Claudine Pérez-Eid

Prevalence of Borrelia burgdorferi Sensu Lato and Anaplasmataceae Members in Ixodes ricinus Ticks in Alsace, a Focus of Lyme Borreliosis Endemicity in France

ABSTRACT Due to the high Lyme borreliosis incidence in Alsace, in northeastern France, we investigated in 2003-2004 three cantons in this region in order to determine the density of Ixodes ricinus ticks infected by Borrelia burgdorferi sensu lato and Anaplasmataceae. The peak density of nymphs infected by B. burgdorferi sensu lato at Munster and Guebwiller, where the disease incidence was high, was among the highest reported in Europe (105 and 114 per 100 m2, respectively). In contrast, the peak density of infected nymphs was low in the canton of Dannemarie (5/100 m2), where the disease incidence was low. The two main species detected in ticks were Borrelia afzelii, more frequent in nymphs, and Borrelia garinii, more frequent in adult ticks. The rates of tick infection by Anaplasma phagocytophilum were 0.4% and 1.2% in nymphs and adults, respectively.

Density of deer in relation to the prevalence of Borrelia burgdorferi s.l. in Ixodes ricinus nymphs in Rambouillet forest, France

The Rambouillet Forest, a Lyme disease-endemic area near Paris, France, was surveyed from September 1994 to October 1995 to determine the risk periods and zones for humans. Firstly, during the period of Ixodes ricinus activity, abundance of nymphs is greater in spring than in autumn. Secondly, we observed significant variation in nymphal abundance between zones according to the density of cervids. The polymerase chain reaction (PCR) was used to detect DNA of Borrelia burgdorferi sensu lato in 461 unfed nymphs. DNA was detected in 38 nymphs (8.2%). By genospecific PCR based on the OspA gene, we detected the three pathogenic spirochetes with occurrences of 10.3, 31.1 and 58.6 for B. burgdorferi s.s., Borrelia garinii and Borrelia afzelii, respectively, indicating that B. afzelii is probably the main Borrelia species in the Rambouillet Forest. Finally, 11.5% of positive nymphs exhibited a double infection. Infection rates of I. ricinus nymphs by B. burgdorferi s.l. were not significantly different throughout the year for a given area, indicating that the risk periods of acquiring Lyme disease are mainly linked to nymph activity and correspond to spring and autumn. Likewise infection rates of nymphs were not significantly different between zones with a high density of deer (more than 100 animals per 100 ha) and zones with lower deer density (less than 20 animals per 100 ha). In addition to the role of deer as an amplifier of tick populations, these data indicate that zones with a high density of cervids should be considered as higher risk areas.

Methodology for Sampling Questing Nymphs of Ixodes Ricinus (Acari: Ixodidae), the Principal Vector of Lyme Disease in Europe

Abstract To assess the Lyme borreliosis vector population density we set up a methodology for sampling the Ixodes ricinus L. population host questing on the vegetation. We focused on the collection of the nymphal stage, which is the principal stage of disease transmission to humans. This study was carried out in Rambouillet forest (Yvelines, France) where seven study areas were demarcated. These areas are maximally homogeneous for plant species using a finer scale than the phytosociological classification as defined by the method of landscape diagnostics. Out of 23 collections performed from March 1997 to May 1998, 2,906 I. ricinus nymphs were collected. The sampling technique chosen was the cloth lure technique. The technical parameters were studied and fixed (cloth type, cloth size, sample size, researcher position). It appeared that toweling was the best cloth type to optimize the number of ticks collected; the position of the researcher had no effect on tick samples. To satisfy the criteria for correct sampling, we studied representativity, randomness, and nonselectivity of our methodology. The spatial distribution of nymphs in a homogeneous area was close to random and thus very few subsamples were needed to obtain a relative density which was representative. No significant differences were found between random samples and following transect samples; and nonselectivity was totally satisfied because we only worked on questing nymphs. We grouped the samples that presented no significant differences to attribute a density index, which varied from 0 to 5. This methodology, applied with the same parameters, offers potential for producing comparable results from studies in different geographical areas and at different times of the years.

Prevalence of antibodies to Borrelia burgdorferi in forestry workers of Ile de France, France

A cross-sectional sero-epidemiological study was conducted on forestry workers, a high risk population for Lyme borreliosis. The prevalence of seropositive forestry workers (indirect immuno fluorescence assay) is 15.2% (n = 211). Almost 70% of participants reported a history of tick bite. Among districts, high seroprevalences were observed in Fontainebleau and Rambouillet; two sites of high risk for Lyme borreliosis. However, clinical prevalence of the disease is very low. During the investigation no active Lyme borreliosis was observed. Thus, asymptomatic infection predominates.

Temporal Distribution of the Annual Nymphal Stock of Ixodes Ricinus Ticks

The human risk of contracting Lyme disease or other tick borne diseases transmitted by the tick species Ixodes ricinus is broadly linked to the tick nymph density. The study was performed in Rambouillet forest (Yvelines, France), a known focus of Lyme borreliosis, from January 1997 to December 1999. We used a nymph sampling methodology which permitted us to obtain a monthly nymph density index (from 0 to 5). Studying the seasonal nymph and larval activity patterns and estimating the larval developmental duration, we demonstrate the existence of an annual nymphal stock. Secondly, we elucidate how this stock is distributed throughout the year, month by month. Its distribution is principally dependent on two factors: the monthly mean ambient temperature and the proportion of active nymphs which find a host each month. Expected monthly nymph densities derived from a theoretical model describing the temperature-dependent stock distribution gave a good fit to the observed densities, accounting for between 76–86% of the monthly variation in observed nymph densities. Predicting the temporal distribution of nymph activity within a stable Lyme borreliosis focus enables more precise identification of risk periods.

The Alsatian tick-borne encephalitis focus : presence of the virus among ticks and small mammals

An extensive epidemiologic survey was carried out from 1970 to 1974 in order to understand the condition of circulation of tick-borne encephalitis virus between ticks and small mammals in the Alsatian focus, France.The virus has been isolated from Ixodes ricinus adult ticks (30 lots out of 369, representing a total of 5617 ticks), and from Ixodes ricinus nymphs (4 lots out of 251, representing a total of 8587 ticks). The virus has also been isolated from 11 pools of rodent organs (out of 3361 rodents), and HI antibodies were detected in 21 out of 8735 rodent specimens. The virus has never been detected in rodent blood, nor in 10,298 ticks collected engorged from 1505 vertebrate hosts.These results show that Alsatian tick-borne encephalitis focus is stable since the activity of the virus is detected every year, and that the focus is an extended one since the virus is isolated from 5 of 6 study sites, as well as in several control sites.

Comparative Behavior of Different Life-Cycle Stages of Ixodes ricinus (Acari: Ixodidae) to Human-Produced Stimuli

Abstract Nymphs of Ixodes ricinus (Linnaeus, 1758), I. scapularis Say, 1821, and I. pacificus Cooley & Kohls, 1943 are epidemiologically the most dangerous stage for transmission of Lyme disease to humans. Many factors play a role in the epidemiological significance of the nymphs. In this study, we address the question of whether nymphs show a greater tendency than adults to accept humans as their host. To evaluate this, we have compared the host acceptance behavior of nymphs and adults (males and females) with respect to a human in Rambouillet forest, a focus of Lyme disease. Individual ticks (nymph, male or female) located on a herbaceous stem were exposed to different stimuli (e.g., approach, stem movement, breathing), and the response of each individual to these stimuli was noted. Tick responses were categorised into classes (from 0 to 3) according to their intensity. Statistical analysis carried out on 22 ticks allowed us to compare the behavior of the nymph stage with respect to males and females. Despite the small sample sizes, it appears that nymphs are more responsive to a human than are the adults.

Use of enzyme-labelled protein G assay for the detection of anti Borrelia burgdorferi antibodies in wild animal sera

A modified ELISA was developed for the detection of anti-Borrelia burgdorferi (Bb) IgG antibodies in wild animal sera based on an Enzyme-Labelled-protein G Assay (ELGA). Microplates were coated with an extract of Bb sensu stricto strain (SV1) as antigen. Specific antibodies of the serum samples were detected by a peroxidase-labelled-protein G. Using comparative immunodiagnosis by means of a passive hemagglutination test (HA), ELGA was tested on 82 roe-deer blood samples. A correlation was found between the two methods (r = 0,66). Good reproducibility of titers was observed by ELGA technique. A minimal cross-reactivity was discovered with Leptospira. ELGA could facilitate the recognition of specific antibodies in collections of wild animal sera.