Molecular evolution of puumala hantavirus in Fennoscandia: phylogenetic analysis of strains from two recolonization routes, Karelia and Denmark.

Like other members of the genus HANTAVIRUS: in the family BUNYAVIRIDAE:, Puumala virus (PUUV) is thought to be co-evolving with its natural host, the bank vole Clethrionomys glareolus. To gain insight into the evolutionary history of PUUV in northern Europe during the last post-glacial period, we have studied wild-type PUUV strains originating from areas along two postulated immigration routes of bank voles to Fennoscandia. Full-length sequences of the S RNA segment and partial sequences (nt 2168-2569) of the M segment were recovered by RT-PCR directly from bank vole tissues collected at three locations in Russian Karelia and one location in Denmark. Phylogenetic analysis showed that strains from Karelia and Finland belong to the same genetic lineage, supporting the hypothesis that PUUV spread to present Finland via a Karelian land-bridge. The Danish PUUV strains showed no particularly close relatedness to any of the known PUUV strains and formed a distinct phylogenetic lineage on trees calculated for both S and M segment sequences. Although no direct link between the Danish PUUV strains and those of the southern Scandinavian lineage was found, within the S segment of Danish PUUV strains, two regions with higher similarity to either northern Scandinavian or - to a less extent - southern Scandinavian genetic lineages were revealed, suggesting evolutionary connections of their precursors.

Amino Acid Sequence↗
PubMed1999

Search for the Ebola virus reservoir in Kikwit, Democratic Republic of the Congo: reflections on a vertebrate collection.

A 3-month ecologic investigation was done to identify the reservoir of Ebola virus following the 1995 outbreak in Kikwit, Democratic Republic of the Congo. Efforts focused on the fields where the putative primary case had worked but included other habitats near Kikwit. Samples were collected from 3066 vertebrates and tested for the presence of antibodies to Ebola (subtype Zaire) virus: All tests were negative, and attempts to isolate Ebola virus were unsuccessful. The investigation was hampered by a lack of information beyond the daily activities of the primary case, a lack of information on Ebola virus ecology, which precluded the detailed study of select groups of animals, and sample-size limitations for rare species. The epidemiology of Ebola hemorrhagic fever suggests that humans have only intermittent contact with the virus, which complicates selection of target species. Further study of the epidemiology of human outbreaks to further define the environmental contact of primary cases would be of great value.

Animals↗
PubMed1997

Stochastic seasonality and nonlinear density-dependent factors regulate population size in an African rodent.

Ecology has long been troubled by the controversy over how populations are regulated. Some ecologists focus on the role of environmental effects, whereas others argue that density-dependent feedback mechanisms are central. The relative importance of both processes is still hotly debated, but clear examples of both processes acting in the same population are rare. Key-factor analysis (regression of population changes on possible causal factors) and time-series analysis are often used to investigate the presence of density dependence, but such approaches may be biased and provide no information on actual demographic rates. Here we report on both density-dependent and density-independent effects in a murid rodent pest species, the multimammate rat Mastomys natalensis (Smith, 1834), using statistical capture-recapture models. Both effects occur simultaneously, but we also demonstrate that they do not affect all demographic rates in the same way. We have incorporated the obtained estimates of demographic rates in a population dynamics model and show that the observed dynamics are affected by stabilizing nonlinear density-dependent components coupled with strong deterministic and stochastic seasonal components.

Africa↗
PubMed1992

Eradication of hantavirus infection among laboratory rats by application of caesarian section and a foster mother technique.

Hantavirus antibodies were demonstrated by the indirect immunofluorescent antibody assay, in the serum of inbred strains of laboratory rats, during the period 1973-1982, at the Unit of Experimental Immunology in the Catholic University of Louvain, Brussels, Belgium. LOU rats, as well as immunocytomas, which were requested by laboratories in the U.K. and The Netherlands, were supplied at a time when the infection was unknown and unsuspected in Europe. Hantavirus-infected laboratory rats were rendered free of virus through re-derivation by caesarian section and suckling by virus-free foster mothers. Immunocytomas were tested for the presence of hantaviruses by implantation into seronegative laboratory rats. The strain of hantavirus causing the laboratory infection was clearly different from the one circulating in free-living bankvoles in Belgium. The exchange of laboratory rats and rat tumours in relation to the potential risk of laboratory-acquired hantavirus infection, is discussed.

Animals↗
PubMed1987

Occurrence and distribution of Hantavirus in wild living mammals in Belgium.

Small mammals were screened for the presence of antibodies to Hantaan virus (HTN) and Hantavirus (HV) antigen in Belgium. Antibody and antigen-positive animals were found in different parts of the country. One insectivore and five rodent species were found positive. The highest prevalence of infection was found in the bank vole (Clethrionomys glareolus). A relation between infected animals and wet habitats was observed. It was obvious that in bank vole the likelihood of infection increased with age.

Age Factors↗
PubMed1987

Partial characterization of a Hantavirus isolated from a Clethrionomys glareolus captured in Belgium.

A Hantavirus was isolated in Vero-E6 cells from lungs of a free living bank vole (Clethrionomys glareolus) captured in Turnhout, Province of Antwerp--Northern part of Belgium. With help of monoclonal antibodies the Belgian Hantavirus isolate could be clearly differentiated from Hantaan virus strain 76-118, Prospect Hill virus strain PH1 and SR11, a Hantavirus isolated from laboratory Wistar rat in Japan, but not from the nephropathia epidemica virus strain Hällnäs.

Animals↗
PubMed1986

Ecological and epidemiological data on Hantavirus in bank vole populations in Belgium.

Epidemiological and ecological data of a Hantavirus infected bank vole population were collected using live-trapping methods. A close association between the distribution of HV-infected bank voles and wet habitat types was found. Several seroconversions were observed during the life of individual bank voles. All seroconversions occurred within the wet habitat types and only after a certain age was reached. Survival of HV-infected bank voles did not differ from not-infected animals. In the laboratory passive antibody transfer was observed from antibody-positive females to their offspring.

Age Factors↗