Immunoglobulin-binding proteins in ticks: new target for vaccine development against a blood-feeding parasite

Humans have a long history of trying to control ticks. At first, attempts focused on modifying the habitat, whereas later efforts relied heavily on the use of chemicals. Current research is directed at finding a vaccine against ticks. A strategy of targeting 'concealed antigens' succeeded with the first commercialised vaccine against the cattle tick Boophilus microplus. However, vaccine development against other tick species appears unsatisfactory to date. Vaccination depends on a specific antibody-mediated immunoreaction that damages the parasite. Immunoglobulin molecules of vertebrate hosts can pass through gut barriers into the haemolymph of ectoparasites while retaining antibody activity. Research on the ixodid tick Rhipicephalus appendiculatus revealed that host immunoglobulin-G in the parasite was excreted via salivation, during feeding. Immunoglobulin-binding proteins in tick haemolymph and salivary glands are thought to be responsible for such excretion. The discovery of an immunoglobulin excretion system in ticks indicates that they have a highly developed mechanism to protect themselves from their host's antibody attack. Such a mechanism questions whether immunization strategies will be effective against ticks, unless they circumvent or disable the ticks' immunoglobulin excretion system.     

Non-viraemic transmission of tick-borne encephalitis virus: a mechanism for arbovirus survival in nature

The vectors of arthropod-borne viruses (arboviruses) become infected by feeding on the viraemic blood of an infected animal. This theory is based on transmission studies involving artificial infection of vertebrate hosts by syringe inoculation. To reproduce natural conditions of virus transmission, infected and uninfected vectors (ticks) of tick-borne encephalitis virus, the most important arbovirus in Europe, were allowed to feed together on uninfected wild vertebrate hosts. The greatest numbers of infected ticks were obtained from susceptible host species that had undetectable or very low levels of viraemia. The results suggest that nonviremic transmission is an important mechanism for the survival of certain arboviruses in nature.     

Modification of the skin feeding site by tick saliva mediates virus transmission.

A tick vector of Thogoto (THO) virus was shown to secrete a factor in saliva which potentiates the transmission of THO virus to uninfected ticks feeding on an apparently non-viraemic host. The effect of the saliva activated transmission (SAT) factor on the virus occurred at the site of inoculation in the skin and was apparent even when the virus was introduced 3 days after the SAT factor. The results suggest that tick saliva can play an important role in disease transmission by virtue of host modification at the site of feeding.     

Modification of the skin feeding site by tick saliva mediates virus transmission

A tick vector of Thogoto (THO) virus was shown to secrete a factor in saliva which potentiates the transmission of THO virus to uninfected ticks feeding on an apparently non-viraemic host. The effect of the saliva activated transmission (SAT) factor on the virus occurred at the site of inoculation in the skin and was apparent even when the virus was introduced 3 days after the SAT factor. The results suggest that tick saliva can play an important role in disease transmission by virtue of host modification at the site of feeding.     

富营养化水体中的溶源性浮游细菌分布与环境因子的关系

使用非侵害性根吸收硝酸盐检测系统,在较低NO3-浓度下,测定10 m mol/L的蔗糖、葡萄糖、果糖、半乳糖、棉子糖、D-甘露醇、甘露糖、阿拉伯糖、乳糖对水稻品种"汕优63"硝酸盐吸收的影响,以10 min为间隔连续测定4 h,结果表明:加入蔗糖后对水稻硝酸盐的吸收有显著的、立即的、持续的促进作用,与加入蔗糖前相比,硝酸盐净吸收率上升了298%,葡萄糖、半乳糖、果糖、棉子糖对水稻硝酸盐的吸收亦有明显的促进作用,上升幅度140%～223%;乳糖、D-甘露醇、阿拉伯糖无明显影响;甘露糖则有抑制作用.蔗糖可能足作为主要的信号分子参与植物硝酸盐吸收的正反馈调控.