Lyme disease The most common tickborne disease in

Lyme disease The most common tickborne disease in the United States is Lyme disease caused by the spirochete Borrelia burgdorferi. Lyme disease ranks fifth among all nationally notifiable conditions.

The lifecycle of blacklegged ticks (Ixodes scapularis and Ixodes pacificus) generally lasts two years. During this time, they go through four life stages: egg, six-legged larva, eight-legged nymph, and adult. After the eggs hatch, the ticks must have a blood meal at every stage to survive. Blacklegged ticks can feed from mammals, birds, reptiles, and amphibians. The ticks need to have a new host at each stage of their life, as shown below: tick most often becomes infected during its larval or nymph stage, when it feeds off small animals like squirrels, mice, or birds that carry the bacteria which causes Lyme disease

Transmission to humans Most humans are infected through the bites of immature ticks called nymphs. In most cases, the tick must be attached for 36 to 48 hours or more before the Lyme disease bacterium can be transmitted. Nymphs are tiny (less than 2 mm) and difficult to see; they feed during the spring and summer months.

Transmission to humans Adult ticks can also transmit Lyme disease bacteria, but they are much larger and are more likely to be discovered and removed before they have had time to transmit the bacteria. Adult Ixodes ticks are most active during the cooler months of the year.

The Tick factor The life cycle and prevalence of deer ticks are strongly influenced by temperature. deer ticks are found mostly in the heavily wooded areas deer ticks are mostly active when temperatures are above 45˚F, and they thrive in areas with at least 85 -percent humidity. Thus, warming temperatures associated with climate change are projected to increase the range of suitable tick habitat and are therefore one of multiple factors driving the observed spread of Lyme disease. Ticks are able to survive in new geographical areas

These maps show the distribution of reported cases of Lyme disease in 1996 and 2014. The incidence of Lyme disease in the United States has approximately doubled since 1991, from 3. 74 reported cases per 100, 000 people to 7. 95 reported cases per 100, 000 people in 2014 (see Figure 1).

The Deer Factor Notably, the white-tailed deer supports the tick, but not the spirochete. These hosts provide the ticks with a bountiful supply of food (i. e. , blood meals), enabling the ticks to live, reproduce, and/or infect a human. Beginning in the second half of the 20 th century, suburbia increasingly crept into forested portions of the Northeast. . Hostcycle image courtesy of Emily M. Eng White-footed mouse and Western Fence lizard images courtesy of Anand Varma

The Mouse factor On the East Coast, the white-footed mouse is the primary host. The rodents occupy more urban and suburban landscapes as their habitat shrinks from development and their range grows as a result of climate change. City parks offer a safe home for these mice, as the parks are often absent of predators like foxes. Hostcycle image courtesy of Emily M. Eng White-footed mouse and Western Fence lizard images courtesy of Anand Varma

The point: multiple factors lead to Lyme disease Increase in ticks + increase in food supply (deer) + increase in carrier (mouse) + human behavior / contact = Increase incidence of disease