Olfaction and How We Use It

How do parasites use olfaction to find their hosts?

Next time you’re drawn to the kitchen after smelling something delicious in the air, you can thank olfaction: your sense of smell. Olfaction is one type of sensory input that we rely on to survive and thrive in our environment. Just like we’re drawn to the smell of particular foods, parasites also use olfaction to sense and guide them to hosts from which they can feed. Parasites affect over one billion people worldwide, causing a variety of health issues including chronic gastrointestinal distress and stunted growth, yet we still understand very little about them. By learning more about how parasites use olfaction to find their hosts, and how the parasitic brain transmits these signals, we can develop more effective treatments to combat these pathogens.

The Science

Elissa A Hallem, PhD - Olfaction research

UCLA Neuroscientist Elissa Hallem’s research focuses on the behavior of parasitic worms seeking out a host based on sensory cues. She seeks to understand how the circuits of cells in the worm brain transmit these cues. When an odor like carbon dioxide or sweat is sensed by an olfactory neuron, it sends a signal to the brain, which influences the muscles to move.  

Dr. Hallem’s lab studies behavior by exposing worms to certain smells and determining whether they move toward or away from the source. In addition to studying parasitic worms, Dr. Hallem’s lab also uses the well-understood C. elegans worm to better understand how the parasitic nervous system evolved to support host-finding behavior. Her findings about the genetics, neurobiology, and behavior of these worms contribute to our understanding of how many parasites work.

The Discoveries

  • Dr. Hallem’s lab found that the human-specific parasite Strongyloides stercoralis, commonly known as the human threadworm, responds to a variety of odors from skin or sweat. Hallem is further investigating the neural circuitry that allows the worm to find its host. Threadworms affect an estimated 30-100 million people worldwide and can cause chronic gastrointestinal distress. Research into how the worm behaves can lead to improved prevention and treatment strategies.
  • Dr. Hallem is also advancing our understanding of how parasites have evolved, and how their behaviors might reveal their evolutionary relationships. She found that different groups of worms respond to different sets of odors. These patterns match the types of hosts they infect and the worms’ lifestyles (for example, whether they infect orally or by skin penetration).
  • Dr. Hallem is the recipient of the prestigious MacArthur “Genius” Fellowship in 2012, awarded for “exceptional creativity” and potential for great advancements.


Hallem Lab