Detection of spirochetes in, and isolation from, culicine mosquitoes.

Abstract

In mosquitoes, spirochetes were first detected in 1907, when Jaffe reported a spirochete in Culex sp. and named it Spirochaeta culicis (Arch. Protistenkd. 9: 100-107.). Spirochetes were also detected in Anopheles funestus and A. maculipennis (Sinton J.A., Shute P.G. 1939: J. Trop. Med. Hyg. 42: 125-126) and in the salivary glands of Anopheles gambiae (Masseguin A., Palinacci A. 1954: Bull. Soc. Pathol. Exot. 47: 3). The presence of the Lyme disease (LD) spirochete, Borrelia burgdorferi has also been reported in mosquitoes and other bloodsucking insects (Magnarelli F.A., Freier J.E., Anderson J.F. 1987: J. Infect. Dis. 156: 694-695). In South Moravia (Czech Republic), spirochetes have been previously observed in mosquitoes (Halouzka J. 1993: Biologia 48: 123-124), and one strain of Borrelia afzelii was isolated from Aedes vexans (Halouzka J., Postic D., Hubalek Z. 1998: Med. Vet. Entomol. 12: 103-105). In this study, we examined 2,583 female mosquitoes collected in South Moravia during the years 1993-1997. In the summer season (June to September), 571 mosquitoes were sampled from various localities and habitats: lowland floodplain forest, mixed oak forest with bushes, deciduous mixed forest and shores of a fishpond covered with reedbelts. Three species of the genus Aedes – Aedes vexans Meigen, 1830, Aedes sticticus (Meigen, 1838), Aedes cantans (Meigen, 1818) and, moreover, Culex pipiens Linnaeus, 1758 biotype pipiens were sampled. During the winter period, 2,012 overwintering Culex pipiens biotype molestus were obtained from cool and humid basement rooms of buildings. The mosquitoes were kept alive at the temperature of about 4°C until dissected. The abdomen content of each mosquito was triturated in a drop of saline and individually examined by darkfield microscopy at a magnification 400×. Specimens with a high number (>100) of motile spirochetes were occasionally inoculated into BSK-H liquid medium (Sigma) supplemented with 5% rabbit serum (Sigma), antibiotics (phosphomycin 100 μg/ml, rifampicin 50 μg/ml), and incubated at 33°C up to six weeks. The mean prevalence of spirochetes in mosquitoes caught in the summer season was 1.9%. In the winter collection, the mean prevalence of spirochetes in Culex pipiens molestus was 5.1% (Table 1). As much as 22 mosquitoes contained more than 100 spirochetes, and 11 of them were inoculated into BSK-H medium. Due to heavy bacterial contamination, only Table 1. Prevalence of spirochetes in mosquitoes.