It has been speculated that soil-dwelling parasitic1 worms use their sense of smell to find suitable hosts for infection. Research published on August 14th in PLOS Pathogens comparing odor-driven behaviors in different roundworm（蛔虫） species reveals that olfactory2 preferences reflect host specificity rather than species relatedness, suggesting that olfaction indeed plays an important role in host location. To study worm olfaction, Elissa Hallem, from the University of California Los Angeles, USA, and colleagues examined the host-seeking strategies and sensory3 behaviors of different roundworms. They compared three skin-penetrating parasitic species, including Strongloides stercoralis, the threadworm that causes the serious and common disease strongyloidiasis, with five other worm species of diverse lifestyles and ecological4 niches5.Some of the species, including Str. stercoralis are cruisers that are highly mobile and actively6 search for hosts, others are ambushers that seem to wait for passing hosts and display little unstimulated movement, and some use an intermediate strategy. All of the worm species studied, regardless of host-seeking strategy, react to different odors. They are attracted by some smells and repelled9 by others, and each species has a unique odor response profile. Str. stercoralis, at its infective juvenile10 stage, for example, is attracted to odors of human skin and sweat. And Haemonchus contortus, which infects cattle, is attracted by odors of grass and cow breath, which puts it in a perfect position to enter the digestive tract7 of its host.Comparing these profiles, the researchers found that those of species with similar hosts were most similar, and this was true even when the species were not closely related. The fact that host specificity rather than relatedness predicts similar olfactory preferences suggests that a worms sense of smell does indeed play an important role in host location and selection.The researchers suggest that the identification of odorants that attract or repel8（击退，抵制） Str. stercoralis and other parasitic nematodes（线虫） lays a foundation for the design of targeted traps or repellents, which could have broad implications for nematode control. And as nearly all of the attractants identified for Str. stercoralis also attract anthropophilic mosquitoes [those that feed on humans] and Str. stercoralis and disease-causing mosquitoes are co-endemic throughout the world, they say their results raise the possibility of designing traps that are effective against both.
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1 parasitic adj.寄生的 参考例句： Will global warming mean the spread of tropical parasitic diseases全球变暖是不是意味着热带寄生虫病会蔓延呢？ By definition,this way of life is parasitic.从其含义来讲，这是种寄生虫的生活方法。
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