Parasitic Worms Sniff Out their Victims

Soil-dwelling parasitic worms sniff out their victims, using their sense of smell to find suitable hosts for infection, according to a new study.

Such odor-driven behavior in different roundworm species reveals that these parasites hone in on certain hosts based on their stench, rather than preferring related species. This suggests that olfaction indeed plays an important role in host location.

The study's findings are detailed in the journal PLOS Pathogens.

To investigate further, lead researcher Elissa Hallem from the University of California, Los Angeles (UCLA) and colleagues examined the host-seeking strategies and sensory 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 ecological niches.

Some of the species, including Str. Stercoralis, are "cruisers," meaning that they are highly mobile and actively search for hosts. Others are "ambushers" that seem to wait for passing hosts and display little unstimulated movement, while some use an intermediate strategy.

All of the studied worm species, regardless of host-seeking strategy, react to different odors. They are attracted by some smells and repelled by others, and each species has a unique response to each.

Str. stercoralis, for example, at its infective juvenile stage 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 tract of its host.

After comparing these odor profiles, researchers found that those of species with similar hosts were most similar, and this was true even when the species were not closely related. In fact, host specificity rather than relatedness predicts similar olfactory preferences. This suggests that a worm's 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 repel Str. stercoralis and other parasitic nematodes lays a foundation for the design of targeted traps or repellents, which could have broad implications for nematode control."