Christine M. Happ

Duration of Tick Attachment as a Predictor of the Risk of Lyme Disease in an Area in which Lyme Disease Is Endemic

Animal studies have shown an exponential increase in the risk of Borrelia burgdorferi infection after 48-72 h of deer tick attachment. Persons with tick bites were prospectively studied to determine if those with prolonged tick attachment constitute a high-risk group for infection. Ticks were identified, measured for engorgement, and assayed by polymerase chain reaction (PCR) for B. burgdorferi DNA. Duration of attachment was determined from the scutal index of engorgement. Of 316 submissions, 229 were deer ticks; 14% were positive by PCR. Paired sera and an intact tick for determination of duration of attachment were available for 105 subjects (109 bites). There were 4 human cases (3.7% of bites) of B. burgdorferi infection. The incidence was significantly higher for duration of attachment > or =72 h than for <72 h: 3 (20%) of 15 vs. 1 (1.1%) of 94 (P = .008; odds ratio, 23.3; 95% confidence interval, 2.2-242). PCR was an unreliable predictor of infection. Tick identification and measurement of engorgement can be used to identify a small, high-risk subset of persons who may benefit from antibiotic prophylaxis.

Mosquito feeding modulates Th1 and Th2 cytokines in flavivirus susceptible mice: an effect mimicked by injection of sialokinins, but not demonstrated in flavivirus resistant mice

Culex pipiens and Aedes aegypti mosquitoes were fed on C3H/HeJ mice and systemic cytokine production was quantified from stimulated lymphocytes harvested four to ten days after feeding. Mosquito feeding on C3H/HeJ mice significantly down regulated IFNγ production seven to ten days post feeding by Cx. pipiens and seven days after Ae aegypti feeding. Th2 cytokines, IL‐4 and IL‐10, were significantly up regulated 4–7 days after Cx. pipiens and Ae. aegypti feeding. The immunosuppressive effect of Cx. pipiens feeding on systemic cytokine production was not evident in congenic flavivirus resistant (C3H/RV) mice, as systemic IFNγ and IL‐2 were significantly up regulated at days 7 and 10, correlating with a significant decrease in IL‐4 10 days after feeding by Cx. pipiens mosquitoes. Inoculation of 5–1000 ng of sialokinin‐I into C3H/HeJ mice mimicked the effect of Ae. aegypti feeding by down regulating Th1 cytokines and significantly up regulating Th2 cytokines four days post inoculation. Injections of sialokinin‐II resulted in only moderate effects on IFNγ and IL‐4 production seven and ten days after injection. Thus natural feeding by two arbovirus vectors had a profound T cell modulatory effect in vivo in virus susceptible animals which was not demonstrated in the flavivirus resistant host. Moreover, sialokinin‐I and sialokinin‐II mimicked the effect of mosquito feeding by modulating the host T cell response. These results may lend new insight into specific aspects of the role of the mosquito vector in potentiating virus transmission in the mammalian host.

Incomplete protection of hamsters vaccinated with unlipidated OspA from Borrelia burgdorferi infection is associated with low levels of antibody to an epitope defined by mAb LA-2

Efforts to develop a recombinant vaccine for Lyme disease have focused on using the outer surface protein A (OspA) of Borrelia burgdorferi as an immunogen. We evaluated the effectiveness of an unlipidated recombinant OspA as a vaccine in hamsters. This molecule is soluble and can be produced in high yield in Escherichia coli, characteristics that permit simple and relatively low cost production. Vaccination with unlipidated OspA protected a substantial portion of animals--59-79%, depending on the challenge strain and route--against moderate doses of spirochetes delivered either by injection or by bite of infected nymphal ticks (Ixodes scapularis). The instances of vaccine failure were associated with development of low levels of antibody to a particular OspA epitope, one defined by mAb LA-2. At least 50 ng ml-1 of LA-2 equivalent antibody was necessary for protection of hamsters. Lower LA-2 equivalent antibody concentrations occurred in unprotected animals in the presence of high-titered polyclonal antibody to native OspA. A competitive binding assay to quantitate this serum fraction is described that should be of use in monitoring the quality of the antibody response to OspA in vaccine trials. Concentrations of LA-2 equivalent antibody parallel the ability of the serum specimens to inhibit the growth of B. burgdorferi in culture.

Infection of Ixodes scapularis (Acari: Ixodidae) with Borrelia burgdorferi Using a New Artificial Feeding Technique

Abstract To study interactions between Ixodes scapularis (Say) and Borrelia burgdorferi, an artificial feeding system was refined to allow controlled manipulation of single variables. The feeding system uses a mouse skin mounted on a water-jacketed glass membrane feeder. I. scapularis were infected using either BSK-H-cultured B. burgdorferi spirochetes or a B. burgdorferi-infected mouse skin as the source of spirochetes. Sixty-six percent of nymphs successfully fed to repletion using the artificial feeding systems with at least 75% of nymphs becoming infected with B. burgdorferi. Strain B31 B. burgdorferi spirochetes from passages 2–17 were equally infectious to nymphal ticks. At concentrations of one spirochete per microliter, 12% of nymphs acquired infection and 14 and 100 spirochetes per microliter resulted in 50 and 100% infection rates, respectively. Eighty-nine percent of nymphs fed by artificial feeding molted to the adult stage. When subsequently fed as adults, these I. scapularis successfully transmitted infectious B. burgdorferi spirochetes to mice.