Résultat de la recherche
Tick bites in a Lyme borreliosis highly endemic area in Switzerland
The duration of tick feeding is an important indicator to evaluate the risk of Borrelia burgdorferi sensu lato transmission, which increases considerably with the blood meal duration. This blood meal duration may be estimated from scutal index, the ratio between body length (idiosoma) and scutum width. For the estimation of blood meal duration in Ixodes ricinus, nymphal and adult female ticks were detached at predetermined intervals (24, 48, 72, and 96 h) from laboratory mice and rabbits and their scutal index calculated. From this, non-linear regression equations were developed to determine the duration of attachment for nymphal and adult female I. ricinus ticks. As part of an epidemiological study addressing the risk of subclinical (seroconversion) and clinical infections after a tick bite in the Neuchâtel area (Switzerland) over 3 years (2003–2005), duration of tick attachment and anatomical site of bites collected on participants as well as seasonal distribution of tick bites were studied. Tick attachment duration was estimated in all ticks collected during this study (n=261). Nymphs were attached for a mean (± standard error, SE) of 31.6 h (±2.6) and females for a mean (±SE) of 29.6 h (±3.2). Most nymphs were removed after 24 h of blood meal whereas most females were removed before 24 h. Legs were the major anatomical sites of bites for women (40.7%), men (44.4%), and almost all age classes. Only children <10 years old were bitten more frequently on the head (41.2%) and on the neck (38.5%) than participants >10 years. The majority of tick bites were recorded from May to July during the 3 years. Attachment sites can influence the discovery of ticks, hence the duration of the tick bite. A detailed body examination after each outing in forest and an early withdrawal of an attached tick is an effective way to prevent Lyme borreliosis.
Investigations on the Mode and Dynamics of Transmission and Infectivity of Borrelia burgdorferi Sensu Stricto and Borrelia afzelii in Ixodes ricinus Ticks
Borrelia burgdorferi sensu lato (sl), the agent of Lyme disease, is transmitted to the host during the blood meal of Ixodes ticks. In most unfed ticks, spirochetes are present in the midgut and migrate during blood feeding to the salivary glands, from which they are transmitted to the host via saliva. In the present study, the efficiency of Ixodes ricinus ticks to transmit B. afzelii and B. burgdorferi sensu stricto (ss) and their infectivity for mice were examined in relation to the duration of the blood meal. In addition, we investigated whether these two Borrelia species can penetrate intact skin. Three modes of infection of mice were studied: tick-bite infection, inoculation of tick homogenates, and transcutaneous infection by topical application of tick homogenates on mouse skin. Transmission of B. burgdorferi sl from I. ricinus nymphs to mouse increased with duration of tick attachment. B. afzelii-infected ticks start to transmit infection earlier (≤48 h) than B. burgdorferi ss-infected ticks. As previously shown for B. burgdorferi ss in Ixodes scapularis, B. burgdorferi ss and B. afzelii in unfed I. ricinus were noninfectious for mice when tick homogenates were inoculated. However, the inoculation of homogenates of ticks fed for 24 h readily produced infection in mice. Therefore, B. burgdorferi ss and B. afzelii spirochetes are potentially infectious in the tick before natural transmission can occur. None of the mice (n = 33) became infected by transcutaneous transmission when tick homogenates were applied on mouse skin, showing that B. burgdorferi ss and B. afzelii are unable to penetrate intact skin, in contrast to relapsing fever spirochetes. This study also shows that B. afzelii is transmitted by I. ricinus to the host earlier than B. burgdorferi ss and that I. ricinus seems to be a more efficient vector of B. afzelii than B. burgdorferi ss.