Victor Luyasu

Determinants of the geographic distribution of Puumala virus and Lyme borreliosis infections in Belgium

BackgroundVector-borne and zoonotic diseases generally display clear spatial patterns due to different space-dependent factors. Land cover and land use influence disease transmission by controlling both the spatial distribution of vectors or hosts, and the probability of contact with susceptible human populations. The objective of this study was to combine environmental and socio-economic factors to explain the spatial distribution of two emerging human diseases in Belgium, Puumala virus (PUUV) and Lyme borreliosis. Municipalities were taken as units of analysis.ResultsNegative binomial regressions including a correction for spatial endogeneity show that the spatial distribution of PUUV and Lyme borreliosis infections are associated with a combination of factors linked to the vector and host populations, to human behaviours, and to landscape attributes. Both diseases are associated with the presence of forests, which are the preferred habitat for vector or host populations. The PUUV infection risk is higher in remote forest areas, where the level of urbanisation is low, and among low-income populations. The Lyme borreliosis transmission risk is higher in mixed landscapes with forests and spatially dispersed houses, mostly in wealthy peri-urban areas. The spatial dependence resulting from a combination of endogenous and exogenous processes could be accounted for in the model on PUUV but not for Lyme borreliosis.ConclusionA large part of the spatial variation in disease risk can be explained by environmental and socio-economic factors. The two diseases not only are most prevalent in different regions but also affect different groups of people. Combining these two criteria may increase the efficiency of information campaigns through appropriate targeting.

Human anaplasmosis in Belgium: A 10-year seroepidemiological study

Human granulocytic anaplasmosis (HGA) is a tick-borne rickettsial infection of neutrophils caused by Anaplasma phagocytophilum. Although the pathogen was known as a veterinary agent as early as 1932, the link with human disease was first established in 1990. In the past decennium, the involvement of HGA as an important and frequent cause of fever with a history of tick bite was increasingly recognized in many regions of Europe. This paper presents a 10-year A. phagocytophilum serosurveillance (2000-2009), wherein 1672 serum samples were tested and 418 were found positive. A total of 111 patients had a history of tick bite, fever, and at least a 4-fold rise in titre and are thus considered to be confirmed cases. These findings suggest that Belgium is a hot spot for HGA infections.

Scouts, forests, and ticks: Impact of landscapes on human-tick contacts

Just as with forest workers or people practicing outdoor recreational activities, scouts are at high risk for tick bites and tick-borne infections. The risk of a tick bite is shaped not only by environmental and climatic factors but also by land management. The aim of this study was to assess which environmental conditions favour scout-tick contacts, and thus to better understand how these factors and their interactions influence the two components of risk: hazard (related to vector and host ecology) and exposure of humans to disease vectors. A survey was conducted in the summer of 2009 on the incidence of tick bites in scout camps taking place in southern Belgium. Joint effects of landscape composition and configuration, weather, climate, forest and wildlife management were examined using a multiple gamma regression with a log link. The landscape was characterized by buffers of varying sizes around the camps using a detailed land use map, and accounting for climate and weather variables. Landscape composition and configuration had a significant influence on scout-tick contacts: the risk was high when the camp was surrounded by a low proportion of arable land and situated in a complex and fragmented landscape. The distance to the nearest forest patch, the composition of the forest ecotone as well as weather and climatic factors were all significantly associated with scout-tick contacts. Both hazard- and exposure-related variables significantly contributed to the frequency of scout-tick contact. Our results show that environmental conditions favour scout-tick contacts. For example, we emphasize the impact of accessibility of environments suitable for ticks on the risk of contact. We also highlight the significant effect of both hazard and exposure. Our results are consistent with current knowledge, but further investigations on the effect of forest management, e.g. through its impact on forest structure, on the tick-host-pathogen system, and on humans exposure, is required.

Multicenter evaluation of a new commercial assay for detection of immunoglobulin M antibodies to Toxoplasma gondii. Multicenter Study Group.

A new commercial assay for detection of IgM-specific antibodies toToxoplasma gondii (IMx Toxo IgM, Abbott, USA), based on microparticle enzyme immunoassay technology, was evaluated at 15 clinical sites in Europe and the USA. Performance characteristics were established by testing clinical specimens collected randomly from pregnant women, blood donors, individuals with suspectedToxoplasma gondii infection and individuals confirmed HIV positive. Reference testing was performed using Toxo-M EIA (Abbott). Specimens evaluated at European sites yielding discordant results between the new assay and the reference EIA were further tested with an immunosorbent agglutination assay; at sites in the USA, discordant results were resolved using Platelia Toxo IgM (Sanofi, France) and Vidas Toxo IgM (bioMérieux, France) assays. In addition, matched plasma and serum, heat-treated and non-heat-treated specimens, and fresh and frozen specimens were evaluated at the USA sites. At European sites the new commercial assay had a sensitivity of 95.6 % (196/205), a specificity of 99.8 % (3,137/3,143) and an agreement of 99.6 % (3,333/3,348) following resolution of discordant results; sensitivity in the USA was 97.4 % (184/189), specificity was 99.8 % (1,204/1,207) and agreement was 99.4 % (1,388/1,396) following resolution. The new IMx Toxo IgM is a sensitive and specific assay for measurement of IgM antibodies toToxoplasma gondii in human serum and plasma.

Individual and environmental factors associated with the seroprevalence of Borrelia burgdorferi in Belgian farmers and veterinarians

Background Lyme disease (LD) is a common tick-borne disease in Europe. Diverse factors at various scales determine the spatial distribution of Borrelia burgdorferi infection risk and a better understanding of those factors in a spatially explicit framework is needed for disease management and prevention. While the ecology of ticks and the landscape favoring their abundance have been extensively studied, the environmental conditions favoring an intense contact with susceptible humans, including groups at risk, are sparse. The aim of this study is to assess which individual and environmental factors can favor B. burgdorferi infection in a Belgian group professionally at risk. Methods Serological results of 127 veterinarians and farmers enrolled in this study were analyzed, taking into account their municipality of residence. Using binary logistic regression and considering interaction terms, the joint effects of landscape composition and configuration, and forest and wildlife management were examined. Results Seven of the 127 workers were seropositive for LD, leading to a seroprevalence of 5.51%. Seropositivity was higher in older persons. The proportion of forest and semi-natural habitats and wetland had a positive impact on LD seroprevalence while arable land–grassland ecotones had a negative one. Our results confirmed the need to consider complex interactions between landscape variables in order to model risk. Conclusions Our data show that LD has to be considered as a risk for farmers and veterinarians. Rather than focusing either on ecological aspects of tick and pathogen distribution or on purely epidemiological aspects such as individual risk factors, our model highlights the role of human–environment interactions in LD risk assessment.

Time trend of clinical cases of Lyme disease in two hospitals in Belgium, 2000–2013

BackgroundAs several studies indicated an increase in Lyme disease (LD), notably in neighbouring countries, concerns have arisen regarding the evolution of Lyme disease in Belgium. In order to confirm or infirm the increase of LD in Belgium, we focused on hospital admissions of patients diagnosed with LD between 2000 and 2013 based on hospital admission databases from two hospitals in Belgium.MethodsHospital databases are a stable recording system. We did a retrospective analysis of the medical files of patients hospitalized with Lyme disease in two Belgian hospitals between 2000 and 2013.ResultsThe annual number of cases of LD for the two studied Belgian hospitals remained stable between 2000 and 2013, ranging from 1 for the Cliniques universitaires Saint-Luc to 15 for the the Clinique Saint-Pierre. No increasing trend were noted in the estimated annual incidence rate but the average estimated annual incidence rate was higher for the hospital Saint-Pierre (8.1 ± 3.7 per 100,000 inhabitants) than Saint-Luc (2.2 ± 1.5 per 100,000 inhabitants). The number of hospital cases of LD peaked between June and November.ConclusionsBased on hospital admissions with LD, no increasing trend was observed for the period 2000–2013 in the two studied Belgian hospitals. This is in line with other studies carried out in Belgium.

Seroprevalence of Borrelia burgdorferi in Belgian forestry workers and associated risk factors

BackgroundAs forest is the preferred environment for ticks, forestry workers are exposed to tick bites and tick-borne diseases. We assessed the seroprevalence of anti-Borrelia burgdorferi (Bb) antibodies and investigated, using an integrated landscape approach, the individual and environmental factors associated with the seroprevalence of Bb in Belgian forestry workers, a high-risk group in Belgium.MethodsA group of 310 Belgian forest workers was examined to assess the seroprevalence of anti-Borrelia IgG antibodies. Using principal component analysis and binary logistic regression, the joint effects of individual characteristics and environmental characteristics were examined.ResultsSixty-seven of the 310 workers were seropositive for Lyme disease (LD), leading to a seroprevalence of 21.6%. The seroprevalence was higher among forest workers visiting forests more frequently (P = 0.003) or who reported over 100 tick bites (P-value < 0.001). The intensity of tick bites and the use of protection measures against tick bites have a positive impact on LD seroprevalence while the quantity of shadow from trees at ground level had a negative one.ConclusionsThis study showed that forest workers are a population at risk for LD and, by extension, at risk for various tick-borne diseases. In addition to the role of the environment, our results also showed the importance of considering exposure when predicting the risk of infection by Bb.