From birth to blood-sucking and beyond, how Ixodes Scapularis does its dirty work
By Anna Almendrala
June 24, 2019
Because of a worldwide explosion in the tick population, Lyme disease is reaching pandemic proportions. Here, a step-by-step guide to how the bugs spread the disease.
Around late spring, ticks begin to hatch from clumps of tiny eggs. Ticks that bite humans can be found in every state and Washington, D.C.
Once hatched, tick larvae, as this next life stage is called, seek their first “blood meal”. Their first hosts are likely to be small mammals, like the white-footed mouse, squirrels, and raccoons, or birds, reptiles, and amphibians.
Once a tick larva attaches to a host, it crawls to the surface of the host’s skin and burrows its feeding tube beneath the surface. As the tick bites, special proteins in its saliva enter the host: One has anti-inflammatory properties that numb the skin to help the tick avoid detection, another is an anticoagulant that prevents blood from clotting, allowing the tick to feed continuously for days.
As the tick draws blood from its host, it can pick up bacteria the host is carrying — including Borrelia burgdorferi, the bacterium that causes Lyme disease — then pass it on to humans.
The tick larva drinks blood over the course of several days until it drops away from its host. By the end of its first year, it will molt and become an immature eight-legged tick, or a nymph.
The nymph is now the size of a poppy seed. It needs a second blood meal to reach its final life stage. If the tick is carrying the Lyme bacterium, it is at this point that it poses the greatest risk to humans.
Ticks cannot jump or fly, so they rest on the tips of grasses. Blacklegged ticks hold onto grass with their lower legs and stretch their upper legs outward to climb onto a host — a behavior called questing. Equipped with photoreceptor cells and other unique sensory organs, ticks have a remarkable ability to sense potential hosts. They can detect movement, body heat, odor, moisture, respiration, and carbon dioxide. Some can even detect shadows cast by nearby creatures.
Symptoms from a bite that comes with a Borrelia burgdorferi infection commonly include a rash, especially a bull’s-eye shaped one, severe headaches, joint pain and stiffness, and fatigue. They typically appear within days of a bite.
When people seek medical care for symptoms that could indicate Lyme disease, doctors typically check their body for a rash and ask if they have had any recent exposure to ticks — especially if they live in an area where Lyme disease is endemic and their symptoms began in late spring or summer. The doctor may also order a blood test to check for Lyme or other tick-borne illnesses. But because the antibodies that indicate the presence of Lyme can take several weeks to appear, a doctor may make a diagnosis and prescribe the treatment without a positive Lyme test.
The typical treatment for Lyme disease is a course of antibiotics that can last up to three weeks. Most people begin to feel better shortly after treatment, but a small minority still experience symptoms for months afterward. This condition, known as Post-Treatment Lyme Disease Syndrome, or PTLDS, affects an estimated 1.5 million people per year.