School of Biological Sciences, University of Bristol, Bristol, United Kingdom.
PLoS Negl Trop Dis. 2012;6(2):e1515. doi: 10.1371/journal.pntd.0001515. Epub 2012 Feb 14.
Unlike other dipteran disease vectors, tsetse flies of both sexes feed on blood and transmit pathogenic African trypanosomes. During transmission, Trypanosoma brucei undergoes a complex cycle of proliferation and development inside the tsetse vector, culminating in production of infective forms in the saliva. The insect manifests robust immune defences throughout the alimentary tract, which eliminate many trypanosome infections. Previous work has shown that fly sex influences susceptibility to trypanosome infection as males show higher rates of salivary gland (SG) infection with T. brucei than females. To investigate sex-linked differences in the progression of infection, we compared midgut (MG), proventriculus, foregut and SG infections in male and female Glossina morsitans morsitans. Initially, infections developed in the same way in both sexes: no difference was observed in numbers of MG or proventriculus infections, or in the number and type of developmental forms produced. Female flies tended to produce foregut migratory forms later than males, but this had no detectable impact on the number of SG infections. The sex difference was not apparent until the final stage of SG invasion and colonisation, showing that the SG environment differs between male and female flies. Comparison of G. m. morsitans with G. pallidipes showed a similar, though less pronounced, sex difference in susceptibility, but additionally revealed very different levels of trypanosome resistance in the MG and SG. While G. pallidipes was more refractory to MG infection, a very high proportion of MG infections led to SG infection in both sexes. It appears that the two fly species use different strategies to block trypanosome infection: G. pallidipes heavily defends against initial establishment in the MG, while G. m. morsitans has additional measures to prevent trypanosomes colonising the SG, particularly in female flies. We conclude that the tsetse-trypanosome interface works differently in G. m. morsitans and G. pallidipes.
与其他双翅目疾病传播媒介不同，雌雄采采蝇均以血液为食，并传播致病性的非洲锥虫。在传播过程中，布氏锥虫在采采蝇媒介中经历了一个复杂的增殖和发育周期，最终在唾液中产生感染性形式。在整个消化道中，昆虫表现出强大的免疫防御能力，消除了许多锥虫感染。以前的工作表明，蝇的性别会影响对锥虫感染的易感性，因为雄性比雌性更容易感染唾液腺（SG）中的布氏锥虫。为了研究感染过程中与性别相关的差异，我们比较了雄性和雌性冈比亚按蚊中肠（MG）、前胃、前肠和唾液腺的感染情况。最初，两种性别中的感染发展方式相同：MG 或前胃感染的数量没有差异，产生的发育形式的数量和类型也没有差异。雌蝇产生前肠迁移形式的时间晚于雄蝇，但这对 SG 感染的数量没有明显影响。直到 SG 入侵和定植的最后阶段，性别差异才显现出来，表明 SG 环境在雌雄蝇之间存在差异。与 G. pallidipes 的比较表明，敏感性存在类似但不那么明显的性别差异，但在 MG 和 SG 中还显示出了截然不同的锥虫抗性水平。虽然 G. pallidipes 对 MG 感染的抵抗力更强，但很高比例的 MG 感染会导致雌雄蝇的 SG 感染。看来这两种蝇种使用不同的策略来阻止锥虫感染：G. pallidipes 强烈抵御 MG 中的初始定植，而 G. m. morsitans 则采取额外的措施来防止锥虫定植于 SG，尤其是在雌蝇中。我们得出结论，在 G. m. morsitans 和 G. pallidipes 中，采采蝇-锥虫界面的工作方式不同。
